Research On Finite-time Control For Spacecraft Rendezvous And Docking

Spacecraft rendezvous and docking is an important space activity of on-orbit spacecrafts such as satellites and space stations,and it is a key technology of manned space activities.In order to improve robustness and convergent performance of the system,much effort has been made in the study of finite-time control methods,but there are few results in the aspect of robust continuity,nonsaturation and reducing control order,implementing physical simulation.Therefore,this paper takes the control for spacecraft rendezvous and docing as the background,focuses on designing finite-time controllers and resolving the aforementioned problems.The main contents are as follows.Firstly,according to the standard cascading characteristic of rendezvous and docking spacecrafts,the continuous finite-time attitude tracking control problem is studied under the condition of external disturbance existing by using the backstepping method.A finite-time controller is designed,which improves the adaptive control law based on the boundary layer.Further,we propose an improved control method with global finite-time stability,the method resolves the problem that finite-time stability is lost within the boundary layer by defining the square of external disturbance boundaries as variables to be estimated.Finally,a finite-time controller with actuator saturation is designed based on the hyperbolic tangent function,to deal with the problem of control input constraint.The three proposed controllers are all continuous and chattering-free.Secondly,in order to improve robustness and convergent performance of the system,the fast terminal sliding mode(FTSM)is used to design robust continuous finite-time attitude tracking controllers for the rendezvous and docing spacecraft with an unknown rotational inertia under the condition of external disturbance existing.The estimating form of rotational inertia is changed by introducing a linear operator,then a robust finite-time control method is proposed by using the adaptive theory and boundary layer theory.Further,by defining the boundaries square of external disturbance and an uncertainty function as variables to be estimated respectively,we design a finite-time controller based on an improved adaptive control,this controller resolves the problem of boundary layer theory.Finally,in order to reduce the control order,a dual closed-loop finite-time control method is presented based on a dual closed-loop control structure.On the basis,we design a dual closed-loop controller with actuator saturation based on the saturation function,the method can resolve the problem of control input constraint.The four continuous controllers have good robustness to the unknown rotational inertia and external disturbance.Moreover,considering the attitude control and position control integratedly,continuous finite-time control methods with coupled attitude and position dynamics for the rendezvous and docing spacecraft are designed under the condition of external disturbance existing.Two finite-time controller are given by using the backstepping method and FTSM.Further,in order to reduce the order of controller and improve its practicability,we propose a dual closed-loop finite-time control scheme by using the dual closed-loop control structure,its structure is of strong adaptability,and facilitates the engineering application.The three continuous controllers contain coupled dynamics,and realize six-DOF coupled control.Finally,the thesis applies finite-time control methods to full-physical simulation experiments of a spacecraft rendezvous and docking to validate the effectiveness of proposed methods.A finite-time control method of automatic mass balancing for the full-physical simulation system is proposed.Further,based on the full-physical simulation system,a full-physical simulation experiment of spacecraft attitude large-angle maneuver is implemented by using the improved continuous finite-time attitude tracking controller based on the backstepping method;a full-physical simulation experiment of spacecraft rendezvous and docking is implemented by using the continuous dual loop finite-time controller with coupled attitude and position dynamics based on the FTSM,the results show that the proposed controllers are feasible and effective.