Composite Nonsingular Terminal Sliding Mode Attitude Controller for Spacecraft With Actuator Dynamics Under Matched and Mismatched Disturbances

In this article, a novel spacecraft composite attitude stabilization scheme based on dual disturbances observers (DDOs) and high-precision nonsingular terminal sliding mode control is presented, with explicit consideration of reaction wheel dynamics and multiple disturbances. First, spacecraft attitude coupling dynamics model is constructed covering reaction wheel dynamics and multiple disturbances. These disturbances include matched disturbances caused by motor counter electromotive force and equivalent mismatched disturbance caused by reaction wheel friction and environment disturbances. DDOs are designed to estimate both equivalent matched and mismatched disturbances, respectively. Subsequently, the high-precision control scheme is designed to compensate the estimated disturbances and attenuate the influence of estimated errors via composite nonsingular terminal sliding mode attitude controller. The closed-loop stability and convergence are proved based on the Lyapunov stability theory. Finally, hardware-in-the-loop experiments are conducted to verify the effectiveness of proposed spacecraft attitude stabilization scheme.