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Thread: Shuttle and any destabilization of space station

  1. #1 Shuttle and any destabilization of space station 
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    Might the shuttle play a role in destabilization of the space station? That is, by changing the moment of inertia by addition of significant mass, one has an enhancing of any angular velocity i.e. angular acceleration.


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  3. #2 Re: Shuttle and any destabilization of space station 
    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by zanardm
    Might the shuttle play a role in destabilization of the space station? That is, by changing the moment of inertia by addition of significant mass, one has an enhancing of any angular velocity i.e. angular acceleration.
    Other than the inconsequential nudge given during docking, The ISS doesn't orbit any differently with the shuttle attached than it does otherwise.


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  4. #3  
    Forum Ph.D. Leszek Luchowski's Avatar
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    I don't see how increasing the moment of inertia would "enhance" angular velocity.

    When two bodies become rigidly connected to each other, the momentum (both linear and angular) of the combined object is the sum of the momenta of the two bodies before the connection.

    The linear velocity of the whole is a weighted sum of the velocities of the two bodies, the weights being the masses. For angular velocity, the situation is more complicated, because moments of inertia don't add together as simply as masses do. I don't have the time to work on all the formulas, but I feel the moment of inertia of the space station combined with the shuttle is greater than the sum of the two, except around the line connecting their centers of mass - around that axis, it is indeed the sum.

    So the rotational speed of the combined body should actually get smaller.

    Imagine a pair of figure skaters performing independent pirouettes in the same direction beside each other, at a distance of about 1m (3ft). Suddenly, they grab each other's hands, so that they become rigidly connected (ouch, the wrist and shoulder joints!). As a tandem, they will continue to spin in the same direction around their common center of mass, but much more slowly. Same applies to spaceships and stations.

    All this being said, I would expect the linear speed of the shuttle to be very carefully adjusted to that of the station before docking. The angular speed of both objects should be very, very close to zero, except around the privileged axes I mentioned above. Otherwise, the docking gear would be ripped off.

    Hope this helps,
    Leszek.
    Leszek. Pronounced [LEH-sheck]. The wondering Slav.
    History teaches us that we don't learn from history.
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