Mars regolith analog

cyclohm · 2003-02-18 23:09:01

With what little we know about the compostion of Mars regolith, how would we go about creating an analog for the purpose of testing methods of determining how to make it arable?

Is NASA JSC-1 Mars soil simulant a true analog, and if so, does anyone here know how to obtain it?

noctis · 2003-02-19 10:28:41

i'm not sure how true it is...
it depends on how much it's been tinkered with to conform with the generally expected composition used to explain away the odd viking results (lots of bizarre superoxides etc.)
which is in my opinion unlikely...
(after all, the organics testing tool didn't pick up life in antarctica, or even *i think* in the american desert...)

cyclohm · 2003-02-21 00:41:37

I assume the superoxides would only exist in the top few centimeters - my understanding is that they are created by the reaction of high radiation on the chemicals in the regolith. If I discard the top layers, I can bypass this problem.

I'm thinking about a senior project for my electical engineering degree (due in June of 2004) and am considering constructing a self contained "Mars Garden." The idea is that I could create an inflatable tube greenhouse with a small robot that would tend plants inside. However, I need to know what to include in the delivery package in the way of nutrients and stabilizers, as I don't want to include the mass of imported planting media. The idea is that it would be something along the lines of a 25 kg mass could be added as a parasitic load on a precursor mission to Mars so that when the manned mission arrived, fresh food would already be waiting for them.

I came up with this idea when I was thinking about the problems of a centerfuge on a spacecraft being used to create "artificial gravity" and the gyroscopic procession that would be induced if the mass of that centerfuge was large enough to support a sizeable garden onboard. I know that it can be accounted for, but simply not bringing a centerfuge along would be an easier solution. Aside from that, what do you do with the centerfuge once you are on the surface? Frankly, I don't think the return on investment is there for growing plants inflight in a Mars Direct style mission.

My next problem would be the materials needed to construct an inflatable greenhouse - Anybody know of an inexpensive UV resistant clear flexible sheet plastic that is not too difficult to work with?

BTW - I found the answer for my earlier question some time later during a web search, as NASA sells their simulant for $1 a pound.

Shaun Barrett · 2003-02-23 23:36:13

Hi Cyclohm!
I think Noctis is right to have doubts about the composition of any presumed 'analog' of Mars soil. The exotic superoxides purported to exist in Martian surface regolith, are a hypothetical creation designed to explain conflicting data from two of the experiments aboard the Viking landers.
As Noctis correctly points out, the overriding data from the Gas Chromatograph Mass Spectrometer (GCMS), which were the kiss-of-death for the positive results of the Labeled Release life detector, have since been thrown into very serious doubt. As Noctis goes on to mention, the same GCMS device failed to detect small (but thriving and reproducing) colonies of bacteria in Antarctic soil samples!!
Despite the passage of a quarter of a century, no plausible and widely accepted model for Martian 'superoxide soil chemistry' has been produced in laboratories. Indeed, no plausible mechanism for the production and persistence of hydrogen peroxide in the Martian environment (on which the whole menagerie of hypothetical superoxides depends) has been produced!

In other words, the whole 'no-evidence-for-life-on-Mars-because-of-bizarre-and-inexplicable-soil-oxides' thing (! ), is a rickety house of cards resting on highly dubious results from an instrument which has since been totally discredited!
Incredible, but true.

NASA is quite happy to continue this charade and, according to my reading of the situation, seems disinterested in re-examining the Viking data or actively seeking any new data in the near future. Why, I don't know.

But, as far as your senior project in electrical engineering is concerned, Cyclohm, as long as you toe the party line and work with a soil analog which satisfies the current paradigm as laid down by NASA, all should be well. I can't see NASA changing its tune before June 2004, when your project is due, unless the European Beagle 2 probe forces them to reconsider. ???

