Research On Guidance And Control Method For Mars Precision Landing

To date, all Mars landers having reached the surface successfully (except”Mars ScienceLaboratory, MSL”) have been targeted to landing sites only by approach navigation beforeatmospheric entry, having resulted in large dispersion ellipses with major axis lengthson the order of100km. Hence only the northern hemisphere of Mars, nor the AncientHighlands of southern hemisphere with higher scientifc value, is available for landing dueto its fat terrain and low elevation. Future Mars missions, for instance, sample returnand human exploration missions, require pinpoint landing capability, defned as landingaccuracy within100m.In this dissertation, the study of Mars EDL technology is conducted from the high-precision EDL trajectory optimization, guidance and control and optimal fuel consumptionwith the”MSL” lander as the model and Mars pinpoint landing mission as the engineeringbackground. The main contents of this dissertation compose as follows:First, using the Newton’s laws of mechanics, the Mars entry dynamic model is estab-lished as the theoretical basis for the trajectory optimization and guidance and control ofthe entry segment.Second, the nominal trajectory of Mars entry is planned, which meets the restrictionof procedure (heating rate, dynamic pressure and overload, etc.) and terminal state con-straints (the longitude and latitude of parachute-opening, altitude, velocity and dynamicpressure, etc). The problems of low Mars atmosphere density and limited control authorityhave been thought over so as to solve the situation of losing track of the nominal trajectorygenerated by control saturation.Then, entry guidance algorithms, guidance using a reference trajectory and guid-ance using a predictor-corrector respectively, designed for the guidance and control of theentry trajectory, have been proposed. The nominal trajectory tracking law has been de-signed by using advance ADRC method, and the comparison with PID method has alsobeen preformed to demonstrate the superiority of ADRC algorithm. A novel sectional-ized predictor-corrector guidance algorithm has been presented by combining the heading alignment and predictor-corrector method. To demonstrate the efectiveness and robust-ness of the ADRC method and sectionalized predictor-corrector method, and the goodperformance of sectionalized guidance in shortening the forecasting time, the algorithmshave been tested with dispersions in entry state and model errors of the Mars atmosphereand”MSL” lander.Finally, consider the lowest fuel consumption, the minimum-fuel during the terminalfuel powered descent phase is investigated and the thrust magnitude is the control variable.The Pontryagin’s maximum principle and initial guess method are applied to transformthe minimum-fuel problem into the two-point boundary-value problem (TPBVP). Then,the shooting method and the PROPT software are used to solve this problem.