Research On Trajectory Optimization And Fault-tolerant Guidance For Reentry Hypersonic Vehicles

As the next generation aircraft with a high degree of integration in aerospace,hypersonic vehicle is an extremely important development direction for future space operations and aerospace transportation systems.Due to the complexity and uncertainties of the reentry process,it is very difficult to design the optimal trajectory meeting the reentry constraints.When faults occur during the reentry flight,the reentry flight will be seriously affected,and even the aircraft will be out of control.Therefore an appropriate fault-tolerant guidance scheme is needed to ensure the safety of the aircraft.In this thesis,the hypersonic reentry vehicle is taken as the research object,and the reentry trajectory optimization problem and the online trajectory reconstruction under failures are studied.Firstly,the background and significance of research are summarized,and the development of hypersonic vehicle is introduced at home and abroad.The reentry problem of the aircraft is analyzed,and the traditional trajectory optimization method and the new development of trajectory optimization methods are reviewed.Some promising fault-tolerant guidance methods are briefly introduced.The nonlinear description with multiple constraints for the reentry trajectory optimization problem is given,and the difficulty of reentry trajectory optimization is analyzed.Secondly,in view of the reentry equation,the constraint conditions and the objective function of the hypersonic vehicle,the improved mesh refinement technique is used to solve the problem of reentry trajectory optimization of hypersonic vehicle.The continuous trajectory optimization problem is transformed into a nonlinear programming problem by using the Runge-Kutta method.Then the improved mesh refinement technique is used to adaptively select the appropriate discrete points to form a new mesh.Based on the new grid,the nonlinear programming problem is solved,and the high precision optimal trajectory satisfying the reentry constraint is obtained.The simulation results show that the trajectory optimization method can solve the reentry trajectory optimization problem of multiple constraints and multiple variables quickly and effectively,which can provide the basic guarantee for the online trajectory reconstruction under the fault.Thirdly,after the fault occurs,because the off-line optimal trajectory may not meet the reentry requirements,the appropriate number of optimization variables,terminal constraint conditions and objective function form are selected considering the effect of the rudder failure on the reentry trajectory optimization.Then,based on the improved mesh refinement technique and the optimal feedback control,the optimal trajectory meeting the reentry flight constraint under the fault is generated continuously,and the guidance command is updated in real time so that the guidance system of the aircraft can have the ability to online reconstruct the trajectory.The simulation results show that the online trajectory generated under the actuator fault can meet the requirements of reentry flight and have good real-time performance,ensuring that the hypersonic vehicle can safely reach the designated area and improve the safety and reliability of the aircraft.Finally,when trajectory reconstruction is performed online,it is assumed that the aircraft is always in the instantaneous equilibrium state during the reentry flight and can accurately track the attitude angle command given by the guidance loop.However,in the actual flight,it is necessary to further consider whether the attitude control system under the fault can accurately track the attitude angle command of the guidance loop.Therefore,the joint simulation is carried out by integrating the guidance loop and attitude loop of the hypersonic vehicle,to realize the preliminarily analysis on the fault-tolerant capability of the whole system under the fault.