Research On Trajectory Optimization And Guidance Approach For Reentry Vehicle With Trim-Flaps

The vehicle with trim flaps is a medium lift-to-drag ratio spacecraft, compared to current mannedspacecraft it has higher lift-to-drag ratio. The flaps can be used to provide enough aerodynamicmaneuverability landing the vehicle in a predetermined place. At present, the aerospace industry inour country is steadily forward, we can choose a vehicle with medium lift-to-drag ratio as anintermediate vehicle to test advanced lifting reentry technology, thermal protection and controltechnology before we start researching single-stage-to-orbit vehicles and two-stage-to-orbit vehicles.The equations of motion for reentry vehicle are presented, and the entry trajectory is described. Thetrajectory characteristics of the vehicle returning from the near-earth orbit and moon are analyzed.Simulation results show that vehicles with medium lift-to-drag ratio can be used for the near-earthmission and lunar mission.The configuration of the vehicle with trim flaps is presented, and flow fields of the vehicle isanalyzed with CFD method, the aerodynamic coefficient is calculated. Two groups of lift coefficientand drag coefficient data are obtained. The simulation data were compared and analyzed. Thelift-to-drag ratio of vehicle with trim flaps is about0.8.The trajectories under different constrains are optimized by applying Pontryagin maximumprinciple on the performance of minimum heat. For the safety of the astronauts, overload constraint istaken under consideration. In order to reduce the dynamic pressure on the trim flaps, dynamicpressure constraint is taken under consideration. Heat rate constraint is taken under consideration toprotect the vehicle from being burned.Reentry trajectory is optimized based on Neural Dynamic Optimization Method. Neural network isintroduced. The theory of NDO is presented and the implementation issues are discussed. Themaximum principle is sensitive to initial values of the state variable.The way combining neuralnetwork method and the maximum principle can solve the problem.The simulation results show thefeasibility of the NDO method. A properly trained NDO can generate feasible and acceptabletrajectory in10seconds when the initial error is not large.A longitudinal predictive reentry guidance law based on the variable universe fuzzy-PI control isdiscussed. Fuzzy control theory is introduced and variable universe fuzzy control is presented. Thecomplexity of the fuzzy control rules is greatly reduced by using variable universe fuzzy controlmethod, simulation results show that the proposed guidance law is very robust to the initial errors and can control the downrange error within30meters.