# Can a reaction wheel be spun up using an external torque and be used as a momentum wheel?

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?

• 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? – ViennaCodex Sep 9 '16 at 11:00
• That could work, thanks... I'll change it... – AliRD Sep 10 '16 at 11:30
• Are you suggesting to spin up the entire satellite to get the reaction wheel going? – Hobbes Sep 10 '16 at 12:29
• 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 – AliRD Sep 11 '16 at 16:05