Research On Finite-Time Control For Rendezvous And Docking Of Space Non-cooperative Target In The Final Approach Phase

As one of the essential technologies to accomplish complicated space mission,autonomous rendezvous and docking is an important step of China’s three-step space strategy and deep space exploration in the future.Under the condition that the relative motion information is incomplete,how to realize the high-precision control of spacecraft attitude and orbit coupling has been a new topic and challenge in the field of rendezvous and docking control,especially for space on-orbit service of spatial non-cooperative target such as malfunction of aircraft maintenance and cleaning of space debris.In this paper,based on space rendezvous and docking between the chasing spacecraft and spatial non-cooperative target as the background,free tumbling spacecraft is taken as the research objective,and then,we investigated finite time control and optimization of attitude and orbit coupling in the final approach phase of spacecraft rendezvous and docking.Firstly,the coupling dynamics model of relative attitude and orbit is established.In accordance with the concept of spiral motion,the attitude motion and orbital motion of rigid spacecraft are described by using the theory of dual qutarnion.A common reference coordinate system is established,and on the basis of the kinematics and dynamics model of the general space vehicle,spacecraft relative attitude and orbit coupling dynamics model is deduced,and the coupling effect of spacecraft relative attitude motion and orbit motion is analyzed and proven.Then,based on the error dynamics model,a finite-time control scheme is designed.In order to meet the requirements of the dynamic performance and the convergence speed,free tumbling spacecraft is taken as the research objective and a fast terminal sliding mode surface is designed to realize the system state’s fast convergence when it’s far from the equilibrium point.Based on the idea of equivalent control,a fast terminal sliding mode(FTSM)finite-time controller is designed under circumstance of external disturbance and system uncertainties.For the realization of the finite time control and strong robustness,state feedback and nonlinear feedback are used as the switching control part,and the equivalent control part is obtained by sliding mode surface and the dynamics equation.The simulation results show that the scheme can guarantee the high accuracy and finite-time convergence of the attitude and orbit coupling control.Finally,the finite time controller is optimized and improved by taking into account thechattering and singularity of the sliding mode control.A fast nonsingular terminal sliding mode(FNTSM)surface with double advantages which conclude fast convergence of fast terminal sliding mode and avoiding singular phenomenon of nonsingular terminal sliding mode is designed.The unknown upper bound of parametric uncertainties and external disturbance are estimated and compensated by adaptive method,and then the adaptive FNTSM(AFNTSM)finite-time control scheme is proposed,the validity of the scheme is proved by the finite-time Lyapunov stability theory.The simulation results show that the chattering problem can be effectively restrained by the improved scheme which has stronger robustness and faster convergence speed.