Trajectory Optimization And Guidance Of Reentry Section Of Hypersonic Vehicle

Due to the broad flight envelops spanning and the specific characteristics,the hypersonic vehicle has attracted considerable attention and become a hot topic in modern research technology.Because of the non-linearity of the hypersonic vehicle reentry process,the complexity of the flight environment and the diversity of constraints,it is difficult to study the reentry process of the aircraft.In this paper,the general purpose of spacecraft(CAV-H)is studied.The trajectory optimization of the aircraft reentry process and the design of the guidance law are taken as the main research contents under the influence of the improved bivariate aerodynamic model.Mainly include the following aspects:Firstly,this paper introduces the background and significance of the research.The origin of the hypersonic vehicle and the development of the present situation at home and abroad are analyzed and the relevant methods and techniques needed for trajectory optimization and reentry guidance in the follow-up work are summarized.Next,the simplified model of the reentry movement of the hypersonic vehicle is given.The process constraints,such as the heat flow rate,dynamic pressure,overload and the terminal constraints which are set to complete the specific mission are analyzed.The aerodynamic model is improved by using the corresponding aerodynamic test data to be more accurate.Additionally,this paper describes the basic principle and characteristics of Gaussian pseudospectral method(GPM)to solve the optimization problem.The problem of continuous and dynamic trajectory optimization is transformed into discrete and static nonlinear programming(parameter optimization).The nonlinear programming problem obtained by discretization using Gaussian pseudo-spectral method has the same agreement with the original optimal control problem.The trajectory optimization of the model described earlier will be completed with use of the GPOPS toolbox and GPM.The maximum horizontal / vertical range is used as the function of performance index,and the optimization is completed with different initial conditions.Finally,the change curves of each state and control input are given and analyzed briefly.The main purpose of this part is to track the reference trajectory,the result of the previous track optimization.Firstly,the system model is simplified,and the corresponding control model is obtained.Next,the conversion relationship between the indirect control input and the direct control input is given.Then,the sliding mode control theory is introduced to design the corresponding guidance law.In this process,the terminal sliding surface and the corresponding controller with an adaptive law are designed firstly.Then,the stability of the system is proved by Lyapunov function.Due to the existence of system interference and external uncertainties,the sliding mode surface s can not strictly converge to zero,so the adaptive parameters will always increase,which affects the control performance of the system.In order to solve this problem,an adaptive law with low-pass filter is proposed,and the corresponding controller is designed.The validity of the two controllers is verified by simulation.Through the comparative analysis of the simulation results,the advantages and disadvantages between the two controllers are obtained.The input saturation of the actuator is a common phenomenon,so in chapter 5,the input saturation problem will be considered.First,this chapter gives a different sliding surface compared with the fourth chapter.Meanwhile,the convergence and convergence time of the sliding mode are proved.According to the situation of interference on the upper bound,it is divided into two cases to discuss: known upper bound and unknown upper bound.When the interference upper bound is known,the anti-saturation controller is designed by sliding mode and it is proved that the system states are the actual finite time convergent.For the case where the upper bound of the disturbance is unknown and the input is saturated,the corresponding controller and auxiliary system are given and it is proved the sliding mode surface and the system state is of finite time convergence.Finally,the effectiveness of the designed control method is proved by simulation.