Mars Atmospheric Entry Guidance Method Based On Drag Acceleration Tracking

With the human exploration of Mars in depth,the future of Mars mission is to achieve the goal of precision manned landing on the Mars surface.The technology of EDL(Entry,Decent,Landing)in the process of Mars landing is one of the key technologies in the future manned landing mission,in which the environment of atmospheric entry phase is the worst,which influences the landing accuracy,and even the landing safety.This paper mainly focuses on the guidance method and trajectory design of Mars atmospheric entry.The main contents are as follows:Firstly,the atmospheric entry motion is modeled.Coordinates and the relevant coordinate system are introduced,the physical configuration of the lander and the aerodynamic model are introduced,too.The environmental model of Mars is determined,the centroid motion equations of the atmospheric entry are given,and the calculation parameters such as range are defined.This is the basic work of the full text,providing a mathematical model for later research.Secondly,considering the many constraints in the task,the reference drag acceleration profile is designed by parametric design analysis after constructing the disk-gap-band parachute box and determining the deployment speed,as a reference curve for the following guidance tracking method.Also a profile online update method is given to correct the range deviation caused by the disturbance.Thirdly,the entry guidance method based on drag acceleration tracking is studied.First the longitudinal motion equations with the drag acceleration as the state variables are obtained by the derivation of the formula for the guidance design.Then,the different guidance law is designed and the mathematical simulation is carried out by using the theory of infinite time state regulator and the pole placement method respectively,while making the analysis and comparison in tracking performance,guidance precision and other indexes of these two methods.Finally,the drag acceleration profile optimization method under the uncertainty is studied.The covariance analysis model is established first,and the feasibility of error estimation is proved by comparing the results of linear covariance recursion and Monte Carlo simulation.In this paper,a optimization method based on covariance analysis is proposed to minimize the sum of the deploy point variance of latitude and longitude.Lastly,the optimal profile and the profile obtained by parametric design are analyzed and compared about the spreading of deploy point by using the former designed tracking law in Monte Carlo simulation.