Marspedia - User contributions [en]

User:Sdubois

2021-05-22T14:27:45Z

Sdubois: /* Original articles authored by Stefan */

[[File:Stefan.JPG|thumb|upright=0.6]]Stefan DuBois began to take a serious interest in space exploration after a combination of witnessing the 2017 solar eclipse as well as the maiden flight of the Falcon Heavy shortly thereafter. He believes that colonizing Mars will be crucial to ensuring mankind's survival as a species, and is excited to use his abilities in whatever small way he can to help make that happen. Stefan holds a Ph.D. in Iberian Linguistics from UC Santa Barbara and coordinates the first-year Spanish program at the University of Denver. If you would like to get in touch with him, feel free to reach out at sdubois0@gmail.com.

==Original articles authored by Stefan==

*[[Radioisotope Thermoelectric Generators: Advantages and Disadvantages]]
*[[Carbon Dioxide Scrubbers]]
*[[Helicopters]]
*[[Hohmann transfer]]
*[[Observing Mars with a Telescope]]
*[[Telling Time on Mars]]

==Other pages to which Stefan has contributed==

*[[Wind turbine]]
*[[Crew 1a and 1b]]
*[[Crew 2]]
*[[Crew 3]]
*[[Crew 4]]
*[[Crew 5]]
*[[Crew 6]]
*[[The Curious Case for Methane on Mars: Methane and Active Organics Discovered on Mars]]

Template:Stefan

2020-04-20T09:38:34Z

Sdubois:

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<div style="margin-left: 128px; margin-top:15px; line-height:2em; ">This article was written by [[user:sdubois|Stefan DuBois]], volunteer for The Mars Society 
It is licensed under [https://creativecommons.org/licenses/by-sa/3.0/ Creative Commons BY-SA 3.0] and may be freely shared, but must include this attribution.</div></div><includeonly></includeonly>
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'''Usage:''' 
For articles Written by Stefan DuBois, volunteer for The Mars Society.

His content is licensed under [https://creativecommons.org/licenses/by-sa/3.0/ Creative Commons BY-SA 3.0] and must include his attribution.

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Radioisotope thermoelectric generator

2020-04-20T09:33:32Z

Sdubois: Changed redirect target from Radioisotope Thermoelectric Generator to Radioisotope Thermoelectric Generators: Advantages and Disadvantages

#REDIRECT [[Radioisotope Thermoelectric Generators: Advantages and Disadvantages]]

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-20T09:32:39Z

Sdubois:

{{Stefan}}
[[Category: Power Systems]]
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: [[Fuel cell|chemical]], [[Solar panel|solar]], and [[Nuclear power|nuclear]]. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' [[Viking 1]] & [[Viking 2|2]], [[Curiosity]]

Future missions such as [[Mars 2020]] and [[ExoMars]] are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) [[Spirit]] and [[Opportunity]] have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Advantages of RTGs==
===Problems with solar===
While solar arrays have traditionally been the most popular choice for spacecraft traveling within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the solar energy: around Earth, 1,374 Watts/m² are available from sunlight, but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass.|alt=|left]]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays;<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref> fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kg (750 lbs), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in [[Photovoltaics|photovoltaic]] technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design for the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, [[European Space Agency (ESA)|ESA]]’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain it for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their target three month lifespan, they were both dependent on small [[Dust devils|dust devils]] clearing dust accumulations off of their solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant 'cleaning events' risk dangerously low levels of power generation. For example, a global [[Dust storms|dust storm]] at one point left the Spirit rover with only 25% of its solar arrays dust-free.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===Benefits of RTGs===
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the location-dependent operation and large size of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011.|alt=|left]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. NASA's Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), for example, has a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs (MHW-RTGs) to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The variant powered by the MMRTG, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG's thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.[[File:RTGs SolarRTGComparison.png|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.|alt=|center|frame]]
==Disadvantages==
===Environmental Risks of RTGs===
====Potential risks====
[[File:RTGs Pu238.jpg|thumb|Radioactive decay makes a Plutonium-238 pellet glow red hot.|alt=|left]]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium-238 (238Pu), is relatively safe in comparison to alternatives. The radiation emitted by the decay of 238Pu primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy [[Radiation shielding|shielding]] for humans or spacecraft, this means that 238Pu poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the 238Pu used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700°C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the case of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release PuO2; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit.

None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant. [[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.|alt=|center|631x631px]]
====Previous accidents====
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred involving RTGs.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>|alt=|left]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. At this stage, nuclear cores are typically ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 service module on reentry, alongside the lunar module which carried the mission’s RTG. |alt=]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed along with the lunar module in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of PuO2 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from danger. In this case, after the explosion of a rocket near the [[Baikonur Cosmodrome|Baikonur cosmodrome]], investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

===Lack of Plutonium===
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of 238Pu in the 1940s, more than 20 kg (45 lbs) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013, with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014, NASA had only 35 kilograms (77 pounds) of 238Pu available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of 238Pu have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. |alt=|left]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>|alt=|center|630x630px]]Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than producing current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" /> The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of 238Pu would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG might necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program.<ref>Titan Mare Explorer. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Titan_Mare_Explorer&oldid=946374069</nowiki></ref> After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of 238Pu production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. 238Pu has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives must exhibit the following qualities:<ref name=":0" />

#Good power density, to account for low energy conversion efficiencies
#Long half-life, to provide useful power output over a long lifespan
#Low shielding requirements, for safety and to reduce interference with science instruments
#High power/mass ratio, to reduce total mission mass

238Pu meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (241Am). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, 241Am is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to 238Pu’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of 238Pu (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by 238Pu. If, however, future RTGs can make efficiency gains offsetting 241Am’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

Needed Articles

2020-04-20T09:29:36Z

Sdubois: /* Mars Spacecraft/Robotic Missions */

This is the global collection of articles that are needed by [[Marspedia]] and shall be a guide for authors, who want to start new articles without knowing which direction to go. Articles with existing links may need expansion.

==Mars Planetary Science==

*List of Mars Calendars
*Mars' Orbital Position
*The Goldilocks Zone
*Martian "Geomorphology". What processes have shaped Mars?
*Martian geomorphology: What processes have shaped Mars?
*What are the different topologies on Mars?
*[[Dust storms|Global dust storms]]
*What is the date on Mars? What year/season/month is it?
*Upper atmosphere chemical processes
*[[Gravity|What do the differences in gravity show us?]]
*Reflectance and emission spectroscopy
*Mineral identification from satellite, balloon, and aircraft carried instruments
*Multispectral and thermal infrared imaging
*Geological processes that have shaped Mars
*[[In-situ resource utilization|What minerals could be mined on Mars?]]
*Mineral spatial distribution
*Subsurface water or ice deposits
*Surface ice at poles
*Surface elevation profiles and maps
*Martian weather
*[[Mars volcanoes]]
*Martian dichotomy
*[[Toponymy of Mars]]
*[[Moons of Mars (Phobos and Deimos)]]
*Organic compounds on Mars
*Liquid water
*Magnetic field

==Mars Spacecraft/Robotic Missions==

*Utility of unmanned missions
*Scientific data (collection/transmission/interpretation)
*Follow the water strategy
*Subsurface search strategy
*On-site organic compound detection
*DNA/RNA analysis chips
*Spectrographic imagery
*Multispectral mineral identification
*Multimission timelines
*Mission sequences
*Current and planned instruments
*Orbital vs. lander vs. robotic exploration
*[[Aerobraking|Aerocapture orbits]]
*[[Mars cycler|Earth-Mars cyclers]]
*[[Fuel|Chemical propellants]]
*[[Nuclear thermal propulsion|Nuclear thermal rockets]]
*[[Ion thruster|Ion propulsion]]
*[[Solar concentrator|Solar mirrors]]
*DNA/RNA analysis chips
*[[Interplanetary communications|Mars to Earth communication systems]]
*[[Areostationary orbit|Equatorial stationary satellites (for communication)]]
*Aeropositioning satellites (analagous to GPS)
*Miniaturized chemical/molecular identification systems
*Laser communication systems
*Advanced sensing
*AI autonomy
*[[3D Printer|3D printing of complex geometries]]
*[[3D Printer|Self-replicating machines]]
*Hybrid machine enhanced biologics
*Exploration missions (list including chronology and instruments)
*Imagery
*Spectroscopy
*[[Interplanetary communications|Communications]]
*Lander mission atmospheric seasonal measurements
*Subsurface drilling and chemical analysis
*Degrees of autonomy
*[[Research|Regolith sampling and mineral identification]]

==Mars Human Exploration==

*[[Transport from Earth to Mars|Transport options]]
*[[Perchlorate|Perchlorates in regolith]]
*Mars Direct rockets
*Reverse thrust rockets
*Parachute-assisted descent vehicles
*[[Fuel|Methane-oxygen rockets]]
*Aerology and minerology mapping
*[[EVA Suit|Hybrid hard shell EVA suits]]
*[[EVA Suit|Skin-tight mechanical counterpressure suits]]
*[[Funding]]: International, national, and commercial
*Human factors in crew selection
*[[Radiation|Radiation protection: in transit and for exploration missions]]
*Physical fitness for exploration missions
*Cross training in skill sets
*[[Gravity|Health effects of microgravity]]
*Psychological stressors in transit
*Medical training for exploration teams
*Medical equipment for exploration teams
*[[Exobiology|Search for life]]
*[[Atmospheric processing|Oxygen from CO2 atmosphere]]
*[[Atmospheric processing|Organic chemicals and fuel from atmosphere]]
*Exploration and science in simulated marssuits
*Long-duration missions
*Human factors studies

==Mars Human Settlement==

*[[Settlement facilities]]
*[[Transportation|Inter-settlement transportation]]
*[[Rovers|Exploration rovers and rover assistants]]
*[[Starship|Falcon Heavy for nonhuman payloads]]
*[[Starship|Big Falcon Rocket for human/nonhuman payloads]]
*[[Life support|Biosystems to maintain 02/CO2 ratio]]
*[[Water Infrastructure|Distribution of water (liquid and ice) on Mars]]
*[[Potable water treatment|Impurities in water on Mars]]
*[[Settlement|Size and specialization of settlements]]
*[[List of martian products|Manufactured products]]
*[[Martian architecture|Architecture of buildings]]
*[[Transportation|Wheeled vs. railed surface transportation]]
*[[Food|Will Martians eat meat?]]
*[[Settlement systems|How will the Martians communicate across the planet?]]
*[[Energy|Total thermal energy need per capita]]
*[[Energy|Total electrical need per capita]]
*[[Food|100% Mars-sourced food production]]
*Crop choices influenced by ability to thrive in Mars environments
*[[ISRU timeline|The listing and timing of materials produced from Mars resources]]
*[[3D Printer|Additive manufacture (incl. 3D printing)]]
*Will individual settlements establish their own societal rules?
*[[Land|Who owns Mars?]]
*[[Interplanetary commerce|Mars, LEO, Moon trade triangle]]
*[[Terraforming|Increase in pressure needed to allow standing liquid pure water on surface]]
*[[Terraforming|Increase in surface temperature to partially melt polar ice caps]]

==Mars Outreach==

*Mars Society chapters
*Mars Society conferences
*MDRS crews
*Mars Society projects
*Mars Society goals
*[[Mars Foundation]]: About the organization
*[[Hillside settlement]]
*[[Plains settlement]]
*About Marspedia
*The Goals of Marspedia
*Explore Mars
*Mars One
*Mars Journal

==Mars Arts and Literature==

*[[List of books set on Mars|chronology of Mars science fiction]]
*lists of Mars science fiction by plot-line focus
*List of plays
*[[List of movies]]
*List of documentaries
*List of TV Series
*List of computer games
*List of board games
*Accuracy of depiction of Mars in popular culture

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-20T09:27:13Z

Sdubois:

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: [[Fuel cell|chemical]], [[Solar panel|solar]], and [[Nuclear power|nuclear]]. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' [[Viking 1]] & [[Viking 2|2]], [[Curiosity]]

Future missions such as [[Mars 2020]] and [[ExoMars]] are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) [[Spirit]] and [[Opportunity]] have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Advantages of RTGs==
===Problems with solar===
While solar arrays have traditionally been the most popular choice for spacecraft traveling within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the solar energy: around Earth, 1,374 Watts/m² are available from sunlight, but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass.|alt=|left]]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays;<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref> fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kg (750 lbs), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in [[Photovoltaics|photovoltaic]] technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design for the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, [[European Space Agency (ESA)|ESA]]’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain it for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their target three month lifespan, they were both dependent on small [[Dust devils|dust devils]] clearing dust accumulations off of their solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant 'cleaning events' risk dangerously low levels of power generation. For example, a global [[Dust storms|dust storm]] at one point left the Spirit rover with only 25% of its solar arrays dust-free.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===Benefits of RTGs===
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the location-dependent operation and large size of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011.|alt=|left]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. NASA's Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), for example, has a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs (MHW-RTGs) to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The variant powered by the MMRTG, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG's thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.[[File:RTGs SolarRTGComparison.png|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.|alt=|center|frame]]
==Disadvantages==
===Environmental Risks of RTGs===
====Potential risks====
[[File:RTGs Pu238.jpg|thumb|Radioactive decay makes a Plutonium-238 pellet glow red hot.|alt=|left]]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium-238 (238Pu), is relatively safe in comparison to alternatives. The radiation emitted by the decay of 238Pu primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy [[Radiation shielding|shielding]] for humans or spacecraft, this means that 238Pu poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the 238Pu used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700°C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the case of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release PuO2; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit.

None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant. [[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.|alt=|center|631x631px]]
====Previous accidents====
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred involving RTGs.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>|alt=|left]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. At this stage, nuclear cores are typically ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 service module on reentry, alongside the lunar module which carried the mission’s RTG. |alt=]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed along with the lunar module in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of PuO2 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from danger. In this case, after the explosion of a rocket near the [[Baikonur Cosmodrome|Baikonur cosmodrome]], investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

===Lack of Plutonium===
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of 238Pu in the 1940s, more than 20 kg (45 lbs) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013, with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014, NASA had only 35 kilograms (77 pounds) of 238Pu available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of 238Pu have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. |alt=|left]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>|alt=|center|630x630px]]Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than producing current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" /> The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of 238Pu would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG might necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program.<ref>Titan Mare Explorer. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Titan_Mare_Explorer&oldid=946374069</nowiki></ref> After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of 238Pu production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. 238Pu has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives must exhibit the following qualities:<ref name=":0" />

#Good power density, to account for low energy conversion efficiencies
#Long half-life, to provide useful power output over a long lifespan
#Low shielding requirements, for safety and to reduce interference with science instruments
#High power/mass ratio, to reduce total mission mass

238Pu meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (241Am). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, 241Am is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to 238Pu’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of 238Pu (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by 238Pu. If, however, future RTGs can make efficiency gains offsetting 241Am’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-20T09:25:29Z

Sdubois:

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: [[Fuel cell|chemical]], [[Solar panel|solar]], and [[Nuclear power|nuclear]]. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' [[Viking 1]] & [[Viking 2|2]], [[Curiosity]]

Future missions such as [[Mars 2020]] and [[ExoMars]] are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) [[Spirit]] and [[Opportunity]] have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Advantages of RTGs==
===Problems with solar===
While solar arrays have traditionally been the most popular choice for spacecraft traveling within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the solar energy: around Earth, 1,374 Watts/m² are available from sunlight, but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass.|alt=|left]]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays;<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref> fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kg (750 lbs), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in [[Photovoltaics|photovoltaic]] technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design for the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, [[European Space Agency (ESA)|ESA]]’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain it for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their target three month lifespan, they were both dependent on small [[Dust devils|dust devils]] clearing dust accumulations off of their solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant 'cleaning events' risk dangerously low levels of power generation. For example, a global [[Dust storms|dust storm]] at one point left the Spirit rover with only 25% of its solar arrays dust-free.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===Benefits of RTGs===
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the location-dependent operation and large size of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011.|alt=|left]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. NASA's Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), for example, has a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs (MHW-RTGs) to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The variant powered by the MMRTG, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG's thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.[[File:RTGs SolarRTGComparison.png|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.|alt=|center|frame]]
==Disadvantages==
===Environmental Risks of RTGs===
====Potential risks====
[[File:RTGs Pu238.jpg|thumb|Radioactive decay makes a Plutonium-238 pellet glow red hot.|alt=|left]]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium-238 (238Pu), is relatively safe in comparison to alternatives. The radiation emitted by the decay of 238Pu primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy [[Radiation shielding|shielding]] for humans or spacecraft, this means that 238Pu poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the 238Pu used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700°C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the case of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release PuO2; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant. [[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.|alt=|center|631x631px]]
====Previous accidents====
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred involving RTGs.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>|alt=|left]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. At this stage, nuclear cores are typically ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 service module on reentry, alongside the lunar module which carried the mission’s RTG. |alt=]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed along with the lunar module in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of PuO2 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from danger. In this case, after the explosion of a rocket near the [[Baikonur Cosmodrome|Baikonur cosmodrome]], investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

===Lack of Plutonium===
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of 238Pu in the 1940s, more than 20 kg (45 lbs) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013, with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014, NASA had only 35 kilograms (77 pounds) of 238Pu available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of 238Pu have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. |alt=|left]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>|alt=|center|630x630px]]Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than producing current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" /> The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of 238Pu would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG might necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program.<ref>Titan Mare Explorer. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Titan_Mare_Explorer&oldid=946374069</nowiki></ref> After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of 238Pu production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. 238Pu has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives must exhibit the following qualities:<ref name=":0" />

#Good power density, to account for low energy conversion efficiencies
#Long half-life, to provide useful power output over a long lifespan
#Low shielding requirements, for safety and to reduce interference with science instruments
#High power/mass ratio, to reduce total mission mass

238Pu meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (241Am). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, 241Am is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to 238Pu’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of 238Pu (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by 238Pu. If, however, future RTGs can make efficiency gains offsetting 241Am’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-20T09:06:35Z

Sdubois: /* Problems with solar */

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: chemical, solar, and nuclear. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' Viking 1 & 2, Curiosity

Future missions such as Mars 2020 and Exomars are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Advantages of RTGs==
===Problems with solar===
While solar arrays have traditionally been the most popular choice for spacecraft traveling within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the solar energy: around Earth, 1,374 Watts/m² are available from sunlight, but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass.|alt=|left]]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays;<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref> fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kg (750 lbs), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in photovoltaic technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design for the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, ESA’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain it for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their target three month lifespan, they were both dependent on small dust devils clearing dust accumulations off of their solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant 'cleaning events' risk dangerously low levels of power generation. For example, a global dust storm at one point left the Spirit rover with only 25% of its solar arrays dust-free.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===Benefits of RTGs===
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the location-dependent operation and large size of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011.|alt=|left]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. NASA's Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), for example, has a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs (MHW-RTGs) to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The variant powered by the MMRTG, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG's thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.[[File:RTGs SolarRTGComparison.png|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.|alt=|center|frame]]
==Disadvantages==
===Environmental Risks of RTGs===
====Potential risks====
[[File:RTGs Pu238.jpg|thumb|Radioactive decay makes a Plutonium-238 pellet glow red hot.|alt=|left]]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium-238 (238Pu), is relatively safe in comparison to alternatives. The radiation emitted by the decay of 238Pu primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy shielding for humans or spacecraft, this means that 238Pu poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the 238Pu used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700°C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the case of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release PuO2; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant. [[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.|alt=|center|631x631px]]
====Previous accidents====
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred involving RTGs.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>|alt=|left]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. At this stage, nuclear cores are typically ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 service module on reentry, alongside the lunar module which carried the mission’s RTG. |alt=]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed along with the lunar module in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of PuO2 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from danger. In this case, after the explosion of a rocket near the Baikonur cosmodrome, investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

===Lack of Plutonium===
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of 238Pu in the 1940s, more than 20 kg (45 lbs) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013, with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014, NASA had only 35 kilograms (77 pounds) of 238Pu available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of 238Pu have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. |alt=|left]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>|alt=|center|630x630px]]Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than producing current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" /> The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of 238Pu would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG might necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program.<ref>Titan Mare Explorer. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Titan_Mare_Explorer&oldid=946374069</nowiki></ref> After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of 238Pu production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. 238Pu has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives must exhibit the following qualities:<ref name=":0" />

#Good power density, to account for low energy conversion efficiencies
#Long half-life, to provide useful power output over a long lifespan
#Low shielding requirements, for safety and to reduce interference with science instruments
#High power/mass ratio, to reduce total mission mass

238Pu meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (241Am). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, 241Am is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to 238Pu’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of 238Pu (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by 238Pu. If, however, future RTGs can make efficiency gains offsetting 241Am’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-20T07:59:31Z

Sdubois:

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: chemical, solar, and nuclear. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' Viking 1 & 2, Curiosity

Future missions such as Mars 2020 and Exomars are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Advantages of RTGs==
===Problems with solar===
While solar arrays have long powered spacecraft within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the solar energy: around Earth, 1,374 Watts/m² are available from sunlight, but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass. '''''Credits: NASA/JPL-Caltech'''''|alt=|left]]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref>—fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kilograms (750 pounds), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in photovoltaic technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design dor the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, ESA’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain the lander for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their three month lifespan target, they were both dependent on ‘cleaning events,’ when small dust devils clear accumulations off of solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant cleaning events risk dangerously low levels of power generation. The Spirit rover, for example, at one point had as low as 25 percent dust-free solar arrays after a global dust storm.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===Benefits of RTGs===
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the large size and location-dependent operation of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011. '''Credit: NASA'''|alt=|left]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) used on the Curiosity and Perseverance rovers, for example, have a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The RTG variant, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.[[File:RTGs SolarRTGComparison.png|thumb|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.|alt=|center]]

==Disadvantages==
===Environmental Risks of RTGs===
====Potential risks====
[[File:RTGs Pu238.jpg|thumb|Ceramic Pu-238 pellet glowing red hot. '''Credit: Los Alamos Natıonal Laboratory.''']]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium 238 (Pu-238), is relatively safe in comparison to alternatives. The radiation emitted by the decay of Pu-238 primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy shielding for humans or spacecraft, this means that Pu-238 poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the Pu-238 used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700 °C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the event of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release Pu02; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant. [[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.|alt=|center]]
====Previous accidents====
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred over the decades.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. Typically at this stage, nuclear cores are ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 Service Module on reentry, alongside the Lunar Module which carried the mission’s RTG. ''Credits: NASA'' |alt=|left]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program [citation]. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged [citation]. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of Pu02 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from harm. In this case, after the explosion of a rocket near the Baikonur cosmodrome, investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

===Lack of Plutonium===
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of Pu-238 in the 1940s, more than 20 kilograms (45 pounds) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013 (???), with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014 (???), NASA had only 35 kilograms (77 pounds) of Pu-238 available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of Pu-238 have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. ''Credits: NASA/DoE''|alt=|left]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />

Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than using this differential to induce current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire to produce current.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" />
[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>|alt=|center]]
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of Pu-238 would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>

The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG mighy necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program. O After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of Pu-238 production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. Pu-238 has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives need to exhibit the following qualities:<ref name=":0" />

#Good power density, to account for low energy conversion efficiencies
#Long half-life, to provide useful power output over a long lifespan
#Low shielding requirements, for safety and to reduce interference with science instruments
#High power/mass ratio, to reduce total mission mass

Pu-238 meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (Am-241). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, Am-241 is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to Pu-238’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of Pu-238 (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by Pu-238. If, however, future RTGs can make efficiency gains offsetting Am-241’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-20T07:57:00Z

Sdubois: /* Problems with solar */

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: chemical, solar, and nuclear. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting some of the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' Viking 1 & 2, Curiosity

Future missions such as Mars 2020 and Exomars are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Advantages of RTGs==
===Problems with solar===
While solar arrays have long powered spacecraft within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the solar energy: around Earth, 1,374 Watts/m² are available from sunlight, but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass. '''''Credits: NASA/JPL-Caltech'''''|alt=|left]]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref>—fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kilograms (750 pounds), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in photovoltaic technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design dor the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, ESA’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain the lander for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their three month lifespan target, they were both dependent on ‘cleaning events,’ when small dust devils clear accumulations off of solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant cleaning events risk dangerously low levels of power generation. The Spirit rover, for example, at one point had as low as 25 percent dust-free solar arrays after a global dust storm.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===Benefits of RTGs===
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the large size and location-dependent operation of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011. '''Credit: NASA'''|alt=|left]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) used on the Curiosity and Perseverance rovers, for example, have a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The RTG variant, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.[[File:RTGs SolarRTGComparison.png|thumb|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.|alt=|center]]

==Disadvantages==
===Environmental Risks of RTGs===
====Potential risks====
[[File:RTGs Pu238.jpg|thumb|Ceramic Pu-238 pellet glowing red hot. '''Credit: Los Alamos Natıonal Laboratory.''']]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium 238 (Pu-238), is relatively safe in comparison to alternatives. The radiation emitted by the decay of Pu-238 primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy shielding for humans or spacecraft, this means that Pu-238 poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the Pu-238 used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700 °C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the event of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release Pu02; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant. [[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.|alt=|center]]
====Previous accidents====
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred over the decades.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. Typically at this stage, nuclear cores are ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 Service Module on reentry, alongside the Lunar Module which carried the mission’s RTG. ''Credits: NASA'' |alt=|left]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program [citation]. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged [citation]. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of Pu02 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from harm. In this case, after the explosion of a rocket near the Baikonur cosmodrome, investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

===Lack of Plutonium===
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of Pu-238 in the 1940s, more than 20 kilograms (45 pounds) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013 (???), with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014 (???), NASA had only 35 kilograms (77 pounds) of Pu-238 available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of Pu-238 have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. ''Credits: NASA/DoE''|alt=|left]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />

Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than using this differential to induce current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire to produce current.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" />
[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>|alt=|center]]
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of Pu-238 would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>

The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG mighy necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program. O After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of Pu-238 production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. Pu-238 has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives need to exhibit the following qualities:<ref name=":0" />

#Good power density, to account for low energy conversion efficiencies
#Long half-life, to provide useful power output over a long lifespan
#Low shielding requirements, for safety and to reduce interference with science instruments
#High power/mass ratio, to reduce total mission mass

Pu-238 meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (Am-241). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, Am-241 is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to Pu-238’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of Pu-238 (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by Pu-238. If, however, future RTGs can make efficiency gains offsetting Am-241’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-20T07:52:39Z

Sdubois:

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: chemical, solar, and nuclear. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting some of the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' Viking 1 & 2, Curiosity

Future missions such as Mars 2020 and Exomars are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Advantages of RTGs==
===Problems with solar===
While solar arrays have long powered spacecraft within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the energy: around Earth, sunlight produces 1,374 Watts/m², but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass. '''''Credits: NASA/JPL-Caltech'''''|alt=|left]]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref>—fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kilograms (750 pounds), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in photovoltaic technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design dor the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, ESA’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain the lander for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their three month lifespan target, they were both dependent on ‘cleaning events,’ when small dust devils clear accumulations off of solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant cleaning events risk dangerously low levels of power generation. The Spirit rover, for example, at one point had as low as 25 percent dust-free solar arrays after a global dust storm.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===Benefits of RTGs===
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the large size and location-dependent operation of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011. '''Credit: NASA'''|alt=|left]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) used on the Curiosity and Perseverance rovers, for example, have a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The RTG variant, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.[[File:RTGs SolarRTGComparison.png|thumb|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.|alt=|center]]

==Disadvantages==
===Environmental Risks of RTGs===
====Potential risks====
[[File:RTGs Pu238.jpg|thumb|Ceramic Pu-238 pellet glowing red hot. '''Credit: Los Alamos Natıonal Laboratory.''']]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium 238 (Pu-238), is relatively safe in comparison to alternatives. The radiation emitted by the decay of Pu-238 primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy shielding for humans or spacecraft, this means that Pu-238 poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the Pu-238 used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700 °C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the event of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release Pu02; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant. [[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.|alt=|center]]
====Previous accidents====
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred over the decades.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. Typically at this stage, nuclear cores are ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 Service Module on reentry, alongside the Lunar Module which carried the mission’s RTG. ''Credits: NASA'' |alt=|left]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program [citation]. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged [citation]. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of Pu02 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from harm. In this case, after the explosion of a rocket near the Baikonur cosmodrome, investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

===Lack of Plutonium===
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of Pu-238 in the 1940s, more than 20 kilograms (45 pounds) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013 (???), with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014 (???), NASA had only 35 kilograms (77 pounds) of Pu-238 available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of Pu-238 have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. ''Credits: NASA/DoE''|alt=|left]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />

Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than using this differential to induce current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire to produce current.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" />
[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>|alt=|center]]
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of Pu-238 would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>

The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG mighy necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program. O After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of Pu-238 production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. Pu-238 has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives need to exhibit the following qualities:<ref name=":0" />

#Good power density, to account for low energy conversion efficiencies
#Long half-life, to provide useful power output over a long lifespan
#Low shielding requirements, for safety and to reduce interference with science instruments
#High power/mass ratio, to reduce total mission mass

Pu-238 meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (Am-241). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, Am-241 is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to Pu-238’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of Pu-238 (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by Pu-238. If, however, future RTGs can make efficiency gains offsetting Am-241’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-19T22:59:59Z

Sdubois:

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: chemical, solar, and nuclear. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting some of the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' Viking 1 & 2, Curiosity

Future missions such as Mars 2020 and Exomars are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Benefits of RTGs==
===Problems with solar===
While solar arrays have long powered spacecraft within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the energy: around Earth, sunlight produces 1,374 Watts/m², but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass. '''''Credits: NASA/JPL-Caltech'''''|alt=|left]]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref>—fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kilograms (750 pounds), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in photovoltaic technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design dor the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, ESA’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain the lander for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their three month lifespan target, they were both dependent on ‘cleaning events,’ when small dust devils clear accumulations off of solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant cleaning events risk dangerously low levels of power generation. The Spirit rover, for example, at one point had as low as 25 percent dust-free solar arrays after a global dust storm.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===General benefits===
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the large size and location-dependent operation of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011. '''Credit: NASA'''|alt=|left]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) used on the Curiosity and Perseverance rovers, for example, have a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The RTG variant, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.[[File:RTGs SolarRTGComparison.png|thumb|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.|alt=|center]]
==Environmental Risks of RTGs==
===Potential risks===
[[File:RTGs Pu238.jpg|thumb|Ceramic Pu-238 pellet glowing red hot. '''Credit: Los Alamos Natıonal Laboratory.''']]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium 238 (Pu-238), is relatively safe in comparison to alternatives. The radiation emitted by the decay of Pu-238 primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy shielding for humans or spacecraft, this means that Pu-238 poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the Pu-238 used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700 °C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the event of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release Pu02; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant. [[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.|alt=|center]]
===Previous accidents===
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred over the decades.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. Typically at this stage, nuclear cores are ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 Service Module on reentry, alongside the Lunar Module which carried the mission’s RTG. ''Credits: NASA'' |alt=|left]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program [citation]. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged [citation]. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of Pu02 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from harm. In this case, after the explosion of a rocket near the Baikonur cosmodrome, investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

==Lack of Plutonium==
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of Pu-238 in the 1940s, more than 20 kilograms (45 pounds) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013 (???), with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014 (???), NASA had only 35 kilograms (77 pounds) of Pu-238 available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of Pu-238 have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. ''Credits: NASA/DoE''|alt=|left]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />

Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than using this differential to induce current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire to produce current.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" />
[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>|alt=|center]]
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of Pu-238 would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>

The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG mighy necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program. O After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of Pu-238 production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. Pu-238 has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives need to exhibit the following qualities:<ref name=":0" />

#Good power density, to account for low energy conversion efficiencies
#Long half-life, to provide useful power output over a long lifespan
#Low shielding requirements, for safety and to reduce interference with science instruments
#High power/mass ratio, to reduce total mission mass

Pu-238 meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (Am-241). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, Am-241 is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to Pu-238’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of Pu-238 (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by Pu-238. If, however, future RTGs can make efficiency gains offsetting Am-241’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-19T22:47:13Z

Sdubois:

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: chemical, solar, and nuclear. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting some of the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' Viking 1 & 2, Curiosity

Future missions such as Mars 2020 and Exomars are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Benefits of RTGs==
===Problems with solar===
While solar arrays have long powered spacecraft within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the energy: around Earth, sunlight produces 1,374 Watts/m², but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass. '''''Credits: NASA/JPL-Caltech'''''|alt=|left]]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref>—fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kilograms (750 pounds), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in photovoltaic technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design dor the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, ESA’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain the lander for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their three month lifespan target, they were both dependent on ‘cleaning events,’ when small dust devils clear accumulations off of solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant cleaning events risk dangerously low levels of power generation. The Spirit rover, for example, at one point had as low as 25 percent dust-free solar arrays after a global dust storm.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===General benefits===
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011. '''Credit: NASA''']]
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the large size and location-dependent operation of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) used on the Curiosity and Perseverance rovers, for example, have a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs SolarRTGComparison.png|thumb|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The RTG variant, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.

==Environmental Risks of RTGs==
===Potential risks===
[[File:RTGs Pu238.jpg|thumb|Ceramic Pu-238 pellet glowing red hot. '''Credit: Los Alamos Natıonal Laboratory.''']]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium 238 (Pu-238), is relatively safe in comparison to alternatives. The radiation emitted by the decay of Pu-238 primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy shielding for humans or spacecraft, this means that Pu-238 poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the Pu-238 used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700 °C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the event of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release Pu02; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
[[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.]]
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant.

===Previous accidents===
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred over the decades.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. Typically at this stage, nuclear cores are ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 Service Module on reentry, alongside the Lunar Module which carried the mission’s RTG. ''Credits: NASA'' ]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program [citation]. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged [citation]. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of Pu02 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from harm. In this case, after the explosion of a rocket near the Baikonur cosmodrome, investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

==Lack of Plutonium==
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of Pu-238 in the 1940s, more than 20 kilograms (45 pounds) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013 (???), with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014 (???), NASA had only 35 kilograms (77 pounds) of Pu-238 available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of Pu-238 have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. ''Credits: NASA/DoE'']]
[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />

Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than using this differential to induce current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire to produce current.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" />
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of Pu-238 would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>

The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG mighy necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program. O After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of Pu-238 production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. Pu-238 has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives need to exhibit the following qualities:<ref name=":0" />

#Good power density, to account for low energy conversion efficiencies
#Long half-life, to provide useful power output over a long lifespan
#Low shielding requirements, for safety and to reduce interference with science instruments
#High power/mass ratio, to reduce total mission mass

Pu-238 meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (Am-241). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, Am-241 is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to Pu-238’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of Pu-238 (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by Pu-238. If, however, future RTGs can make efficiency gains offsetting Am-241’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-19T10:43:00Z

Sdubois: /* ASRG */

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: chemical, solar, and nuclear. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting some of the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' Viking 1 & 2, Curiosity

Future missions such as Mars 2020 and Exomars are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Benefits of RTGs==
===Problems with solar===
While solar arrays have long powered spacecraft within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the energy: around Earth, sunlight produces 1,374 Watts/m², but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass. '''''Credits: NASA/JPL-Caltech''''']]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref>—fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kilograms (750 pounds), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in photovoltaic technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design dor the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, ESA’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain the lander for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their three month lifespan target, they were both dependent on ‘cleaning events,’ when small dust devils clear accumulations off of solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant cleaning events risk dangerously low levels of power generation. The Spirit rover, for example, at one point had as low as 25 percent dust-free solar arrays after a global dust storm.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===General benefits===
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011. '''Credit: NASA''']]
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the large size and location-dependent operation of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) used on the Curiosity and Perseverance rovers, for example, have a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs SolarRTGComparison.png|thumb|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The RTG variant, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.

==Environmental Risks of RTGs==
===Potential risks===
[[File:RTGs Pu238.jpg|thumb|Ceramic Pu-238 pellet glowing red hot. '''Credit: Los Alamos Natıonal Laboratory.''']]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium 238 (Pu-238), is relatively safe in comparison to alternatives. The radiation emitted by the decay of Pu-238 primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy shielding for humans or spacecraft, this means that Pu-238 poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the Pu-238 used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700 °C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the event of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release Pu02; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
[[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.]]
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant.

===Previous accidents===
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred over the decades.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. Typically at this stage, nuclear cores are ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 Service Module on reentry, alongside the Lunar Module which carried the mission’s RTG. ''Credits: NASA'' ]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program [citation]. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged [citation]. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of Pu02 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from harm. In this case, after the explosion of a rocket near the Baikonur cosmodrome, investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

==Lack of Plutonium==
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of Pu-238 in the 1940s, more than 20 kilograms (45 pounds) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013 (???), with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014 (???), NASA had only 35 kilograms (77 pounds) of Pu-238 available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of Pu-238 have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

==Future Developments in RTG Technology==
===ASRG===
[[File:RTGs ASRG.jpg|thumb|NASA’s canceled Advanced Stirling Radioisotope Generator. ''Credits: NASA/DoE'']]
[[File:RTGs Stirling.png|thumb|The four stages of a beta configuration Stirling engine. The gas begins on the cool end, between the two pistons (1). As it cools and contracts, the pistons are drawn inwards, and the gas flows around the outside of the green displacer piston towards the hot end of the engine (2). The heated gas expands and pushes both pistons, including the blue work piston, to the right, driving the flywheel and converting heat energy into mechanical energy (3). Finally, the displacer piston moves left as the heated gas moves around it towards the cool end, where it loses heat and begins the cycle anew.<ref name=":9">Woodford, C. (2020, April 10). ''How do Stirling engines work?'' Explain That Stuff. <nowiki>http://www.explainthatstuff.com/how-stirling-engines-work.html</nowiki></ref>]]
One of the most promising future technologies which could potentially replace the MMRTG powering NASA’s current missions is the Advanced Stirling Radioisotope Generator (ASRG). First created in 1816, the conventional Stirling engine has served a variety of purposes, from wood-fired stove fans to battery chargers on nuclear submarines.<ref>''Modern Uses of Stirling Engines''. (n.d.). American Stirling Company. Retrieved April 19, 2020, from <nowiki>https://www.stirlingengine.com/modern-uses/</nowiki></ref> The engine uses a small amount of gas (also called a ‘working fluid’) contained within a fixed area which is heated on one end and cooled on the other. Two separate, reciprocating pistons help direct the movement of the working fluid and harness the energy from its expansion to perform mechanical work.<ref name=":9" />

Like conventional RTGs, the ASRG would use the heat produced by the decay of a radioisotope along with the cool surrounding environment to form the temperature differential for its Stirling engine. But rather than using this differential to induce current across thermoelectric couples, the ASRG uses the heat source to move a magnetized piston through a coil of wire to produce current.<ref name=":10">NASA. (2013). ''Advanced Stirling Radioisotope Generator (ASRG) Fact Sheet''.</ref> The benefit of this alternative is that it is far more efficient: the MMRTG used on Curiosity and Perseverance only converts around 8% of its heat energy into electricity.<ref name=":0" />
[[File:RTGs ASRGPullApart.png|thumb|[https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo ASRG pull-apart animation]]]
The ASRG design, however, would outperform the MMRTG by a factor of four, meaning only one quarter of the amount of Pu-238 would have to be included to generate the same amount of power.<ref name=":0" /><ref name=":7" /><ref name=":11">Advanced Stirling radioisotope generator. (2019). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Advanced_Stirling_radioisotope_generator&oldid=925822564</nowiki></ref>

The principal downside of the ASRG design is that this efficiency comes at the cost of moving parts, sacrificing the long-term reliability of the solid-state MMRTG. Furthermore, the vibrations induced by the ASRG could have negative repercussions for sensitive scientific instruments attached to the spacecraft.<ref name=":0" /> Finally, the loss of the excess heat produced by the MMRTG mighy necessitate the inclusion of an alternative heating system, thereby increasing complexity and mass.<ref name=":10" />

In order to ameliorate concerns about longevity, one could use helium as the working fluid to provide the function of a hydrostatic bearing and thereby prevent nearly all friction between the pistons and the cylinder walls—this approach is predicted to give an operational lifetime of 17 years. Two properly-aligned and synchronized sets of two-piston systems could also cancel out the majority of vibrations.<ref name=":10" />

A number of missions had proposed the use of the ASRG system, notable among them the canceled Titan Mare program. O After developing the ASRG design for over a decade, however, NASA canceled its production in 2013, citing a combination of budget constraints and the resumption of Pu-238 production obviating the immediate need for more efficient RTGs.<ref>Green, J. (2013, November 11). ''Important Changes in the NASA Planetary Science Division’s (PSD) Radioisotope Program | Planetary News''. <nowiki>https://www.lpi.usra.edu/planetary_news/2013/11/15/important-changes-in-the-nasa-planetary-science-divisions-psd-radioisotope-program/</nowiki></ref> According to Wikipedia, NASA maintains a small investment in the development of the technology through several private companies, but the most recent updates to these projects are listed as having occurred in 2016, so the present state of these projects is unknown.<ref name=":11" />

===Alternative Isotopes===
Another option for improving RTGs is changing the fuel source. Pu-238 has historically been the most popular choice, but alternative radioisotopes exist. To be effective in RTGs, these alternatives need to exhibit the following qualities:<ref name=":0" />

# Good power density, to account for low energy conversion efficiencies
# Long half-life, to provide useful power output over a long lifespan
# Low shielding requirements, for safety and to reduce interference with science instruments
# High power/mass ratio, to reduce total mission mass

Pu-238 meets all four of these requirements, while alternatives such as Strontium-90, Polonium-210 (used in older Russian RTGs), and Curium-242/244 fall short in one or more areas.<ref name=":0" />

The most promising alternative is Americium-241 (Am-241). Favored by the European Space Agency<ref name=":2" /> and currently used in smoke detectors and moisture gauges, Am-241 is far more plentiful due to being a by-product of regular nuclear reactors rather than weapons-grade refineries.<ref name=":0" /> It has a half-life of 432 years compared to Pu-238’s 88, making it superior in category 2 above.<ref name=":2" /> On the other hand, it suffers in categories 1 and 3: it has roughly one quarter the power density of Pu-238 (0.15 Watts per gram<ref name=":2" /> vs. 0.56<ref name=":0" />) and emits high levels of gamma radiation, a more hazardous form of ionizing radiation than that produced by Pu-238. If, however, future RTGs can make efficiency gains offsetting Am-241’s reduced power density, it may come to be a more popular fuel source.<ref name=":0" />

==References==
<references />

File:RTGs ASRGPullApart.png

2020-04-19T10:32:51Z

Sdubois:

Retrieved from https://www.youtube.com/watch?v=dizf5OanlzY&feature=emb_logo

File:RTGs Stirling.png

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Sdubois:

Retrieved from https://www.explainthatstuff.com/how-stirling-engines-work.html

File:RTGs ASRG.jpg

2020-04-19T10:18:48Z

Sdubois:

Retrieved from http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

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Sdubois:

{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: chemical, solar, and nuclear. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting some of the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' Viking 1 & 2, Curiosity

Future missions such as Mars 2020 and Exomars are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Benefits of RTGs==
===Problems with solar===
While solar arrays have long powered spacecraft within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the energy: around Earth, sunlight produces 1,374 Watts/m², but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass. '''''Credits: NASA/JPL-Caltech''''']]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref>—fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kilograms (750 pounds), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in photovoltaic technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design dor the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, ESA’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain the lander for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their three month lifespan target, they were both dependent on ‘cleaning events,’ when small dust devils clear accumulations off of solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant cleaning events risk dangerously low levels of power generation. The Spirit rover, for example, at one point had as low as 25 percent dust-free solar arrays after a global dust storm.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===General benefits===
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011. '''Credit: NASA''']]
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the large size and location-dependent operation of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) used on the Curiosity and Perseverance rovers, for example, have a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs SolarRTGComparison.png|thumb|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The RTG variant, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.

==Environmental Risks of RTGs==
===Potential risks===
[[File:RTGs Pu238.jpg|thumb|Ceramic Pu-238 pellet glowing red hot. '''Credit: Los Alamos Natıonal Laboratory.''']]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium 238 (Pu-238), is relatively safe in comparison to alternatives. The radiation emitted by the decay of Pu-238 primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy shielding for humans or spacecraft, this means that Pu-238 poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the Pu-238 used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700 °C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the event of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release Pu02; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
[[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.]]
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant.

===Previous accidents===
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred over the decades.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. Typically at this stage, nuclear cores are ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 Service Module on reentry, alongside the Lunar Module which carried the mission’s RTG. ''Credits: NASA'' ]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program [citation]. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged [citation]. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of Pu02 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from harm. In this case, after the explosion of a rocket near the Baikonur cosmodrome, investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

==Lack of Plutonium==
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of Pu-238 in the 1940s, more than 20 kilograms (45 pounds) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013 (???), with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014 (???), NASA had only 35 kilograms (77 pounds) of Pu-238 available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of Pu-238 have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" /> The upcoming Dragonfly mission to Titan also calls for an RTG of the same style, although it leaves open the possibility of other radioisotope alternatives.<ref>Lorenz, R. D., Turtle, E. P., Barnes, J. W., Trainer, M. G., Adams, D. S., Hibbard, K. E., ... & Ravine, M. A. (2018). Dragonfly: A rotorcraft lander concept for scientific exploration at titan. ''Johns Hopkins APL Technical Digest'', ''34''(3), 14.</ref>

== Future Developments in RTG Technology ==
===ASRG===
===Alternative Isotopes===
==References==
<references />

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

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{{Stefan}}
[[File:RTGs OpEnv.png|thumb|Operational envelope for different power conversion technologies ]]
Spacecraft have three main options for power generation: chemical, solar, and nuclear. To the general public, the last of these sources may conjure images of reactors using fission processes, and many probes (particularly those launched by Russia<ref name=":0">Karacalıoğlu, G. (2014, January 16). ''Energy Resources for Space Missions –''. Space Safety Magazine. <nowiki>http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/</nowiki></ref>) have successfully employed such systems. Most nuclear-powered probes traveling beyond Earth orbit, however, have instead utilized radioisotope thermoelectric generators (RTGs), which harness the heat produced by radioactive decay rather than a nuclear chain reaction. RTGs offer an alternative to the more typical solar power when conducting missions where sunlight is scarce, as occurs when traveling to the outer solar system or the dusty atmosphere of Mars.

==How RTGs Work==
Although RTGs use radioactive fuel to generate electricity, they should not be confused with nuclear reactors. The latter harness the energy produced by controlled fission or fusion processes, but no chain reaction takes place in RTGs.
[[File:RTGs Thermocouple.png|thumb|Electricity production in an RTG. Radioactive decay heats one side of a thermocouple (1). An electric current is produced on the opposite, cooler side (2), then tapped from terminals connected to the thermocouple (3), producing power (4). ]]
Instead, unstable radioactive materials known as radioisotopes produce heat as a by-product of their radioactive decay as emitted particles transfer their energy into surrounding atoms.<ref>Decay heat. (2020). In ''Wikipedia''. <nowiki>https://en.wikipedia.org/w/index.php?title=Decay_heat&oldid=951406419</nowiki></ref> This decay takes place within a shell of semiconductors which generates an electric current when each end is exposed to differing temperatures due to the [[w:Thermoelectric_effect|thermoelectric effect]]. Simply put, charge carriers diffuse away from a heat source and build up at the cold end of a material; in semiconductors, these charge carriers can be electrons (“[[w:Extrinsic_semiconductor#N-type_semiconductors|n-type semiconductors]]”) or electron holes (i.e. a position where an electron could exist; these semiconductors are called “[[w:Extrinsic_semiconductor#P-type_semiconductors|p-type]]”). By connecting n-type and p-type semiconductors with a metallic strip, electrons flow between the two once heat is applied, generating an electric current. This connection of n- and p-type semiconductors is called a thermocouple.<ref>Alfred. (2018, October 25). ''How Thermoelectric Generators Work''. Applied Thermoelectric Solutions LLC. <nowiki>https://thermoelectricsolutions.com/how-thermoelectric-generators-work/</nowiki></ref><ref>James, L., & Granath, E. (2020, February 19). ''Understanding the difference between n- and p-type semiconductors''. Power & Beyond. <nowiki>https://www.power-and-beyond.com/understanding-the-difference-between-n-and-p-type-semiconductors-a-905805/</nowiki></ref>

In RTGs, the thermocouple’s heat source comes from the radioactive decay of the RTG’s fuel source heating the interior of its thermoelectric shell, while the exterior is kept cool by the surrounding atmosphere or vacuum. As long as a constant temperature gradient is maintained, electricity will be produced.<ref name=":0" /><ref name=":7">''U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/</nowiki></ref><ref name=":1">Nerlich, S. (2010, October 9). Astronomy Without A Telescope—Solar Or RTG? ''Universe Today''. <nowiki>https://www.universetoday.com/74755/astronomy-without-a-telescope-solar-or-rtg/</nowiki></ref><ref name=":2">''Nuclear Reactors for Space—World Nuclear Association''. (2020, April). <nowiki>https://www.world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space.aspx</nowiki></ref>

==Previous Missions Utilizing RTGs==
[[File:RTGs PreviousMissions.jpg|thumb|Diagram depicting some of the missions carrying RTGs beyond Earth orbit as of 2014. ]]
Beginning with the navigational satellite Transit 4A in 1961, RTGs have long served as power sources in spacecraft.<ref name=":0" /> Successful missions include the following:<ref name=":1" /><ref><code>Robinson, David Gerald. Mars Science Laboratory Launch Risk Analysis Summary. United States.</code></ref><ref name=":3">Allison, P. R. (2016, January 21). ''What will power tomorrow’s spacecraft?'' <nowiki>https://www.bbc.com/future/article/20160119-what-will-power-tomorrows-spacecraft</nowiki></ref><ref name=":5">Siegel, E. (2018, December 13). ''NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions''. Forbes.Com. <nowiki>https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#634152fe1c18</nowiki></ref>

*'''Earth orbit:''' the Transit program, Nimbus III, LES 8 & 9, Russian Cosmos navigation satellites
*'''Lunar surface:''' China’s Chang’e landers; Apollos 12 and 14-17 successfully deployed RTGs to power their Lunar Surface Experiments Package (ALSEP)
*'''Interplanetary:''' Pioneer 10 & 11, Voyager 1 & 2, Galileo, Ulysses, Cassini, New Horizons
*'''Martian surface:''' Viking 1 & 2, Curiosity

Future missions such as Mars 2020 and Exomars are also scheduled to employ RTGs as power sources.<ref name=":2" /><ref name=":4">Leone, D. (2014, November 17). ''EPA Finds No Show-stoppers with Radioactive Battery for Mars 2020''. SpaceNews.Com. <nowiki>https://spacenews.com/42588epa-finds-no-show-stoppers-with-radioactive-battery-for-mars-2020/</nowiki></ref>

Other missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity have employed radioactive heater units (RHUs) which are similarly based on the decay or radioisotopes. As their name implies, however, RHUs are used for heating rather than power generation; for this, both MERs relied on solar arrays.<ref name=":2" />

==Benefits of RTGs==
===Problems with solar===
While solar arrays have long powered spacecraft within the inner solar system, solar intensity decreases according to the inverse-square law.<ref name=":0" /> That is, a craft twice as far from the sun will only receive one quarter the energy: around Earth, sunlight produces 1,374 Watts/m², but this falls to 50 Watts/m² near Jupiter, and 1 Watt/m² at Pluto.<ref name=":3" /> This means that the farther from the sun a solar-powered spacecraft travels, the larger the solar panels it must carry.
[[File:RTGs JunoBus.jpg|thumb|Juno’s three solar arrays are able to power the spacecraft out as far as Jupiter, but come at a cost in terms of size and mass. '''''Credits: NASA/JPL-Caltech''''']]
The Juno mission to Jupiter, for example, holds the record as having traveled the farthest from the sun while sustained by solar power.<ref>''News | NASA’s Juno Spacecraft Breaks Solar Power Distance Record''. (2016, January 13). <nowiki>https://www.jpl.nasa.gov/news/news.php?feature=4818</nowiki></ref> In order to accomplish this feat, it is equipped with three 2.7 by 8.9 meter (8.9 by 29.2 feet) solar arrays<ref name=":0" /><ref>''Juno Solar Panels Complete Testing''. (2016, June 24). NASA. <nowiki>http://www.nasa.gov/mission_pages/juno/news/juno20110527.html</nowiki></ref>—fully extended, these arrays cover [https://www.youtube.com/watch?list=PLTiv_XWHnOZpM1iLQr95P4KDXYiYnJUOE&time_continue=12&v=EOZtqcOMx-A&feature=emb_logo roughly the size of a regulation basketball court]. The arrays themselves total 340 kilograms (750 pounds), over three times the weight of an RTG system.<ref>Brakels, R. (2016, July 6). ''Why NASA Chose Solar Power Over Nuclear For The Juno Space Probe''. Solar Quotes Blog. <nowiki>https://www.solarquotes.com.au/blog/nasa-chose-solar-power-nuclear-juno-space-probe/</nowiki></ref>
[[File:RTGs FutureSolar.png|thumb|2007 NASA report demonstrating hypothetical power generation of next-generation solar array technology in the outer solar system. ]]
While advances in photovoltaic technology may allow for solar-powered probes to function as far out as Saturn in the near future,<ref>Benson, S. W. (2007, November 8). ''Solar for Outer Planets Study''. Outer Planets Assessment Group.</ref> the required increases in probe size and mass will correspondingly add to the cost of launch.

