Attitude tracking control of a spacecraft using single gimbal control moment gyros and momentum wheels

Attitude tracking control for a spacecraft with Single Gimbal Control Moment Gyros (SGCMGs) and Momentum Wheels(MWs) as hybrid actuators was investigated. As the usual steering laws can not ensure the full controllability of SGCMGs and can not output command torque exactly, a scheme of hybrid actuator consisting of SGCMGs and MWs was proposed. At first, the dynamic model of the system with the hybrid actuator was constructed, and an altitude tracking control law based on the model was designed. By means of singular value decomposition, the command torque is distributed to SGCMGs and MWs, enabling MWs generate the torque along the singular direction when SGCMGs are near singular states. Then, the steering laws were designed respectively for SGCMGs and MWs. The simulation results have shown that, the hybrid actuator can generate exact torque and the SGCMGs are still controllable when singular states appear. Therefore, the validity of the steering law and the feasibility of the hybrid actuator scheme are demonstrated.