Online Estimation Of Aerodynamic Parameters And Advanced Skip Entry Guidance Design Of Lunar Spaceship

The velocity of lunar return spacecraft nearly reaches the second cosmic velocity when it arrives at the inter reentry point.To meet mission needs,skip reentry trajectory is often used to reduce the overload and heat current peak.Due to the complicated external environment and force situation,guidance has been one of the difficult and key points of skip reentry.Based on this background,several problems related to guidance technology of skip reentry are studied.The main work of this dissertation includes:Related technical problems of the skip reentry are studied,and the guidance law is designed.(1)The key problems of skip reentry guidance are discussed from three aspects:inclination angle amplitude profile,tilt angle flip logic and fast prediction and correction.A new guidance method based on numerical prediction-correction is proposed.(2)The analysis of amplitude profile of the optimum inclination angle shows that the differences between constant inclination angle profile and the complex form inclination angle profile(such as piecewise linearity,constant + linearity,and so on)are not too much in satisfying the range constraint,maneuverability and maximum overload.(3)Monte Carlo simulation shows that atmospheric density and aerodynamic coefficient error have the greatest influence on reentry trajectory,which needs to be estimated and revised online.The prediction-correction method for online estimation and correction of aerodynamic parameters based on Kalman filter is studied.(1)The error generation mechanism of atmospheric density and aerodynamic coefficient is analyzed.And the essential cause of the influence of process parameter error on prediction-correction guidance method is explained.(2)The approach to estimate aerodynamic parameter on-line with self-carrying sensors is studied.An on-line method of aerodynamic parameters identification and estimation based on Kalman filter is proposed.(3)The influence mechanism of the process parameter error on prediction-correction method is analyzed.A prediction-correction method based on on-line estimation and correction of aerodynamic parameters is proposed.Different on-line identification and correction strategies are proposed according to reentry trajectory characteristics and different disturbance models of the modification factor.Through Monte Carlo simulation,the effectiveness,robustness and range adaptability of the proposed method are verified.The way to solve the problem of large amount of calculation and poor real-time performance of traditional numerical prediction-correction method is studied.A prediction-correction guidance method based on fuzzy logic is proposed.(1)The numerical prediction-correction reentry guidance strategy is analyzed.And the fuzzy relation between the predicted landing point deviation with tilt angle adjustment and flight residual energy is obtained.(2)Based on the fuzzy control theory,the fuzzy logic system is designed with the predicted landing point deviation and flight residual energy as inputs and the tilt angle correction as output.(3)The fuzzy logic system is used to improve the correction part of the prediction-correction method,reducing the calculation time and calculation amount of the guidance instruction.A prediction-correction method based on fuzzy logic is proposed,and the validity and robustness of this method are verified by simulation analysis.