Indeed, an all-solar configuration was considered for the Cassini mission to Saturn.<ref>''Cassini Final Environmental Impact Statement | NASA Solar System Exploration''. (1997, September 24). <nowiki>https://solarsystem.nasa.gov/resources/17808/cassini-final-environmental-impact-statement/</nowiki></ref> Sporting four solar arrays, each five times larger than those of the Hubble Space Telescope, this design increased the spacecraft’s dry mass by 1,337 kg (2,948 lbs) and would have exceeded the maximum launch capacity of the Titan IV (SMRU)/Centaur by almost a ton. The weight of the panels on another proposed design dor the mission greatly increased the spacecraft’s moment of inertia and thereby the difficulty of turning and maneuvering the probe. This would have significantly limited the mission’s scientific output due to factors such as reduced target tracking capability leading to lower image quality, and a loss of observation time while rotating to communicate with Earth.

In addition to the design challenges which face solar-powered systems, complications may arise over the course of their mission: fragile solar arrays are vulnerable to debris, particularly as size increases, and no sunlight will be available while on the far side of a planetary body.

This latter consideration is particularly relevant for rovers and landers who may need to spend long periods of time in obscured regions.<ref name=":0" /> Notably, ESA’s Rosetta mission successfully landed a probe on the comet 67P/Churymov–Gerasimenko in 2014, but it bounced into the shadow of a cliff where its solar panels were unable to generate additional charge. The lander’s on-board batteries were only able to sustain the lander for 64 hours, a much shorter time period than the anticipated mission duration.<ref name=":2" />

Similar complications can arise from atmospheric conditions which reduce the amount of sunlight available. Although both rovers of the solar-powered MERs program long outlived their three month lifespan target, they were both dependent on ‘cleaning events,’ when small dust devils clear accumulations off of solar panels.<ref>O’Neill, I. (2014, April 21). ''Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)''. Space.Com. <nowiki>https://www.space.com/25577-mars-rover-opportunity-solar-panels-clean.html</nowiki></ref> These chance-reliant cleaning events risk dangerously low levels of power generation. The Spirit rover, for example, at one point had as low as 25 percent dust-free solar arrays after a global dust storm.<ref name=":6">''Final Environmental Impact Statement for the Mars 2020 Mission''. (2014). Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf</ref>

===General benefits===
[[File:RTGs MMRTG.jpg|thumb|NASA’s current RTG design, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has powered the Curiosity rover since 2011. '''Credit: NASA''']]
Because RTGs do not rely on energy from sunlight, they do not suffer the disadvantages posed by the large size and location-dependent operation of solar arrays. No matter their distance from or orientation to the sun, RTGs will continue to produce electricity as long as the radioisotope remains active.
[[File:RTGs MMRTGPullApart.png|thumb|[https://www.youtube.com/watch?v=4qkvoVRdoNg Pull-apart animation of MMRTG:] ]]
The lifetime of an RTG is therefore limited only by the half-life of the fuel source, with power output shrinking by a small fraction each year as a consequence of radioactive decay. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) used on the Curiosity and Perseverance rovers, for example, have a minimum guaranteed lifetime of 14 years.<ref>NASA. (2013). ''Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Fact Sheet''.</ref> On the other hand, by powering down an ever-increasing number of instruments, NASA engineers have stretched the operation of Voyagers 1 and 2—launched in 1977—for almost half a century. They expect the spacecrafts’ Multihundred-Watt RTGs to provide sufficient power for at least one scientific instrument through 2025, and data could potentially continue to be returned through 2036.<ref>''Voyager—Frequently Asked Questions''. (n.d.). Retrieved April 19, 2020, from <nowiki>https://voyager.jpl.nasa.gov/frequently-asked-questions/</nowiki></ref>

Further longevity is provided by the fact that RTGs are self-heating and have no moving parts, which helps them survive the harsh conditions of space and planetary surfaces with a relatively small level of risk.<ref name=":0" /><ref name=":2" /><ref name=":3" />
[[File:RTGs SolarRTGComparison.png|thumb|Mars Science Laboratory Environmental Impact Statement comparing solar- and RTG-powered alternatives. The RTG variant was anticipated to be able to achieve all scientific objectives anywhere between 60°S to 60°N, while the solar-powered variant could only have done so without hibernation at 15°N.]]
All of these factors played a role in the selection of RTGs for the Curiosity and Perseverance rovers. For both rovers, solar-powered alternatives were considered, but these would have placed substantial limitations on rover operations in terms of accessible latitudes, percentage of the year during which the rover could operate, and total mission lifetime.<ref name=":4" /> For full effectiveness, the solar-powered variants would have been confined to a narrow band of latitudes near the equator which receive the necessary sunlight year-round and where panels could remain relatively free from dust. The RTG variant, on the other hand, could operate equally well across a wide range of latitudes.

Because the design of Perseverance was based so closely on the RTG-powered Curiosity, switching to a solar variant faced an additional obstacle in that it would have necessitated substantial design changes—and therefore technical risk—from the proven heritage model. This would have included a small (<10 kg or 22 lb) mass increase chiefly from the solar array support equipment, a revamped thermal design to accommodate electrically-generated heating rather than using that coming from the MMRTG thermal energy, and potential changes in the accommodation for the mission’s scientific instruments.<ref name=":6" /> The RTG alternative was therefore retained for Perseverance as well.

==Environmental Risks of RTGs==
===Potential risks===
[[File:RTGs Pu238.jpg|thumb|Ceramic Pu-238 pellet glowing red hot. '''Credit: Los Alamos Natıonal Laboratory.''']]
RTGs are not, however, without their drawbacks. Given their use of radioactive material, they obviously pose environmental risks that solar panels do not. The most commonly-used radioisotope in RTGs, Plutonium 238 (Pu-238), is relatively safe in comparison to alternatives. The radiation emitted by the decay of Pu-238 primarily takes the form of alpha particles, which can be blocked with a thin sheet of paper or even the outer layer of one’s skin.<ref name=":0" /><ref name=":2" /><ref>''Radiation Basics''. (2014, November 12). [Overviews and Factsheets]. US EPA. <nowiki>https://www.epa.gov/radiation/radiation-basics</nowiki></ref> In addition to reducing mass requirements in terms of heavy shielding for humans or spacecraft, this means that Pu-238 poses little danger unless pulverized into particles fine enough to inhale. Should this occur, it would cause severe damage to internal organs, particularly the skeleton and liver.

In order to mitigate these risks in the event of a crash landing or failed launch, the Pu-238 used in RTGs is combined with oxygen to create ceramic pellets of plutonium dioxide (PuO2). This substance forms a crystalline lattice which breaks into large chunks rather than fine, inhalable particles. It also has an incredibly high melting point, remaining solid at up to 2700 °C, and is extremely insoluble in water should it splash down in an ocean.<ref name=":5" /> This already sturdy substance is further reinforced with its own corrosion- and heat-resistant shielding in the form of iridium and high-strength graphite, followed by an aeroshell which protects against the heat of atmospheric reentry.<ref name=":0" /> All of these factors combine to greatly reduce the risk of contamination in the event of a failed launch or crash landing.
[[File:RTGs MMRTGAccidents.png|thumb|Even in the unlikely scenario of a launch accident occurring, the Mars 2020 Environmental Impact Statement predicts an even smaller probability of any radioactive material being released.]]
Given the already low probability of a launch accident, the probability of one resulting in the release of radioactive material is even lower. The Environmental Impact Statement for the Mars 2020 rover, for example, quantifies this risk by stating that there is a 1 in 2,600 chance of a launch accident that would release Pu02; this includes accidents at launch, prior to reaching Earth orbit, and after reaching Earth orbit. None of these three situations were predicted to induce near-term radiological fatalities, but the additional mean number of latent cancer casualties was anticipated to increase by 0.29, 0.20, and 0.0026, respectively. To contextualize these numbers, the report states, “The average maximum dose to any member of the public from an accident with a release in the launch area would be equal to about 3 months of exposure to natural background radiation for a person living in the United States.”
[[File:RTG ComparisonSummary.png|thumb|Comparison of the three alternatives considered for the Mars 2020 rover: RTG-powered, solar-powered, and solar with lightweight radioisotope heating units. The RTG-powered alternative offers the greatest potential for scientific return, although there is some danger of radioactive contamination in the event of a launch accident.]]
Despite the improbability of radiological fatalities due to the launch of the rover, it should be noted that this number would drop to 0 in the proposed solar-powered variant.

===Previous accidents===
While the anticipated risk of launch accidents is low and any radiation-related fatalities even lower, the fact remains that numerous accidents have occurred over the decades.<ref name=":0" />
[[File:RTGs Cleanup.jpg|thumb|After the crash of Cosmos 954, the US and Canada cooperated in a massive clean-up effort to sweep 124,000 square kilometers of Canadian territory over the course of one year. The USSR later paid three million Canadian dollars in expense compensation.<ref>''3-2-2-1 Settlement of Claim between Canada and the Union of Soviet Socialist Republics for Damage Caused by “Cosmos 954” (Released on April 2, 1981)''. (1981, April 2). <nowiki>https://www.jaxa.jp/library/space_law/chapter_3/3-2-2-1_e.html</nowiki></ref>]]
Some of these have released radioactive material high in the Earth’s atmosphere, as occurred when the 1964 US Transit 5BN-3 mission failed to achieve orbit and entered the record as the first nuclear accident in space. In 1978, the USSR Cosmos 954 scattered around 50 kg of uranium-235 over northern Canada after unintentionally reentering the atmosphere. Fortunately, the area’s low population density meant that only a small number of residents were exposed to radiation, and none of those were seriously harmed.

Other accidents have deposited radioactive material into the ocean. The US Nimbus B-1 was destroyed shortly after launch in 1968 as part of a necessary abort protocol, dumping the RTG into the Santa Barbara Channel off the coast of California. The RTG was recovered five months later and found to be intact, indicating that no radioactive contamination had occurred.<ref name=":0" /><ref name=":5" />

In 1983, the USSR Cosmos 1402 satellite reached the end of its operational period. Typically at this stage, nuclear cores are ejected into an orbit above the Earth which is much higher (and therefore safer, although it remains theoretically possible that a collision between nuclear debris in these graveyard orbits could bring them back down to Earth). In this case, however, the planned separation did not occur, and the reactor splashed down with the rest of the spacecraft somewhere in the South Atlantic Ocean.<ref name=":0" />
[[File:RTGs Apollo13.png|thumb|Left: the Apollo 14 ALSEP RTG, almost identical to that carried by Apollo 13. Right: The Apollo 13 Service Module on reentry, alongside the Lunar Module which carried the mission’s RTG. ''Credits: NASA'' ]]
A similar unplanned ocean reentry occurred in the famed case of Apollo 13. Each of the Apollo missions following the first landing on the moon carried with them an RTG as part of the ALSEP program [citation]. These RTGs were to be left on the lunar surface to power a series of science instruments, but in the case of Apollo 13, the mission was aborted before any landing was attempted. Instead, the lander was brought back with the crew to Earth, serving as a life raft after the service module was damaged [citation]. The astronauts returned to Earth safely in Apollo 13’s command module, but their RTG crash landed in the Pacific Ocean’s Tonga Trench. It is estimated that the RTG’s 3.9 kg of Pu02 will remain radioactive for two millenia, although water testing has indicated that no contamination has occurred as a result of the heat shield rupturing on reentry.<ref name=":0" /><ref name=":1" />

While RTGs are designed to prevent accidental contamination through pulverization, a 1970 account demonstrates that keeping the radioactive source concentrated in one large chunk does not completely protect humans from harm. In this case, after the explosion of a rocket near the Baikonur cosmodrome, investigators searching for a nuclear battery found it in the possession of Soviet soldiers—the guards had found it in the wreckage and had kept it as a hand-warmer. The report does not detail whether the soldiers suffered any adverse effects, but such an anecdote illustrates yet another way in which failed launches can potentially endanger the populace.<ref name=":0" />

== Lack of Plutonium ==
The environmental drawbacks of RTGs are arguably minor in comparison to the issue of limited supply. After the discovery of Pu-238 in the 1940s, more than 20 kilograms (45 pounds) per year were produced throughout the Cold War as a byproduct of the production of nuclear weapons.<ref name=":0" /><ref name=":5" /><ref name=":8">Griggs, M. B. (2015, March 11). ''NASA Can Make 3 More Nuclear Batteries, And That’s It''. Popular Science. <nowiki>https://www.popsci.com/nasa-can-make-3-more-nuclear-batteries-and-thats-it/</nowiki></ref> With the rise of nuclear non-proliferation, however, production halted and the US has since primarily relied on supplementing its remaining stocks with purchases from Russia.

Production resumed in limited quantities in 2013 (???), with the hope of producing up to 1.5 kilograms (3.3 pounds) per year by the early 2020s. This amount would be far less than Cold War levels, but could still help supplement decaying stockpiles.<ref name=":5" /> As of 2014 (???), NASA had only 35 kilograms (77 pounds) of Pu-238 available, with roughly half of that quantity having decayed to the point where it no longer met minimum energy requirements for new missions.<ref name=":0" /><ref name=":7" /><ref name=":8" />

Historically, somewhere between 3 to 11 kilograms (7-24 pounds) of Pu-238 have been used per RTG-powered mission. This means that NASA only has enough for 2-3 more missions using current technology.<ref name=":0" /><ref name=":7" /><ref name=":5" /><ref name=":8" /> One of these is already committed to the Perseverance rover, which will launch to Mars with an RTG in 2020.<ref name=":7" /><ref name=":8" />

==References==
<references />

File:RTGs Apollo13.png

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Retrieved from https://www.universetoday.com/wp-content/uploads/2010/10/RTG21-580x232.jpg and https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#336224201c18

File:RTGs Cleanup.jpg

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Retrieved from http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

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Radioisotope Thermoelectric Generators: Advantages and Disadvantages

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File:RTG ComparisonSummary.png

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Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

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File:RTGs MMRTGAccidents.png

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Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf

File:RTGs Pu238.jpg

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Retrieved from http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/

File:RTGs SolarRTGComparison.png

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Retrieved from https://mars.nasa.gov/mars2020/files/mep/Mars2020_Final_EIS.pdf

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

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File:RTGs MMRTGPullApart.png

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Retrieved from https://www.youtube.com/watch?v=4qkvoVRdoNg

File:RTGs MMRTG.jpg

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Retrieved from https://spacenews.com/u-s-plutonium-stockpile-good-for-two-more-nuclear-batteries-after-mars-2020/

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

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Radioisotope Thermoelectric Generators: Advantages and Disadvantages

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File:RTGs FutureSolar.png

2020-04-19T08:50:29Z

Sdubois:

Retrieved from https://www.lpi.usra.edu/opag/nov_2007_meeting/presentations/solar_power.pdf

File:RTGs JunoBus.jpg

2020-04-19T08:46:34Z

Sdubois:

Retrieved from https://www.nasa.gov/mission_pages/juno/news/juno20110527.html

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-19T08:38:09Z

Sdubois:

File:RTGs PreviousMissions.jpg

2020-04-19T08:35:04Z

Sdubois:

Retrieved from http://www.spacesafetymagazine.com/aerospace-engineering/nuclear-propulsion/energy-resources-space-missions/

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-19T08:23:47Z

Sdubois:

File:RTGs Thermocouple.png

2020-04-19T08:13:18Z

Sdubois:

Retrieved from https://inl.gov/wp-content/uploads/2014/10/AtomicPowerInSpaceII-AHistory_2015_chapters1-2.pdf

File:RTGs OpEnv.png

2020-04-19T08:04:49Z

Sdubois:

Retrieved from https://www.lpi.usra.edu/sbag/meetings/jan2011/presentations/day1/d1_1200_Surampudi.pdf

Radioisotope Thermoelectric Generators: Advantages and Disadvantages

2020-04-19T08:00:36Z

Sdubois: Created page with "{{Stefan}}"

User:Sdubois

2020-04-19T07:59:34Z

Sdubois: /* Original articles authored by Stefan */

[[File:Stefan.JPG|thumb|upright=0.6]]Stefan DuBois began to take a serious interest in space exploration after a combination of witnessing the 2017 solar eclipse as well as the maiden flight of the Falcon Heavy shortly thereafter. He believes that colonizing Mars will be crucial to ensuring mankind's survival as a species, and is excited to use his abilities in whatever small way he can to help make that happen. Stefan holds a Ph.D. in Iberian Linguistics from UC Santa Barbara and volunteers for the Mars Society as part of the Marspedia editorial subcommittee. If you would like to get in touch with him, feel free to reach out at sdubois0@gmail.com.

==Original articles authored by Stefan==

*[[Radioisotope Thermoelectric Generators: Advantages and Disadvantages]]
*[[Carbon Dioxide Scrubbers]]
*[[Helicopters]]
*[[Hohmann transfer]]
*[[Observing Mars with a Telescope]]
*[[Telling Time on Mars]]

==Other pages to which Stefan has contributed==

*[[Wind turbine]]
*[[Crew 1a and 1b]]
*[[Crew 2]]
*[[Crew 3]]
*[[Crew 4]]
*[[Crew 5]]
*[[Crew 6]]
*[[The Curious Case for Methane on Mars: Methane and Active Organics Discovered on Mars]]

Helicopters

2020-04-12T20:31:29Z

Sdubois:

{{Stefan}}
[[File:Marscopter.jpg|thumb|upright|Artist's conception of NASA's Mars Helicopter planned for inclusion on the Mars 2020 mission.]]As of the time of writing, helicopters have not yet flown on [[Mars]]. Achieving heavier-than-air flight on the planet faces several obstacles, chief among them the [[Environmental conditions#Atmosphere pressure|low atmospheric density]] as compared to Earth. Yet, if helicopters were demonstrated to be feasible, they would fill a gap between ground-based and orbital exploration, offering aerial reconnaissance and light payload transportation capabilities to [[rover|rover missions]]. Farther in the future, manned exploration would similarly benefit from semi- or fully-autonomous helicopter support. A proof of concept flight model, the [[#NASA's Mars Helicopter|Mars Helicopter]], is currently scheduled for inclusion on NASA’s [[Mars 2020]] mission.
==Benefits==
Helicopters operating on Mars would provide a variety of benefits. Whereas the cameras or sensors of satellites must operate from hundreds of kilometers above the planet, skimming over the surface at altitudes ranging from tens to hundreds of meters offers the possibility of collecting data which cannot be obtained from orbit.<ref name=":0">Kiger, P. J. (2019, June 27). Can a Helicopter Fly on Mars? NASA Says Yes. Retrieved July 19, 2019, from HowStuffWorks website: <nowiki>https://science.howstuffworks.com/mars-helicopter.htm</nowiki></ref> For example, higher-resolution imagery from these heights may reveal dangers or optimal paths for exploration which would not be evident from satellite photos, thereby improving the efficiency and safety of manned and robotic expeditions on the surface.

While manned exploration of Mars may lie in the relatively distant future, supplementing existing rover missions with aerial support offers more immediate advantages. A flying platform could cover large areas which would be prohibitively time-consuming for its rover companion, or carry instruments and cameras over steep or rough terrain too difficult for exploration by land-based robots.<ref name=":0" /> It could also carry small payloads, deploying multiple scientific instruments over a tract of land<ref name=":0" /> or ferrying samples from the collection site to a Mars ascent vehicle for return to Earth.<ref name=":1">Mars Helicopter a new challenge for flight. (2018). ''Universe'', 1–3. Jet Propulsion Laboratory.</ref>

Once humans set foot on the planet, helicopters could continue to act as advance scouts in much the same way as for rovers, exploring terrain too difficult or time-consuming for manned exploration and aiding in the search for resources.<ref name=":0" /><ref name=":2">Howell, E. (2019, June 7). NASA’s Mars Helicopter Whirls Through Tests on Way to 2020 Launch [Wetensch. publicatie--]. Retrieved July 19, 2019, from Space.com website: <nowiki>https://www.space.com/nasa-mars-helicopter-final-testing.html</nowiki></ref> Furthermore, they could offer a rapid delivery system for emergency supplies or parts for repairs.<ref name=":0" /> All of these tasks, particularly if automated with the help of machine learning, would reduce the man-hours required of early settlers and explorers, who will be few in number and whose labor can then be directed towards other projects.<ref name=":0" />

==Obstacles==
[[File:Kamen-ROMAR.jpg|thumb|upright=0.9|1960s concept art of a helicopter employing tip-jet rotor propulsion. Later discoveries regarding the thin nature of Mars’ atmosphere revealed such a design to be unfeasible, as a manned vehicle of this style would likely be too heavy to function.<ref>Kaman ROMAR – Aerospace Projects Review Blog. (2017, June 11). Retrieved July 19, 2019, from Aerospace Projects Review Blog website: <nowiki>http://www.aerospaceprojectsreview.com/blog/?p=2993</nowiki></ref>]]The implementation of helicopters on Mars faces several challenges, the most daunting of which being the fact that Mars’ atmosphere is substantially thinner than that found on Earth. Mars' atmospheric density on the surface is roughly 60 times less than Earth's, while its mean surface pressure is 160 times less.<ref>Wiiliams, D. R. (2018, September 27). Mars Fact Sheet. Retrieved July 27, 2019, from <nowiki>https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html</nowiki></ref><ref>Williams, D. R. (2019, April 22). Earth Fact Sheet. Retrieved July 27, 2019, from <nowiki>https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html</nowiki></ref> To offer a practical point of comparison, the highest recorded flight reached by helicopters on Earth lies around 40,000 feet—even on the surface of Mars, a craft would start from the equivalent of 100,000 feet in altitude on Earth.<ref>Northon, K. (2018, May 11). Mars Helicopter to Fly on NASA’s Next Red Planet Rover Mission [Text]. Retrieved July 19, 2019, from NASA website: <nowiki>http://www.nasa.gov/press-release/mars-helicopter-to-fly-on-nasa-s-next-red-planet-rover-mission</nowiki></ref> The corresponding decrease of [[Gravity|gravity]] (38 percent of that on Earth) does not fully offset the thinner atmosphere,<ref>Allain, R. (2018, May 16). The Physics of NASA’s New Mars Helicopter. ''Wired''. Retrieved from <nowiki>https://www.wired.com/story/the-physics-of-nasas-new-mars-helicopter/</nowiki></ref> meaning that only recent innovations in lightweight electronics and battery technology have rendered the possibility of a helicopter capable of lifting its own weight feasible.<ref name=":0" />

In addition to the difficulties of generating lift in such a thin atmosphere, the [[Speed of light#Consequences of the Speed of Light|communications delay]] between Earth and Mars (from 4-24 minutes, depending on the planets’ relative orbital positions<ref>Time delay between Mars and Earth. (2012, August 5). Retrieved July 19, 2019, from Mars Express website: <nowiki>http://blogs.esa.int/mex/2012/08/05/time-delay-between-mars-and-earth/</nowiki></ref>) make manual piloting an impossibility for any human not themselves present on the planet,<ref name=":0" /><ref name=":3">Sharma, S. (2018, May 14). NASA’s Mars Helicopter: Small, Autonomous Rotorcraft To Fly On Red Planet. Retrieved July 19, 2019, from International Business Times website: <nowiki>https://www.ibtimes.com/nasas-mars-helicopter-small-autonomous-rotorcraft-fly-red-planet-2680575</nowiki></ref> and the lack of a major global [[Mars#Aereology (Martian Geology)|magnetic field]] means the helicopter cannot use a compass for navigation.<ref name=":4">JPL Mars Helicopter Scout. (2019). In ''Wikipedia''. Retrieved from <nowiki>https://en.wikipedia.org/w/index.php?title=JPL_Mars_Helicopter_Scout&oldid=904852493</nowiki></ref> Finally, a helicopter must be able to overcome all of these obstacles with materials capable of withstanding the g-forces and vibration of a rocket launch from Earth, as well as the sub-100 degrees Fahrenheit nighttime temperatures.<ref name=":0" />

==NASA's Mars Helicopter==
[[File:MarsHelicopter.jpg|thumb|left|The Mars Helicopter will arrive attached to the underside of the Mars 2020 rover.<ref name=":2" />]]Despite the impediments to such a mission, the Mars 2020 rover will carry a prototype helicopter to test the feasibility of future flights on Mars. In January 2019, NASA’s Mars Helicopter successfully completed a flight in a simulated Mars environment, with the thin atmosphere replicated via a vacuum chamber<ref name=":2" /> and the low gravity simulated via a motorized lanyard which pulled up on the craft as it flew.<ref>Wall, M. (2019, March 29). Ready for the Red Planet! NASA’s Mars Helicopter Aces Key Flight Tests. Retrieved July 19, 2019, from Space.com website: <nowiki>https://www.space.com/nasa-mars-helicopter-aces-flight-tests.html</nowiki></ref> Carrying no scientific instruments, the helicopter’s primary objective will consist solely of replicating this success on the red planet and thereby demonstrate the feasibility of powered flight for future missions.<ref name=":0" /><ref name=":2" />

The helicopter itself weighs less than 4 pounds (1.8 kilograms) and sports two 4-foot (1.2 meter) long counter-rotating coaxial rotors. This design was chosen over a tail rotor due to considerations of the available space on the rover.<ref name=":0" /> The blades themselves will spin about 10-times faster than those of an Earth helicopter, at 2,300-2,900 revolutions per minute.<ref name=":0" /> Other features include an in-built [[Solar panel|solar panel]] for charging,<ref name=":0" /> a heating mechanism to counteract frigid nighttime temperatures,<ref name=":3" /> a solar tracker camera for navigation,<ref name=":4" /> and the ability to receive commands from the ground before carrying out the flight autonomously.<ref name=":3" />
[[File:Marscopter Attached.jpg|thumb|The Mars Helicopter, visible in the lower center of the image, attached to the underside of Perseverance.]]
After arriving at Mars attached to the underbelly of the rover, the helicopter will detach at a suitable take-off site some 60-90 days after landing.<ref name=":1" /><ref name=":3" /> The rover will then separate itself from the helicopter by a minimum safe distance of 100 meters, initiating a 30-day test consisting of up to 5 flights of increasing distance and complexity.<ref name=":1" /><ref name=":3" /> The first of these will involve hovering at 10 feet (3 meters) for 30 seconds, and subsequent flights will last up to 90 seconds while remaining within a 1 kilometer radius of the rover for radio signaling purposes.<ref name=":1" />

If successful, these flights will constitute the first flight of a heavier-than-air aircraft on Mars.<ref name=":0" /> This will pave the way for larger helicopters, with current Mars lander designs permitting craft weights of an estimated 20-30 kilograms (44-66 pounds) and payload capabilities of 0.5-2 kilograms (1.1 to 4.4 pounds).<ref name=":0" />

==References==
[[Category: Surface Vehicles]]
<references />

File:Marscopter Attached.jpg

2020-04-12T20:28:27Z

Sdubois:

Retrieved from https://mars.nasa.gov/news/8645/mars-helicopter-attached-to-nasas-perseverance-rover/

Crew 6 - Crew Reports

2020-03-17T00:24:45Z

Sdubois:

[[Category:MDRS Crew Reports]]
==April 24, 2002==
===Science Overview - Penny Boston===
Coupled Mineralogy & Geomicrobiology in Hot & Cold Deserts on Earth and Mars

'''Primary Questions'''

Do desert surface rinds reliably record climatic conditions?

Are desert surface rinds indicators of microbial activity?

Do surface materials and processes in deserts indicate anything about the subsurface mineralogical, hydrological, & microbial conditions?

'''Primary Hypothesis'''

We suggest that the chemical and microbial processes that occur in surface desert varnish and other arid land weathering rinds are related to the pedogenic (soil-building) and geomicrobiological processes that we are studying in arid land caves.

We propose that a set of fundamental processes (e.g. the formation of clays, chemical formation of oxides of Mn, Fe, and Rare Earth Elements, and microbial activity) occur in both environments (surface and subsurface).

We predict that the production of characteristic thin surface rinds is produced by the action of weathering, diurnal and seasonal thermal oscillation, and possibly insolation on the above set of fundamental processes. The fluffy, low-density subsurface cave materials (known as corrosion residues) are due to long-term stable thermal and humidity conditions, and the absence of weathering factors on those same fundamental processes. Because of the perceived relationships between surface processes and subsurface analogs, we are provisionally renaming cave corrosion residues "speleosols", i.e. soils formed in caves.

'''Science Context of MDRS Mission Within Existing Studies'''

My science agenda for MDRS is to try to identify and characterize surface processes that have microbial significance and may also reflect related subsurface processes (e.g. in caves, voids, aquifers, and shallow subsoils). In particular, manganese and iron oxide desert rinds and surface carbonates are relevant to Mars and we are actively studying related materials in arid land caves.

'''Specific Science Goals'''

#Locate desert varnish and other oxide rinds, carbonate and other lateritic surface deposits with potential microbial communities (active or fossil remains).
#Survey potential microniches for organisms, e.g. rock cracks, larger fissuring, subsoil layers, undersides of unattached rocks, etc.
#Conduct yes/no in situ activity tests for the presence of enzymes extruded into the environment by microbes (exoenzymes). Followup quantitative work in future missions.
#Produce a combination geological/mineralogical/bioactivity map of selected subsites.
#Collect materials for future study (functioning as a human "sample return" mission) a. sterile hand samples of materials b. SEM mounts on stubs c. enrichment culturing to isolate organisms of specific types d. frozen samples for later DNA analysis
#Photodocumentation of sites, textures, appearance.

'''EVA Activities'''

*Walking reconnaissance
*Exploring with rock hammer
*Digital photography
*Mapping, sketching, surveying in points etc.
*Testing for carbonates (HCl)
*Grab sampling of (rocks and unconsolidated materials)
*Microsampling (scraping of rinds, digging out material from cracks, etc.)
*Preservation samples (in glutaraldehyde)
*Baseline data acquisition (e.g. temperature, humidity, etc.)
*In situ exposure experiments
*Inoculating culture media with samples
*Collecting DNA samples on dry ice at very end of mission tenure

'''Environmental Materials of Interest'''

*Desert Varnish on surface rocks
*Undersides and cracks in varnished rocks
*Desert Pavement, Cemented or semi-cemented
*Paleosols (if any)
*Surface Carbonates (caliches, efflorescence crusts, etc.)
*Other weathering and oxidation rinds (e.g. dendrites, clays, etc.)
*Cryptogamic soils (desert soils bound by microbial filaments and polysaccharides)
*Any volcanic materials, e.g tuff, ash, lava, etc., especially those with surface rinds
*Putative lakebeds or playas
*Tafoni in any rock type, e.g. sandstones mostly
*Travertine deposits (both ancient and active)

===Personal Journal - Sam Burbank===
'''April 23, 2002''' - It's a long drive from SF to Hanksville Utah. I arrived on Tuesday evening around midnight. A call home to report being safe, then the drive trough the sparely populated, long and thin town. A couple of more miles to the turnoff I hoped I'd remember from working on the hab in December. The moon was rising and the winding dirt road visible. So tired. What were we doing here?

I expected to find my crew members there, to turn a corner (many corners to turn) and find a lit place, see their truck, last man in. But every corner was dark, dark red rock with streaks of white or gray running through them.

I'd been here before, and knew the hab is tucked away from the main road. It's visible but not obvious, and so I slowly turned each corner, flashlight in hand. Is that the hab or a big rock? No...yes, there is was, but totally dark. The hab. I saw most of the frame go up in December, but none of the walls or roof. Now here it was, so much taller than I imagined (same impression with the hab on Devon Island), and lit only by moonlight, the only sound coming from the torn wall of the next door greenhouse flapping in the warm breeze.

I walked around the thing three or four times. Where was everyone? Was it open? It was. Peaked in through the airlock, flashlight darting around as if in a low budget sci-fi film. There were the used looking suits, hanging empty, one with a marker pen taped to the sleeve, one with a mission patch from the last rotation, crew 5, stuck to the chest. I moved further inside, now into the science room. It looked just as lived in, as if when I came in the front, the inhabitants slipped out the back. I found myself quickly turning around with the flashlight, expecting some movement behind me.

Up the stairs to the living room: plants, coffee maker, table and chairs. Someone's home. What to do? My crew would be here soon, so I would just wait.

There was an unlit candle on the main table (no power anywhere in the hab), so I lit that and brought out my luggage and miscellaneous gear, and loaded it all upstairs. Then I pulled out my guitar (part of one of our main experiments) and quietly strummed, the little candle glowing, moonlight beaming through the roof window, creating a pool of light on the floor to my right. Would they come tonight?

An hour of so went by, and soon it was past 2:00AM and it was time to go to sleep in this dark little hab. I picked a stateroom (choice of 6!) and loaded my stuff in there, assuming the others would come in soon, but they never did that night. I woke up alone in this now clear and bright spaceship, made a cup of coffee, felt very much like a character in some lost twilight zone episode: Alone on Mars!

So an unexpected little one man simulation. I drove back to town and found two of our crewmembers, Penny and Steve, driving in with a truck load of gear, met them. And then stuck with them, and have been with them since.

There is plenty of room here in the hab for all if everyone is mindful of the others. Still, I'll always remember my first night in the MDRS, alone on some planet, a planet with lots of time for guitar playing, and a big beautiful moon, happy to illuminate a lone abandoned research station, and happy to have new company.

==April 25, 2002==
===Captain's Log - Frank Schubert===
We are nearing the end of the first day of simulation for crew six at MDRS. It was hectic as expected. Settling into the hab takes time and this crew was no different. We are impressed by crew fives fidelity and reporting and plan to carry on with that tradition.

As an example, we are fueling the generator while in suits. By being careful and slow it is possible to do the job without getting any gas on the suits. Of course, everything takes longer in the suits.

Last night we discovered that the toilet was malfunction and about to overflow. Steve volunteered to empty it and with the help of Sam he was able to dispose of most of the waste. The odor became overpowering and we had to open the doors and put the fan in the portal on the roof blowing the smell out the doors. In the morning when the fan was off the odor returned and we made the decision to take the toilet out and go to a camp toilet. Our local contact had donated five chairs and we modified one to work as the toilet. Again, Steve and Sam went to work and removed the offending toilet. The hab now smell fresh and spirits had lifted considerably.

The new water pump also malfunctioned after one use. We replaced it with the pump that was intended for the emitter field. This is not a problem as the warm weather and the wind have made the leach field work well.

Kelly has been a little bit under the weather and she has spent most of the day taking it easy. She seemed better in the afternoon.

Ephimia has been a real source of information on the ISS as she works in the human factors directly. We are all amazed at how much our problems parallel those that the astronauts are having. Like us, they also have power problems and have to cook with limited power. They also have odor problems. This all makes us feel like a real crew.

The crew is taking personality tests today. Ephimia is studying the human factors of a Mars crew for Johnson Space Center and we are all curious to see how we score on these tests.

Today's EVA was done by Steve, Penny. It was a scouting EVA with Steve taking Penny to Lith Canyon. During the trip back, Penny was making a turn and got her boot stuck on the shift lever. Then her glove caught on the handle and she took a spill. When she got back to the hab she was quite sore but ok for the most part. She will be sore for a couple of days but will be ok. Lucky for her I brought my pain pills from my accident.

Sam, Kelly and Frank worked on setting up the recording studio. We had already set up a smaller digital recorder and had already written several short riffs. We plan to start collaborating with the musician's back on Earth this weekend.

Ephimia, Sam and Steve are handling the cooking chores with grunt help from Frank. Tonight after the reports we plan to watch a movie and hit the sack early for a big day of science and music tomorrow.

More later.

===Proposed Schedule - Crew 6===
{| class="wikitable"
|07:00
|Crew wake
|-
|07:30
|ATV training for new crew
|-
|08:30
|Breakfast
|-
|09:00
|Psych study briefing and instructions
|-
|09:30
|Commence IVA activities

*Breakfast cleanup
*Studio construction and set up
*Science lab setup
*Psych study test completion
*Lunch preparation
*Dinner preparation
|-
|14:00
|EVA preparation
|-
|15:30
|Prebreathe
|-
|15:50
|Begin EVA

*show and tell practice EVA (Boston, Morphew, McDaniel)
*IVA dinner prep
|-
|18:00
|End EVA
|-
|20:00
|Report preparation
|-
|21:00
|Scheduling and ops (daily planning) meeting
|-
|22:00
|Presleep activities
|-
|23:00
|Sleep
|}

===Biolet Replacement - Crew 6===
Dispatch to Mission Support: 04/25/2002 - 09:21

Mission support:

After several hours of miserable work cleaning the overflowing biolet, beginning at 12:30am, ending at 2:30am, the crew has decided to remove the biolet from the habitat. The stench filling the habitat poses serious crew health, safety, morale, and productivity risks. The biolet apparently hadn't been emptied during Crew 5, and possibly never. Crew 6 emptied 5 full trays (approximately 80-100 lbs/36-45 kgs) of excrement, and it is still half full.

We will be constructing our own toilet and using plastic bags to contain our waste.

Crew 6

===Engineering Report - Kelly Snook===
Dispatch to Mission Support: 04/25/2002 - 20:54

'''Water Pump Failure''' - The second water pump seems to be functioning, but not with enough power to pump water up to the tank on the upper deck. One crewmember has gone in search of another pump with the goal of resuming sim tomorrow with a new pump.

'''Biolet Failure''' - The biolet was successfully extracted from the habitat today and the bathroom was swabbed down several times with mops, sponges, disinfectant, and water. This was a several hour process requiring breaking of sim to dispose with the biolet and its waste. A new toilet seat using the bag method will be built for use during the rest of the mission.

'''Issues for Mission Control:'''

*Please advise what to do with the 200 lbs/90 kg of human waste currently in the back of the pickup truck
*Please advise what to do in the future with the bags of waste that will be produced, as we have no agreement with the city for disposal of human waste.

'''Computer Connectivity''' - no crewmember has had success connecting their individual laptops to the internet. We have been able to "see" the network by obtaining IP addresses from the server, but no one has been able to get out to use the internet or check e-mails. Issues for Mission Support: Any advice from previous crewmembers (especially Bill Clancey or Crew 5) would be most welcome.

'''Radio Equipment''' - there are only two functioning headsets for EVA. EVA was conducted today with one crewmember using a handheld radio talking through the helmet. Please send new functioning radios before our overnight EVA currently scheduled for May 4th.

'''EVA Equipment''' - Boots and gloves were too large for P. Boston. Boots were several inches too long and resulted in ATV accident. Crew are OK, but this is a serious issue that should be addressed for safety reasons. Smaller boots and gloves should be available for smaller crewmembers.

'''ATVs''' - One of the small Kawasaki ATVs was overturned today due to the oversized boots. No serious injuries, but handlebars are bent. No action necessary by Mission Support. Repairs will be made by crew engineers.

'''Habitat Chairs''' - Current chairs are inadequate. They break at a very high rate and there are currently at least 8 broken chairs on the premises. MS should stop buying this brand of chairs. New chairs have been donated to the hab by L. Ekker, so there are enough until the rest of the green folding chairs break.

'''Kitchen Tools''' - Please advise on status of hotplate purchase and shipment. Crew meals have been planned and shipped by the Natural Epicurian Center in Austin, and require heavy preparation. Aside from the hotplate, we need another non-teflon steel frying pan, tupperware, serving utinsils and more serving dishes.

'''EVA Support''' - One Maintenance EVA is planned for tomorrow evening to install the new generator, and to do minor repairs on the greenhouse, including watering plants. Request advice from Mission Control regarding whether it's desirable to try to repair the solar water pumps and other greenhouse systems.

Crew 6

==April 26, 2002==
===Captain's Log - Frank Schubert===
Today we all got up on schedule and started the day with cleansing tea (yuck) and something that looked like rice and tasted great.

By 08:30 we were planing the day and checking the Mission Support messages.

The mood of the crew has improved tremendously since we removed the biolet toilet.

The hab is now almost odor free both upstairs and down. A throne was made out of one of the seats donated by Larry Ekker and it works well. We keep the bathroom fan on most of the time. I am amazed at how odor affects the crew. I felt a general lack of energy yesterday. Today the spark is back for Crew 6.

The musicians tested the acoustics of the hab and the consensus is that we will just record everything in the lab. We will hook up with Mutato Musica (Devo Studios) in Los Angles and Submarine Studios in San Fransico this weekend. Kelly, with help from Frank spent several hours setting up the studio. Kelly also spent a lot of time getting the Internet connection working. We have some tricks to squeeze more music though our ailing Internet connection and plan to use them all. We started recording in the afternoon and it is as special as I have ever seen. The excitement level is very high. Today we recorded two songs we wrote, "I Am Going To Mars," "M.F.C.," and one cover song, "Under the Milky Way." We will send them out tonight and see what the musicians do with them. During one track, Steve came down and built Crash, (aka Penny Boston) a footrest. Kelly sampled it and put it in the song. Quite cool.

Kelly is turning out to be a top flight engineer. She is quick and accurate. Sam and I consider us very lucky. We were worried that the rest of the crew might get sick of hearing the same song several times. They seem to really like it. The music has a very positive affect on the crew and morale rose as we created the music. Ephimia is taking note.

The wind picked up this afternoon. Personally, I like the wind. The hab is rock steady in the wind. The weather pole squeaks and moans as the wind whistles past the satellite dish. By six the wind was blowing fiercely. This is typical for this area. A storm blew over as we watched the Moon rise. This is also typical. The rain clouds pass over Hanksville and don't leave a drop.

Steve and Sam did a long maintiance EVA today. They worked on the ATV that Crash had the mishap with. They also hooked up the third pump. That one burned out in three minutes. Steve brought it in and he is going to take the three pumps that don't work and try to make one that does. Failing that, we will run the hose in to the first floor. The emitter pump works to the first floor. We will then bucket brigade the water up to the holding tank.

Ephimia has given us all personality tests. I want to know if I passed but she won't tell me. She is gaining a lot of data from this crew. Apparently we are acting a lot like the crew on ISS.

The food experiment seems to be a success. We are all feeling good and have lots of energy. More on that from Ephi.

Steve continues to be the man when it comes to fixing things. He has repaired the pump, made a second recording table, and has also worked out a way to fill the jenny cans in the suit. That is helping out sim. No one has been out without a suit since yesterday and we hope to keep it that way.

Penny did a great job with the computers today. She got the network up and running and now we can have three computers on the Internet at once. She is a bit sore today and so we put off the science EVA for one more day. I felt a little guilty that we got so much work done on the music today. We plan to hit the science hard tomorrow and make up for the lost time. Tomorrow morning Ephimi and I are going to find the spot I found two months ago that has a large amount of deseart varnish. We will bring back several samples.

Keeping a schedule is the hardest part of the day. We start out on schedule and by the middle of the day we are behind. Today it was the computers and the comms for Kelly and Penny. For Steve, Sam and Frank it was getting the water pump working. For Ephimia it was food preparation. These tasks always seem to take longer, no matter how much thought and preparation we do. Ephimia has told us the on ISS it is the same problem. This crew is learning to adapt and constantly improving out scheduling. There will be more in this subject.

===Proposed Schedule - Crew 6===
'''Goals for the day:'''

*Studio set-up, music tests
*Generator install
*Greenhouse maintenance
*04/27 Science traverse planning, study waypoints
*GIS computer install

{| class="wikitable"
|07:00
|Crew wake
|-
|07:30
|Breakfast preparation
|-
|08:00
|Breakfast
|-
|08:30
|Day planning briefing
|-
|09:00
|IVA operations - studio set-up, toilet seat construction, science lab set-up, GIS computer install
|-
|10:00
|Begin lunch preparations
|-
|10:00
|Crew exercise (2 hours for non-EVA crew)
|-
|12:00
|Lunch
|-
|12:30
|Afternoon IVA operations - continue morning ops
|-
|16:00
|Dinner preparation
|-
|18:00
|Dinner
|-
|19:00
|Maintenance EVA - GreenHab and Generator
|-
|21:00
|End EVA
|-
|21:30
|Evening planning meeting
|-
|22:00
|Presleep activities
|-
|23:00
|Sleep
|}

===Engineering Report - Kelly Snook===
'''Urgent Issues:'''

'''Waste''' - We do not believe that burying the waste is a viable solution. It is neither environmentally responsible nor physically feasible to dig that big of a hole. The biolet is not functioning enough to handle the waste. This is also not a good solution because the biolet would have to be located right next to the habitat (for power) and would have to be continuously manned.

We're laughing a lot about this, but these are serious issues that need to be addressed immediately!

'''Water Pump''' - Both new water pumps in the last 2 days have blown out. One crewmember drove to Grand Junction yesterday to buy the second pump, which failed immediately (within 5 minutes) today on EVA installation. This brand and size will not work to overcome the pressure head. Please confirm receipt of this message tonight and fedex us a water pump tomorrow. If we do not have a pump, we face at least an hour a day of water portage, which is unacceptable given the ambitious scientific agenda of this mission. The water pump should have the following specifications:

*> 1.5 HP
*Standard size fitting (1.5") - rig it up so it has male garden hose fittings on both ends
*Capable of establishing a pressure head of water at a height of at least 40 feet in a .75" hose
*Capable of running on 20 Amps or less
*If the pump is not submersible, make sure it has a pickup filter (brass mesh)

If Mission Support (or HQ) cannot fedex us the pump tomorrow, we will conduct a FULL SIM EVA to Home Depot in Grand F. Junction (on film) on Sunday. The analog here would be driving a rover to a previous landing site and pillaging the reckage.

'''Radios''' - We have a 4 person overnight EVA scheduled for next week. We are going to need functioning radios for that. The answer to your question about the radios is yes…the headsets are here, but only two are functioning.

'''Other Issues:'''

'''EVA Suits''' - 3 Suits were cleaned today (full of dirt, rocks, tape). 3 suits remain to be cleaned. Two helmets lack connection hardware for air supplies. Currently 4 helmets are are functioning. At least 3 backpacks are functioning. QUESTION: Are the helmet parts available somewhere in the habitat?

'''Computer Connectivity''' - After about 20 man-hours of concentrated effort, we were finally able to connect our laptops. The documentation on this procedure is severely lacking in the hab. Especially troublesome was the fact that when the settings on the main HabCom got accidentally changed, there was no documentation on how to set those up. The only documentation we could find for that required logging onto the internet. More documentation is necessary - at the very least, the Starband manuals or other supporting information.

'''ATVs''' - Damaged ATV was repaired successfully on EVA. All damage was cosmetic. QUESTION: Is there an ATV manual?

'''Toilet''' - A new toilet was constructed by cutting a hole in one of the folding chairs, in which plastic bags will be used for depositing solid waste.

'''GreenHab''' - Plants were watered today, but no significant work was done on any of the greenhouse systems.

'''Recording Studio''' - Music recording studio was successfully set up today and the first song recorded. Song will be sent to remote studios tonight and some delayed-live collaboration will occur with the SF studios. First attempts will be made to use the online collaboration software.

'''EVA Details:'''

We had 3 EVAs today, all for Maintenance.

Today's first EVA commenced at approximately 11am. This was designated M-1, devoted exclusively to maintenance tasks. Steve McDaniel and Sam Burbank were the EVA contingent and Frank Schubert on IVA assisting them.

'''EVA mission objectives were:'''

#To install Flotec water pump in outside reservoir to replenish inside water reservoir.
#Repair ATV from yesterday's spill
#Secure building materials for the studio construction
#Fill generator gas tank

Note: Flotec Pump burned out (impellers destroyed after 10 minutes or less of operation). Therefore, reinstalled submersible sump pump. This method requires manual bucket brigade filling from hose. This is at least the third Flotec pump failure since the first week in February. CLEARLY, this pump is not performing well in this environment and another solution MUST be sought. Sam Burbank had to break sim last to attend to this problem driving 4 hours round trip to Grand F. Junction and this was very disruptive of our collective work. This effort proved fruitless since the pump immediately disintegrated.

'''Toilet Replacement Activities:'''

Frank Schubert modified an existing metal chair to serve as a more comfortable holder for the plastic bags into which we are depositing feces and associated materials.

Computer connectivity problem with laptops still plagued us today until a solution in midafternoon. Between Penny and Kelly, 10 hours were expended on the problem today. Over the past several days, Sam and Penny have additionally spent about 8 more hours. A CLEAR writeup that is easily accessible to a new incoming crew is essential. We will undertake this task over the course of our tenure so that future crews will be able to waste less of their limited time on avoidable delay of their real tasks.

