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At first glance, a new concept for a NASA habitat on Mars looks like a cross between Mark Watney's inflatable potato farm from "The Martian" and the home of Luke's Uncle Owen on Tatooine from "Star Wars."
[...] The "Mars Ice Home" is a large inflatable dome that is surrounded by a shell of water ice. NASA said the design is just one of many potential concepts for creating a sustainable home for future Martian explorers. The idea came from a team at NASA's Langley Research Center that started with the concept of using resources on Mars to help build a habitat that could effectively protect humans from the elements on the Red Planet's surface, including high-energy radiation.
Langley senior systems engineer Kevin Vipavetz who facilitated the design session said the team assessed "many crazy, out of the box ideas and finally converged on the current Ice Home design, which provides a sound engineering solution," he said.
The advantages of the Mars Ice Home is that the shell is lightweight and can be transported and deployed with simple robotics, then filled with water before the crew arrives. The ice will protect astronauts from radiation and will provide a safe place to call home, NASA says. But the structure also serves as a storage tank for water, to be used either by the explorers or it could potentially be converted to rocket fuel for the proposed Mars Ascent Vehicle. Then the structure could be refilled for the next crew.
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(Score: 2) by Immerman on Wednesday January 04 2017, @06:33PM
I agree that sand is probably a better bet for long-term construction, but for quick-and-ready (and especially semi-autonomously constructed) shelter, water has a lot to offer.
For the purposes of constructing early bases, it's probably safe to assume that both water and sand are both available in effectively unlimited quantities. After all your construction site is almost certainly going to be located near a confirmed glacier to provide the growing colony with water, and you'll only need a tiny percentage of it to build early ice structures.
As for why not use sand - a few reasons spring to mind:
- First off health and aesthetics: Ice gives you light and, if frozen clear enough, a view. You're not going to want to spend a lot of time outside on Mars without a good reason, that radiation is a killer in the long term, so that ~600W /m^2 of natural sunlight shining through the dome is going to be the closest thing to relaxing outside you can get on a regular basis.
- Ice will be far more structurally sound and easy to build with - all you have to do is essentially inflate a "balloon" mold with ambient CO2 and pour water into it so that it freezes into an unbroken rock-hard structure as it fills. Your mold doesn't even need to be strong enough to support more than maybe an inch of liquid water as you can simply add water slowly enough so that lower levels get frozen solid as fast as you're adding more water. And the mold can potentially double as the airtight membrane necessary to securely lock in the air as well (since air can flow even through solid ice, though slowly).
Compare that to sand, where even thin sand bags will involve a great deal more material being brought to Mars than the ice-mold strategy - simply because there's so much more surface area between "bricks" than on the surfaces of the final structure, which is all the mold has to cover. And either the bags have to be strong enough to provide the long term structure, or you need a binding agent that's probably at least as massive as a strong bag, and any binding agent or "rebar" almost certainly has to be brought from Earth as well, at least for early structures. And you'd better hope there are no unexpected chemical impurities in your sand that interfere with the curing process - there's lots of volatiles in Mars sand that could potentially contribute to or interfere with the curing process - concrete is a complex chemical science. And once it's all done... even assuming securely interlocking bricks, you still have a stack of Legos, maybe glued together (more material from Earth...), which will be nowhere near as strong as a single giant block of ice. Not nearly as air-tight either.
- Another factor is ease of construction. Think of what it takes to build with sand: you have to collect the sand while avoiding hitting large rocks that might damage the machinery, and sorting out smaller rocks that might jam things up or puncture your sandbags. Maybe you could build some sort of hovercraft-esque "air curtain" vacuum system that generates enough localized air pressure to just vacuum up the sand?
Then you have to stack the sandbags in a stable structure, which is no easy feat - typical sandbag construction involves a lot of "feel" to avoid destabilizing the walls before the dome is complete, since you're dealing with quasi-fluid sacks rather than rigid bricks, and even with rigid bricks you tend to build tall semi-conical domes unless you're using lots of scaffolding to hold up the walls during construction (which between the semi-autonomous construction and transport rom Earth probably aren't realistic). Interesting spaces, but not especially efficient in terms of how much useful space you get for the materials used. Plus, you really want to include some sort of bonding agent between bags to avoid sliding - even rolls of barbed wire work between tiers of tough sand bags, but we're talking a lot of material being brought from Earth.
Compare to water: the hardest part is going to be collecting it. Maybe some sort of grinding/chipping machine to create ice gravel or shavings that can be easily collected - there shouldn't be any rocks, etc. in or on a glacier as Mars has minimal geologic activity and wind pressure, so no easy mechanism for large objects to accumulate on top of the ice. Then melt the "gravel" (electric heating from nuclear or large solar deployment? Put it in a pressurized dome with a big fresnel lens on top?) and then pump the water into the mold. Done.
