Engineering Asked by Kosmas Giannoutakis on November 6, 2020
If we could be able to construct a gigantic hollow sphere, multiple elevators/chambers can glide in the interior of the sphere, accelerating and decelerating without colliding, providing artificial gravity of 1G. The sphere of course has to be gigantic so that the angular acceleration would be significantly less than the acceleration of the chamber, in order to minimize the coriolis effect. Could a solution like that to the artificial gravity problem be feasible?
[EDIT]
Ok let’s simplify it a bit. Instead of a sphere, imagine a giant ring structure in space which stays still (doesn’t rotate). In the internal surface of the ring there is an elevator that can move along the circular path of the ring’s interior. The elevator starts to accelerate forward with 1G (following the circular path). Because of the huge proportions of the ring, the centrifugal force will increase but slowly. The key concept is to satisfy the following equation: forward acceleration + centripetal acceleration = 1G. So as we reach higher speeds, the forward acceleration of the elevator has to be reduced. When the centripetal acceleration reaches 1G, the forward acceleration has to be 0. At this point the coriolis effect will be most severe. From that point the elevator decelerates but the equation: backwards acceleration + centripetal acceleration = 1G, still applies. Another important thing is that there is a distinct chamber that floats inside the elevator, so that it can rotate and stay in the same position for the person that is inside.
A more concrete question is how big has to be that ring structure in order to provide 1g artificial gravity for 1 hour (30 minutes accelerating and 30 minutes decelerating the elevator)?
TLDR: No this is not feasible.
Let's run some numbers. Let's just say you want Earth normal gravity, 1g = 9.8 m/s^2. Rour elevator starts at one side of your structure, and starts accelerating until it gets to the center. At that point, it's going maximum speed. You need then to start decelerating. Then you'll get to the other edge of the sphere and reverse the process. So you'll have +1g for some time, and then -1g for some time, then +1g again, etc.. When you flip from +1g to -1g, what seems to be the floor becomes the ceiling and vice versa. This flipping is going to be the problem. At best, it will be an inconvenience. At worst the person in the elevator will get nauseous and vomit. The feasibility question comes down to how long can you go before you have to flip? Let's just say that you wanted to make it 5 minutes between flips. The distance traveled under constant acceleration is given by $X = 0.5at^2$. For a=9.81 m/s^2 and t=5*60, the radius of your sphere is going to be 441 kilometers or 275 miles. For reference the moon is about 1000 miles. So your sphere needs to be one quarter of the size of the moon. That's going to be impossible to build for a very long time. Maybe technology will get there eventually, but not soon.
Now you could mitigate the size a bit by saying that you only want 1/2 of earth normal gravity, and you're willing to go 1 minute between flips. Flipping once a minute will be super inconvenient. And the size is going to be 8.8 km or 5.5 miles long. Still way out of reach of current technology (for reference the ISS is just over 100 m long).
Answered by Daniel K on November 6, 2020
It is a straightforward design exercise to make a ring-shaped space station and set it into rotation, choosing the RPM and ring radius so as to develop 1 G of centripetal acceleration at its rim.
For small radii, you would also have a number of goofy second-order effects that would set your semicircular canals into a tizzy, making you vomit. All the "practical" designs for ring-shaped space stations are those with large radii (many meters).
Answered by niels nielsen on November 6, 2020
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