Research On Control Technologies For Micro-Nano Satellite Relative Motion

In recent years,the development of micro-nano satellite has gradually turned from on-orbit technical validation stage to application operational stage.Higher autonomy,flexibility,agility and inter-satellite coordination are necessary features in micro-nano satellite orbital maneuver control for future-oriented micro-nano satellite space missions.Thus the control technology of relative orbital maneuver is not only the key to determine the mission class of micro-nano satellites,but also the focus of research at this stage.For the relative orbital maneuver control issues of micro-nano satellite platform,on-board resources and control capabilities are restricted,with more restrictive conditions and significant disturbances.It is more difficult to achieve remote autonomy,rapid maneuver,and optimal trajectory.Therefore,the robust control is harder to achieve and the accuracy is difficult to improve.This thesis takes relative orbital maneuver control issues of micro-nano satellite as research object,to establish a complete trajectory planning and control scheme for autonomous high-precision relative motion control.The constraints of mission requirements,on-board resource,and control capability have been comprehensively considered,and the maneuver is oriented to typical long distance relative motion from hundreds of kilometers to meters.Typical relative motion scenarios,such as approaching,rendezvous,flying around,hovering,etc.,are achieved by low cost.The main research contents of the thesis are as follows:Firstly,the trajectory planning of relative motion under the constraints of relative measurement and control of micro-nano satellite are studied.According to the characteristics of relative navigation in the whole process of long-distance relative motion,the whole maneuver process is decomposed in three stages of long-distance,middle-distance and short-distance.Optimal trajectory planning algorithms are carried out with the goal of optimizing propellant consumption.In the long-distance stage,a trajectory planning model is given based on natural periodic relative trajectory under maneuver time and horizon constraints.In the middle-distance stage,based on relaytype thrust model,linear trajectory planning model is established by applying discrete dynamics model and a great variety of linear constraints,including state,control and boundary constraints.In the short-distance stage,considering the random obstacles caused by uncertain surface features of the non-cooperative target satellite,improved A* network search algorithm is used to achieve randomized optimal trajectory and avoid to fall into nonconvex obstacles.By setting different extend path weight,control frequency and maneuver cost are reduced.Through the above-mentioned staged trajectory planning methods,the entire maneuver process can meet the control constraints and terminal accuracy requirements,and the gradual convergence of the long-distance approaching trajectory to the target position is realized,the propellant consumption of the motion is optimized,and the online optimal trajectory of the whole maneuver process is determined.Secondly,aiming at the disturbance and uncertainty of control system,closed-loop control methods for relative motion are proposed to make the motion state converge to the desired trajectory.Based on the linearized dynamic model,the control law of the linear quadratic optimal(LQR)control method is derived for small disturbance maneuver scenarioes.The robust margin of LQR control is wide,and the closed-loop optimal control is easy to implement.Based on the T-H equations relative dynamic model which is applicable to any orbit eccentricity,the sliding mode variable structure control(SMC)method is presented in response to strong external disturbances and high uncertainty in control system.By constructing sliding mode switching surface,the SMC has completely robust for external disturbances and uncertainty of the control system.Under the conditions of strong nonlinearity,high uncertainty and other strong disturbance factors of the control system,the auto disturbances rejection control(ADRC)method is introduced.A method of introducing a known dynamic model into the state observer is proposed to reduce the system observation pressure.The simulation results of these control strategies are provided in this thesis,and indicated that the relative motion control system has a good suppression effect on non-ideal factors.This combined closed-loop control scheme solves the problem of restraining the non-ideal factors in each stage of maneuver.Under the conditions of control constraints and various disturbances,the combined closed-loop control scheme meets the trajectory accuracy requirements of the complete motion at the optimal control cost.Thirdly,design and modeling methods of the micro propulsion system are proposed,which meet the control requirements for the mission and on-board resource constraints.A pretreatment method for stepwise vaporization of liquid ammonia propellant with low heating power consumption is proposed,and based on this,design of self-managed vaporization propulsion system that meets the relay-type output thrust mode is developed.The modeling of the micro propulsion system can be divided into the operation components process part that can be modeled by thermodynamics and the vaporization process part that cannot be directly modeled.The output control quantity model of the thrusters is also established.By the mathematical model of the micro propulsion system,static and dynamic responses are studied separately,and the design iteration cost is reduced.Under the environment of MATLAB/Simulink,the micro propulsion system mathematical model simulation iwas carried out established to carry out simulation verification for evaluating the performance of the system and to provide theoretical basis and optimization data for the design of micro-propulsion system,so as to reduce design iteration and test costs.Finally,based on the relative motion control system proposed in the thesis,a full mathematical simulation system is established,and a complete full-process maneuver simulation verification is implemented.A developing high-orbit micro-nano satellite,which weighs 40 kg and carries the liquid ammonia micro propulsion system proposed in this thesis,implements the relative motion mission.Under the guidance of the main satellite and limited distance autonomous navigation guidance,the trajectory planning and maneuver control methods proposed in this thesis are used to transfer from 30 km to 30 m from the target satellite.The simulation integrates typical maneuver scenarios such as approaching,flying around,hovering,etc.,and validates the effectiveness of the controller design,trajectory planning and control method proposed in this thesis.In summary,the analysis methods,models and solutions of micro-nano satellite relative motion technologies are systematically studied in this thesis.Application design is also carried out in the typical relative motion scenarios.The methods proposed in this study cover various typical missions of micro-nano satellite relative motion control,and provide theoretical basis for future high-class application tasks,such as building distributed micro-nano satellite system,on-orbit service,as well as spatial situation recognition.The research provides technical support for technical realization of the high-class orbit application and lays a certain foundation for further exploring the orbital control technologies of micro-nano satellites.