Crew 6

===Martian Food Tips - Crew 6===

*Morning Tea is essential for easing digestion, for hydration, adding minerals to the body, increasing strength and endurance, and enhancing general overall health. It is best to drink 1 hour before your meal to ensure maximum benefit. Make a big pitcher of twig tea to last a few days and reheat it to use in morning tea or to drink after meals. DO NOT microwave the tea to reheat it for making morning tea.
*Drink a little tea after your meal rather than during your meal. Drinking during your meal will dilute digestive juices and increase the probability of flatulence. Also drink liquids warm or at room temperature rather than iced. This is especially true when drinking around meal times. Iced or cold beverages slow and inhibit digestion.
*Use condiments (about 1 teaspoon per meal) on your grains. Tekka, shiso powder, gomasio (sesame salt), and AO nori flakes are all condiments that will add minerals to your diet, reduce fatigue, increase strength, and enhance general overall health.
*Chew your grains very well (30-50 times per bite). This is essential for getting the maximum energy from your food. Grains are a complex carbohydrate that provide incredible time-release energy but need to be chewed well in order to derive maximum energy potential.
*Eat some form of "pickle" (2-3 tsp per person per meal) with every meal. This will also help you digest, assimilate and derive maximum energy potential from your grains. It will also help overall digestion by restoring natural intestinal flora that your body needs. Takuan, tamari daikon, sushi ginger, umeboshi plums, and sauerkraut are all forms of "pickle" that have been provided for you.
*Use salt and shoyu only in cooking to avoid excess thirst. Use condiments at the table in place of "salt and pepper".
*Eat some sort of miso-flavored soup each day. This will aid in digestion, provide an excellent source of protein, B12, and good bacteria to restore natural intestinal flora. Use a variety of vegetables in your miso soup and always use wakame sea vegetable. You can just cut wakame into the soup with scissors when it is dry. Use about 1 inch or more of wakame per cup of soup. Sometimes you can add large portion of vegetables and purée the soup. This works well with things like onions and carrots, onions and cauliflower, onions, carrots and cabbage, or with leftover grains, vegetables, or beans. Remember when using leftovers to always add some fresh vegetables to the soup as well. If you choose not to eat soup for breakfast, make it for one of the other meals. Additional onions, celery, cabbage, carrots, daikon, rutabaga, turnips, burdock, celery, parsnips, broccoli and leeks, have been provided for soup ingredients.
*Always soak your grains and beans (except red lentils) for maximum digestibility and assimilation. Use rice soaking water but discard bean soaking water and add fresh for cooking.
*Always use either a pinch of sea salt or 1 inch of kombu sea vegetable per cup of dry grain for minerals and to bring out the maximum potential of grain.
*Always cook beans with 1 inch of kombu per dry cup beans. Add salt or shoyu to season the beans at the end of cooking. DO NOT salt beans until they are already cooked. Cook an additional 5-10 minutes after salt or shoyu is added to the beans.
*Vary your breakfast porridge or just use condiments on top of your grain porridge and leave out the raisins in your morning grain if you find flatulence to be problem. Mixing grain and fruit can sometimes be gas forming for some people.
*Use fruit and soymilk in desserts rather that eating it raw or drinking it as a snack on a regular basis.
*It is best to enjoy dessert about 1 hour following a meal.
*Make sauces to go on any of the grains, beans or vegetables. Additional ingredients have been provided for you to make sauces on a regular basis. Choose from tahini, shoyu, umeboshi vinegar, rice vinegar, balsalmic vinegar, herbs, miso (always dilute with a little warm water for maximum digestibility), etc.
*Additional chips, crackers and vegetables have been included for snacking.
*Store unwashed, dry produce in green Evert-Fresh bags in refrigerated space if possible to keep it fresh and crisp for two weeks. The most important things to store in the bags are the greens and the more perishable items.
*Cooked grains and vegetables are OK left out in counter, covered w/ sushi mat, overnight or during the day. Crew 6

==April 27, 2002==
===Captain's Log - Frank Schubert===
The winds have increased. We had to cancel the scheduled EVA this morning. This is very frustrating for the crew. We have a site that we want to take samples from and Penny has been waiting for those samples. Hopefully the wind will die down this afternoon.

We had to do several mantinace EVAs this morning to work on the power. Steve, Sam and Frank worked out the bugs with the power, as it was not functioning properly. The main power was coming off of one 15-amp fuse. This was causing the breaker to pop. We rewired the panel and spit the circuits into two runs. Then we hooked up a second breaker from the generator. I will be very happy to get the new generator.

The music project went well today. We wrote and recorded two songs. Then we sent them to Submarine Studios in San Francisco. Our little tricks with the Internet worked and we were able to upload a 5mb file in about 15 minutes. They got it and started working on it. Tomorrow we will try to upload a 200 mg file. That will go to Devo Studios in L.A. It will be 6 discrete tracks to which they will add another 12 or so tracks and send it back. Kelly is a wiz as a recording engineer. She has a trick she does with the drum tracks. She loops them instead of recording right off the drum machine and so the other musicians will have an absolute zero time point. Sam has such a wonderful voice. He and Kelly are doing to harmonies and they generally get them in one or two takes.

The set up we are using has 24 tracks so we are never at a lost for tracks.

Ephimia continues to fascinate us with stories of ISS. She is amazed at how similar life at MDRS is to ISS. She has observed that we have developed a scapegoating mentality. This happens when a small group is isolated and uses an outside group or individual to vent its frustrations. On ISS the scapegoat is Mission Control.

We are going onto day four without going out of the hab without a suit for any reason.

We had visitors yesterday. They were a family from New York. They had read about the MDRS in the New York Times. Steve was out on a maintenance EVA and he intercepted them before they came to the hab. They took pictures of Steve and the hab and were very polite.

Steve took Ephimia on an EVA to acquaint her with the ATVs. It was her first time but she did a great job. They drove to Schubert trail and then to the top of the ridge. We didn't do any other EVAs as the wind was daunting, 80mph gusts plus. The Mars flag didn't make it in the wind. Luckily we found it before it blew to Kansas and we will put it back up tomorrow if the wind dies down.

Kelly, Sam and I will stay up late tonight to finish the next song. The quality of the recordings is better than most studios I have been in, and it is a great motivator.

More Soon.

On to Mars!

===Proposed Schedule - Crew 6===
'''Goals for the day:'''

*Studio set-up, music tests
*Generator install
*Greenhouse maintenance
*04/27 Science traverse planning, study waypoints
*GIS computer install

{| class="wikitable"
|07:00
|Crew wake
|-
|07:30
|Breakfast preparation
|-
|08:00
|Breakfast
|-
|08:30
|Day planning briefing
|-
|09:00
|IVA operations - studio set-up, toilet seat construction, science lab set-up, GIS computer install
|-
|10:00
|Begin lunch preparations
|-
|10:00
|Crew exercise (2 hours for non-EVA crew)
|-
|12:00
|Lunch
|-
|12:30
|Afternoon IVA operations - continue morning ops
|-
|16:00
|Dinner preparation
|-
|18:00
|Dinner
|-
|19:00
|Maintenance EVA - GreenHab and Generator
|-
|21:00
|End EVA
|-
|21:30
|Evening planning meeting
|-
|22:00
|Presleep activities
|-
|23:00
|Sleep
|}

===Engineering Report - Kelly Snook===

*'''Computers are virus-free''' - Norton has been run on HabCom and all personal machines, with no instances of infected files.
*'''Water System''' - We will look at rigging pumps in series via an intermediate reservoir to generate enough pressure head to fill the second floor tank. URGENT REQUEST: Please send Hanksville contact to fill the water tank on Sunday.
*'''Electrical Re-configuration of Habitat''' - Circuits inside the habitat were reconfigured from one circuit to two separate circuits with independent breakers, after 4 power failures in the morning. Computers and sensitive instruments are on one circuit, while kitchen appliances and other more volatile systems are on the other. This will save hours of time rebooting computers.
*'''EVA Suit Human Factors Analysis''' - The human factors specialist (E. Morphew) conducted an initial EVA suit analysis during one of the maintenance EVAs today (see separate report before end of mission). Radios continue to be problematic. For maintenance EVAs near the hab, we have begun using exclusively the handheld radios through the helmets. This works some of the time. Today the wind was so strong that we resorted to hand signals through hab portals to communicate with the EVA team.
*'''Advanced ATV Training''' - One maintenance EVA today included advanced ATV training in preparation for challenging scientific traverses scheduled over the next week.
*'''Recording Engineering''' - Initial studio setup is complete, and two songs have been successfully recorded and sent to remote studios using two different methods of on-line collaboration. We see this as a good analog for many science and engineering tasks to be done on Mars. The tasks are technically challenging, intellectually demanding, data-intensive, and impossible without advanced planning, real-time coordination, and creative collaboration. We are using Digidesign's ProTools LE system running on a Digi001 and an Apple Macintosh Titanium Powerbook (on loan from Digi (www.digidesign.com)). Digidesign's DigiStudio (with Rocket Networks) has proven to be extremely useful and easy to use, and we are looking forward to feedback from the remote musicians and engineers. '''Note:''' Any musicians wishing to collaborate from their own ProTools studios are invited to contact us via Mission Control to request permission to access our DigiStudio folder. Songs recorded in our MDRS Extremophiles Studio have thus far included vocal tracks (on a B.L.U.E. Dragonfly mike on loan from Guitar Center in Houston, TX), drum machine tracks, piano/organ (Yamaha P20 also on loan from Guitar Center), electric and acoustic guitar, electric bass, flute, banjo, percussion instruments, and sampled sounds from the hab. Mission Control can expect to be contacted on Monday night to facilitate collaboration with It's Not Rocket Science Studios in Houston, Texas. We will attempt to upload full sessions to the Digistudio site, if we can successfully transmit files that large (about 10-50 mb). The whole crew is contributing to these creative projects, with some crewmembers even collaborating to write poetry and lyrics. This project has been a morale booster for the crew, especially after the successful initial setup of the studio and demonstration of the collaboration infrastructure with Earth studios. '''Request for Advice:''' We would like to use the piano as a MIDI keyboard to call banks of sounds (the Yamaha is very limited in its sounds). Could someone at Mission Control find a musician who might know of a good way to access more sounds (perhaps downloading from the web)?
*'''Large File Transfer Protocol Established''' - For those studios who are not equipped with ProTools or DigiStudio, we have successfully set up FTP servers to transmit compressed MP3 files for collaboration. We are able to downlink 5 mb files to earth (upload to FTP site) in about 20 minutes, and uplink (download from FTP sites) in 4 minutes. This will be sufficient for our collaboration goals if we are able to maintain the systems performing at this level.
*'''Food Experiment''' - Cooking and food preparation continue to require approximately 10-15 man-hours a day, but the crew is healthy and is enjoying the food. We will make bread for the first time tomorrow, which is a source of excitement for the crew. Menus and more details on the food are being posted in a separate report. The vegetables are beginning to cause odors in the habitat due to limited refrigerated storage and repeated power failures. '''Crew 6'''

===Operations Report - Crew 6===

*'''Crew Schedules''' - beginning to stabilize, and planned schedules are starting to resemble more the actual activities. One of the major exploration science experiments on this mission involves rigorous scheduling and task planning to compare plans made well in advance with adjusted plans made the night before each day of activity. Both sets of plans are then compared to detailed records of what actually happened. We are beginning to quantify the impact of contingencies, failures, and misestimates of time on operations and schedules. Examples of comparisons of scheduled and actual activities will be posted tomorrow in the form of jpgs.
*'''Contingencies and Failures''' - Today's main contingencies were repeated power failures, lack of water pump, and computer down-time (due to power failures).
*Four separate EVAs were conducted today to deal with the power outages and electrical reconfiguration. Two science EVAs are planned for tomorrow to collect desert varnish samples for analysis in the hab.
*'''IVAcomms''' - The design of IVAcomm facilities for support of EVA teams is a stationary radio mounted on the wall next to the HabCom computer. We have found this to be suboptimal, as IVAcomm duties typically require only occasional communications and the handheld radios seem much better suited to efficient crew task scheduling. Crewmembers frequently parallel process several tasks at once, and IVAcomm duties are often shared amongst IVA crew. '''Crew 6'''

===Menu Modifications - P. Boston===
'''Rating:'''
{| class="wikitable"
|
{| class="wikitable"
|'''1'''
|'''Inedible'''
|-
|'''2'''
|'''Yech''', but it IS organic carbon
|-
|'''3'''
|'''OK''', but I wouldn't serve it at anybody's bar mitzvah
|-
|'''4'''
|'''Surprisingly good''', considering how it looks
|-
|'''5'''
|'''Best thing since sliced bread''', I plan to serve it to
me mum on her next birthday
|}
|}
Breakfast Simplification & Yummification of Twig Tea:

'''Rice in pressure cooker''' (cooked last night), cinnamon, raisins, and honey added this morning and heated. 4 +.

'''Twig Tea''' modified with water and some apple juice (much yummier). 2 to 3.
----Lunch Punting:

Making Veggie-heavy souplike food because of veggie storage problems.

'''But Jim!!! Is It REALLY Life as We Know It? Stew'''

(Created by Penny). 3 to 5.

*Every questionable veggie in site
*Broken up chunks of tofu jerky
*Throw in blobs of three kinds of miso
*Throw in a packet of seaweed miso instant soup (healthy but quick and yummy)
*Two blobs of wholegrain mustard
*A few pinches of dill
*A few tsp of vegetable boullion

#Chop questionable veggies as finely as time will allow (!).
#Find a pan big enough (this is the hard part)
#Saute veggies, put in pan
#Saute tofu, put in pan
#Cover with water
#Put the rest of the ingredients into the pot, bring to slow boil.
#Simmer til the cows (or EVA team) come home!

----Dinner:

'''Fresh tossed romaine salad with Balsamic vinegar and oil dressing.''' 3 to 4.

'''Japanese Fried Noodles and tempeh''', (see Dawn's recipe). 4 to 5

Recipe was unclear in places. Also, the sautéing of the vegetables was insufficient to cook them. When noodles were done, vegetables were unpleasantly undercooked. We wound up overcooking the noodles to make the veggies adequately cooked. Logistical difficulties with utensils included more food than skillet and the habitually underpowered cooking surfaces. We added scallions to the sautéed tempe instead of the noodles. We used Chinese cabbage as the leafy green in the noodles.

'''Tempeh''' 4 to 4+

'''Effie's Burning Tongue Espresso Tofu Cheesecake''' -- in a Banana walnut, toasted sunflower seed crust with cherry topping (created by Effie) Effie said 2 (it sucks). Others said 3 to 4+. Effie and Steve experienced a peculiar burning in the mid region of their tongues upon consumption. Kelly experienced feelings of well-being and companionable love waves.

'''"Crust"'''

*toasted sunflower seeds (sautéed in oil)
*banana chips
*walnuts
*sweetening agent (honey)
*cinnamon

Put all crust ingredients in food processor, chop finely.

'''Filling'''

*Cream Tofu
*Chocolate covered espresso beans
*TBS sugar
*Honey

Put all ingredients in food processor and puree.

Layer half of the Crust mixture in bowl, layer half of the filling, layer remaining crust and then remaining filling. Chill for an hour. Dehydrated cherries were sweetened with honey and agave nectar, moistened with a small amount of water and heated. They were individually spooned onto servings.

===Personal Journal - Sam Burbank===
Mars as Mirror

I was in a bad mood last night. To much social time, too much work and too little sleep. Small hab, far from home. It took two hours to do the dishes (these macrobiotic meals require tremendous amounts of prep time for the chefs, and use many containers; in this case, three frying pans, 4 pots, 1 wok, 1 pressure cooker, and a food processor). I was beat. But we needed to fill the generator if we wanted power through the evening, and I had mentioned earlier that I'd do it. So it was 10:00 now (I still had had no chance to send even a quick email home) and was time to get suited up and into the airlock to go perform this necessary and rudimentary task.

Thank goodness I realized, even in a bad mood, to pay close attention to how this felt, because I think this may have been the real deal. This was when the sim really began for me.

Suit up, comms check, airlock. Wait. How much time left, Hab? Over. Wait.

So here is an irritated guy in a spacesuit, sitting in an airlock and not wanting to be there. Now you're in a simulation! How much more time, hab? Over.

Door opens, garbage out, walk past the greenhouse to the generator: purpose, intent. Begin filling (and it was low). Try to keep the gas off the gloves. How to see if it's near the top? Full. Replace caps to both cans and to the generator.

Back to the front of the hab, grab the garbage, walk it to the garbage pile; flashlight on red rock, crunchy footsteps, scratched face shield. Wait, don't need the flashlight, there was enough moonlight if you walked carefully. Crunch, crunch. Color from moonlight. Such a red place.

I walked back around the hab, ready to get back in the airlock, and then I looked up and stopped for a moment, frozen.

The hab, straight in front of me, was framed between the greenhouse to the left and the nearly-full moon hovering on the right, an imaginary line running from the bottom left to the upper right of the hab, as if painted by one of the old masters. The hab windows shined like a lighthouse. No movement inside. Everyone sitting and working, just as I left them, no doubt. But something had now changed for me.

Hab, may I take a few minutes to just sit? Over.

I sat on a stratified-looking rock outcropping, just where it should have been, and let my eyes drift from the low hills to the northeast, to our small home, to the now well used ATV trail running to the hab. And finally to our big moon, bouncing all of this sunlight light back to Earth. And I felt overfilled by the scene (like our generator!), mentally equivilant to being speechless.

Look at this planet. What if this was the only way to see it? What if, over the course of say the next year and a half, you were just going to see this area, maybe a diameter of 20 miles, and it would always be in a spacesuit with scratches on the face shield and a loud fan in your ear? I think you would fall in love with the Earth. You would, as I did, pull up a handful of dirt just to feel the texture, the grit of the rocks and sand and silt. The world you're small spaceship is sitting on.

Would you feel this way because this looks like Mars, because that's the world you dream of one day seeing? No, the shock is remembering the Earth is a planet, and it's part of the universe we so long to see and explore, and we forget to see it.

Lock yourself up for a while, work too hard, sleep too little, get grumpy. Then put on a spacesuit and sit in an airlock and wait. Finally, walk outside. You'll soon have dirt in your gloves too. You'll too will look up at our moon, trying to focus through salt water and scratched Plexiglas, and wonder how you were lucky enough to visit this planet first.

==April 28, 2002==
===Proposed Schedule - Crew 6===
Science EVA S2 planned for 04/27 did not happen and has been postponed until 04/28. Crew slept late 04/27, due to overexhaustion and sleep times past 4am. The group movie planned for the evening of 04/27 also did not happen, but a nice spontaneous group lunch happened around 3pm. Science lab setup activities were bumped due to electrical system overhaul and other maintenance tasks. The music and food experiments happened as planned and were successful.

6:00 Generator refill EVA (every generator refill is done in full suits (FULL SIM)) and waste removal

7:30 Crew wake, breakfast prep

08:30 Breakfast

09:30 EVA S2 Prep

10:00 EVA S2 - Science EVA to look for Frank's Desert Varnish Site and collect biology samples (F. Schubert and K. Snook)

IVA - videography (S. Burbank)

psych and human factors evaluation (E. Morphew)

macrobiotic food experiment (S. McDaniel)

science lab setup (S. McDaniel and P. Boston)

10:00 Lunch prep

12:00-13:00 Lunch

14:00 IVA - music collaboration with remote studios

psych and human factors evaluation (E. Morphew)

ProTools tutorial and music collaboration with Earth (K. Snook and S. Burbank)

macrobiotic food experiment (S. McDaniels, K. Snook)

science lab setup (P. Boston)

Non-EVA crew exercise (P. Boston and S. McDaniels)

16:00 EVA - Desert Varnish sample collection (E. Morphew, S. Burbank)

17:00 Dinner prep

19:00 Dinner

20:00 Planning meeting and reports

21:00 Group activity - Japanese Anime Movie

23:00 Pre-sleep and sleep

===Engineering Report - Kelly Snook===
'''Water''' - Water was delivered today. First set of showers tomorrow. We are still doing bucket brigade for water to kitchen.

'''EVAs - 2 science EVAs were executed today:'''

*'''Morning EVA''' (Schubert, Snook) - collected desert varnish to sample for Boston
*'''Afternoon/Evening''' EVA (Morphew, Burbank) - tested microbiology sampling equipment and protocols. Interesting detour along Highway 24 on return trip. EVA suits performed beautifully.

'''Comms''' - Radio repeater not functioning, which limits EVA distance. Maintenance EVA will be performed tomorrow or Tuesday to attempt a repair if it turns out to be dead battery in the repeater. Request: please advice on make/model of battery inside the repeater so replacement can be installed if necessary.

'''Electricity''' - New hab wiring was successful - today the kitchen breaker tripped inside the hab. Computers and other sensitive equipment were not affected. No other power failures today.

'''Health and Safety''' - Protocols and equipment are being improved. More on this tomorrow.

'''Food''' - Nothing to report. Food continues to be delicious and time consuming.

'''Studio''' - Another song ("Goin' to Mars") is being recorded as I type this. This report will be brief. Poetry and lyrics are being generated by several crew members.

'''Captain''' - Captain Schubert is recording at the moment and won't be sending a Captain's Log tonight.

'''Operations''' - Crew getting very good at logging schedules and helping with planning. Collecting very good operations planning data.

'''Crew 6'''

===EVA Science Tool Test Protocol - P. Boston===
'''Small Tool Manipulation, Sample Acquisition, and Sterile Procedures Conducted in Suit - P. Boston'''

The cumbersome restrictions of the suit, helmet, and gloves make many normal tasks and motions difficult or impossible. We will try various tools and methods to accomplish a set of both generalized and experiment-specific tasks that are routinely used in field geomicrobiology, mineralogy, and ecological studies.

Activities include the following, going from lesser to greater fine motor skills:

#Simple hand samples collected in sterile Whirlpaks
#Comparison of different sizes and types of forceps for manipulating small samples
#Flame-sterilizing small tools with ethanol and lighter while not setting gloves on fire.
#Gluing tiny samples onto SEM stubs
#Screwing and unscrewing small culture tubes and inoculating media with sample.
#Exoenzyme procedure: i.e. placing damp(fragile), sterile impregnated filter papers on surfaces, positioning sterile foil packets over them, putting in alkaline reaction stop solution, and retrieving the filters untorn.

Kelly Snook and Frank Schubert will test the first procedure during a full sim EVA to a desert varnish site previously scouted by Frank. Ephie Morphew and Sam Burbank will test all of the remaining procedures during a full sim EVA at another site.

'''Details of Procedures:'''

#Sterile Whirlpaks will be opened by pulling on the two yellow tabs on the bag. Holding the outside of the bag, place the inside of the bag over specimen rock or chunk of material and scoop into the bag by squishing the bag around the object, turning bag over to upright position and letting material drop in. Twirl bag shut and bend in ends.
#Take a selection of different forceps instruments and test the ability to pick up rocks of various sizes and shapes, small pieces of loosely consolidated materials, lichens, surface scrapings and mud patterns. Note the difficulty of wielding various tools and other drawbacks or advantages with the different sizes and styles. Will forceps in both hands help in manipulation? Do two people function better in manipulation than one?
#Flame sterilizing is easier done with two people in almost all circumstances. Person 1: Dip business end of tool to be sterilized into small bottle of ethyl alcohol (ethanol) that you are holding. Person 2: Apply lighter, torch or other ignition device produced flame to the tool to light the alcohol. When using the tool first, repeat several times. Repeat between procedures that either touch different samples or are placed into different media or solutions, or anytime that a tool is accidentally brushed or touched to a non-sterile surface.
#SEM stubs are small aluminum discs with a stem onto which samples are affixed for later coating with metal and analysis in scanning electron micrography. Usually needlepoint forceps are used to delicately manipulate the sample onto the disc. Conventional model glue (e.g. Duco Cement) is applied in a small drop to the disc and the sample is placed on it. Care must be taken to let the glue dry prior to packing or shaking the sample vials.
#A variety of screwcap culture tubes are used to collect living organism samples in attempts to enable them to grow in captivity for further study. There are many kinds of media (bug food) that we use for various purposes. First, just to see if we can get anything to grow we use different kinds of media in hopes that something we offer will suit someone that we have captured. In other cases, we start by knowing that we want organisms that can do a particular type of metabolism. We make media that can indicate the presence of a byproduct of the metabolism that is of interest, e.g. by changing color, liquefying, or producing gas. Lastly, enrichment cultures are those that attempt to capture organisms that live by using a particular substance. We make bug food that contains only that substance. Whomever grows on it is suspected of being able to use that substance upon future verification experiments. Screwcap tubes are small and it is critical to keep the lip of the tube untouched and sterile. Samples are either plucked with sterile forceps, scraped with a sterile knife blade, collected with a sterile inoculating loop, or scooped with a small sterile metal spatula. The material is then placed in the tube and the tube is immediately capped. This procedure will be challenging with gloves on.
#I have developed imprint exoenzyme assays to detect the presence and rough quantification of surface activities of organisms on rocky surfaces. All organisms exude substances into their environments. Frequently, these are enzymes that are characteristic of a particular metabolic process or other chemical transformation carried out by the organisms. We use a variety of substrates that various bug enzymes can act on. These are tagged with a chemical functional group that is not fluorescent when attached to the main substrate molecule, but becomes fluorescent when cleaved from that substrate by the appropriate enzyme if it encounters it on the sample surface. The way we usually do this is to have whirlpak bags with filter paper circles impregnated with the tagged substrates. Flame sterilized forceps are used to pull these out and place them on the surfaces. Pre-sterilized aluminum foil sheets are pressed over the filter to make it conform to the rock surface. These are left in place from 10 minutes to many hours depending upon the environmental conditions at a given site. Then the foil is lifted off, the filter paper is manipulated with forceps into an alkaline solution that stops the reaction. The filter is put on the foil, wrapped for protection and then returned to the lab for further processing and inspection with an epifluorescent microscope.

===Tool Test - Post EVA Briefing - Ephi & Sam===
They had no problem getting stuff out of the small plastic box. Tabbed ziplocks work well and are grippable with the gloves. Untabbed ziplocks can be clumsily wrangled open but why bother?

'''Difficult or Impossible to Use Tools:'''

*Gripper tool needs bigger holes (glove fingers don't fit)
*Small spatula sucks, can't be gripped with gloves.
*Needlepoint forceps are hard to use and can't handle most sample types
*Larger forceps are no more useful than their widest opening point. The very large ones are simply longer and harder to handle for most samples.

'''Good Tools:'''

Reverse forceps are great. The holding upon release feature and the parallel surfaces while in use are the important features.

Large weighing spatula works well for unconsolidated materials and is useable in the gloves.

Since width is really the controlling parameter, we can redesign bigger flat-bladed reverse forceps to handle larger samples.

A fliptop ethanol container rather than a screwcap bottle would be helpful.

'''Exoenzyme Deployment:'''

The placement of the soaked filter papers in the sterile foil wrappings on rock surfaces was surprisingly easy. They had no problems with either the folded or the rolled trial versions of the foil.

==April 29, 2002==
===Captain's Log===
[[File:Crew6 FieldEVA.jpg|thumb|Sam and Ephimia in the field getting samples]]
Today was the most productive day yet. It has taken several days to get up to speed but we are now working with full weight on all fronts. Science, music and human factors.

Penny is feeling much better now and was in the lab for several hours. The set-up is complete and all the samples were inspected. Steve spent the several hours in the lab too. The microscope had been partially disassembled and Steve put the UV fluorescence parts back on the scope. He then subjected the samples to the OPH assays. He was very happy with the samples that Sam and I collected on our EVA today.
[[File:Crew6 Flag.jpg|thumb|The Flag of Mars waves in the desert winds]]
The EVA that Sam and I went on was a long excursion north of the hab into the Tank Wash area. We were searching for a trail that will lead up the valley to Factory Butte. I had seen the trail from the air last year. This area has numerous shallow canyons, (approximately 1 meters) which outflow to the Muddy River. The sandstone channels in this area are part of the Bushy Basin Member of the Morrison Formation. Several of these channels were undercut by erosion and they had collapsed forming small caves, small boulder fields. In many of the smaller washes we found potholes. In these potholes we found evidence of biological material. After several tries and deadends we found an old mining trail. This trail looked to be about 25 years old and if not for our experience on ATVs we would not have attempted it. We pressed on and it was quite rewarding. At one stop we came across several specimens of desert varnish. We collected them in the bags that Penny had supplied us with and moved on. Later we found what appeared to be endolithic material in a rock we broke open. Steve confirmed this find. Several of these channels were undercut by erosion and they had collapsed forming small caves and small boulder fields. In many of the smaller washes we found potholes. In these potholes we found evidence of biological material. At this point we were out of sample bags so we plan to go back to the area with the next couple of days and bring back samples for Steve and Penny.
[[File:Crew6 SamFrankATV.jpg|thumb|Sam and Frank with stuck ATV]]
We were able to make it about 2/3s of the way up the valley before my ATV started running low on gas. This was not the place to run out of gas so we reluctantly turned back. Before turning back we came across the Muddy River. Of course we had to try to cross it. On the way back across the river both Sam and I became mired in the sand. We had visions of Devon Island.

Ephimia continues to collect valuable data on this crew's behavior. In fact she stated she feels overwhelmed by the amount of data she is getting. Our strict adherence to sim is producing some interesting results. We all feel that we have been here much longer than 6 days. We have had several heated discussions. The interesting part of these discussions is that there is never anyone to blame. The kids at heart in this crew are acting very mature. I have not laughed so much in years. Humor seems to permeate everything we do. Steve has instituted a joke session after dinner. So far he has the largest repertoire of jokes although Sam has quite a few zingers. Last night we had some of Steve's bean burritos.

Almost all the bugs have been worked out of the hab. After changing the breakers we have had no more blown fuses on the generator. Since we have to suit up to fix the breaker this is a real blessing.
[[File:Crew6 SamKelly.jpg|thumb|Sam and Kelly in the studio]]
Kelly gets the inspiration award for the day. It happened when Sam's brother Josh sent us a piece of music he wrote for us last night. Kelly was so impressed she stayed up all night adding parts to the music. This morning when we woke up we were treated to a beautiful piece of music. Our music experiment is going very well. We have several songs in the works and have connected with several studios back on Earth. It is amazing the connection we make with these musicians. Music is the universal language and we are connecting on a technical and emotional level with people we never see. The music has had a great effect on the crew morale. I was afraid that we would bother the other crewmembers by playing songs over and over but they seem genuinely happy to be part of it and are helping and adding parts every day.
[[File:Crew6 SamSamples.jpg|thumb|Sam in the field collecting samples]]
The food experiment is going well. Last night we had some of Steve's bean burritos. They were great. Our health and energy is at a high level. The meals are really good and the social aspect of eating together at least twice a day has been very good for morale. We suspect that on a real Mars mission the crew would not have time to cook like this. Although the cooks, (not me, I do dishes), say that they are getting faster and faster every day. It would be good to send a trained cook on a Mars mission.

More later.

===Engineering Report===
Crew is time limited and sleep-deprived. Reports may be thin and short for the next couple days until our day off (Wednesday).

'''Radio Communications''' - We have repaired the repeater problem by reassembling the receiver unit inside the habitat. An EVA was conducted successfully today to distances of 7 or 8 miles. We have received the new radios from headquarters and will test them out tomorrow. We have three separate EVA's scheduled for tomorrow in close proximity to the habitat.

'''Water pump''' - The sump pump that is being used to pump water into the first floor of the habitat was fixed today. The activation arm had been jammed down.

'''Reports and Logging''' - The NASA reference documentation and preliminary operations manuals schedule one hour of report writing a day, no group planning meetings, and no time for work-related e-mail processing. This is proving to be impossible to maintain. This crew spends at least several hours a day doing work-related report writing, logging of schedules, logging of experiments, and planning the day's and next day's activities. We continue to keep detailed logs of our time spent Next week we will attempt to follow the split ops approach with three teams of two following independent schedules. This week has been each person independently scheduled/tasked. The crew has prepared EVA reports, HSO reports, a Captain's Log, and anecdotal journals to be attached to this report today. Photos will follow tomorrow. Serious videography for the National Geographic documentaries has started with S. Burbank both inside and outside the habitat.

'''Science Lab and field microbiology''' - The autoclave was set up today, the microscope UV fluorescence microscope lenses and filters had been taken off. They have been re-installed and the optics realigned. More work needs to be done on this. P. Boston will conduct a walking EVA in the vicinity of the habitat. Microbiology field protocol tests were done by Sam and Ephi yesterday (see their EVA report and Penny's report attached).

Tomorrow we will set up the GIS computer that Jean has sent and begin the process of tabulating our EVA data. Results will be posted as soon as possible.

'''Music''' - This is turning out to be one of the most successful projects of the mission. Last night was another major milestone. Joshua Burbank and Jeremy Bloch sent rough fragments of a song, which were then arranged and augmented through the night by the Extremophiles. When the rest of the crew awoke this morning, a new piece had emerged. We will be writing about this experiment in more detail and posting the report within the next few days. We are having some issues with DigiStudio, and would really appreciate some assistance from Mission Control or other musicians reading this report. Our question is how to find more details on the status of an "upload" when posting a new session to the projects list. We experience frequent internet interruptions and we don't know whether there is any way to find a log of how much of a file was uploaded (or indeed whether it is still being uploaded). We will attempt to contact our Digidesign reps directly to ask this question, but if you can assist, we'll look forward to your help.

Our crew has been enjoying the beats and rhymes of E=MC Hawking.

'''Random delivery notes''' - We were delivered a box apparently intended for someone in California with a return address in Hanksville. There are no markings on it at all for the Mars Society. We opened it for security/safety reasons and found a pillow inside. We'll send it back next time we get a delivery. We still have not received the kitchen supplies, but we're doing fairly well with what we have, combined with our new electrical system.

'''Waste''' - We are still looking to Mission Control or HQ to solve the waste issue. We should (and physically cannot) bury it, we cannot process it in the biolet, and it cannot sit in the back of the pickup truck for more than another week (because we have to use the truck to transport our gear back to Earth).

'''Patch''' - We're putting the finishing touches on our mission patch. We will post it as soon as it's finalized

'''Safety Protocols''' - We're still working on these.

'''Crew Schedule for tomorrow'''

*3 EVAs planned - One morning (Boston, Morphew, McDaniels), One afternoon (McDaniels, Schubert), one Evening (Snok, Burbank) Major IVA activities - Science Laboratory preparation and sample analysis.
*Kitchen duties - We have developed a proper kitchen duties task schedule which is posted in the hab and which will help in the management of the food and its impact on the rest of our work. Schedule will be posted tomorrow.
*Music - Kelly will lead a ProTools tutorial in the morning and the Extremophiles will continue collaboration with Submarine and It's Not Rocket Science Studios. Some of the crew's poetry will be used to inspire 2 new songs tomorrow.
*Videography - photographs are being prepared for posting tomorrow. We are not neglecting this important duty, we were just left with a habitat in such dire need of overhaul that it has taken us 4 days to (quite literally) dig out.
*Exercise - All crew members will be conducting walking EVAs tomorrow, so no separate exercise is planned.

===Health and Safety Report===
A major health hazard was resolved with the removal of the malfunctioning BioLet this last week. The BioLet was full to overflowing, and had to be manually discharged of its contents. Those persons who actually contacted the human feces, while nauseated many times over the hours-long ordeal, did not appear to contract any waste related enteric disease. The head facility was completely doused with bleach and antiseptic, and an individual bag approach has been instituted. While this alleviates the immediate concerns of health vis-à-vis the BioLet, it does not provide any solution for the proper disposal of this hazardous waste (now lying bagged in the back of the Society's Ford pickup.

Dr. Boston and CO Schubert are each nursing soft tissue injuries. Each seems to be on the mend and getting back into their full crew roles.

The macrobiotic diet seems to be a healthy one, with few complaints. Adding freshly made bread to the diet seemed to brighten the meals.

Fresh water was added to the outside reservoir today. I reiterated that the tank should be washed out, and filled only with Hanksville publicly-supplied water.

==April 30, 2002==
[[File:Crew6 EphimiaATV.jpg|left|thumb|Ephimia exploring on the ATV.]]
[[File:Crew6 FrankHandMirror.jpg|center|thumb|Frank in Sam's hand mirror.]]
[[File:Crew6 FrankNewGround.jpg|left|thumb|Frank explores new ground.]]
[[File:Crew6 KellyStudio.jpg|center|thumb|Kelly engineering in the studio.]]
[[File:Crew6 Music.jpg|left|thumb|Music from Earth.]]
[[File:Crew6 SamKellyStudio.jpg|center|thumb|Sam and Kelly in the studio.]]

==May 1, 2002==
[[File:Crew6 SteveEVA.jpg|left|thumb|Steve on water repair EVA]]
[[File:Crew6 SteveSeaweed.jpg|center|thumb|Texan Steve with seaweed]]
[[File:Crew6 FrankPennyKelly.jpg|left|thumb|Frank, Penny and Kelly]]
[[File:Crew6 FrankRocksOut.jpg|center|thumb|Extremophile Frank Rocks Out]]
[[File:Crew6 SamATV.jpg|center|thumb|Sam repairing an ATV]]

===Captain's Log===
Today was our official day off. And so we did things that were fun. Kelly, Sam and I recorded a song that Sam has written called She's so Smart.

Steve and Penny spent the day in the lab working on the samples that we have collected during the stay. Ephimia spent the day working on the questionnaires she had given us.

In other words our day off was the same as other days. Well, we did sleep late.

We are now sitting around and telling jokes and eating the nachos that Steve has made.

Penny is feeling a lot better today. She spent several hours in the lab. We are all relieved. She has been in a lot of pain up until today. Now that she is feeling better we can tease her about the crash again. Ha ha.

The only EVA today was Sam shooting outside scenery shots for the special he is doing for National Geographic Channel. He came in just in time for the nachos. Sam is an excellent producer, cameraman and writer. We are all excited about his work and can't wait to see how good we will look. Many of us are planning to be movie stars after his work comes out.

Kelly is in the studio working on a song that Steve wrote. It is a lullaby that he wrote for his son twenty years ago. He was humming it the other day and when I heard it I fell in love with it. Kelly picked up on it right away and has put some beautiful music to the words. Sam and I will put parts to the music tonight.

We now have seven songs complete and about 10 more that are ready to start work on. Mark Mothersbaugh and Bob Casale have a song they are sending us. We also have received a song from Sam's brother Josh and a song from the band The Bad Mintons in Portland. We are expecting a song from Derek Smith in Toronto in the next day or so.

So, it is my day off and I am going to make this short.

More later.

==May 2, 2002==
[[File:Crew6 SteveMicrobes.jpg|left|thumb|Steve McDaniel Gets Down for OPH Microbes]]
[[File:Crew6 SchubertsTriumph.jpg|center|thumb|Schubert's Triumph]]

===Captain's Log - Frank Schubert===
[[File:Crew6 MuddyMonolith.jpg|left|thumb|Schubert with Muddy Creek Monolith]]
[[File:Crew6 SEMSamples.jpg|thumb|Penny Boston Taking SEM Samples]]
The wind came back. At one point it really shook the hab. Until that point I have had not worried about the hab. That gust startled me. I thought the hab had actually moved a couple inches. But not to worry. This ship is solid and took the beating in stride.

I used to keep a journal like this. I stopped when I realized that there were so many days that were the same. This is something that a Mars crew will have to deal with. The music has helped greatly in this area. We do at least one new song a day. The songs sometimes set the attitude for the day. We have stayed away from achy breaky songs. There are others that can write those. We tend to stick to happy or fun songs. So, that sameness is the feeling that I am fighting as I write this. I will press on.
[[File:Crew6 Monolith2.jpg|left|thumb|Muddy Creek Monolith]]
[[File:Crew6 WallStrata.jpg|thumb|Muddy Creek Canyon Wall Strata]]
Yesterday was somewhat different. We had a visit from a German film crew. We had told them about our strict adherence to sim and they were very cooperative. We had them follow Steve and Penny on a sample collection EVA. This was a walking EVA and Steve and Penny found lots of samples. We also gave the film crew a radio so they could hear our communications. They are going to do a internet interview with us in the morning and then come back on press day to do the individual interviews and film the inside of the hab.

Crew 6 had two EVAs yesterday. The EVA that Steve and Penny did was done around the hab. We really did pick a great spot. The EVA crew collected more good samples on that EVA than any of the others. This was Penny's first trip out of the hab since her accident. Penny is a real trooper and she gave it all she had.

She came back exhausted but happy.
[[File:Crew6 FactoryButte.jpg|left|thumb|Factory Butte Pinnacle]]
[[File:Crew6 Panoramic.jpg|thumb|Factory Butte Panoramic]]
The second EVA was done as an exploration sortie. Steve and I went looking for the trail that I had seen from the air in January. The day before we had followed the Muddy Creek almost 20 miles to the north. We found an entrance to the Goblin Valley and some spectacular scenery. But there is no trail up the Skyline Ridge. Today we headed west through the Coal Mine Wash. The going was slow as we came to many dead ends in the dune like mounds that make up most or the wash. We finally broke out into the wash floor. We started noticing more dirt bike tracks and cow dung. We headed west across the baked surface making good time. The valley started to narrow and we came across a small creek. After another ten minutes it looked like we had come to a dead end. We were still happy, as we had gone far further than any other EVA to date. We could see Factory Butte but it looked like we wouldn't get there. Then I saw it. In a small washout area to left there was a trail that was cut into the side of the cliff. It was the trail that I had seen from the air. We both let out a yell. The trail was very steep for the first 100 feet with a vertical drop off on the left. Not a trail for a novice but both Steve and I have a lot of experience on ATVs so we hit the trail. After the first steep section the trail leveled out into a narrow valley that was strewn with huge boulders. Several of these boulders had very large patches of ancient desert varnish. Penny will be drooling when she sees this.
[[File:Crew6 Psychoanalysis.jpg|left|thumb|Ephimia Morphew Psychoanalyzes Dirt]]
[[File:Crew6 DesertVarnish.jpg|thumb|Ephimia Morphew Collects Desert Varnish]]
I would guess this trail was cut by a bulldozer about 40 years ago and there were several places where we had to cut around the fallen rock.

Near the top was another steep section that was about 30 feet long. We stopped and looked at eachother. This was it. As we came over the top the Factory Butte came into view. It is such an impressive structure and the lighting was spectacular.

We drove up the base and radioed the hab. They asked for proof so we took several pictures and then headed back as it was getting late and we wanted to mark the trail through the dune area.

This trail will open up the Capital Reef area to the hab. It was a great find.
[[File:Crew6 Lesson.jpg|left|thumb|Dr. McDaniel Gets A Lesson in Desert Varnish From Dr. Boston]]
[[File:Crew6 Lab.jpg|thumb|Steve in the lab]]
The hab is operating well. Our low-tech solution to the toilet has worked out great. There is no odor in the hab except for the toilet room itself. We leave on the fan in that room and it is not too unpleasant.

Our health is good. My airplane injuries are healing well. I cut off the cast on my wrist the other day. It had gotten wet and was starting to irritate the skin. I now duct tape it on when I got outside.

Penny is feeling much better and working in the lab quite a bit.

Our macrobiotic diet has worked out well. I don't think a Mars crew would make it the exclusive diet, but there are parts of it that work well. As far as nutrition goes, it is good. The problem is the time it takes to prepare it. On the way to Mars and on the way back it would be fine.
[[File:Crew6 Singing.jpg|left|thumb|Kelly singing in the studio]]
[[File:Crew6 Guitar.jpg|thumb|Frank's fingers on guitar]]
We are connecting with Devo Studio and Submarine studios tomorrow and hope to have an almost live session.

More soon.

On to Mars

===EVA Report - Penny Boston===
[[File:Crew6 EphimiaKelly.jpg|left|thumb|Ephimia and Kelly]]
[[File:Crew6 OscarDonut.jpg|thumb|Oscar T. Donut - Crewmember No. 8]]
Steve McDaniel, Ephimia Morphew, and Penny Boston performed a 2.5 hr walking EVA on Thursday morning. Good black desert varnish and fresh fracture surfaces were found and sampled for SEM, OPH, and bulk sample for media making. Several interesting visual potential biosignatures were noted on the way to Schubert's Pass. Some "young" appearing desert varnish of a very orange color on buff sandstone is visible right along the road. This is overlaid with black dendrites or possibly lichen. Significant bleaching spots in red sandstone blocks further along the road was associated with black wormlike patterns. Whether these are lichenous, varnish-like, or mineral inclusions remains to be seen. An additional sampling trip will be scheduled to directly culture these materials. Additional, grey pitting on buff sandstones and a white limy sandstone were also noted.
[[File:Crew6 Dinner.jpg|left|thumb|Crew 6 at the dinner table]]

===Night of the Twin Moons - Penny Boston===
Dateline: Red Planet

May 2 - Habtown

Today, astronomers report seeing thousands of tiny, green, Martian Bunnies pour from their dens and come out to celebrate the May on Mars Festival. Singing (not easy in the thin Martian air), Dancing (much easier in the low Martian gravity), and chemolithotrophic absorption of delicious reduced iron and manganese was on the Agenda for Fun.
[[File:Crew6 Poem1.jpg|thumb|© 2002 R.D. Frederick ]]
The Martian Bunnies from the Planet of Two Moons send Happy May Day greetings to all Earthling Bunnies of the Planet of One Moon!

______________________________________________________

Tonight is the night when the moons are twin

The haze in the sky is sparkling and thin,

And little green bunnies and little green hares
[[File:Crew6 Poem2.jpg|thumb|© 2002 R.D. Frederick ]]
Come out from their craters everywhere.

______________________________________________________

They dance and cavort to a fast Martian jig,

And pass round the Marshine & each takes a swig.

On old Mt. Olympus, they play games of chance,

Dress up in galoshes and do a dust dance.

______________________________________________________

[[File:Crew6 Poem3.jpg|thumb|© 2002 R.D. Frederick ]]

And just before dawn on this Marsbunny Fest

The bravest, bold bunnies each do their best

To gain the Queen's favor by jousting the Bane,

The Monster of metal that sits on the plain.

______________________________________________________

[[File:Crew6 Poem4.jpg|thumb|© 2002 R.D. Frederick ]]
Now it is day and the moons move away,

The haze in the sky thickens to grey,

And little green bunnies and little green hares,

Go back to their craters and curl up in pairs.

==May 3, 2002==
===Mission Update - Kelly Snook===
Mission Support:
[[File:Crew6 PookyEVA.jpg|thumb|Pooky in airlock preparing for EVA]]
Dinner was delicious, and we just had a short but very efficient meeting to plan the weekend. We're really getting in a groove. Today all six of us were on IVA, and no EVAs were performed with the exception of an EVA to the roof to re-set the Starband dish and the EVAs to fill the generator.
[[File:Crew6 PennyPooky.jpg|thumb|Penny & Pooky extract a fossil]]
[[File:Crew6 PookyDesertVarnish.jpg|thumb|Pooky samples young desert varnish]]
[[File:Crew6 PookyPolkadot.jpg|thumb|Pooky examines a polkadot rock]]
[[File:Crew6 PressureBubble.jpg|thumb|Sam & Kelly test the EVA Pressure Bubble]]
[[File:Crew6 ChitChat.jpg|thumb|Pressure Bubble Chit-Chat]]
[[File:Crew6 EphiPooky.jpg|thumb|Ephi & Pooky consult on EVA technique]]
[[File:Crew6 MicrobialLeeching.jpg|thumb|Pooky studies microbial leaching]]
Tomorrow we're sending three people back to Factory Butte, and Sunday we're doing an overnight EVA that will require two crewmembers to go out and set up camp to prepare for the 4 that will go overnight. Tonight we'll be preparing a number of reports for you (and the web): the Engineering report (me), a science report (Penny and Steve), a Captain's log (Frank), and a music report (might be sunday (Sam, Kelly, and Frank)). The second set of Psych tests from our onboard Psychology experiment were completed today. We have not yet taken the psych test you requested. Could you give us more info about this? Who is conducting the experiment? To whom will the results be given/available? Our operations experiment continues to go very well - we are sticking to the nightly planning/scheduling meetings and logging all of our activities. We're not doing this electronically, however. An attempt was made today to transfer the data from the record forms into electronic format, and the process proved to be so tedious and time consuming, I don't think we're going to be able to send it to you before the end of the mission.

We'll write more about this in the engineering report, but we did not yet gather waypoint data for the Factory Butte route. The route takes VERY advanced ATV skills, and Frank still wants to explore a more accessible route. The team is going out again tomorrow and will take some GPS training before going so they can track their route.

Today we wrote lyrics and added some parts to "Here on Earth" (Kelly Snook and Josh Burbank from Submarine Studios in SF), started recording two that were previously written ("Mr Robinson" by Sam Burbank and "Miss You" by Frank Schubert), added some parts to one ("She's Leaving the Earth" - from the Portland collaborators), and generated more poetry and lyrics (Steve McDaniel). Penny and Ephi have written a special version of "I've been Cheated" that should be entertaining. We have had some quite windy days and our uplink speeds have been giving us increasing problems. After reseting the dish today, though, things seem to be going faster. We finished uploading all the parts to "We're the Martians" for DEVO to work on in their studio tomorrow. Have you had a chance to look at the FTP site or listen to any of the music? We think you will really appreciate the song "Here on Earth".

We just wanted to get this little update to you before you leave, since the report preparation will take several hours and they won't come in until late tonight. There are a couple of things we urgently need - could you call Larry first thing in the morning and ask him to bring us as soon as possible:

* As many AA batteries as can be found in Hanksville
* A couple of boxes of small plastic garbage bags (smaller than kitchen bags, for like bathroom-sized bins)
* One six-pack Dr Pepper (SHHH this is a secret suprise for one of our crewmembers)

More later - feel free to post this message on the web, if you think it is relevant. I'll try to get at least the engineering report to you before 10pm, depending on activity from It's Not Rocket Science Studios (Houston) in the next hour.

Kelly

===OPH Kill Experiment - Penny Boston===
Steve McDaniel's OPH activity experiments have shown several samples with significant enzyme activity. In order to distinguish whether the activity is due to something in solution in the supernatant after he has Vortex mixed them or if it is on the surfaces of organisms and whether it is heat sensitive. We began this process by running heat killed and non-treated sample pairs with the OPH colorimetric indicator. The heat-killed specimens failed to react. The untreated specimens reacted as they had in initial trials. Further extrapolations will be investigated in the coming several days.

So far, out of 13 samples, we have seen 4 strongly positive reactions. The remaining 9 were negative or only weakly positive. All negative samples did show evidence of microorganisms on optical microscopic inspection.

We are doing an array of standard optical staining procedures on heat fixed samples of positive and negative controls and unrehydrated ground samples.

