Research On Dynamics And Control Of Flux-pinned Spacecraft Relative Motion

With the emergence and development of new space missions such as rendezvous& docking,formation flight,on-orbit services and space-based confrontation,the dynamics and control of spacecraft relative motion have arisen as research frontiers and hotspots in the aerospace field.Conventional attitude and orbit control devices such as thruster,reaction flywheel and control moment gyro are usually utilized to control the spacecraft relative motion,but defects like propellant consumption,plume contamination,function limitation and lack of flexibility exist.In recent years,the utilization of inter-satellite column force,electromagnetic force and flux-pinning force to control spacecraft relative motion has become a new research direction.Owing to the unique passive stability,the flux-pinning force shows special application value and potential and also brings new challenges for the dynamics and control of spacecraft relative motion.Concentrating on the dynamics and control issues of flux-pinned spacecraft relative motion,this paper mainly performed researches on the modeling and mechanics analysis of flux-pinning interaction,dynamics modeling using Kane method,relative equilibrium analysis and 3DOF relative state maintenance control based on ESO& LQR.(1)Modeling and mechanics analysis of flux-pinning interaction.Based on the flux-pinning interaction mechanism,frozen image model and the hypothesis of magnetic dipoles,the modeling method for flux-pinning interaction is presented.Moreover,based on the constrained three magnetic dipoles relations,the far-field flux-pinning force/torque models are derived,the analytical expressions of flux-pinning force/torque in one-dimensional and two-dimensional cases are given and the variation rules of flux-pinning force/torque with external magnetic dipoles moving laterally,moving vertically and rotating are analyzed.Finally,the definition and expression of flux-pinning stiffness are presented,with the passive stability analyzed.(2)Dynamics modeling using Kane method and relative equilibrium analysis.The relative motion modeling theories of vectorial mechanics and multi-body dynamics as well as its application features in spacecraft relative motion modeling under flux-pinning interaction are analyzed.Futhermore,in view of two satellites aligned with orbital radial,along-track and normal directional,Kane method is applied to derive the nonlinear dynamic model for flux-pinned two-satellite relative trajectory motion based on the attitude assumption.Moreover,combined with the mechanical properties of flux-pinning interaction,the conditions for three static configurations are derived by analyzing the existence of the relative equilibrium.The multi-solution problems of the relative equilibrium under orbital radial configuration and the existing conditions and solving approaches under along-track and normal directionl configurations are discussed respectively.Finally,the open-loop stability and controllability of the linearized systems under three static configurations are analyzed.(3)3DOF relative state maintenance control based on ESO& LQR.Considering the requirements of relative state maintenance and combined with the linearized model derived from the nonlinear dynamic model under the “small perturbation” assumption,the optimal controller based on LQR(Linear Quadratic Regulator)is derived to realize the feedback control near the relative equilibrium.And the ESO(Extended State Observer)is adopted to estimate the unmodeled dynamics of the system and the external disturbance and to give feedback compensation.Numerical simulations are carried out to verify the validity of the proposed algorithms at last.In conclusion,this paper preliminarily investigates the dynamics and control issues of flux-pinned spacecraft relative motion,proposing the modeling approaches,dynamics properties and control algorithms,which provide a technological foundation for further researches on flux-pinning on-orbit application.