Robust Anti-unwinding Control For Rigid Spacecraft

Attitude control is the essential prerequisite to guarantee the success of the space missions.Recently,space missions,such as earth observation,rendezvous and docking,deep space exploration become more and more difficult,which requests the attitude control system with high precision,fast converge speed and strong capability of reliability.However,the inherently nonlinear dynamics of spacecraft and the complexity of the space environment make it difficult to design attitude controllers.Furthermore,due to the fact that the traditional control method cannot be applied to variety of new space activities,it is necessary to design controllers for these newly proposed missions.Taking the external disturbance,unwinding phenomenon,actuator saturation constraints and actuator faults into consideration,several attitude controllers are proposed in this paper based on homogeneous theory,sliding mode technology and backstepping method.Under the proposed controllers,energy consumption can be reduced and system performance involving robustness,convergence speed and accuracy will be improved to a great extent.Control strategies on basis of homogeneous theory cannot deal with the external disturbance,which will be improved by the proposed controllers.Fault-tolerant attitude controllers with the capability of avoiding unwinding,finite-time anti-saturation attitude controllers without unwinding and fixed-time anti-unwinding attitude controllers are firstly proposed in this paper.The main content of this paper can be summarized as:1.The robust attitude stabilization control problem for rigid spacecraft has been investigated based on unit quaternion in this paper.Firstly,the attitude dynamic and kinetic equations are transformed to a Euler-Lagrange equation.Then,the properties of the Euler-Lagrange system,homogeneous theory,integral sliding mode technology and full-order sliding mode method have been used to design controllers for spacecraft,including integral sliding mode attitude controller,adaptive integral sliding mode attitude controller,finite-time integral sliding mode attitude controller,adaptive finite-time integral sliding mode attitude controller and full-order sliding mode anti-unwinding attitude controller for rigid spacecraft.The external disturbance and high frequency chattering can be totally dealt with by the integral sliding mode control strategy and the full-order sliding mode method,respectively.2.Based on the rotation matrix,finite-time attitude atracking control problem has been investigated in this paper.Firstly,homogeneous theory is applied to design finite-time attitude tracking controllers for microsatellite with the attitude velocity information being measurable and unmeasurable,respectively.Then,backstepping method can be used for controllers design under the assumption of bounded external disturbance.Finally,with or without the attractive region constraint,fast terminal sliding mode technology is used to construct adaptive attitude tracking controllers.Simulation results reveal that the proposed sliding mode controllers can track the reference attitude in finite time with desired control accuracy and convergence rate.3.Considering the external disturbance,actuator saturation constraint and actuator fault,the finite-time attitude tracking problem has been investigated in this paper.Firstly,a fault-tolerant control scheme is established.With adaptive law estimating the minimum value of the fault,terminal sliding mode method is applied such that the attitude system has strong robustness to the external disturbance and actuator fault.Then,an anti-saturation controller is proposed to handle the external disturbance,parameter perturbation and input saturation constraint.With the attractive region constraint,the proposed controller can track the desired attitude in finite time.4.The fixed-time attitude tracking control problem for spacecraft without unwinding has been investigated.Firstly,without taking the external disturbance into consideration,two fixed-time attitude controllers are proposed for microsatellite based on rotation matrix.Then,taking the external disturbance into consideration,the fixed-time attitude controllers are developed when the upper bound of the external disturbance is available.Convergence times of the fixed-time controllers are decided by the control parameters rather than the initial values of system states.Simulation results can demonstrate the effectiveness of the proposed controllers.Simulation comparisons giving in this paper can show the advantage of the proposed controllers.Finally,it gives conclusions and the future work of this paper.