Research On Finite-time Control Of Spacecraft Rendezvous And Docking In An Elliptical Orbit

Space technology, one of the most highly sophisticated techniques of science and technology in the world today, is also an important embodiment of comprehensive na-tional power and the level of national science and technology. The rendezvous and docking of spacecraft is a significant procedure to conduct deep space exploration and expand human living space, and one of the hotspot issues in aerospace field as well. Space rendezvous and docking is the key technology and prerequisite to accomplish spacecraft on-orbit servicing, such as supplies of space stations, exchange and rescue of astronauts, on-orbit assembly and maintenance,. Meanwhile, autonomous rendezvous and docking is the development trend of spacecraft rendezvous and docking, of which the final approach phase is of vital importance. Based on the background of spacecraft rendezvous and docking in an elliptical orbit, this dissertation focuses on the problems of relative position and relative attitude control design for the final approach phase of rendezvous and docking, and proposes a proper control scheme with finite-time con-vergence theoretically.Firstly, mathematical models utilized for analyzing problems of spacecraft ren-dezvous and docking are established, relative orbit dynamic model, attitude dynamic and kinematic model included. Based on the commonly used fundamental coordinate system, the relative dynamics in an elliptical orbit, namely, the Lawden Equations, is given. The quaternion method is introduced and used to describe the attitude dynamic and kinematic model.Secondly, the finite-time control method which has stimulated extensive research interest in recent years is presented. Then the paper introduces the definition of the finite-time stability, and judgment theorems of the finite-time stability of control sys-tems are given.Then, we propose finite-time controllers based on the conventional FTSM model and improved FTSM model for the Lawden Equations in the presence of external dis-turbance by utilizing the finite-time control method. Simulation examples are given to elucidate the effectiveness of the proposed approaches.Sequentially, considering the coupled control problem of autonomous rendezvous and docking with a free tumbling target, in view of the established coupled dynamics of relative position and attitude with unknown but bounded external disturbance, a control scheme with finite-time convergence is put forward by taking the control input satura- tion into consideration. Numerical simulation of the closed-loop system validates the control effect.Finally, the article gives a summary of work has been reserched and puts forward its own viewpoint on directions and problems for further research.