Robert Ehrlich, a physicist at George Mason University, sent in the following reply:

"As in the movie '2001,' the space station would presumably be in the shape of a giant spinning torus or doughnut, with gravity pointing outward from the spin axis, so that your head would point towards the central axis.

"The strength of gravity would depend on the rate of spin. If the station had a diameter of 640 meters, it would need to rotate about once per minute to simulate the Earth's gravity. Only if the space station had a fairly small diameter would simulated gravity feel any different from the real thing. For small diameters, the strength of gravity would vary at different points of your body depending on their distance from the axis of rotation, with the result that you would be slightly stretched. For example, if the radius of the space station were only 20 meters (about 10 times your height), gravity would be 10 percent stronger on your feet than your head when you were standing upright. For a 150-pound person, it would feel like a 15-pound force were stretching you.

"The main problem regarding feasibility today would be the difficulty of constructing a large space station that had sufficient structural strength to remain intact under the simulated gravity."

John Taylor of NASA's Marshall Space Flight Center in Huntsville , Alabama, explains why nobody is racing to exploit artificial gravity just yet:

"We go to space to get away from the Earth's gravity; we have no incentive to try to create it artificially.

"The international Space Station is above all a human physiology research facility. Before we can ever hope to explore the solar system, we first need to know what effects long-term exposure to the hostile space environment will have on the human body. We already know that in the absence of gravity we see rapid changes in such things as bone mass and muscle mass. Radiation poses unknown hazards as well.

"Aboard the Space Station scientists will try to sort out the attacks and possible countermeasures. They will also carry out important microgravity research. Both the physiology (life sciences) and microgravity (biotechnology, materials etc.) research depend on the absence of gravity. Any attempt at artificial gravity would turn Space Station into little more than an observation platform.

"Once we have the answers we seek, we may find that it would be beneficial to use artificial gravity for long-term travel in space. Or maybe not. If we do want to try this for some reason, it could be achieved by having two Space Station-sized modules attached end-to-end to a central node or core. These could be rotated around the core. Or, you could simply swing a pair of modules on opposite ends of a long tether, with nothing in the middle. Right now, creating artificial gravity is not very high on anybody's priority list, so not much effort is going into this kind of engineering. But we do know how to do it, at least in principle.

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