Fault-tolerant attitude control systems for a satellite equipped with Control Moment Gyros

In recent years, there has been a requirement for accurate and agile attitude control of satellites. To meet this demand there has been an increasing use of Control Moment Gyros (CMGs), which can generate much higher torque than reaction wheels that are used as conventional spacecraft actuators. Furthermore, it is important for attitude control systems to be fault tolerant. In a conventional 4 CMG system, the CMGs are placed in a pyramid mounting arrangement with a skew angle set to 54.74 degree. The maximum angular momentum of the CMG system is changed according to the skew angle. A suitable skew angle should be designed to consider normal and failure situations. Moreover, the suitable parameters of satellite attitude and CMG control systems are changed according to the skew angle. Therefore, this paper proposes a design method for fault-tolerant attitude control system. In the proposed method, the skew angle and the parameters of the control system are tuned simultaneously using a genetic algorithm. To verify the fault-tolerance of the proposed method, numerical simulations for the case where one CMG has failed are carried out.