On Robust Attitude Maneuver Control Of Flexible Spacecraft

With the development of space science technology,modern space missions,such as remote sensing and formation flying,require spacecrafts to achieve rapid attitude maneuver with high pointing precision and stability.The attitude control performance depends not only on hardware configurations,but also on attitude control law.Considering the actual demand of rapid slewing and high pointing precision,for the rigid-flex coupling,disturbance torque and output feedback control problems in the flexible spacecraft attitude control system,this thesis focuses on the robust attitude control law design so that rapid attitude maneuver can be achieved with high pointing accuracy.The main works and contributions lie in the following:Aiming at reducing vibrations excited by attitude maneuvering,this thesis proposes a transient process by combining path planning with the input shaping technique so that the flexible appendages' vibration excited by attitude maneuvering is effectively suppressed.For the attitude maneuver control of flexible spacecraft without angular velocity feedback,a fuzzy active disturbance rejection controller is proposed.Specifically,an extended state observer(ESO)and a fuzzy nonlinear feedback control law,which can adjust feedback parameters by fuzzy control online,are designed.Simulation results demonstrate the proposed transient process and attitude controller without angular feedback could suppress appendages' vibration and realize attitude maneuver.In order to achieve robust attitude control of the flexible spacecraft with disturbance,two robust attitude controllers based on sliding mode control are proposed.To reduce chattering,a sliding mode attitude controller based on exponential reaching law is designed,in which the arctan function is employed to replace the sign function.Then,considering the boundaries of the disturbance and the coupling effect unknown,an adaptive radial basis function(RBF)neural network is designed to estimate and compensate the influence caused by coupling and disturbance.Based on this,an adaptive sliding mode attitude controller is proposed,which can suppress the disturbance and chattering under lack of boundary information about external disturbance and coupling effects.Finally,the simulation results demonstrate the effectiveness of the proposed robust controllers.To satisfy the attitude control requirements of high pointing accuracy,high stability and rapid maneuver,this thesis investigates a finite-time attitude maneuver control problem for a flexible spacecraft and proposes three finite time terminal sliding mode attitude control laws.Specifically,for the case that the upper boundary of disturbances and coupling effect can be obtained in advance,a robust discontinuous fast terminal sliding mode based finite time attitude controller is designed.Then,the controller is further enhanced by an adaptive scheme to deal with the more practical case that the boundary is unknown.The enhanced version is continuous and chattering-free.Furthermore,in order to avoid the singularity phenomenon,this thesis proposes a fast nonsingular terminal sliding mode surface and designs finite time attitude controller.Finite-time stability of the systems is proved via Lyapunov technique rigorously.The effectiveness and robustness of the proposed controllers are demonstrated via numerical simulation.To improve the attitude control performance further,robust attitude controllers based on the internal model principle are presented so that asymptotic disturbance rejection and the convergence of modal variables can be achieved.For suppressing vibration,by analyzing the dynamic characteristics of appendages and properly choosing Lyapunov functions,this thesis proposes a robust state feedback controller that can guarantee the convergence of modal variables.Specifically,the measurement state variables for the controller are only the attitude angle and the angular velocity.Aiming at achieving asymptotic disturbance rejection,based on the internal model principle,disturbance compensators with linear and nonlinear dynamics are designed respectively to account for the time-varying disturbances generated by linear and nonlinear exosystems.Combining the feedback controller and the compensators,two robust Lyapunov-based controllers have been designed.Numerical simulation results are exhibited to demonstrate the effectiveness and benefits of the proposed controllers.