Research On Attitude Control Of Spacecraft With Rotating Scan Imaging Payload

With the rapid development of space technology and the increasing complexity of space missions,Earth observation spacecrafts need to break through the existing bottleneck of imaging technology and improve the spacecraft’s coverage of the ground.To meet the technical application requirements of the Earth observation mission,a spacecraft model equipped with a spinning scanning imaging payload and rotating sails is developed.In this paper,the spacecraft attitude control problem with external perturbations,model uncertainties,and system uncertainties such as actuator failures is investigated in detail.Then,different control strategies are proposed to solve the attitude stability control problem of the complex system.The main contents of the dissertation are as follows.For the spacecraft equipped with a rotating payload and rotating symmetrical solar panels,considering the effects of load rotation,solar wing rotation and coupling effects on the attitude motion of the spacecraft,the spacecraft dynamics model is developed using the Lagrange method.The proposed spacecraft dynamics model can describe the translational and rotational motion of the spacecraft and its associated components combined with the dynamics model of the mechanical bearing.Based on the variation of the magnetic gap of the magnetic levitation bearing,a simplified dynamics model of active magnetic bearing with five degrees of freedom is developed using the equivalent stiffness and equivalent damping methods.In the case of spacecraft with mechanical bearings,the dynamic equations are transformed into second-order pseudo-linear equations on basis of quaternions.The control system for the described spacecraft model is designed based on higher-order full-drive theory.A suitable controller is designed through the direct parameterization of the spacecraft model,and the optimal configuration of the free parameter matrix in the controller ensures the stability and superior dynamic characteristics of the system.Then,considering the dynamic and static imbalance of the rotating payload,two attitude dynamics models are developed,respectively.One regards the imbalance as a source of the disturbance.In the other model,the payload and platform are considered to couple with each other.A non-singular sliding mode surface is designed based on the error angular velocities and error quaternions of the spacecraft,and finite-time attitude controllers are proposed based on the sliding mode surface.The stability of the spacecraft system is analyzed by means of the Lyapunov equation.Numerical simulations verify the effectiveness of the proposed control method and its superiority over other control strategies,and illustrate that the proposed sliding mode controller can achieve high-precision stable control of the platform and high-precision stable scanning imaging of the payload.In the case of spacecraft with a magnetic levitation bearing.Firstly,the sliding surface is designed to control the current of the magnetic levitation bearing,and thus the magnetic gap can be adjusted.Then,the fixed-time and prescribed-time sliding mode control strategies are proposed for the spacecraft attitude control system.The stability of the system is analyzed and the numerical simulation results are given.Those are demonstrated to verify that the proposed controller can achieve a stable rotation of the scanning imaging payload and the sails,and stabilize the platform attitude.It is also illustrated those strategies meet the control accuracy requirements.Considering the model uncertainty and the actuator failure of the spacecraft,an adaptive disturbance observer is used to compensate for the disturbances,and fuzzy control algorithms are effectively used to deal with the system uncertainties.A fault-tolerant control strategy is proposed combining fuzzy control and sliding mode control.The numerical simulation proves that the proposed fault-tolerant control strategy combining fuzzy control and sliding mode control has strong robustness and the control parameters can converge to the vicinity of the equilibrium point in a finite time,and the proposed control strategy can achieve fast response and high control accuracy of attitude control.