Research On Methods Of Reentry Trajectory Online Planning And Guidance For The Lifting Vehicle

The lifting reentry vehicle is an important direction in the future development of aerospace.In the re-entry process,the lifting vehicle has a higher speed and a longer range,so it needs to endure greater constraints such as heat and dynamic pressure.And reentry trajectory planning and correlation guidance are difficult to implement.This article takes the lift vehicle as the research object and mainly solves the key technical problems of the lift vehicle reentry trajectory online planning and guidance.The kinematics model of lift vehicle in reentry process and the relevant constraints are the basis of reentry trajectory planning and guidance.The three-degree-of-freedom reentry motion model of the lift vehicle is derived.After the flight state is normalized,the motion with time is transformed into a model with energy as the independent variable.The formulas of the heating rate,load factor,and dynamic pressure,the main constraints to consider during reentry,are carried.It lays a foundation for trajectory characteristic analysis,trajectory planning and guidance method research.To study the reentry trajectory planning and guidance methods,it is necessary to understand the reentry trajectory characteristics.Therefore,reentry trajectory characteristics need to be analyzed.Based on the simplified longitudinal motion model,the mechanism of equilibrium glide and undulating flight is analyzed,and the characteristics of equilibrium glide and undulating flight trajectory are verified by simulation,focusing on the influence of undulating flight on the range compared with equilibrium glide.The simulation results show that the reentry range is directly related to the lift-drag ratio and has little relation with the trajectory form.The analysis of trajectory characteristics provides some reference for trajectory planning and guidance method research.Under the current technical conditions,the reentry trajectory generated by optimization is inefficient and difficult to meet the requirements of online application.Therefore,trajectory planning and guidance methods that can meet the requirements of online application need to be studied.An online analytical trajectory planning method based on the reciprocal profile of drag acceleration is proposed.The process constraint and equilibrium glide constraint are transformed into drag acceleration reciprocal corridor constraint.Then the upper and lower bounds of the range are calculated by using the analytical calculation method of range proposed.After that,the trajectory that meets the requirements of the range can be planed analytically.In order to verify the feasibility of trajectory planning,adaptive hp-Radau pseudo-spectral method is used to solve the optimal trajectory offline for comparison.The results show that the method proposed in this paper is of high efficiency,the calculation time is reduced to within 0.015 s under the Matlab environment,and the accuracy meets the relevant requirements.On this basis,a method of online trajectory analysis update is proposed.The with drag acceleration tracking guidance algorithm combined,a new online trajectory planning and guidance method is proposed.Simulation results show that the proposed method has high accuracy,online update trajectory time is less than 0.005 s,and has high accuracy and efficiency for a variety of deviations and tasks,and higher algorithm robustness.The predictive correction guidance method based on online iterative calculation is characterized by high precision and flexibility,and as an important developing direction of computational guidance,it has attracted much attention.However,the iterative calculation efficiency of this method is low and it is difficult to be applied online under current technical conditions.Therefore,the method needs to improve the efficiency for online application.The basic principle of a numerical prediction correction guidance method is given and the simulation is performed.Aiming at the disadvantage of low efficiency of iterative integral calculation,a method is proposed to fit the nonlinear relationship between the initial bank angle and the range-to-go by the neural network,and thus the reentry guidance method based on neural network fitting is constructed.The results show that the computational efficiency of the neural network is higher and can reach within 0.001 s under the Matlab environment.At the same time,the altitude profile and the drag acceleration profile corresponding to the bank angle profile are obtained by using the equilibrium glide condition.Then a Gauss integral instead of numerical integral is proposed to calculate the range-to-go.Finally,based on the obtained altitude profile,a method of correcting the altitude using moving horizon method is proposed,thus forming an analytical predictor-corrector guidance algorithm based on equilibrium glide condition.The results show that the computational efficiency of the proposed method can vary flexibly with the guidance period,and the computational efficiency is high;at the same time,the accuracy is improved;the method has high adaptability to deviation and task,strong robustness and online application potential.