Fault tolerant attitude control for small satellites by using single gimbal control moment gyros and magnetic torquers

A fault tolerant control scheme is proposed for attitude maneuver of a small satellite by using single gimbal control moment gyros (SGCMGs) and magnetic torquers (MTQs). First, the dynamic model of rigid spacecraft using SGCMGs and MTQs is established and the faults of SGCMGs are modeled as additive and multiplicative unknown dynamics. By designing a well-tuned Linear Extended State Observer (LESO), the dynamic uncertainties, external disturbances and the partial loss of SGCMGs effectiveness are estimated exactly and compensated actively in real time without knowing the accurate spacecraft model. Then, based on singular value decomposition theory, the command torque is decomposed and distributed to SGCMGs and MTQs respectively, and SGCMGs only need to output the torque component orthogonal to the singular direction when encountering singularity, ensuring the controllability of SGCMGs. By comparing with a conventional PD control method, the numerical simulations demonstrate that this scheme can tolerate potential SGCMGs faults and resolve the singularity problem, maintaining the desirable stability and performance of the satellite.