Research On Skip Reentry Guidance For Lunar Spaceship Return Trajectories

The velocity of lunar return vechiles reaches second cosmic velocity while itarrives at the inter reentry point. The maximal load and heat current of skip reentrytrajectory is smaller and it can expand optional reentry range. The guidance is thedifficult and key point of skip reentry for its complicated process and difficulties incontrol. At the background of lunar return spacecraft reentrying, the thesis trys to solvesome problems in it. The work in this thesis consists of following parts.Fistly, methods of designing nominal trajectory are studied.(1)The influnce ofdifferent bank angle profiles do on trajectory is researched, the results show thatsubsection constant bank angle profile is best for limiting maximal load and reservingability for range adjustment.(2) The cause of cross range enlargement in Kepler phaseis analysed and a subsection control method is proposed. The lateral guidance isdesigned based on the method and solves the problem successfully.(3) The motionalcharacteristics of skip reentry are analysed. The results show that velocity control infirst reentry phase has magnitude influnce on configuration of reentry trajectory.Thecharacteristics of Kepler phase and influnce of aero dynamic are also analysed.Secondly, methods of tracking a norminal trajectory are studied and an algorithm isdesigned.(1) A method of constrain maximal load is adopted to manage the velocity ofthe lowest point in first reentry so that the flight ability of lunar return spacecraft isguaranteed.(2) Varous condition errors will diverge in Kepler phase. A method byrectifying bank angle profile to compensate error in second reentry point is adopted.(3)The validity and robustness of the guidance algorithm is testified by simulation andresults show a good performance.(4) The requests to guidance algorithm as range ofmission enlarged are analysed and results show that the pricision on velocity control ishighly significant. The method of tracking a norminal trajection is difficult to handlelarge range reentry mission because of its principium.Thirdly, methods of combined guidance are studied and an algorithm is designed.(1) The influnces of different switch points on configuration of reentry trajection areanalysed and the method of designing a prodictable variable is analysed.(2) Thevalidity and robustness of the guidance algorithm are testified by Monte-Carlosimulation and the results show a better performance than norminal trajectory trackingguidance.(3) The method shows a good performance on flexibility among differentmission ranges and it maintains a good validity and robustness in simulation.