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The Question

(Submitted February 04, 1998)

Will it ever be possible for a space ship to have gravity while in space?

The Answer

Gravity is the least understood of the four basic forces in Physics (Gravity, Electricity & Magnetism, and the Strong and Weak Nuclear Forces). We do know how to describe it, and understand it seems a property associated with mass. There is no known mechanism at this point for artificially creating gravity, other than having a suitably large mass at hand.

However, that's not to say you could not "fake it", so to speak. You could keep a rocket constantly accelerating at 9.81 meters per second per second, and then flip the rocket around halfway to your destination and constantly accelerated in the opposite direction the rest of the way. Anyone in the space vehicle would feel as if they were experiencing gravity on Earth, except for a few dizzy moments when the spaceship gets flipped around. However, there's a little problem of having to have fuel enough to keep a rocket firing at that high a rate the whole time. Even the largest rockets NASA and the Russian Space Agency have will only burn for a few minutes before running out of fuel: the rest of the journey for space vehicles is done "coasting" to their destination and then using much smaller rockets to adjust their speed to slow down or change their orbit.

Another "trick" would be to make the entire space vehicle spin. Imagine a ball on a string: you can twirl it around and feel the string tugging on your arm. If you have a bucket of water on a string, you can twirl it around and if you twirl it around fast enough, the water stays in the bucket even if you spin it so it goes upside down during part of the swing. The same thing could be done in space: take two space vehicles and connect them on a tether and make them swing around each other to generate a sense of gravity. Theoretically, this is a very attractive idea; early tests with Gemini XI and XII showed that, while it was possible to generate microgravity (too weak for the astronauts to feel), stationkeeping of two tethered spacecrafts was very difficult. NASA has also flown a couple of shuttle missions attempting to deploy a tethered satellite. There were several goals with the tether system, but at least one was to work out how to deploy tethered systems in space.

Jesse Allen
for Ask an Astrophysicist

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