Finite-Time Attitude Stabilization of Flexible Spacecrafts via Reduced-Order SMDO and NTSMC

Abstract

Attitude control performance of spacecraft is inevitably affected by internal and external disturbances such as vibrations of flexible appendages, payload motions, actuator faults, and environmental disturbances. To suppress the effects of these disturbances on attitude control performance, this paper proposes a reduced-order sliding mode disturbance observer (SMDO)-based nonsingular terminal sliding mode controller (NTSMC). First, a reduced-order SMDO is designed to estimate the lumped disturbance including all the internal and external disturbances. Compared with conventional SMDOs, the proposed SMDO has enough robustness to the uncertainties of the disturbance model, but with a lower observer order because estimation of the system state is not required. Second, a nonsingular terminal sliding mode controller plus a feedforward compensator are designed to achieve finite-time attitude stabilization of the spacecraft in the presence of internal and external disturbances. Because most of the disturbances are compensated by SMDO-based feedforward, only a small switching gain is needed in the sliding mode controller. As a result, the chattering phenomenon of the controller can be alleviated. Finally, both the theory analysis and simulation results show the effectiveness of the proposed control scheme.