Integral sliding mode control of small satellite attitude motion by purely magnetic actuation

This paper deals with the purely magnetic attitude control problem. Nonlinear equations of attitude motion under environmental disturbances are presented. It is observed that the environmental disturbances affecting the control system appear as unmatched uncertainties. The controlled dynamic system can be represented in regular state-space form, which allows appropriate controller design. Attenuation of the disturbance effects on the steady-state behavior of the attitude angles is still an important problem in small satellite missions. Therefore, the integral sliding mode control method is used to solve the purely magnetic attitude control problem. The control torque vector at the output of the controller acts on the spacecraft after successive manipulations in magnetic actuation and interaction steps. The magnetic attitude control system is designed by using Lyapunov's direct method in the framework of sliding mode control theory. The performance of the resulting control system is evaluated through realistic simulations, and it is seen that the integral sliding mode controller has a superior steady-state performance with respect to the nominal controller.