Trajectory Optimization And Tracking Control For The Mars Entry Phase

The process of Mars landing can be divided into three stages: Mars entry,descent,and landing.The Mars entry phase begins when the detector enters the Martian atmosphere and ends when the parachute is opened.Since the aerodynamic environment in the process of Mars entry phase is the most severe phase of the whole Mars exploration and landing process,at present,one of the most effective methods to improve the precision of the final landing accuracy is applying effective guidance control during the Mars entry phase.Therefore,in order to improve the landing accuracy of the Mars detector,the trajectory optimization problem and tracking guidance algorithm of the Mars atmospheric entry phase are studied in this thesis.The details are as follows:A reference trajectory optimization method which combines the standard particle swarm initial value optimization and hp adaptive Radau pseudospectral trajectory optimization is proposed.Based on the analysis of the dynamic model of the Martian atmospheric entry phase and considerations of the initial and final values,boundaries,and security constraints on the process of Mars atmospheric entry phase,taking the fuel optimization as the performance index,the initial values of longitude and latitude,path angle,heading angle and bank angle are optimized by using standard particle swarm optimization algorithm,and then the optimized initial values are applied to hp adaptive Radau pseudospectral method to find a reference trajectory of the Mars atmospheric entry phase that satisfies both the constraints and the performance index.Taking the cosine value of the bank angle as the control variable,a terminal sliding mode control algorithm is introduced and the algorithm is improved to make it suitable for the Mars atmospheric entry phase: saturation control is introduced to limit the boundary of control variable;hyperbolic tangent function is introduced to replace the symbolic function in the sliding mode surface function and the controller function to solve the chattering problem inherent in sliding mode control;the angular velocity and angular acceleration of the bank angle are restricted to prevent the sudden bank angle changes.The improved terminal sliding mode control algorithm is used to track the reference trajectory of the Mars atmospheric entry phase,and the correctness and effectiveness of the algorithm are verified by MATLAB simulation experiments.On this basis,1000 times Monte Carlo parachute opening points distribution simulation experiments are performedwith considering the uncertainties of initial state and aerodynamic coefficient.Finally,the parachute opening points are all distributed in a circle with a radius of 10 km,the robust performance of the algorithm is verified.