Contact modeling and anti-disturbance control of flexible spacecraft for failed satellite detumbling

On-orbit detumbling of failed satellites has become an urgent mission nowadays. An efficient detumbling approach is to use a servicing spacecraft mounted with highly flexible operation devices to manipulate the failed satellites. The contact processes are crucial for detumbling dynamics analysis. The traditional Coulomb friction model is commonly used for describing contact processes. However, due to the unwanted discontinuity at some critical points, this model is detrimental to the accurate dynamics analysis. Besides, severe impactive disturbance caused by contact processes makes the existing controllers difficult to meet the demand for the strong robustness and high accuracy. To solve these problems, the LuGre friction model is utilized to characterize contact processes by integrating a dissipative contact force model, based on which the detumbling dynamics is studied through comparative analysis. Moreover, a novel anti-disturbance controller is proposed by combining a fast terminal sliding mode control and an adaptive finite time disturbance observer in a unified framework, wherein the observer is employed to effectively estimate the disturbance without requiring the upper bound information of the disturbance and its derivative. A prominent advantage of the proposed controller is that the finite time stability can be achieved a priori with consideration of disturbance rejection performance. Extensive simulations are carried out to validate the effectiveness of the improved model and proposed controller.