Research On Spacecraft Electromagnetic Docking Control And Experiment Method

Space rendezvous and docking(RVD)using intersatellite electromagnetic interaction is a technological innovation and advanced research hotspot in the field of spacecraft relative motion control.As a new type of space noncontact force/torque,intersatellite electromagnetic interaction is produced by the interaction among electromagnet-based devices on spacecraft and acted on each spacecraft.Since intersatellite electromagnetic interaction has many distinct advantages,e.g.,the consumption of renewable energy rather than propellant,no plume contamination,and continuous and reversible controllability,it is especially suitable for micro-spacecraft on-orbit servicing tasks.In fact,the difficulty of spacecraft electromagnetic docking control mainly comes from the control of intersatellite electromagnetic interaction and the new characteristics that is introduced into docking dynamics by intersatellite electromagnetic interaction,such as model uncertainties,unknow external disturbances,strong nonlinearity,and strong coupling.In order to address the problems involved in spacecraft electromagnetic docking control,this dissertation carries out the theoretical and technical researches on electromagnetic docking dynamics modelling,docking control methods of fully-actuated and underactuated spacecraft,docking trajectory fast optimization and ground electromagnetic docking experiment.In terms of the basis of electromagnetic docking dynamics,the corresponding coordinate systems and their transformation relations are firstly given.Then,the exact model and the far-field model of intersatellite electromagnetic interaction are briefly derived,and the influence of relative distance,relative attitude and electromagnet-based device parameters on far-field model error is studied.In addition,the relationship of magnetic moment direction and energy consumption in the condition of desired electromagnetic force is derived to obtain the optimal magnetic moment direction,which provides the theoretical foundation for the settings of simulation conditions in the later chapters.Based on the model derivation and error calculation above,the orbit dynamics and attitude dynamics of space electromagnetic docking are established,and some calculation formulas of various external disturbances are given.Secondly,the electromagnetic docking control method of fully-actuated spacecraft is studied.Forcing on the problem of dynamics model uncertainty caused by the far-field model,two model modification methods of the electromagnetic force far-field model are proposed to improve the applicability of the far-field model in electromagnetic docking control.Based on the modified model,a feedback linearization-based nonlinear controller is designed,and the effectiveness of the model modification is verified by comparing the control effects with and without modification.Considering the requirements of strong robustness,high control accuracy,fast convergence,and soft docking of electromagnetic docking control,and aiming at the problems of strong nonlinearity,strong coupling,model uncertainties and unknown external disturbances,a disturbance observer-based global fast nonsingular terminal sliding mode control method is proposed.The stability of the closed-loop system is proved and the superior performance of the proposed method is verified by comparing the control results of three simulation scenarios.Considering the constraints of micro-spacecraft on mass,volume,power consumption and performance of micro-spacecraft,electromagnetic docking control methods of underactuated spacecraft in two task modes are investigated to solve the six degree of freedom docking control problem in which only one single coil equipped on each spacecraft.These two task modes are one single underactuated micro-spacecraft docking control with the magnetic moment direction of the large spacecraft is fixed and two underactuated micro-spacecraft docking control.For these two modes,the electromagnetic docking dynamics models of one single underactuated spacecraft and two underactuated spacecraft are established respectively,and the generation methods of desired relative position sequences and desired attitude sequences are proposed,and an improved 3rd-order exact robust differentiator is proposed to generate the smooth desired attitude differential information.Furthermore,an asymptotically stable controller for one single underactuated spacecraft docking and a finite-time controller for two underactuated spacecraft docking are designed.The simulations are conducted to verify the proposed controllers.Further considering the optimization of docking procedure and the autonomy of the generation of the optimal trajectory,the on-line trajectory optimization method of electromagnetic docking is studied.According to the characteristics of the electromagnetic docking problem,the corresponding trajectory optimization model is established.Firstly,from the perspective of improving the solving accuracy of the trajectory optimization,the continuous optimal control problem of electromagnetic docking is transformed into a discrete nonlinear programming(NLP)problem by using Radau Pseudospectral Method(RPM),and the transformed discrete state variables and control variables satisfy the dynamic constraints at collocation points.Secondly,in order to improve the efficiency of the optimization algorithm and get the best out of the mathematical advantages of convex optimization algorithm such as rapidity,globality and certainty,the successive convexification method and a newly designed hybrid successive convex programming method are proposed respectively for the problem above to convexify the nonconvex constraints.Then,the NLP problem is further transformed into a series of convex subproblems and the rapid trajectory optimization algorithm for space electromagnetic docking is designed.Finally,the numerical optimization experiments are conducted to validate the correctness,effectiveness,and rapidness of the proposed algorithm.Finally,the physical simulation experiment of electromagnetic docking is carried out.First,the ground experiment scheme is outlined,and the overall designs of chasing spacecraft and target spacecraft is presented,respectively.According to the overall technical indexes and experiment requirements,the on-board subsystem,the measurement and control subsystem,the power subsystem and the structure subsystem are designed in detail.Then,the ground electromagnetic docking dynamics model is designed,and the translational controller and rotational controller are designed.The test process,the experiment process,and the experiment results are given in the last.In summary,this dissertation focuses on the research of spacecraft docking control method based on intersatellite electromagnetic interaction.The electromagnetic docking control methods for fully-actuated and underactuated spacecraft are studies,a fast trajectory optimization algorithm of electromagnetic docking is proposed,and the physical simulation environment of ground docking experiment is established.The research achievements of this dissertation may provide theoretical foundation and experimental basis for the application of intersatellite electromagnetic interaction in the field of spacecraft relative motion control.