Research On Dynamics And Control Methods For Spacecraft Electromagnetic Docking

With the sustained development of on-orbit servicing technologies such as onorbit assembly and on-orbit maintenance of large spacecraft,space docking technology has received extensive attention from researchers.However,jet propulsion technology is mostly used in traditional space docking,which has the issue of fuel consumption,and brings light pollution,heat emission,and corresponding vibration disturbance to spacecraft with optical loads.Compared with traditional docking methods,electromagnetic docking technology,as a new type of propulsion technology,has distinct advantages over other docking mechanisms,e.g.,it does not require propellant,nor docking impact or plume contamination,with continuous,reversible and synchronous controllability.This dissertation mainly studies the dynamics and control problem of space electromagnetic docking,including coupled orbit-attitude dynamics modeling and related linearization problems in electromagnetic docking,disturbance observer-based and intermediate state observer-based relative motion control problems,and coupled orbit-attitude control problem.The main contents of this dissertation contain the following parts:Linearized models of orbit dynamics and coupled orbit-attitude dynamics for electromagnetic docking are established considering strong nonlinearity and coupling problems in electromagnetic docking dynamics.First,the far-field model of the spacecraft electromagnetic force/torque is established,and the multi-source external disturbance that the electromagnetic docking system may be subjected to is analyzed from the perspective of disturbance force/torque.Then,taking into account the strong nonlinearity and coupling of the system,the trajectory linearization method is used to process the electromagnetic force/torque model,based on which the linearization models of orbit dynamics and attitude dynamics is established,and corresponding state-space forms are given.Finally,considering the coupling of orbit-attitude in the electromagnetic docking process and the attitude dynamics coupling between the two spacecraft,the linearization form of the far-field model for electromagnetic force/torque of the two spacecraft is derived,and the linearization model of coupled orbit-attitude dynamics is established,and corresponding state-space form is given.A disturbance observer-based control method is proposed for electromagnetic docking considering external disturbance,actuator fault,orbital eccentricity,unknown spacecraft mass,input magnitude and rate constraints.First,the unknown spacecraft mass,orbital eccentricity,external disturbance and actuator fault are separated into lumped disturbance.Then,a disturbance observer is designed,based on which an anti-disturbance controller is developed,and the input magnitude and rate constraints are considered,and the uniform ulimate boundedness of the system is proved.Simulation results show that compared with the benchmark/optimal sliding mode controller,the proposed controller has more acceptable control and application concomitant;compared to linear quadratic regulator controller,the developed controller can significantly improve the steady-state accuracy of relative position and velocity.An intermediate state observer-based anti-disturbance H∞ control method is proposed considering external disturbance,actuator fault,unknown spacecraft mass and state,orbital eccentricity,measurement error and input constraint.First,an intermediate variable is introduced,and an intermediate state observer is designed based on this,which can simultaneously estimate relative motion and lumped disturbance information.Then,an anti-disturbance H∞ control method is given,which explicitly considers the input constraint problem,and the uniform ulimate boundedness of the system is achieved.Simulation results show that compared with the disturbance observer-based controller in previous chapter,the proposed intermediate state observer-based anti-disturbance control method can significantly reduce the stabilization time,and improve control force utilization efficiency.Two global asymptotically stable control methods are proposed consider ing the multi-dimensional,strong nonlinear and coupled orbit-attitude problem of electromagnetic docking.First,the trajectories of relative motion and attitude maneuver of the two spacecraft are segmentedly planned,and the characteristic time points are given.Second,the sliding mode controller is designed based on the integral sliding surface and the finite time reaching law to ensure that the system state reaches the sliding surface in a finite time,and finally converge to a small bound containing equilibrium.Then,an adaptive variable structure controller is designed to ensure that the errors of relative position and attitude angle asymptotically converge to a small bound containing equilibrium.Simulation results show that the developed sliding mode controller has superior performance compared with the adaptive variable structure controller in terms of the application effect and the convergence speed of the relative position error.