==May 6, 2002==
===Engineering Report - Penny Boston===
The conditions in the hab have stabilized as we have developed coping strategies for our numerous problems. However, as the season progresses, heat in the hab is becoming a problem. Clearly, we are near the end of the functionally useful field season. Afternoon heat load on the hab has made the thermal conditions very uncomfortable from approximately 2pm until about 3am when the desert night chill finally sucks enough heat away.

Heat is becoming a problem during EVA. We have attempted to conduct them in the mornings and late afternoons, but this is operationally difficult and even those times are now uncomfortably hot.

'''Recent Highlights:'''

* Bucket brigade is our permanent solution to the water pump failure
* Massive human waste pile from the Biolet has been disposed of and is no longer an issue.
* New radios are not usable. See explanatory note below.
* Dish drainer needs replacement. The configuration is inadequate to the volume of dishes produced from a single meal for 6 people and items are always falling to the floor or back in the sink. We recommend a drainer with closed ends rather than a simple rack.

'''Note on radios:''' We are grateful to Mission Control for sending the new radios. Alas, extensive testing of the new radios has proved disappointing. All transmission are muffled even between people at the hab. Even on Channel 2:00, all transmissions are indistinct even with fresh batteries. We do not have a solution to this problem and are speculating that there is an inherent flaw in the radio design?

===EVA Report - Penny Boston===
The overnight EVA that took place the evening of May 5 into the mid morning of May 6 was very useful but placed significant demands on both the EVA and IVA crew.

Base camp was set up by Ephi Morphew and Steve McDaniel during the late afternoon EVA of 5 May. The site had been selected during a prior EVA by Ephi and Penny Boston. It is located just off the road to Schubert Pass, approximately 100 m from the pass summit on the Hab side. The area is nice and level with minimal small pebbles but abundant larger rocks for camp use.

It was very hot and windy, thus pitching camp was difficult. Staking tents proved untenable. The bentonite hardpan is typically a few inches to tens of inches deep. It is virtually impossible to break through for staking purposes. At the same time, the fluffy upper layers have no cohesion and do not support stakes. Thus, guy wire rigging attached to rocks was essential to support tents. ''Steve recommends that the guy wires be pre-tied onto the tents back at the hab because of the difficulty of executing knots with gloves on.''

Moving large rocks to secure the tent guy ropes caused Ephi to overstress old injury sites, vertebral discs L3, L4, and L5. She did not realize this until later in the evening when she began to experience pain and stiffness. Her mobility has been seriously compromised since this reinjury.

If possible, prior knowledge of likely wind patterns at a given season might help avoid camp establishment during high wind periods. Rain flies were hard to deploy in wind and probably not necessary as the incidence of rainfall at this season is very low.

The EVA team of Kelly Snook, Sam Burbank, and Penny Boston left for the remote site at about 8:30pm. Kelly rode an ATV with gear and Sam and Penny walked. The stroll under the brilliant, starry sky in the stark hills and landforms of the desert was described as "magical" by Sam. It was a spirit-lifting experience for all of us.

Overnight EVA Scenario - For the purposes of simulation, we envisioned a perimeter around the three tent cluster at the camp site that was enclosed in an inflatable bivouac allowing shirt-sleeve conditions within this bubble. Fortunately, the air was completely still for most of our stay so this contributed to the ambiance. Within this "bubble perimeter", Kelly Snook set up her small portable telescope and we watched planets, especially Jupiter and its beautiful moons, in the photometric seeing conditions.

Kelly worked on musical themes and fragments during the late night hours. Sam did some filming. The crew chatted about astronomy, life, and times until about midnight or so when sleep overcame them, one by one. At approximately 3:30am, Penny took a 45 minute foray to look for fluorescent minerals or organisms using longwave (~360nm) and shortwave (~310nm) ultraviolet lights. In the morning, Sam and Kelly worked on music and fleshing out the fragments that Kelly had developed over night while Penny photographed the rock formations, fossils, and textures within the bubble perimeter.

Steve McDaniel arrived at camp on an ATV at about 9:30 to start striking camp. At 11am, the Overnight crew left to return to the Hab. The trip was very slow due to immobility and pain in Penny's leg and lower back. We discovered that there are many, many, many tiny baby steps between Schubert Pass and the hab.

We are planning another EVA to Factory Butte for 7 May for sample collection.

===Health & Safety Report - Steven McDaniel===
On the evening of May 5th, we prepared a base camp in full simulation for use by an overnight EVA (see enginnering reporet). Crewmembers Morphew and McDaniel pitched three tents and made camp in Schubert Pass. As with almost all such sites in the area, the hardpan of bentonite made the use of tent stakes impossible, and we had to resort to securing the tents with guy wires to large stones. In the process of gathering stones, Morphew reinjured a back injury to vertebrae L3-5 (per Morphew) and has been having trouble sleeping and moving around. Treatment has involved mild massage, analgesics, and cold compresses (per Morphew).

There appears to be only one key to the lock box.

I am still in need of directions as to how to find the bimonthly reporting sheets.

===Interplanetary Collaborative Music Project - Sam Burbank, Kelly Snook, & Frank Schubert===
'''The Interplanetary Collaborative Music Project''' (ICoMP) is an experiment in technical and creative collaboration. Participants in the project are working together under the simulated constraints of a human Mars mission to produce a body of work that brings together musicians and engineers from both on Earth and on Mars. The two-week ICoMP experiment is being conducted in the Mars Desert Research Station, a two-story simulated Mars Habitat located in the Utah desert. This area of Utah looks like the Mars of popular imagination with its red rock, huge buttes, and stratified cliffs. The landscape is remote and barren, and the habitat provides an environment for researchers to experience the isolation and other unique elements of living and working on Mars.

The MDRS is being crewed by scientists, engineers, and artists from around the world, representing groups like NASA, The European Space Agency, and numerous universities and private organizations. The ICoMP experiment will occur during Crew 6, the final crew for the 2002 field season. Crew 6 will occupy the research station from April 24th to May 8th.

Background

Three members of Crew 6 initiated the ICoMP experiment: Kelly Snook, Frank Schubert, and Sam Burbank. The remaining three members of Crew 6 are participating in various ways by writing poetry, lyrics, or contributing other creative ideas to the project.

NASA's current reference mission for a human Mars exploration calls for a two and a half year journey, with about 40% of the time in transit, and 60% spent on the surface of the planet. Because of the time delay between Mars and Earth, Mars explorers will be able to speak only with the other crew members. They may send video messages and e-mail to Earth, but always with a delay (from about 6 minutes up to 45 minutes round trip, depending on where Mars and Earth are relative to each other during their 780 day cycle). This type of limited communication means that the Mars crew will naturally become more autonomous than previous exploration crews in Earth orbit or on the Moon. A new paradigm of scientific, engineering, and creative collaboration must be pioneered to optimize the quality and effectiveness of input from Earth, while allowing the crew the flexibility to conduct operations as they see fit. Issues such as technical troubleshooting, both on Mars and on Earth, become much more difficult in this scenario. In collaborative situations, input from both sides might cross paths, or fail to reach the other side in time to produce desired results or prevent problems. Protocols and procedures must be developed to facilitate symbiotic relationships between Earth-bound and Mars researchers.

The issues of communications, protocols, and troubleshooting will be encountered for every kind of task performed on Mars. The ICoMP experiment was chosen to explore these issues in the context of a creative project for which success and failure could be easily defined and assessed. In the MDRS, ICoMP is treated as a scientific experiment. However, there are other interesting elements of the experiment that are relevant to long-duration spaceflight missions. Mars crews will get to know each other very well. They will have trained for years together on Earth, and we must assume they will be screened for compatibility as much as for their individual capabilities. But no matter what level of training, seeing the same faces and hearing the same voices day in and day out will sometimes be difficult. Within such a long a mission, crews will have down time. How will they occupy that time, find activities between the science and the constant work of exploration that encourage good physical and mental health? What can be done during those two and a half years to create an harmonious environment? Music may be one good solution.

Methodology

Crew 6 is collaborating with musicians from various locations on earth, each with markedly different technical recording and communication capabilities, and each with different creative strengths and talents.

A low-mass but high-performance recording infrastructure was required for deployment in the field (MDRS). The system had to fit on a desk and support multi-track recording and playback, and interface with the various instruments brought by the participants of the MDRS. This computer also had to be capable of communicating with the satellite dish on the MDRS and subsequently with the computers in studios on Earth.

A standard recording technique is being implemented. Most songs start with a rhythm track, then guitar and voice are added; then keyboards, bass, etc. When a song has been sufficiently developed, the component tracks are mixed down to a compressed stereo 10 to 1 audio file and transmitted to a server on Earth where the studios there can access it and add to the tracks as they see fit (violin, voice, drums, etc). When Earth studios have made their contribution, the files are sent back to the MDRS and where the collaboration continues. The fidelity of these tracks being passed back and forth between planets is relatively low, but they act as placeholders and allow the different participants to know what is being added to the songs. When crew 6 returns to Earth, the full resolution components from each song will be combined from the various studios into a final mix in one studio.

This process can occur in reverse as well, with Earth studios generating the initial work and transmitting that to Mars for embellishment.

The ICoMP team in the MDRS is running Protools recording software on a G4 powerbook (512 ram, 30 gig drive) with a Digi 001 breakout box routed through a Magma PCI to PCMCIA adapter. A variety of microphones are being used, with a Blue Dragonfly utilized for vocals and acoustic guitar and the pre-amp built into the 001. MDRS musicians brought two electric guitars, an acoustic guitar, an electric bass, a banjo, a flute, a weighted key electric piano (with a number of different sounds), many harmonicas (low mass), and some percussive instruments.

The communication system is a standard Starband dish communicating with a geosynchronous satellite. Upload speed is about as fast as a standard modem (5kbps), while the download speed is more like DSL (150kbps). One complication has been wind. Winds around the MDRS have reached 80 mph, and during those times it has been difficult to transmit files. Crews on Mars may experience similar troubles with communications depending on Mars weather conditions or communication satellite coverage.

The music files have been downlinked to Earth in one of two ways. One method has been to load the compressed rough mixes of ongoing work directly to an FTP site. All of the contributing studios and musicians have access to that server and can use the rough mixed songs in whatever kind of digital recording infrastructure they have.

The other method has been to upload entire work in progress ProTools recording sessions to a server provided by DidiDesign called DigiStudio. Files can be sent at 6 to 1 compression (very little sound degradation) and exactly the same session as is used by crew 6 becomes accessible by collaborators on Earth using ProTools. This method has higher fidelity and more flexibility for those receiving the work in progress, but requires particular software and high data transfer rates to be effective.

No final mixes will be done in the hab. The science room where the recording system is situated works well for recording separate takes, but doesn't offer the kind of sonic isolation needed to produce final songs. Once back on Earth, all of the files will be gathered to one studio and mixed.

Preliminary Observations

It was assumed that three of the crew members would create all the music in the hab, but as the simulation evolves, all of the crew members are interested in contributing to the project. The music has become one of the primary activities for most members. Those not playing or singing are writing lyrics and giving ideas for song structure.

The collaboration between MDRS members and people on Earth has also been interesting. The initial hypothesis was that this sort of collaboration might provide a feeling of expansiveness for participating crewmembers and have seen such a result now numerous times. They have friends they're working with outside of the spacecraft. This seems to be the case.

Additionally, some songs have originated on Earth, one from Submarine Studios in San Francisco (Joshua Burbank), and one from Mykle systems lab in Portland, OR (The Bad Mintons), and a third from Houston, Texas (Chelsea Beauchamp and Celeste Tamarriello). It's interesting to receive these more complete songs from so far away and allows a glimpse into what it's like for those on Earth receiving music from Mars; the musicians have put great effort into these pieces, and the impression is something like receiving a care package or of having visitors. When the music is shared, the hab feels bigger.

Initial observations by some of the participants in the MDRS crew is that this is a different dynamic from that sometimes experienced between exploration crews and mission support or science backrooms. Those interactions are sometimes tense and unproductive, and sometimes even acrimonious. Even within the MDRS simulation, there was a notable contrast between the nature and flavor of collaboration on ICoMP and the interactions between the MDRS crew and Mission Support on more general issues. Analysis of the ICoMP methods and data will assess the processes of collaboration that were successful and positive with the intention of applying this to future Mars mission tasks in general.

==May 7, 2002==
[[File:Crew6 EphiHab.jpg|thumb|Ephi at the Hab Airlock]]
[[File:Crew6 FossilOyster.jpg|thumb|Fossil oyster bed with scale]]
[[File:Crew6 FossilOyster2.jpg|thumb|Fossil oyster bed with scale]]
[[File:Crew6 DrumHelmet.jpg|thumb|Martian Percussion: Helmet as drum]]
[[File:Crew6 FossilShell.jpg|thumb|A fossil shell impression]]
[[File:Crew6 MusicHelmet.jpg|thumb|Music collaboration through helmet]]
[[File:Crew6 LimySandstone.jpg|thumb|Midshot of limy sandstone]]

===Final Captian's Log - Frank Schubert===
I have not written a log in a couple of days. I pulled my wrist and it became extremely painful to type. It is much better now and I will write my final log today, as tomorrow is press day and then I will be heading back to Denver.

Today we did our last official EVA today. Sam, Steve and I went on a mapping trip to Factory Butte. We laid out the trail with the GPS and also worked on finding an easy way through the wash area. The wash is very difficult as the dunes are comprised of what feels like talcum power. The wheels spin easily in this material and the ATVs can get bogged down quickly. We were successful in finding a path but there were still several places where I would not want a novice rider to go.

Once in the valley floor we proceeded quickly to the trail up the cliff. Before we proceeded up we took a secondary trail that went further up the valley. This trail ended at a waterfall area with a deep pool of water at its base. This is a very beautiful place. We stayed for awhile and then took some samples and moved on.

When we came to the trail Sam went ahead and filmed Steve and I going up the ("Billy Goat trail") steep part of the train and then again in the valley of the big boulders. Then we proceeded straight to the Factory Butte where we took GPS waypoints and more samples. We stayed there admiring the butte for awhile and then headed back the hab. The repeated traveling over the same route has created a trail of sorts. Hopefully it will remain until next season.

Sam has a joke about our crew. It would take just six weeks on Mars for us all to be dead. We have three members now with injures. My injures were sustained before I got here but Penny and Ephimia have succumbed to the rigors of Mars. Ephimia over did her part in setting up camp for the overnight EVA and the next day was in a lot of pain.

Penny had cracked her rib on an EVA the second day. It was a freak accident as the place where she flipped the ATV was on a gentle turn on the road. It was a combination of the gloves and boots being too big for her and her loosing her balance. She is much better now and a total trooper. She still managed to get her science done.

I am about 75% functional but have had a lot of pain in my wrists and knee. The EVAs do my knee in. I should say in the hab but can't resist exploring this terrain. I can't imagine how it would be for an injured crewmember on Mars.

The Hab continues to function well. We have had no blown breakers on the generator and have been up to a 19-amp draw several times. The new generator has arrived but we chose to store it until next season as it take several hours to hook it up an also it runs on LP gas. Our low-tech toilet works well. With the new generator we will have the power to run the Incinolet but might choose to continue with the current set up as the odor is much less now.

The kitchen is functioning well now that we don't blow the breakers when we have more than one appliance on at a time. It has been very hot outside but in the hab the temp is cool. We have put the fan in the roof port a couple of times and that does the trick.
[[File:Crew6 EVACamp.jpg|thumb|Night EVA Campsite]]
[[File:Crew6 DetoxSamples.jpg|thumb|Organophosphorus Detoxification Survey samples]]
[[File:Crew6 DetoxSamples2.jpg|thumb|Organophosphorus Detoxification Survey samples]]
[[File:Crew6 DetoxSamples3.jpg|thumb|Organophosphorus Detoxification Survey samples]]
[[File:Crew6 BlackOrange.jpg|thumb|Black spots on orange]]
[[File:Crew6 PolkaDots.jpg|thumb|Orange & black varnish with polka-dots]]
[[File:Crew6 OrangePolka.jpg|thumb|Orange rock with polka-dots]]
[[File:Crew6 Dendrites.jpg|thumb|Orange varnish with black dendrites]]
[[File:Crew6 SeriousPolka.jpg|thumb|Serious polka-dottage]]
[[File:Crew6 TalonatedFacies.jpg|thumb|Tafonated facies weathering out]]
[[File:Crew6 TalonatedSurface.jpg|thumb|Tafonated surface]]
[[File:Crew6 TafoniPits.jpg|thumb|Tafoni pits with finger]]
[[File:Crew6 TafoniPits2.jpg|thumb|Tafoni pits closeup]]
[[File:Crew6 MethBlue.jpg|thumb|Meth blue microscope field of view]]
Water consumption has been low. About 30-40 gallons a day. We have been taking few showers. This works for us as we have such a sweet crew. Ha ha.

Speaking of the crew we have had no fights, arguments or sulking. This crew gets along beautifully. We have heated discussions at the dinner table. They are passionate but never mean or selfish. We have developed a mode of communicating that is real and to the point. A strong bond has developed among these relative strangers and we will continue to be friends for a long time. Ephimia is administering the final debriefing of the crew. These debriefs take one hour and are very comprehensive. Ephimia has collected a lot of data from this crew and its isolation. She plans to publish a paper on her findings.

The following is a summary of our mission goals and our success at meeting those goals.

'''Science and Exploration Objectives:'''

# To discover and reliably detect surface indicators of subsurface mineralogical and microbiological activity (desert varnish and other surface rinds) We made a good start in this. We were able to locate enzymataic activity capable of detoxifying organophopros nerotoxins. We were able to determine this same activity was clearly associated with micorbiological components of the rock and soil samples. We were able to make cultures of some of the phophros samples. We located a variety of unusual and distinctive surface colors and textures that may be associated with microbological activity. Further analysis of collected samples and living cultures will be preformed back in our labs on Earth. Attempts will be made to date the various components of rinds and varnishes.
# To quantify microbiological activity levels using exoenzyme assays, for example organophosphorous hydrolaise. Yes. See above.
# To continue the geologic and biological characterization of the local area. We collected close to 100 samples and recorded their locations with GPS and pictures. We also did several recon EVAs and discovered routes to the Goblin Valley and also the Factory Butte. We also found a route to the Muddy River where it enters the Coal Mine Wash. We have recorded all these routes with GPS and located them on the maps.
# To test Mars surface operations as specified in NASA documentation with integrated elements of science, exploration, and environmental constraints. This crew followed a NASA blue book plan for the Mars Reference Mission plan very closely. We conducted this sim with the highest fidelity possible. The crew never went outside without a suit on and conducted all our activities under the sim protocol. We made several discoveries that will be reported to NASA. The obvious on was the trouble that we had keeping to the schedule. According to Ephimia this is a common problem at the ISS.
# Exercise, food and psychological human factors. We found it very hard to keep to the exercise schedules. When crew members went on EVAs we considered that exercise. Kelly and Ephimia were the most successful in doing exercises. We stuck to our food regiment. It wasn't hard, as we had no other food. We found that the food preparation time became a problem. This diet provided enough energy for the crew. Some members experienced some discomfort in switching to this diet. Others experienced excess gas. With some modification this diet has potential. Ephimia says she has more data than she expected to get on human factors. The isolation this crew experienced was a source of information for Ephimia. The way we settled the problems and difficulties showed a cohesive and well-adjusted crew.
# To develop systematic exploration tools for use in and around the habitat, including GIS software, maps, and exploration logs in consistent units and coordinates. This is an area that we got very little done. Although we logged all the EVAs and coordinates we didn't get to using the GIS software.
# To collaborate between the habitat and remote groups of scientists, engineers, and musicians under constraints of delayed communications and limited data transfer rates. This is an area where we had great success. We were able to communicate with the musicians around the world on a technical and emotional level. We shared music and collaborated on songs. Several of the songs that we worked on brought back comments like, "That is exactly what we had in mind." Ect ect. Sam, Kelly and Frank worked hard on making our soundtrack for a Mars Mission and we now have over 20 songs to pick from. We also worked with Mission Support in a constructive way. They carried the ball several times for us. We had some miscommunication that was mostly on our part. We were grateful for all the help that Mission Support gave us.
# To examine the interrelation between crewmember personalities, tem interaction, stress effects, and their impact on mission-relevant factors (ie. Productivity, safety, meeting mission objectives/science, etc.) This goal was met by Ephimia and will be in her report in great detail.
# To work as remote liaison to disseminate video and other information about crew activities to Earth and to characterize a documentarian's role within a planetary exploration crew. Sam did a wonderful job of documenting this crews activities. He is a technical genius and very sensitive to our needs and expectations. You will see this crews adventures on National Geographic Channel next month.
# To assess the effect of a vegetarian macrobiotic diet on the crews health and productivity. This goal was met and examined. See #5.

This is the end of my reports. I have enjoyed this stay with these wonderful people and will remember it all my life. I have made some strong and fast friends and shared my life with people that I trust. That I was elected captain of such a professional and highly trained crew was an honor. Did we accomplish real Mars research? Maybe yes, maybe no but we really tried. It was hard suiting up at midnight to fill the generators. The diet we experimented with was less that filling many times. Filling out the daily logs was often a pain. Several times we stayed up through the night working on our projects. We laughed, we cried and we gave a little blood to this effort. I am moved by the time, effort and money this crew put into our stay here. I don't know if we will make a difference or not but no one can fault us for not trying.

My hope is that we made some progress towards the Mars effort. We gave it our all and this became a real mission to us all.

Over and out.

On To Mars!

===Science Report - Penny Boston===
'''''Note:''' Due to the space necessary for music activities in the lower floor and injuries sustained by Penny Boston, adjustments were made in the location of some of the scientific facilities. Microscopes were moved to one end of the workbench in the upper floor to allow Penny to work in greater comfort and without going up and down the stairs so frequently.''

'''Desert varnishes, rinds, and other possible biosignatures''' - This area exhibits numerous types of visually distinguishable oxide rinds, discolorations, erosion pits, and other potential biomarkers.

'''Orange and polka dotted sandstones''' - The most exciting find involves the polka dotted rocks found largely in conjunction with a interbedded harder sandstone facies within the Morrison bentonites. This thin (10-30cm) layer has bright orange rind on flat exposed surfaces. This rind occurs by itself on many rock faces but is also accompanied by an overlay of dark semi-dendritic, to circular dark spots that resemble manganese dendrites or the manganese rich spots that we find in certain arid land caves. There are also dark polka dots on the same sandstones, presumably on younger fracture faces. These features could be consistent with theories advanced in the literature that iron oxide varnish deposition occurs during drier epochs and manganese oxide layers are microbially formed during somewhat wetter intervals. The possibilities for dating the orange oxide layer, the overlying dark putative manganese dendrites and the isolated dark dots on fresh surfaces are unclear. It is possible that 36Cl- dating, 14C, or other radiogenic incorporation may shed some light on relative ages of these various surface colorations. However, all of these techniques suffer from some methodological problems and are difficult to interpret.

Culture specimens have been scraped from all of these types of materials and inoculated into a variety of six manganese media types and six iron media types to see whether any organisms can be enriched from them. The growth times for such chemolithotrophic organisms is typically many weeks to years so results will take a while to manifest. Another followup on this material will be energy dispersive spectroscopy (EDS) to determine the elemental composition of the colorations compared to parent rock. This will be done in conjunction with SEM (scanning electron microscopy) to image any existing organisms and lithified organisms that may be on the surface.

'''Dark Desert Varnish''' - In the vicinity of the Hab, there are numerous instances of the typical shiny, blue-black coating common in many desert areas. Primarily this has formed on the red sandstones dotting the outflow plains. However, there is a wide variety of assorted rock types presumably transported from the nearby Henry Mountains. Many chert examples, poorly formed geodes with agatized centers, quartzites, partially metamorphosed sandstones, chlorite pebbles, even micaceous quartzites. A dark quartzite is the only of these rock types that seems to have a desert varnish coating. At least they have dark rinds. The nature of these awaits further confirmation back in our labs on Earth.

Cultures, and SEM specimens were collected from one of these black desert varnish sites and dealt with as above. In prior work on specimens from central New Mexico, we have found a wide variety of living organisms and preserved and silicified colonies of microcolonial fungi, bacteria, and algae on both sandstones and partly silicified rocks of other types.

'''Tafoni''' - There are many instances of elaborate, convoluted tafoni-type erosion in white to buffy sandstone layers both within the Morrison Formation and in some spots in the Dakota Sandstone caprocks. Tafoni refers to decementation of sandstones resulting in swiss cheese like holes in surfaces, columns, networks, and often overhangs and cavities in cliffs.

Some of the tafonified regions here seem to be associated with extensive horizontal oyster bed layers. Some are associated with apparently non-fossil bearing sandstones some of which are horizontal but some are in tilted bedding planes. Originally, we speculated that the tafoni pits in horizontal surfaces were the result of subsequent weathering in impression pits of oyster shells that had weathered out. This may be the case for the oyster beds, but obviously not for the other sandstones. Extensive tafoni erosion has occurred in some sandstone cliff faces in the Lith Canyon area. These may or may not be associated with large flooding events. Episodicity of flooding events is not known at present, but there are extensive fluvial deposits of poorly sorted and loosely consolidated deposits at canyon margins. Flow patterns are visible on unconsolidated fines from minor flow events. Large rocks clearly transported by water dot the channels and are testimony to the vigorous nature of at least some flooding events.

'''Leached Red Sandstones''' - Dark red sandstone, rounded boulders dot the roadside on the way to Schubert Pass. The notable feature on these are white leached spots with dark lumpy, often with wormlike dark objects adhered to the surface. We have examined these leached areas. Two hypotheses seem reasonable. Possibly the dark objects were deposited in the original sediments of the sandstone. The chemical and/or microbiological action at that time may have leached iron from the surrounding area and concentrated it into the dark areas. Alternatively, based on our observations of leaching in parent rock by the manganese and iron oxidizing bacteria in our caves, it could be a more recent phenomenon. If the former hypothesis is correct, then we would expect to see the dark objects and leached spots throughout the rock material. If the latter hypothesis is correct, the dark accumulations and leached spots should be confined to the outer layers of boulders and other sized rocks. We have not had the opportunity to test this by breaking open a boulder yet. We may try it on EVA tomorrow on Press Day.

'''Fluorescence tests''' - The Overnight EVA reported on previously yielded some interesting tidbits of information. The green bentonite clays exhibited weakly fluorescent yellow patches of perhaps a few centimeters in diameter widely scattered. These patches were not visible by sunlight the next morning.

The polka dotted rocks described above showed a narrow band of weak fluorescence at the margins of the dots. We speculate that this may be an advancing front of a chemical or mineral transformation that produces a transient fluorescent state.

The bottoms of the tafoni pits showed weak fluorescence. The leached spots on the red sandstone glowed bluish white, but not really fluorescently.

'''OPH Continuation Experiments''' - Steve has completed the OPH testing on 30 different environmental samples. Trend is toward more positives than negatives over all. Additionally, this trend holds across many rock substrate types, geographic location around the area, and altitudinally. Microenvironments of sample acquisition ranged from riparian to high desert. All of the samples that are positive appear to be mixed cultures of algae, several morphologies of bacteria, microfungi, even a few diatoms thrown in. Which specific organisms may be involved in the OPH reaction is unknown at present.

Every stab culture inoculated over the past week is growing somebody: The medium was formulated using material from sample #5 plus small amounts of R2A low carbon medium. Future plans include isolation of individual strains from the primary cultures in the presence of OPH-sensitive compounds in the growth media.

===HSO End-of-Rotation Report - Steve McDaniel===
In summary of previous reports:

# ATV-related injury to crewmember 1, on the mend, nothing but routine medical intervention required.
# EVA lifting re-injury of existing L3-5 vertebrae to crewmember 2, on the mend, nothing but routine medical intervention required.
# Hygiene problem averted related to overflowing, malfunctioning human waste disposal unit
# Net2Phone system never functioned properly due to software failures; however, medical team very responsive through e-mail.
# Macrobiotic diet caused some gastric distress to certain crewmembers, but preventative intervention appeared to resolve most problems.

===Bi-Monthly Safety Inspection Checklist - Steve McDaniel===

# '''Fire Extinguishers pressurized to normal limits'''Lower Deck, Central - Yes Lower Deck, EVA Prep Room - Yes Upper Deck, Central - Yes Upper Deck, Kitchen - Yes
# '''KellySmoke/CO Detectors respond to manual testing'''Too'''Kelly'''ls area, Lower Deck - Yes '''Kelly'''Science Area, Lower Deck - Yes S'''Kelly'''tairwell, Upper Deck - No '''Kelly'''Central platform, Upper Deck - Yes Ceiling, Loft Area - Yes
# '''KellyFire Escape Ladder'''Emergency Exit clear and u'''Kelly'''nimpeded - Yes Ladder unimped'''Kelly'''ed, deployable - Yes
# '''KellyPersonalKelly''' '''Protection''' '''KellySystem (PPEs)''' O'''Kelly'''ven Mitts hanging in kitch'''Kelly'''en, good r'''Kelly'''epair - No Disposable Gloves in Science Area - Yes Protective Eye Gear in Science Area - Yes Disposable Dust Masks in Science Area - No Hard Hat at top of Loft Ladder - No
# '''KellyFirst Aid Kit'''In Good Repair - Yes'''Kelly''' American Red Cross First Aid book stored with F'''Kelly'''irst Aid Kit - Yes

'''Missing items (accoKellyrding to contents list):'''

Apart from items '''Kelly'''listed on the last Bimonthly HSO Safety Chec'''Kelly'''klist, Crew 6 has not utilized any but: one elastic wrap tape; several bandaids.

Crew 5 - Crew Reports

2020-03-17T00:24:39Z

Sdubois:

[[Category:MDRS Crew Reports]]
==April 7, 2002==
===Commander's Logbook===
Today was off-sim as we moved in the hab and became familiar with the systems. All times are MDT. We have a great crew:

'''0200''' Arrival in Hanksville from Salt Lake City. We drove in two minivans, full to the top with gear, newly purchased supplies, and the crew of six.

'''0645''' The alarm goes off, time to have one last very long hot shower and prepare for the short trip to MDRS. Few of us have slept soundly, for we are stilled keyed up from the evening before and full of excitement for the day's activities. The day is brilliant with achingly long clear horizons and a fresh northerly breeze.

'''0810''' Arrival at MDRS. The crew that greets us is clean, cheerful, and eager to relay the tricks. Judith Lapierre has organized a nicely printed list of handover topics, with assigned crew members. I review it and quickly rattle off the corresponding people in my crew who will pair off for the coming hour of learning and sharing.

'''0930-0945''' Rotation 5 departs in two vehicles, we begin to feel the peacefulness of the place.

The rest of the day is a blur of unpacking supplies, organizing computers and setting up lab and recording gear. Frank Schubert, Dewey Anderson, and Brian Enke arrive to swap in a new generator, reorganize flows and sensors in the greenhouse, and attach a greenhouse door. We have brought a 5' square projection screen and attach it just above the staterooms; we intend to use it to project our daily and evolving plan.

'''01500-1700''' Our first meeting: We discuss Safety (a briefing and forms to fill); Mission Support communications protocol (all incoming messages about the mission must go through them first; we forward everything we receive for them to handle); our daily schedule (tentatively start the primary EVA at 1600 with dinner at 2000 merged with the debrief); chores (assignments with rotations were worked in detail); reporting (follow the previous crew's pattern, but the summary will be written by our resident journalist, David Real).

'''1730-1900''' ATV training and more organization, refilling the generator, etc.

Our sim begins tomorrow with an extensive planning meeting. One objective of this rotation will be to plan two weeks in advance in full detail. We want to determine to what extent we can project our intentions, and to understand how and why they change from day to day. If we are on a late EVA schedule, then reports will be written the next day. So Mission Support will always be a day behind. Can we compensate by projecting more than two days in advance what we plan to do?

'''Bill Clancey'''

'''MDRS Rotation 5 Commander'''

==April 8, 2002==
===Commander's Logbook===
The previous evening we enjoyed a peaceful dinner and mostly spend the evening setting up and organizing the hab. We are too tired to watch a movie. Our bedtimes vary between 2245 and 0030.

'''0800-0900''' The crew has rested well and smiles in conversation over breakfast.

'''0900-1130 Planning meeting:''' We extensively review our objectives, methods, and constraints, and individual plans. Planning will be a key part of this rotation. We will plan forward as much as possible, including a schedule for the day. We will forward this to mission support. We will then review and replan the next day. A single document will be edited as we proceed, allowing easy comparison of our expectations and time estimates.

One question is whether we can reach a steady state by which we are able to notify mission support reliably of our plans two or three days in advance, so they may assist us. Our reports will tend to be a day delayed because of late afternoon EVAs running until dinner. To begin the process, we ask mission support for waypoints of areas known to be always wet, occasionally wet, always dry, and windy.

The crew also begins personal logs of when they sleep, do chores, or prepare reports. This is on top of group logging of water and soap usage.

'''1200-1400 Lunch:''' getting remaining laptops on line; understanding problem with UPS generator, processing mail.

'''1400-1630''' Greenhouse EVA in full-suit by Nancy and Vladimir to plan seedlings. Proceeded by an extensive training session for the crew. Operation completed entirely on schedule.

'''1630-1700''' Half-hour moment to catch our breaths and debrief. This was unscheduled but necessary before launching into the next EVA.

'''1700-1730''' The EVA crew prepares, others work on learning to transfer files, using the full panoply of methods we have brought along: Compactflash (PC) card, CD-R, USB drives, and floppies. This was not scheduled, but is necessary for reporting tonight.

'''1730-1930''' Second EVA for the new crew (Vladimir and I had a great deal of experience on suited EVAs at FMARS). Andrea, David, and Jan go on a pedestrian EVA to measure wind in various sites for a future experiment.

'''1930-2000''' Catching up on mission support's responses to us, and logging our 2000 dinner

'''Bill Clancey'''

'''MDRS Rotation 5 Commander'''

===Day 1 Report===
Life on Mars Can Be Brutal

By David Real / Belo Interactive

Lost supplies of critical medicine. Computer failures. Even unannounced alien visitors. All on four hours of sleep. And, officially, it's not even Day One yet on the Red Planet.

Five scientists and a reporter locked themselves away Monday for a two-week stay in an isolated area of Utah for a research project sponsored by NASA and the Mars Society, an organization advocating exploration of the fourth planet as soon as possible.

The goal: simulate the conditions of a restrictive encampment on the Mars surface, add some top-flight scientists from around the world, and see what happens. Perhaps problems discovered during an exercise on Earth could play a critical role in preventing a crisis in space.

"This rotation is especially interested in planning," said Dr. William J. Clancey, a NASA scientist who is commanding the mission at the Mars Desert Research Station. "Can we plan our work for several days in advance, at least, so Mission Support will have enough details to help us."

Dr. Clancey, 49, is chief scientist for Human-Centered Computing at NASA's Ames Research Center in Sunnyvale California.

During the next two weeks, his crew will bunk in an unusual two-story structure that looks like a cross between a white grain silo and a stubby Apollo space capsule. The stark, reddish terrain appears eerily similar to the Martian landscape.

The crew can emerge only in tightly controlled circumstances, wearing fabricated spacesuits and communicating via handheld radios with their fellow crew members inside their temporary home away from Earth. Talking with Mission Control during an actual mission to Mars would be pointless, when a reply from such a distance would take 10-40 minutes.

The other members of the crew on this mission are:

*'''Dr. Vladimir Pletser''', 46, is a native of Brussels, Belgium. He is an astronaut candidate for Belgium working at the European Space Agency and is also project manager for an instrument being developed for the International Space Station.
*'''Dr. Nancy B. Wood''', 60, an experimental scientist with a doctorate in microbiology from Rutgers University. She is interested in how microorganisms adapt to harsh environments, such as could be found on Mars.
*'''Jan Osburg''', 30, an aerospace engineer at the Space Systems Institute in Stuttgart, Germany. His specialty is human spaceflight and design of inhabited space systems.
*'''David Real''', 49, a journalist for Belo Interactive and a former reporter and assistant Metro editor for The Dallas Morning News. He and Dr. Clancey were roommates at Rice University in the early 1970s.
*'''Andrea Fori''', 32, a planetary geologist and systems engineer with Lockheed Martin Space Systems Co. in Sunnyvale, Calif. She helped choose a landing site for the first NASA mission designed to bring back rocks from Mars.

The team assembled in Salt Lake City late Saturday, spent several hours and hundreds of dollars buying food and other provisions, and finally embarked on a five-hour drive to Hanksville, arriving about 2 a.m. Sunday.

After four hours of sleep, the crew boarded two vans jammed with equipment and provisions and headed toward the Hab to relieve the current crew, the fourth to make a two-week stay. Less than two hours later, Dr. Judith Lapierre, a space scientist at the University of Quebec in Hull, handed command of the Habitat to Dr. Clancey, and a new chapter had begun. It didn't begin auspiciously. A crew member discovered that one of his bags containing vital prescription medicine had been lost. Fortunately, another bag carried his backup medication.

Attempts to hook up the crew's computers to the base station were unsuccessful. By choice, there is no telephone service available, in order that the project may more closely mimic the isolation that crews will face on Mars. So the Habitat's satellite dish provides the only authorized connection to the outside world via the Internet, and computer networking is vital.

After several hours of unpacking, the crew met to learn the rules of everyday life on the station and to assign mundane chores, such as cleaning toilets and cooking dinner.

Our organizational meeting was interrupted several times by visitors who lived nearby and had learned of the Mars mission. They would be our last for the next two weeks.

The day ended shortly after midnight with an exhausted crew, and no solution to our computer problems.

The next day, however, would officially kick off the simulation. On Monday morning, the hatch would close on planet Earth and the crew would open the doors on its new mission: exploring a future on Mars.

===Health & Safety Officer Reports===
Jan Osburg Reporting

'''Safety:'''

Fire safety information and emergency procedures were compiled and posted on the second level. Locations of fire extinguishers and emergency egress routes were clearly marked. To prepare crewmembers for a possible evacuation using the roof hatch escape route, Nancy taught everyone how to use the "roof rope" to rappel down a vertical wall.

'''Health:'''

Procedures for medical emergencies were compiled from the HSO manual and posted near the HabComm station. No injuries or illnesses were reported.

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' Water consumption in the last 24 hours: 150 l (40 gallons), which seems high considering that nobody took a shower. Potential culprits: leaks, not fully established water discipline, or (most likely) the planting/seeding of the GreenHab trays which took place today (see science and EVA reports).

'''Power and Fuel:''' The new generator, which was installed yesterday by Frank Schubert and his team, works flawlessly. The only blackout occurred when too many kitchen appliances were running (but it was worth it, our DGO - Director of Galley Operations - of the day, Vladimir, produced excellent meals!) We are currently refueling the generator in the morning before 09:00h, then in the afternoon around 16:00h, and finally before going to bed, around midnight. We have not run out of fuel yet, so this schedule seems to work.

'''EVA Equipment (including ATVs and PEV):''' Yesterday, we also received three brand new ATVs, on loan from sponsor Kawasaki. They run great, and we are looking forward to many exciting motorized EVAs. Lamont took the three old ATVs back. Today's EVAs went fine, but some recommendations were already issued:

*The Platypus water bags and associated hoses should be replaced every month or so to mitigate potential hygiene problems. Spares should be stored at the hab.
*The mouthpieces should be disinfected before a new crew uses them (by immersion in Ethanol?).
*Each crewmember should have a "personal" helmet assigned to him/her during a rotation, to assure maintenance and reduce hygiene concerns.
*Small topo maps of the area with superimposed lat/lon or UTM coordinate grid, laminated and mounted on a board, would help with navigation and documentation of EVA traverses.

'''Safety:''' No Data Received

'''Computers and Communications:''' A UPS was installed to assure HabComm power supply during generator failures/refueling. Testing revealed some problems which will have to be fixed before the UPS can be considered operational. Most crewmembers' computers were successfully connected to the MDRS LAN. The Net2Phone link to the Flight Surgeon was successfully tested.

'''General Maintenance & Waste Management:''' Biolet seems to be working properly, however it is clearly operating on the edge of its capacity. Recommendation for subsequent hab designs: provide two Biolets to a) provide a backup in case one breaks down, and b) reduce continuous load by half, which should result in significantly less olfactory impact.

'''GreenHab:''' No Data Received

===Geology Report===
Andrea Fori Reporting

The Rotation #5 geology study plan was discussed with the team in the morning meeting. During this rotation, we intend to accomplish two goals.

'''Goal 1:''' As the last formal crew of the first MDRS season we will broadly assess the geological achievements and process used by the last four crews. This information, synthesized into a series of reports over the course of our two weeks here, will describe the information from two perspectives a) From the perspective of the Earthbound scientist. Assuming that an Earthbound scientist would have only access to the information posted on the web, I'm going to look at ways posted info can be better communicated so that scientists can use the info being sent back from the red planet. b) From the perspective of the in-person view. As a traveler who arrives at Mars after others have begun research, I need to determine if I can decipher notes and gain an understanding of the local geology, reproduce EVA's, figure out where samples are from, etc. The team will be conducting EVAs during this portion of the study to verify our findings. Weaving in what I believe Earth-bound scientist would want to know, from the perspective of planetary geologists, astrogeologists and geo-engineers I'll make suggested improvements for how and what information is recorded and relayed.

'''Goal 2:''' Create an overall geological primer of the area so that a non-geologist staff crew member can gain a basic understanding of the local geology.

===EVA 61 Report===
18:20-19:18 - Duration: 3:18-4:36

'''Objective:''' To plant seeds in both rock wool cubes and potting soil to set up GreenHab experiment.

'''Personnel:''' Vladimir Pletser, Nancy Wood in full suit; Bill Clancey in helmet only to photograph.

'''Methods:'''

Experimental test to compare four rapidly sprouting seed types (alfalfa, arugula, radish, and tatsoi) planted in both rockwool and potting soil. Both will be kept damp with the same circulated Greenhab water preparation. Seeds in potting soil will be kept moist manually. Germination times will be observed and compared, as well as relative growth rates. Observations will be carried out by all crew members; those on EVA will do it in full suit, while maintenance and measurements will be done by VP and NW and others simulating the proposed "virtual tunnel".

'''Lessons Learned:'''

We prepared for this by setting up a procedure for planting single seeds (which varied in size), since this is very difficult to do with the suit gloves on. It was still difficult and time-consuming, and sometimes more than one seed was deposited. It would be helpful to have a small workspace in the GreenHab.

===EVA 62 Report===
18:20-19:18

'''Objective(s)''' The intent of this EVA was to search for a windy and dusty location for Nancy's "Transportation of bio materials via wind" study to be set up during a future EVA. This EVA was also an introductory, brief pedestrian, familiarization exercise for the three participants.

'''Accomplishments'''

We identified three locations for Nancy to install her sample collection stations. The locations are local, open, high spots where it appears likely that relatively high amount of dirt would become airborne. We recorded GPS coordinates and maximum wind speed that occurred during a 10-second period (see map).

'''Lessons Learned/Misc. Notes'''

Some adjustments need to be made to the suits for more a more proper fit. Dave's headset became disconnected and he was not able to participate in Capcom communications. Communications originating from Capcom were often relatively loud and muddled - suggestion was made to speak in a normal tone and 30-60 cm away from the wall-mounted unit.

==April 9, 2002==
===Commander's Logbook===
Dr. Bill Clancey Reporting

The previous evening we worked on reports after dinner until about 2230, then we reviewed my DVD compilation, "Best of Devon 2001," consisting of artistic and humorous videos from my stay in FMARS and the Haughton-Mars base camp last July.

'''0910-1010''' Planning meeting. We are picking up speed, as our plans evolve from initial thoughts to a series of steps and follow-ups. We are still not looking ahead beyond the present day, but focusing on immediate, pressing needs.

'''1010-1300''' Individual work: Reporting, reviewing previous crew's reports, handling visitor requests (not allowed, this is a simulation of a crew on Mars), and a variety of personal tasks, such as medications review and reading a geology primer of the region.

'''1300-1415''' An unexpectedly formal, long, and delightful lunch prepared by today's Director of Galley Operations, David Real. We sit and talk about a recent astrobiology press release and what could be learned about publishing information about scientific work before it is has been peer-reviewed.

'''1430-1500''' Andrea Fori, our resident geologist/engineer, presented an introduction to geology and regional formations. The crew finds this fascinating and useful.

'''1600-1730''' A lengthy EVA preparation, including equipment cleaning, testing, and suiting up.

'''1730-1915''' A mobile (ATV) EVA to seek wet areas for soil sampling. This will be reported in detail separately.

'''1915-2030''' Cleanup and email. Reading my email and reporting is taking at least a fourth of my time.

'''2030''' dinner is announced-- Mexican-Martian Treat with Martian "Eggs" over Pineapple (it's a Martian yoke, get it?)

'''Bill Clancey'''

'''MDRS Rotation 5 Commander'''

===Health & Safety Officer Reports===
Jan Osburg Reporting

'''Safety:'''

Some fuel spilled during generator tank refueling. Lesson learned: always watch the tank level during refueling!

Also, trash bags stored in rear airlock were found to block easy egress (escape route).

A fire drill was held after dinner. The HSO activated a fire alarm on the first level and announced that the Biolet was on fire. Crew response was well coordinated, following the fire procedures posted yesterday. The commander and a crewmember "fought" the simulated fire using handheld extinguishers while the rest of the crew was ordered to evacuate. After the "fire" was extinguished, a debriefing resulted in various updates of the fire procedures. Recommendation: six disposable emergency smoke hoods (e.g. Evac-U8 brand) should be kept on the upper floor to permit crewmembers to escape down the main ladder in spite of smoke, thus giving them a better chance of controlling fires on the first level and avoiding use of alternate evacuation routes (window/ladder, roof hatch). HSO will also investigate possible use of potable water tank/pump and additional hoses for firefighting.

'''Health:'''

Inventoried and reorganized the MDRS first aid kit. Most items were present in sufficient quantities; some were added by HSO.

The first aid supplies were arranged into seven components:

*A general-purpose first aid case
*A small first aid kit to be taken on EVAs (stored in main airlock)
*A case with first aid material for eye injuries
*A box with non-prescription medications
*A lockbox with prescription medications (to be released by order of Flight Surgeon only)
*A box with miscellaneous bulky first aid equipment (cervical collars, books, …)
*A box with additional consumables, mainly extra bandaging material, for refilling the other first aid kits

'''Medical incidents:'''

*Two band-aids and Neosporin were issued for treatment of a minor skin abrasion
*The DGO (Director of Galley Operations, i.e. cook) touched a hot onion and suffered a first-degree burn on a knuckle (first aid measure: application of cool water for 5 minutes).

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' Water consumption in the last 24 hours: 130 l (34 gallons). Recommendation: it would be nice to have a water meter in the potable water line, to get more accurate water use figures. Currently, water use is measured by reading the water level of the tank using a handwritten, external scale on the tank.

'''Power and Fuel:''' Generator fuel is running low, available supplies will last until tomorrow (Wednesday) afternoon. Mission Control was contacted to arrange for resupply through local support.

Recommendation for future generators: get one with a large built-in tank so only one refill per day (or even less) is required.

'''EVA Equipment (including ATVs and PEV):''' GPS units for EVA use were set to the required coordinate system (UTM, NAD 27 datum) so waypoints can be directly plotted onto the USGS topo map in the hab, and recorded on the EVA database spreadsheet on Habcom.

EVA communications broke down during todays EVA due to problems with the radios. Recommendation: acquire ruggedized, easy-to-operate handheld radios that can be operated with EVA gloves on (and by relatively inexperienced personnel). These are available for FRS frequencies, so the repeater and the Habcomm base station can still be used. Also regarding the radios, a portable/wireless headset for the Habcomm operator would be nice so he/she could walk around the hab while still being "on-call" for EVA requests. And, finally, the PTT button for the radios should be replaced by a VOX circuit (that activates the emitter whenever the microphone picks up sound above a certain - adjustable - level).

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' Nothing to report.

'''General Maintenance & Waste Management:''' The "composting material" bucket for the Biolet is slowly being emptied; resupply is required soon.

'''GreenHab:''' (see "Biology" report)

===Geology Report===
Andrea Fori Reporting

We tried to reach a previously recorded waypoint today (see EVA #63 report). The intent of this exercise was to become comfortable with the Because the terrain is so varied, it was impossible to find the waypoint without destroying a fair amount of vegetation. It's obvious that the route that was taken to reach a waypoint should be recorded as well as the waypoint for future reference. Work continues on generally assessing achievements and processes.

===EVA 63 Report===
18:20-19:18 - Bill Clancey, Andrea Fori & Nancy Wood

'''Objective(s)''' To obtain sample for setup of ecosystem columns; attempt to revisit Waypoint 86, known to be usually wet.

'''Accomplishments'''

We departed on ATVs in the direction of Waypoint 86. Since the attempted route was impractical and a thunderstorm was visible nearby, we returned by the same route. Three vials of red-brown soil were collected at the confluence of two obvious dry rivulets to provide a sample of "intermittently wet" material. This site is now designated Waypoint 108, coordinates 5 18 180E, 42 50 504N

After returning the ATVs to the Hab, we proceeded a short distance to rock outcroppings obviously subjected to storm drainage and which were covered with ochre-colored microbial material. A small pebble covered with this growth was collected for biology experimentation. Waypoint information on this site will follow.

'''Lessons Learned/Misc. Notes'''

Samples required for biology projects were collected successfully. Route finding to previously established waypoints is nontrivial and requires advance planning.

==April 10, 2002==
===Commander's Logbook===
Dr. Bill Clancey Reporting[[File:DavidRealEVAPrep.jpg|thumb|David Real finds a quiet corner (the EVA Prep Room) to interview Andrea Fori.]]We were all tired again last night, so we skipped the movie session. But as usual some of the crew were writing reports past midnight and even until 0200.

'''0345''' Traversing to the toilet, I discover I've left the time lapse video running. It's a serendipitous, for now we have a record of when everyone went to bed. The time lapse for the 20 hours or so I have captured (one 320x240 pixel frame every 3 seconds) is about 750 MB. I turn it off before returning to my stateroom.

'''0715''' I awaken at almost the same time each day. Whatever bug I might have picked up over the weekend appears to have passed; I feel almost rested. However, everyone else is sleeping later today. I turn on the hot water heater and wait 45 minutes, using the time to bring back our internet connection. It proves difficult, so finally I decide to take a shower. A previous crew had reported it's not warm; I say it's not cold. There's always a temptation for me to tell the crew, "If you were at FMARS on Devon Island, you'd see..." For starters, the upper deck is always at least 20C in the morning, a rare temperature during July in FMARS.

I record the temperatures for the past 24 hours:[[File:NancyWoodHabLab.jpg|thumb|Nancy Wood is happy and productive in the hab's lab.]]

Maximum outside 27.8 C (82 F); Maximum inside 25.6 C (78.1 F)

Minimum outside 10.8 C (51.4 F); Minimum inside 18.4 C (65.1 F)

'''0815''' The crew is stirring; I turn to my email so I can review mission support's responses during our morning meeting.

