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#21
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Technologies for Moon mission useable for missions further out
Michael Turner wrote:
"Someone last year grew some plant in a Moon regolith imitation. It isn't the most fertile soil but you can grow stuff in it." In the sense of providing support for roots and holding moisture, perhaps. However, there seem to be qualitative differences between lunar regolith simulant and real lunar regolith, none of them good: http://www.lpi.usra.edu/decadal/leag/DavidJLoftus.pdf http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2193.pdf To a reasonable first approximation, this stuff is nanometric silicon oxide, subject to meteoritic and space-radiation processes that leave the dust particles with lots more sharp edges -- at least when compared to their terrestrial semi-analogues like official NASA lunar regolith simulant. Nasty stuff you wouldn't want accumulating in your lungs or wending its way through your GI tract. I wouldn't think that you would grow food in the regolith. For food crops you use fertile soil. You grow plants selected for good growth in regolith, grow them, harvest them and send them for the methane digester. You would probably add a little fertilizer to the regolith to accelerate the process but not much, the idea is to transform the regolith into soil for food crops. This situation might argue for making your own dirt, by grinding up rocks with less hazardous material and chemical properties. Grinding up rocks to make soil? A waste of energy? Perhaps not. Maybe it would just be a by-product of the sort of machining that would fall right out of tunneling, and in general out of developing underground habitat. Lava tubes are, of course, made by volcanic lava flows. Volcanic processes produce rich soil on Earth. (The biggest carrot I ever saw was at a market in the Aso-san caldera on Kyushu in Japan.) Perhaps the Moon and Mars are much the same in this respect, they've just never had plants taking any advantage of it. That makes sense to me. Even if you are growing non edible plants solely fore the methane digester, avoiding those nasty sharp edges is a plus. Alain Fournier |
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Technologies for Moon mission useable for missions further out
In article ,
Michael Turner writes: To repeat: greenhouses on the Martian surface will get exactly one benefit from being on the surface: direct daytime pass-through of sunlight at frequencies useful for photosynthesis. That's IT. That seems to be quite a significant advantage, not a minor one. How do you propose to illuminate your greenhouses if not by direct sunlight? You need either something like 10 MW/hectare if you do it with efficient electric lighting or a collector on the surface at least as big in area as your greenhouse plus at least a square meter of light pipe per hectare if you do it that way. Heat loss of a surface greenhouse won't be trivial, but it's only about 30 kW/hectare even if the greenhouse is a perfect emitter. Probably a factor of 10 improvement is possible by using low-e coatings, depending on how much trouble it is to keep dust off them. -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#23
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Technologies for Moon mission useable for missions further out
Rebooting this discussion:
Let me suggest that the question be turned on its head: given the likelihood that survival modes on both the Moon and Mars would be very similar, what technologies would be location-unique? I think these technologies will mostly be resource-determined, but with some exceptions. Would you consider "proximity to the Earth" a "resource"? Well, in a way: close proximity opens up much vaster *human* resources. Certain operations might be practical to teleoperate from Earth, in the case of the Moon, that would definitely NOT be candidates for terrestrial teleoperation in the case of Mars. However, in general, by "resource", assume that I mean immediately available minerals, gases, energy sources, etc. Examples: Mars lacks: - strong sunlight - high daytime temperatures The Moon is significantly lacking in: - carbon (CO2 is most of Mars' atmosphere) - nitrogen (N2 is around 3% of Mars' atmosphere) Both are problematic for water supply, but Mars has ice caps, at least. The Moon? Over the long run, the cheapest place from which to fetch water for a lunar base might actually end up being Phobos, of all places, via the Interplanetary Transport Network. (That is, IF Phobos' carbonaceous chondrite content is confirmed, and IF it's the right H2O-rich type of carbonaceous chondrite.) Actually, mining and shipping from Phobos might be an area of technology overlap: useful in the long term for a Moon base, for supplying water and other volatiles and minerals that are trace on the Moon; but also useful to reduce short-term costs of Mars base set-up, until Mars surface ISRU can get into full gear. Mars might still be volcanically active: http://www.space.com/scienceastronom...sm_041222.html The Moon? Decidedly dead in this respect. So on Mars, you might use