Can an astronaut rotate herself?

In summary: The astronaut can use her arms to swing her legs around so she is facing the station.OK, of course the astronaut is not a rigid body ... so she can rotate herself. Thank you!
  • #1
physicstudent_B
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Homework Statement


An astronaut has been left outside the space station, her back towards the station. The astronaut is not rotating (angular momentum ~ L = 0) and cannot reach anything. Is it possible for the astronaut to rotate herself into facing the space station?

Homework Equations


Conservation of angular momentum

The Attempt at a Solution


I think that the astronaut cannot rotate herself only by moving. So the answer would be no. She could maybe throw something from her backpack (if she has something) to change her angular moment.
 
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  • #2
Do some research on the "Falling Cat Problem" :wink:
 
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  • #3
OK, of course the astronaut is not a rigid body ... so she can rotate herself. Thank you!
 
  • #4
Nearly 50 years ago I failed to convince a visiting Russian physicist that this was possible. I was handicapped by being a mere maths undergrad in a slightly off-axis swivel chair and the worse for vodka. The two historians and the lawyer also present were no help.
 
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  • #5
And there was no Youtube 50 years ago.
(look at 5:45)
 
  • #6
Even if the astronaut were a rigid body, he or she could still rotate albeit inefficiently. For example, let the astronaut raised his hands over his (her) head, and consider this the initial orientation. Now if (s)he moved his arm forward, his legs would go backward. When the astronaut moved his arms over his head again, the astronaut would return to the initial orientation. Now if the astronaut moved his arms out to one side, the legs would go to the other side. When the astronaut returned his arms directly over his head, (s)he would again return to the initial orientation.

Now assume the astronaut moved his arms forward so his feet went backward. Now the astronaut moves both arms to one side, and his legs go the the other side. Now the astronaut moves his arms directly over his head again, (in one step; not the two steps (s)he took to get to the side). The astronaut would have his/her arms directly over his head, but (s)he would have rotated. This is because, as is well (should be) known to students of college freshman mechanics, finite rigid body rotations are non-commutative.

As a grad student, I briefly talked to some (other) grad students and they do not buy this argument, but at the same time they could not refute it.
 
  • #7
mpresic said:
let the astronaut raised his hands over his (her) head,
Bit of a struggle for a rigid body.
 
  • #8
to Hauspec, Granted. The astronaut would have to be a collection of coupled (assumed rigid) bodies rigid arms and legs. Maybe the analysis of the falling cat is the best idea.
 

1. Can an astronaut rotate herself in space?

Yes, an astronaut can rotate herself in space by using the principle of conservation of angular momentum. By changing the distribution of her mass or extending her limbs, she can alter her rotational speed or direction.

2. How does an astronaut rotate herself?

An astronaut can rotate herself in space by using her arms, legs, or any other part of her body to push against the air or objects around her. She can also use a device called a "manned maneuvering unit" to control her movements.

3. Is it possible for an astronaut to rotate herself without any external force?

Yes, it is possible for an astronaut to rotate herself without any external force by changing the distribution of her mass. This is known as the "tuck and roll" technique, where the astronaut pulls her arms and legs close to her body and then extends them out in a different direction to change her rotation.

4. Can an astronaut stop herself from rotating in space?

Yes, an astronaut can stop herself from rotating in space by using the same techniques mentioned before. By changing her mass distribution or using her limbs to counter-rotate, she can cancel out her rotational motion.

5. How do astronauts use rotation in space missions?

Astronauts use rotation in space missions to control their movements and orientation. By rotating themselves, they can move towards or away from objects, adjust their position for tasks, and stabilize themselves during spacewalks. They also use rotation to simulate gravity during exercise and to help adjust their body's fluid balance in microgravity.

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