Talk:Experimental setup

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Experimental setup assumptions for greenhouse heating

The assumptions for the experiment are not best related to what is needed for an economic greenhouse on Mars. Plants do not need 20 C constantly to survive and produce a crop. If they go down to 2 C many plants just slow down. In my household garden I did not worry about plants dying unless there was a frost. Since some plants can grow at 12000 feet altitude, they should be able to get by with only 63% of atmospheric pressure. People can operate at a little less than one half an atmosphere on the side of Mount Everest if they have oxygen enrichment, but no plants or animals live at 0.15psi pressure as found on Mars. Heating from sunlight is exactly what would be needed for an economical greenhouse on Mars. There should be flat windows level with the ground for a soil sheltered Martian greenhouse. The windows should be triple or quadruple paned glass for good insulation. About 8 feet wide and 400 foot long windows of multiple 8 inch square panes in a steel frame could hold the pressure and allow considerable heating by real greenhouse effect (as opposed to the atmospheric heating of planets that is only similar to the heating in greenhouses). Numerous windows with the corresponding greenhouses beneath them could be separated by enough space for long flat mirrors to direct a double dose of sunlight into one greenhouse row without shading the next if that is found to be necessary. I suspect that instead there will be a need for radiators to provide sufficient cooling.
At 0.63 atmospheres pressure, there would be 39 tons of upward force on each 8 foot square section of greenhouse roof. That could be reasonably anchored to the dirt with structural steel. Plants are very adaptable and could be bred to get along with less intense than usual Earth level sunlight, as indeed many plants on Earth now are adapted to growing in shady areas. Growing food would be more expensive on Mars than on Earth, at least at first, but if there is an economic product on Mars that can pay for the greenhouses, they are not impossible.--Farred 01:56, 30 November 2009 (UTC)
My intention is to reduce the experimental setup effort by defining a constant temperature, only for the experiment. Yes, you are right, the real greenhouse temperature will not be constant due to the fact that plants live in cycles as much as almost every living thing is. Plants can, however, not transform light energy to chemical energy at low temperatures very efficiently. We have to find an optimum, because light energy is a valuable resource on Mars. So it won't help us to slow down the metabolism of the plants. -- Rfc 19:43, 1 December 2009 (UTC)
My idea for a greenhouse on Mars would be to have it heated by sunlight and the greenhouse effect. This should have the window roof of the greenhouse covered at night perhaps with the mirror and thermal insulating cover sharing structure. At window uncovering in the morning, there would still be too little light to maintain the greenhouse temperature, but plant growth and metabolism could still occur as the temperature slowly drops. As the sun gets higher in the sky, the greenhouse is heated again by sunlight. The temperature does not remain constant but within a range in which plants grow with reasonable efficiency. Making a mathematical model of such a greenhouse would be a daunting project for me. I still have other unfinished projects to get to. My guess would be that direct solar heating would be the most economical form of heating.
Occasionally dust storms on Mars last for months. Farming on Mars like farming on Earth may have to put up with some crop losses. Predicting these storms in advance would be an advantage.
I have heard rumors that plants can survive greater radiation doses than people. Four panes of glass would not stop enough radiation for a human living space but plants might thrive.
Agriculture on Mars should be mechanized much as it is mechanized in the United States, or more so. A 1000 acre wheat farm is typical in the United states. I can only guess at the number of employees on such a farm. I guess 4. As to the number of employees for a Martian greenhouse, the number of employees per acre on a wheat farm should be a more reasonable target than the number of employees per acre in the typical Earthly greenhouse. The initial construction of a highly automated set of greenhouses would be a considerable task.--Farred 09:08, 4 December 2009 (UTC) changed (much it is) to (much as it is) --Farred 23:52, 14 July 2010 (UTC)
Sounds good, may be too good. I really like the idea of a passive greenhouse, for it would save huge amounts of energy. Problem is, glass reflects a substantial part of the incoming sunlight, especially from the infrared. Additionally, the Martian sunlight is not as powerful as the terrestrial sunlight. You seem to be quite sure about the idea. Can you give calculation or other evidence about the viability of such a passive greenhouse? -- Rfc 20:43, 7 December 2009 (UTC)
I would like to give you numbers to substantiate my claim that greenhouse agriculture is possible on Mars, and awaits only the solution of economic problems to become a reality. First, it is not necessary to have the full intensity of sunlight that exists at the position of Earth's orbit to sustain agriculture. Edmonton Canada at 53.5 degrees north latitude is in the center of a rich agricultural region. Because the sun never gets more than 60 degrees above the horizon during the middle of summer, the area never gets more than 87% of the sun intensity that occurs when the sun is at zenith. Iceland which is all north of the 63 degree latitude never gets more than 77% of the direct overhead solar intensity, but still grows adequate grass for sheep, potatoes, and in greenhouses other vegetables.
The mirrors that I suggest for Mars for increasing the incident sunlight on the greenhouse roof would not be what I would call passive. Mechanisms would need to move them to track the sun during the day and to cover the greenhouse roof at night. Accurate modeling would be needed to discover with reasonable certainty whether such mirrors are needed or not. Flat mirrors should be able to about double the light intensity on the greenhouse, giving more intense sunlight than at either Edmonton or Iceland. So, if greenhouses can work for growing vegetables in Iceland, they should work on Mars. The reflection of light from a glass/gas surface is about 4%. This varies as the angle increases from normal. About 70% of the light should get through a quadruple pane greenhouse roof. This should be sufficient. The reflection of infrared is actually an advantage, because it helps to keep heat in the greenhouse. Accurate modeling should indicate whether triple or quadruple pane windows are needed. If the need for augmenting the ordinary sunlight on Mars is more than I suspect, there is also the possibility of a slight cylindrical curvature in the mirrors that direct sunlight into the greenhouse, concentrating it. All that stands between us and agriculture on Mars is money and engineering.--Farred 17:21, 14 January 2010 (UTC) (small change) --Farred 23:36, 14 July 2010 (UTC)

Just a thought: How does water condensation on the inside of the greenhouse affect heat and light from sunlight? Also consider effects of dripping condensation on materials framing the glass. Miros1 06:16, 18 June 2012 (UTC)

Condensation dripping off the inside of a greenhous roof is something to be avoided. It can be avoided by having sufficiently insullating glass (as referred to above as "triple or quadruple pane windows"), dry gas moving between pane layers, and sufficiently dry air in the greenhouse. There is a required humidity for plant health, so there is a minimum temperature allowable for the inside surface of the windows. - Farred 12:58, 18 June 2012 (UTC)