'''0910''' Morning Planning Meeting: Most of the crew are still eating, but we launch into the meeting. I want to reinforce this regular schedule and begin by promising we will hold to an hour, as we do. I save and rename the previous day's plan, review the important new items (our communications protocol, a new task for the Engineer--to charge and test the suit radios and backpacks, and our need for fuel before nightfall). We review the action items from yesterday, reminding people of open tasks. We then formally go through each person's plan for the day. Afterwards, I forward this plan to Mission Support so they can track our activities and intentions.[[File:VladimirPletser.jpg|thumb|Vladimir Pletser learns about the Ecologger system for the Greenhouse, using a tutorial prepared by R.D."Gus" Frederick (Mars Society - Oregon Chapter)]]A key activity today will be to prepare an EVA plan for the remainder of the mission, including at least one EVA/day. We decide to base this on Nancy Wood's soil sampling and my interest in creating an illustrated geology primer. It develops that our key problem is separating the prevous rotation's records ("waypoints") into those useful for finding routes and those that mark places of interest. Yesterday, we found that it is difficult to go back to waypoints because most do not have routes indicated. We ask mission support for help. They have sent an updated list of candidate waypoints for us to examine, but it is empty (probably just a shortcut). Reporting this problem becomes another task on my to do list.

We record the basic schedule for the day on a simple pad, so we can compare our plans to what happens.

'''1010-1300''' Individual work. Vladimir and Nancy are learning about the Ecologger for the greenhouse. They follow Gus Frederick's tutorial and set up the program. Andrea is still struggling with a PC that has locked her out, but she uses the hab computer to review previous records. Jan gets busy with the radios. David interviews Andrea. I am busy with email and chores, finding only 10 minutes to talk to Andrea about our EVA plan--nearly 1.5 hours late and a sliver of needs to be done.[[File:JanDishes.jpg|thumb|Jan has splinted the dish drainer with duct tape, a pen, and a pencil]]

'''1300-1350''' We enjoy an informal lunch together. This is a key moment to take a breath and sit back. We have been buzzing around the hab all morning, and this will continue for at least another six hours into the evening. This time to regroup keeps us going.

'''1350-1420''' Individuals scramble in ways that are difficult to track--for I use these few moments to take a nap. (The time lapse video will later help me reconstruct what everyone else was doing.)

'''1420-1445''' Jan gives a very clear, basic introduction to the GPS system, how to use these devices, and how they relate to the maps left behind in the hab. We must be careful especially to recognize when a position lock has occurred (difficult to see with the helmet), so we can record new waypoints.

'''1445-1625''' I'm back with email for the third time today, handling press requests. We explain that a closed simulation is like Mars--no visitors. We will be the first MDRS rotation to be truly isolated, save for periodic fuel and water resupply visits from Lamont Ekker, our vital link to Hanskville, Earth.[[File:JanOsburgFly.jpg|thumb|Jan Osburg outdoes himself yet again, improvising fly paper made from duct tape and molasses.]]

'''1625-1810''' I prepare dinner: A rich vegetarian tomato sauce, spaghettini, and bean salad. I also wash the day's dishes. We've learned that astronauts are using wet towels for some clean up on the International Space Station. Will MDRS provide lessons that ISS cannot, given that we have gravity here and can wash dishes normally in a sink?

'''1810-1910''' I rearrange the stereo speakers for our movie tonight (we need an RCA jack extension), take photos of Nancy working in the lab, and coordinate with David the publishing of photos on the web. Packaging 10 photos has taken me over an hour today, including downloading from the camera, backup, cataloging, selecting the best from 240 photos, and writing captions. The first two attempts to send these photos fails from the network problems.

'''1910-1948''' I write this report. Including this time, I've spent at least 5 hours at my laptop processing email or writing today. This is surely a big activity for all of us--and those not actively using a laptop are often trying to get it to work (e.g., David spent about an hour adjusting his PC to recognize a USB flash drive).

'''1950-2000''' Out on the rocky plains, among the rounded hills of our Morrison Formation setting, the EVA crew of Andrea and Vladimir has reported back some interesting route-finding, which they will report separately. (Our EVA and science reports, as well as photos, will be posted when we have time to prepare the materials, usually within two days.) We ask them to return as it is getting dark and dinner is ready.

'''Bill Clancey'''

'''MDRS Rotation 5 Commander'''

===Health & Safety Officer Reports===
Jan Osburg Reporting

'''Safety:'''

An additional fire extinguisher was discovered in the EVA prep room next to the main airlock. It was checked and its position marked.

A smoke detector previously mounted on the side of the main stairs was removed, as there is already a smoke detector in the stairwell. It was remounted on the third level, near the roof hatch, as this is where all smoke from the hab will rise to.

In the evening, as a thunderstorm was passing over the hab, lightning occurred in the vicinity. The question arose whether the hab had sufficient lightning protection; the answer is being awaited from Mission Support.

The metal weather station pole on top of the hab was definitely not grounded, and static buildup was heard and felt that increased in intensity until we observed almost continuous sparking where the pole passed through the hab roof close to a metal roof beam. As this presented a fire hazard, the crew prepared for a rapid response to an eventual fire. After the thunderstorm passed and the static electricity generation subsided, the weather pole was grounded by connecting it to the metal roof structure using the ATV starter cables and a clamp. This is only a temporary fix, and a permanent solution has to be found.

'''Health:'''

A big ol' fly was observed escaping from the Biolet after the lid was opened. It was subsequently hunted down and brought to justice. We will have to keep an eye on the situation.

Two small insects and some minor dirt particles were discovered upon inspection of the outside potable water tank. We will have to clean it before the next refill.

No medical incidents were reported.

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' Water consumption in the last 24 hours: 195 l (51 gallons), due to 5 crewmembers taking a shower in the morning.

'''Power and Fuel:''' The remaining 19 l (5 gal) fuel can was emptied into the generator tank around 10:30h this morning. Lamont came by around 19:00h and extracted more fuel from the barrel by tilting it. He will bring two full barrels tomorrow.

Generator fuel consumption: approximately one five-gallon can (19 l) every 10 hours, equaling 45 l (12 gal) per day. One barrel (55 gal) will therefore last for 4.5 days if used only for the generator. Of course, if fuel is used for ATVs, this number will be lower.

It was discovered that oil was leaking from the air filter of the generator. Investigation revealed more oil inside the air filter casing. This might be due to a recent topping-off of the generator oil, however we will observe this in case the leak continues. (Follow-up: oil does not leak while the generator is running, it only seems to leak when the generator is stopped. Strange.)

'''EVA Equipment (including ATVs and PEV):''' Radios were checked and two sets of batteries were replaced. Headsets were checked and two broken attachment clips were replaced. Headsets are now stored in individual Ziploc bags to avoid tangled wires.

Some radio settings were changed to improve performance:

*Set TX power to HIGH
*Activated key beep (every time a key is pressed, a beep sounds; this replaces the missing tactile feedback when wearing EVA gloves)
*Activated "Over" beep (this sounds every time the PTT button is released and thus saves the operator from having to say "Over" at the end of every transmission)

The present radios also have a VOX setting, but sensitivity seems not high enough for use with helmet-mounted microphones. This leaves detachable PTT keys as the best option for fatigue-free operation of PTT keys, which would also permit to keep radios protected in EVA suit pockets.

The new high power setting of the radio also allows Habcom operator to use a spare handheld radio so he/she does not have to stay close to the wall-mounted Habcom station any more.

An introductory lesson covering GPS navigation basics and operation of GPS receivers was given. A two-page GPS quick reference was created for use by EVA crew during EVAs.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' Computers: nothing to report.

Communications: see "EVA Equipment", above

'''General Maintenance & Waste Management:''' The "composting material" bucket for the Biolet was refilled from one of two big bags of composting material found near the back airlock.

Due to windspeeds of 75 km/h during gusts, the EVA team took down the MDRS flag on their way out. It was stored in the lab area on the lower floor.

'''GreenHab:''' (see "Biology" report)

===Geology Report===
Andrea Fori Reporting

We set out today to capture GPS coordinates where they were missing from the former EVA waypoints (see EVA #64 report) and to make another attempt at reaching waypoint #86. We were unsuccessful in reaching the waypoint thus reinforcing the necessity to record the route. We conducted a wonderful broad survey of the area and obtained more photos for the geology primer.

===EVA 64 Report===
18:20-19:18 - Andrea Fori & Vladimir

'''Objective(s)''' The intent of this EVA was to collect GPS coordinates with elevation for the Greenhab and the points where Nancy collected samples yesterday during EVA 63 (2 locations). This EVA was also a re-attempt to reach waypoint #86.

'''Accomplishments'''

We collected coordinates for the green hab and the first of Nancy's bio collection sites. We spent 2 hours trying to reach waypoint 86 with no success. However, we passed Candor Chasma, took photos for the geology study, got stuck on a sand dune and on the way home had a spectacular view of the hab from a nearby ridge. Just before entering the hab, we collected coordinates for Nancy's second sample collection site.

'''Lessons Learned/Misc. Notes'''

Finding a previously recorded waypoint can potentially be challenging to impossible if the route taken was not recorded. The local terrain is extremely variable and one wrong turn can result in one not being able to reach the destination.

Another lesson learned - Sand dunes approximately 3 feet high and wide are to be avoided.

==April 11, 2002==
[[File:Crew5Radio.jpg|thumb|Vladimir Pletser and Jan Osburg arranged a radio so it could actually be seen while being used.]]

===Commander's Logbook===
Dr. Bill Clancey Reporting

Last night during dinner, we were treated to a bizarre lightning experience. Sparks were arching from the metal weather mast (an interesting concept in itself) to the frame of the hab above the upper deck. These sparks became more insistent and louder, then finally the landscape flashed with light as a bolt struck nearby. The sparking stopped. We continued eating, and then it all started again. The storm passed before long, and we heard rain. Now we know what it is like to live inside a Faraday cage.

After I washed the dinner dishes (we are an egalitarian bunch), and after we finally forced the LCD projector to accept my laptop's video, we watched "Red Planet." Although bearing little resemblance to our situation (or what anyone might reasonably expect), we enjoy the overtones of travel to Mars and the sight of the planet (filmed in Jordan and Australia). Most of us are asleep before 0100.

'''0720''' The hab is noticeably colder, the sky clear, and my crewmates sound asleep. It's another slow start and struggle to get my computer back on the internet, involving three of us experimenting with different cables in different places. Simply rebooting everything works, until we must turn off the power to refill the generator. And then we re-reboot.

Meanwhile, I have restarted the time lapse video, had a glass of orange juice, and recorded the temperatures:

Maximum outside 26 C (78.8 F); Maximum inside 25.6 C (78.1 F)

Minimum outside 5.6 C (42.1 F); Minimum inside 18.6 C (65.5 F)

'''0830''' I'm finally on line and reading last night's mail from mission support. They are doing a superb job. Everything is answered and with a final summary of open items.

'''0905-1020''' Morning Planning Meeting: We appear to be hitting our stride. The crew is volunteering multiple activities per person, and we are carrying over things from the previous day. Having recorded yesterday's plan, I can see what people said they would do, which I would have otherwise forgotten. This helps me monitor our productivity, which is becoming a topic to consider.

We are all feeling productive, but why? I ask myself, what have I done in the past day that makes me feel productive: Writing about new ideas; cataloging and selecting photographs; writing regular reports; taking good photos; everyone else being happy and productive; having the time lapse working (full day); and (somewhat oddly) having watched a movie.

What makes me feel unproductive? How about having spent two hours trying to email 10 photographs? (I repackage them to send one at a time, then I use a graphics program to cut the compressed size in half to about 200k. Still after nearly 30 hours, I have one more to force through again.)

We are all monitoring our progress. And on our fourth day it appears right to be taking stock. I resolve to ask the crew about this at dinner. Are you feeling productive? Why or why not?

'''1020-1300''' Individual work. While trying to send those photos, I read a NASA report from June 1975, "An Optimum Organizational Structure for a Large Earth-Orbiting Multidisciplinary Space Base," by James M. Ragusa, then of JFK Space Center. Twenty-two analog social systems are compared along different work, interpersonal, and organizational parameters. The missions include Skylab, Bomber Crews, Antarctic Stations, Mental Hospital Wards, a research submarine, R&D; Laboratories, and so on. Oddly, "Exploration parties and Expeditions" doesn't make the top-10 cut, because the imagined "Space Base" would not involve traveling over a physical environment and would have a more tightly coupled interaction with a support organization. Though the conclusions would have to be reworked for a "Mars Base," the approach is broad and useful. Only two items seem especially dated, 1) the reference to values that "accept the American way of life" and 2) the mockup of a space station module, which vaguely resembles an old mainframe computer room!

'''1300-1430''' Lunch, including a tutorial by David Real on how to help media understand what we are doing here. David has prepared a full-page handout that fascinates us. We realize two things: 1) the oversimplifications that make us cringe (e.g., the CBS Evening News title, "Mars Madness") may be helpful in getting the attention of a large audience, and 2) it is our responsibility to construct succinct, specific, and imaginative talking points. Just as one would prepare for a public talk, we need to prepare to talk to the press. We decide to work on this and have another meeting before our open house at the end of the rotation. Inspired by the discussion, I already have a new slogan, "If you liked Tang, you'll love Mars."

'''1430-1530''' More individual work. I notice people are gravitating to favorite places. You can usually find me in my stateroom, and David also works on his laptop in his stateroom. Vladimir would prefer to do that too, but his ethernet cable is not connected. So he sits along the workstation area just next to Jan. Jan may also be working at the wardroom table, where he likes to lay out medications and medical gadgets. Or he might be anywhere, as he silently fixes and improves things all over the hab. Andrea is always seated at the hab computer, working on a comprehensive EVA plan for the next eight days. (She would apparently prefer to be using her own laptop at the workstation area. She's still locked out by a security system meant to prevent improper use of her computer, and meanwhile is unable to get the password because the powers that be are trying to page her!) Meanwhile, Nancy is happily growing things in the biology lab. She and Vladimir also work in the greenhouse. The first seeds have sprouted; Vladimir asks: seeing this, what does it mean to you?

'''1530-1930''' We begin an interleaved double EVA, following a schedule I've posted on the wall:

'''EVA 65:''' Nancy and David, walk to windy spots to deploy a "wind catcher" (you'll have to read her report) -- 1545 suitup; 1630 egress; 1700 return.

'''EVA 66:''' David, Bill, and Vladimir to take ATVs to furthest areas to survey our domain, so we can better understand the map and past EVA reports -- 1615 suitup; 1700 egress; 1930 return.

The schedule is kept, except our egress is 30 minutes delayed by an experiment in wiring Vladimir's radio up his sleeve, so he can see it (what an idea). This works well, though next time he'll move it further from his wrist.

In considering our recent EVA experience, I realize that navigation is a fundamental problem in exploration. Historical explorers knew this very well, but few of us have first-hand experience in exploring huge tracts of new land. I need a voice in my helmet that tells me where I am relative to my (GPS-defined) destination and what direction to go. Handling paper maps or even a GPS is tedious and unnecessary. Beyond this, we need some way for routes to be found from Earth and communicated to us on Mars. This time we've stayed on the main roads and well-defined ATV trails, though I will need to study the map to know exactly where I have been.

Sighting the hab on our return at dusk, I imagine the warm and comfortable rooms inside; it sits elegantly white and sturdy, nestled in a small elbow of line of rounded orange hills, feeling like a refuge--our habitat. You know that, seeing the Mars hab on Mars itself, our future explorers will surely feel this same gratitude and pleasure.

'''2040''' Dinner is delayed, but I'm glad to have extra time to write my report. Vladimir entertains the crew with the telescope, pointing out the sights. Nancy says, "What could possibly be better than viewing an absolutely magical sky, while somebody else is cooking dinner?" Everyone laughs.

'''Bill Clancey'''

'''MDRS Rotation 5 Commander'''

===Health & Safety Officer Reports===
Jan Osburg Reporting

'''Safety:'''

Using the potable water pump for firefighting was evaluated. Firefighting with this pump seems advisable in case the hab fire extinguishers have been used up and the fire is still not under control. Proposed procedure (will be tested during another fire drill tomorrow):

#During evacuation, one of the generator refill team takes the water pump from its storage place in the tools area near the rear airlock. He also takes the orange extension cord from the tool bench closet. He moves both to the outside potable water tank and immerses the suction hose of the pump into the tank.
#He proceeds to the generator and disconnects the green power cable from the generator plug panel.
#He then goes back to near the water tank and unplugs the yellow extension cord leading to the hab from the orange generator cable (plug is located approx. 3 m NW of the potable water tank). He connects the orange extension cord to the orange generator cable. Now the hab should be without electrical power, thus eliminating the risk of electric shock during subsequent firefighting.
#In the meantime, the other generator team member removes the sprinkler hose and attaches one end to the water pump outlet. She then takes the other end and gets ready to fight the fire.
#After making sure that the hab has no electrical power, the first generator team member connects the water pump cable to the other end of the orange extension cord to start the water pump. He then assists the other generator team member with firefighting. The airlocks were identified as possible "safe havens" where crew could retreat to in case of rapid decompression of hab. This requires that the airlocks are build large enough to can accommodate all crewmembers as well as their EVA suits, and still have enough remaining space to allow crewmembers to don the suits.

'''Health:'''

Another big ol' fly was observed (and killed) in the Biolet room. As an immediate measure, two pieces of duct tape were coated with a mix of molasses and honey, thus converting them into makeshift fly paper, and suspended from the ceiling in the affected area. Looks like fly season just opened...

No medical incidents were reported.

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' Water consumption in the last 24 hours: 176 l (46 gallons), with one shower taken.

The water refill hose developed a bent spot where it enters the hab close to the roof due to the bending radius there being to small. This should be fixed to avoid excessive load on the water pump. Recommendation: provide a second water pump to assure hab water supply in case the main one breaks down (it seems to be operating at the limit of its specs). The water tank will be refilled by Lamont tomorrow.

'''Power and Fuel:''' Lamont brought the fuel just in time for the next refill. The hab now has more than a week's supply of generator and ATV fuel.

The generator oil leak seems small enough not to require any major repairs; we just have to keep an eye on the oil level and top it off every day.

Recommendation: TYVEK suits should be provided to generator refill team members to protect them from eventual gasoline spills, and to keep the gasoline smell/vapors away from their clothing.

Generator fuel consumption: approximately one five-gallon can (19 l) every 10 hours, equaling 45 l (12 gal) per day. One barrel (55 gal) will therefore last for 4.5 days if used only for the generator. Of course, if fuel is used for ATVs, this number will be lower.

It was discovered that oil was leaking from the air filter of the generator. Investigation revealed more oil inside the air filter casing. This might be due to a recent topping-off of the generator oil, however we will observe this in case the leak continues. (Follow-up: oil does not leak while the generator is running, it only seems to leak when the generator is stopped. Strange.)

'''EVA Equipment (including ATVs and PEV):''' Vladimir tested a new way of mounting the EVA radios to improve ergonomics: duct-taped to the lower left sleeve, with the headset wire running inside the sleeve. This is compatible with the EVA suit mirror wristband and an attached watch, making the left arm the "utiliy" arm and leaving the right free.

Recommendation: as the radios seem to require lots of batteries, rechargeable battery packs and associated chargers should be acquired, as the radios are designed to accommodate them easily.

EVA backpack 5 is down with a battery problem (switch, fuse and fans work, but the battery is dead and refuses to accept charging current). Recommendation: provide a battery charge status indicator on the EVA backpacks.

Another issue that came up during debriefing was the fact that about 30 minutes of oxygen prebreathing time would probably be required on a Mars base. To simulate this, a supply of general-purpose filter masks should be provided so EVA crew experiences realistic constraints before commencing EVA.

From today, every EVA crew will take along 20 m of strong rope for towing of ATVs and for belaying of crew during pedestrian descents, duct tape, a compass as a backup navigation aid, and a small first aid kit.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' David updated and revised the MDRS IT Manual, incorporating our lessons learned.

To connect portable computers to the hab stereo system, a long (10 m) audio cable with 3.5mm jacks is needed, along with an adapter from 3.5 mm to audio cinch (standard amplifier input). This equipment is available in all electronics stores.

Communications: see "EVA Equipment", above

'''General Maintenance & Waste Management:''' The two small general-purpose multimeters in the tools area do not work. A high-quality multimeter should be acquired (the existing Fluke 32 mentioned in one of the earlier reports is designed only for high-voltage, high-amp applications). A stock of long nails, wire, and rope in various diameters should be provided.

'''GreenHab:''' (see "Biology" report)

===Geology Report===
Andrea Fori reporting.

More photos for geology primer obtained. Explored area.

===EVA 65 Report===
Duration: 16:22-17:10 - David Real & Nancy Wood

'''Objective(s)''' Pedestrian EVA to install windblown dust collection devices at waypoint 102, which was previously established to be windy. A preliminary hole was dug before inserting the bamboo stakes on which the collection vials were mounted. The open end of the vials were facing the prevailing very light breeze.

'''Accomplishments'''

This was an easy EVA, and GPS navigation to the waypoint was straightforward.

===EVA 66 Report===
18:20-19:18 - Duration: 17:20-19:30

''(coincidentally these are within ten minutes of EVA 63)''

'''Personnel:'''

Bill Clancey (reporting), Vladimir Pletser, and David Real

'''Objective(s)''' To become oriented to major geological features around the hab; to find previously documented waypoints; and to investigate two routes Clancey had been shown during the March reconnaissance.

'''Accomplishments'''

We departed on ATVs north, in the direction of Waypoint 18, to find outcroppings noted by a previous crew. We visually identified these, but not definitively. The GPS reading was inconsistent with the previous record. We proceeded down the road towards Waypoint 15, but encountered a herd of Martian cattle on the road (named by their uncanny resemblance to Earth cattle). With the cattlemen nearby, we chose to avoid disturbing the herd and reversed course. On return, we chose an ATV trail towards the West and verified that it would bring us to the Mid-Ridge Planitia. Along the way, we noted often wet ravines and a grassy filled-in pond that might be of interest to Nancy Wood.

Passing the hab, we continued south, looking for a previously used route to the Mid-Ridge Planitia. After becoming familiar with the area, but not finding any obvious west-trending roads, we returned to the hab. A GPS reading for the turnoff would have been useful.

On return, we found that the waypoints we recorded for intersections do not correspond to the map; the cause is yet to be determined.

'''Lessons Learned/Misc. Notes'''

We confirmed the lesson of EVA 63 that route finding to previously established waypoints is nontrivial and requires advance planning. We determined that every crew member going on an EVA must be able to use a GPS. We require maps that we can mark in the field. An ideal system would provide audio directions through the helmet and enable voice commanding for waypoint setting, while driving, rather than the current tedious GPS device manipulations.

==April 12, 2002==
===Commander's Logbook===
Dr. Bill Clancey Reporting

Dinner was delayed until well past 2100, but most of us did not mind, for we had so much to do. We were treated to Jan Osburg's spicy Candor Chasma Chicken and potatoes. Afterwards, I showed my "Devon Video Shorts," ranging from the humorous (ATV stuck in a creek) to the thought-provoking (Jim Rice talking about Mars) and the sublime (a helicopter ride to Thomas Lee Inlet, with music prepared for the Grand Canyon). My stateroom light was out at 1140, which seemed too late.

'''0700''' I sneak out of my stateroom in a towel and flip on the hot water heater.

'''0715''' Feeling rested, I dress and egress, and this time find Nancy preparing coffee. I record the temperatures:

Maximum outside 23.4 C (74.1 F); Maximum inside 25C (77 F)

Minimum outside 11C (51.8 F); Minimum inside 17.5C (63.5 F)

I allow Nancy the first shower, and sit down to begin reading email--still an hour before I will have breakfast. Quickly enough, I get my chance to wash, and feel invigorated. This is the way to start a day, for sure, but our rationing does not allow it often. (Indeed, we are running short of water and expect to be reprovisioned today. But our supplier never shows up.)

After a quick breakfast of juice and cereal, I check the Hanksville weather--a dramatic change from the previous day: Temperatures rising to the upper 80s are forecast this weekend, with possible snow showers Tuesday and a low of 25F! I enter all of this in my mission planning table; on a whim I'm checking how forecasts change from day-to-day. Is the crew's daily planning any better or worse?

'''0905-1040''' Morning Planning Meeting. We seem to have more to discuss than before, and feel too pressed for time to give the topics justice. Indeed, one topic is productivity. I mention to the crew that in four full days there has only been one report (Real's story) on top of the EVA reports and required reports that Jan and I write. We have agreed that daily reporting of science is not necessary, but we had also agreed that two reports would have been completed the previous day. Where is the time going?

Andrea says she needs at least 15 minutes of uninterrupted time to do anything. I point out that we have daily "individual work" time before lunch of at least two hours and often three! Vladimir explains that it's the little things that take time --email with family and colleagues (should that be more stringently controlled on Mars?), and all of the myriad details of work itself. He illustrates with the example of fetching the datalogger from the greenhouse, downloading data, determining that values are not as expected, debugging the problem, fixing the problem, and returning the datalogger to the greenhouse. One can easily spend an hour doing that, when all that was intended was to verify that a task done yesterday had succeeded. Later in the morning we observe another example: Vladimir and Andrea must refill the generator, which causes a hab power failure, which requires the internet to be rebooted, which holds up anything we were in the middle of doing online.

Despite this, when we make the rounds, everyone speaks convincingly of having felt very productive on multiple occasions in the past few days. Andrea has produced an EVA plan for the remainder of our rotation. Nancy has set up the lab to her liking and started experiments. David has written two lengthy stories. Jan has reorganized the med kits ("into logical elements"), and Vladimir has begun a variety of plant growing experiments.

We briefly consider how things might be different if mission support imposed deadlines or we were trying to communicate with colleagues who were assisting us back home. Would priorities change?

We also determine that we are spending five hours a day in group meetings and meals. We clearly like to be together. But several people are quick to volunteer that they could be content to grab something and go back to work, eating alone, as they do at home. Instead, we've made lunch into an elaborate social event, and added a tutorial session afterwards, that extends the time to two hours. We resolve to cut this back and save the next tutorial for the inclement weather. Now, if this had been a Mars mission, we would have just had six months living together on the outbound journey. We'd be looking more outwards into the land around us, than inwards into the minds of these interesting new friends we just met not even a week ago.

Further showing the need for automation, we decide we should create an audio recording to send to mission support. This adds 15 minutes to the meeting, first to explain what we are doing, and then pass the recorder around. I then ask, who will download this data and send it to mission support? We look around silently. (As I write at 2051, nobody has found time to do this.)

'''1040-1315''' Individual work. I download, backup, catalog, and sort my photos from yesterday so I can show Andrea the geological features. As we meet (an EVA-planning subcommittee) I opine again that I would be content to have mission support give us a list of places to go, with routes, and full instructions. I can't believe I'm thinking this, when the opposite conclusion seemed so obvious to me on Devon Island in 1998: Surely the crew would want to plan their excursions themselves. At least in rotation 5's "wholistic simulation" experience, we are busy enough handling equipment and reporting, and would be happy to offload some of the planning.

Andrea and I review her plans and reorganize the EVAs, considering the weather, specific objectives for the rotation, and individual schedules (don't send the Director of Galley Operations out on a late-afternoon EVA). At the end of this exercise, I believe the planning work has really only just begun. When will we find time to do this? Would mission support on Earth tolerate our preference to plan one day at a time, each morning?

'''1315-1340''' We have a less formal, quicker lunch. Vladimir asks if it's okay to leave the table to get back to work, the chorus says yes!

'''1347''' Andrea announces that after nearly 5 days of waiting, she's received the information she needs to unlock her computer. She says she's felt withdrawal, not being able to see her familiar screen. She must wait a bit longer, for now she is the computer's administrator and must figure out how to restore her personal settings.

Meanwhile, David and I review our GPS units and set waypoints, so are ready for the planned EVA.

'''1415-1430''' Nancy shows me a nicely prepared tool kit of materials, with written instructions, for retrieving her experiment apparatus on a nearby hill.

'''1440-1815''' David, Andrea, and I go on a mobile EVA (#67) to carry out Nancy's plan. We have learned that each EVA should have a major objective, which is pursued first. The samples in the bag, we move on the secondary objective, to find a route I was shown in March, for hiking up above the Dakota formation to oyster beds of the Cretaceous period. We lack waypoint information for the turnoff, so I follow a four-wheel drive road on the map. It is too far south. Retracing our steps we eyeball the ridge, which I recognize and wind up exploring a side wash. This is very interesting and I feel good to be inspecting hidden gullies just as we do on Devon Island. Even the many rocks remind me of Devon. An ironic thought: in the very act of exploring, the memory of another place makes the new setting enjoyable.

Returning to the main road, we proceed back north, and now I spot the track and the path itself, visible not that far away. From the main road, it seems steeper than I expected, so I had ignored it on the first pass. (What really do we know about the perception of navigation?) The rest of the EVA is uneventful, as we achieve our objective. All along the way, I ask Andrea how I should interpret various colors, layers, and shapes. Driving back, I start to understand that a lay person expects every single layer to have a name, but it seems that they are only categorized broadly by type (color, content, and so on) and named by characteristic examples (e.g., The Salt Wash Member of the Morrison Formation). I have learned the basics: The layers are grouped by Member, Formation, and Period. Now what of my idea of having characteristic photos of each member? Does that make sense? Our books show drawings, but not photographs of typical rocks and features. Why not?

'''1815-2030''' I feel overwhelmed with tasks: Write up EVA 66 from yesterday, prepare more photos for the web, write my log, review the science report. All this before dinner.

'''2037''' David warns to save your work. The power fails and Andrea and Vladimir, the team on duty, refill the generator. In the dark upper deck of the Mars Desert Research Station, we are all hauntingly lit by our laptop screens. Jan, always at the ready, is holding a flashlight for Nancy in the galley.

Tonight is Yuri's Night, so we will celebrate with a special meal, music, and a movie.

'''Bill Clancey'''

'''MDRS Rotation 5 Commander'''

===Health & Safety Officer Reports===
Jan Osburg Reporting

'''Safety:'''

Nothing to report.

'''Health:'''

Biolet: see engineering report.

No medical incidents were reported.

Crew morale received a boost by celebrating Yuri's Night.

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' Nothing to report, except that the outside water tank needs refilling. Water consumption in the past 24 hours: 160 l (43 gal), with two people taking showers.

'''Power and Fuel:''' Lamont brought 4 liters of oil for the generator and the ATVs.

'''EVA Equipment (including ATVs and PEV):''' Suit backpack 5 was checked and a blown fuse diagnosed. Mission Support was contacted to inquire about replacing fuse (2 A) with 2.5 A fuse.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' The battery of the existing Fluke 32 multimeter was exchanged (a 9V cell; we are out of these and need more); afterwards, it worked fine (but still for AC only). It was used to check out the new UPS, which was subsequently declared operational. The Hab computer, its monitor, and the Starband satellite terminal are now connected to its buffered output plugs, giving us 10 minutes of assured communications in case of generator failure or maintenance, and relieves us of the task of having to shutdown the computer every time the generator is refilled.

One problem with running any UPS in the hab is that anytime the generator reaches its performance limit, i.e. power demand is high, the voltage goes down to around 100 V. This seems to be the threshold for the UPS to switch from regular to battery mode. So, with the voltage oscillating around 100 V during high-load activities such as cooking, the UPS constantly changes modes, each change accompanied by a beep. This poses no short-term problem (apart from the annoying beep), but will surely ruin the UPS battery within a few weeks. Maybe this is what happened to the previous UPS.

After long e-mail conversations with her IT support, Andrea's computer was brought back to life and is now cooperating with the local MDRS network. Her productivity has already gone way up

<nowiki>;</nowiki>-)

'''General Maintenance & Waste Management:''' The Biolet was checked, as it seemed to get full. Both fluid check hoses were empty, which is nominal. The biomass in the receptacle was manually stirred (using a long stick…) to smoothen it and improve composting effectiveness. Disposable gloves were worn throughout the maintenance activity. The TYVEK suits requested yesterday would have come in handy for this task, too.

'''GreenHab:''' (see "Biology" report)

===Geology Report===
Andrea Fori Reporting

Another geology EVA achieved today (see '''EVA #67 Report'''). We visited the boundary between the Jurassic and Cretaceous periods and digitally recorded the transition. Just above the boundary was an expansive field of fossilized oyster shells. Had a briefly exciting encounter with some erosional features that closely resembled dinosaur vertebrae.

===EVA 67 Report===
<blockquote>'''EVA Scenario Overview'''
We had two main objectives for our EVA on Friday, April 12, 2002. The first objective was to retrieve two sample containers designed to collect wind-blown grit. The containers had been placed by an EVA team a day earlier, on Thursday, April 11. The EVA team also collected two dry samples from the same site. The second objective was to discover and document a path that would enable future explorers to visit the oyster fields that are indicative of the Cretaceous era south of the Hab.
'''DATE: 04-12-02EVA Highlights (EVA CDR)'''

*We successfully retrieved Nancy's samples.
*We turned off the road in pursuit of the oyster bed at new Waypoint 109, N 4248712, E 518896
*We found faux dinosaur bones at new Waypoint 110, N 4248618. E 517873, then discovered this layer is prevalent throughout the immediate region.
*We found an oyster bed at new Waypoint 111, N 4248629, 517882

'''PRE EVA OPERATIONS'''Both the CDR and MDRS2 took the time to familiarize themselves with the GPS equipment, one supplied by the Hab and one a personal item.
Nancy Wood, the biologist in charge of the experiment to collect wind-blown grit for further analysis, fashioned a kit to expedite the timeline for the EVA team. The kit included two labeled lids for the plastic sample containers at the site, and a marked label that also served to seal the samples from contamination. A marked paper-backed label was partly peeled from its sticky backing and a pipe cleaner attached to it in order to make it easier for the EVA crew to detach the label and apply it correctly to one of the containers that had two holes pierced into its walls. Two other sample containers were also labeled so they could be identified later. Nancy prepared the instructions for the collection in advance, since she was not a part of the recovery EVA team. This may become standard for field scientists who can direct others to collect samples while they remain in the Hab to do more pressing and productive work.
All three EVA members also wore mirrors on their forearms to monitor the progress of the others as a safety measure.
'''AIRLOCK INGRESS/DEPRESS'''
Normal ingress and depress. Radio checks completed. The EVA crew was greeted immediately be the other three crew members in celebration of Yuri's Night.
'''HAB EVA MONITORING'''
</blockquote>
{| class="wikitable"
!NOMINAL EVA COMM/SAFETY CHECK
(Hourly Operation)
!Comm ck
1
!Comm ck
2
!Comm ck
3
!Comm ck
4
!Comm ck
5
!Comm ck
6
|-
|'''TIME'''
|1545
|
|
|
|
|
|-
|'''EVA #'''
'''(If Simultaneous EVAs)'''
|
|
|
|
|
|
|-
|'''ATV Odometer'''
'''OUT/IN'''
|
|
|
|
|
|
|-
|'''REPORTED MAP LOCATION'''
|WP 102
|
|
|
|
|
|-
|'''REPORTED STATUS'''
|OK
|
|
|
|
|
|-
|'''Auxiliary Information'''
|Position Check
|
|
|
|
|
|}
<blockquote>'''EVA MONITORING'''Terrain prevented communication between the Hab and the EVA team near the Jurassic/Cretaceous boundary. The Hab reported that voices were heard but words could not be deciphered. The EVA team also could hear some of the words from the Hab, but it was difficult to carry on communication.
'''POST EVA INGRESS AND CLEANUP'''
Normal ingress and cleanup was done.
'''EVA CREW: COMMENTS/OBSERVATIONS/LESSONS-LEARNED'''
'''EVA CDR:''' Nothing beats being with specialists in their home turf. You have the opportunity to ask about what you see. But you learn by just watching where the specialist goes and what she looks at. Just seeing Andrea kneeling over the faux bones showed that she found these rocks interesting, too. Then she looked around for something similar, showing us by example how to interpret most any odd feature we might ever see.
'''EVA MDRS1:''' It was fascinating to be able to put my finger on the boundary between two significant periods in geological history: splitting Jurassic from Cretaceous . The oyster fields seemed like such a happening place to be. There were these huge mounds of oysters, hanging out and having a great time.
'''EVA MDRS2:''' I was struck by how prepared Nancy Wood was when she asked us to retrieve her dust samples from Way Point 102. She had thought of almost every contingency. The only unforeseen problem was unzipping the zip-lock bag. When Nancy learned of our troubles, though, she had a solution: Just grab the sides of the bags and pull. That would force the zippered bag open without fumbling for the top edge of the bag with bulky gloves.
I was also struck by the open expanse of the oyster field, which seemed to just open up under our feet once we reached the top of the plateau. A truly incredible experience. Nearby were also interesting examples of ruby-colored quartz and some translucent ones, too.
</blockquote>

===Crew 5 Profile - Andrea Fori===
By David Real / Belo Interactive

'''Aboard The Mars Desert Research Station, Utah''' - Talking about life on Mars can sometimes seem as much philosophy as science - just like life on Earth.

"We don't know what we don't know," said Andrea Fori, 32, a planetary geologist specializing in Martian geology. "That's good information."

Considering the grand scope of the physical universe -or even the internal universe that each individual carries inside - we know very little, Ms. Fori said. But it's a start, whether it's Mars or Earth.

"When you are aware that you're lacking information, you're much more informed than when you don't know what information you're missing," she said.

She is working hard to reduce that information gap by donating two weeks of her vacation to a project in the Utah desert. The Mars Desert Research Station is a project of the Mars Society, a group advocating exploration of the Red Planet as soon as possible.

A half-dozen explorers are living in an isolated station that mimics some of the living conditions and problems that astronauts could face.

Ms. Fori already has experience helping to resolve more earthly problems.

Every time a thunderstorm boils up and pictures of clouds dash across a television screen, it's a good bet that the images came from a satellite she helped to build.

As a systems engineer at Lockheed Martin Space Systems Co. in Sunnyvale, Calif., she helped to integrate the world's first weather satellite - TIROS, or Television Infrared Observation Satellite. She planned how the prorgam was handled and ensured that the requirements of the project were met throughout its design and production.

Geologists will be among the first to visit Mars, she said. That's why the experience of simulating a Martian research habitat and participating in field trips - extra-vehicular activities, or EVAs - is so important.

"We will definitely need to do geological studies in person," she said. "This exercise of living in the Hab, planning, and then putting on a suit and conducting geological studies is really practical.

"When you put on a 30-pound spacesuit and you bend over and try to pick up a rock, it's difficult. Without going through the motions of doing it, you wouldn't necessarily know that.<nowiki>''</nowiki>

She said a problem that made her computer inoperable was the biggest obstacle she faced during the simulation.

"To not have that working smoothly is extremely disruptive," she said. "It's changing my whole mind frame; I'm not able to plan; three days have gone by and I haven't gotten anything done in terms of practical EVAs; and it's just really posing a big problem in many aspects of everyday life."

However, she said she was pleasantly surprised by the camaraderie that has developed among the six crew members, despite the cramped conditions of the 4 ½-by-10-foot state rooms.

"The food and the living conditions and living on top of everybody has actually gone better than I thought it would,<nowiki>''</nowiki> she said. "I expected it to be more difficult psychologically.

"The lack of privacy, being dirty, not having good food to eat - I thought all those things would make your mind frame skewed to thinking about those issues instead of accomplishing something on EVAs. But the domestic issues have been less of a problem."

Ms. Fori, who grew up in Coxsackie, N.Y., near Albany, said she never thought that she would study geology.

"No pet rocks," she said.

But she changed her mind during her undergraduate years at Hartwick College in Oneonta, N.Y.

"I just thought it would be really neat to learn about the Earth," she said.

Her career took another turn in 1994 when she turned to planetary geology and decided to study Mars for three years to earn her masters degree at the Mackay School of Mines at the University of Nevada at Reno.

"I was never a space buff as a kid," she said. "It came through education. I was exposed to this world of really, really exciting research that was going on."

During graduate school, she received funding from NASA to investigate the mechanics of geologic faulting on Mars, such earthquakes.

In the summer of 1997, she was one of about a dozen people selected from a nationwide search for the 10-week Astrobiology Academy at the NASA Ames Research Center in Sunnyvale, Calif.

She worked with Dr. Jack Farmer, a leading biologist/geologist, to select a landing site for the 2005 Mars mission that would pick up rocks and return them to Earth. The mission to Parana Valles, potentially rich with fossils, was postponed after the loss of two NASA Mars probes a few years ago.

In the summer of 1999, she was among 80 students worldwide chosen for a 10-week-program at the International Space University in Thailand. The students were able to talk to the heads of many space agencies around the world to come up with a strategy for exploring the solar system.

"The intent is not necessarily to come up with something spectacular," she said "The intent is to learn to work together, think through ideas, and ideas for international space agencies to consider."

She said the cultural hurdles were difficult to overcome because students from some nationalities deferred to Americans and Canadians in group discussions without offering their ideas.

Now that she is in the Utah desert, she said she welcomed the opportunity to break from her routine at Lockheed Martin and focus once more on her love for Mars and geology.

"You can get in a rut building a spacecraft, and you need to step back sometimes and say, 'All right, what's the big picture here? What, as a human race, are we working toward?' So it's kind of a reality check for big goals as a human race.

"I've had a great experience. It has been a lot of fun and it has renewed my enthusiasm for Martian exploration."

==April 13, 2002==
===Commander's Logbook===
Dr. Bill Clancey Reporting

Dinner again was after 2100, which allowed me to write yesterday's report. Our Yuri's Night repast, prepared by Nancy, was a feast: Pasta salad, beef stew, and warm fruit medley. She explained how, fitting the seven continents theme of the Night, all the ingredients had come from around the world: Sun-dried tomato from South America, bell peppers from North America, honey from Africa, olives from Europe, rice from Asia, and (perhaps) the Shiraz wine grapes originating in Australia. Jan provided an equally eclectic musical mix on his laptop, illustrated by Winamp's psychedelic and hypnotic graphics. Afterwards we settled down to watch the movie 2010, which we had carefully chosen from the hab's library. Alas! The container was empty, so we settled for "Outland," which had the virtue of being short (David asked, "When do the special effects begin?"). We toughed it out and retired for bed, exhausted. My light was out at 0115, though Vladimir and Andrea still had to refill the generator.

'''0700''' I awake, not thoroughly rested, but it feels time. Almost... 0740 I realize I'm not going to sleep any more. An azure sky fills my portal, enticing me to start the day.

During a trip to the toilet during the night, I had seen Jan's note on the sink on the lower deck: We have only 2 gallons of water in the tank, and are to use water only for drinking and teeth brushing. I learn as others awake that the pump had broken, so the remaining 30 gallons or so in the outside tank are not accessible. (Writing reports like this, I repeatedly discover that I do not always retain incidental details: Does the tank hold 300 gallons? Is it 1.5 meters high? What kind of plastic is it? I do not have this kind of mind.)

So the day has begun off balance, with a feeling of slipping sideways, not following the course. My breakfast is delayed by new decisions (should I take the remaining milk for cereal? will we have coffee?). In the meantime, I record the temperatures:

Maximum outside 19.4C (66.9 F); Maximum inside 23.4C (74.1 F)

Minimum outside 4.2C (39.6 F); Minimum inside 16.1C (61 F)

This coldest night was welcome. The storms of yesterday have given way to a brilliantly clear day, heating up fast.

'''0905-1030''' After breakfast, it's evident that we won't start with a meeting--we need water, so we all head outside in our civies. We've decided we should siphon the water into 2.5 gallon jugs. We try Vladimir's first idea of putting the tank on sawhorses (actually, his first idea was "seahorses"), but it is too heavy by far. So we jockey around, tossing out ideas: Roll it up the hillside? Prop it up on a ladders? Getting the tank on its side proves easy enough, and we prop it up with the ladders and rocks. What, no duct tape? (We actually look around, checking for a use for it.)

Jan has sterilized some clear tubing from the lab, and wearing his pink rubber gloves, and towering a bit over even me, in crew cut and glasses, he is quite the German engineer. We follow along.

Then a new problem: The tubing is floating to the surface and won't fill. Jan directs Andrea to get a large spoon from the galley. She returns and we attach it to the tubing end with duct tape. Voila! It works.

Meanwhile, Vladimir has shown me the pump. I see a plastic-rubber gadget, mostly in pieces. It appears to have something to do with moving water. What happened? Probably while pumping near the bottom, the hose came out and the pump ran dry. It appears irreparable.

Andrea and David proceed to bring down the power to refuel the tank. Oh well. I had started this rotation with the primary question, how do chores affect science productivity? I make a note to remind the crew to be recording all this time spent away from our supposed "work."

'''1030-1230''' Individual work time. We send out urgent reminders to mission support. We not only need water, we now need a pump or at least some clean buckets. We are glad to find a reply from Mark Klosowski, Capcom of Northern California's mission support team. Lamont will be coming with water this afternoon. We weren't in danger of course, but we are glad not to have to break sim to get water from town. (Unless you are a backpacker, you cannot understand the jarring feeling we experience when we inadvertently see the van parked behind the hill. WHAT IS THAT? You mean people tie themselves into those seats, and are raced across the landscape?)

I'm trying to understand where the time is going. Here's an example. I'm poking around the hab computer, learning more about the GPS software, following welcome pointers from Andrew Hoppin (Crew 4) and Frank Crossman (mission support). David is by my shoulder, evidently interested in the Excel waypoint database, so he can set coordinates in his GPS for the upcoming EVA. I open the file and he asks if I will copy it to his floppy. But the copy operation aborts because the file is too large (how could the operating system not know that a floppy is smaller than 2.8 MB?). I try using "Save as," but no change. Maybe it is the format, save as Excel97. Nothing happens. Windows has crashed? We talk for awhile and walk away. Minutes later, ready to reboot, I notice the operation completed. Hmm. Oh. Now the file is 28 MB. (Laugh or cry? Laugh or cry? That's computers today.) David decides to create a new copy of the file so he can read the numbers (the photographs are making the rows so large, you can't easily read the coordinates). This takes yet more time because the copy and paste operation doesn't work. Now does anyone remember, before the computer became the center of our attention, what were we trying to do? (I think I lost it somewhere around 1987, when I stayed up half the night reading MacWorld.)

'''1230-1330''' Lunch. We decide to keep our plates for dinner. Now I have a plate, fork, cup, and glass in my stateroom.

'''1335-1500''' I have settled down to read and think. The group seems more content with the reporting process today. Maybe it takes a week to get into it. Maybe I had to make a point of it.

Now I work on the photographs. I'm the only one uploading them, what's the problem? David's camera was in a bag inadvertently taken away by Crew 4 (and then FedEx put it on the wrong truck). Vladimir can't charge his batteries. Nobody else has a digital camera. (I later find Andrea does, but can't download from the microdrive. I loan her a flash card. Still later I find a Type II adapter in the detritus around the hab computer.) I ask Nancy to learn to use the digital camera in the hab.

I recognize that several times today a problem has come up or maybe I've been asked to do something. My reflex is to take it on myself. But my thought is to delegate. And so I do. Jan catches whatever I toss his way: the water, the maps, the digital camera. I start saying to others, "Ask Jan to help you." It's now obvious, he's the Executive Officer, my second in command.

I overhear Nancy saying she is tired, getting less sleep than she needs. Andrea agrees and offers to have dinner ready earlier. But Vladimir says he sleeps better in the morning and likes the later meal. Nancy says the first light wakes her up (it peeks in through an electrical outlet).

Vladimir is calling me. Time to help him, David, and Jan into their suits. (Notice the problem? Three people going out, and four or five are fully occupied in the exercise.) After the suiting up, which took 40 minutes, we send the crew on their way on ATVs.

I return to my stateroom to read. Then Lamont arrives with the water. Never a dull moment. How to wrestle tons of water off a trailer? Use the minivan as a counterweight or the hab? Choices, choices. I'm told they pulled a strut off the hab the last time they tried this. And what would it do to our rented van? I opt for the hab. It looks sturdy. Lamont repositions his truck, fastens a chain to a web belt and tightens it up around the tank. I ask how should we signal a problem. Lamont says he'll stop if he hears anything. Andrea and I agree a simple scream will do. But the tank slides out smoothly and soon rests onto the sand near the hab. I say, that was easy--and if this were a cartoon, the hab would now fall over the other way.

It's 1.5 hours since lunch and I have barely had 10 minutes to read the geology books I've carried into my stateroom. Nancy makes some coffee, I opt for a nap.

'''1520-1800''' Finally some uninterrupted time to read. I breeze through four books, skimming the sections on the Morisson formation. I learn that it's perhaps the most-studied geological layer because it's so rich in dinosaurs...and uranium, an unexpected combination. Andrea suggests that it's also because the layer is so visible. We don't know the geology of the area around Cambridge so well, she says.

As I read the books, I don't find the color photographs I would prefer. But there are some pictures and they help. In my two trips to MDRS, I have learned more about geology from climbing one hill, than in my entire life, as we hiked from the Morrison Formation of the Jurassic into the Dakota Sandstone and landed on the "mid-ridge planitia," the lower Cretaceous below Skyline Ridge. After that steep climb through mostly purple clay, you arrive on a huge, unexpectedly flat grassland--with hills of oyster shells! Millions of them. I've made a note of the species, "Gryphaea Newberryl," starting in the Albian layer of the early Cretaceous. I could get into this, this chant, this scientific incantation that rolls off the tongue. But it's the hike that stays with you, not the names. A breathlessly steep hill, and then an arrival in a more recent age. An understanding of the layering, the lake, creek, and sea alluvial plains. Deposited layers, washing upon themselves, eroding into the past and depositing more. Hundreds of feet thick. Millions of tons layered and washed away again. The stuff inside, the fossils, the minerals, the sand and stones. And what, Gastroliths? Stones from dinosaur stomachs? Could we find those? I am hooked.

What is the geological story of Mars? Did its weather change? Did deposits come and go? Are there layered formations? The clues are just arriving: Layers, yes. Water deposits? Maybe. Windblown dust or sand? More likely. A large part of exploring Mars is about geology. And so I have come to MDRS partly to learn about geology. Astronauts training for Mars will do the same. In fact, why not here?

'''1800-1855''' Still quiet with three of the crew on EVA. I walk around and think about my observations. What am I forgetting? Review my notes, my plans. We need an experiment with mission support: Can they follow an EVA if we send back time-delayed audio recordings of radio reports? Andrea and Nancy are excited by the idea, and email confirms interest back home. So a Sunday afternoon exercise takes shape.

'''1855''' The EVA crew returns (after faking that they are out of fuel within sight of the hab). After the usual wait, we open the hatch. The sight is jarring. Even now, even after being in Flashline Arctic Station and even a week here, I cannot grasp it: Three spacemen in full gear are standing before me! (And probably the Apollo astronauts scrambling back on board the Lunar Module smelled, too.)

