What are Reaction Wheels?

Reaction wheels or momentum wheels are flywheels that are used to provide attitude (orientation) control and stability to a spacecraft. There is no air resistance in space and as a result when a reaction wheel turns in one direction the spacecraft tends to turn in the opposite direction as per Newton’s Third Law. Therefore, by maintaining the rotation of one reaction wheel, a single axis of the spacecraft is stabilized and with a minimum of three wheels that are spinning in three directions.

The reaction wheels are fixed in place they spin at a very high rate of revolution which is around 1000-4000 revolutions per minute, which builds up angular momentum. Therefore, to change the orientation of the spacecraft the rate at which the wheel spin can be changed. As a result, this rate of change produces a torque that causes the spacecraft/satellite to change its direction. The main advantage of the technology of reaction wheels is that it works on electricity alone which means that there is no need for the use of liquid propellant to change the direction of the spacecraft.