geothermal sources of energy, conveniently continuous and proximate to lava tube habitats, instead of two-week solar heat buffers as you would on the Moon. If you lucked into a superabundance of heat from geothermal, even if it's low grade heat, the Mars surface greenhouse idea starts to make sense again, because keeping it warm through nights and winters wouldn't cost so much. And so on. Think in terms of what's likely to be *relatively* cheap at one destination vs. another. Work out locale-specific solutions. Everything else is likely to be the same, or at least very similar. Some of it is necessarily speculative -- e.g., we don't know the composition of Phobos yet, and we don't know if there's significant, accessible, near-surface geothermal on Mars. Still, you don't have to shackle yourself to any single set of assumptions, and there might be lots of different locale-specific ways of doing things. -michael turner On Jun 10, 8:36 am, Alain Fournier wrote: Let's assume a new program for lunar missions is started. Let's also assume it is posited as Bush had did it, saying we are going to the Moon, and should go to more distant places after. What technologies could be developed for a Moon mission that would be useful for a Mars mission and/or a mission to the asteroids? Or another way to say this, what technologies that would be needed for going to asteroids or to Mars would be useful to have for Moon missions, even if the technology might not be worth the trouble to develop solely for lunar missions? For example, a few weeks ago, Fred J. McCall was proposing to use a cycler for missions to the Moon. A lunar cycler that would have been developed solely for lunar missions would not be of much use for going to Mars. But if you know that you are later going to Mars, then you can put some extras on the lunar cycler, such as having a garden where crops are grown and a solar storm shelter. Those would be valuable experiences in preparing for a Martian or asteroidal mission. It probably is not worth the trouble to do so if you are only going to the Moon. But if you are going to develop the technology anyway for Martian missions, might as well integrate them in the lunar mission. Another example might be an orbital fuel depot. The purpose of my question is to try to find the best way to return to the Moon and avoid it being Apollo redux. To make the next "small step for a man", a step towards God knows where. Alain Fournier |
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Technologies for Moon mission useable for missions further out
Alain, I think you need to look at the actual scientific literature on
surface greenhouse designs for Mars. Loss of greenhouse heat through radiation is Problem #1, during the night, and even during the day when it's winter on Mars. All the other problems I mention are still big problems, but they are nothing compared to radiative heat losses. From what I can tell, although they don't come right out and say so, NASA has abandoned research on Mars greenhouses precisely because nobody has a solution to this radiative heat-loss problem (except perhaps the Zubrinistas, who would tell you to take along a nuclear power plant). If you want the benefits of direct pass-through of sunlight into a surface greenhouse, you have to recognize that it's a two-way street, with infrared going in the opposite direction. The calculations show it's not worth it. NASA won't tell you this because their pictorial propaganda strategy for Mars missions is still stuck in the von Braun era. But I think if you revived von Braun and briefed him on what we now know about Mars, he'd be scratching his head over those rosy Mars surface base "artist conceptions" that are still circulating. Getting rid of waste heat from habitat won't be the problem on Mars that it was for ISS and spacecraft in general. Heat *retention* will be the problem. Low levels of sunlight, conduction into bedrock, convection via a surrounding atmosphere -- ISS enjoys none of these benefits for purposes of heat rejection. Even being in low-Earth orbit exposes ISS to infrared heat flux from the Earth's surface far in excess of what the Mars landscape typically generates. Though Mars conditions would be "features" for ISS thermal management if you could miraculously supply them in controllable moderation at ISS, all of them actually turn into serious heat-loss problems when you get to Mars. (Long before that point, actually, when designing for the lunar night -- to tie this back to the subject line.) -michael turner On Jun 21, 7:48 pm, Alain Fournier wrote: Michael Turner wrote: On Jun 18, 12:14 pm, Alain Fournier wrote: "I'm not sure exactly how one would pressurize such lava tubes." I have not proposed pressurizing lava tubes. I was addressing an apparent concern of yours: whether they had enough volume for agriculture. Well, yes at first you do have enough volume in the lava tubes for agriculture. But I think, I'm not sure, that agriculture would be done in a volume which is bigger than the habitat, and that it would be cheaper to make this volume a lower pressure compartment than the habitat. Therefore, the farming module and the habitat