'''1915-1925''' Vladimir calls me outside to watch him dig up the sump pump. Can we use this for moving water from the outer tank into the internal tank in the loft above the staterooms? It appears new. But would it contaminate the drinking water? We need to ask Frank. Which means we need to ask mission support. But we want to use the pump now. I write down the make, model, and company. Perhaps we can find information on the net.

'''1925-2040''' I try to begin writing my report, but it is time to eat. The EVA group reports on their journey. Surveying the full extent of our ATV range was a great idea, they agree. They report having followed all the trails to the end--to cliffs, to a river, to dead-end canyons, to remote plains. Surely, having established an ability to move around safely, we'd do the same on Mars: Drive around, check the views, examine your setting from all angles. Establish some roads, mark the waypoints. Draw a map. The crew reports good places for Nancy to sample.

I describe the plan for tomorrow. We need a rest. Sleep as long as you like, no meeting in the morning. Read or catch up on your reports if you wish, your choice. A joint, time-delayed exercise with mission support begins sometime after 1400.

'''2040-2240''' I retire once more to my room to write. FMARS was not a good test of the staterooms. They were cold, dark, and poorly lit. Here I have a window, a bed instead of a ledge, a corner desk, carpeting, sufficient plugs. The upper bunk is like sleeping in a tree house. The lower is a nook, a comfortable niche.

Outside my stateroom around 2100 there was a great commotion as the group filled the water tank in the loft by a water brigade. I exited briefly to turn on the video recorder. This is one of my tricks: Letting cameras observe where I cannot be. Based on all the noise and laughter, this will be fun to watch and study.

Thinking about the day, I realize we are very friendly with each other, but a week is too soon to be close. That's a distinction we don't often have the chance to experience.

'''Bill Clancey'''

'''MDRS Rotation 5 Commander'''

===Health & Safety Officer Reports===
Jan Osburg Reporting

'''Safety:'''

During generator refill, the team waterproofed all live outside extension cord connectors, to avoid short-circuit and shock hazards in case of rain.

'''Health:'''

We had to siphon water from the outside potable water tank into water containers due to the breakdown of the water pump last night. Receptacles and siphoning tubes were disinfected with Hydrogen Peroxide before using them. The water, which contained some particulate contaminants (dust, several deceased insects) was run through a coffee filter before consumption.

Before refilling, the indoor tank was disconnected from the main water pipe, completely emptied and thoroughly cleaned, including a final disinfection with hydrogen peroxide.

Recommendation: the indoor water tank should be emptied and cleaned at regular intervals, as there was a fair amount of particulate residue inside, and the walls were partly covered with a brownish substance.

No medical incidents were reported.

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' The electric water pump was damaged beyond repair last night during refilling of the inside water tank. This was probably due to the suction hose not being fully immersed into the water, as the outside water tank level was very low. The dry running caused the plastic impeller blades to overheat and melt, thus also contaminating part of the water hose.

This morning, strict water rationing was instituted: water for drinking and tooth brushing only, everything else, from hand washing to sponge baths to dishes cleaning, to be done using wet wipes - heck, what's good enough for ISS crew is good enough for us :-). The remaining water from the potable water tank was siphoned into disinfected empty water containers (see also today's HSO report). To achieve this, the potable water tank was turned on its side so the opening was near the ground, and then rolled onto two ladders that were stacked on the ground on top of each other, to provide the elevation necessary for siphoning. The tank was secured using sawhorses and boulders, and siphoning resulted in about ten gallons of water.

This amount lasted throughout the day, and in the afternoon, much to our relief, Lamont refilled the water tank. As the pump is still out of service, the crew refilled the cleaned inside water tank (see HSO report) using the bucket brigade approach and two buckets that Lamont had also brought at the request of Mission Support. The 230 l (60 gal) tank was filled in about thirty minutes.

Total water consumption today: approximately 60 l (15 gal) due to water rationing.

Recommendations: provide backup water pump (see also engineering report dated 10-APR-2002), and do not squash empty water containers, as they might have to be used for water transportation. Also, keeping some clean, transparent tubing at hand will help with siphoning.

'''Power and Fuel:''' Nothing to report.

'''EVA Equipment (including ATVs and PEV):''' Nothing to report.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' Another try at connecting the new UPS to the hab computer/starband was made. Results: no problems up to now. We hope for the best...

'''General Maintenance & Waste Management:''' Nothing to report.

'''GreenHab:''' (see "Biology" report)

===EVA 68 Report===
<blockquote>'''EVA Scenario Overview'''We had four major objectives for our EVA on Saturday, April 13, 2002. The first objective was to determine a path to waypoints 32 and 33, with the constraint that we would have to follow unmarked terrain directly north of the Hab. The second objective was to find a wet point for Nancy so she could set up an experiment for ecosystem columns during a subsequent EVA. The third objective was to find a lake near waypoint 18 and determine if that could be another wet point for our biology experiments. A fourth objective was to travel these routes to determine the accuracy of previous waypoint coordinates.
'''DATE: 04-13-02'''
</blockquote>
{| class="wikitable"
!EVA Scenario
!Exploration,
experiment setup,

waypoint verification
!
!
!
|-
|EVA HAB COMM (S)
|Andrea Fori,
Nancy Wood
|
|
|
|-
|
|CDR
|MDRS1
|MDRS2
|MDRS3
|-
|EVA CREW
(Name/#)
|Pletser/6
|Osburg/1
|Real/3
|
|-
|EVA START
TIME (MDT):
|14:20
|EVA STOP TIME
Scheduled/Actual:
|19:00/18:55
|
|}
<blockquote>'''EVA Highlights (EVA CDR)'''Special attention was given in the pre-EVA briefing to carefully prepare the navigation. All intended GPS Waypoints visited by previous crew were entered in the several GPS's taken on this EVA expedition.
Several spots of interest were visited and unmarked routes were explored. As reported further, it became soon evident that navigating by GPS alone in unmarked territory is not an easy task. Revisiting waypoints of previous crew with only GPS coordinates but without a description of the location is not obvious. This feeling was further augmented by the divergence of readings from the three GPS units.
Furthermore, some dirt roads indicated on the 1987 edition of the US Geological Survey map have disappeared with time and replaced by other tracks.
Despite this background, we managed to achieve all goals of this EVA, and more, as we explored as well the passage beyond Waypoint 34. Some features, roads and junctions were named and new waypoints were logged. The EVA team did a good job on this four and half hour expedition.
'''PRE EVA OPERATIONS'''We spent about 30 minutes poring over the waypoints map on the Hab wall next to the Hab Comm. This allowed the EVA members to set their objectives for the EVA in accordance with the intentions of Hab CDR William Clancey.
As we determined a specific route, our concern about the validity of previous waypoints and our confidence in waypoint coordinates mounted. We agreed to input the coordinates into three brands of GPS units and test them under real-world conditions. This preparation lasted 1 ¼ hours.
We then asked Nancy Wood to brief us on her experiment to construct a biology experiment using ecosystem columns. She told us that she had already found soil for the dry and occasionally wet part of the experiment, but needed another site with soil that was constantly wet or moist.
We were also asked to take out the trash from the back airlock.
'''AIRLOCK INGRESS/DEPRESS'''Normal ingress and depress. Radio checks were completed. Two civilians were seen wandering around outside the Hab, but were gone by the time we emerged. As soon as we emerged, however, Lamont arrived with a filled tank of water. We offered to help, but CDR Clancey said we should continue our EVA. If we were needed, we would be asked to return. However, that turned out not to be necessary.
'''HAB EVA MONITORING'''
</blockquote>
{| class="wikitable"
!NOMINAL EVA COMM/SAFETY CHECK
(Hourly Operation)
!Comm ck
1
!Comm ck
2
!Comm ck
3
|-
|'''TIME'''
|1426
|1556
|1845
|-
|'''EVA #'''
'''(If Simultaneous EVAs)'''
|
|
|
|-
|'''ATV Odometer'''
'''OUT/IN'''
|
|
|
|-
|'''REPORTED MAP LOCATION'''
|Hab airlock
|waypoint 32
|Outside Hab
|-
|'''REPORTED STATUS'''
|OK
|OK
|OK
|-
|'''Auxiliary Information'''
|
|
|
|}
<blockquote>'''EVA MONITORING'''Numerous attempts were made to contact Hab Comm throughout the EVA, with only one success at waypoint 32. Other attempts, on both frequencies 200 and 201 failed.
'''POST EVA INGRESS AND CLEANUP'''
Normal ingress and cleanup was done.
'''EVA CREW: COMMENTS/OBSERVATIONS/LESSONS-LEARNED'''
'''EVA CDR:''' Leaving the Hab to the North, we soon turned West in search of a dirt road indicated on the map to turn North again in search of the first WP 22. We could not locate it precisely due to imprecision in the location of the dirt road (confused with other ATV traces), but the following WPs were identified with a certain level of confidence. WPs 29, 30, 31(oyster field), 32 (onion tea), 33 (geodetic point), 34 were found and revisited. The turn at WP 34 was missed and we continued on our way to follow the canyon road, until a Y ravine, where we backtracked. We found the correct turn at WP34, en route to WP 32 and Lowell Highway. From the junction (Dimitri's corner), we took to the North to WP 15 (dead end, on top of a canyon in front of a river). Upon return, we visited the WPs 18 and 26 and locate the water feature indicated on the map, a reservoir created by the US Dept of Interior Affair. Further down the road, a soil sample was collected four our Biologist from a intermittently wet area (abundant grass growing at this spot). The return to the Hab was eventless except for the beautiful dramatic scenery.
As a lesson learned for future expedition, WPs should be noted with their GPS coordinates AND with an obvious feature description to guarantee a positive redundant recognition method, to allow future revisiting crews to compensate the obvious lack of precision of actual GPS systems.
'''EVA MDRS1:''' Thorough preparation - poring over the waypoints map, programming our GPS units with the waypoints we would visit during our EVA and the routes connecting them, preparing sketched strip maps of our route - paid off, as we succeeded in visiting all the waypoints. This was my first motorized EVA, and I enjoyed the great scenery that unfolded around us as we traveled along our chosen route. Weather was perfect, and ATVs as well as suits performed flawlessly.
'''EVA MDRS2:''' As soon as we started our EVA, we determined that there was a margin of error in our readings from our three different GPS units. At our first measurement, David's Magellan Lazer 12 read E 517840, N 4251355; Jan's Magellan 3000 read E 517854 N 4251043 - and then started changing over time to read E 517703, N4251282 - and Vladimir's GPS read E 517776, N 4251557.
This confirmed our doubts about the accuracy of our measurements, not to mention those of previous crews. However, because we had previous waypoints loaded into our GPS units, we were able to maneuver. Combined with the help of a compass to guide us between waypoints, we were able to ascertain that we were in the general vicinity of a particular waypoint. However, this issue should be resolved before other rotations are dispatched to MDRS. Either measurements should be restricted to the Hab GPS units, or more expensive and accurate GPS units should be purchased.
I also must add that our visit to waypoint 15 was well worth the time. The view from the Dead End part of the trail looked out over a canyon with a flowing river and a panoramic view of stark mountains. Extremely beautiful and a great future picnic spot.

We also found a field of oysters at waypoint 31 that was an amazing site. It further underscores the diversity of the geology of the site.</blockquote>

==April 14, 2002==
===Commander's Logbook===
Today is Sunday, time for a change of pace. We had decided the night before that everyone could sleep in, there would be no formal meeting. And we will have a special EVA in the afternoon.

'''0640''' Having turned out the light about 2340, I am already awakening with the first light of day, but turn over and fall fast asleep...

'''0835''' I wake, dress, and handle the usual routines, including recording the temperatures of the past 24 hours:

Maximum outside 24.5 C (76.1 F); Maximum inside 24.5C (76.6 F)

Minimum outside 7C (44.6 F); Minimum inside 16.4C (61.2 F)

I decide to make a big breakfast of cheese eggs, ham, and toast. Nancy is awake and makes the coffee as usual. It tastes great as I read the Mono Lake Newsletter. We don't have a newspaper of course, so I find nature magazines and the like to be good reading at breakfast, a habit I picked up during the Haughton-Mars Expedition in1999.

'''1000-1215''' I read parts of Charles Perrow's book, "Normal Accidents," to get ideas for a simulation exercise we are designing for the afternoon. We've enlisted mission support's participation to follow us during an EVA. Perhaps there will be multiple, interacting failures...

'''1215-1320''' Lunch segues into a meeting to review the EVA plan. Nancy, accompanied by Andrea and Jan, will go to two spots close to the hab to deploy some instruments and take samples. David and Vladimir will work in the greenhouse. I'll copy all audio reports for about 90 minutes to mission support, at about 5 minute intervals, with 5 minutes time delay. Can mission support keep track of what is happening? Can they provide help if we encounter problems?

'''1320-1437''' Over an hour passes "getting ready." It's one of those mysterious time sinks we keep falling into.

'''1437-165'''5 The EVA proceeds according to plan, except for a combination of human error (J&A; separate from N), mechanical failure (the greenhouse zipper jams, trapping D&V;), unfriendly environment (it is hot and windy; we find many cougar tracks), system design limits (radios are finicky; the generator requires fuel), and disruptive procedures (I must leave the hab to refuel, because everyone else is away). Although I've hatched this plot (a sim within the sim) and refined the script with the crew, I become caught myself in its clutches. I have little time to read the emails coming in from mission support, as I try myself to remain in contact with the crew. Mission support provides some good advice about the zipper (wait for Nancy to get back) and the cougar (they send a web page). They are not overly concerned that two crew members were lost and two were trapped in the greenhouse. Did my own apparent lack of concern prompt this cool reaction? Or perhaps the remoteness and time delay made them feel like passive observers.

'''1655-1710''' We find ourselves sitting around the table together as if it is a meeting. We have a meeting instinct, I think. Or an eating instinct, for it is snack time.

'''1710-1830''' I write up the sim more formally and discover my trackball mouse doesn't work. Another 15 minutes of lost time. I clean the inside, no dice. I try holding it in different ways: intermittent failure. I works in my hand, but not on the table. Must be the flat surface. Maybe the three little rubberized disks on the bottom flattened; maybe the middle needs to be able to move. Duct tape to the rescue. But alas, it doesn't work. Again, I explore. Works in the air. Works when pressed forward. Doesn't work where it needs to be on the desk. Maybe the wire is broken? I look inside, nothing obvious where a break could be. No way to stabilize it. I look again at the desk. A huge knot hole in the pine surface. Nothing obvious. Then I notice the light on the surface. Very bright sunlight enters the portal over my left shoulder. It is the light: When it shines on the left (thumb) button, the vertical motion doesn't work. When it shines on the right (palm) button, the horizontal motion doesn't work. Move it forward into the shade and it works fine. Twenty minutes later the sun's angle has changed and it works fine no matter where I place it. Tilt it on sideways so light shines into the green buttons, and the problem occurs again. There must be an optical sensor inside. How odd, it's a trackball mouse, not an optical mouse.

Where does the time go?

The day will end with Vladimir and Andrea playing chess, personal work at computers, and dinner, followed by a movie. The wind is blowing for the first time in several days; the weather vane is creaking loudly, like an old boat mast. We take down the Martian flag.

Bill Clancey

MDRS Rotation 5 Commander

===Health & Safety Officer Reports===
Jan Osburg Reporting

'''Safety:'''

We successfully ran an EVA emergency simulation to test communications and CapCom/Mission Support procedures (see also Commander's Log).

Due to the cougar tracks discovered during this EVA, a "MDRS Mountain Lion Safety" sheet was compiled from information forwarded by Mission Support, and posted on the back airlock.

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' Still no pump, which means we still try to save water as we have to bucket-brigade every drop up to the third level of the hab. Sponge baths and dishwashing is allowed again, though.

'''Power and Fuel:''' The generator refused to start last night until we set the choke to half. With that, it started flawlessly.

'''EVA Equipment (including ATVs and PEV):''' According to Mission Support's suggestion, I installed a 2.5 A fuse in backpack # 5. It now is operational again.

After the experience with handheld GPS receivers during the past several EVAs, it would be nice to have one professional-quality, survey-type GPS unit available that we could e.g. mount to an ATV cargo rack to help us with navigating and accurately determining new waypoints (or finding old ones). Installing padded utility trays on the front ATV cargo racks for storage of handheld GPS units during transit might also be helpful, as the handheld models take several minutes to lock onto the GPS satellite signals during every stop, and reception during transit is insufficient due to the receivers being stored close to the body of the respective EVA crewmember, which effectively blocks out half of the satellite signals.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' The UPS ended up totally drained, so I had to remove it. All computer stuff is now hooked up to a regular surge-protector outlet. Possible reason for this failure: the constant cycling from battery to normal mode during hab voltage fluctuations (see previous engineering report), and the three-times-per-day power outages (every time the generator is refueled) that draw down the battery (according to the manual, it needs 16 hours to charge). So any UPS to be used in MDRS must have:

*a trigger voltage below let's say 90 V,
*a battery large enough to cover three ten-minutes outages per day,
*and a chargin system that recharges it within five hours.

Alternatively, we might install a generator that provides more maximum power (and thus more stable voltage), has a bigger tank, and can be refueled without switching it off.

'''General Maintenance & Waste Management:''' The weather station is not working; maybe its electronics were messed up by the same surge that fried my electric razor's recharging circuitry this morning...

Due to high winds, the Mars flag was brought in.

'''GreenHab:''' (see "Biology" report)

===EVA 69 Report===
Nancy, Andrea, and Jan

Technical Log:

'''Objectives:'''

#Placement of biodetectors
#Participate in communication simulation

'''Personnel:'''

*Commander: Nancy Wood Suit 6
*Jan Osburg
*Andrea Fori
*HabCom: Bill Clancey

'''Airlock timeline:'''

'''Departure ingress:''' 14:30

'''Departure egress:''' 14:35

'''Return ingress:''' 17:25

'''Return egress:''' 17:30

'''New waypoints:''' None

'''Route:''' wps 102, 105, 102, Hab

'''Communication checks:'''

Communication logs already provided in detail as part ot the simulation scenario.

'''Special circumstances:'''

As noted, the biology activities were carried out under partial sim; however, I used gloves and wore a helmet for all detector placement, so that the slide manipulation, etc. was realistic.

'''Conclusions/lessons learned:'''

Efficient field work under windy conditions requires careful preparation.

'''Summary:''' While the overall goal of this pedestrian "partial sim" (helmets and gloves) EVA was a simulated "normal accident" scenario conducted with mission support, we also put in place two biological detection devices. We encountered fairly high wind speeds and high temperatures. Our route went from the Hab to waypoint 102, to install a windblown dustcatcher, to waypoint 105 to place microscope slides in the lichen-rich areas. After the biology placements, the team returned to waypoint 102, and then to the Hab, in accordance with the scenario script.

'''Commander's Narrative (Nancy Wood):'''

The previous placement of dust catchers at wp 102 was unsatisfactory, perhaps due to lack of wind and/or design problems. The dust catcher deployed this time was a slightly different design, and it was certainly windy. In fact, it was so windy during the day of April 15 that it will be fortunate indeed if it is still in place. Waypoint 105 is an area of resistant sandstone containing numerous potholes covered in luxurious lichen growth. This area is clearly subjected to periodic heavy water flow. Since it was previously shown that the organisms present attach to glass slides under wet conditions, I decided to place slides in several dry areas at this location to assess whether attachment is possible. Slide placement under windy conditions is difficult, but four were installed with attached fluorescent pink telltales. Further details will be included in the next biology report. On route back to wp102, as per the scenario, I observed deer tracks in the sandy outwash downstream from the potholes.

===Chairs===
[[File:JanOsburgStairs.jpg|thumb|Jan Osburg climbs the stairs carrying a chair to the second floor workstation at the Mars Desert Research Station near Hanksville, Utah. Photo Credit: David Real / Belo Interactive]]
By David Real/Belo Interactive

'''Aboard The Mars Desert Research Station, Utah''' - It's amazing how quickly the mundane things of life can suddenly take center stage, just by being scarce.

Take chairs, for instance.

Six chairs for six people doesn't seem so bad. Plus one extra. (A second chair collapsed the other day, so it's now in the trash.)

So we have six chairs arranged around our second-floor kitchen table for meals, plus one spare.

We have more chairs than we need, really.

Except that Dr. Nancy B. Wood, our biologist, needs one for her laboratory downstairs, so we don't really have a spare chair anymore.

Except that three of us now want a chair to help us when we don our spacesuits next to the air lock downstairs, so we really lack three chairs.
[[File:JanOsburgComputer.jpg|thumb|Jan Osburg's computer is ready to work but Jan is not – someone has stolen his chair from his workstation at the Mars Desert Research Station near Hanksville, Utah. Photo Credit: William J. Clancey / NASA Ames]]
Except that we need another chair for the person working at the main computer terminal. And another three for people who like to use their personal computers in their rooms while they work on their reports.

Really, we need another seven chairs.

Plus maybe an eighth for whenever you want to look outside the main porthole to the outside world, whichever one that is - Mars or Earth, depending on your mindset. The round window stands about 5 feet above the floor, while directly underneath stands a 3-foot-wide table for computers and supplies that keeps anyone from getting too close to the window.

So a person's view starts about a football field away from the Habitat. It would be nice to stand on a chair and look almost straight down. That's where the red-green-blue stripes of the Mars Society flag flies, and where the ATVs are parked, and where people begin their cross-country missions. It's a particularly fine photo-op spot for a Kodak moment, even from the Hab window.

So, definitely eight more chairs are needed.
[[File:100things4people.jpg|thumb|A hundred things and four people.]]
Plus, there are lots of shelves that are too high to reach without chairs. At 5-foot-3, Andrea Fori needs a chair to reach the water glasses, which are stored on the top shelf of the 6 ½-foot-tall cupboard. Then she needs a reach of another two or three feet, so she can stretch over the drainboard that juts out from the wall and prevents her from reaching the glasses in the cabinet.

So, it is obvious that nine chairs are essential for the proper operation of the Hab.

Then there's all the storage space downstairs on the main floor. Those shelves must be almost 7 ½ feet tall, just below the ceiling. So another chair would be optimal.

That's 10 chairs that we have on our most-wanted list. Let's throw in two more as replacements for those that might break.

So we're all agreed that another dozen chairs is the minimum amount to operate this Hab safely and efficiently.

But wait. How ridiculous to pine away for a dozen chairs that will never appear anyway, since we are supposedly in the cold, remote reaches of space.

We will just move chairs around to fit our needs.

How simple and elegant a solution. We ourselves control our fate, not the stars.

But it's time for lunch, and there are no chairs around the kitchen table. This is a problem that surely cannot stand - or else we will be forced to. Come out, chairs, wherever you are!

There are only a handful of chairs upstairs. Where are the others? Ah, on the first floor.

Race downstairs - well, not really race. The stairway is of minimalist design, even by forgiving stair standards.

There are 10 steps, plus another step down to the main Hab floor. It's not even a proper stairway - more like a wooden ladder bolted between two floors at a dizzyingly steep angle.

There is enough room on each step to put your heel down and not much else. It's possible to feel much safer by sliding the back of the ankle and calf down the higher step to the lower one, thereby gaining a surer footing, but at the expense of shaving off a layer or two of skin from the back of your leg. That's a fair trade - these stairs look imposing enough to break two necks in one tumble, if one had that many necks.

Downstairs, there are two chairs easily spotted, which are painstakingly transported upstairs, step by step, hanging daintily off the right shoulder while the left hand is hanging onto the railing for dear life.

Grab a chair from the main computer terminal, and two more from the desk underneath the porthole. So we now have five chairs for a crew of six. Five? Where is the missing chair? Probably downstairs near the air lock.

Should we go back down to have a look? Having survived the trip once, it's probably best not to push one's luck.

It's got to be upstairs somewhere. In the commander's room? No. In Vladimir Pletser's room? No, again. Someone has leaned a ladder against the door of my room to reach the water tank on the ceiling of the staterooms. It's easy to move the ladder and strap it down out of the way.

Now I should check my room, but someone asks me where the sixth chair is.

Maybe it's in your room, I respond. Check. Check now.

No? Hmm. Where could it be. No need to check my room, anyway. There's no way it could be there. I would remember if it were.

Now all the others are looking for the missing chair. It's holding up lunch, and everyone is hungry. People shout at others to look in their rooms. Nothing. I deny that the chair is in my room. We are at an impasse. And no one wants to seem to go back downstairs for another look.

Finally, enough accusing stares prompt me to look in my room.

Ah, well. There it is.

See, I didn't sleep well last night. Got up too early. Been working longer hours than one should.

And, as previously mentioned, at least another dozen chairs are needed for the safe and efficient operation of the Hab.

Minimum.

==April 15, 2002==
===Commander's Logbook===
Dr. Bill Clancey Reporting

Some of us were to bed a little earlier last night. We all enjoyed the first part of the movie, "Dune" (year 2000 TV version). My light is out by 2300. But just before retiring I make a note about today's work: I will do "snaplists" and photograph the hab more thoroughly.

'''0706''' It is stuffy and warm. I turn over again.

'''0730''' I dress in shorts, my Northern California Mars Society t-shirt, and sandals. The clothes are all clean, but I feel grungy. Hmm, is that smell the rest of my clothes or me?

The usual routine: Bathroom, glass of water and a vitamin, start the time lapse video, and record the temperatures:

Maximum outside 19.5 C (67.1 F); Maximum inside 22.8C (73 F)

Minimum outside 15.1C (59.2 F); Minimum inside 18.1C (64.6 F)

It is warm for so early in the morning (67F). The sky is mostly cloudy. I go to Weather.com for the report. Wind is back in the forecast. Over the past five days, I recorded the following forecasts for today:

Forecast for today: Windy 78 Yesterday today was forecast to be: Windy 79 Two days ago the forecast for today was : Ptly Cldy 82/38 Three days ago: Ptly Cldy 80/25 Four days ago: T-Storms 81 Five days ago (last Wednesday): T-Storms 75

The forecast a day in advance is reliable, but everything else (at least in the past week) keeps changing. Don't like the weather forecast? Just wait a while.

'''0915-1030''' Morning Planning Meeting. We review the status of report writing (good), I give guidelines for the rest of the week. Then we go around, asking what each person for plans for the day. Ideas about EVAs are noted but held aside. Yes, there are more reports to write or finish, data to retrieve from the greenhouse, waypoint and EVA charts to update, soil sampling equipment to prepare, and so on.

Then we discuss EVAs for the remainder of the week, factoring in objectives (exploration, sampling, photography), personnel (trying to give each person at least two opportunities), where people have been and want to go, and chore assignments. I record in the EVA spreadsheet cell for today: "Hab pedestrian sample (NV + B photo) + (JA suit hr later) to river wp 14 then continue; retrieve 102 wind catcher (JVA)." Later I write this on the schedule board. (But the second half will never happen.)

Next we discuss and plan water and fuel. Jan will send a note to mission support about a desired fuel delivery today or tomorrow and then again Friday. Finally, we agree to watch Dune Part II this evening.

It was a classic planning session, and I'm glad I have most of it on videotape.

'''1015-1115''' I fiddle with email and photographs, and make a template for snaplists. A snapshot captures a moment visually; a snaplist captures it in a list: Every 15 minutes I list in a table where everyone is and what they are doing.

With my Mac on the PC network, I send my template to the hab computer and print it. (Later I search on the net, but find no Macintosh driver for this printer.)

'''1115-1215''' Individual work. The wind is picking up. David prepares lunch.

'''1215-1300''' Lunch: Spicy pepper cheese broccoli soup, tuna "fajitas", chips, cheese, and apples. Very satisfying.

A pattern emerges: Some of us are reactive, jumping up to do something different when the thought strikes us: During lunch Jan sends a note to mission support about the wind. David goes down to the freezer to take out something for dinner. I'm very reactive. Before lunch (when Jan was in the loft measuring the wind speed through the hatch), I selected the barometer on my watch, then I thought to photograph Jan and the dust blowing outside. I see Vladimir working around the plants, so I take a photo. I then notice the south portal is flopping open and dust is on the computer, so I elicit Jan's help to close it. He goes to get some screws. My stateroom window is creaking; I notice dust all over, and get duct tape to hold it closed. I take more pictures of the dust storm. Jan announces it is now 56 mph.

Yet in all this, Andrea, David, and Nancy stay in one place: Andrea is at her computer in the workstation area; Vladimir is at the hab computer downloading data from the Ecologger; Nancy is working in the lab on the lower deck; David is working in the galley.

I had noticed this same pattern when I did time lapse recordings of the Haughton-Mars work tent in 1999--some people stayed seated for an hour or more, others moved every few minutes.

Are there two different states of mind or modes of concentrating: Reactive and fixated? Are these personality differences or changing during the day or in different circumstances? How do these modes affect productivity? These are both forms of concentration: One changes easily, the other stays focused on one activity.

'''1300-1330''' Individual work. Interestingly, what people were doing at 1300 they were all still doing at 1315. Evidently, we are now all concentrating on a single activity.

'''1330-1600''' Nancy, Vladimir, and I begin a subgroup activity that continues for 2.5 hours. Nancy has prepared sample 'devices' to be used to gather soil around the hab. Vladimir will assist and I will document. Nancy has nicely (once again) laid out labeled ziplock bags with collection devices. She explains the procedure to me and Vladimir. This is a pleasant change, for no scientist ever did this with me at Haughton. Nancy likes to show and tell what she is doing in advance. It makes learning a lot easier.

The dust storm outside makes the EVA especially exciting. What a gift for a photographer! Dust bands are blowing horizontally, with long visible curving lines twisting around painted hummocks, and just a gray-white gauze in the distance. Above the sky is blue-gray, but mostly cloudy. Is the wind more important than water in shaping this landscape?

All goes well until an equipment bag is dropped. The animate wind plays a game with us. The bag is just out of reach, once, twice--just jump and you can stop it. But in that hesitation of getting ready to jump, the bag soars up into the air, far far away. So far you must laugh. It is hopeless. Regrouping, Vladimir suggests that we abort the EVA and reconfigure the equipment.

Meanwhile, back inside, a fixated crew: Andrea and Jan at their workstations, David in the galley.

Nancy and Vladimir return to the EVA with all their equipment tethered by ribbons and redistributed: What Vladimir must reach is in Nancy's pockets, and vice versa. I videotape this session. It is a stunning example of collaboration, use of tools designed for gloves, and struggling with the wind. Zubrin was right about grit and determination. But I think Mars will supply the sand.

'''1600-1653''' Mostly individual work. Nancy and Vladimir, now back from their EVA, are wandering or perhaps getting resettled. They move (independently) from the mess table to the CD player to the floor (eating a snack) to staterooms. Everyone else stays put.

'''1653-1713''' The bucket brigade: We refill the water tank in the loft. Five of us make short work of this, but after 20 minutes of lifting 2-5 gallon containers, you are glad it is over.

As we work, I am wondering how to simulate this in the "work practice" modeling tool we are developing at NASA/Ames Research Center. The trick is modeling the container being handed over. Each person must release, but only after the next person in line has gotten hold. I notice that we say things like, "Okay" or "Got it." Of course, as the person releasing the container, you can feel the change in weight. Here's another case where modeling the physical world (with gravity or not) is necessary for modeling human behavior.

'''1713-1930''' Individual work again. The wind is really picking up. Unfortunately, the hab's weather station has been off line for over a day. We are unable to restart it and have asked mission support for help (there's a phone number, but it's not much use here on Mars).

A few people take the opportunity for showers. Most are working in one place again, distributed almost evenly from the hab computer, workstation area, staterooms, and in the laboratory. Stopping what I am doing every 15 minutes to record our activities is not difficult--I find that everyone tends to work in one preferred place or to move between two places (David moves today between the galley and his stateroom; Andrea moves between the hab computer and her laptop). This individual stability helps maintain privacy, as well as predictability in sharing the space.

At this time, I send an email to my colleagues at Ames. I want them to begin thinking about designing software that will make the GPS unit fully invisible to an explorer. I don't want to wait for a satellite fix; I don't want to transcribe readings. I don't want to ever know the coordinates at all, let alone have to manually enter or compare them or number waypoints. I want a program to answer questions while I'm on EVA: "Has anyone taken samples near here before?" I also want the program to tell me things like: "Warning, you are within 10 minutes of the reserve fuel supply required for safe return to the hab." Being here at MDRS this past week has given me very clear ideas about the navigation assistance and other monitoring required during remote exploration on ATVs. Until now, back at Ames and JSC, we weren't sure what to build; we had the methods, but not the requirements. That's why I call what we are doing here "empirical requirements analysis"--finding out what you need to build by doing simulations in the field.

At 1815 the generator is refilled, and we hear the familiar ring as the power (and lights) go out. A light rain begins around 1845 and by 1930 the sun is backlighting clouds in the northwest, where it has been solid gray-white all day. The front is passing through. A new minimum for the day occurs (65F). The forecast maximum of 78 didn't come close (only 72F). But it was windy! If the sound weren't enough, including the wind vane creaking and cracking, we can sometimes feel the hab shaking slightly.

'''1945-2045''' We hear crackling of sparks in the loft and my computer cursor freezes. There is a flash of lightning. We shut down the network and close our computers. Just in time for dinner. Tonight it's pork fajitas (without the quotes). Andrea asks, how could we be so hungry again?

At dinner I ask, "Do you feel isolated here?" Nobody does. Why not? We realize isolation or remoteness has several dimensions. Are you physically alone? No, we have more company than we usually do at home. We spend more time in group activities than we do at work or home. Are we isolated from the outdoors? No, we go on EVA often enough (and for safety we do not wear suits when refueling the generator). Are we isolated from civilization? No, Hanksville (as small as a town can be), is twenty minutes by four-wheel drive, and we could walk there without much trouble. We are really isolated in only one way: We have essentially no interaction with other people (aside from our fuel and water supplier). I remind the group that were we to be transported back to Salt Lake Airport, we would dumbstruck by the crowds.

So how does the isolation we experience at MDRS compare to Mars or FMARS in the Arctic? FMARS is more like Mars in being more completely isolated from civilization. Both MDRS and FMARS are unlike Mars in our contact with the outdoors (we can feel and breath the air, even in suits). But MDRS, during my rotation at least, is isolated from other people, so it is more like Mars than FMARS (where the press visits almost daily or even lives with us, and base camp with dozens of people and daily roar of planes or helicopters is much closer than Hanksville).

At MDRS we are surrounded by many square miles of open land, our private backyard--somewhat like camping in a carefully chosen mountain valley. We feel secure and not isolated. We are caught up in our activities with each other. We are busy all the time. It seems unlikely that the first crew on Mars will ever feel lonely. Yet, what do we know? We have been here just over a week. How would we feel after a month? A year? That's why simulated missions are necessary.

2000 The wind is getting ferocious. Over 60 mph was forecast, and it's surely more than the 55 mph we recorded earlier, for now the hab vibrates more often and the wind mast is continuously banking, twisting, squeaking--like an old wooden boat grinding against its moorings.

By 2115 it is over, the wind that has dominated our thoughts all day and forced an EVA to be postponed, leaves us alone among the sand, rocks, and hummocks. Alone together.

Bill Clancey

MDRS Rotation 5 Commander

===Health & Safety Officer Reports===
Jan Osburg Reporting

'''Safety:'''

The wall-side ladder handrail had some rough spots that were covered with duct tape to prevent people catching splinters.

Recommendation: the projecting platform underneath the roof hatch should be fitted with railings to keep people from accidentally stepping over the edge.

Another recommendation: every crewmember should bring a pair of sun/wind/dust goggles (military surplus, or e.g. ski masks), in case some non-suited outdoor activity is required during a sandstorm.

'''Health:'''

No medical incidents were reported.

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' Another bucket-brigade refill of the 230 l (60 gal) inside water tank was accomplished in just under 30 minutes. This is less time than it took us using the electric water pump!

'''Power and Fuel:''' Even though the UPS is no longer being used on a regular basis due to the issues with fluctuating voltage in the hab and frequent power outages (see previous engineering report), it now serves an important function: It is kept fully charged underneath the hab computer station, ready to supply ten crucial minutes of power to the hab computer and the Starband satellite link. This now assures that we can send off a "Mission Support, we have a problem" e-mail in case the generator fails to restart or we run out of fuel.

'''EVA Equipment (including ATVs and PEV):''' Nothing to report.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' The LAN broke down today for unknown reasons. It took the better part of three hours to fix it.

'''General Maintenance & Waste Management:''' The roof covers were put under quite a bit of strain during todays sandstorm, with peak wind speeds of 90 km/h (56 mph) creating a strong lift force due to the dome-shaped roof.

For the same reason, the roof hatch was secured by tying the emergency escape rope to one of its handles.

The sandstorm also threatened to blow out the south window on the first floor, so an additional screw was put into the frame to hold it in place.

'''GreenHab:''' (see "Biology" report)

===Geology Report===
Andrea Fori Reporting

EVA cancelled due to a ferocious wind/sand storm. Spent the day working on reports and reading about local geology.

===EVA 70 Report===
'''EVA SCENERIO OVERVIEW'''

We had two objectives for our EVA on Monday, April 15, 2002. The first objective was to deploy a new windblown dust collector near t
[[File:Crew5 ValdimirPlant.jpg|thumb|Valdimir measures plant growth.]]
he Hab. The second objective was to collect samples of soils in the immediate vicinity of the Hab to assess the bacterial contamination that human activities introd
[[File:Crew5 EVAParts.jpg|thumb|Mostly materials to be taken on EVA.]]
uce in the environment. Six samples were to be collected in two radial directions at distances of 1 m, 5 m and 20 m

'''DATE: 04-15-02'''
{| class="wikitable"
!EVA Scenario
!Dust collector deployment;
Bio samples collection
!
!
!
|-
|EVA HAB COMM (S)
|Andrea Fori,
Jan Osburg
|
|
|
|-
|
|CDR
|MDRS1
|MDRS2
|MDRS3
|-
|EVA CREW
(Name/#)
|Pletser/1
|Wood/6
|
|
|-
|EVA START
TIME (MDT):

1st attempt
|14:18
|EVA STOP TIME
Scheduled/Actual:
|15:00/14:35
|
|-
|EVA START
TIME (MDT):

2nd attempt
|14:59
|EVA STOP TIME
Scheduled/Actual:
|15:00/16:00
|
|}
[[File:Crew5 ValdimirDustStorm.jpg|thumb|Valdimir takes a bearing by the MDRS in the dust storm.]]
'''EVA Highlights (EVA CDR)'''

The weather has dominated our EVA today. A severe sandstorm was blowing nearly all day with winds from the South with an average speed of 60 km/h and gusts in excess of 80 km/h. As these conditions are likely to be encountered by Martian astronauts during sandstorms on Mars, it was decided to carry on only the pedestrian EVA close to the Hab to fix a dust collector and to collect soil samples from six locations. The entire EVA activities was to be documented by photography by the Mission Commander.

In a first attempt and despite the difficulty of standing stable due to the strong wind, we succeeded in fixing the dust collector near the flag pole and in collecting one sample close to the Hab. Unfortunately, the bag with the sample vials was blown away by the strong wind. The EVA was aborted and we returned to the Hab to take new vials and to reconfigure our equipment. All equipment, bags, tools were tethered and the content of our pockets were exchanged, i.e. the content of the EVA CDR pockets was place in the pockets of the EVA MDRS1 suit and vice-versa, in order to allow an easier
[[File:Crew5 JanRoute.jpg|thumb|Jan examines a route.]]
handling in and out the other crew member suit pockets.

The second attempt was more successful as we managed to secure the dust collector apparatus and to collect the remaining five samples and to take compass bearings of the sample location with respect to the Hab.

'''PRE EVA OPERATIONS'''

The crew biologist, Nancy Wood, briefed us (V. Pletser and B. Clancey) on the two EVA goals and the methods intended to be used. Samples of 0.5 ml of surface soil were to be collected at two locations ("undisturbed" and "contaminated") at three distances from the Hab. The collection vials were small (1.5 ml) snap-cap vials color-coded and placed in ziploc bags, and soil was collected with the large end of a 5-ml pipettor tip. Both vials and tips were alcohol-sterilized before placing in bags.
[[File:Crew5 Counters.jpg|thumb|We sometimes have as much stuff on the counters as in the cabinets.]]
The weather situation was closely monitored by the Mission Commander from the Satellite channel. In view of the strong wind conditions, it was decided to cancel the second exploratory EVA that was supposed to take place later in the afternoon and to conduct only the first pedestrian EVA, because it was important to obtain the samples and the EVA team could return to the Hab quickly if the situation deteriorated. Methods of measuring distances and angular bearings were rehearsed and agreed.

After the first EVA abort, and upon return to the Hab, a new strategy was adopted where all equipment was tethered and the procedure was modified to better take into account the strong wind conditions. The second collection attempt proceeded smoothly and all samples were collected successfully. This sample collection method is very straightforward and would be routine in calm conditions.

'''AIRLOCK INGRESS/DEPRESS'''

Normal ingress and depress for both EVA attempts. Radio checks were completed for both EVA attempts. Strong wind
[[File:Crew5 OpenDoor.jpg|thumb|An open door policy.]]
gusts made opening the outer hatch door difficult.

'''HAB EVA MONITORING'''
{| class="wikitable"
!NOMINAL EVA COMM/SAFETY CHECK
(Hourly Operation)
!Comm ck
1
!Comm ck
2
!Comm ck
3
!Comm ck
4
|-
|'''TIME'''
|14:18
|14:30
|14:59
|14:50
|-
|'''EVA #'''
'''(If Simultaneous EVAs)'''
|
|
|
|
|-
|'''ATV Odometer'''
'''OUT/IN'''
|
|
|
|
|-
|'''REPORTED MAP LOCATION'''
|Hab Airlock
|Around Hab
|Hab Airlock
|Around Hab
|-
|'''REPORTED STATUS'''
|OK
|Abort EVA
|OK
|EVA Completed
|-
|'''Auxiliary Information'''
|
|
|
|
|}
'''EVA MONITORING'''
[[File:Crew5 DustStorm.jpg|thumb|A dust storm at MDRS, lasting about eight hours.]]
Communications were conducted between EVA crew members and with Capcom on channel 200 without difficulties.

'''POST EVA INGRESS AND CLEANUP'''

Normal ingress and cleanup was done after both attempts.

'''EVA CREW: COMMENTS/OBSERVATIONS/LESSONS-LEARNED'''

'''EVA CDR:''' It was a difficult EVA despite the relative simplicity of operational objectives due to the strong wind and the sand storm. It was nevertheless an excellent exercise that demonstrated:

*The feasibility of EVAs in sand storm conditions similar to what can be expect on Mars;
*The importance of carefully planning every steps and details of operations, particularly in these difficult weather conditions;
*The importance of properly prepare and secure all equipment.[[File:Crew5 Multipurpose.jpg|thumb|The crew uses different spaces for multiple purposes (Nancy, Vladimir, Andrea, and Jan).]]

Despite the adverse conditions, all the goals of the EVA were achieved and all samples were collected and brought back to the Hab lab.

Two bearings were taken for the locations of the sample collection:

#197 deg, from geographical North (210 deg. from magnetic North);
#111 deg, from geographical North (124 deg. from magnetic North).

Distances were measured with rolling tape measure. One of them eventually got blocked, most likely because of the sand.

In such conditions, both EVA crew members felt the intensity of the sand storm and dust and sand were found inside the EVA suit and the helmet.

'''EVA MDRS1:''' It would have been easier if it was not that windy!

==April 16, 2002==
===Commander's Logbook===
Today was a thin day. Like a single-reed instrument playing one note. Three of us were preoccupied by chores. I am DGO, Director of Galley Operations. By 1800 I had spent nearly four hours in the galley, cleaning and cooking. It'll be another hour of dinner preparation and then cleanup. So the better half of the day is devoted to chores, not my real work. For David and Nancy, it was somewhat similar--the oil funnel blew away last night, requiring some jury-rigging. Then they noticed all the detached guy wires flailing around the greenhouse. Then they had to move the fuel into all the smaller containers, so our supplier could take away the barrel. And then they had to refuel the ATVs. Altogether about two hours. Between the three of us, one crew member day was devoted to chores. Not bad, but we have other things to do.

'''0540''' I'm awakened by the back hab hatch tapping. I find the ropes holding it inside aren't tight. Pulling the hatch closed, I try to remember how to tie a proper hitch. Hours later I will awaken with the visualization clear in my mind.

'''0730''' A different day--the sky is clear blue again, the land bright orange sandy desert. And coffee is brewing. I have a shower and record the temperatures:

Maximum outside 22.2 C (72 F); Maximum inside 25.3 C (77.5 F)

Minimum outside .1 C (32.2 F); Minimum inside 16.6 C (61.9 F)

Our fancy weather station is still inoperable, probably fried by the lightning the other night. The news from the manufacturer is to send it in for repair--a long trip from Mars. I wonder what the manufacturers will say then?

Eating breakfast, I spread myself around almost the whole table. I realize for the first time that I had been feeling cramped at lunch and dinner. I deliberately place my juice, toast, coffee, magazine, camera, and notebook as if I own the table myself.

'''0915-0945''' One crew member is still asleep, but the planning meeting proceeds--in record time. The EVA will carry over from yesterday (postponed by the dust storm). I go around, reading what each person said they would do yesterday, asking whether it was completed, and what is planned for today--MBO, Management By Objectives, on a daily basis. We are almost done, when the sleepy sixth crew member arrives. His plans are noted, and we finish with a short discussion of what we learned in the Arctic station that we're applying here. First I acknowledge the parts I've borrowed: The general shape of the day, the reporting, equal sharing of cooking and cleaning up, and movies. I then rattle off a list of what I've done differently:

*No press or other visitors (this is a simulation, not an exhibit)
*Explicit list and assignment of chores, so nothing is done by default
*Written daily and weekly plan
*Discussion before the rotation about my intentions as commander and solicitation of individual interests and expectations
*Distributed submission of reports to Capcom at Mission Support (monitored through the written plan)
*At least one major science summary report per discipline per week, rather than a daily report. The daily CDR Logbook, Engineering, EVA, and Health/Safety reports tell the minutia of the day.
*All mission support goes through Capcom, but once a conversation is established (e.g., with Gary Fisher regarding Greenhab), we only copy Capcom.

My personal style as leader is to manage traffic, not to be the bottleneck. When told of a plan to bring the generator down for a second time in the morning (which I thought was unnecessary), I didn't express my opinion, but rather brought the issue to the Engineering Officer to handle. My job is not to decide or control everything, but to act as the switch, the delegator, the interpreter of roles and responsibilities. So the work is distributed as much as possible, and I am freed to worry about the big picture and new concepts, such as designing our emergency EVA the other day--and today, cooking.

'''0945 -1230''' Individual work. We are all busy writing, transferring files, and forwarding reports to mission support. As DGO, I lead the group into a new world of traditional white bread. I start making a loaf about 1130. Bread won't be delivered on Mars, we'll make our own using these nifty bread machines. This one has a glass window and we all enjoy peeking at its progress as it whirs and stirs and beeps for the next three hours.

Nancy is just nearby, and says she's never had an office with bread machine. And that's the point: In MDRS WE live and work in one place. The distinction between "work life" and "home life" doesn't make sense. Of course, this is not new, it's true on sailing ships and submarines, too, as well as research stations in the Antarctic or other scientific expeditions.

1230-1315 I announce "Commander's lunch special." Which means that because lunch materials are getting sparser, all I can dream up is a collection based on the color orange: Cheese, oranges, salmon, Chicken Ramen (packages are orange), and of course Tang. I move all the other stuff, with different colors, to the other end of the table. It is conceptual art, and edible.

As lunch finishes, I pronounce in a flourish that everyone should just leave their plates and glasses on the table--a pregnant pause as all respectfully acknowledge the DGO's task--but then I add, "Because you're going to use everything again at dinner!" As if I could get away with not cleaning up.

1315-1900 The entire afternoon is devoted to an EVA for Andrea, Vladimir, and Jan (see the report for EVA 71). This gives Nancy, David, and me a new experience, first, a new combination of people left alone in the hab, and second, the space available to us has just doubled. When the bread maker beeps I joke that we should eat the loaf ourselves and start another.

During this time, David has been revising the hab's computer manual and written instructions on handling the radio station adjacent to "hab com." Nancy was writing reports and following up on her microbiology testing. I cataloged the photos for the past three days, selecting some for our web site, and others that Andrea might include in her geology primer (at least I'd like to know what I photographed).

For dinner I've prepared meatballs and sauce, combining a can of tomatoes, two bottles of prepared sauce (leaving behind the R*** for another rotation), with spices, onions, celery, and carrots. I start the water for the pasta an hour early so it will be hot when I need it.

About 1800 Larry Ekker arrived with a pile of Federal Express packages, including David's lost red bag. Finally he has his camera. He shows me a charger that he believes will work with Vladimir's camera, which has been operative since last week. I immediately recognize it: The very same charger used by my mini-DV camera, and point to it on the shelf. With a shared fatalistic humor, we realize this charger will work.

Moving around the hab today, I realize how familiar our life here has become. I am reminded of that moment April 8th when I asked Andrew Hoppin how it felt to be leaving, and he said how much they wanted to stay. I wondered when I would feel that way. It happened today. We are leaving. The time is drawing to a close. Soon it will be over.

1935 I hear Andrea on the radio, "Vladimir, where are you going?" And then, "Back to the hab." I smile just to hear their voices. David laughs, "Did I say dinner at 815?" Moments later, we're at the east portal, watching them drive up. Three people in space suits driving ATVs. A familiar sight.

Bill Clancey

MDRS Rotation 5 Commander

===Crew 5 Profile===
By David Real/Belo Interactive

'''Aboard The Mars Desert Research Station, Utah''' - If anyone looks like he has the right stuff for space, Dr. Vladimir Pletser does.

Powerful body, military-style crewcut, easy grin, team player. And then he's got that inner something -a certain confidence and poise brought by years of experience.

Others must have seen it, too.

Which is one of the reasons he is an astronaut candidate for Belgium's space program and, since 1985, a staff member of the European Space Agency. He is also one of the crew members spending two weeks at the Mars Desert Research Station, a project sponsored by the Mars Society, which promotes exploration of the Red Planet.

Would he go live on Mars if the trip were offered?

"I'll be signing immediately, signing with both hands, both feet,<nowiki>''</nowiki> said Dr. Pletser, 46. "Yes, I'll be gone, sure. Even if we do not return. A one-way ticket would be fine for me.<nowiki>''</nowiki>

Although Dr. Pletser has not yet been to space, his experiments have - he has degrees in mechanical engineering and physics, with a doctorate in astrophysics.

One of his experiments flew on a Space Shuttle mission in 1998 with John Glenn Jr., the first American astronaut to orbit the Earth.

