Research On Skip Reentry Trajectory Optimization For Low L/D Vehicles

At present,China’s aircraft still use low lift-to-drag vehicles in the task of reentry.And the design of the guidance law is particularly critical in this process,for improper design of the guidance is likely to pose a serious threat to the lives of pilots.Therefore,in order to ensure the safety of the pilot in the manned space in reentry mission and to ensure the safety of the aircraft to return to the scheduled landing point,it is necessary to exert an effective control strategy and optimized method in the reentry guidance process so that the reentry targets of the aircraft are within the safe range.This thesis mainly studies the algorithm of the guidance control and the optimization of overload constraints for aircraft reentry.It includes the following four aspects:1)Establishing reentry simulation platforms.According to aircraft reentry dynamic model of low L/D vehicles,reentry simulation platforms are established.Error perturbation parameters are configured,and the error data sets are generated according to the different requirements for the Gaussian distribution and uniform distribution respectively.Different ranges of latitude and longitude are set up and the actual reentry flight environment of the aircraft is simulated according to the requirements of different reentry tasks.2)Proposing a hybrid guidance method.This thesis studies the standard orbit tracking guidance method and the predictor-corrector reentry guidance approach.Although the standard orbit tracking guidance method is relatively simple,it is very sensitive to the initial value of aircraft reentry.The predictor-corrector reentry guidance approach is quite precise in real time,but it has more requirements on computer performance.Based on reentry overload and the requirements of landing accuracy,this thesis combines the standard orbit tracking guidance method and the predictor-corrector reentry guidance approach into a hybrid guidance strategy.It can,under the premise of ensuring the accuracy of landing effectively,reduce requirements of aircraft on the computer performance and ensure actual engineering application.3)Proposing a load-relief strategy based on the bank angle of the 2th reentry and verifying its feasibility.This thesis analyzes the characteristics of overload in the return mission and proposes a reentry load-relief strategy.In the process of reentry,due to the bank angle of the 2th reentry plays a decisive role in the whole process,it is critical in the distribution of the two overload peaks throughout the process.The optimization of the bank angle of the 2th reentry can effectively control the overload peak in the reentry process.Simulation experiments of multiple ranges show that the load-relief strategy reduces the overload peak significantly.4)Improving particle swarm optimization algorithm and optimizing overload and landing errors.The particle swarm optimization algorithm is applied to overload control and trajectory optimization,and the optimal bank angle is automatically programmed.And the constraint of the landing error is added to the search process,so as to realize the optimization of constraint parameters such as overload and landing error.Finally,the Monte Carlo simulation is used to test the whole system,which proves that hybrid guidance strategy can achieve satisfactory precision.At the same time,the proposed optimization strategy can effectively reduce the overload in the process of reentry and so it has some robustness.