Adaptive cascade control design for flexible satellite attitude under multiple unknown uncertainties and structural vibrations

This paper presents a novel adaptive cascade control design for attitude tracking and vibration suppression of a flexible satellite. The proposed control design, named the Adaptive Flatness Sliding Mode Positive Position Feedback (AFSM-PPF), incorporates dual-loop attitude controllers, combining the differential flatness and sliding mode control approaches. The outer loop is employed to track a smooth attitude trajectory of the flexible satellite based on differential flatness technique, while the inner loop is used to effectively manage the variations of angular velocity feedback under the effect of multiple unknown uncertainties. In addition, a Positive Position Feedback (PPF) compensator is incorporated into the inner loop as an auxiliary controller to suppress structural vibrations caused by flexible satellite appendages, thereby improving attitude control performances. The Lyapunov synthesis, through the intermediary of the corollary of Barbalat’s Lemma, proves the stability of the resulting closed-loop system. Compared to other existing controllers, the verification results demonstrate that the suggested cascade controller achieves effective attitude tracking performance.