Water stablization of rotating haitats.

[Pye-rate]

Water, water everywhere but not a drop to drink. Most of the water purification can be done centrifugally. The solids will separate out in a few hundred meters leaving water. The water can be sterilized by going through UV transparent pipes on the surface the flow into lakes flash steamed by solar concentrators. The steam goes into condensers outputting clean, sterile water flowing into water storage pipes.

Now to my point! All this moving water can control speed, gyroscopically steer, even stop and reverse spin of a habitat. All done with gear that has to be there anyway. This is what I mean by use physics to solve your problems, not machines.

[JoeStrout]

I'm skeptical about stopping (let alone reversing) the spin of a habitat just from shifting the water it contains — for this to work, your habitat would have to be mostly water, or your water would have to be circulating at hundreds of miles per hour, or both, for this to work.

But yes, you certainly could make minor adjustments to the spin and (more practically) keep the colony properly balanced around its spin axis by shifting water between reservoirs.

I even suspect (but have not proven to my satisfaction) that if you had a continuous river all the way around a habitat, that it would naturally rebalance the habitat without any pumping at all.  The reasoning goes like this: suppose the habitat gets a little off center.  Now one side is further from the spin axis, and thus feeling more pseudogravity.  Water will flow in that direction, shifting the center of mass in that same direction as well.  This will stop when the center of mass starts to get closer to that side, with the end result that everything should stay perfectly balanced.

I'm not 100% sure that's true, but it'd sure be nifty if it is.  And it could be tested in a benchtop experiment by some enterprising youth as a science fair project!

[Pye-rate]

In some of the colony designs I've seen suggested in the Space Settlers group in yahoo water is as high as half the mass of the habitat because they use it for shielding. moving that much water will move the habitat.

[JoeStrout]

True enough. That's an awful pricey shielding material, though... lunar regolith is likely to be a lot cheaper. Or just good ol' fashioned dirt, which you are probably going to want under your feet anyway.

[Pye-rate]

Not really. Find an iceteroid in a useful orbit.

[Pye-rate]

Here is a reason why active water stabilization of habitats. All the habitats I have seen described use ground transportation. Rotational and antirotational masstransit will affect rotation. Transit perpendicular to rotation will affect stability. Nobody seems to be taking this into account. The mass difference is inconsequential is not acceptable, the effect is cumulative.

This is where my argument for aerial masstransit comes in. The amount of torque applied to the habitat by the movement of air is far less than that of ground transit. The further travel by air the less torque applied compared to ground transit. Every movement applies torque on Earth or in space, however in space the mass of the habitat is small enough that torque applied must be compensated for.

[JoeStrout]

Wouldn't the effect only be cumulative if the mass transit were always in the same direction? Seems to me that if the trains run both ways, the effect would tend to cancel out.

[Pye-rate]

This is where good design comes in. Imagine rush hour in any major city, most of the traffic is in one direction. That amount of mass movement would affect the habitat. Design the habitat to prevent that from happening. I have seen some designs that must have done by an uncivil engineer, put all the people in one and the machinery in another. This is a reminder that your dynamic balance has to include the movement of mass.

[JoeStrout]

All good points — though keep in mind that, unlike space colonies, Earth cities aren't round.    I suspect the movement in a space colony, even at rush hour, will be considerably more balanced.

But certainly stuff is moving around.  Some sort of compensation system will be needed.  I'm still not sure whether having a central river (or equivalent network of reservoirs connected by passive pipes) will automatically rebalance it; I think it might.  If not, pumping water actively will certainly do it, as would a series of weights hanging from the outside of the hull, that can be reeled in and out.

More than one way to make that cat-fur coat.

[Pye-rate]

Drawbacks to coco clock weights; response speed/slow, mass to be spun up/ the waters is going to be there anyway, more machinery= more heat sources, spacecraft/ running into all those lines, in short weights on strings is not a safe of viable system.