ADAPTIVE SLIDING MODE ADRC FOR ATTITUDE TRACKINGWITH ACTUATOR SATURATION AND UNCERTAINTIES

An adaptive sliding mode control (SMC) based on the active disturbance rejection control (ADRC) scheme is put forward for spacecraft attitude tracking problems, in which there exist saturations, uncertainties, and disturbances. First, the attitude tracking problem is transformed into an attitude stabilization problem by designing the adaptive sliding mode surface, in which the adaptation of the parameter is governed by the steepest descent algorithm. Second, the sliding surface is divided into a definite term with input and a general uncertain item based on the active disturbance rejection ideal. Third, the extended state observer (ESO) is applied to estimate the general uncertain item. Meanwhile, an unknown positive saturation degree coefficient is constructed to deal with the actuator saturations, and the adaptive law is induced by stable analysis. Finally, the input to state stability theory is applied to analyse the stability of the closed-loop system, and the feasibility of the scheme is verified by simulations.