Research On Spacecraft Integrated Orbit-attitude Modeling And Control Methods

The modeling and control of spacecraft's attitude and orbit are key enabling tech-nologies for the success of many space missions.Therefore,a huge number of researches have been conducted by experts in home and abroad in recent decades.Traditionally,the modeling and control of translational and rotational motion of a spacecraft are described independently with the mutual couplings neglected,which leads to poor control results With the rapid development of space technology,to satisfy the control requirement of future missions,high precision control should be guaranteed.Thus,the translational and rotational motion should be considered in a coupled six-degree-of-freedom(6-DOF)framework.According to the above analysis,this thesis will concentrate on exploring new technologies and methods for the integrated orbit-attitude modeling and control of spacecraft operating near Earth.The main contents of this dissertation are as followsFor the relative position tracking and attitude synchronization control problem,the mathematical tool Lie group SE(3)is adopted.Firstly,using the exponential coordinates on SE(3)to describe the configuration(position and attitude)tracking errors,the relative 6-DOF coupled model is developed in the presence of model uncertainties and external disturbances.Then,a traditional fast terminal sliding mode controller is proposed to guarantee that the tracking control objective comes true.Considering that the existing of sign function in the controller will cause the chattering phenomenon,an adaptive sliding mode controller is designed.The stability of the closed-loop system is proved by Lyapunov method.Finally,the effectiveness of the proposed controllers is illustrated through numerical simulationsIn the sequel,for the same mission,a robust adaptive controller integrated with an extended state observer(ESO)is proposed to solve coupled spacecraft tracking maneu-ver in the presence of model uncertainties,external disturbances,actuator uncertainties including magnitude deviation and misalignment,and even actuator saturation.More specifically,employing the exponential coordinates on SE(3)to describe configuration tracking errors,the coupled 6-DOF dynamics are developed for spacecraft relative mo-tion,in which a generic fully actuated thruster distribution is considered and the lumped disturbances are reconstructed by using anti-windup technique.Then,a novel ESO,devel-oped via second order sliding mode control technique and adding linear correction terms to improve the performance,is designed firstly to estimate the disturbances in finite time Based on the estimated information,an adaptive event-triggered fast terminal sliding mode controller is developed to guarantee the asymptotic stability of the resulting closed-loop system such that the trajectory can be tracked with all the aforementioned drawbacks ad-dressed simultaneously.Moreover,the event-triggering strategy updates and allocates the control signal to the thrusters at prescribed discrete events and is shown to significantly reduce the data-rate requirement.The stabilities of the observer and controller are proved by Lyapunov method.Finally,the effectiveness of the proposed schemes is illustrated through numerical examplesFor the optimal orbit transfer maneuver of thrust-vectoring spacecraft,where the chaser spacecraft is equipped with only one impulsive thruster fixed in the body frame,while the thrust direction is pointed using attitude control of the spacecraft,an improved particle swarm optimization(PSO)algorithm is employed to generate an optimal multiple-burn trajectory in terms of thruster pulse duration and required attitude,and the terminal conditions are met by Lambert method.A finite-time attitude sliding mode control de-signed by the attitude error function on SO(3),is proposed to ensure that this required thrust vector is met exactly at the prescribed time.The proposed improved PSO algorithm is compared with one which utilizes a conventional PSO and is shown to significantly im-prove performance.In addition,the set-point attitude control is illustrated,in simulation,to deliver the required thrust direction at the prescribed timeFor the relative position tracking and attitude synchronization control problem of spacecraft formation flying(SFF)under changing topologies,the relative 6-DOF dynam-ics of the SFF system are developed firstly in the form of a standard Euler-Lagrange formulation,where modified Rodrigues parameters(MRPs)are applied herein to describe the relative rotational dynamics and the relative translational dynamics are established in the LULH frame of the virtual leader.Then,a robust adaptive finite-time sliding mode controller is proposed such that the followers will track their desired states with respect to a virtual leader and keep their relative states fixed in the presence of model uncertainties and external disturbances.Furthermore,a modified controller integrated with collision avoidance(CA)scheme generated from an artificial potential function(APF)is designed to guarantee inter-agent collision avoidance during the maneuver.The resulting closed-loop systems are proved to be finite-time stable using Lyapunov theory.Finally,numerical examples are presented to show the effectiveness of the proposed schemes.