Fuzzy Disturbance Observer Based NTSM Attitude Control for Combined Spacecraft

The service spacecraft captures the target spacecraft and forms a combined spacecraft, which is a complex, nonlinear, and coupled system with much uncertain parameters. Targets may also have autonomous maneuverability and output resistance torque to hinder the service spacecraft from performing on-orbit missions. To solve these problems, a fuzzy disturbance observer based nonsingular terminal sliding mode (NTSM) attitude controller is proposed. Firstly, the state-space representation of system is developed based on the attitude mathematical model of combined spacecraft. Next, an adaptive fuzzy disturbance observer is designed to approach the generalized disturbances including uncertainties of inertia, resistance torques of target spacecraft, external disturbance torques and so on. The observation error is proved to be uniformly bounded by constructing Lyapunov function. Then, based on the fuzzy disturbance observer, a NTSM controller with high control performance is designed to stabilize the attitude of combined spacecraft. Finally, simulations results verify the good tracking and control performance of the control strategy.