Mars Direct

Mars Direct is a sustained humans-to-Mars plan developed by Dr. Robert Zubrin that advocates a minimalist, live-off-the-land approach to exploring the planet Mars, allowing for maximum results with minimum investment. Using existing launch technology and making use of the Martian atmosphere to generate rocket fuel, extracting water from the Martian soil and eventually using the abundant mineral resources of the Red Planet for construction purposes, the plan drastically lowers the amount of material which must be launched from Earth to Mars, thus sidestepping the primary stumbling block to space exploration and rapidly accelerating the timetable for human exploration of the solar system.

History of Development

In 1989 President George Bush called on NASA to take men to Mars. NASA made a plan that was "ambitious" which called for tripling the size of the space station (with giant hangers for in orbit construction), building a massive moon base, using lunar materials to build a giant space craft (>1,000 tonnes mass). This space craft would have nuclear engines which were not designed yet, (and not the ones used to go to the Moon). This craft would spend 18 months traveling to and from Mars, would allow 1 month on Mars for exploration, just enough time to plant flags and footsteps on the planet, before returning home. This was named the 90-Day Study on Human Exploration of the Moon and Mars," which came to be called the "90-Day Report".

It was estimated that this would cost more than $450 billion dollars, which would make it the most expensive project since World War II. Congress balked, and zeroed out all expenditures for this project.

People speculated that this project was not designed to get to Mars cheaply and efficiently, but rather satisfy every department in NASA. Those that wanted to go to the moon got a Moon base. Those that wanted to work on nuclear engines go that. Those that wanted a in orbit construction and expansion of their space station got their dream. Rather than making a low cost, efficient mission plan, it was designed to make the careers of people in the aerospace industry.

Robert Zubrin, working at the time at Martin Marietta felt that the plan was incoherent and got permission of his managers to build a cheaper, more practical plan. Zubrin and another engineer David Baker worked on the Mars Direct plan, which would use local resources to create the fuel to return home, (greatly reducing the amount of mass to be sent to Mars).

That year, Jim French published an idea in the Journal of the British Interplanetary Society suggesting that a fuel manufacturing plant be sent to Mars first. However, the crewed space craft had to land within hose length of this factory, which was deemed too dangerous. Zubrin came up with the idea of launching the return vehicle plus the fuel plant ahead of time. If the crew could land within rover distance of the return vehicle (say 1000 km or closer), they could return. Even better, they would have a fully refuelled return vehicle waiting for them before they left Earth.

Baker suggested the name for this new mission plan: "Mars Direct".

The same government office that priced the 90 day report at $450B priced the Mars Direct plan and found it would likely cost $55B, 1/8 the cost.

At NASA the idea met with mixed enthusiasm. Some loved the idea of a practical Mars Mission, others were unhappy that it 'dejustified' their pet projects. However, over time, Mars Direct came to shape NASA's Mars plans.

Overview of Mission Architecture

The general outline of Mars Direct is simple. In the first year of implementation, an Earth Return Vehicle (ERV) is launched to Mars, arriving six months later. Upon landing on the surface, a rover is deployed that contains the nuclear reactors necessary to generate rocket fuel for the return trip. After 13 months, a fully-fueled ERV will be sitting on the surface of Mars.

During the next launch window, 26 months after the ERV was launched, two more craft are sent up: a second ERV and a habitat module (hab), the astronauts’ ship. This time the ERV is sent on a low-power trajectory, designed to arrive at Mars in eight months – so that it can land at the same site as the hab if the first ERV experiences any problems. Assuming that the first ERV works as planned, the second ERV is landed at a different site, thus opening up another area of Mars for exploration by the next crew.

After a year and a half on the Martian surface, the first crew returns to Earth, leaving behind the hab, the rovers associated with it and any ongoing experiments conducted there. They land on Earth six months later to a hero’s welcome, with the next ERV/hab already on course for the Red Planet. With two launches during each launch window – one ERV and one hab – more and more of Mars will be opened to human exploration. Eventually multiple habs can be sent to the same site and linked together, allowing for the beginning of a permanent human settlement on the planet Mars.

Radiation Dosage

Radiation does damage to living cells. Prompt doses (which happen in a short time) are more dangerous than chronic doses which occur over a long time. (Chronic doses give the body time to repair the damage, where as a prompt dose overwhelms the cellular repair.)

Radiation damage to living beings is measured in Sieverts or rem. (1 Sv = 100 rem.) See Radiation for more information.

A prompt dose of 1 Sv might cause radiation sickness (some people won't notice anything). 2 Sv will cause radiation sickness in everyone. At 3 Sv a prompt dose might cause death. At 5 Sv most people will die, unless they get care in a hospital. Above 8 Sv, almost everyone will die, even with the best medical care.

In addition to short term effects, moderate doses of radiation cause long term health effects, which lower the maximum age you can reach (mostly from cancer). The authoritative report: Biological Effects of Ionizing Radiation (BEIR) found that 0.1 Sv of radiation will cause a 1.8% chance of a fatal cancer within 30 years. Now an average person has a 20% chance of dying of a fatal cancer, so if our Mars mission would get a total radiation dose of 50 mSv, then the chance of the astronaut getting a cancer rises from ~20% to 21%.

Radiation Dose from Mars Direct Mission Plan

The most dangerous radiation on a Mars Mission will be from Solar Flares. The worst solar flares in history were in February 1956, November 1960, and August 1970. For the discussion below, we will assume that the average radiation from these three flares happens once per year during our Mars mission. (So the actual doses will likely be lower.)

