Attitude Stabilization Control For Combined Spacecraft

On-orbit service is a space technology for orbiting spacecraft maintenance,component replacement,fuel filling,orbital debris cleaning,which can effectively improve the performance of spacecraft,extend the service life of spacecraft,and recover economic losses caused by spacecraft failure.It has very important practical significance and theoretical research value.The attitude control of the combined spacecraft after capturing the target is an important part of the on-orbit service task,and is the premise and basis for completing the subsequent complex operations.Since the target spacecraft affects the parameters and structure of the combined system,the combined spacecraft is a complex time-varying nonlinear system with parameter uncertainty and dynamic coupling.Due to its internal factors,the combination spacecraft also has problems such as control signal discretization,actuator saturation,and unmeasurable angular velocity.These factors have brought great difficulty to the design of the combined spacecraft attitude control system.Therefore,this thesis is dedicated to investigating the problem of the attitude control method of the combined spacecraft after the target acquisition in the orbital service mission.The main contents include:The attitude model of the combined spacecraft after target acquisition is established,including the kinematic model of the combined spacecraft,the deterministic dynamic model and uncertainty dynamic model of the combined spacecraft,and the dynamic model of partially constrained combined spacecraft.To solve the attitude control problem of the combined spacecraft with unknown parameters,two adaptive finite-time control methods are proposed.Firstly,for the combined spacecraft system with unknown external disturbance,a finite-time controller based on integral sliding mode is designed.To cope with the quantization problem caused by the discrete control signal,an improved quantizer is designed,which effectively reduce the chattering problem caused by quantization and has a lower communication frequency.Then,an adaptive method is used to compensate the external disturbance and quantization error.Secondly,for the combined spacecraft with inertia uncertainty and external disturbance,an observer-based attitude controller is proposed.An improved super twisting observer is used to observe the total uncertainty of the combined spacecraft,and the finite-time controller is designed by backstepping method with the observed value.The designed controller can implement finite-time attitude control of combined spacecraft.To solve the attitude control problem of the combined spacecraft with completely unknown parameters,two model free controllers are proposed.Firstly,a novel approximate optimal model free attitude controller based on the adaptive dynamic programming theory is proposed.Action and critic neural networks are employed to approximate the control law and the iterative cost function,respectively.A convergence analysis of the proposed controller with finite iteration is made.Two-layer neural networks with deep learning across all layers are used,which has a better learning efficiency.The stability of neural network is also analyzed.Secondly,an output feedback attitude controller based on prescribed performance method is proposed.A tracking differentiator is used to estimate the unavailable angular velocity of the combined spacecraft.Then,a prescribed performance control scheme is developed,wherein,the attitude and attitude velocity of combined spacecraft are guaranteed with the prescribed performance.The convergence of the proposed controller is also analyzed.To solve the attitude control problem of partially constrained combined spacecraft with completely unknown parameters,two data driven controllers are proposed.Firstly,an attitude controller based on model free adaptive data driven method is designed.The generalized disturbances composed of external disturbances and dynamic linearization errors are reconstructed by a discrete extended state observer.The input saturation is overcome by introducing an antiwindup compensator.Numerical simulations are carried out to demonstrate the effectiveness and feasibility of the proposed controller.Secondly,a novel forecasting based data driven model free adaptive sliding mode attitude control is developed.The forecasting based data driven model free adaptive controller is developed to ensure its adaptation to various working conditions by simultaneous adjustment of controller parameters with online and offline input–output measurement data.Then,a sliding-mode-based supplementary controller is introduced to improve the tracking performance in terms of robustness.The simulation results verify the effectiveness of the proposed control method.