I'm doing a project on being able to create Earth like conditions in space. Basically its artificial gravity on space stations. I have a few thoughts and I just need to know if they're right so I don't go wandering a long a path and find out its the wrong one! I'm mostly using the concept of rotating space station, with people sticking to the edge. First of all I'll need to use equations for circular motion, the centripetal acceleration: a = v^2 / r and for people to feel Earth-like gravity, the acceleration will need to be 9.81 ms^-2, the acceleration due to gravity. Now, something I'm not sure about. Does the mass of the space station make a difference? Would I only be using mass in equation if I was calculating the centripetal force (m*v^2 / r) for an object with mass "m" inside the space station? --- Also, I was thinking of how you could actually get the station to rotate. Currently satellites have rockets so they can blast themselves in to the right orbit if they start to wander. But I don't like the idea of having rockets, I thought of something else. Space Station 5 from 2001 is a good basis for what I was thinking. It has 2 rings. I thought it would be possible to make one ring rotate the other. It is on Earth, tie a wheel to a motor and the wheel spins. But if the motor is on one ring, rotating the other, what is to stop the motor ring rotating? Nothing. So if the motor at the centre of Ring A was to rotate an identical Ring B at twice the velocity required for the aritifical gravity then both rings would move, in opposite directions at the same speed. Ring A relative to Ring B is rotating at the same speed as the motor but its actual speed is half that because half the motor is using half the energy to rotate itself (and Ring B) So ignoring the fact construction of such a thing would be hard and expensive, is that what would happen in theory? If Ring A + Motor = Ring B (or would their masses not make a difference?) I'm wondering because I don't think I've read any concepts like that, most things I've read just state that "it rotates", so I'm thinking I may have missed something obvious and don't want to put it in to my project if its totally wrong.