The Robust Attitude Control Of High Precise Spin Stabilized Satellite

As a novel imaging mode for small satellites,the spin imaging mode based on spin stabilized satellite owns the advantages of large-scale coverage and high efficiency.This method has important application value in tasks of wide-area targets searching and fast search imaging,therefore,it has attracted wide attention.A high-accuracy attitude control method for the platform of the spin satellite is well studied in this paper.The content of the thesis could be concluded as follows.The finite-time adaptive tracking controller considering the nonlinearities uncertainty of the spacecraft rigid dynamic model.The high-accuracy and fast tracking of relative reference trajectory can be realized based on the proposed controller.The standard sliding mode is modified to improve the speed of system convergence,and finite-time sliding mode is designed based on the fraction order feedback of quaternion.The singularity problem led by the finite-time control is solved by using the characters that the direction of the Euler axis is invariable and its derivative is zero when rotating around the Euler axis.In finite time,the system converges along the sliding surface to the equilibrium point.Then,adaptive control is designed to deal with the model uncertainty.The update law of rotation inertia estimation is designed by proposing a costate-correction adaptive update law with a convergence rate slower than the system convergence speed rate,the fractional order feedback term is designed and a finite-time adaptive controller is given to realize fast and high-accuracy tracking of the reference trajectory for rigid satellite with model uncertainty.As for the dynamic model of spin satellite with flexible appendages,a state observer is designed for observing the vibration of flexible appendages.The effect of vibration is suppressed by using the flexible modal estimation,and high-accuracy finite-time tracking control with the consideration of flexible appendages is realized.Firstly,the standard first-order system model for flexible modal is established based on the standard second-order model of flexible appendages and the satellite attitude dynamics model without considering external disturbances.Secondly,the attitude angular velocity information and the input signal of the control system are regarded as the quantities observed by a linear system,and the fractional order of the feedback signal is used to construct the state observer correction signal to realize the flexibility vibration state observation of finite-time stability characteristics.Then a fractional order finite-time sliding surface is given based on the Modified Rodriguez Parameter(MRP)model and a finite-time controller is designed by using this sliding surface.And the singularity problem of the controller is avoided by using the modified Rodriguez parameter derivative reasonably.Simulation results show that adding control terms to the estimated results of the flexible modal vibration based on the state observer can eliminate the disturbance torque of the flexible system to the satellite body,and the fast and high-accuracy tracking of the satellite platform relative to the reference trajectory under the condition of the flexible appendage vibration can be realized.As for the dynamic model of spin satellite with flexible appendages considering model uncertainties and external unknown disturbance torques,a robust PID tracking controller with limited control torques and slew rate is designed to track the reference trajectory accurately,which is conducive to direct engineering application.Firstly,the integral term of classical PID controller is modified and the angular velocity term,attitude parameter term and motion equation term are added.At the same time,the coupling terms of attitude angular velocity,quaternion,integral term and flexible modal term are constructed in Lyapunov function to simplify the form and structure of derivative function.The stability of high-order system is proved and the system constraints on control parameters is greatly simplified.Finally,the constraints of system control torque and attitude angular velocity are introduced,and the relationship between them and control parameters is analyzed.The strict and relaxed constraints of system parameters for control parameters are given,which is beneficial to engineering application.Simulation results show that the control algorithm can achieve high-accuracy tracking of reference trajectory for satellite platform under various disturbances and system constraints.