module would be quite different from one another. So as you said below, there is no reason to make it directly part of the habitat it can be separated. If the plants need protection from radiation then, making this agriculture module also in the lava tube makes sense. If the plants can use direct sunlight, I would think that doing so would be cheaper. "... But longer term, using the entire volume of the lava tube is a very interesting prospect. But then again, longer term, you will probably have much a bigger population and you might want to use the entire lava tube for human occupation and let the farming be done in greenhouse on the ground." When would that be? When Mars has a population of millions? Yes that's about it. It won't be this decade :-) You seem to be assuming that every inhabited lava tube must grow its own food. Well, how French of you! ;-) I'm a francophone but not French. I have been to France but only visited it for 15 minutes (the time to wait for the train change going from Germany to Belgium). But I think France has a very extrovert economy with lots of imports and exports, I don't know why you would consider it to be French to grow locally. Why can't some lava tubes become more specialized for food production, others for habitation, if the initial tube gets too crowded for farming? There will be no shortage of lava tubes for the time being. There are major industrialized nations on Earth that get by fine without 100% food self-sufficiency. I live in densely-populated Japan. My kiwi fruit comes in from sparsely-populated New Zealand. A lovely country. I really liked my trip over there. I hope you don't buy their japanese grown cantaloupe to often :-) [For those who don't know Japan, they have some special kind of cantaloupe which is horrendously expensive, something like 6000 yens or 60 US$ per fruit] To repeat: greenhouses on the Martian surface will get exactly one benefit from being on the surface: direct daytime pass-through of sunlight at frequencies useful for photosynthesis. That's IT. Everything else about being on the surface is just a source of added problems. Solving problems costs money. Money that nobody will pa y if there are cheaper solutions that are just as good. Yes that is the benefit. The benefit of being underground is that you get radiation protection and I'm not sure that is needed for plants. The lost of heat, might not be a serious problem either. The habitat in the cave will be automatically very well insulated because it is in a vacuum in a cave, you will need to radiate heat away. And because their is no outside atmosphere (or very little in the case of Mars) lost of heat is only through radiation. Which benefit and and which cost are the greatest I don't know. Radiating all the heat through the greenhouse at night, at least on the Moon is problematic, so heating the greenhouse at night would probably be done. That is not very difficult. Is it cheaper to do than to collect the energy on the surface and sending it to an underground greenhouse, I don't know. Alain Fournier |
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Technologies for Moon mission useable for missions further out
This paper
http://www.marshome.org/files2/Hublitz1.pdf is very suggestive of the difficulties. Note Fig. 8: even if you assume efficient multi-layered insulation covering the surface greenhouse at night, you have net heat loss except for a brief noonday period. Also note: this is, they say, when "the sun is at zenith" -- i.e., high summer. Consider the logistics and the risks of adding and taking off that insulating cover, every dawn and sunset, with dust blowing around. With a thin transparent shell underneath, how long before you're looking at serious abrasion of it? They don't talk about that. Look at Fig. 12: for the same level of food production, artificial lighting within a shell of permanent insulation requires only about half the area of the smallest proposed structure that would need to be on the surface (their "hybrid" artificial/natural light greenhouse): about 80 m^2 per person. Non-hybrid approaches would require more than 5 times as much area. The heat requirements during the average day net out to be large; the heat requirements to get through the night without removable insulation are overwhelming. If the floor of a Martian lava tube were only 50 meters wide, you'd only need a 50 meter length of it for a farm for 6 people, assuming their calculations for a permanent-insulation greenhouse. Lunar lava tubes can be hundreds of meters wide. Lengths can run to kilometers, so scaling food production to any population growth wouldn't be a problem. Fig. 5 points out the obvious: greenhouse *shell* mass savings in terms of growth *area* are much better for low-pressure natural/hybrid lighting. But see Fig. 13.: it's not all about the shell. Far from it. Don't forget crop *yield* per unit area, either. That's Fig. 12. Even on their own optimistic terms, the argument for being on the surface isn't very strong. Hybrid lighting at low pressure gives you the lowest mass requirement, but not by much. They don't look at the option of piping sunlight in via fiber optics (though they do mention it.) Using incandescent light can generate heat, and that's a source of heat they look at -- but where do you get the needed electricity from? Without nuclear power, you'll need large PV arrays, collecting weak sunlight. They only look at greenhouse structural mass calculations -- but if you're inefficiently converting solar radiation to electricity, then back to light and heat again, that's a lot more mass to bring in, in the form of extra PV arrays. More efficient, I would think, to conserve heat under permanent insulation, while piping collected daylight in. Different crops would require different minimum light levels anyway -- a surface greenhouse won't necessarily be the most efficient distributor of sunlight for optimal photosynthesis. In which case, being on the surface doesn't really solve many problems for you. It mainly creates problems, the biggest being: heat loss. -michael turner On Jun 21, 7:48 pm, Alain Fournier wrote: Michael Turner wrote: On Jun 18, 12:14 pm, Alain Fournier wrote: "I'm not sure exactly how one would pressurize such lava tubes." I have not proposed pressurizing lava tubes. I was addressing an apparent concern of yours: whether they had enough volume for agriculture. Well, yes at first you do have enough volume in the lava tubes for agriculture. But I think, I'm not sure, that agriculture would be done in a volume which is bigger than the habitat, and that it would be cheaper to make this volume a lower pressure compartment than the habitat. Therefore, the farming module and the habitat module would be quite different from one another. So as you said below, there is no reason to make it directly part of the habitat it can be separated. If the plants need protection from radiation then, making this agriculture module also in the lava tube makes sense. If the plants can use direct sunlight, I would think that doing so would be cheaper. "... But longer term, using the entire volume of the lava tube is a very interesting prospect. But then again, longer term, you will probably have much a bigger population and you might want to use the entire lava tube for human occupation and let the farming be done in greenhouse on the ground." When would that be? When Mars has a population of millions? Yes that's about it. It won't be this decade :-) You seem to be assuming that every inhabited lava tube must grow its own food. Well, how French of you! ;-) I'm a francophone but not French. I have been to France but only visited it for 15 minutes (the time to wait for the train change going from Germany to Belgium). But I think France has a very extrovert economy with lots of imports and exports, I don't know why you would consider it to be French to grow locally. Why can't some lava tubes become more specialized for food production, others for habitation, if the initial tube gets too crowded for farming? There will be no shortage of lava tubes for the time being. There are major industrialized nations on Earth that get by fine without 100% food self-sufficiency. I live in densely-populated Japan. My kiwi fruit comes in from sparsely-populated New Zealand. A lovely country. I really liked my trip over there. I hope you don't buy their japanese grown cantaloupe to often :-) [For those who don't know Japan, they have some special kind of cantaloupe which is horrendously expensive, something like 6000 yens or 60 US$ per fruit] To repeat: greenhouses on the Martian surface will get exactly one benefit from being on the surface: direct daytime pass-through of sunlight at frequencies useful for photosynthesis. That's IT. Everything else about being on the surface is just a source of added problems. Solving problems costs money. Money that nobody will pa y if there are cheaper solutions that are just as good. Yes that is the benefit. The benefit of being underground is that you get radiation protection and I'm not sure that is needed for plants. The lost of heat, might not be a serious problem either. The habitat in the cave will be automatically very well insulated because it is in a vacuum in a cave, you will need to radiate heat away. And because their is no outside atmosphere (or very little in the case of Mars) lost of heat is only through radiation. Which benefit and and which cost are the greatest I don't know. Radiating all the heat through the greenhouse at night, at least on the Moon is problematic, so heating the greenhouse at night would probably be done. That is not very difficult. Is it cheaper to do than to collect the energy on the surface and sending it to an underground greenhouse, I don't know. Alain Fournier |
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Technologies for Moon mission useable for missions further out
In article , I wrote:
How do you propose to illuminate your greenhouses if not by direct sunlight? You need either something like 10 MW/hectare if you do it with efficient electric lighting The Hublitz et al. paper referred to elsewhere http://www.marshome.org/files2/Hublitz1.pdf gets 2.3 kW/m^2, a factor of two worse than my estimate. Their estimate was for high pressure sodium lights while mine was for LEDs, which are more efficient. Heat loss of a surface greenhouse won't be trivial, but it's only about 30 kW/hectare Sorry, I dropped a couple of decimal places there and also used too low a temperature. The correct figure is about 400 W/m^2 _if_ the greenhouse is a perfect emitter. That's still less than the power needed for artificial lighting but not by as large a factor as I found originally. Bringing in sunlight from outside requires about a square centimeter of light pipe or fiber per square meter of greenhouse; that part was correct. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
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Technologies for Moon mission useable for missions further out
Heat loss of a surface greenhouse won't be trivial, but it's only
about 30 kW/hectare even if the greenhouse is a perfect emitter. Really? Is the following paper way off? http://www.marshome.org/files2/Hublitz1.pdf Fig. 7 shows upwards of 80kW for a 90 m^2 area, just in heat loss at night. A hectare would be over 100x that much. Note that the heat-flow profile is based on the sun being "at zenith" -- i.e., high summer on Mars. Did the authors somehow miss a couple orders of magnitude? Or am I reading it wrong? I don't think this is a problem you can solve with some special coating on your greenhouse shell. -michael turner On Jun 27, 11:11 pm, (Steve Willner) wrote: In article . com, Michael Turner writes: To repeat: greenhouses on the Martian surface will get exactly one benefit from being on the surface: direct daytime pass-through of sunlight at frequencies useful for photosynthesis. That's IT. That seems to be quite a significant advantage, not a minor one. How do you propose to illuminate your greenhouses if not by direct sunlight? You need either something like 10 MW/hectare if you do it with efficient electric lighting or a collector on the surface at least as big in area as your greenhouse plus at least a square meter of light pipe per hectare if you do it that way. Heat loss of a surface greenhouse won't be trivial, but it's only about 30 kW/hectare even if the greenhouse is a perfect emitter. Probably a factor of 10 improvement is possible by using low-e coatings, depending on how much trouble it is to keep dust off them. -- Steve Willner Phone 617-495-7123 swill...@ cfa.harvard.edu Cambridge, MA 02138 USA |
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Technologies for Moon mission useable for missions further out
Michael Turner wrote:
This paper http://www.marshome.org/files2/Hublitz1.pdf Thanks for the interesting link. is very suggestive of the difficulties. Note Fig. 8: even if you assume efficient multi-layered insulation covering the surface greenhouse at night, you have net heat loss except for a brief noonday period. Also note: this is, they say, when "the sun is at zenith" -- i.e., high summer. Consider the logistics and the risks of adding and taking off that insulating cover, every dawn and sunset, with dust blowing around. With a thin transparent shell underneath, how long before you're looking at serious abrasion of it? They don't talk about that. Right, I wouldn't think that kind of insulation would be helpful on Mars. On the Moon maybe because of longer nights and because MLI is more efficient in vacuum than in the Martian atmosphere. Alain Fournier |
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Technologies for Moon mission useable for missions further out
Michael Turner wrote:
Rebooting this discussion: Let me suggest that the question be turned on its head: given the likelihood that survival modes on both the Moon and Mars would be very similar, what technologies would be location-unique? I think these technologies will mostly be resource-determined, but with some exceptions. Would you consider "proximity to the Earth" a "resource"? Well, in a way: close proximity opens up much vaster *human* resources. Certain operations might be practical to teleoperate from Earth, in the case of the Moon, that would definitely NOT be candidates for terrestrial teleoperation in the case of Mars. However, in general, by "resource", assume that I mean immediately available minerals, gases, energy sources, etc. Examples: Mars lacks: - strong sunlight - high daytime temperatures The Moon is significantly lacking in: - carbon (CO2 is most of Mars' atmosphere) - nitrogen (N2 is around 3% of Mars' atmosphere) Both are problematic for water supply, but Mars has ice caps, at least. I think the easiest supply of water for a colony on Mars would be extracting it from the atmosphere. The colony would more likely be in equatorial regions than in polar regions and even though water vapour is only a small fraction of the atmosphere, you don't need to move your equipment around to extract it. You just set up a water extractor and let it run continuously, it can run automatically. The Moon? Over the long run, the cheapest place from which to fetch water for a lunar base might actually end up being Phobos, of all places, via the Interplanetary Transport Network. (That is, IF Phobos' carbonaceous chondrite content is confirmed, and IF it's the right H2O-rich type of carbonaceous chondrite.) Actually, mining and shipping