P.S. I should clarify something about the GCMS. It was designed to detect organic material - NOT life. The fact that it detected no organic material was taken to mean that no bacteria, alive or dead, were present in the regolith, although the Labeled Release experimental data were strongly indicative of actively metabolising microorganisms. The problem was simply that you would need at least 10,000,000 bacteria in the soil (alive or not) for the GCMS to detect organic material. The LR device is capable of detecting the metabolic products of as little as 50 organisms! Thus, in a harsh environment like Mars, where the population of microorganisms could well be small (as in Antarctic soils), the GCMS was too insensitive to detect the amounts of organic material involved.

cyclohm · 2003-02-25 01:34:03

Hello Shaun,

Interesting answer, but I am assuming that even if there is life currently on Mars, when exposed to the near Earth conditions in my artificial environment it will die. I want to plant tomatoes and lettuce and let xenobiology be left to those who care. Should there be an interaction between lifeforms or should the Martian life suddenly take hold in my near-earth environment, a possiblity which I consider remote, I'm sure that it would provide very intersting results. Aside from that, it's really not within the design problem to figure out how best to deal with little Mars critters eating my lettuce, as Malathion or Chlordane probably could be imported.

However, the problem at hand is that I need to have input from knowledgable people about how to do this, and seeing as I cannot discount your theory, I need to accept it as a possibility. I know that we have little true knowledge of Mars, but from what we do know, how close do I need to be in order to design this device? Even if considered simply as an experiment to answer the question "Can we grow food in Mars Regolith?" the design of the electo-mechanical elements remains the same. I feel that when an experiment of this nature is carried out on Mars, if the native life suddenly springs up there will be more questions to answer than I can even consider trying to answer.

Thank you for your input.

Shaun Barrett · 2003-02-25 19:12:27

I understand that you want to do Martian farming, Cyclohm, and simply want some Martian soil to do it in. And I recognise that questions relating to 'xenobiology' are not the point of the exercise.

However, in view of the extremely dubious current model for the Martian regolith, with its hypothetical self-sterilising superoxides, it looks like an impossible situation for you. Even if you accept the long-standing NASA model, you then enter a minefield of confusing and probably conflicting attempts by various laboratories to create a soil analog which mimics the behaviour of the soils at the Viking sites. And, to the best of my knowledge, no single concoction of minerals and chemicals has been satisfactorily shown to do that!
To my way of thinking, for reasons I can only guess at, NASA has been chasing its tail on this question for years. Because the verdict on the Viking experiments was "no life found", the chemistry of the Martian soil has had to assume fantasmagorical characteristics to explain the Labeled Release results - results which, using the principle of Occam's Razor, are most simply and easily explained by bacterial metabolism.

Where does that leave you? Up sh**-creek without means of propulsion!
There just isn't any agreed soil analog for Mars which makes any sense.

I note your assumption that any Mars microbes exposed to your "near Earth conditions" will die.
This may not be the case.
The Labeled Release (LR) experiment obtained results consistent with the metabolising of nutrients in moistened Martian soil by Martian bacteria. When another sample of the soil was heated to 130 deg.C for some hours, it failed to respond to the nutrient 'broth'. Again, this was consistent with the bacterial hypothesis - any microbes having been killed by the heat.
Interestingly, another soil sample, heated to 51 deg.C for some hours, still responded positively to the nutrient - but at a reduced rate. This seemed to show that at least some of the putative Martian organisms had survived the lesser heat.
At least as far as temperature goes, if there are Martian bugs, Earthly conditions probably won't kill them. So you will need that Chlordane!!!

(Another interesting point is that no superoxide soil chemistry model would have been affected by temperatures of 130 deg.C. And this is even more emphatically the case for temperatures of 51 deg.C !!
Now let me see ... What's the most likely agent in Martian soil which would be neutralised by heat sterilisation and half-neutralised by a lesser degree of heat sterilisation?
Hmmm.
Any takers? :;): )

soph · 2003-02-25 19:18:05

Sounds like enzyme denaturing to me ???

Shaun Barrett · 2003-02-25 19:52:04

Yeah!!
If they roasted me at 130 deg.C for a few hours, I can tell you what it would do to my enzymes!!! ...

cyclohm · 2003-02-25 22:39:39

Okay, I'm with you. I don't see a flaw in your thinking at this point, although I can't imagine why NASA would bother to cover this up except to keep people from freaking out. (Which, with the state of education in the USA, I can easily see.) I can just imagine the theological reprocussions among the stupids on this planet, an angry mob of bible thumpers rioting at KSC, and every grey haired old lady across the land would write her senator to tell him how much this has upset the congregation down at Wednesday night bingo. Science is just so evil.

