Research On Entry Guidance Methods Based On Analytical Theories

With the frequent space exploration in recent years,the research on entry trajectories planning,guidance and control system designing has attracted great attention.This dissertation focuses on the guidance algorithm based on analytical solution according to academic demands.High-precision analytical solutions are obtained by analyzing the entry motion characteristics.The solutions are applied to predictor-corrector entry guidance,which greatly shortens the planning time of entry trajectories and improves the real-time performance of predictor-corrector entry guidance.Firstly,the entry motion characteristics are analyzed based on entry motion equations and entry guidance demands.1)The motion equations and definitions of some important parameters for entry vehicles are given as the basis of following research.2)A detailed and overall description of entry guidance problems is provided,including the demands on entry mission,the constraints and disturbance factors in entry guidance,as well as a clear background for the following entry trajectories planning and entry guidance.3)The motion characteristics of entry's initial descent phase and glide flight phase are analyzed according to the different phases of vehicles' entry.Secondly,based on the tracking guidance of Shuttle entry profile,the profile is improved for easier on-line planning.The entry profile planning method further changes into a new entry guidance algorithm combining with a track law.1)Based on the analysis of constraints,the profile is improved and can make a rapid on-line replanning according to the condition of the entry vehicle.2)Combining with a track law and aerodynamic parameters identification method,an entry guidance algorithm is obtained.3)The validity and robustness of the entry guidance algorithm is tested by numerical simulations.Thirdly,the analytical solutions of lift entry's initial descent phase and glide flight phase are developed respectively and a predictor-corrector entry guidance algorithm is developed based on it.1)On the basis of the entry motion characteristics,the analytical solutions of initial descent phase and glide flight phase are developed and tested respectively.2)A new entry trajectories planning method is developed based on the analytical solutions.By correcting the trajectory parameter,the entry vehicle can be guided towards the destination.The numerical simulation shows that the new method has a good performance on validity and robustness,and it also has less computation.3)By reducing the order of the motion equations with analytical solutions,the computation in numerical prediction is lowered.Therefore,a reduced-order three-dimentional entry trajectory planning method is developed.Finally,two entry guidance algorithms are developed for skip entry and glide entry based on the analysis of their entry motion characteristics and the problems in semi-lift entry.The key methods of the two entry guidance algorithms are energy management and analytical solutions respectively.1)An entry energy management method is developed based on the analysis of the motion characteristics of skip entry.By handling the energy of the skip point,the flight ability of the entry vehicle is well controlled.The entry guidance algorithm developed based on the energy management method is tested by numerical simulation.The results show good validity and robustness.2)The analytical solutions are applied to lunar capsule entry.The performance of the entry guidance algorithm based on analytical solutions demonstrates good validity and robustness.3)The motion characteristics of lunar capsule skip entry and glide entry are compared respectively.And the entry guidance algorithm based on these two entry methods are analyzed as well.This dissertation has given the description of entry guidance problems,relevant design and analysis of lift/semi-lift entry motion characteristics.The entry trajectory planning methods and entry guidance algorithm are provided based on it.The work in this paper is to boost the development of lift/semi-lift entry guidance algorithm.