Simple as the tether-based gravity system sounds, the details of such an apparatus are a bit more complex. The G force that the people inside the system will feel depends on a couple of factors: the length of the spin arm (which is measured from the centre of gravity located exactly between the centres of the the weight and the ship, to the outer edge of the spaceship hub) and the number of rotations the system will make per minute.
There are two ways that a gravitational force can be generated. The first way involves a fast speed of rotation and a short spin arm. This is a nice, compact little system which does create artificial gravity, and doesn’t cost a whole lot to build. However, it has some pretty bizarre side effects which make living in it quite uncomfortable! One problem with short spin arms is gravity gradients. A gravity gradient is present when the pull of gravity at one point is different than the pull at another point. Consider a two-meter tall astronaut. If he were standing in a 4-meter rotating station he would literally feel light-headed, since his head (which is near the axis of rotation) would weigh 50% less than his feet!
The Coriolis effect is another, more harmful side effect which disturbs the body’s balance system. A useful analogy to the Coriolis effect is a clock. Picture a huge clock with the second hand in motion. Now imagine trying to walk a straight line along the hand toward the center of the clock; you can't, because the forward motion of the hand sweeps you off into a slightly elliptical path instead. Another example is the way water swirls down the drain instead of dropping straight down the pipes. If you consider that the canals of the inner ear, which control orientation and balance, are no more than tiny liquid-filled pipes, it’s easy to understand why the Coriolis effect is a problem!
The second, and better, way to generate artificial gravity is to have a slow rotation and a long spin arm. That means that the ship and tether combined will be huge (the size of the space ship in 2001: A Space Odyssey). Although such a system would cost a lot more money to build, it feels a lot more natural to the people who live in it, and it has no side effects. If you were going to be spending months, even years, away from Earth and your family, you’d probably want to live in comfort!
