Research On Dynamics And Control Of Lorentz-augmented Orbit And Attitude Motion

A Lorentz spacecraft actively modulates its surface charge to generate Lorentz force via interaction with the planetary magnetic field.The induced Lorentz force could be utilized as propellantless propulsion for orbital and attitude maneuvering.With the augmentation of Lorentz force,the Lorentz spacecraft is advantageous over traditional ones in reducing the propellant consumption,enhancing the maneuvering ability,and extending the system lifetime.But,due to the physical mechanism of Lorentz force,it always acts in the direction perpendicular to the local magnetic field.Thus,the orbital and attitude dynamic systems of a Lorentz spacecraft are instantaneously underactuated.Also,the orbit and attitude dynamic systems are highly nonlinear and coupled.Hence,the main technical obstacles that hinder the theoretical development of the Lorentz spacecraft include underactuation,inherent nonlinearity,and dynamic coupling.This dissertation presents an in-depth research into the dynamics and control of Lorentz spacecraft orbit and attitude motion.It proposes a reduced-order sliding mode or backstepping control methodology for a class of underactuated system,and presents a set of decoupled or coupled controllers for Lorentz spacecraft orbit and attitude dynamic systems.Also,it provides insight into the design of Lorentz-augmented space missions,such as spacecraft hovering,formation flying,and rendezvous.The main enhancements and contributions of this dissertation are summarized as follows.In the part of orbit control of Lorentz spacecraft,the fully actuated control method for Lorentz-augmented relative orbit motion is firstly studied.By modeling the Lorentz spacecraft as a charged point mass and approximating the geomagnetic field as a tilted magnetic dipole,a dynamical model that characterizes the orbital motion of a Lorentz spacecraft about an elliptic orbit is developed.In this fully-actuated dynamic system,the hybrid control inputs consist of the Lorentz force and the thruster-generated control force.Based on the characteristics of different missions,including spacecraft hovering,formation flying,and rendezvous,analytical or numerical methods are used to solve the open-loop optimal hybrid control inputs for these different missions.In view of the external disturbances and linear or nonlinear system uncertainties,sliding mode control,adaptive control,and neural control methods are adopted to propose four kinds of fullyactuated state feedback controllers.Also,the corresponding optimal distribution laws of the hybrid control inputs are designed.Furthermore,to accommodate the cases without velocity measurements,another three kinds of observers and corresponding fully-actuated output feedback controllers are proposed.Then,the underactuated control problem of Lorentz-propelled relative orbit motion is studied.For the underactuated case with the loss of radial or in-track thrust,feasibility analyses on three kinds of underactuated relative orbit control missions in both circular and elliptic orbits are firstly conducted,including underactuated hovering,formation reconfiguration,and rendezvous.For underactuated hovering in circular orbits without radial or in-track thrust,the set of feasible hovering position for either underactuated case is analytically solved.To fulfill underactuated hovering control in the presence of unmatched disturbances and input saturation,a novel reduced-order sliding mode or backstepping control approach is proposed,based on which three kinds of underactuated state feedback controllers are proposed.Meanwhile,the indirect method for eliminating the singularity problem in the conventional terminal sliding mode is also enhanced by ensuring the continuity of arbitrary order derivative of the sliding surface at the switch points.For underactuated formation reconfiguration in circular orbits in the absence of radial or in-track thrust,analytical solutions to optimal reconfiguration problems are derived,and a novel underactuated collision-avoidance maneuvering strategy is also proposed to prevent the collisions between spacecraft.In view of the factors including unmatched disturbances,parameter uncertainties,and collision avoidance,finite-time stability of system disturbed by vanishing perturbation is studied,based on which three kinds of underactuated state feedback controllers are then designed.Furthermore,for the underactuated cases without velocity measurements,another problem arising from the simultaneous loss of thrust and velocity measurements is observed,that is,the unknown parameter problem.To solve this newly-found problem,two kinds of adaptive reducedorder observers and corresponding underactuated output feedback controllers are proposed.Notably,all of the aforementioned underactuated control schemes without intrack thrust can be realized by a Lorentz spacecraft.In the part of attitude control of Lorentz spacecraft,a new fully actuated spacecraft attitude control system propelled by the Lorentz torque and magnetic torque is designed.The dynamic model of Lorentz spacecraft attitude motion driven by the hybrid Lorentz and magnetic torques is firstly developed,based on which the charging strategy capable of decoupling the orbit and attitude motion is proposed.Also,the optimal distribution law of the Lorentz and magnetic torques is analytical solved,and the corresponding optimal hybrid inputs consisting of the charges and the coils’ magnetic moments are thereafter derived.In view of the unknown disturbances and model approximation errors,adaptive sliding mode control technique is utilized to design the fully actuated attitude tracking controller,and decoupled orbit and attitude control of the Lorentz spacecraft is achieved.In the part of concurrent orbit and attitude control of Lorentz spacecraft,a coupled control scheme is proposed.Both kinematic and dynamic models for coupled relative orbit and attitude motion of Lorentz spacecraft are developed in representation of dual quaternions.In the event that the reference information is only available to part of the deputy spacecraft,finite-time observer,collision-avoidance maneuvering strategy,and sliding mode controller are designed to achieve distributed six-DOF orbit and attitude synchronization control.Also,the coupled control scheme can be realized by a Lorentz spacecraft.The optimal distribution laws of the hybrid control inputs are analytically solved,and charging strategy that manages both orbit and attitude control is designed.To sum up,this dissertation presents a comprehensive study into the dynamics and control of Lorentz spacecraft orbit and attitude motion.The novel reduced-order sliding mode or backstepping control theory holds theoretical reference value for underactuated system control.Besides,this dissertation put forwards a new fully actuated spacecraft attitude control system driven by the hybrid Lorentz and magnetic torques,and presents systematic decoupled or coupled control scheme designs for Lorentz spacecraft orbit and attitude motion.The aforementioned theoretical results are expected to promote the application of space environment forces and the development of propellantless space missions.