Close-Range Rendezvous Control For Spacecraft Based On Finite-Time Stability

Spacecraft rendezvous is one of the most important technologies in aerospace field,which has wide range of applications,such as on-orbit service,assembly of large-scale space structure and space interception.The scheme for attitude and position is the key that determines whether rendezvous can success or not.As the space missions becoming more and more complex,the requirements of the spacecraft attitude and postion control become higher as well.In traditional rendezvous missions,the attitude of the target is static with respect to the inertial coordinate system,where the attitude and position control systems can be designed separately.Moreover,to guarantee the success of missions,the control laws need to provide high control accuracy and fast response speed.However,traditional separated attitude and position control schemes can not fulfill the requirements of some severe situations,for instance,the targets are spinning and the docking ports keep changing position.Since both high accuracy and stability for attitude and position control with rapid convergence rate are required in these space missions,integrated attitude and position control schemes take the coupling influences between the rotation and translation into consideration,and use the same control laws to control the attitude and position motion simultaneously,which can improve the control accuracy,the efficiency and the system performance significantly.Hence,the research on attitude control,position control and integrated attitude and position control for spacecraft has vital theoretical significance and application value.This present dissertation first reviews and analyses some existing research results,then concentrates on the problems of attitude control,position control and integrated attitude and position control for spacecraft.Some factors like external disturbances,actuator faults and unmeasurable velocity are taken into consideration.Finite-time and fixed-time control methods which have the characteristics of rapid convergence rate and strong roubustness are developed.The main contents of this dissertation are listed as follows.Relative attitude control of the chasing spacecraft is researched under the circumstances that the attitude of the target keeps static.In that case,high-accuracy control scheme for spacecraft attitude is the base of realizing further position control design.First,a fixed-time control method based on "adding a power integrator technology" is developed for attitude system.The stability analysis for the closed-loop system is conducted with considering and not considering disturbances respectively.When the disturbances are not considered,it can be proved that the relative attitude and angular speed can converge to the origin in finite time with the upper bound of the settling time independent of initial conditions.Also,the control system is robust to initial conditions.When considering the disturbances,it can be proved that the relative attitude and angular velocity can converge to a neighbourhood containing the origin in finite time.Then,by thinking of circumstances that the angular velocity sensors are in fault or not used to save cost,an output feedback control method that without angular velocity feedback is developed based on "adding a power integrator technology".By the stability of the closed-loop system,it can be proved that the relative attitude and angular velocity can converge to the origin in finite time without considering the disturbances,and can converge to a neighbourhood containing the origin in finite time when considering the disturbances.Relative position control of the chasing spacecraft is researched under the circumstances that the attitude of the target keeps static.Assume that the docking port of the chasing spacecraft has been in alignment with that of the target,and the chasing spacecraft do not need to adjust its attitude any more.First,without considering the disturbances,a position control method is developed based on nonsingular terminal sliding mode control.The proposed control method adopts switching structure with the sine function to avoid singularity,which is different from the classical nonsingular terminal sliding mode control.It can be proved that relative position and velocity can converge to the origin in finite time.When considering the disturbances,an adaptation function is utilized based on the method proposed above to deal with the disturbances.In that case,relative position and velocity can converge to a neighbourhood containing the origin in finite time,which is proved through theoretical analysis.Then,by thinking of designing controller without velocity feedback,a finite-time velocity observer is developed.When not considering disturbances,the proposed observer enables observation errors to converge to the origin in finite time.If taking the disturbances into account,the proposed observer enables observation errors to converge to a neighbourhood containing the origin in finite time.Considering the integrated attitude and position control problem of spacecraft rendezvous when the target is spinning.In some practical space missions,the target spacecraft may tumble freely owing to lacking of energy or actuator faults.To approach and dock with such kind of target,the integrated attitude and positon control that can simutaneously control attitude and position of the chasing spacecraft is researched.First,a fixed-time 6 DOF controller is designed based on homogeneous method without considering disturbances,which makes spacecraft system converge to the equilibrium in fixed time.When considering disturbances,another fixed-time 6 DOF controller based on nonsingular terminal sliding mode method is developed,and adaptive law is employed here to deal with the disturbances.It is proved that the system can converge to a neighbourhood containing the equilibrium in fixed time.Then,when taking actuator faults into consideration,a fault tolerant control scheme is studied for spacecraft integrated attitude and position control.Finally,for the case of output feedback control,a fixed-time observer is designed to estimate unknown relative angular velocity and relative velocity,which guarantees the observation errors converging to the origin in fixed time.