Phoenix Lander Preparing For Martian Touchdown

[Broomstick]

There is also the issue of experience and personnel. We have theory on how to build big in space, and certainly the current space station is giving us some small experience, but I am certain that as we scale up we'll encounter problems time and again. Additionally, personnel will be needed for those things we can't automate, which means lifting them and their life support to orbit.

Yes, but the same is true for a large planet-side base. We don't have much experience building large airtight structures in uninhabitable environments either.

Oh, we don't? What do you call submarines? (Which, by the way, endure much greater pressure differentials than space habitats).

Why is gravity all bad? We don't know if humans can live long-term in microgravity, we don't know if we can reproduce in it, if such children would be healthy. Obviously, if we go into space at some point that "experiment" will occur, but if the answer is "no, microgravity is not compatible with normal lifespans or human reproduction" then Mars starts to look a LOT more attractive. There might be other reasons we'd want to conduct business at the bottom of a gravity well.

If you want gravity in space you can just use centrifugal gravity. Just build a big ring and mount your habitat modules on it and spin it, or arrange your habitat modules at the end of a long tumbling pole or tether. You don't need to put yourself at the bottom of a gravity well to have gravity. In fact centrifugal gravity is arguably better as you can vary it to your choosing: you could have zero gee facilities in the middle and varying levels of gravity as you move out, optimized to whatever your needs are.

Spin g's present the potential problem of coriolis forces. That may or may not be a problem.

There are potential problems structural strength if the spinning structure is large enough or moving fast enough, as it will be under tension.

Although spin g's would certainly be an asset and well worth developing.

[Gil Hamilton]

I haven't been able to find any definite statements on what sort of materials would be needed, though it would certainly be easier than an Earth elevator in terms of material strength. One big problem though is Phobos, which orbits below Mars GEO and would collide with the elevator. You might be able to put an active avoidance system on the elevator, or more ambitiously use a mass driver to shift Phobos's orbit so it's out of the way (perhaps use it as the elevator's counterweight).

On this, I've heard of Martian space elevator schemes that try to actually use Phobos as part of the construction of the space elevator and eject the mass you don't use.

[Junghalli]

Oh, we don't? What do you call submarines? (Which, by the way, endure much greater pressure differentials than space habitats).

Oh, I thought you were talking about big habitats. Large enough to hold cities.

Anyway, the kind of environmental conditions a lunar or Martian base has to deal with are rather different than those a submarine has to deal with, but yes, we're not totally inexperienced when it comes to building things to survive adverse conditions. We're not totally inexperienced when it comes to building space stations either. Building a larger space station is a simple matter of scaling up stations like Mir and ISS. The real unprecedented problems come in if you want it to have centrifugal gravity (and for stuff like closed ecologies, but a planetside habitat has the same issues).

Spin g's present the potential problem of coriolis forces. That may or may not be a problem.

It becomes a problem if the station rotates around 3 times a minute or more, it causes nausea (ref). It does mean that rotating stations will probably need quite large diameters, on the order of hundreds of meters to a kilometer or more (depending on whether you want full Earth gravity or are willing to settle for something more like Mars gravity). That is somewhat inconvenient but it doesn't necessarily mean the station has to be very massive - at the most basic level you just stick the habitats at the ends of a long pole, or probably even a rope if you can make one of sufficient strength.

There are potential problems structural strength if the spinning structure is large enough or moving fast enough, as it will be under tension.

That's possible, I'm not an engineer so I'm not really qualified to evaluate this. However, I will point out that that we've built ferris wheels (which are structually quite similar to a wheel-arrangement rotating station) up to >150 meters in height, and these are constructions that must stand up vertically under the full force of Earth's gravity, which is probably a lot more structural stress than any space station will have to endure.

[hongi]

Ice perhaps?

[The Vortex Empire]

Looks like ice to me.

[Patrick Degan]

ZERG: Fool! You left the hatch to number zloyt entrance uncovered! The Earth probe will see it!