Finite-time Attitude Control For Tethered Satellite System In Deep Space

With the growing development of aerospace industry, using multi-body spacecraft formations to explore the deep space has become a new trend. Multi-body tethered satellite system,a special modus in the field of spacecraft formation, has many advantages such as high accuracy, fast response and less fuel consumption. In this paper, the platform attitude control problem of multi-body rotating tethered satellite system, which is affected by external disturbances and system uncertainties, is solved. This paper is supported by the research subject “Research on dynamics and control of tethered satellite system in deep space”. The main contents of this dissertation are as follows:The platform attitude dynamic model of multi-body rotating tethered satellite system is established by using Euler-Lagrange. And then model simplicity method is used to decouple the above model in order to build distributed attitude motion equations of multi-body rotation tethered satellite system. Based on attitude motion equations mentioned above, considering the effects of external disturbances and system uncertainties, an adaptive nonsingular terminal sliding mode controller is designed in this paper first. A classic nonsingular terminal sliding surface is selected to avoid singularity of the controller and ensure pratical finite time stability and fast response of the system. In order to guarantee the robustness of controller, the adaptive law is introduced to compensate for external disturbances and system uncertainties. And finally, the effectiveness of the designed adaptive nonsingular terminal sliding mode control scheme is proved by using numerical simulation.A finite time attitude control law incorporating a disturbance observer is proposed for attitude control problem of multi-body rotating tethered satellite system with external disturbances and system uncertainties. This control tragedy, utilizing fast nonsingular terminal sliding surface, not only avoid the singularity of controllers, but also accelerate the convergence speed of system states. Simultaneously, in order to lower the effects of external disturbances and system uncertainties and improve control accuracy, the disturbance observer is designed. The Lyapunov stability analysis is performed to show that the system states are finite time stable and that the sliding mode surface can reach a small region of origin. Finally, numerical simulation demonstrates the effectiveness and superiority of second proposed control schemes with disturbance observer.On the basis of finite time feedback control schemes, adaptive finite time feedback controller based on disturbance observer is designed to complete the attitude control problem of multi-body rotating TSS. Compared to Terminal Sliding Mode control laws, singularity problem is avoided by using finite time feedback controller. And the expression of controller is more concise and versatile. By introducing adaptive law to estimate the final convergence neighborhood of observer errors, the tunable parameters of attitude controller do not depend on the performances of designed disturbance observer anymore. According to the Lyapunov stability theory and the finite time technique, the designed adaptive finite time feedback control based on disturbance observer can achieve system practical finite time stability. Finally, the numerical simulation indicates the effectiveness of proposed attitude control law.