Guidance Methods For The Mars Atmosphere Entry

In the Mars landing exploration mission,the lander flies into the Martian atmosphere at hypersonic speeds.The choice of lift entry type and the use of closed-loop guidance technology,to improve the landing accuracy,enhance landing safety,and then successfully achieve a soft landing Mars exploration,is of great significance.This thesis combines the National Basic Research Program of China(973 Program)project "Planetary Surface Accurate Landing Navigation Guidance and Control Research" and China's first Mars landing exploration mission in 2020,and studies in-depth the problem of Mars hypersonic entry guidance design,for the purpose of addressing the technical difficulties of both safe and successful landing and improved landing accuracy.According to the need of Mars entry guidance,the commonly used coordinate system and the mutual conversion relationship in the modeling process are defined.According to the characteristics of the small lift-drag ratio of the lander and the environmental characteristics of the Mars,the flight path control mode and flight dynamics model of the lander are described.On this basis,the dynamic models of three degrees of freedom and six degrees of freedom are established.Through the mathematical simulation analysis,the rationality and validity of the established dynamic model are verified.The entry guidance method based on perturbation theory is studied.According to the requirements of landing exploration task to entry guidance,the design and analysis of the reference trajectory are carried out.On this basis,the perturbation guidance law is designed.Through the three-degrees-of-freedom Monte Carlo simulation,the robust performance of the method in response to the multi-source disturbance environment of Mars is analyzed.And the sensitivity analysis of important disturbance factors is carried out to verify the inherent shortcomings of this method under the condition of large disturbance.The entry guidance method based on predictor-corrector is studied.In order to solve the problem that the constraint equation may not have a root in the process of predictive correction when the terminal flight error is zero,the Gaussian-Newton numerical correction method based on step size control is used.The robustness of the linear tilting angle profile as a design scheme is verified by mathematical simulation,and through the sensitivity analysis,we point out the contradiction of the excellent robustness of the predictive correction guidance method to the accuracy of the voyage control under the condition of large disturbance and the performance degradation of opening the parachute.The flight mission design and the six-degree-of-freedom simulation are carried out to comprehensively evaluate the flight trajectory performance of the designed entry guidance plan in the Mars landing exploration mission.The simulation results show that the designed guidance plan is reasonable and feasible,and can meet the constraint requirements of the task.The advantages and disadvantages and technical difficulties of the two guidance plans are summarized,and the result show that they have the reference value of engineering application.