Momentum Wheel

Momentum wheels are similar to reaction wheels but are typically larger and spin at a more constant speed to provide gyroscopic stability. They operate on the principle of conservation of angular momentum: as the wheel spins, the spacecraft body tends to remain stable against external disturbance torques. Unlike reaction wheels, which change speed to actively control attitude, momentum wheels are often used for passive or semi-passive stabilization. A common configuration is a single momentum wheel aligned with the pitch axis, providing stability for Earth-observation satellites that need one axis consistently pointed at the ground. Momentum wheels build up stored momentum from external torques over time and must be periodically desaturated using thrusters or magnetorquers. They are heavier and draw more power than reaction wheels but provide inherent stability that simplifies attitude control for certain missions.