from Phobos might be an area of technology overlap: useful in the long term for a Moon base, for supplying water and other volatiles and minerals that are trace on the Moon; but also useful to reduce short-term costs of Mars base set-up, until Mars surface ISRU can get into full gear. Phobos is still quite deep in the Martian gravity well. Why not go get it in the main asteroid belt? Mars might still be volcanically active: http://www.space.com/scienceastronom...sm_041222.html The Moon? Decidedly dead in this respect. So on Mars, you might use geothermal sources of energy, conveniently continuous and proximate to lava tube habitats, instead of two-week solar heat buffers as you would on the Moon. If you lucked into a superabundance of heat from geothermal, even if it's low grade heat, the Mars surface greenhouse idea starts to make sense again, because keeping it warm through nights and winters wouldn't cost so much. Geothermal is not so easy on Earth. It would be much more difficult on Mars. I think it would be easier to bring along a chunk of radioactive material for a heat source than to do geothermal. But if you are in a lava tube, you might not need much of a heat source, your problem is going to be radiating your excess heat out. I'm not saying this is a difficult problem, just that heating a habitat inside a lava tube and in what is basically a vacuum is not a problem. Alain Fournier |
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Technologies for Moon mission useable for missions further out
"But if you are in a lava tube, you might not need much of a heat
source, your problem is going to be radiating your excess heat out." You keep ignoring how cold it is there, and how vast these lava tubes can be. Even assuming you did need some kind of heat rejection, you have the planet's own surface into which it can be conducted. You can't do that on a spacecraft. -michael turner On Jun 29, 11:31 am, Alain Fournier wrote: Michael Turner wrote: Rebooting this discussion: Let me suggest that the question be turned on its head: given the likelihood that survival modes on both the Moon and Mars would be very similar, what technologies would be location-unique? I think these technologies will mostly be resource-determined, but with some exceptions. Would you consider "proximity to the Earth" a "resource"? Well, in a way: close proximity opens up much vaster *human* resources. Certain operations might be practical to teleoperate from Earth, in the case of the Moon, that would definitely NOT be candidates for terrestrial teleoperation in the case of Mars. However, in general, by "resource", assume that I mean immediately available minerals, gases, energy sources, etc. Examples: Mars lacks: - strong sunlight - high daytime temperatures The Moon is significantly lacking in: - carbon (CO2 is most of Mars' atmosphere) - nitrogen (N2 is around 3% of Mars' atmosphere) Both are problematic for water supply, but Mars has ice caps, at least. I think the easiest supply of water for a colony on Mars would be extracting it from the atmosphere. The colony would more likely be in equatorial regions than in polar regions and even though water vapour is only a small fraction of the atmosphere, you don't need to move your equipment around to extract it. You just set up a water extractor and let it run continuously, it can run automatically. The Moon? Over the long run, the cheapest place from which to fetch water for a lunar base might actually end up being Phobos, of all places, via the Interplanetary Transport Network. (That is, IF Phobos' carbonaceous chondrite content is confirmed, and IF it's the right H2O-rich type of carbonaceous chondrite.) Actually, mining and shipping from Phobos might be an area of technology overlap: useful in the long term for a Moon base, for supplying water and other volatiles and minerals that are trace on the Moon; but also useful to reduce short-term costs of Mars base set-up, until Mars surface ISRU can get into full gear. Phobos is still quite deep in the Martian gravity well. Why not go get it in the main asteroid belt? Mars might still be volcanically active: http://www.space.com/scienceastronom...sm_041222.html The Moon? Decidedly dead in this respect. So on Mars, you might use geothermal sources of energy, conveniently continuous and proximate to lava tube habitats, instead of two-week solar heat buffers as you would on the Moon. If you lucked into a superabundance of heat from geothermal, even if it's low grade heat, the Mars surface greenhouse idea starts to make sense again, because keeping it warm through nights and winters wouldn't cost so much. Geothermal is not so easy on Earth. It would be much more difficult on Mars. I think it would be easier to bring along a chunk of radioactive material for a heat source than to do geothermal. But if you are in a lava tube, you might not need much of a heat source, your problem is going to be radiating your excess heat out. I'm not saying this is a difficult problem, just that heating a habitat inside a lava tube and in what is basically a vacuum is not a problem. Alain Fournier |
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