Research On Reentry Guidance And Trajectory Reshaping For Reentry Hypersonic Vehicles

Because the stability and security of reentry hypersonic vehicles are very important,an appropriate fault-tolerant scheme is needed to ensure the safety of the hypersonic vehicles.This thesis addresses the guidance and trajectory reshaping for reentry hypersonic vehicles in the presence of vehicle failures.Firstly,the background and the significance of the research are introduced,and the knowledge about hypersonic vehicles is summarized.Furthermore,an overview of the reentry guidance problem which is the core problem of this paper is provided,the current research status of reentry guidance technology and trajectory reshaping technology of hypersonic vehicles is presented,and the main problems in the existing achievements are analyzed.Secondly,an improved predictor-corrector reentry guidance law for hypersonic vehicle is proposed to generate the reentry nominal trajectory,and the trajectory satisfies all constraints.In order to overcome the disadvantages of the fixed angle of attack in the guidance algorithm,the overload is taken as an intermediate variable in this paper.Using the theory of feedback linearization to design guidance law on both lateral and longitudinal,and the lateral maneuver strategy is added to make the vehicle deceleration.The command of non-fixed angle of attack and smooth bank angle are obtained,and the reentry guidance task of hypersonic vehicle is completed.This method can provide the basic guarantee for the online trajectory reshaping under the fault.Thirdly,for the safety reentry flight problem of hypersonic vehicle under the fault,a robust trajectory reshaping algorithm is proposed based on the neighboring feasible trajectory existence theorem(NFTET)under the large failure of the vehicle.In the nominal case,using the improved predictor-corrector guidance law based on the feedback linearization theory to generate the reentry trajectory.Since the NFTET only applies to the occurrence of small failures,to ensure the vehicle can still land with high precision safely under the large failure,the robust trajectory reshaping algorithm is designed based on NFTET,and the higher landing accuracy of the flight path is obtained.Finally,the guidance command is introduced into the attitude control,and an adaptive fault-tolerant integrated guidance and control(IGC)is designed for hypersonic vehicle in the presence of uncertain parameters and torque faults.According to the reentry guidance mission,the coupling relationship between the guidance and the attitude is considered.The Takagi-Sugeno fuzzy model is used to approximate the complex interference term caused by unknown parameters and additive faults,and the parameter projection is introduced to design adaptive law to estimate unknown external disturbances and torque failure.The adaptive parameters are designed in controller based on Lyapunov stability theorem,and the controller is obtained for online updates.The design of adaptive fault-tolerant IGC scheme is completed,and improves the autonomous fault-tolerance ability of hypersonic vehicle.