Why and how is momentum dumping performed on spacecraft?

Momentum dumping removes accumulated angular momentum from reaction wheels/CMGs. Accumulation causes: External torques (solar radiation pressure, gravity gradient, atmospheric drag, magnetic), Unbalanced thruster firings, and Internal disturbances (rotating antennas, mechanisms). When wheels approach saturation (maximum speed), control authority reduces. Dumping methods: Magnetic torquers - coils interact with Earth's magnetic field, no propellant, but limited torque and effectiveness depends on orbit/attitude, common for LEO; Thrusters - direct momentum transfer, faster but uses propellant. Strategy: Scheduled dumps based on accumulation rate, Real-time monitoring of wheel speeds, Dump during eclipse (for power margin), and Coordinate with attitude control. Dump frequency depends on disturbance environment: LEO with magnetic torquers may dump continuously; GEO may dump weekly with thrusters.