I hope this hasn't been brought up and I did a search in this topic in the interest of not posting a repeat so here goes.
I was reading the Bad Astronomy review of Red Planet and he mentioned that he was all aflutter when he noticed the space station had two rotating rings each going in opposite directions to keep the station itself from spinning. I included the passage at the bottom of the post.
But anyway, even if there was only one ring would it be possible to put another ring within that single larger ring and have it rotate in the other direction? Wouldn't this have the same effect and consolidate the size of the station/ship? Can I watch space movies where the spacecraft have only one spinning ring and still feel content because I can *assume* they check this website regularly and already thought of the ring-in-a-ring possibility?
Incidentally, they used spinning wheels on the ship to simulate gravity, which would work. I was amazed to see two wheels, spinning in opposite directions. This is exactly what you want to do! If you have only one wheel spinning, the ship itself will try to spin in the other direction (this is called ``conservation of angular momentum'', for those of you that love jargon). Having a second wheel spinning in the opposite sense counteracts that. Also, a single spinning wheel makes it very difficult to steer the ship, so having a second one again counteracts that. Very well done, and fine attention to detail on the part of the crew of the movie.