Assuming that there is some kind of bio activity present, what you have told me seems to indicate that I could include the ability to heat sterilze the regolith before closing the "greenhouse." Although this includes more mass in the package, it leads me down the path of a thermoplastic greenhouse. Something that I can inflate and is flexible until the temprature is raised above 130? C, then becomes hard. Perhaps I can do it the other way, use an thermosetting plastic that has a catalist that produces an endothermic reaction to sterilze the regolith? (I don't know of such a plastic off the top of my head that is also transparent.) The amount of energy to heat even a small amount of regolith to 130? C is quite large, so it seems the bigger I make this greenhouse the less it will cost to include the sterilizer (in terms of produced food/O2 vs payload weight - when does it become cheaper to just send the product than to send the factory?)

However, I still cannot see the return on investment of the payload in sending a hydroponic setup to when it's entirely dependent of Earth to send the chemicals to keep it running. I would think it would have to be something we could send that could reduce human waste (by mixing it with the regolith) into a useful product, and the answer I come up with is potting soil. (no pun intended.) You know, what do you think about the sterilizer being part of the waste treatment system? I think I could include the possiblity of the system being used at first to treat regolith by itself, then when humans arrive, treating solid waste as well. I assume that I would want to mix the two, and the heat source could be used to extract water from the regotith as well... Humm.. I have some research to do.

Thanks guys - keep the comments coming.

RobertDyck · 2003-02-26 01:11:52

I am also interested in Mars regolith simulant. I have ignored the question of life, and left that for others to debate. My interest is what the mineral composition of Mars regolith is so I can make a simulant. I have been working on a CIPW analysis, and trying to get geology professors to help me. However, one of the papers I have accumulated includes creation of the superoxides by exposing regolith simulant to UV light under Mars atmospheric conditions. The superoxides are created. Does it explain everything in the biology experiments? I don't know and that isn't my concern. My concern is to identify the minerals with sufficient confidence to create a simulant that can be used by someone wanting to build a Mars rover test facility, or a Mars Garden.

Shaun, could you send to me a copy of the papers you are referencing?

I have an elemental comparison of results from Viking Lander's X-ray fluorescence and Mars Pathfinder's APXS instrument, against JSC Mars-1 and Santiam Mars-2. The last simulant is volcanic cinders from a Mars Society member. The simulants are too high in aluminum and titanium, too low in iron and magnesium, and are missing sulphur and chlorine. JSC Mars-1 has too little sodium; Santiam Mars-2 has too little potassium and phosphorus. I would post the results, however I can't see how to post a table.

Shaun Barrett · 2003-02-26 02:42:46

Hi Robert!
First of all, I must make a correction to one of the temperature figures I used. In my posts above, please substitute 160 deg.C for 130 deg.C.
This substitution does not alter in any way the substance of the arguments put forward.
I apologise for the error, which resulted from my relying entirely on memory of texts I hadn't read for some time.

The originator and designer of the Viking Labeled Release (LR) experiment is Dr. Gilbert V. Levin, founder of Biospherics Incorporated. Among many published papers and other writings, he contributed a chapter to the book "Mars The Living Planet" by Barry E. DiGregorio.
With regard to the superoxide hypothesis, which you've touched on in your post here in this thread, Dr. Levin has this to say in chapter 9 of that book :-

"In the twenty years since Viking many attempts have been made in various laboratories to duplicate the LR Mars results by nonbiological means. Our own laboratory spent three years in this effort. Hydrogen peroxide, superoxides, metalloperoxides, peroxide complexes, UV light, and ionising radiation were tested against Mars analog soils prepared by NASA based on Viking analyses of Martian soil, various clays, minerals, and other surrogate soil substrates. We applied a wide range of environmental conditions to the test procedure. LR radioactive solution and its single components were applied to the samples in a Viking-type LR instrument. A wide range of control regimens was used. Under extreme conditions unrealistic for Mars we were able to force positive results. However, no simulation of the Mars LR data could be produced in any of our experiments or those of others when materials and conditions known to obtain on Mars were used. We have published on all of our efforts and on those of others that have been published or otherwise come to our attention. A plausible reproduction of the Mars LR data by nonbiological means remains to be demonstrated."