Another experiment is set for the International Space Station in a few years.
{| class="wikitable"
|Dr. Pletser floats upside down in an Airbus cabin during the weightless portion of a parabolic flight in October 2001. Dr. Pletser is a member of the crew at the Mars Desert Research Station near Hanksville, Utah. Photo Credit: European Space Agency
|}
To reach outer space himself, however, Dr. Pletser is taking a different approach - he is getting there 20 seconds at a time.

As manager of the European Space Agency's aircraft parabolic flight program, he flies on specially equipped airplanes that duplicate zero gravity when they go into free fall during a roller-coaster type of maneuver.

The pilot puts the aircraft into a steep climb, creating twice the force of gravity on its occupants, and then cuts the engine. As the aircraft falls to Earth, a weightless condition is created for about 20 seconds, which is used for astronaut training and scientific experiments in microgravity. Then the pilot pulls the aircraft out of its steep, 45-degree dive, again making passengers feel as if they weighed twice as much as they really do.

Dr. Pletser has done this 3,250 times, accumulating more than 18 hours of weightless experience.

Newcomers are advised to take it easy on their first flight because of the severe stress on the body. Dr. Pletser advises them to lie on their backs while experiencing twice Earth's gravity for the first time. If all goes well, they can try sitting up the next time.

During the weightless condition, first-timers tend to react instinctively - which is the wrong thing to do.

"With zero G, you notice the newcomer because they start to swim," Dr. Pletser said. "The reaction is that you want to propel yourself, and your reflexes react like in water.

"Of course, it's totally different because of kinetics and the viscosity of air. So you can flap your arms and kick your legs - it would not help at all, except maybe to hit someone."

Nausea is also common for about half of those who experience zero gravity because of motion sickness, Dr. Pletser said. Fortunately, he is immune.

But no one escapes the physical demands of the maneuvers, which put a severe strain on the heart, muscles and skeleton. During a standard 2 ½ hour flight, there are 30 parabolas producing a total of 10 minutes of weightlessness. Usually there are three such flights during a one-week campaign, normally Tuesday through Thursday.

"After a certain number of parabolas, you're exhausted," Dr. Pletser said. "You want to crash out in the afternoon or evening. On Thursday, you're totally liquefied."

The flights are necessary, however, to train astronauts and test equipment before being sent into space, even for a short period.

"There's no need to go to space for some experiments,<nowiki>''</nowiki> Dr. Pletser said. "If you're well-prepared and your experiment is well-designed and well-conceived, 20 seconds is all the time in the world that you need."

He has flown these missions with the National Aeronautics and Space Administration, the Russian space program and the 15-nation European Space Agency.

His current experiment, which would fly into space in 2004 or 2005, is what he calls a Protein Crystallization Diagnostic Facility. The experiment exploits the fact that, during weightless conditions, it is possible to build protein molecules with very large crystalline structures that is not possible otherwise. That makes it easier to analyze them on Earth with an X-ray diffraction machine, and determine the three-dimensional structure of the molecule. Then it's possible to predict how they would interact with other molecules.

"Basically, this is the idea of developing new medication, new molecules for pharmaceutical purposes, to fight infections and viruses," Dr. Pletser said. "It's basic research that we do as a first step toward applied research later on, that will benefit mankind on Earth."

Although NASA may dominate space headlines in the United States, the Russians have held the world record for the number of satellites in space since Sputnik was launched in 1957, he said.

And the European Space Agency has played a vital role, too, helping build part of the Hubble space telescope. In 1983, one of agency's astronauts, Ulf Merbold of Germany, was the first non-American to fly on a Space Shuttle mission. Another astronaut, Jean-Pierre Haignere of France, spent more than six months on the Russian space station MIR, the longest flight ever performed by a non-Russian astronaut.

And the agency's Automated Transfer Vehicle, boosted into space by the Ariane 5 heavy-lift launcher, is expected to help keep the football-field-sized International Space Station from falling from orbit during its lifetime. All of these missions by the European Space Agency would launch from the Guiana Space Center in Kourou, French Guiana.

So far, Dr. Pletser has been nominated but not yet accepted as an astronaut. Still, he remains optimistic.

"For the moment, I am still waiting, expecting to one day fly to the Space Station,<nowiki>'' he said. "I still have hope. When I see, for example, people like John Glenn flew at 77, there'</nowiki>s no age limit.

"Shuttle commanders typically are in their late 50s, between 50 and 60. So you have a lot of experience, but still you<nowiki>'re fit and you pass the medical.''</nowiki>

For the Mars Society, Dr. Pletser has conducted experiments at Devon Island in the Arctic to determine whether it would be possible to detect underground water on Mars using seismic shock waves, much like oil exploration on Earth.

His current mission at the Mars Desert Research Station will help determine if it is feasible to grow food in a greenhouse on Mars.

And then someday, for Dr. Pletser, it's on to Mars.

===Geology Report===
Traveled to the north edge of the USGS Skyline quad (to Muddy Creek) and previously visited waypoints 15, 32, 33, 34, 35, and 36 (see EVA #71 report). The region is characterized by fine mudstone layers intermixed with volcanic ash. As one progresses north and up in elevation up "Lowell highway" (the main dirt road that passes the hab) the red layers near the hab give way to lighter colored ash. On the dirt road to waypoint 33 the ash is a distinct dirty gray. We then passed through a narrow and scenic canyon of characteristically red Morrison formation to the Muddy Creek. The area immediately surrounding the creek is a sticky clay (of course we became stuck in the clay).

Continued to work on assessment of previous activity and geology primer.

===EVA 71 Report===
'''EVA Scenario Overview'''

The main objectives were:

*to find the best way from the Hab to Muddy Creek;
*to take muddy soil samples near and under the river;
*to retrieve other bio sample collectors at various locations;
*to document by photography some interesting geological features.

'''DATE: 04-16-02'''

'''Personnel:'''

'''Commander:''' Vladimir Pletser (EVA-6)

Andrea Fori (EVA-1)

Jan Osburg (EVA-2)

HabCom: David Real

'''Airlock timeline:'''

'''Departure ingress:''' 14:47

'''Departure egress:''' 14:52

'''Return ingress:''' 19:40

'''Return egress:''' 19:45

'''New waypoints:'''

'''Format: WP#, WP name, datum used, Easting, Northing, Altitude [m], Date, Time:'''

120, Andrea's Quarry, NAD27, 518931, 4256548, 1369, 16.04.2002, 16:05h

121, Robbi's Bed, NAD27, 519265, 4256818, 1391, 16.04.2002, 16:18h

114-2, Ravine Y, NAD27, 517412, 4256334, 1407, 16.04.2002, 17:32h

122, The Pillar, NAD27, 518173, 4257061, 1365, 16.04.2002, 17:46h

123, River Crossing, NAD27, 518380, 4257530, 1343, 16.04.2002, 17:50h

124, Rope Rescue, NAD27, 518293, 4257917, 1343, 16.04.2002, 18:44h

'''Route:'''

(by waypoints, in this sequence, including new waypoints) 1, 115, 116, 117, 120, 121, 117, 15, 117, 116, 115, 32, 33, 34, 114, 122, 123, 122, 114, 34, 33, 32, 115, 1

'''Communication checks:'''

Check time: 14:52

EVA team location: Hab airlock

Status: OK

Additional notes:

Check time: 15:00

EVA team location: in front of Hab

Status: Deploy flag; retrieve dust catcher

Additional notes:

Check time: 19:35

EVA team location: on way back

Status: report on return and proceeding to collect last dust catchers

Additional notes:

Check time: 19:40

EVA team location: Hab airlock

Status: OK

Additional notes:

'''Special circumstances:'''

'''Two situations were ATVs got stuck:'''

#one ATV while crossing the river for the second time. Was towed out by another ATV
#the three ATVs got stuck in turn at 'Y ravine junction' in canyon road. Needed three crew members to pull/push it out of sand (2 crew members to push, one to activate the accelerator handle and pull).

'''Conclusions/lessons learned:'''

The main objectives were:

*to find the best way from the Hab to Muddy Creek;
*to take muddy soil samples near and under the river;
*to retrieve other bio sample collectors at various locations;
*to document by photography some interesting geological features.

The EVA crew managed to get to the river after hours of exploring possible routes, and even crossed it successfully. The way back was challenging, with ATVs getting stuck in the muddy riverbed and in the loose sand of the approach trail. But the EVA crew made it back, and had a great time!

'''EVA CDR:''' The EVA crew left the Hab at 15:00 and after retrieving the first dust collector near the Hab and re-erecting the Martian flag, left on ATVs in a Northerly direction on the Lowell Highway. Several points en route were measured again using our very handy GPS, but we still managed to have somehow different readings. Our geologist Andrea took several photos of interesting features, mainly rocks and various geological layers. We passed 'Dimitri's corner' and the 'Brussels sprout' marks, to go further to the 'Route 66' mark. From there we turned to a westerly direction to try a new route to the river. The main dirt road quickly ended in several paths among the rocks that we explored one by one, and taking GPS coordinates each time we could not go any further because of a dead end or a cliff. We decided to backtrack to 'Brussels sprout' to try a different road from there, but to no avail. We backtracked again and went back to 'Dimitri's corner' to take the other dirt road leading to the geodetic point further up west. From the geodetic point, we turned North and followed the main canyon, first following a path on top of the canyon, then gradually coming down by different ways and eventually arriving in the canyon itself. We followed the canyon road and passed the point where we could not proceed any further previously. We called that point the Y Ravine junction, as two ravines come together making it nearly impossible to pass.

We managed to find a way to pass eventually to continue among further dramatic landscape. We found the access to the river at the end of that canyon and we ended up on a sort of beach. Two mud samples were collected and we decided to cross the river and to explore its other side. We drove upstream to soon arrive in front of rock formations that we could not climb with the ATVs. We had to cross again the river. Leading this expedition, I tried to pass first and, although the first few meters went fine, I soon realize that my ATV rear wheels got sucked in the mud and started to sink deeper and deeper. I could no longer go forward or backward and the engine stopped. We quickly devised a rescue plan by radio with Jan and Andrea for them to go back where we crossed initially, to cross back and to meet on the other side. Luckily, we took a long rope that Jan had on his ATV. Attaching the rope to our both ATVs allowed Jan to tow me out that mud trap. Once safely on a sort of little island in the middle of the river, I could restart the engine and finish the crossing. This rescue having eaten most of our remaining time, we decided to drive back to the Hab by the shortest way. On the way back, the three of us got stuck in turn at the Y ravine junction. It took the three of us to pull and push together each ATV out of the soft sand ravine. We made it eventually back to the Hab, after having retrieved on our way two other dust collectors. A great ride! A five hours expedition in the desert and in these beautiful Martian like landscapes! Some lessons learned with relevance to Mars exploration, e.g. a stranded crew that manage itself to rescue one of his members.

'''EVA MDRS1:''' I felt this was a great team building exercise. This MDRS rotation provided my first experience on an ATV and on this EVA, I really was able to push the limits and explore the area much farther than I would be able to do on foot. Being able to explore such a wide area provided a comprehensive understanding of the local geology. I took many photos, most of which I will use to build a geology primer of the area.

I also had the opportunity to test falling over in an EVA suit. I jumped across a ravine to assist in pushing Jan's ATV up a hill and misjudged the balance required to land with the 30 lb suit on. After clearing the ravine I toppled over onto the ground face first. My crash landing was lacking so much grace that I started laughing. The suit was so heavy that it prevented me from being able to right myself - feeling like a turtle stuck on its back made the situation even funnier. I was able to move only one arm (my other arm was stuck underneath my body) and one leg that I was trying desperately to use as a lever. Of course my radio was also wedged underneath my body so I couldn't communicate the status of my situation. Vladimir stabilized the ATV on the side of the hill and Jan ran over to me to provide assistance. The good news is that although they're awkward the suits provide much protection.

'''EVA MDRS2:''' Interesting, long (5 hours) exploratory EVA. We made good use of the GPS and the map. The river crossing at WP 123 (and WP 124) was a challenge, successfully mastered thanks to good preparation (we had a rope with us!) and ATV maneuvering (and lifting) skills by all EVA crew. A great team experience.

==April 17, 2002==
===Commander's Logbook===
Last night we watched the third and final part of Dune, the TV movie version from 2000. It kept our attention until almost midnight. The story of a desert planet felt appropriate. Like the Arakis people, we treat water with respect. (Spend 20 minutes hauling 500 lbs of it up 20 feet and you'll conserve, too.)

'''0710''' I awaken with surety, easy with the routine. As some cognitive theory predicts, procedural steps move forward, so today I even open my laptop in my stateroom and call up the weather before breakfast. I treat the water and vitamin, ready at hand, as the first installment.

The temperatures for the past 24 hours are:

Maximum outside 19.1 C (66.4 F); Maximum inside 21.5 C (70.7 F)

Minimum outside 11.1 C (52 F); Minimum inside 17.2 C (63 F)

The weather is good, but cool. Another day for long sleeves and perhaps a sweater in the hab; we choose not to turn on the heat. The forecast is humorous to review:

Forecast for today: Partly Cloudy & Wind 68/31 (previously forecast yesterday to be) 71/38 (previously) Scattered Showers 70 (previously) Cloudy 81/31 (previously) 74/34 (previously) Partly Cloudy 71/33 (previously) Showers 74 (previously) Partly Cloudy 76.

Out of eight forecasts for today, four were "partly cloudy," two were cloudy, and three predicted rain. The temperature forecast for today ranged from 68 high to 81 high. The forecast shifted between dry and rain four times. The actual weather: Partly cloudy & wind, 70F. Conclusion: For this area at this time of year, ignore forecasts beyond tomorrow.

'''0915-1000''' The planning meeting goes quickly again. We are ready to get on with the day. We start filling in items to complete before our rotation completes. There are only three days of work, Saturday being reserved for the press.

Here's our plan for the day:

* EVA: Andrea, Bill, and Nancy to Lith Canyon1400 egress, 1700 return
* Andrea: Geology Primer; Review EVA 71 report.
* Bill: Fuel and water chores; Fill in EVA spreadsheet on A's door; Give geology photos to A
* David: Another 30 min interview with J; Interview B from 6-dinner? Story on DGO coming.
* Jan: Director of Galley Operations (DGO); check out biolet again, too full; model water usage.
* Nancy: Fuel and water cores; Lab work on soil cultures + columns from mud samples + plate dust catcher from flag area.
* Vladimir: Greenhouse repair w/ J; Start 2nd science summary; Write procedure for single-person EVA suit-up; completing EVA 70 & 71 reports.
* Maintenance plan: Refill H2O tank 1800; New H2O pump coming; Look for scorpions in staterooms; Larry coming with fuel tonight (will pump into barrel).
* Group activities: Dinner 1900; View planet line up by 2000; 2100 Lectures by B and J?

----'''1015-1040''' Nancy and I are the generator team today. We fill the jugs, emptying the barrel and refill the ATVs.

'''1040-1215''' I process my email and write field notes. As I check around, I realize I know where everyone is and what they are doing. The previous two days I checked every 15 minutes and kept records. The patterns were obvious. And thanks to the daily plan, if I don't see someone, I can guess where they are. It took more than a week to grasp these patterns, but after 10 days, I am secure knowing what everyone is doing.

I am drawing many conclusions today. I write my ideas in a field notes file: about videotaping (2 hours a day is enough, but it's wise to bring two 90 minute tapes/day), a survey to give the crew, and use of space (the lower deck is only used for EVA prep, as a lab by one person, and for the toilet/shower).

My "snaplists" showed that each person spends time in only two or possibly three places. It's like having a favorite chair at home. So why do three of us use the staterooms during the day, but the other three do not? Lighting? Access to internet? I create a table and quickly realize that no two staterooms are the same. Shelves are the most obvious difference. But one person uses shelves for clothing, the other uses the same space for a desk (he has an internet connection). Should every stateroom have a portal? I think mine makes the space into a real bedroom-office. The person on the other side of the hab (same space, mirror reversed) wishes he had a window. But two crew members with inside staterooms disagree; one wants it, the other does not. Based on my experience at FMARS, I believe you can't know what a portal is like until you have one.

'''1215-1300''' Lunch by Jan. I am eating too much here, but indulge again--a good idea given the EVA planned for the afternoon.

'''1315-1745''' A, B, and N go on an ATV EVA (ETD 1400). We bring the GPS. As I write, I'm exhausted from our trip, which was fully satisfying. The weather was very windy (sustained at 15 mph, gusting to 25 mph), but mostly sunny. Our objective was to find the fossils in Lith Canyon that I had seen in March during the scouting trip. Using the GPS and map, we proceed on foot from a likely location. There's a canyon out there all right, but not the one I remember. I know we had walked in more from the west, so I suggest we circle around.

But first I have the idea of following the established 4-wheel drive road further to the east to confirm its location for Vladimir. After awhile, I recognize an area where we saw the cattle ranchers last week. It is a smooth, broad wash, bending northwest. I suggest we take it, just because it is so inviting. At the head of this wash, I see bare branches poking over a ridge, reminding me of a tank (artificial pond) I saw in March. And the high layered cliff to the north looks familiar. Let's walk. We find interesting rocks and an apparent salt pan, and then I see the drop off and high gray ridge of small stones. This is it! I exclaim. We've found the place I visited in March.

After showing Andrea and Nancy the fossils, I lead them carefully into the canyon (more like a ravine). Photo ops galore! I show them what Margorie Chan pointed out on my last visit, explaining the local geology to our geologist, and hoping for details. Details arrive in unexpected ways. As we are standing by a clay-like gray-green variegated hill, Andrea says, "There's much more volcanic ash here than I expected." "Oh," I say, "This is volcanic ash?" Now, to realize how funny this is, you must know that we drove past by square miles of this gray-green stuff, and this is the first time its identity has been confirmed. It's like being on a golf course and saying, "Oh, this is grass?"

Nancy says she is thrilled to be in the canyon, she has seen nothing like it. And her pleasure makes the outing more enjoyable for me, too.

We followed the ravine for awhile, until it broadened and the truck tracks became more obvious down the middle. I want to know how someone drove in here, but it's getting late and windier, with gusts causing us to lose balance, so we walk cross-country on an obvious trail back to our ATVs.

The drive back is longer than I expected. The wind is now gusting over 40 mph. The sand hits our helmets like pellets. Even if Mars had a breathable atmosphere, explorers would be glad to have a protective helmet like ours. Along the road, the color and elevation change is much more obvious than before. It's a long way, several miles. I try to push the speed, but Nancy drives more considerately. Probably wise, given our outfits and the wind. We notice that when we stop our ATVs blow backward rather fast, even when in gear.

'''1745-2015''' The remainder of the crew greets us as we greeted them yesterday. They are happy to hear our stories and happy that we had a good time.

I am most struck by our luck. I had only found the desired ravine by poking around. The previously recorded GPS wasn't near a turnoff; it marked a destination, not a route. And besides, in March we hiked, now we are on ATVs coming from a road (walking in from the opposite direction). It is another lesson in navigation. Really, has cognitive science studied it at all? I know only of a study of taxicab drivers in different cities, relating maps to routes and drawings of visualized relationships. Navigating in the desert (or Mars) is much more complex--many land forms look the same (another hummock, outcropping, ridge, ravine, etc.). Our memory is strongly episodic, which means what you recall is sequentially ordered and bound to perceptual experience. The angle you approached a place, even how fast you were moving, will influence your later recognition and ability to return. What are the individual differences? Can we train people to navigate better?

Before dinner the crew refills the water tank again via bucket brigade. Then Nancy and I refill the generator. Today Vladimir, Jan, and David were busy fixing the greenhouse and refilling its water system. So chores are taking a lot of our time. For me, it's just over an hour today, less than the four hours yesterday. It's another failure for "task analysis"--the crew had previously determined that it takes five people to refill the water tank, but we quickly decide it's better to involve all of us. Better for what? Why do all the analyses of work talk about efficiency and optimization? Optimal for what?

When I returned from the EVA, I found a new manual from Vladimir on my desk, a careful write-up for an alternative way of donning an EVA suit--alone! I am struck by his initiative and effort. When time is fully scheduled or dominated by group activities, there is no time for creativity. I am glad to see that people have been inspired here and had time to act on their ideas. Yesterday David wrote a cheat sheet for changing the mode of the radiostation. Last week Jan reordered all the medications and wrote up emergency procedures, which he posted on the walls. (Two more Jan's and the hab will be wallpapered.) Work is much more than assigned tasks (writing daily reports, chores, and EVAs). There must be space for personal interests and inventing alternatives or whimsical improvements. These acts make the hab alive.

'''2015''' Jan calls us for dinner, my leftover linguine and meatballs (Andrea called it "Valles Marinaras"), followed by a three-cheese sauce on boiled potatoes and canned mackerel. As another sign we're reaching the end of the rotation, someone asks when we should leave on Sunday. The sojourn of Rotation 5 is ebbing.

Bill Clancey

MDRS Rotation 5 Commander

===GreenHab Report===
We have inspected the greenhouse with Jan this morning after the strong winds we had these last two days (actually, it still blows strongly now).

# The structure seems still OK. We tighten the cargo straps around the cylindrical surface and we re-tighten the 6 ropes holding everything. We put duct tape on the hooks holding the cargo straps to avoid them coming loose.
# There are damages to the material that makes the cylindrical wall of the greenhouse. We could see three places where the wind torn apart that material (on top and on both sides). It seems useless to repair that with duct or transparent tape: first, difficult to access with wind still blowing, second the wind will rip it apart again immediately. So we left as is. For the next technical crew to repair or fix it more permanently.
# The 'door' with zipper that was placed Sunday 7 April by Frank and his guys as repair was blown away. First the tapes holding the blue sheet were blown away, then at lunch time today, the zipper completely disappeared; that is the zipper was fixed/glued originally on the blue sheets. Well, the wind blew that away and ripped apart the blue sheet (see photo). So we taped it back as much as we could, but this definitely need a more permanent fix/repair. For the next crew.
# I have added this morning two more buckets of water to the blue tank where the pump is still active. The feeding hoses that arrive to the distribution racks came loose several times from their attachments and were put in place but again be blown away by the wind. This afternoon, we topped the blue tank up until half height.

I have attached some photos, (below), for you to better visualize the problems that we have. The most damaging cause are the strong gusts of winds that pull everything away. In general, I think that the design of this greenhouse was not conceived to support winds like we have here, and should be reassessed for utilization on Mars.

For example, if a cylindrical shape has to be kept (for pressurization), why not put one of the circular side on the ground and keep a vertical cylinder architecture. You end up with a greenhouse where you can put more racks, a lesser height and less surface to the wind. Let us know if there is anything else that we should do.

Please forward this to Frank Schubert.

===Health & Safety Officer Reports===
'''Safety:'''

This morning, a crewmember reported having seen a small scorpion in her stateroom, racing across the sleeping bag. Crewmembers were advised to check inside their boots before putting them on, and to make sure there are no unwelcome guests inside their sleeping beds before using them at night.

The scorpion was apprehended after dinner and met its fate at the hands of our valiant biologist. A comparison with pictures published in various treatises available on the Web resulted in a positive identification:

"Centruroides exilicaude", a most venomous variety found in places such as Mexico and, alas, southern Utah. Its potent neurotoxin causes respiratory failure, amongst other things. One down, TBD to go...

An overview of specific first aid measures for scorpion stings was downloaded from the web and posted on the first floor.

During the afternoon, another crewmember found a spider inside a T-Shirt. There is more life on Mars than we would like.

This issue of critters is compounded by lack of shelves in the staterooms: crewmembers are forced to store their belongings and clothing in a big heap on the ground, which makes searching for "intruders" much more difficult.

'''Health:'''

One fingertip band aid and Neosporin was issued to a crewmember with a minor cut on the thumb.

===Engineering Report===
''Jan Osburg''

'''Water Systems:''' The water tank was refilled for the third time by bucket brigade. This time it took us thirty minutes, as the water level in the tank is getting lower and thus the pressure differential is decreasing.

'''Power and Fuel:''' Larry refilled the gasoline barrels.

'''EVA Equipment (including ATVs and PEV):''' During yesterday's EVA, we found out that the ATVs do have a parking brake: the little black lever in front of the left brake lever can be used to set the brake; release is by pulling the main lever back and letting it go again.

We also found out that some previous crew had left sleeve holsters for our EVA radios, thus making the duct taping of radios to the suit sleeves unnecessary.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' Nothing to report.

'''General Maintenance & Waste Management:''' Nothing to report, except that tomorrow will be Biolet servicing day.

'''GreenHab:''' (see "'''GreenHab Report'''")

===Geology Report===
Traveled to Lithe Canyon with Nancy and Bill (see '''EVA #72 report'''). We encountered petrified wood, fossilized dinosaur bones and what appeared to be fossilized roots of large ancient trees. We walked along the floor of Lithe Canyon assessing canyon walls and poking around for fossils. There were clear examples of sandstone deposited in a shallow, calm environment and more course sediments deposited in a deeper or more violent environment. Crossbedding examples were readily found. An ash deposit we came across contained fist sized igneous sphericals.

===EVA 72 Report===
'''EVA SCENERIO OVERVIEW'''

The objective of the EVA on Wednesday, April 17, 2002 was to find the ravine known as Lith Canyon, previously shown to Bill Clancey on March 10 during the MDRS Science Group scouting weekend. Although a waypoint was known, it was in latitude-longitude coordinates and the route was a several hour crosscountry hike; today we were in suits on ATVs. A secondary objective was to reconcile the 4-wheel drive road on the Skyline Ridge map with our plotted waypoints.

'''DATE: 04-17-02'''

'''EVA Highlights (EVA CDR)'''

After searching with one failed attempt, we stumbled on the ravine. See the Commander's Logbook for April 17, 2002. Wind gusted to 40mph from the south on return walk to ATVs, developing to dust storm conditions during the drive back to the hab.

'''PRE EVA OPERATIONS'''

Nothing significant.

'''AIRLOCK INGRESS/DEPRESS'''

Nominal. Strong wind gusts made controlling the outer hatch door difficult.

'''HAB EVA MONITORING'''

Nominal.

'''EVA MONITORING'''

Nominal.

'''POST EVA INGRESS AND CLEANUP'''

Nominal.

'''EVA CREW: COMMENTS/OBSERVATIONS/LESSONS-LEARNED'''

'''EVA CDR:''' See '''Commander's Logbook'''. The 4-wheel drive road shown on the map does not reconcile with our GPS readings. Apparently the road is more to the west.

We had equipment difficulties in saving waypoints (this must be automated) and in operating the digital camera in the dust. The hab's Kodak camera malfunction half-way through the EVA and had to be repaired.

'''EVA MDRS1:''' "It was a great day for geology: dinosaur bones and fossilized roots. On the way back, I was in first gear trying to go forward on the ATV, but the wind was blowing me backwards!"

'''EVA MDRS2:''' ''(Asked for some "pithy comments," Nancy replied:)'' "Driving back in the wind and glare I found soaring glorious. So many points of wonder in that canyon. It was a shame we couldn't linger. There were fossils and water-filled potholes, so many layers of different chemistry, patterns of wind and water formation. There were unique mineral deposits-cobalt blue and violet, that I haven't seen anywhere. And it was so beautiful that the physical discomfort of an ill-fitting suit, heavy backpack (I was hot and sweaty by then), and trying to stand up against a 40 mph wind, didn't matter. I was worthwhile to have done that. I had felt guilty going out because I had so much to do, but I am so glad I went, I had a wonderful time, a memorable time."

==April 18, 2002==
===Commander's Logbook===
Last night I was exhausted from the EVA, a combination of being outdoors in the dry sun and heavy winds and hiking up and down the ravine (the fan needs a high-speed for pumping in more air on the uphills). But before sleep, Nancy and I had to refill the generator one last time. It was very cold, about 45 F. The weather is not too hard to figure out here, at least as it occurs. There are huge winds from the south, with dust. This goes on for six or more hours, then the cold front comes in from the northwest with ominous clouds. Of course, it doesn't rain much here. The temperature then drops, and the next day is crystal clear. That's happened twice in the past week.

'''0723''' I'm awake, feeling somewhat rested, but ready for a vacation. Nancy and I refill the generator before breakfast. I don't think the Mars crew could keep up our pace for long. Every day is work, our life is work, life support is work. We never really have time to just relax, unless you count watching a film while you are just able to keep your eyes open.

Here are the temperatures for the past 24 hours:

Maximum outside 21.6 C (70.9 F); Maximum inside 22.1 C (71.8 F)

Minimum outside 5.7 C (42.3 F); Minimum inside 15.7 C (60.3 F)

Temperatures have been trending downwards. Unlike the past two crews, we haven't had problems with overheating in our suits. They feel great with just light pants and a long-sleeve t-shirt (and wool cap).

For breakfast we have Jan's Honey Grain Wheat bread, timer-baked to fill the upper deck with aromas at 0730. It has expanded to fill the entire cavity of the machine. Why? Perhaps too much water or yeast. But it is warm and tastes great.

'''0915-1023''' Our morning planning meeting goes well. We are really filling in all the squares now. There are lists of things for everyone to do today and tomorrow. We review the Saturday Open House plan, trying to schedule the nine crews (TV and press) so they have exclusive time with me and someone else, and then are shepherded through the rest of the day. Vladimir will illustrate how to don the suit without help, which I call "the reverse Houdini."

The day hereafter falls into chunks--broad activities:

* '''Morning Individual Work (1030-1230)''' -- reports, photos, lab work, email, greenhouse, etc.
* '''Lunch (1230-1315)''' -- Nancy prepares soup, cheese, crackers, and pears with raisin sauce. Our conversations continue for quite a pace, suggesting to me that we really need some time to unwind.
* '''Afternoon Lab Tour (1315-1400)''' -- at my request, Andrea and Nancy give us a videotaped tour of the lab facilities and stored samples. My impression is that the geology area needs work, but biology is impressive. Andrea and Nancy will be submitting separate reports assessing what's here and making recommendations.
* '''Afternoon Individual Work (1400-dinner)''' -- more of the same, except Jan treats the hab to a sensory feast by doing something to the biolet, which I don't care to visualize. I'm sure he will tell us at dinner that it is better now. At 1630 Nancy and I refill the generator. At 1900 the power goes out because the DGO has turned on the crock pot and a burner when the breadmaker was going. Unfortunately, the breadmaker displays HHH and beeps when I return. I can't find what HHH means (but I'm guessing "HOT"). The instructions explain that power failure during baking is fatal, you must put the bread in an oven. We have no oven. I manage to put it on BAKE, but 1 hour is the only choice, and it only needs 45 minutes. I think that will work.
* '''Afternoon EVA (1559-1850)''' -- Jan and Vladimir head out to Skyline Ridge for adventure. I like to remind people that we are going to Mars not only for science, but to explore--like mountain climbers. That's my personal opinion, and I find it motivating. (When our crew returns they are content, but not happy. One ATV has a flat.)
* '''Early Evening Individual Work (1850-dinner)''' -- this is the gift of the day, when dinner is delayed and there is more time to get things done. Now is when I write these reports.
** Dinner
** Evening Individual Work
** Evening Entertainment

How people perceive time is important in scheduling work. You may be busy all day and not get done what you set out to do, and say afterwards, "I got nothing done." Interruptions or unexpected problems can cause that. Weeks and months have rhythms, too. That's why we have persisted as a crew for almost two weeks on a schedule that could not continue. We know that Saturday will bring a change of pace, and Sunday most of us will be flying home.

Except for making bread, the video tours, the generator, and lunch, I have spent the entire day in my stateroom at my computer. Here is the day, not as exciting as yesterday, but productive:

# Wrote EVA 72 report.
# Put geology-related photos on compact flash card for Andrea.
# Transferred, backed up, and cataloged photos from the past two days. Put photos from yesterday on compact flash card for Andrea. Then used a Photoshop custom action to prepare the photos for the web; wrote captions; and tried to email them on our slow line.
# Completed designing a human factors survey for the crew and emailed it to them.
# Processed a ton of email, moving most of the regular work items into my "TO PRINT" folder for consideration at home. Read all the MDRS-related mail carefully, including the crew's reports.
# Wrote a handout for the Open House, including a detailed schedule and one page summary of our research themes and methods.

Maybe tomorrow I will read a book.

Bill Clancey

MDRS Rotation 5 Commander

===Crew 5 Profile===
Crew 5 Profile - Jan Osburg

By David Real / Belo Interactive

'''Aboard The Mars Desert Research Station, Utah''' - Taking the first step toward becoming a space station designer probably began when Jan Osburg was 10 years old.

He tried to fix his father's broken eight-track tape recorder.

"I took everything off that you can take off with a screwdriver,<nowiki>''</nowiki> Mr. Osburg said. "I just fiddled with it - disassembled it, assembled it - and then it suddenly worked again."

Twenty years later, Mr. Osburg is far from the family tape player and his hometown of Ettlingen, Germany, but close to his passion for making things work.

He is a research engineer and lecturer for the Space Systems Institute at the University of Stuttgart in Germany. He studied there under Dr. Ernst Messerschmid, one of Germany's first astronauts and director of the European Astronaut Center.
{| class="wikitable"
|Jan programs his GPS receiver at his computer for an upcoming EVA from the Mars Desert Research Station in Utah. Photo Credit: David Real / Belo Interactive
|}
In a few weeks, Mr. Osburg will defend his doctoral dissertation at the university and move to Columbus, Ga., with his wife Jennifer and daughter Clara, almost 2. It will be a homecoming of sorts for Mr. Osburg, who earned his master's degree in aerospace engineering in October 1996 from the Georgia Institute of Technology in Atlanta.

Ahead of him is a hunt for a job that will enable him to continue his work in the conceptual design of manned space systems, including the integration of related fields, such as architecture, psychology and medicine.

Currently he is solving engineering problems as a volunteer crewman at the Mars Desert Research Center, which is run by the Mars Society to promote the exploration of the Red Planet.

And there were many problems to solve, whether it was an electric generator that wouldn't start, a blown fuse on a spacesuit backpack or a broken water pump. The crew also relied on him to explain how to use a GPS unit, fix a digital camera, connect computers on an internal network, and protect them from static electrical discharges during dust storms. He also served as the team's Health and Safety Officer.

Mr. Osburg, 30, is the youngest on the six-member crew, but was selected as second in command of the Habitat during the group's two-week stay in the Utah desert.

His primary interest is in the design of the Hab and its ability to function as a planetary exploration base. He said its basic design was sound and perhaps could stand on the Martian surface one day. On the first floor are main and rear air locks, plus a lab and workshop area. On the second floor are the crew's living and work areas, with a loft topping off the structure.

But the value of the Mars simulation at the Hab lies in its research into how people might live and work together aboard such a base.

"You don't try to build the perfect Hab right from the beginning after only doing a lot of paper studies," he said. "You just see what works, what doesn't work, and you fix it in small steps."

For an engineer who can fix most things that go wrong, individual pieces of equipment are almost of secondary concern. Nearly everything will be different to a degree - spacesuits, internal layout of the station, water supply. Anytime humans are part of the equation for a space station, the solution is constantly changing, he said.

"You have to approach it in a holistic way - integrate everything - because for the person using it, everything seems like one integrated structure that completely determines their lives," he said.

Because of the constantly shifting relationship between man and machine, simulating a working Martian space station is the only way to predict the problems that future crews will face. That enables engineers to design solutions in advance on Earth, rather than in the isolation of space.

"I'm really convinced that the first crews who go to Mars will somehow profit from the experience that we have gained here," he said. "It keeps them from having to reinvent the wheel - and they won't have time to invent anything. They'll just have to rely on things working."

Mr. Osburg is passionate about his belief that society has a basic obligation to break the bonds of bureaucracy and explore space - what he calls frontier ideology, a concept that he said still exists, to a degree, through the freedom of America.

"Civilized society is too far removed from this frontier experience," he said. "I really think society needs some outlet for the people who tend to be more individualistic, who have initiative and … where you have pioneers who do something. And Mars - space flight in general, especially manned space flight - opens up the next frontier."

He credits the Mars Society and its president, Dr. Robert Zubrin, for leading the charge to open up space to exploration through projects such as the Mars Desert Research Station.

Their work not only fosters scientific research, but creates the public knowledge and goodwill that is necessary for such Mars exploration to succeed, he said. People must be convinced that going to Mars is feasible, necessary and the right thing to do, despite the costs involved.

For some people, he said, space travel will always be an extravagant waste of money.

"If these people had been in power back in 14-something, then Columbus wouldn't have discovered the U.S.," he said.

Mr. Osburg would like to be one of the first to explore Mars, but recognizes that his chances are remote because of his height and eyesight - he is 6-feet-4-inches tall and slightly short-sighted.

"I would love to go, of course," he said. "My family would even support it. But I'm realistic enough to know that I'm not going to make it through the selection process."

But exploration of Mars is a tough, long-term project that will take centuries, which is why Mr. Osburg is donating his free time to the research being done at the Habitat in the Utah desert. He said he is committed to helping in whatever way possible.

"I have a unique opportunity to experience firsthand all the problems, all the different aspects involved," he said. "But also I see this as more of a personal thing: I get to contribute. Even if it's just a small thing to help make life easier for the first astronauts on Mars."

===Journalist's Report - Space Food===
By David Real/Belo Interactive

'''Aboard The Mars Desert Research Station, Utah''' - If an army travels on its stomach, then food for a mock Mars crew is none other than the prime directive.

Woe to anyone who would impede or block any sector of the universe from its quest to satisfy an insatiable appetite.

Even the science experiments are not immune. It can be a very short leap from lab dish to appetizer plate.

Crew member Andrea Fori noted in a science log that the radishes had grown 4 centimeters (1 ½ inches, in regular talk) during an experiment testing the possibility of growing food in a greenhouse.

Her next entry read: "Yummie, yummie, yummie. I have radishes in my tummy."

Life is tough in outer space for veggies.

There is also bad news ahead for future space explorers: there are no maids on Mars. It's a do-it-yourself deal, commander, or face hunger pangs.

So, as one of its first missions, the crew devised a plan to make sure that hefty portions of properly prepared food were on the table for each scheduled meal.

They created the position of Director of Galley Operations, which quickly suffered the fate of all science: it became an acronym. Namely, DGO.

How do these things get started?
{| class="wikitable"
|Andrea Fori assesses the culinary viability of experimentally grown radishes. Photo Credit: Dr. Vladimir Pletser / European Space Agency
|}
"Well, it's a kind of disease," said crewman Jan Osburg, who is a scientist with the Space Systems Institute at the University of Stuttgart in Germany. "On one hand, it makes sense because you have precious little time to communicate, and you have to be very clear. So you just have this tendency to come up with acronyms.

"DGO - we just made it up for fun, to ridicule the acronymitis. But it stuck, and it's cool, and this is how it gets started."

Rearranging a few letters in DGO results in actual words, such as GOD and DOG. Both are appropriate to the job title.

The crew rotates the title and the duties daily, so the rest can concentrate, with as few interruptions as possible, on the real work of science experiments and regular station life.

But when a crew member's turn comes around every six days, be prepared to work like a dog. In addition to cooking meals, one should be prepared to bus tables, wash dishes, boil tea and set out snacks.

No job is too menial - emptying the garbage is also a daily requirement. One trashcan is strategically placed under the first-floor bathroom sink, probably because there are no drain pipes connected to the sink. Who said there weren't plumbing problems in space?

Could things get worse? You bet your phaser pistol they can.

The worst job is emptying the trashcan next to the biological toilet - designed for four, but servicing six, although none too well.

To account for a severe problem with, let us say, capacity, the crew has agreed that most toilet paper, within reason, will be placed in the trashcan, rather than the toilet.

Enter the DGO and the job's most odorous - if not onerous - duty.

On the other hand, the power of the DGO approaches that of a minor deity when it comes to mealtime.

Most of the contents of a Fred Meyer grocery store in Salt Lake City were carted away by the team before starting their two-week stay at the Mars Desert Research Station.

Three shopping carts were piled high to overflowing with family-sized portions of pork chops, peanut butter, Dijon mustard, sliced ham, fruits and vegetables, coffee, and countless other items, including Tang, nectar of the astronauts.

Clerks were sent flying through the store to return with hard-to-find items as an endless conveyor belt rolled the goods to the cashier, who was very friendly to us.

Once the food reaches the Habitat, however, the DGO of the day exercises authority with autonomy.

There is but one commandment: Antagonize not the DGO, lest you face a dinner of cold tuna on crackers.

If the DGO is pleased, the fare can be marvelous. A cup of hot tea can be steaming at your side with a simple nod of the head; a splendid, four-course dinner is normal fare every other day or so.

Of course, no self-respecting DGO could serve such Earth-bound concoctions as fajitas or spaghetti. They become Martian Lander tuna sandwiches, Valles Marinaras linguini and meatballs, and Solis Salmon Salad.

The miracle is that any meals get cooked at all.

The dorm-sized kitchen refrigerator is so small that most of the food shares space with biological experiments in the lab icebox.

The microwave is said to work occasionally.

There is no oven or stove, only two hot plates that tend to blow the circuit breaker for the entire complex if another major appliance is on at the same time: say, a coffee maker.

Once the power is restored - it takes a 5-minute trip to reset the remote electric generator behind the Hab - the hot plates enter their warm-up phase. After 10 minutes or so, they give off the heat of a small light bulb.

For those in a hurry, pancakes sometimes just turn out to be lukewarm, pasty flour.

During breakfast recently, the DGO asked for dinner suggestions.

"There are a lot of potatoes," answered the Hab's commander, NASA's William J. Clancey. "You might as well get them going now."

Humor in the Hab - that's really how things get done.

===Diary===
By Vladimir Peltser

Hello everybody,

Realized today that it will be soon over. Still so much to do. Photos are coming in a parallel e-mail. Martian regards to all!

Vladimir

Bonjour a tous,

On s'est rendu compte aujourd'hui que ce serait bientot fini. On a encore tellement a faire. Les photos arrivent en parallele. Bien amicalement

Vladimir

'''Thursday 18 April 2002, Day 12'''

'''Martian greetings, Earthlings!'''

Big excitement yesterday evening, as Nancy found a scorpion under her bed. After verification on the Web, it was a Centruroides Exilicauda. Venomous and lethal for children. Amazing, such a little animal, 2.5 cm, and so antipathetic. We were reminded to verify our shoes in the morning as they like dark, warm humid spots.

The weather turned cold during the night. The coldest temperature was 5 deg. C. This morning during our briefing we discussed the coming end of our simulation. It is true that time has passed so quickly and that we were so busy, that nobody r5eally realized that we are nearly at the end. In three days, we will be leaving. In fact the isolation will stop on Saturday already, as we will have the visit of nine media representatives, European and US television and newspaper journalists. After isolation, it will be invasion. So we started to prepare with the help of David, our resident journalist, what to say and how to say it. Tomorrow will be a big clean-up day also. Our Station Engineer Jan Osburg noticed that the biolet was not functioning optimally (to put it as an understatement ...). So he decided to give it a good cleaning before tomorrow. We had to open all doors and hatches and for once the blowing wind was more than welcome.

This afternoon, everybody had a lot of things to do and to finish as suddenly everybody realized that in a couple of days, it would be all over. Nobody really was interested in an EVA, except for Jan and myself. So, we suited up in the middle of the afternoon and did a few things in the greenhouse, like replacing the data logger and brushing up the solar panels (yes, that is also something that Astronauts on Mars would have to do after each sand storm). We proceeded then to Candor Chasma to revisit this splendid place that we visited on day 4 with Andrea. It seemed to me that it already changed after the sand storm and rain we had over the weekend. Could it be that landscapes on Mars are equally rearranged by wind like they are on Earth?

We left Candor Chasma to attack the next piece on our program, which was to find a way to climb Skyline Rim. Well, Skyline Rim is quite another affair, and a big one. It is a huge plateau made of cretaceous sandstone and rising nearly 130 m above the surrounding plain. Not easy to pass and not easy to climb with ATVs. So we tried first toward the North without success, and then we went southward, to try to go around. And we drove, we drove, until we could not drove any farther as we came across a small river, but still no way in sight to climb Skyline Rim. We noticed as well that Jan's ATV had a flat tyre, so we decided that it was time to come back. We measured on our way coordinates of several geodetic points in the desert, so as to be able to relocate on the map our exact path. We came back safely to the Hab well in time for dinner.

Our plants are going well, thank you. They are growing like mad: the tallest radish stem is now 10.5 cm and it is caught back by a tatsoi stem with the same height in the lab downstairs. Which one will win? We should know Saturday night when we will harvest them all and make a (small) salad. This evening, we will feast on Nirgal sate prepared by Nancy. Don't ask what it is. I think there are meat, unknown vegetables and some herbs from our Martian greenhouse. These are what makes it so special.

This evening also we will have a break and watch a DVD. Discussions are on-going whether it would be Matrix, Spaceballs or Starship troopers. Well, you see, life is going on and the day is coming to an end with humans having the same preoccupations like in any other house on our planet, whether it be Earth or Mars.

On to Mars!

Vladimir
----'''Jeudi 18 avril 2002, Jour 12'''

'''Salutations martiennes, Terriens!'''

Gros tohu-bohu hier soir: Nancy a découvert un scorpion sous son lit. Apres verification sur le Web, il s'agissait d'un Centruroides Exilicauda. Venimeux et mortel pour les enfants. Surprenant, un si petit animal, à peine 2.5 cm et si antipathique. On nous a rappelle de vérifier nos chaussures au matin, comme ils aiment les endroits sombres, chauds et humides.

Le temps est devenu froid pendant la nuit. La temperature la plus basse etait de 5 deg. C. Ce matin, pendant notre briefing, nous avons discute de la fin approchante de notre simulation. Il est vrai que le temps a passe si rapidement et que nous étions tellement occupe que personne ne s'est réellement rendu compte que nous approchions de la fin. Dans trois jours, ce sera fini. En réalité, l'isolement prendra fin samedi déjà puisque nous aurons la visite de neuf groupes de journalistes des télévisions et presse écrites américaines et européennes. Apres l'isolation, l'invasion. Nous avons commence à préparer avec David, notre journaliste résidant, ce qu'il fallait dire et comment le dire. Demain sera un grand jour de nettoyage. Notre Ingénieur de service, Jan Osburg, a remarque que la toilette bio ne fonctionnait pas de manière optimale (pour dire le moins ...). Il a donc décide de la nettoyer avant demain. Nous avons du ouvrir toutes les portes et hublots et le vent pour une fois était le bienvenu.

Cette après-midi, tout le monde avait un tas de choses a faire et a terminer comme soudainement tout le monde a réalise que dans quelques jours tout serait termine. Personne n'était donc vraiment intéresse par une sortie en EVA, a part Jan et moi-meme. Nous nous sommes habilles au milieu de l'après-midi et avons commence par arranger quelques affaires dans la serre, comme remplacer l'enregistreur de paramètres atmosphériques et brosser les panneaux solaires (oui, c'est quelque chose que les astronautes sur Mars devront faire régulièrement après chaque tempête de sable). Nous sommes ensuite partis vers Candor Chasma pour revisiter cet incroyable endroit découvert avec Andrea le quatrième jour. Il m'a semble que l'endroit avait change après la tempête de sable et les pluies que nous avons eu ce week-end. Serait-il possible que les paysages sur Mars soient également réarrangés par le vent comme sur Terre ? Nous avons quitte Candor Chasma pour attaquer la prochaine étape de notre sortie: trouver une voie d'acces a Skyline Rim.

Mmmh! Skyline Rim est une autre affaire, une grosse affaire. C'est plateau surélevé immense datant du Cretace et s'élevant à 130m au-dessus de la plaine environnante. Pas facile a passer, ni a monter avec les ATVs. Nous avons d'abord essayer par le Nord mais sans succès, puis par le Sud pour essayer de le contourner. Et on a roule, on a roule, jusqu'a une rivière encore une fois infranchissable, sans passage en vue pour monter Skyline Rim. Comme l'ATV de Jan avait un pneu plat et qu'il n'est pas facile de trouver un garage dans le désert, nous sommes rentres à faible allure. En route, nous avons pris également les coordonnées GPS de quelques points géodésiques dans le désert, afin de nous permettre de retracer notre chemin sur la carte. Nous sommes finalement arrives sans problèmes au Hab.

Nos plantes vont bien, merci! Elles poussent sans arrêt: la tige de radis la plus longue est à maintenant 10.5 cm and elle est rattrapee par une tige de chou tatsoi qui a la meme hauteur dans le labo au rez-de-chaussee. Qui va gagner ? On devrait le savoir samedi soir quand on les récoltera tous pour en faire une salade.

Ce soir, notre festin sera fait de sate Nirgal, prépare par Nancy. Ne demandez pas ce que c'est. Il y a de la viande, des légumes non identifies et quelques herbes qui viennent de notre serre martienne. C'est ce qui rend ce plat si spécial.

Ce soir aussi, nous avons droit a souffler et nous regarderons une DVD. On hésite entre 'Matrix', 'Spaceballs' et 'Starship troopers'. Et bien, vous voyez, la vie continue et la journée tire a sa fin avec des humains ayant toujours les mêmes préoccupations comme dans n'importe quelle autre maison sur notre planète, qu'elle soit la Terre ou Mars.

Bonne soirée martienne, Terriens!

En avant, Mars!

Vladimir Pletser

===Geology Report===
Andrea Fori Reporting

Worked on primer and geology work summary. Plan to submit tomorrow.

===Health & Safety Officer Reports===
Jan Osburg Reporting

'''Safety:'''

Nothing to report.

'''Health:'''

Nothing to report.

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' Nothing to report.

'''Power and Fuel:''' Nothing to report.

'''EVA Equipment (including ATVs and PEV):''' The automatic transmission ATV has developed an air leak in the left front tire which we will have to fix before taking it out on EVAs again.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' Nothing to report.

'''General Maintenance & Waste Management:''' The "Biolet" (pronounced vile-let) composting toilet was serviced today, i.e. the bottom tray collecting the end product of whatever biochemical process is going on inside was removed, emptied into a plastic bag, and put back again. Simple as its sounds, due to the hazardous and olfactorily challenging nature of its contents, this procedure took the better part of an hour. Level 4 biohazard gear would have been appreciated, but lacking that, an improvised facial protection combined with sturdy rubber gloves (brought from Europe for just that purpose) was better than nothing. Those Tyvek suits are sorely needed, not just for generator refueling...

Instead of disposing "of the humus by mixing it with soil or compost and trench[ing] it around ornamental trees and plants" as suggested by the Biolet user's manual [sic], it was quadruple-bagged and put into the garbage collection area by the members of EVA 72, who were quite glad to be equipped with helmets, gloves, and a ventilation system.

'''GreenHab:''' The strong winds in recent days have completely destroyed the greenhouse door, which was temporarily fixed with - what else - duct tape to avoid further damage to the greenhouse structure.

===EVA 73 Report===
'''EVA SCENERIO OVERVIEW'''

There were three main objectives to this EVA:

* to do some maintenance at the greenhouse (replacing the data logger, dusting off the solar panels);
* to reckon the area of Cando Chasma canyon;
* to explore and try to find a new route leading onto Skyline Rim from the east.

