Why doesn't NASA build rotating spacecraft to simulate gravity?
Since traveling to Mars or further in zero gravity is unhealthy for the passengers. Why doesn't NASA have a rotating spaceships? Let's say we two seperate sections at a radius of about a 1000 feet with the fuel tank in the middle (the non-rotating part).
Well, creating a rotating spacecraft is simple in theory, but extremely difficult in practice. Just as an example, if you had a spacecraft such as yours (and just to make the numbers easier let's make it 1000 meters in radius) you'd need to accelerate the ends of the ship up to 100 meters/second or 360 kilometers/hour. And it'd have to rotate once every 62.8 seconds. This would take a lot of fuel to get the spacecraft rotating that fast, and the stresses that the ship would have to endure would be immense (meaning very heavy construction that'd need to be lifted into space). Most spacecraft we're able to launch today are actually very light and brittle since it costs roughly $1 million per pound just to lift something into space.
But probably more important is the question of how to build it. You wouldn't be able to construct a ship like that on Earth. It'd have to be assembled in space. Meaning you'd need a permanent space station in Earth orbit. Furthermore, the design of the ship would have to be "perfect" since even the slightest asymmetries in the mass distribution would be difficult to deal with. You might even have to take into account the movement of the astronauts within the ship itself (much like you have to get weighed when getting on a small plane). I mean, we can do this sort of thing technologically speaking (and have had the ability for quite some time) but the costs would be astronomical (pardon the pun). It is much more cost efficient to simply have the astronauts exercise several hours a day than to build a rotating spacecraft. Russian astronauts aboard Mir have shown that it is possible for them to live in space for extended periods of time (well over a year) with reparable side effects.
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