Dr. Levin's chief collaborator, Dr. Patricia Ann Straat, also contibuted to the same book. Here is a direct quote of some of her comments on the Viking Labeled Release (VLR) experiment:-
"One of the VLR samples tested was obtained from under a Martian rock; it gave a response similar in magnitude to that obtained from a sample on the exposed Martian surface, showing that the active agent was neither destroyed by UV light nor dependent on it.
Most provocative of all was the so-called cold sterilisation data, the pre-heating of the Martian sample to approximately 50 degrees Celsius prior to adding nutrient. This mild treatment resulted in approximately 2/3 reduction in the magnitude of the positive response. Because few chemicals are known that exhibit such heat sensitivity, and because microbial life on this cold planet might be expected to show intolerance to such 'elevated' temperatures, these data provided the strongest support for the life hypothesis on Mars."

Drs. Levin and Straat have published a great deal of material. As I have indicated, much of what I write in posts to New Mars comes from my own memory of material I have read over the years. Some comes from science magazines, some from books, and some from the internet. Most, if not all, of this material contains references to the papers published by the scientists concerned, but I do not have immediate access to lists of such references, for obvious reasons.
However, if you could be more specific about which parts of my posts about the LR experiment you are most interested in, I will be happy to track down the appropriate references.
I'm hoping that the above quotes might have already covered some of these points.
Thanks, Robert, for your interest in this subject - which I find to be extremely intriguing (not least because of NASA's apparent indifference to its implications).

cyclohm · 2003-03-04 02:26:53

Okay, guys - here is what I have so far...

I aquired 2 pickup loads of "Tagro" from the City of Tacoma, WA - they make this compost from sewer solids, sand, and sawdust. (www.tagro.com) I figure that after a short period of time the ingredients should be fairly easy to come up with on Mars, except for the sawdust. I still need to do more research on what to use BEFORE the people arrive, but I am leaning toward adding the mass needed to carry a small amount of chemicals to get things started. I put most of the Tagro into raised beds in my back yard, and have planned on planting several varieties of veggies this year.

I have also aquired some MicroTina Tomato seeds from the Utah State University, which are now potted in 6 inch pots on my window sill in a mix of Tagro and potting soil. I was only given a very limited amount of seeds, so I started several in the hopes of growing plants to generate enough seed to make it through this experiment. (If I have any left over, I will be happy to share, but you may have better luck getting them straight from USU yourself.) I figure that space will not be as much of a premium on Mars as it is in transit, so the super dwarf plants will not be as big of a requirement on Mars as they would be on the space station, but I can easily get baseline data from USU for these tomatos. I need to decide what other crops will make it, I want to keep them small but at the same time I would like to include as much variety as possible. Any suggestions? Beans and rice...what else?

As for raising the levels of sulfur and chlorine in the soil simulant, would you guys think that just adding powdered sulfur and a chloinator (I am thinking bleach, but that's sodium hypochlorate - I don't think that will be close enough, but raw cholorine is some pretty nasty stuff to be playing with) would be enough? I have no way of testing the chemical makeup of whatever I do use, but a general idea would be helpful. I currently plan on getting the greenhouse roughed out first, then tackling the equipment to prep the regolith.

Another problem I am facing is temp. I can create -40? conditions fairly easily using liquid CO2 (in 1000 psi bottles) but I don't know if I can generate enough delta T to test the materials and heater system. It would not be too hard to extrapolate the data to Mars conditons, but I don't think it would be accurate enough. My first thought on this is to generate material that can hold delta T of 200?C+ while staying flexable, transparent and holding 5+ psi of pressure, testing at an elevated temp (160?C internal, -40? external) but I don't think that it would be a good model, as the properties would not be the same. Anybody know enough about thermodynamics to tell me how to do this?

Finally, a Mars-Mix atmosphere should be easier to deal with, as I have access to liquid CO2. I guess that I'm going to have to come up with a way to make it, but I don't think it will be too difficult to do - perhaps mix it as a gas in a bag by weight? Any ideas?

Now, with all this being thought of, keep in mind that I don't mind ommiting parts of reality to keep within the scope of the project. This is an EE project, realisim will get me an A but the electronics need to work to pass.

dickbill · 2003-03-04 10:20:49

Shaun,

What you suggest is amazing ! but I am still septical. Since you have the book of Dr Levin, can you also mention (briefly) the Viking and other experiments and scientific results which suggest that there is NO life on Mars ?

