Asymmetric full-state constrained attitude control for a flexible agile satellite with multiple disturbances and uncertainties

In this paper, an asymmetric full-state constrained attitude control method for a flexible agile satellite with multiple disturbances and uncertainties is proposed. Both the attitudes and angular velocities of the flexible agile satellite are guaranteed in the asymmetric/symmetric bounds by utilizing the time-varying integral barrier Lyapunov function (TVIBLF) and constant integral barrier Lyapunov function (IBLF) respectively. Compared with the existing error-based barrier Lyapunov functions, the asymmetric TVIBLF does not need error transformation, relaxes the conservation of the initial requirements, and has more compatibility. Furthermore, the proposed asymmetric TVIBLF can deal with the asymmetric time-varying constraints without loss of generality. In addition, the high-frequency flexible vibrations, inertial uncertainties, and unknown external disturbance torques affected on the agile satellite are considered respectively. On one hand, a modal observer is utilized to suppress the high-frequency flexible vibration effects on the attitudes. On the other hand, the inertial uncertainties and unknown external disturbance torques are estimated with a multi-variable nonlinear disturbance observer. Therefore, both the asymmetric full-state constrained performances and robustness of the attitude control system for the flexible agile satellite are achieved. The stability of the closed-loop system is proved and numerical simulations have validated the effectiveness of the proposed method.