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I know that a momentum wheel has a momentum offset and a reaction wheel does not. So, I'm not expecting just this answer. But my question is:

Is there any difference between these two in component and internal operation level? Or, let's put it this way: Can a reaction wheel be spun up using an external torque (i.e. thrusters or magnetorquers) and be used as a momentum wheel or become (in a sense) a momentum wheel?

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  • $\begingroup$ What if you changed the title of the question to: Can a reaction wheel be spun up using an external torque and be used as a momentum wheel? $\endgroup$ – ViennaCodex Sep 9 '16 at 11:00
  • $\begingroup$ That could work, thanks... I'll change it... $\endgroup$ – AliRD Sep 10 '16 at 11:30
  • $\begingroup$ Are you suggesting to spin up the entire satellite to get the reaction wheel going? $\endgroup$ – Hobbes Sep 10 '16 at 12:29
  • $\begingroup$ No, If you exert an external torque and try to cancel it with RW, you will cancel it, but the RW will finally saturate and turn into a momentum wheel... also, check the Puffin's answer, explained this quite good $\endgroup$ – AliRD Sep 11 '16 at 16:05
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Yes, many models of reaction wheel/momentum wheel are useable in both modes of operation, it really just comes down to the control algorithm.

As a clarification in terminology, for a wheel to rotate with respect to the body of the satellite it is mounted in all that is required is for the wheels drive motor to be turn on. In isolation, an assuming that the satellite is in orbit rather than in a ground test, the reaction through the motor drive will be that both the wheel and the satellite body will adopt a net rotational rate with respect to inertial space. The rates will be of opposite sign and of magnitudes inversely proportional to their inertias. If the satellite body is required to be stationary then some external torque needs to be applied to keep it so.

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