I always thought that the possibility of life on Mars was rejected because the experimental results against life were much stronger than the results suggesting life. However I have been confused when I read that the organic material detector experiment in viking was incapable to detect organic material in antartica soil, suggesting a possible false negative result on Mars. Things are not so clear now.

RobertDyck · 2003-03-04 12:22:35

I doubt that chlorine bleach is the best choice for regolith simulant. Some chlorine and sodium probably combine to form salt. However, some chlorine will be tied up in the mineral chlorapatite, and sodium in albite (a constituent of feldspar). There may be a small quantity of sodium in a type of clay called corrensite, an iron form of smectite.

I would point you to the soil page on the Winnipeg chapter web site to see the results I have so far of my analysis of Mars regolith. However, it doesn't include clay and published results from the TES instrument on MGS indicate roughly 12% clay. Clay is a much more complex mineral than something like feldspar so the CIPW analysis is more difficult. I am still hoping to get a local geology professor to help me with that.

I kind of chuckled at your discussion of temperature. It has gotten as cold as -40?C outdoors here in Winnipeg, on the coldest day of the year and only once every few years. Right now it is -23?C and the weather channel predicts a high of -18?C (0?F). That's real temperature, not wind chill.

Shaun Barrett · 2003-03-04 18:53:00

Hi Dickbill!
First let me say that it seems I have instigated a small parallel thread-within-a-thread here! Cyclohm has so far been very patient with this slight hijacking of his subject and I really don't want to detract in any way from his very worthy research efforts into Martian food production.
However, it does seem to me to be inescapable logic that, where research is being done into the suitability of Martian soil for agriculture, any dispute as to the chemical composition of that soil is relevant to the discussion.
With that as my excuse, and with cyclohm's gracious permission, I'm happy to continue this line of reasoning.

[Hey Cyclohm! Thanks for your indulgence in this matter up to now. If you say you want me out of your thread, I'll go gracefully and without rancour! ]

Getting back to your question, Dickbill, the book I quoted from is a library book - I don't actually own it. I actually returned the blessed thing just yesterday, as it happens! But that's not a problem. I'll go and get it again - today if I can manage it.
And you are quite correct that the data from the other Viking experiments, the Gas Exchange and the Pyrolitic Release experiments, gave ambiguous results. I won't attempt to describe those results from memory (having already demonstrated the limitations of my memory earlier in this thread! ) but I'll be perfectly happy to present a precis of that data's salient points when I get the book back. And I'll use as much direct quotation as possible in order to maximise objectivity and minimise the taint of any personal bias on my part.
I think what is important here, at least as far as semantics is concerned, is the use of the word 'evidence'. Dr. Levin has always maintained that his LR results constituted evidence for the existence of living organisms in the Martian regolith (not proof - evidence). If you understand the meaning of the word 'evidence', it's simply not possible to argue with that assertion. But NASA denies this. Their position, since the 70s, has been that no evidence for life was found. Ensuing research, particularly with regard to the fatal insensitivity of the GCMS, has made NASA's position on this point increasingly untenable. But have they modified their stance on this vitally important point? Not a bit of it!!
Why?!!
???

I'll come back to you on this as soon as I get the chance.

cyclohm · 2003-03-06 03:04:28

Hello Guys,

Shaun, I don't mind the discussion about the possiblity of anything on Mars, if there is one thing I have learned from our esteemed publick edukashun sistem it's that science is about disproof, not proof. (Well, that and for some reason it's important for engineers to speak a foreign language, know how to tell VanGogh from Dali, play important team sports like soccer and should not take too many math classes, as only 20 credits count toward a degree... but I digress.) So far, nobody has disproved life on Mars as far as I am aware, although I admit to being a skeptic. Regardless, the fact that I would have to deal with "life" in the form of microbes in human waste anyway means that martian life does not impede my project any. it's just another justification for the sterilization. It would probably be just good engineering pratice to include the capability to heat Mars regolith to 200? C anyway, as I suspect that I will have to anyway in order to make ariable soil.