And for longer term construction, consider that your ice dome could act as extremely solid scaffolding. Imagine: instead of building with sand bricks, first build a "quick and easy" ice-dome, then just bury it in a pile of sand and binding agent (preferably vacuum curable, otherwise you need a second pressure dome around the whole thing). Once the "concrete" dome has cured, you have a nice solid self-supporting structure, and can then thaw the ice dome and extract the water and mold to use over and over again. If you can find a way to make a binding agent from local materials you could potentially build a great many sand domes using just a single often-patched ice-dome mold to make the temporary scaffolding.
And I would think that establishing local sources of bulk construction materials would be a fairly high priority once food and water recycling have been established - after all every pound of cargo space not used to import bulk materials is a pound that could be instead dedicated to things that are far more difficult to produce without the established ecosystem and industrial capacity of Earth.
(Score: 2) by Immerman on Wednesday January 04 2017, @06:53PM
Sorry, seem to have missed the bit about mixing water with the sand.
The water-sand mixture does seem to have promise, but has downsides as well, especially for early construction: now you have to mine both sand *and* water, and you have to make sure your sand doesn't "clog up" in the mold since it doesn't flow nearly as well as water.
You also no longer have the benefit of abundant natural sunlight, and you've dramatically weakened the ice by including myriad stress points in the crystalline structure along the edges and points of every grain of sand, though honestly you've probably got strength to spare unless your dome is huge - to get enough "stuff" between you and space to provide roughly the same shielding as the sea-level atmosphere on Earth you need to 1 atm, or about 1033 g/cm3 - about 10m worth of material. I think I heard that ice works particularly well though, so pure ice might not need to be quite as thick. And I suppose the ideal would really only be about 3/4 atm, since you're only getting about half the solar radiation to begin with (so about 1/4 less total radiation, since cosmic radiation makes about half the total on Earth and should be roughly the same anywhere in the solar system.
(Score: 2) by bob_super on Wednesday January 04 2017, @08:44PM
On the other hand, non-water bricks don't need to be kept at uncomfortable temps to retain structural integrity.
(Score: 2) by Immerman on Wednesday January 04 2017, @10:08PM
On the other-other hand - you're on Mars. Everything exposed to the ambient environment will always be far more than uncomfortably cold, including the outside of your habitat, no matter what it's made of. You're going to want a nice thick layer of insulation regardless - that may as well be inside the structure that's protecting you from sandstorms and radioactive death from above. You have to cover a lot less surface area that way thanks to the walls being several meters thick, which means a lot less stuff shipped from Earth. And can use the thermal mass to average out the daily extremes, so your insulation can be optimized against a fairly constant bone-chilling cold, rather than the daily fluctuation between pleasantly cool and "my arm just shattered" on the exposed surface.
Plus you have the advantage of readily available vacuum supplied free, which makes for incredible insulation. Make the interior of the ice dome mold out of something like IR reflective like mylar "space blanket" material, and then inflate a somewhat smaller dome "tent" inside it, while leaving a vacuum gap between them, and you'll virtually eliminate thermal transfer between the inside of the tent and the ice dome.
I agree it's not an ideal long-term solution, but it would seem to be a robust solution for establishing a "foothold" habitat to give early colonists spacious radiation shelter using almost exclusively local materials, and equipment they'd want to have available anyway (ice mining will after all be the first step in producing water for drinking, watering crops, and producing fuel for future trips back to Earth.)
And as I mentioned, it also lends itself to acting as the scaffolding for more robust structures. Heck - you could even bury your initial ice-dome in "Mars-crete"(once you figure out how to make it), and then melt the ice to enlarge your shielded dome's diameter by many meters without having to moving anything built inside. You'd still probably want to put the insulation on the inside though - for the simple reason that the dome is still going to seek thermal equilibrium with the incredibly cold ground, and insulation that can both nearly stop that thermal flow while also supporting the humongous weight of the dome is going to be a major engineering challenge. Much easier to just build an insulated floor and walls inside the dome.
And actually - ice might still have a serious advantage in terms of ease of repair. Over time the mass of the dome will almost certainly cause the ground to settle unevenly, creating cracks in the dome. With an ice dome you could potentially just (carefully!) melt the damaged section and let it re-freeze for a near-perfect fix. Patching concrete fractures in contrast is much more difficult. So long as ice is readily available, and the local environment is perpetually sub-freezing anyway, it actually has some really nice structural properties.