Research On Navigation And Control During Mars Orbit Insertion

Mars orbit insertion is the premise of successfully entering the orbit of Mars and the key to the success of the Mars exploration mission.At the same time,there are many risks in this phase,such as large communication delay between the spacecraft and the earth,and many unkown environment factors.Therefore,it is necessary for the Mars probe to have the ability of autonomous navigation and control in the Mars orbit insertion phase.Based on the first Mars exploration mission of China in 2020(Tian Wen-1),this thesis focuses on the autonomous navigation and control during the Mars orbit insertion phase,aiming at three problems: how to determine the position and speed of the probe relative to Mars,how to generate the optimal orbit control strategy,so that the probe can be captured by Mars and enter the predetermined elliptical orbit with the minimum fuel consumption,how to control the thrust engine,make the control error less to the acceptable range,and meet the orbit and attitude control index.The main contents are as follows:First of all,in view of the great change of dynamic environment in the process of Mars orbit insertion phase and the strong nonlinear and coupling characteristics of the exploration control system,the requirements and working sequence of the spacecraft’s navigation and control tasks are analyzed,the Mars gravitational model and the near Mars multi-body dynamic model are established,and the changes of dynamic characteristics and the generation mechanism and propagation characteristics of various errors in models during Mars orbit insertion phase are analyzedSecondly,in view of the real-time and accuracy requirements of autonomous navigation and control of probe in Mars orbit insertion phase,an autonomous navigation method based on the combination of astronomical angle measurement and speed measurement is proposed,and a measurement model based on the image of Mars and the frequency shift of star spectrum is established.The observability of the navigation system is analyzed,and the ephemeris error and measuring instrument of the navigation target are given The mathematical model and statistical characteristics of the error source of the sensitivity equivalent measurement model are studied.The transfer mechanism of the error in the nonlinear dynamic model of the detector orbit is studied.The mapping relationship between the measurement error and the navigation accuracy is established,and its influence on the navigation performance is analyzed.On this basis,a multi-source,multi-mode,time-varying,nonlinear integrated navigation information fusion algorithm is proposed to realize the continuous,autonomous,real-time and high-precision navigation of the Mars orbit insertion phase,and provide the optimal estimated navigation information.Thirdly,in order to meet the control demand of Mars orbit insertion phase under the condition of limited thrust and ensure that the Mars probe can safely and efficiently achieve the Mars orbit insertion,the thesis analyzes the inertial constant attitude control strategy,the constant angular rate control strategy,and the anti track control strategy.A dual-step optimization scheme based on a combined intelligent algorithm is proposed to optimize the orbit change parameters of the orbit insertion phase.The simulation and analysis of three optimized strategies are briefly carried out.Results show that the proposed scheme can effectively avoid the influence of different optimization algorithms on the optimization results,and can further improve the optimality of the solution.The effect of thrust deviation,navigation error,attitude control error and other factors on the capture trajectory control is analyzed,and the engineering feasibility analysis of three acquisition strategies is also given.Then,aiming at the attitude control problem under the condition of system parameter uncertainty,external interference and actuator saturation characteristics,a hierarchical saturation PID controller is proposed.The proposed controller can give full play to the control ability of the actuator and ensure the stability of attitude tracking.Then an adaptive sliding mode controller for the detector in the process of Mars orbit insertion is designed,and its stability is proved by Lyapunov approach.Simulation results show that the designed controller can still achieve high control accuracy and stability under system error and uncertainty.Finally,based on the real-time simulation platform,the dynamic simulation environment of Mars probe is built,and hardware in loop simulation is carried out to realize multi vector fusion of speed measurement and navigation,adaptive nonlinear navigation state estimation,guidance and control law of Mars orbit insertion.The navigation performance and control algorithm efficiency are compared and evaluated to verify the effectiveness and performance of autonomous guidance and control scheme of Mars orbit insertion.