If one of these flares occurred during the flight from or to Mars, the crew would get 380 mSv in the space craft. But if they have a radiation storm shelter which they go into for the 2 to 7 hour solar storm they would take 80 mSv. On Mars the thin atmosphere stops most lower energy particles so in such a solar storm they would take 100 mSv if they were outside the Habitat Module, or 30 mSv if they were inside the Hab. (Or no extra radiation if the solar storm happened at night.) If sandbags were placed on top of the Hab, this dose could be reduced a bit more.

The other form of radiation is Cosmic Rays. This is a steady drizzle of radiation with such high energies that they can't be shielded against, so you just endure them. They come from all directions of the sky. But if you are on a planet, half the cosmic rays are shielded by the planet itself.

The Mars Direct plan is a conjunction type mission, where they spend 6.5 months going to Mars, 6.5 months returning to Earth, and a stay on the planet for 16 months. (An opposition type mission spends less time in space, requiring a Venus fly by. But it is worse plan, since the crew only has 1 month to explore Mars.)

Radiation On A Mars Mission

Mission Section	Conjunction Mission	Opposition Mission
Cosmic Rays in Transit	318 mSv	47.7 mSv
Solar Radiation in Transit	55 mSv	96 mSv
Cosmic Rays on Mars	106 mSv	8 mSv
Solar Radiation on Mars	41 mSv	3 mSv
Mission Total	520 mSv	584 mSv

So we would expect 0.52 Sv for the entire mission. This is less than several cosmonauts have experienced on the Mir space station, and there are no reported radiation effects. See Long Duration Space Flight.

Zero Gravity on Mars Direct Mission

There are many documented health problems which arise from people spending long periods of time in zero gravity, so this mission avoids them by providing spin gravity on the way to and from Mars.

When leaving Earth, the upper stage booster is normally thrown away. On this mission, it is kept, and placed on the end of a long cable. The space craft and upper stage are spun, to provide gravity. At the end of the mission, the cable is cut before the space craft is landed on Mars, so there is no long duration period of zero gee.

The faster the system is spun the higher the gravity provided. For most of the trip, people could be at one Earth gravity, but for a month before landing this could be reduced to Mars' 0.38 gee to accustom the crew to Martian conditions. On the trip home, the gravity should be set at 1 gee for the whole trip.

Landing area

What is the best landing site? A good answer to this question is the southern plains of Lunae Planum just north of Ophir Chasma (on the equator at 65° long W.). This places the base at an average elevation (between 6 and 7 km) and within a couple of thousand km’s of most of the scientifically interesting sites on Mars.

Advantages of This Mission

There are several advantages which include:

• By creating fuel on Mars with hydrogen brought from Earth, much less mass needs to be shipped to Mars, greatly reducing launch mass (and therefore cost). This hydrogen can be shipped in the form of liquid hydrogen, or benzene. (The latter brings more hydrogen in a space storable form, but requires more complex chemistry to create the rocket fuel.)
• By using a direct launch to Mars, risk is reduced since two separate launches to not have to be mated together with an orbital rendezvous. Certainly dozens or hundreds of launches are not required to build a huge space craft. This reduces expense and increases safety.
• By making methane / oxygen fuel on Mars, plenty of fuel can be made for the rovers, which allow a great range in exploring interesting sites hundreds of kilometres away from the base. This greatly improves the value of the mission.
• A nuclear power plant on the planet means that the mission will be energy rich, allowing high density data transmission back to Earth, and plentiful energy for science and life-support. This increases safety, and the value of the time spent on Mars.
• A high energy mission can melt water out of permafrost and experiment with industrial processes, which improves the value of the mission.
• The conjunction class mission, reduces the amount of radiation exposure compared to the opposition class mission (which does a swing by past Venus). 550 days on Mars rather than only 30 days. 360 days in space rather than 610 days. The opposition mission also swings past Venus, so the solar radiation will be more intense.
• The conjunction class mission, increases the amount of time spent on Mars, allowing more exploration and science to be done.
• A radiation storm shelter will be provided to provide safety from a massive solar flare, if the crew is unlucky enough to experience one during the mission.
• The third stage booster will be kept, and attached via a long line. The habitat (hab) and the third stage will be swung around this tether to provide Mars' gravity while traveling in space, to completely avoid a weightless environment. This improves safety.
• By choosing a travel time to Mars (about 6.5 months), the crew is on a 'free return' trajectory where if they choose NOT to land on Mars, they return to Earth exactly 2 years after launch. This means that the Earth will be there, when they arrive back at Earth's orbit. This increases safety, if for some reason they have to abort the landing.
• The second Earth Return Vehicle (ERV) is launched on a slower trajectory, so if the crew can not land within 1,000 km of their own ERV, the second one can land beside them, with the pilot on Mars directing it down. This improves safety.
• A fully fuelled ERV is waiting for the crew before they launch. This improves safety.
• Enough food and supplies are brought to last the full crew for more than 26 months past their normal return time. If for some reason they can not return, they can survive long enough to allow another mission to be sent to rescue them. This improves safety.
• Sandbags can be filled with soil to increase radiation protection by putting sand bags on the roof of their habitat (hab). If locally sourced water can be found, water (which is an excellent neutron absorber), can also be used. (By using local materials for radiation protection, the cost of the mission is reduced. (Tho for a 1.4 year stay on the surface, the amount of radiation is not a critical problem without this step.)

Robert Zubrin discusses the advantages of such a mission in some detail in his book, "The Case For Mars", IBSN 9-781451-68113.

Variations of this plan

There have been several variations of this plan.

• NASA created a 'Mars Semi-direct' mission with 6 crew which was based on ideas of Mars direct.
• Robert Zubrin created a version using Falcon Heavy boosters (for supplies) and a Falcon 9 booster (man rated) for a 2 person exploration team.
• A Moon Direct mission was proposed by Zubrin, as a lower cost way of exploring Luna.