Variable-structure controller of small satellite fine attitude

A small satellite fine attitude control system is analyzed and designed. This attitude control system consists of 3 orthogonal reaction wheels, whose low-speed friction disturb small satellites attitude pointing accuracy and stabilization. A mathematical model of the low-speed friction used in simulation is presented in this paper, and a variable-structure attitude controller is designed to suppress this disturbance. Being independent of the friction model, the variable-structure controller avoids the difficulty to get an accuracy model, and is more robust. Furthermore, compared with PID controller, it resolves the disturbance of the low-speed friction to attitude, and greatly improves small satellites attitude pointing accuracy and stability. Finally, the simulation results prove that the variable-structure controller can provide the pointing accuracy of 0.3 ° and the stability of 0.001 °/s.