'''DATE: 04-18-02'''

'''EVA Highlights (EVA CDR)'''

'''Personnel:'''

Commander: Vladimir Pletser (EVA-6)

Jan Osburg (EVA-5)

HabCom: David Real, Andrea Fori

'''Airlock timeline:'''

Departure ingress: 15:59

Departure egress: 16:04

Return ingress: 18:46

Return egress: 18:51

'''New waypoints:'''

Format: WP#, WP name, datum used, Easting, Northing, Altitude [m], Date, Time

125, Sagan Street Topo 1 (WP067?), NAD27, 517122, 4251253, 1389, 18.04.2002, 17:02h

126, Sagan Street Topo 2, NAD27, 516338, 4251249, 1401, 18.04.2002, 17:05h

127, Clara's Corner (WP 66?), NAD27, 516026, 4251242, 1410, 18.04.2002, 17:14h

128, Clara's Cliff, NAD27, 515395, 4251284, 1405, 18.04.2002, 17:22h

129, Copernicus Hwy Topo A, NAD27, 515995, 4250793, 1401, 18.04.2002, 17:44h

130, Copernicus Hwy Topo B, NAD27, 515494, 4249083, 1393, 18.04.2002, 17:52h

131, Copernicus Hwy Topo C, NAD27, 514986, 4247658, 1300, 18.04.2002, 17:58h

132, Telegraph Point, NAD27, 514757, 4246687, 1291, 18.04.2002, 18:05h

133, Savannah, NAD27, 515008, 4246078, 1340, 18.04.2002, 18:13h

'''Route:''' (by waypoints, in this sequence, including new waypoints)

MDRS, 106, 112, 125, 126, 127, 128, 127, 129, 130, 131, 132, 133, 132, 131, 130, 129, 127, 112, MDRS

'''Communication checks:'''

Check time: 16:04

EVA team location: Hab airlock egress

Status: OK

Additional notes:

Check time: 16:16

EVA team location: around Hab

Status: Finished to do chores at greenhouse, leaving for Candor Chasma

Additional notes:

Check time: 16:47

EVA team location: between Candor Chasma canyon and Hab

Status: back from Candor Chasma, en route to Skyline Rim

Additional notes:

Check time: 17:28

EVA team location: In front of Skyline Rim

Status: en route southward parallel to Skyline Rim

Additional notes: via repeater (channel 201), bad line

Check time: 18:46

EVA team location: In airlock

Status: OK

Additional notes:

'''Special circumstances:'''

One ATV had a flat tire that grew worse with time, but was still Ok to drive slowly.

'''EVA CREW: COMMENTS/OBSERVATIONS/LESSONS-LEARNED'''

Always carry a can of fix-a-flat on long-range EVAs.

'''EVA CDR:''' The first part of the EVA took about 15 minutes to replace the data logger and to dust off the solar panels in the greenhouse. I had some difficulties entering the greenhouse with the EVA suit while the temporary door was taped all around, but eventually managed.

We left for Candor Chasma and we soon found a way to enter into the canyon. We followed the canyon till the end to exit through sand banks. I have the impression that the canyon has changed since the last time I visited it about a week ago, probably under the action of the wind and rain.

We then left for the Skyline Rim with the intention to try to find a way to climb on top Skyline Rim. Arrived at Clara's Corner, we continued straight on. To no avail, as the track ended in front of the cliff. We decided to come back at Clara's Corner and to go south to follow the track more or less parallel to the Skyline Rim, to see whether it would be possible to go around. We drove quite a while, without seeing any possible road. We eventually came across a road (R24) and further on a river. As there was still no visible possibilities of climbing the Skyline Rim plateau, and as Jan's ATV had a flat tire, we decide to come back to the Hab. En route, back and forth, we stopped at several locations and at several geodetic points to take GPS coordinates and recorded as Waypoints in the EVA chart. All in all, an enjoyable outing with the ATVs.

'''EVA MDRS1:''' We first stopped at Candor Chasma, a ravine with fascinating geological formations one kilometer east of the Hab. Afterwards, we went west to Midrange Planitia via Skyline Rim. New GPS readings were taken there, at Clara's Corner, and at various topographic survey markers (to calibrate the GPS receiver). We did not find any route leading to the top of Skyline Rim, but we found an interesting vegetated area that we dubbed "Savannah", just south of highway 24. One of the ATVs developed a flat tire during the EVA, so we could only proceed slowly and had to turn around earlier than planned. Nevertheless, a successful EVA even if we did not find a way around the steep cliffs of Skyline Rim.

==April 19, 2002==
===Commander's Logbook===
As I looked around the hab today, cleaned from top to bottom by a responsible and still enthused crew, I felt the first pangs of homesickness, of leaving this place. We have had a productive and happy time, and I am already plotting my next visit (or two).

Today was a welcome change of pace, devoted to final report writing and cleaning up. We had our usual morning meeting, on time despite some late night work by Nancy and others. Our evenings have been shifted late, with dinner often at 9 pm, and our movie (last night the droneful "Starship Troopers") only starting at 10.

My thoughts and writing today seem like the many deposits we have seen, crossing and varying in color and size, falling over the present to be the layers of tomorrow.

I forgot to record the morning meeting, and I didn't update the weather forecast in the daily plan. In my mind our time here is over. We are already drifting on, thinking about next week.

Here are the temperatures for the past 24 hours:

Maximum outside 20.7 C (69.3 F); Maximum inside 22.1 C (71.8 F)

Minimum outside 3.1 C (37.6 F); Minimum inside 15.6 C (60.1 F)

Curious, the inside temperatures were virtually identical to yesterday. The weather is fine--mostly clear, calm, with intense sun. It's a day to be in the sun. Of course, if you've been following this log, you know that in the weatherman's crystal ball today has been variously cloudy and partly cloudy, ranging from a high of 61 to a high of 78. Not once in the past week has the actual clarity of today's sky been foreseen.

Tomorrow nine crews from international TV and the press will come to our open house: ARD TV, TechTV, RTL TV, Fox-10 TV, plus Der Spiegel, Axel Springer, FACTS (Swiss), Svenska Dågbladet, and the Sunday Telegraph of London. One group showed up today, angling for a privileged interview, circling our hab like cowboys on the hill. I put a sign on the lower portal, saying if they didn't go away, I wouldn't see them tomorrow. Eventually, they left. My challenge is to explain why this behavior shows a complete misunderstanding of what we have been doing here. This is a research effort--what we see and do is controlled, it's not an exhibit.

We scheduled our day to wrap up our work: David's interview of me; final reports by Andrea, Jan, Nancy, and Vladimir; revising and printing the schedule and fact sheet for tomorrow's open house visitors.

'''Around 1130''' we had yet another bucket brigade. I naively asked to have an outside position, for until now I haven't seen how that part of the job is done. Jan readily agreed, a wise choice--the easy siphoning method would no longer work. We improvised a scoop from our water pitcher, attaching a clean safety strap, so I wouldn't lose it in that cavernous plastic vat. After some fumbling, the job went quickly. I enjoyed being outdoors and talking with Andrea (as opposed to standing at the top of the stairs and moving between Vladimir and Nancy in the loft). I have often thought that a Mars crew of six would learn each other's skills (called "cross-training" in business offices). So maybe a geologist would return to Earth an accomplished engineer (if this seems far-fetched, read Andrea's biography).

After a very pleasant lunch organized by Andrea (the highlight: hard-boiled eggs on tortillas), we held to our scheduled clean-up. At the morning meeting, we had listed every hab area and made assignments. Now the crew spent over two hours vacuuming, reorganizing, washing, and throwing out unnecessary items throughout the hab. The hab roared with energy and determination. David cleaned the sink and shower, Jan ordered the shop's workbench and shelves, Andrea cleaned the galley, Vladimir vacuumed everything (forever it seemed), and I mopped the toilet floor and wiped everything clean. We were amazed by the new feeling of a dust-free, uncluttered, and newly spacious interior--that "new hab" feel.

In the afternoon I took a gratifying nap. Looking up through the square portal of my stateroom, I imagined that I was on a spacecraft, landed on Mars. I have been here for months, this is my place, with my bed, clothing, and desk. These are the only people I know. We are here to study the surrounding region of this planet. We must maintain our life support--the power, the water, the greenhouse. We go on EVAs, cook, cleanup, converse, write, read and write email, watch movies. I think again, we six people are alone together for three years. What would that be like? I would prefer to be here with my wife, as three couples. I cannot imagine a monastic existence (a minimal existence) in such close quarters for three years. The Space Shuttle or Station model is not appropriate for such long durations. Of course, sailing expeditions had dozens of people for often over a year. But total isolation for three years was not planned, it was not just a group of six, and not so confined.

How long could the crew of Rotation #5 continue? Certainly another week, and with more experimental equipment (e.g., teleoperated vehicles), we could easily be busy for a month. We are temperamentally very compatible, having really to adjust only for different sleep and wake times. Enjoying eating certainly keeps us together; we are all good cooks. And every combination appears to work, as we've demonstrated on our EVAs.

This will be my last report. The separately posted schedule for the Open House (April 20) summarizes our research themes and methods. Later papers will analyze the data and what we have learned. I am eager to return with our NASA/Ames and Johnson Space Center robotics project, called "Mobile Agents." I want to tackle the navigation problem here, the communication problems, waste water management, and expedition memory (exploration database). I want to experiment with a full-time mission support.

Speaking of which, the Northern California Chapter of the Mars Society provided a fully reliable and professional service these past two weeks. We are extremely pleased by the work especially of Mark Klosowski in serving as "Capcom" on most days, and all of the other volunteers. This group actually supported the mission, handling fuel, water, and other supply issues every day. They provided maps, references to past work, and suggestions for our EVAs. Without a telephone (making our simulation more realistic than FMARS), we relied on mission support for every contact. Every message was sent through Capcom, copied only by agreement with identified specialists (e.g., Gary Fisher with Greenhab). Web posting went smoothly, too.

'''1850:''' Jan and I have refilled the generator. It needed oil, but we couldn't find the funnel--gone in the wind. Looking up and around after my search, I am struck by the privilege of being here. Not just walking through or driving by. We are staying here, amid these hills, now darkening and cooling in the waning light. We are alone here in this sandy basin. How grand to own a home in this place! I glance over at the Mars Desert Research Station, straight bright-white and tall, the Mars tricolor fully out in the breeze. Yes we are here, in this place and in our minds, Mars on Earth.

Bill Clancey

MDRS Rotation 5 Commander

===Geology Summary===
By Andrea Fori

'''Geology Goal #1 as defined in the first report for Crew #5 MDRS rotation'''

As the last formal crew of the first MDRS season the geological achievements and process used by the last four crews will be broadly assessed. This report will describe the information from two perspectives a) From the perspective of the Earthbound scientist. Assuming that an Earthbound scientist would have only access to the information posted on the web, I'm going to look at ways posted info can be better communicated so that scientists can use the info being sent back from the red planet. b) From the perspective of the in-person view. As a traveler who arrives at Mars after others have begun research, I need to determine if I can decipher notes and gain an understanding of the local geology, reproduce EVA's, figure out where samples are from, etc. The team will be conducting EVAs during this portion of the study to verify our findings. Weaving in what I believe Earth-bound scientist would want to know, from the perspective of planetary geologists, astrogeologists and geo-engineers I'll make suggested improvements for how and what information is recorded and relayed.

'''Part A) Assessment of approach and actual assumption of what has been done from the "Earth-bound" remote perspective (assuming one has access only to the website).'''

'''What's on the website -'''

The website contains reports from EVAs and geological studies conducted throughout each crew rotation. The reports document coordinates of sites of interest, a description of the local geology at that point and identification of any discovered fossils. Photographs are generally included in the EVA and geology reports where necessary to clarify or enhance the report. There is also a comprehensive spreadsheet that characterizes each waypoint with coordinates, elevation, objective, catchy title, and brief geological or biological description. With access only to the website it appears as though the Martian crew has spent time exploring the area, characterizing the local geology in areas which appear interesting.

'''Is this the right approach?'''

The approach at first glance seems appropriate for a Martian crew. However, there are a number of geological issues that realistically would be addressed first upon arrival before exploring the area (see suggested improvements). Depending on the objectives of the analog research station simulation, these more pressing issues should be considered for incorporation into the "day in the life" of the analog crews.

Assuming that these more pressing issues have been addressed and the crew is in the exploration stage, the first season of geological exploration at MDRS has been productive. The recording of EVA# and comprehensive Waypoint #s is effective.

'''Can this information be communicated better?'''

As an Earthbound geologist one would only be able to gain info from the website on specific locations in the vicinity of the hab. A critical exercise in conducting geological studies would be to synthesize the information into a regional geological primer of the area in order to communicate a broad sense of the geological environment. This happens to be my second goal for the MDRS Rotation #5 (see other final geology report).

The use of pre-established templates for recording relevant EVA and waypoint information makes the process go much smoother. Crew #5 has continued to improve the in-house spreadsheet (as every other rotation has done) to include information that we feel would be helpful and eliminated information that made the spreadsheet too cumbersome to use. The use of an EVA reporting template is also effective in communicating relevant information to Earth in a familiar format.

Radio communication needs to be improved dramatically. Channel 2.00 only functions on low frequency reliably within ~1/2 mile from the hab and only with new batteries and without obstruction (like a hummock). Channel 2.10 (using the repeater) is almost entirely non-operational. Radio communication etiquette should also be established (or use military protocol) and followed.

Millions of dollars will be invested in sending a crew to Mars. Personally, I would want to see much more information relayed to Earthbound scientists than the description of a few local waypoints.

'''Part B) Assessment of in-house material from the perspective of the in-person view - as a traveler who arrives at Mars after others have begun research.'''

'''What's in the hab?'''

As suspected, there is a lot of information in the hab that is not communicated via the regularly submitted geology reports. There is a paper map that records all waypoints on a transparency with a permanent marker. This could easily be accidentally destroyed; it's a nice visual reference, but not a permanent source of information. There are many random notes on paper piled in random corners of the hab, on poster board tacked on the wall, notes in personal logbooks lying around, and files and information on the computer from previous rotations. There are rock samples piled in a corner of the lower level.

'''Is this the right approach?'''

The information regarding the geological surveys that have been conducted is scattered and unorganized and without searching for hours through the data, it's impossible to know what information is here and what has been accomplished. There needs to be a formal organization of material, both on the hab computer and for hardcopy (like a filing cabinet). These formats must be followed in the future to ensure continuity between crews. There should be a well laid-out long-term agenda for simulated Martian geological exploration and for MDRS, the plan should be implemented little by little by each crew. Right now, each crew is apparently reinventing the wheel so to speak by simply exploring and creating new waypoints.

'''Can I decipher notes and gain an understanding of the local geology, reproduce EVA's, figure out where samples are from, etc.'''

I thought that this would be an exercise in only determining the ability of the former crews to communicate their findings. It turned out to be much more. The notes and reports are clear and easy to understand. Personally, I believe they should put the description of local geology into the regional geological context. The next step was for the team to go out and try to relocate waypoints that have already been identified as points of interest. Surprisingly, this was exceedingly difficult. The local terrain makes it almost impossible to reach the more obscure sites without knowing the path that was taken to arrive to the waypoint originally. The routes taken should be marked clearly on a large and small-scale map. This brings me to the next point, mapping. The identification of waypoints has been done in many ways. They've all been located on the wall map, but for each formal report, they are presented in a different way. There has been communication from Crew 4 (Andrew Hoppin) regarding the use of GIS to report waypoints in UTM using a consistent mapping tool. I did not have a chance to use this tool, but I do think it's an excellent step in formalizing a mapping process. As far as the lab is concerned, many samples have been collected, but there is no formal record for associating a sample with a location. In some cases the sample is marked with a rock type identification and a general area (like limestone from Candor Chasma). I don't think this is sufficient because not all samples are marked with rock type and only a few have any indication of source. The samples are scattered throughout the lower level; some even decorate the upstairs living area. There should be a formal cabinet for sample collection and a hardcopy and electronic form for recording samples. Need to develop a uniform polished reporting scheme.

Navigation was the single biggest headache for geological expeditions. The use of GPS was found to be inconsistent, unreliable, and our datum points we never in the same place. This made retracing previously recorded waypoints very difficult. Exploration was simple, but to find a point of interest, record an unreliable waypoint and then send another crew out to the waypoint using GPS was futile. Our compasses often swung wildly (even inside the hab) posing the question of a reliable navigation tool for Mars.

'''Miscellaneous'''

Suits are cumbersome, gloves are awkward and it's challenging to pick up and collect rocks, it's way too difficult to climb any sort of slope to reach a point of interest. Realistically need suits to be custom fit and lighter to cover a large distance. After a week, donning the suits became a chore. For a long term mission, this should not be worked out previous to travel.

'''Assumptions made here at MDRS'''

Of course at this stage in preparing for Mars exploration, many assumption have to be made in order to facilitate the simulation. These are the assumptions I have found to have been incorporated into the MDRS simulation related to geology:

* The crew has arrived safely and is healthy and ready to conduct EVAs
* The crew has already identified a geologically stable and safe place to set up their hab
* They have successfully constructed the hab
* They have successfully constructed the GreenHab

'''More realistic approach/suggested improvements'''

The general assessment of local geology is great, however for a real mission a geologist would need to address specifics from three topics: practical, pressing, and popular. This isn't meant to sound catchy, rather these are the issues I expected and would hope to see in future simulations so that the trials and tribulations of going through the studies are ironed out before we actually send someone to Mars.

First, let's look at the practical needs of a Martian crew. Assuming the crew safely lands, a hab must be set up. Is the ground stable? Is the landing site and the region within a practical distance sandy or is there a regolith that may be used for stabilizing the hab? Is the area located on an active fault that possesses a high risk of catastrophic structure failure? Is the region characterized by shifting jointing that would slowly deform the hab? How does one in a space suit go about stabilizing a hab? Currently, the MDRS hab is stabilized by long I-beams drilled into the ground by humans using the conveniences of heavy machinery without being encumbered by spacesuits. It would be useful to determine if a hab can be constructed by people in suits. Perhaps this exercise can be slated for a future and more accurate simulation, but I think it's at least important to characterize the region from a geological engineering perspective.

Once set up for survival on the Martian surface, the crew will need to address some key issues, the most critical of which is how to return to Earth. Can fuel be made as predicted and practiced on Earth? The Mars Society analog research stations should include going through the motions of creating fuel, and reconfiguring a spacecraft for the return flight in a spacesuit.

The popular issues are intended to collect information from Mars that would answer the many questions we have generated here on Earth but are unable to confirm without field investigation. Is the evidence we've used to indicate the previous existence of water on Mars accurate? Have we assumed correctly? Was there water on Mars? Is there currently water on Mars? The polar ice caps are composed of what? Is there a permafrost layer? Can we do the studies necessary to answer these questions in spacesuits?

There are many issues to be addressed prior to going to Mars. I feel the Mars Society analog research stations is an excellent way to prepare ourselves.

===Health & Safety Officer Reports===
'''Safety:'''

Some additional safety-related signs were printed and posted in preparation for tomorrows Open House - yes, there was some uncovered wall space left for this.

'''Health:'''

Nothing to report.

===Engineering Report===
Jan Osburg Reporting

'''Water Systems:''' Nothing to report.

'''Power and Fuel:''' We tried out a new way of refueling the generator this morning. After moving the full gasoline barrel close to the wall separating the generator from the fuel storage area, the pump hose was long enough to go directly into the generator tank. This keeps us from having to use the gas cans. Due to the amount of fuel left in the pump hose after pumping ends, care must be taken not to overfill the tank. The gas containers were topped of and now act as a two-day reserve.

'''EVA Equipment (including ATVs and PEV):''' The air compressor was found and used to refill the left front tire of the automatic-transmission ATV. All three ATVs are now operational again.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' Nothing to report.

'''General Maintenance & Waste Management:''' After lunch, the whole crew spent about three hours cleaning and organizing the hab in preparation for tomorrow's Open House. It struck us that we could have done such a cleaning-up on our first day here, which would have resulted in much improved habitability… Now the next crew can look forward to taking over a much more spacious, organized place.

'''GreenHab:''' (see "Biology" report)

==April 20, 2002==
===Commander's Logbook===
Dr. Bill Clancey Reporting

Today we had the first MDRS Open House from 900-1600. It was a full success. We were visited by crews from ARD TV and RTL TV (German), TechTV (San Francisco), Fox-10 TV (Phoenix), Der Spiegel (German magazine), FACTS (Swiss magazine), Dagbladet Daily (Norwegian), and the Sunday Telegraph of London. Most stayed for the entire day. The schedule included private interviews (often focusing on Jan Osburg from Germany) and a group photo shoot as Jan and Vladimir Pletser donned suits and went on a simulated EVA. We served a buffet spread of tuna, cheese, salads, pickles, soup, and crackers, thoughtfully prepared by Vladimir.

Everyone was in good spirits, and Rotation 5 unanimously agreed that this approach was far preferable to being interrupted during our "sim," when we were busy working. Having everyone visit together allowed us to prepare the hab for visitors, including signs and a handout. Also, by scheduling this day for the end of our rotation, we were able to describe what we accomplished in a coherent, complete way.

Having so many visitors at one time was not a problem. First, we gave each team an hour or half-hour on the upper deck for a quiet interview. During the photo shoot on the lower deck, we noticed that the writers, still and video photographers sorted into groups, and found ways to stand out of each other's way. In particular, Vladimir suited up in the EVA prep room while Jan was in the lab area. Video photographers stood at the bottom of the stairs, with writers arrayed around the perimeter of the lab. Still photographers looked in from the main hatch, taking turns to make photos through the airlock. (I assured them that although the light was better on the "front porch" it would be meaningless to show someone suiting up outside the hab. Some things just need to be explained.)

As we anticipated, there was a general circus outside, as Jan and Vladimir rode around, providing photo opportunities from the surrounding hills. Andrea stood outside, acting as "capcom," using the radio to good effect to relay the reporters' desires. Everyone appeared to be having a good time.

The reporters left by 1600, as we had asked, and we were once again alone in the hab.

We strongly recommend the "Open House" approach to future crews, especially when a closed simulation is desirable for human factors and operations research.

Bill Clancey

MDRS Rotation 5 Commander

===Geology Summary===
By Andrea Fori

'''Geology Goal #1 as defined in the first report for Crew #5 MDRS rotation'''

As the last formal crew of the first MDRS season the geological achievements and process used by the last four crews will be broadly assessed. This report will describe the information from two perspectives a) From the perspective of the Earthbound scientist. Assuming that an Earthbound scientist would have only access to the information posted on the web, I'm going to look at ways posted info can be better communicated so that scientists can use the info being sent back from the red planet. b) From the perspective of the in-person view. As a traveler who arrives at Mars after others have begun research, I need to determine if I can decipher notes and gain an understanding of the local geology, reproduce EVA's, figure out where samples are from, etc. The team will be conducting EVAs during this portion of the study to verify our findings. Weaving in what I believe Earth-bound scientist would want to know, from the perspective of planetary geologists, astrogeologists and geo-engineers I'll make suggested improvements for how and what information is recorded and relayed.

'''Part A:''' Assessment of approach and actual assumption of what has been done from the "Earth-bound" remote perspective (assuming one has access only to the website).

'''What's on the website -'''

The website contains reports from EVAs and geological studies conducted throughout each crew rotation. The reports document coordinates of sites of interest, a description of the local geology at that point and identification of any discovered fossils. Photographs are generally included in the EVA and geology reports where necessary to clarify or enhance the report. There is also a comprehensive spreadsheet that characterizes each waypoint with coordinates, elevation, objective, catchy title, and brief geological or biological description. With access only to the website it appears as though the Martian crew has spent time exploring the area, characterizing the local geology in areas which appear interesting.

'''Is this the right approach?'''

The approach at first glance seems appropriate for a Martian crew. However, there are a number of geological issues that realistically would be addressed first upon arrival before exploring the area (see suggested improvements). Depending on the objectives of the analog research station simulation, these more pressing issues should be considered for incorporation into the "day in the life" of the analog crews.

Assuming that these more pressing issues have been addressed and the crew is in the exploration stage, the first season of geological exploration at MDRS has been productive. The recording of EVA# and comprehensive Waypoint numbers is effective.

'''Can this information be communicated better?'''

As an Earthbound geologist one would only be able to gain info from the website on specific locations in the vicinity of the hab. A critical exercise in conducting geological studies would be to synthesize the information into a regional geological primer of the area in order to communicate a broad sense of the geological environment. This happens to be my second goal for the MDRS Rotation #5 (see other final geology report).

The use of pre-established templates for recording relevant EVA and waypoint information makes the process go much smoother. Crew #5 has continued to improve the in-house spreadsheet (as every other rotation has done) to include information that we feel would be helpful and eliminated information that made the spreadsheet too cumbersome to use. The use of an EVA reporting template is also effective in communicating relevant information to Earth in a familiar format.

Radio communication needs to be improved dramatically. Channel 2.00 only functions on low frequency reliably within ~1/2 mile from the hab and only with new batteries and without obstruction (like a hummock). Channel 2.10 (using the repeater) is almost entirely non-operational. Radio communication etiquette should also be established (or use military protocol) and followed.

Millions of dollars will be invested in sending a crew to Mars. Personally, I would want to see much more information relayed to Earthbound scientists than the description of a few local waypoints.

'''Part B:''' Assessment of in-house material from the perspective of the in-person view - as a traveler who arrives at Mars after others have begun research.

'''What's in the hab?'''

As suspected, there is a lot of information in the hab that is not communicated via the regularly submitted geology reports. There is a paper map that records all waypoints on a transparency with a permanent marker. This could easily be accidentally destroyed; it's a nice visual reference, but not a permanent source of information. There are many random notes on paper piled in random corners of the hab, on poster board tacked on the wall, notes in personal logbooks lying around, and files and information on the computer from previous rotations. There are rock samples piled in a corner of the lower level.

'''Is this the right approach?'''

The information regarding the geological surveys that have been conducted is scattered and unorganized and without searching for hours through the data, it's impossible to know what information is here and what has been accomplished. There needs to be a formal organization of material, both on the hab computer and for hardcopy (like a filing cabinet). These formats must be followed in the future to ensure continuity between crews. There should be a well laid-out long-term agenda for simulated Martian geological exploration and for MDRS, the plan should be implemented little by little by each crew. Right now, each crew is apparently reinventing the wheel so to speak by simply exploring and creating new waypoints.

'''Can I decipher notes and gain an understanding of the local geology, reproduce EVA's, figure out where samples are from, etc.'''

I thought that this would be an exercise in only determining the ability of the former crews to communicate their findings. It turned out to be much more. The notes and reports are clear and easy to understand. Personally, I believe they should put the description of local geology into the regional geological context. The next step was for the team to go out and try to relocate waypoints that have already been identified as points of interest. Surprisingly, this was exceedingly difficult. The local terrain makes it almost impossible to reach the more obscure sites without knowing the path that was taken to arrive to the waypoint originally. The routes taken should be marked clearly on a large and small-scale map. This brings me to the next point, mapping. The identification of waypoints has been done in many ways. They've all been located on the wall map, but for each formal report, they are presented in a different way. There has been communication from Crew 4 (Andrew Hoppin) regarding the use of GIS to report waypoints in UTM using a consistent mapping tool. I did not have a chance to use this tool, but I do think it's an excellent step in formalizing a mapping process. As far as the lab is concerned, many samples have been collected, but there is no formal record for associating a sample with a location. In some cases the sample is marked with a rock type identification and a general area (like limestone from Candor Chasma). I don't think this is sufficient because not all samples are marked with rock type and only a few have any indication of source. The samples are scattered throughout the lower level; some even decorate the upstairs living area. There should be a formal cabinet for sample collection and a hardcopy and electronic form for recording samples. Need to develop a uniform polished reporting scheme.

Navigation was the single biggest headache for geological expeditions. The use of GPS was found to be inconsistent, unreliable, and our datum points we never in the same place. This made retracing previously recorded waypoints very difficult. Exploration was simple, but to find a point of interest, record an unreliable waypoint and then send another crew out to the waypoint using GPS was futile. Our compasses often swung wildly (even inside the hab) posing the question of a reliable navigation tool for Mars.

'''Miscellaneous'''

Suits are cumbersome, gloves are awkward and it's challenging to pick up and collect rocks, it's way too difficult to climb any sort of slope to reach a point of interest. Realistically need suits to be custom fit and lighter to cover a large distance. After a week, donning the suits became a chore. For a long term mission, this should not be worked out previous to travel.

'''Assumptions made here at MDRS'''

Of course at this stage in preparing for Mars exploration, many assumption have to be made in order to facilitate the simulation. These are the assumptions I have found to have been incorporated into the MDRS simulation related to geology:

* The crew has arrived safely and is healthy and ready to conduct EVAs
* The crew has already identified a geologically stable and safe place to set up their hab
* They have successfully constructed the hab
* They have successfully constructed the GreenHab

'''More realistic approach/suggested improvements'''

The general assessment of local geology is great, however for a real mission a geologist would need to address specifics from three topics: practical, pressing, and popular. This isn't meant to sound catchy, rather these are the issues I expected and would hope to see in future simulations so that the trials and tribulations of going through the studies are ironed out before we actually send someone to Mars.

First, let's look at the practical needs of a Martian crew. Assuming the crew safely lands, a hab must be set up. Is the ground stable? Is the landing site and the region within a practical distance sandy or is there a regolith that may be used for stabilizing the hab? Is the area located on an active fault that possesses a high risk of catastrophic structure failure? Is the region characterized by shifting jointing that would slowly deform the hab? How does one in a space suit go about stabilizing a hab? Currently, the MDRS hab is stabilized by long I-beams drilled into the ground by humans using the conveniences of heavy machinery without being encumbered by spacesuits. It would be useful to determine if a hab can be constructed by people in suits. Perhaps this exercise can be slated for a future and more accurate simulation, but I think it's at least important to characterize the region from a geological engineering perspective.

Once set up for survival on the Martian surface, the crew will need to address some key issues, the most critical of which is how to return to Earth. Can fuel be made as predicted and practiced on Earth? The Mars Society analog research stations should include going through the motions of creating fuel, and reconfiguring a spacecraft for the return flight in a spacesuit.

The popular issues are intended to collect information from Mars that would answer the many questions we have generated here on Earth but are unable to confirm without field investigation. Is the evidence we've used to indicate the previous existence of water on Mars accurate? Have we assumed correctly? Was there water on Mars? Is there currently water on Mars? The polar ice caps are composed of what? Is there a permafrost layer? Can we do the studies necessary to answer these questions in spacesuits?

There are many issues to be addressed prior to going to Mars. I feel the Mars Society analog research stations is an excellent way to prepare ourselves.

===Health & Safety Officer Reports===
Jan Osburg

'''Safety:'''

Nothing to report. The next crew should bring an extra fire extinguisher to be kept next to the generator.

'''Health:'''

Nothing to report. The next crew needs to bring the following supplies to replenish the first aid kit:
{| class="wikitable"
|'''Item'''
|'''Specified Location'''
|'''SpecifiedQuantity'''
|'''ActualQuantity'''
|'''MissingQuantity'''
|-
|Pad, sterile, oval
|EVA Kit
|2
|1
|1
|-
|Wipe, antiseptic/cleansing
|EVA Kit
|10
|8
|2
|-
|Pad, sterile, oval
|Eye Kit
|5
|4
|1
|-
|Bandage, elastic, ACE
|First Aid Kit 2
|1
|1
|-
|Band-Aid, fabric, medium
|First Aid Kit
|10
|5
|5
|-
|Blanket, emergency, Mylar
|First Aid Kit
|2
|0
|2
|-
|Pad, sterile, 8 cm x 8 cm (3x3)
|First Aid Kit
|6
|4
|2
|-
|Splint, finger, wood (tongue depressor)
|First Aid Kit
|3
|2
|1
|-
|Clove oil, 50 ml
|Non-Prescription Meds
|1
|0
|1
|-
|Mylanta DS tabs
|Non-Prescription Meds
|50
|0
|50
|-
|Pepto-Bismol Chewables 262 mg
|Non-Prescription Meds
|50
|0
|50
|-
|Pseudoephedrine 20 mg
|Non-Prescription Meds
|100
|4
|96
|-
|Compazine suppositories 5 mg
|Prescription Meds
|4
|0
|4
|-
|Compazine tablets 10 mg
|Prescription Meds
|10
|0
|10
|-
|Keflex 500 mg
|Prescription Meds
|30
|0
|30
|-
|Band-Aid, small
|Spare Supplies
|10
|5
|5
|}

===Engineering Report===
Jan Osburg

'''Water Systems:''' The inside water tank was refilled for the last time today using the bucket brigade approach. The new crew should bring a new water pump, and a refill of the external water tank will be required sometime next week.

'''Power and Fuel:''' The direct fueling approach works great and is about twice as fast (and twice less spill-prone) than the old gas can approach. Larry replenished the gas barrels today, so the hab's fuel supply should last well into next week. As the generator starter battery was empty, the loose black battery cable was connected to the appropriate terminal (using a binder clip, as no machine screws were found in the hab). The next crew should bring a new funnel to refill the generator oil (the previous one was blown away by the wind).

'''EVA Equipment (including ATVs and PEV):''' Nothing to report.

'''Safety:''' (see "'''Health and Safety Report'''")

'''Computers and Communications:''' Nothing to report. Starband worked fine during the whole rotation. Thanks to the previous crews for fixing it!

'''General Maintenance & Waste Management:''' Things to bring for the next crew:

* Machine screws, various sizes, in sufficient quantities
* Generator oil refill funnel
* Nails, various sizes, in sufficient quantities
* Tyvek suits, assorted sizes, at least 10, for generator and Biolet servicing
* Sturdy rubber gloves (not exam gloves), at least 10 pair, for generator and Biolet serving and general housekeeping chores
* More Platypus ziplok-back water bags
* Platypus water bag drying inserts
* Laminated REI topo maps of the area
* Small wall hooks to put in staterooms and bathroom
* More shelving for staterooms
* Small lights as task lighting in lower floor lab area
* Watering can for the GreenHab
* Good quality (Fluke) general-purpose multimeter
* Soldering iron
* Lightning protection system for weather station pole
* Water pump that can survive running dry
* Rechargeable batteries for radios (with charging station)
* LOTS of AA batteries
* Face masks for simulation of prebreathing (30 min before each EVA)
* 3.5 mm audio extension cord (10 m) to hook up notebooks to stereo
* Audio adapter from 3.5 mm to RCA/cinch standard stereo input jacks
* Flypaper for Biolet room
* Telescope
* Two new chairs (two got broken during our rotation)
* Tool cabinets
* Tool organizers
* Anti-Scorpion traps
* Shade for East upper floor window

'''General suggestions for improvement:'''

* Second Biolet
* A window in every stateroom
* Antistatic carpet on the upper floor
* Smooth-finish working surfaces, especially in the galley area (for hygiene reasons)
* Some filing cabinets on upper floor
* Bigger generator tank
* Ventilation slats in stateroom doors
* Water meter (maybe even with automatic logging)
* Install Adobe Acrobat (PDF writer) on Hab computer
* Get five-client license for Hab computer WinProxy

'''GreenHab:''' (see "Biology" report)

===Crew 5 Profile - Bill Clancey===
By David Real/Belo Interactive

'''Aboard The Mars Desert Research Station, Utah''' - Finding butterflies in the harsh Utah desert seems just as unlikely as finding one on Mars.

But NASA scientist '''William J. Clancey''' says he has collected plenty of butterflies - and that they will help land a human crew on Mars before 2020.

A butterfly - elusive, ephemeral and precious - is the term he uses for scientific data before it becomes scientific theory.

During a two-week stay at the Mars Desert Research Station in Utah, the 49-year-old New Jersey native led a team of six explorers in a setting that simulated, as closely as possible, a scientific colony on the Red Planet.

The crew even donned fabricated spacesuits with bulky gloves and balky radios. Then they tried to navigate using a handheld GPS unit. The Global Positioning System, which uses a network of satellites to pinpoint a position on Earth, usually displays 15 digits on a small screen to mark a location.

How did things go during a simulated space walk on the Martian surface?

"It<nowiki>'s ridiculous,'' Dr. Clancey said. "Manipulating a GPS unit in the field, wearing gloves, is absurd. We can't push the buttons, we can't read the screen, we can't coordinate the map with the units. And why are we dealing with all these numbers? That's what a computer is supposed to do.''</nowiki>

Add another butterfly to the collection.

His solution is to build a mobile exploration system that integrates voice recognition and computer systems with GPS and artificial intelligence programs.

Talk to the computer over the microphone in the spacesuit helmet, and the computer talks back, with directions to the location wanted. When astronauts return to their rooms back at the space Habitat, maps showing the route they took have already been printed by the computer.

Such a problem may seem obvious, but others are not. That's where Dr. Clancey feels he has an edge, using an approach he learned after his formal schooling.

He received his bachelor's degree in 1974 at Rice University in Houston, where he was a roommate with this reporter. He then earned his doctorate from Stanford University in 1979 in computer science, specializing in Artificial Intelligence. He currently works at the NASA Ames Research Center in Mountain View, Calif., and for the University of West Florida in Pensacola.

But he learned a new holistic approach to solving problems when he started a 10-year career in 1987 at the Institute for Research for Learning in Palo Alto, Calif.

The new techniques turned regular problem-solving on its head. Instead of making computes smarter, the task was to study people in the workplace and help them do their jobs - a discipline called cognitive science. It not only drew on computer science, but psychology, neuroscience, anthropology and sociology.

The approach assumes that work is a creative process, which is neither routine nor mechanical, and that the informal, social aspects of work contribute to job success.

In other words, people are the key. Rather than throw computer technology at people, Dr. Clancey said, the researcher lives and works alongside them and involves the workers in designing a solution.

The implication was that traditional ideas about Artificial Intelligence computing and problem-solving were wrong. Computers could beat the world's top chess champions, but only because chess was a game with a fixed set of rules and legal moves.

In most other applications - such as exploration of Mars - the mission changes dynamically, but traditional problem-solving approaches didn't.

"If you've got a bunch of people building computer systems based on a theory of knowledge and memory and learning that is wrong - and putting that into work - they are rigidifying the workflow and how people solve problems," Dr. Clancey said. "They're preventing the work from getting done."

To solve problems that crop up at the Habitat, run by the Mars Society, Dr. Clancey is observing scientists who are working under simulated conditions that future astronauts may face on Mars.

"I'm studying the Hab, its layout, what people do, where they do it, and when they do it," Dr. Clancey said. "We're dealing with the total system."

He used time-lapse photography to record the movements of the crew on the main floor of the Hab from 7:30 a.m. to 11:30 p.m. daily. He also manually documented the activities of each crew member every 15 minutes for two days.

The goal? Find more butterflies that could reveal future problems and solve them on Earth before astronauts face them on Mars.

When NASA turns its attention from the International Space Station, which should be completed in 2005, a mission to Mars could be the next major project for the space agency, Dr. Clancey said.

"It's the closest planet to us, and one where we can walk on the surface and we can build houses and we can live," he said. "Mars has areas that look like there were seas. It has water. It has ice.

"And it might have had life. It might still have life."

With a national commitment, explorers could be on the surface of Mars within 10 years, he said.

The effort would require great strides in scientific hardware - some of which has not yet invented.

Dr. Clancey said the situation is similar to that faced by President John F. Kennedy when he challenged America to reach the Moon by the end of the decade, saying that the effort would rely on "using materials not yet developed."

Those materials were ready in time for the Apollo 11 to land on the Moon in 1969.

"That's the way we look at Mars," Dr. Clancey said. "That we will be using materials, using an understanding of gravity and human physiology, methods of automating life-support systems, and exploration - not yet developed. But we have confidence that we have the pieces and can put it together."

===Crew 5 Open House===
'''Welcome to the MDRS5 open house!''' We are pleased to show you the MDRS Habitat ("hab") and answer your questions.

We are the fifth crew to occupy the hab during this first field season. Data on our rotation can be found at the following locations:

* [[Crew 5 - Crew Bio|Crew 5 Biographies]]
* [https://www.marssociety.org/ Mars Society Home Page]
* [https://mdrs.marssociety.org/ Mars Desert Research Station]
* [https://web.archive.org/web/20051228125750/http://bill.clancey.name/ Further Information about Mars Analog Research]

Please note that we have a closed biological toilet designed for 6 people or fewer. It is at capacity and can only be used by visitors for emergencies. (The toilet has a urination funnel that operates on a separate septic system and is available.)
{| class="wikitable"
| colspan="2" |'''Schedule'''
|-
|900-1100
|ARD TV (Christine Schiffner): hosts Bill & Jan, then David at 1100
|-
|1000-1100
|TechTV (Bob Hirschfield): Bill & Andrea, Andrea
|-
|1100-Noon
|RTL TV (Ralf Hoogestraat): Bill & Jan, Vladimir
|-
|Noon
|Der Spiegel (Marco Evers): Bill & Jan, Nancy
|-
| colspan="2" |'''Lunch Break'''
|-
|1300-open
|Video Tour (hab, donning suit, ATV): Bill, Vladimir
|-
|1400-1500
|Fox-10 TV (Miguel Marquez): Bill & Nancy, David
|-
|1430-1500
|FACTS (Rainer Klose): Jan, Andrea at 1500
|-
|1500-1530
|Dågbladet Daily (Orjan Ellingvag): Bill, Nancy at 1530
|-
|1530-1600
|Sunday Telegraph of London (Charles Laurence): Bill
|}
Facts about rotation #5:

# '''This was a closed simulation, isolated from other people, as on Mars:'''
#* No conversations are possible with Earth, only email (with 5-20 min delay)
#* All mission-related messages were mediated by mission support
#* Mission support was provided by the Northern California Chapter of The Mars Society
#* Fuel and water were resupplied by a paid contractor in Hanksville, UT
# '''The team was chosen to cover basic research activities at MDRS:'''
#* '''Bill Clancey''' - Computer Science, Cognitive Science
#* '''Andrea Fori''' - Geology
#* '''Jan Osburg''' -Engineering, Health, and Safety
#* '''Vladimir Pletser''' - Geophysics, Horticulture
#* '''David Real''' - Web Journalism
#* '''Nancy Wood''' - Biology
# '''Research Themes'''
#* Expedition Memory: Can a geologist understand the work performed by previous rotations and build on it to develop a simple geology primer of the region?
#* What is the effect of chores (life support maintenance) on science productivity?
#* How does maintaining a greenhouse affect a scientific expedition?
#* How do plans develop and change during the mission?
#* How can the methods of waypoint marking and route planning & finding be automated?
#* How can Earth's "mission support" understand and assist Mars surface exploration, given the distance and time delay?
#* What is the extent of exploration possible by different modes of travel (foot, ATV)?
#* How is public and private space used? How can the hab's layout be improved?
#* How do individual and group activities interact? How should a long-duration mission (3 years) be scheduled?
#* If there is life on Mars, how do you take a sample that has it?
# '''Human Factors Data Collection Methods'''
#* Ethnography by Participant Observation (studying practices by being a member of the group)
#* Time Lapse Video of the upper deck throughout the rotation
#* Video recording of all planning meetings
#* Logging where everyone is and what they are doing every 15 minutes (two consecutive days)
#* Log of water use per day
#* Personal logs of time devoted to chores/maintenance and reporting
#* Complete records of all email with mission support
#* Written daily and mission plans revised daily
#* Post-rotation surveys
# '''Special Experiment for Time-delayed Mission Support'''
#* We simulated a multiple-failure situation: becoming lost during an EVA (human error), a stuck zipper (mechanical failure), wind and heat (environment condition), and radio problems (system design).
#* Audio recordings of communications between remote teams and the habitat were transmitted to mission support with five-minute delay
#* Mission support attempted to follow along ("situational awareness") and provide advice via email.
#* Early analysis indicates that a five-minute delay in a fast-changing situation makes active participation by mission support difficult.

User:Sdubois

2020-03-17T00:22:39Z

Sdubois: /* Other pages to which Stefan has contributed */

[[File:Stefan.JPG|thumb|upright=0.6]]Stefan DuBois began to take a serious interest in space exploration after a combination of witnessing the 2017 solar eclipse as well as the maiden flight of the Falcon Heavy shortly thereafter. He believes that colonizing Mars will be crucial to ensuring mankind's survival as a species, and is excited to use his abilities in whatever small way he can to help make that happen. Stefan holds a Ph.D. in Iberian Linguistics from UC Santa Barbara and volunteers for the Mars Society as part of the Marspedia editorial subcommittee. If you would like to get in touch with him, feel free to reach out at sdubois0@gmail.com.

==Original articles authored by Stefan==

*[[Carbon Dioxide Scrubbers]]
*[[Helicopters]]
*[[Hohmann transfer]]
*[[Observing Mars with a Telescope]]
*[[Telling Time on Mars]]

==Other pages to which Stefan has contributed==

*[[Wind turbine]]
*[[Crew 1a and 1b]]
*[[Crew 2]]
*[[Crew 3]]
*[[Crew 4]]
*[[Crew 5]]
*[[Crew 6]]
*[[The Curious Case for Methane on Mars: Methane and Active Organics Discovered on Mars]]

Crew 1a and 1b

2020-03-17T00:22:33Z

Sdubois: Created page with "Crew 1 of the Mars Desert Research Station ran from February 7 - 20, 2002. The following information is available on this crew: *Crew 1a - Crew Bio *Crew 1a - Crew Repo..."

Crew 1 of the Mars Desert Research Station ran from February 7 - 20, 2002. The following information is available on this crew:

*[[Crew 1a - Crew Bio]]
*[[Crew 1a - Crew Reports]]
*[[Crew 1b - Crew Reports]]

[[Category: MDRS Crews]]
[[Category: Mars Desert Research Station]]

User:Sdubois

2020-03-17T00:17:06Z

Sdubois: /* Other pages to which Stefan has contributed */

[[File:Stefan.JPG|thumb|upright=0.6]]Stefan DuBois began to take a serious interest in space exploration after a combination of witnessing the 2017 solar eclipse as well as the maiden flight of the Falcon Heavy shortly thereafter. He believes that colonizing Mars will be crucial to ensuring mankind's survival as a species, and is excited to use his abilities in whatever small way he can to help make that happen. Stefan holds a Ph.D. in Iberian Linguistics from UC Santa Barbara and volunteers for the Mars Society as part of the Marspedia editorial subcommittee. If you would like to get in touch with him, feel free to reach out at sdubois0@gmail.com.

==Original articles authored by Stefan==

*[[Carbon Dioxide Scrubbers]]
*[[Helicopters]]
*[[Hohmann transfer]]
*[[Observing Mars with a Telescope]]
*[[Telling Time on Mars]]

==Other pages to which Stefan has contributed==

*[[Wind turbine]]
*[[Crew 1]]
*[[Crew 2]]
*[[Crew 3]]
*[[Crew 4]]
*[[Crew 5]]
*[[Crew 6]]
*[[The Curious Case for Methane on Mars: Methane and Active Organics Discovered on Mars]]

Crew 1a - Crew Bio

2020-03-17T00:12:26Z

Sdubois:

==Robert Zubrin==
===Speciality===
Commander Phase A - Astronautical Engineering

==Tony Muscatello==
[[File:TonyMuscatello.jpg|thumb]]
===Speciality===
Commander Phase B - Chemistry
===Bio===
Tony Muscatello wears many hats in the Society. Besides serving as the Mission Support Director, he also contributes to crew training. Tony is a research chemist working at Pioneer Astronautics in Lakewood, Colorado on in-situ resource utilization (ISRU), especially the production of fuels and oxygen from the martian atmosphere and soils. Tony is a founding member of the Mars Society and treasurer of the Rocky Mountain Mars Society.

==Heather Chluda==
===Speciality===
Aeronautical Engineering

==Jennifer Heldmann==
===Speciality===
Geologist

==Steve McDaniel==
[[File:SteveMcDaniel.jpg|thumb]]
===Speciality===
Biologist
===Bio===
C. Steven McDaniel received his Bachelor of Science degree in Biology from the University of Texas in 1974, a Master of Science degree in Genetics from Texas A & M University in 1976, and his Ph.D. in Biochemistry from Texas A & M University in 1985.Dr. McDaniel obtained his Doctor of Jurisprudence degree from the University of Houston in 1991.

Since receiving his JD, Dr. McDaniel has specialized in intellectual property litigation.Dr. McDaniel is admitted to practice before the United States Patent and Trademark Office, the Court of Appeals for the Federal Circuit, the Fifth Circuit Court of Appeals, the Southern, Western, Eastern and Northern Federal District Courts of Texas and the Texas State Courts.His trial experience includes cases tried in Federal Courts in the Southern District of New York, Eastern District of Pennsylvania, Western and Eastern Districts of Texas, and several cases in the Southern District of Texas, and Texas State District Courts.He has also litigated before the U.S. Patent Office Board of Patent Appeals and Interferences.

Dr. McDaniel's areas of technical expertise includes organic chemistry, biochemistry and molecular biology. He has authored technical papers published in such scientific journals as the Journal of Bacteriology, Maize Genetics Newsletter, The Journal Of Protein Chemistry, Genetics, And In Vitro.Dr. McDaniel has extensive experience in procuring patents in his technical area before both U.S. and foreign patent offices.Since beginning his practice as a patent agent in 1989, Dr. McDaniel has procured patents for the Texas Heart Institute, Aronex Pharmaceuticals, Inc., Ceres Technologies, Inc., California Institute of Technology/Jet Propulsion Laboratory, Sulzer Medica, Inc., Intermedics Orthopedics, Baylor College of Medicine, Rice University and NASA-JSC, among others.

Dr. McDaniel is the Managing Partner in Reactive Surfaces, Ltd., a biotechnology company he founded to commercialize enzymatic additives to surface coatings such as paints.The company isolates useful exo-enzymes that can be formulated into additives useful in detoxifying nerve agents and pesticides.

==Frank Schubert==
[[File:FrankSchubert.jpg|thumb]]
===Speciality===
Architect & Lead Guitar
===Bio===
Frank Schubert is an architect and builder from Denver, Colorado. Frank has been involved in the construction of the Flashline Station and the Mars Desert Station. He is also the principal architect and builder of the Euro Mars Research Station. Frank has lived in Denver for the last 12 years. Before that he lived in Los Angles where he worked as a musician.

==Troy Wegman==
===Speciality===
Biologist

==Andy de Wet==
===Speciality===
Geologist
===Bio===
Andy de Wet is an Associate Professor of Geosciences at Franklin & Marshall College in Lancaster, PA. He received a BSc with Honors in Geology from the University of Natal in Durban, South Africa and a PhD in Geology from the University of Cambridge, England. He is interested in the geological evolution of Mars and how geologists will be able to conduct field work on the surface of Mars. He teaches a course called "Life on Mars?" which compares the geological evolution of Earth and Mars and explores the possibility that life evolved there.
[[Category:MDRS Crew Bios]]
[[Category:Mars Desert Research Station]]