My impression of RobertDyck's assesment (Very nice by the way, some real thought went into it and it shows.) is that the chlorine may be in a form that's fairly easy to deal with anyway, and may just need to be left alone. The concept of bubbling CO2 though the reglith had occured to me, but it seems to me that it would make more sense to try and seperate the materials out that could be useful, like iron. What is to prevent me from heating the regolith to 200? C and injecting some donor material to react most of the chlorine out? For that matter, I can use the same heat process to help reduce the iron oxide to iron, and enable me to remove some of it with a magnet. I know we don't know what the compounds that contain the chlorine are, but would it be an unreasonable assumption that it cannot be reduced to a tollerable level by heating and providing a donor material for it to bond out with? I don't think the sulfur would be too big of a problem, but?? Interesting questions none the less.

I live near Seattle, and it does not get -40? here. I think that if it became -18? C here, people here would freak out. What materials do you use in your greenhouses? Have you had much success yet in getting a crop to grow over the winter?

Thanks for the help - I will be building a website with my project on it in the future so I can share anything I learn from this.

Shaun Barrett · 2003-03-10 01:37:18

Many thanks Cyclohm for your witty and magnanimous acceptance of my parallel thread!!

(I were hedgamacated meself, ya no! )

I can see why you're so pleased with Robert Dyck's input, by the way. I've always found his comments to be extremely well thought out and informative.

(I've made my excuses to Dickbill over at 'Viking Labeled Release' about the other two life experiments I promised to provide information on. )

cyclohm · 2003-03-31 01:01:15

I just wanted to update everyone on my progress and see if anyone had further inputs on the direction I am heading. I've put about 6-8 or so hours of "real work" into this in the last month, I'm not in a hurry and so much of what I am trying to figure out is just basic ideas.

I've been looking around on the web for material that is transparent, has a wide temp range and a good insulation capability. What I have found is that I can pick any two of the above.

So, I decided that what I wanted was a UV shielded plastic that was transparent with as wide of a temp range as possible. Now, the thought is, build up layers separated by air pockets at low pressure, like bubble wrap packing material. Now, as a vacuum is better at reducing heat conduction, how would you make bubble wrap that has vacuum pockets and make the whole shebang compact enough to fit on a small lander? (I've arbitrarily decided that I want to target the size of a loaf of bread for this project collapsed, with the size of components determining the size of the greenhouse proper.) What I have figured out is that by using an inflatable support structure, I think I can hold layers of plastic mechanically separate from each other. The question is 1) does anyone know of a better way to make this work and 2) how can I draw a vacuum through a tube made of readily collapsable material? I think there is a solution here, but I'm not sure yet what it could be.

I've planted 8 microtina tomato seeds, and now have 7 healthy plants. This is in straight Tagro mix under an 80 Watt flourescent wide spectrum light connected to a christmas light timer on my workbench. The Tagro does not stink much, it really does not smell like what it is. I've set the timer to a 14 hour on cycle and the room heat is about 20? C. They are about 5 cm tall, and have 2 or 3 true leaves above the seed leaves that have yet to drop off. The whole point of this was only to get myself able to produce a crop indoors and to generate extra seeds for me to use later. I'm a little low on temp and a little short on light for what USU recommends, but I seem to be doing okay for now.

I have also planted a variety of vegetables outdoors in the Tagro mix, right now only early season stuff like peas and beans but will get later season veggies planted as soon as it warms up.

I've also started collecting vegan information, so I can decide what crops are most critical to grow. I figure that I will concentrate on beans, rice and tomatoes. I know that a wider variety would be desired, but my understanding is that if you have these three, you can survive. I have also tired several tofu dishes and "meatless" food products (veggie dogs and gardenburgers) and have decided that I love animals, as they taste great. Not that the vegan products are really awful, just tasteless and bland.

One other thought came to mind - most of these products are soy based, but what about mushrooms? They would not require a greenhouse, and I suspect that it would be fairly simple to transport a spore impregnated log to Mars without much trouble. Any thoughts? What kind of plant based food should I work on growing - is there anything I'm forgetting?

Thanks for your inputs.

