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Astronaut in Space With a Spinning Gyroscope

  1. Aug 26, 2014 #1
    One particular experiment that I remember from a visit to a Science Center is the one involving a revolving platform and a gyroscope.

    The user spins the gyroscope - a heavy wheel on an axle and stands on the platform which is free to rotate about its vertical axis.

    As I distinctly remember, suddenly moving the gyroscope, rotating it while holding the ends of the axles, caused me, the gyroscope and the platform to rotate left or right.

    If an astronaut on a spacewalk holds a spinning gyroscope twists it right or left or in any direction, will it not cause him to rotate?

    Could such a device be used to orient the astronaut without using external jets or rockets?
     
  2. jcsd
  3. Aug 26, 2014 #2

    Nugatory

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    it will.

    Yes, but jets or rockets also allow the astronaut to move from one place to another. The gyroscope won't do that.
     
  4. Aug 26, 2014 #3
  5. Aug 26, 2014 #4
    Do we have a 'reactionless' propulsion device here then?

    I am a little surprised by the answers, since Professor Laithwaite and Sandy Kidd both attracted much criticism by suggesting something along these lines.
     
  6. Aug 26, 2014 #5
    Wow there actually is such a device;

    Thanks to "Voko" for the link. Once again I am shown something in Wikipedia I did not know exists:

    https://en.wikipedia.org/wiki/Control_moment_gyroscope
     
  7. Aug 26, 2014 #6

    Nugatory

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    We do not, because there's no propulsion happening. All the astronaut can do is remain in one spot while changing the direction he's looking. There's a perfectly good action-reaction pair between the astronaut and the gyroscope.
     
  8. Aug 26, 2014 #7

    A.T.

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    The center of mass is not accelerated by this. The total angular momentum is constant. See also cat righting reflex:

    https://www.youtube.com/watch?v=yGusK69XVlk
     
  9. Aug 26, 2014 #8
    Back to the platform, though, if a moving platform that I am standing on can be made to rotate using a gyroscope, would it be possible to translate that rotation to a forward motion of the platform through gearing the platform to wheels?
     
  10. Aug 26, 2014 #9

    A.T.

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    Why so complicated? Gear the gyroscope directly to the wheels, and use it as a flywheel.
     
  11. Aug 26, 2014 #10

    Nugatory

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    Yes, but that's no more a reactionless drive than is the motor of my car, which is connected by suitable gearing to the wheels. You won't get any forward motion unless there's something for the wheels to push against - in space the car would just sit there with its wheels spinning.

    If we're on the ground so that wheels do have something to push against, we'd be better off using the electricity that's spinning the gyroscope and operating the gimbal to run an electric motor connected directly to the wheels.
     
  12. Aug 26, 2014 #11
    But you have to admit it is curious, though, propelling a vehicle totally through internal means - only mechanical input that is transmitted through gyroscopic forces - still not reaction-less?
     
  13. Aug 26, 2014 #12

    Nugatory

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    No more curious than the way that my car propels itself "totally by internal means" until the fuel tank runs dry. It took power to spin up that gyroscope, and it takes power to operate the gimbals, and that power came from somewhere - either an onboard electrical generator or charged batteries that will have to recharged or replaced when they are exhausted.
     
  14. Aug 26, 2014 #13

    A.T.

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    You need a ground reaction force to propel a car via wheels. How is that "reaction-less"?
     
  15. Aug 26, 2014 #14

    Dale

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    Since when is the ground "totally internal" to a vehicle?
     
  16. Aug 26, 2014 #15
    Well OK, maybe it is 'reaction less power transmission'. We could use the rotation of the platform to charge a battery and run the vehicle with that.

    I am just asking if Newton's Laws will be violated - it seems hard to say.
     
  17. Aug 26, 2014 #16

    A.T.

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    Where exactly do you see a potential violation of which law?
     
  18. Aug 26, 2014 #17

    Bandersnatch

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    Perhaps you're missing one important point here - once you connect the gyro to some transmission system that actually does work(by accelerating the centre of mass of the system, or maintaining motion against friction, or charging some batteries), the gyro will slow down and stop. You'll only transfer the energy that had been put into spinning the gyro to some other form.
     
  19. Aug 26, 2014 #18

    Nugatory

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    If by "run the vehicle" you mean propelling it forward, you can't do that without the action-reaction pair you get from the wheels pushing on the ground.

    If by "run the vehicle" you mean "operate its internal electrical systems, or even make the wheels spin idly", then many posts back I pointed out that there is a perfectly good action-reaction pair between the astronaut and the gyroscope so the rotation of the astronaut in place is not reactionless.

    It's easy to say: No.
    If you think see a violation of any one of them, ask about it.
     
  20. Aug 26, 2014 #19

    Dale

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    Nothing that you have described even remotely implies a violation of Newton's laws. I am not even sure what makes you think that it would.

    If you have wheels pushing on the ground you do not have a reactionless anything, you have a reaction with the ground. If you are in space using gyros to alter your orientation then you do not have a reactionless drive because you are not being driven anywhere.

    In space both the linear and angular momentum stay constant. On the ground the linear and angular momentum change according to the external force and torque provided by the ground.
     
  21. Aug 27, 2014 #20
    First we had an astronaut in space. We know he can change his spatial orientation by using a gyroscope.

    Next we have a person on a revolving platform on the ground - a platform rotates, but there is not motion in any direction, that is, the center of gravity does not get translated.

    Now the person on the platform on the ground move horizontally by rotating the gyroscope in a particular direction? No, this cannot be done.

    If a vertical gyroscope is moved to horizontal position, as I recall the force will tend to rotate the entire system.

    Now the question is, can the forces generated by moving a gyroscope be used to create forward motion, without any movement of mass.

    This can be done through electricity, that is, using the rotation of the platform to generate a current that then drives an electric motor.

    Basically you are using the forces generated within an entirely self contained unit (think of a man in a box, on a platform ) to create motion
     
    Last edited: Aug 27, 2014
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