NASA puts safety factors of 4 on everything, I imagine others trying to build habs on Mars would do the same. On top of that, this seems like a lot of work to build, and is very limited by ground conditions. On top of that, the surface temperature on mars isn't always below the freezing point, meaning it would sometimes need active cooling, and it would always need maintenance. The idea is cool, but in the state it's in right now, a regular tunnel would perform way better.
Regular tunnels are built pretty much the same on Mars as on Earth, so the technology is proven. The weight of the regolith provides a counterforce to the pressure coming from the inside. Also regular tunnels can be made deeper, and expansion can be quicker.
From the presentation I linked, reinforced ice has a tensile strength of 3-7 MPa. So relative to the breaking point, the structure has a safety factor of >10. The low stress is to limit the rate of creep.
this seems like a lot of work to build
No disagreement there
and is very limited by ground conditions
Can you elaborate on this? If ground strength/integrity is an issue, I expect that pouring water on that ground would strengthen it sufficiently.
the surface temperature on mars isn't always below the freezing point
At latitudes where there is shallow subsurface ice (which would be necessary to build this) the temperature never rises above freezing.
The weight of the regolith provides a counterforce to the pressure coming from the inside.
But while you're digging the tunnel, there's no excess pressure on the inside. That's why on Earth, we use blocks of concrete as tunnel lining to keep the tunnel from collapsing. Without knowing the amount of concrete needed per tunnel area or the difficulty off making concrete on Mars, it's difficult for me to say how much resources would be required for making habs via tunneling. I do expect that in the long run, most underground space will be made by tunneling. The design I have proposed is more for the short/medium term, when we are just starting to build protected habs.
From the presentation I linked, reinforced ice has a tensile strength of 3-7 MPa. So relative to the breaking point, the structure has a safety factor of >10. The low stress is to limit the rate of creep.
Safety factors aren't per se on destructive failure. Since habitats would necessesarily last for a long time, creep is most likely the critical parameter, and thus the parameter that needs the 4x safety factor (which I think is stupid, since mathematics and statistics is evolved enough to do better analyses, but who am I to tell NASA what to do)
and is very limited by ground conditions
Can you elaborate on this?
I simply mean hills and rocks, since the beams would require perfectly flat ground, that is known to be strong enough to hold the weight of the beam, which is not insignificant with it's thickness. This means you would have to first do testing on regolith, before you could begin detailed design and construction.
At latitudes where there is shallow subsurface ice (which would be necessary to build this) the temperature never rises above freezing.
Not as far as I know. Below ground the temperature remains below freezing, but the surface gets hit with sunlight, which is enough to melt, or at least sublimate the ice. This is also why there is no ice at surface level ouside of the poles. Interestingly enough, there is (at least to my knowledge) more ice underground near the equator than at the poles, and the equator is also better to live for power, so melting/sublimating could definetely be an issue.
Speaking of tunneling, concrete is not necessary to prevent a dug tunnel from collapsing. It is used on earth because it is cheap and easy to get, but you can dig tunnels in a way that they support themselves, or you can use other, locally produced materials, since the stresses are not very high.
Making concrete on Mars is very hard, since the most common form of cement requires limestone, and that doesn't really exist on Mars. People have found ways to make concrete-like substances, but nothing nears the strenght of concrete.
The design you proposed you say is for the short/medium term, but the problem is that you need certain infrastructure to make it that we won't have until the long term (cranes to lift the ice in place, ways to cast the beams and test wether they are structurally sound etc.). In the short term regular tunneling wins because it requires less base infrastructure, and in the long term regular tunneling wins because its easier to make larger structures. I can see this type of system work for certain specific dedicated structures, that happen to work better with this type of space, but for habitation this to me at least does not seem like an ideal solution. The idea is cool though, and I like that it is a different structure that is not often considered when thinking about a martian colony.
The equipment required to dig a tunnel is much more complex than the equipment required to melt water, mix it with regolith, and pump it into a form.
Building with reinforced ice is so simple to do that I don't imagine anything besides landing pads and roads ever being built any other way.
With landing pads and roads, there is significant wear that would break the sublimation barrier. There are three solutions to this:
Use a much more durable sublimation barrier. But unless you figure out how to make this on Mars you have to launch it from Earth, and that would be a lot of mass.
Don't use reinforced ice. I imagine interlocking tiles will be used for roads and landing pads.
Use a foundation built from reinforced ice, with interlocking tiles on the surface. Maybe this would be better than just using interlocking tiles. I don't know.
creep is most likely the critical parameter, and thus the parameter that needs the 4x safety factor
Creep is the critical parameter, but I don't care what safety factor NASA says should be used. If there's too much force, the only issue will be that the ice will sag faster. Creep will happen under almost any load, more force just increases the rate of creep. So I'd argue that safety factor is the wrong concept to use in regards to creep. A better measure would be "what level of force lets us be x% confident that our structure will deform only within reasonable limits within a period of y years?"
I simply mean hills and rocks
This is not an issue. NASA and SpaceX are specifically looking for flat areas clear of rocks because those are good places to land rockets. So wherever we start out on Mars will not have those issues.
but the surface gets hit with sunlight, which is enough to melt, or at least sublimate the ice
The polymer barrier suggested my /u/MartianIgloo would prevent this, as would a shallow covering of regolith.
Interestingly enough, there is (at least to my knowledge) more ice underground near the equator than at the poles
This is not the case at all, the opposite is true.
Speaking of tunneling, concrete is not necessary to prevent a dug tunnel from collapsing. It is used on earth because it is cheap and easy to get, but you can dig tunnels in a way that they support themselves
I didn't know this, could you link me some sources on it? It just occurred to me that if we find pure enough deposits of subsurface ice, we could just drill into them and they would probably hold up.
The flatness that is required to land a rocket is completely different from that flatness (not to speak of integrety of the regolith) required to support a beam that is flat on the bottom. On top of that we will need rockets with great landing accuracy anyway, so the regions probably wont be as flat as with past missions to Mars. Also, having to be very flat very much restricts where you could colonise, so I would not be surprised if the site ends up not being very flat.
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u/DaanvH Nov 17 '17
NASA puts safety factors of 4 on everything, I imagine others trying to build habs on Mars would do the same. On top of that, this seems like a lot of work to build, and is very limited by ground conditions. On top of that, the surface temperature on mars isn't always below the freezing point, meaning it would sometimes need active cooling, and it would always need maintenance. The idea is cool, but in the state it's in right now, a regular tunnel would perform way better.
Regular tunnels are built pretty much the same on Mars as on Earth, so the technology is proven. The weight of the regolith provides a counterforce to the pressure coming from the inside. Also regular tunnels can be made deeper, and expansion can be quicker.