Space Settlement FAQ's]

I wrote (11/11):

>Although the Moon and Mars have low
>gravity, a sleeper car on a circular track can
>perform artificial gravity the same as a spinning
>platform, at a greatly reduced cost.

Mike Combs wrote (11/12):

>Perhaps, but why compare this with orbital habitats? Do you plan to built
>10,000 person permanent settlements on sleeper cars on circular tracks?

At some point hundreds of people will be involved
in mining on the moon and asteroids before an
orbital habitat is constructed. I would disagree with "hundreds" (the NASA-Ames Space Settlement studies assumed a lunar crew of only around a dozen or so supporting the construction of a Stanford Torus), but agree the mining camps will certainly precede the large, orbital habitats. For reasons of
efficiency and health these people should spend as
much time as practical under a 1 G environment. I agree 100%, but what does this have to do with the original objection? I had written that one advantage of an orbital location over a planetary one as a site for permanent settlement was that in orbit we could rotate to simulate whatever gravity is desired, while on planetary surfaces we have to take what we get. You began talking about sleeper cars on circular tracks. Unless one can build habitats on the moon or Mars which spin around on circular tracks and can accommodate 10,000 to 10,000,000 people, then there's no use in arguing with the original point. Those constructing the orbital habitats can be shuttled
to a Moon base for 1 G time more efficiently than
traveling back to the Earth. Perhaps, but the transportation costs of this would still be significant. This cost could be eliminated entirely by building structures in orbit which rotate for artificial gravity. The transportation costs for shuttling hundreds of people back and forth from the moon could pay for a great deal of space construction. I think thedisconnect here is that you've decided building these circular tracks and wheeled vehicles will for some reason be cheaper than building a structure in space and setting it rotating. I'm not at all convinced this would be the case, provided we're talking comparable capacities. It's true that the Coriolis effect on the inner ear sets certain constraints, but this only sets a minimum value on the rotation axis, not the mass of the structure.The very first "construction shack" needn't necessarily be a sphere or cylinder. It could be a dumbbell shape. It's rotation axis may of necessity be as long as that of Island One, butsuch a structure could be only a small fraction of the mass. It is by far cheaper to keep someone traveling in a
circle than to degrade their health and ship people
back and forth to the Earth. Agreed, but the cheapest option of all is to simulate gravity near the construction site. There's more than one design out there which would accomplish this with discarded Space Shuttle ETs. One needn'tbuild Island One just to provide workers with some spin gravity. I would expect that circle tracks will be a permanent
companion feature of all factories and outposts on low
G bodies with human workers. Mars has high enough gravity
this will likely be unnecessary. We can expect (or hope) that 1/3 G will be sufficient, but we cannot know for sure until we actually perform the experiment. Mars has water-ice
ready to be mass driven to wherever needed. Mars would be a poor choice as a source of needed water. The gravity well is much steeper than that of the moon, and we don't have a vacuum at the surface which means mass driver operations will be problematic. The lunar mass driver proposal was dependent on a unique dynamic characteristic of the Earth-Moon L-2 point. There would be no corresponding point for Mars. Payloads could not be launched into Mars orbit without orbit circularization engines, which would mean the payloads would have to be much more sophisticated, and far larger, than what O'Neill had proposed for the moon. The lunar poles and NEOs would be far better sources of water for space operations. The Moon
may have some cometary water at the poles in deep craters
but Mars is certain to have a great deal more. The undeniable fact that Mars has more may not be relevant if it's far more difficult to get it away from Mars. The lunar ice might well be depleted in a generation or so, but by then we would be more likely to be extracting water from asteroids than exporting out the the steep gravity well of Mars.

Regards,

Mike Combs