Great question, and one I spent a lot of time considering. I propose that the goal should be to maintain as close to perfect balance as possible, and there are two systems I will be suggesting.
First off, in any such rotating spin-gravity station, the center of gravity will *always* be shifting, whether from several people moving from one section to another, or plumbing issues, or shifting of storage supplies - there's just no way to maintain perfect balance without constant adjustment.
The first half of the design I propose will consist of inflatable pods, each surrounded with about @20cm of water for radiation shielding - that sounds very expensive in terms of launch-to-orbit costs, but the numbers seem to indicate that everything can be built for less than what it cost to complete the ISS ($100B-$150B). There would be a system of piping running the entire circumference, and when the mass of one inflatable pod (or series of pods) changes, water would be pumped in or out of attached reservoirs to maintain balance.
The other system I propose, I think, would be much better. Each pod in the habitable ring would be attached to a central hub by four (currently commercially-available) cables, and each cable is strong enough to support the mass of the pod by itself (redundancy is crucial, as always). On each cable there will be a counterweight that automatically travels up or down the cable to constantly adjust the balance of the pod(s) in question in relation to the whole. The way I see it, the counterweights would need to move slightly even for one human moving from one pod to another.
The great thing about the second system is that if it works as advertised, the connections between the pods would remain perfectly sealed, with no wear-and-tear from even minuscule degrees of wobbling.
In any case, both systems would require constant monitoring and adjustment, and so would be best left to the most robust computer controls we can design.
IWhat do you think? And on a side note, this is a short version of an article I'll be publishing two or three stories in the future.