RobertDyck · 2003-03-31 09:28:09

Now you're getting into greenhouse design. If you want an exact design for Mars, for the outer layer I suggest 2 mil Teflon FEP film with the same coating as V-KOOL. For the inner layer I suggest 1 mil Tefzel film. Teflon FEP has a bursting strength of 11 psi for 1 mil film at +25?C. If the interior pressure is 5 psi, that provides a 2.2 times safety margin for 1 mil film alone, but strength can be affected by temperature. You will notice Tefzel does not have bursting strength published, but tensile strength for Teflon FEP is 3000 psi at break for 1 mil film, while Tefzel is 5000 psi at break for 1 mil film. The space between the films could be pressurized more than Mars exterior, but less than the greenhouse interior. This would hold the inner layer up by gas pressure, preventing the cushion or bubble-wrap puffiness. The gap could be filled with argon gas extracted from Mars atmosphere to reduce heat conduction. To prevent convection the gap should be between 1/4" and 3/4" wide. (What ever that works out to in metric.) If the gap is too small heat will directly conduct between layers, if it is too great the gas will convect (circulate from rising heat on one side and falling cold on the other).

Designing for Earth requires more practical requirements. Tefzel is often sold for greenhouses on Earth, stretched across a frame. To prevent tearing from wear and occasional bumping, 2 mil thick Tefzel is recommended. Unless you live in a high-UV area, use of Teflon FEP is not necessary; it would be easier to get Tefzel. Applying a metal sputter-coated layer to Teflon FEP or Tefzel is not something you can do economically, but you can purchase V-KOOL film (previously called Solis film). You can consider either applying the V-KOOL film to the outer layer or seeing if the polyester film has sufficient strength to stand alone as the inner layer. I suspect the film is too flimsy to stand alone, and it is designed to stick to some other surface so preventing it from sticking to the outer layer may be close to impossible.

RobertDyck · 2003-03-31 14:12:02

I don't know of any plants that can withstand 6-10mbar pressure. Garden plants require similar pressure to humans, and do require oxygen. I suggest more nitrogen and CO2 and less oxygen than the habitat. Plants can be "inoculated" with appropriate nitrogen fixing microbes.

The greenhouse for the initial Mars mission will not be a valley filling thing; just a greenhouse perhaps 6 metres by 15 metres. Filling the inter-layer gap with pressure higher than outside but lower than the interior permits monitoring that pressure to detect leaks. A drop in pressure would indicate a leak in the outer layer; an increase would indicate a leak in the inner layer. The material itself could be reinforced with glass fibres; this would increase strength as well as providing a rip-stop, but would make the material translucent rather than transparent. As a backup, notice I suggested each layer be strong enough to support greenhouse pressure on its own. A leak on one layer would just collapse the temperature insulation. Cells have a couple problems: 1) cell walls provide a thermal bridge to let the cold in; 2) it is hard to maintain proper layer spacing to prevent convection. Preventing large pillows that would support convection would require very small cells, basically bubble-wrap. Bubble-wrap as a great number of cell walls, so a great number of thermal bridges. Cell walls also interfere with visibility if you are attempting to maintain a "window". Finally, bubble wrap would require a machine to inflate the bubbles and seal them. A double layer design without any cells can be simply inflated on Mars.

Bill White · 2003-03-31 15:21:02

What you say has already been done. It's called aerogel, and it's an incredibly good heat insulator. Also there are versions of it that are quite transparent.

Many months ago, I recall looking at a University of Wisconsin website concerning aerogel research.

It seems that making aerogels in zero-gee greatly increases transparency. THe U of W project involved making sheets of aerogel in the "Vomit Comet" - - the 30 seconds of zero gee was sufficient to manufacture essentially transparent aerogel.

I am also enthused about the potential of using areogels in the construction of any permanent settlement. Use the aerogel as you would panes of glass, perhaps with multiple layers like Thermopane windows.

University of Wisconsin aerogel link

RobertDyck · 2003-03-31 15:23:54

I asked my aerospace engineer friend to do a thermodynamic calculation for the greenhouse. Her rough calculation was based on a single layer greenhouse with no spectrally selective coating or other insulation. The preliminary calculation showed overheating in the day and freezing at night. Spectrally selective will reflect some heat during the day, and help keep heat in at night. I'm not sure the double-layer design is necessary for temperature control, but it is still a good idea for safety. Because Mars atmosphere is so thin there is very little heat loss to the air. Insulating the floor may be more important. Remember the ground is freezing cold.

I was originally thinking of a bubble-wrap filled with more argon gas, and a hard walking surface applied on top. The alternative is a walking surface with stand-offs and the underside filled with spray-foam insulation.

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