Abstract: In this paper, 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 disturbs 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 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

Key words: small satellite at t itude cont ro l, react ion w heels low -speed frict ion, variable-st ructure cont ro l