Hey all, I'm starting a project on reaction wheels and I have a simple question on operation. Are the wheel(s) constantly spinning at a relatively high speed, and in such a matter attitude control is achieved by changing the rate of spin? This would seem logical to me, but I could also imagine another situation where the wheels aren't spinning when the spacecraft is launched into orbit. Then the wheel could be spun in either direction, slowly compared to the previous case, to achieve the desired control. If the former is true, would the wheel be spun up on during launch or after in space? I would assume on Earth because otherwise you'd have to bleed off a lot of rotational energy somehow. On a similar topic, am I correct in saying that a reaction wheel and a momentum wheel are indeed different things? I think the momentum wheel is basically a fast/relatively heavy reaction wheel that is used to fix the spacecraft on the plane of rotation. It's basically the same idea as one of those toy gyroscopes, right? (to be clear, not a gyro that measures angular rate of change) Thanks, I was having trouble finding a definitive answer on either point.