Spacecraft momentum dumping using less than three external control torques

Control methods have been developed to remove the accumulated angular momentum in momentum wheels of spacecraft using two or one external control torques. Momentum wheels are used in spacecraft attitude control system to stabilize the desired attitude of the spacecraft consuming renewable electrical energy. The disturbance torques on the spacecraft increase the angular momentum of the spacecraft. This change results in speeding of the momentum wheels. The angular momentum stored in the momentum wheels should be removed by implementing external torques to prevent saturation of the momentum wheel motors. Control algorithms have been devised to remove the angular momentum in spite of loosing external torque control about one or even two of the principal axes of the spacecraft due to failures. The angular momentum of the corresponding momentum wheels is removed by performing attitude maneuvers. The spinning speed of the remaining wheels is then ceased using conventional momentum dumping methods. The attitude of the spacecraft is finally corrected to the desired direction. The proposed control laws are proven to be globally stable. Numerical simulations illustrate successful and smooth performance of the laws.