## Reaction wheels

Dears,

I would like to know a basic thing, why does the Satellite doesn't rotate with the spinning wheel momentum wheel inside it?

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 Mentor Why should it? If there is a reaction wheel, the satellite has to maintain its spin, to account for friction. If the relative spin (wheel<->satellite) is constant, angular momentum conservation gives a constant angular velocity of the satellite (usually chosen to be 0).
 But for a geo satellite it has an angular velocity equal to earth's rotation,right? So the angular velocity is not zero but constant. This angular rotation is provided by the wheel?

Mentor

## Reaction wheels

That is an angular velocity as seen in the frame of earth, not for the satellite itself.
I don' think I understand what you really want to know.

Satellites do not need those wheels (but they can be useful).

 Mentor That is an angular velocity as seen in the frame of earth, not for the satellite itself. I don' think I understand what you really want to know. Satellites do not need those wheels (but they can be useful).
 What i want to know is that a satellite having a spinning momentum wheel on 1 axis with constant angular velocity doesn't cause rotation on the satellite itself? But if the wheel speed is increased or decreased it will cause satellite to rotate. Is it explainable with any equation?
 Mentor This is just conservation of angular momentum (in the frame of the satellite). With a frictionless reaction wheel (or a real wheel where friction is countered by a motor), there is no torque on the satellite, so it does not begin to spin.

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