Drag-free Satellite And Its Formation Capturing Control With Prescribed Performance

With the successive proposals and implementation of space gravity detection missions such as GOCE,GRACE,Tianqin,and Taiji,the drag-free satellite technology has been developed in the direction of multi-test masses,multi-working mode,and multisatellite formation,which leads to higher requirements on the control performance,especially the capture control performance in the scientific preparation phase.This thesis focus on the nonlinear capture issues,which include the desired attitude capturing control,the multi-test masses capturing control,and the desired formation configuration capturing control.Combined with advanced control theories such as prescribed performance,backstepping,sliding mode control,and intelligent control,more in-depth research has been carried out,which can be mainly summarized as follows:For the problem of the desired attitude capturing control,an event-triggered adaptive attitude tracking and fault-tolerant control strategy with prescribed performance has been developed.Firstly,to avoid the unwinding and singularity problems,the attitude tracking error kinematics and dynamics are directly formulated on the SO(3),which transforms the desired attitude capture problem into an attitude tracking problem.Then,with consideration of the tracking performance constraints,uncertain model parameters,and time-varying thruster faults,the controller is designed under the Backstepping synthesis framework,where an appointed-time performance function combined with the asymmetric barrier Lyapunov function is employed to realize the prescribed performance metrics on attitude and angular velocity tracking errors,the critic-actor neural networks,and adaptive technique are implemented against the disturbances,faults,and uncertainties and to optimize the tracking performance,a novel exponential event-triggering rule is employed to reduce the update times of the controller,and a stability proof of the proposed controller has been derived.Simulation results demonstrate that the desired attitude can be captured according to the mission-oriented performance requirements.For the problem of multi-test masses capturing control,the position and attitude capturing control of multi cubic test masses have been investigated first,and an eventtriggered adaptive composite capturing control strategy with prescribed performance has been proposed.With consideration of the capturing performance constraints,unknown external disturbances,and so on,the controller is designed based on the prescribed performance method,where a double-level structure with appointed-time performance functions is utilized to construct the prescribed performance capturing controller,the adaptive dynamic programming is employed as the supplement controller to enhance the robustness and optimize the capture performance,a mixture threshold event-triggered mechanism is used to deduce the update frequency of the actuator,and stability proof of the proposed controller has been concluded.Simulation results demonstrate that the position and attitude of test masses can be captured successfully within the mission-defined performance behaviour.Then,the collision-free capturing control of double spherical test masses has been investigated,and two kinds of event-triggered adaptive capturing control strategies with prescribed performance and collision avoidance are proposed.Under the B ackstepping synthesis framework and aiming at the position-level and doublelevel performance requirements,the controllers have been designed in consideration of capturing performance constraints,collision risk,etc.,where the potential function-based algorithm is employed to avoid the collision,the appointed-time performance function and asymmetric barrier Lyapunov function are utilized to prescribe the capture performance envelope,the uncertain model parts and total external disturbances are respectively solved by the RBF neural network approximation and adaptive disturbance estimation,a relative threshold event-triggered mechanism is embedded to deduce the response frequency of the actuator,and stability proof of the proposed controller has been finished.Simulation results demonstrate that the test masses can be captured successfully,and the potential collision risk can be avoided within the mission-defined performance behaviour.For the problem of desired formation configuration capturing control,it has been divided into the inner-formation micro configuration capturing control of the reference drag-free satellite and the outer-formation composite configuration capturing control of around drag-free satellites,which are implemented to build the formation inertial reference and establish the desired formation configuration.Firstly,by taking the Earth’s gravity field detection mission as the background,a follower-rounder inner-formation micro configuration and a wheel-pendulum-follower(backup)composite formation configuration have been designed as the reference trajectories.Then,with consideration of the formation performance constraints,unknown external disturbances,uncertain model parameters,limited communication,etc.,an event-triggered inner-formation adaptive sliding mode tracking control strategy with prescribed performance has been proposed,where the exponential performance function and barrier function are implemented to design the performance bounds for tracking error,the adaptive sliding mode is utilized to overcome the influence of unknown external disturbances,a relative threshold event-triggered mechanism is embedded to reduce the response times of the actuator.Furthermore,an outer-formation cooperative adaptive control strategy with prescribed performance and event-triggered communication has been proposed,where an event-triggered communication scheme is chosen to deduce the communication frequency,an appointed-time performance function is employed to prescribe the performance bounds on relative orbit errors,the critic-actor neural networks,and adaptive integral sliding mode technique are implemented against the disturbances,faults,and uncertainties,and to optimize the tracking performance.The stability analysis of both controllers has been finished respectively.Simulation results demonstrate that the inner-formation micro configuration and the outer-formation composite configuration can be captured respectively according to the mission-defined performance boundary,which means the desired formation configuration can be established successfully.