Detumbling dynamics and fixed-time disturbance rejection control for a flexible malfunctioning satellite

A servicing spacecraft mounted with compliant flexible devices has recently emerged as a novel and popular approach for detumbling malfunctioning satellite. Mounting numbers of works have been devoted to the detumbling dynamics and control. However, almost all studies on the dynamics do not consider the effects of the flexible panels of the satellite. In addition, since the flexible panels bring considerable influences on contact processes, the contact-induced disturbance with large amplitude easily causes the spacecraft instability, posing detrimental impacts for accurate and efficient operations. To conquer the above problems, the dynamic model of the flexible satellite is established by means of the natural coordinate and absolute nodal coordinate formulations, providing a foundation for the dynamic analysis. Besides, a novel fixed-time disturbance rejection detumbling controller is proposed based on fast terminal sliding mode control technique, wherein the fixed-time convergent observer is constructed to effectively estimate the disturbance without requiring the upper bounds of the disturbance and its derivative. This controller can significantly improve convergence performance and tracking accuracy, facilitating the spacecraft to realize accurate and efficient operations. Extensive simulations are conducted to reveal the effects of the flexible panels, and validate the effectiveness of the proposed controller.