Momentum Wheel

A momentum wheel operates similarly to a reaction wheel but spins continuously at a high nominal speed to provide gyroscopic stabilisation (momentum bias) to the spacecraft. The angular momentum resists disturbance torques, keeping the satellite's attitude stable. Small speed variations around the nominal rate provide fine attitude adjustments in one axis. Momentum wheels are commonly used in three-axis stabilised GEO communications satellites, often paired with thrusters or magnetorquers for control of the other axes. A control moment gyroscope (CMG) is a related device that tilts a spinning wheel to produce large torques — used on the ISS.