Research On Relative Position And Attitude Coupled Controller For Approaching And Docking Of Rigid Spacecrafts Within A Short Distance

Approaching and docking autonomously with a freely tumbling spacecraft, whose positionand attitude are time-varying, leads new challenges to space missions, such as repairing afailure satellite, refueling a powerless satellite and so on. The technology of approaching anddocking to an out-of-control target spacecraft, which has a widespread application prospect inthe future spacecraft mission, and whose mathematic model is strongly coupled and nonlinear,is becoming a hot and difficult problem. In this dissertation, relative position and relativeattitude controllers are investigated for approaching and docking within a short distance. Inthe first, a finite-time controller is proposed for the attitude tracking control system. Then arelative position and attitude coupled controller is developed for approaching and docking.The main contents of the dissertation are as follows:An exponent nonsingular fast terminal sliding mode (ENFTSM) control law is investigatedin this paper for a rigid spacecraft with redundant thrusters in which thruster faults, andcontrol input saturation as well as external disturbances have to be explicitly consideredsimultaneously. More specifically, in this proposed controller, faster convergence ofspacecraft attitude tracking is achieved and shorter reaching time can be guaranteed. Whenthruster fault occurs, the control parameters are adjusted dynamically in such a fashion that nofault detection and isolation mechanism is required in advance, and only the remaining activethrusters are assumed to be able to produce a combined force sufficient to allow the spacecraftto perform the given operations within the saturation magnitude. Lyapunov stability analysisshows that the resulting closed-loop system is stable.Relative position and attitude coupled control algorithm combined with sliding mode andadaptive control techniques is developed for the highly nonlinear and coupled system, inwhich the unexpected disturbed, and configuration uncertainties are considered explicitly. It isnoted that the proposed controller can rigorously enforces actuator-magnitude saturationconstraints and make the closed-loop system attenuates the disturbance with L-2gain. Theassociated stability proof is constructive and accomplished by the development of a novelLyapunov function candidate. Numerical results show that these methods achieve goodtracking performance under the multi-constraints mentioned above.