Trajectory Optimization And Tracking Guidance For Mars Landing

On May 15,2021,the Tianwen-1 probe carried the Zhurong rover successfully landed in the pre-selected landing area,and successfully realized the "circumnavigation,landing,and patrol" mission.The Mars rover is mainly divided into three stages(Entry Descent Landing,EDL)from de-orbiting into the atmosphere to finally achieving landing.The guidance and control of the entry section and the power descent section determine the s uccess of the probe’s landing,and also affect the probe’s landing accuracy.Therefore,this article has carried out related research on the guidance and control of the Mars rover’s entry and power descent stage.The main content of this article is divided into four parts:First of all,this article introduces the entire landing process of the Mars probe and the classification of the probes,and conducts related investigations on the guidance law design of the entry section and the guidance law design of th e power descent section respectively,leading to the main content and structural arrangement of each chapter of this article.Secondly,this article models the detector dynamics and gives the corresponding mathematics and control preliminary knowledge to pave the way for the content of the subsequent chapters.Then,for the guidance problem of the entering section,this paper is based on the nominal trajectory guidance scheme,and for the non-convex constraint,the first-order Taylor expansion method is used to locally approximate the solution of the nonlinear equation,and then the nonlinear programming problem is transformed into solving multiple Sub-problems of convex optimization.According to the establishment of the sequence convex optimization to solv e the entering segment trajectory optimization problem model and algorithm flow,the optimized nominal trajectory is obtained,and the sliding mode tracking guidance law based on drag acceleration is designed to track the nominal trajectory,and achieve a fast and high speed of the nominal trajectory.Precision tracking.Next,for the guidance law design of the three-degree-of-freedom dynamic descent section,this paper adopts the scheme of nominal trajectory optimization and tracking guidance.In terms of nominal trajectory optimization,this paper adopts two methods,direct convex optimization and sequential convex optimization,to solve the two situations of fixed terminal time and variable terminal time respectively.The direct convex optimization soluti on is fast and can quickly solve the fuel-optimized trajectory,but it requires a fixed terminal time.For this problem,this paper uses sequential convex optimization to solve the problem of fixed terminal time in direct convex optimization.The simulatio n results show that both methods have achieved good results,and the optimal fuel trajectory and optimal terminal time are optimized.For the nominal trajectory tracking,based on the fast terminal sliding mode control,this paper gives the design process of the control law,proves the stability of the controller,and obtains the conclusion that it converges to the equilibrium point in a finite time.At the same time,the simulation results show the correctness of the designed control law.Finally,this paper aims at the trajectory optimization problem of the dynamic descent section in the case of pose coupling,by introducing the quaternion and the rotational angular velocity,the dynamic equation of the pose coupling is obtained,and the sequential convex optimization algorithm of the dynamic descent section with six degrees of freedom is constructed.And solves the problem that the terminal time is not fixed.In addition,this paper also studies the optimal fuel landing problem under the relaxation of slop e constraints,and gives the corresponding solution and simulation results.