Calculation of Lunar Libration Parameters Using VLBI Observations and Improvement of Lander Positioning and Velocity Measurement = 利用 VLBI 观测量对月球天平动参数解算及着陆器定位和测速的改进

Abstract

Objectives: The lunar libration parameters are important parameters that affect the positioning accuracy of the Chang'E ‐3 lander. Studying the lunar balance dynamic parameter estimation methods is of great significance to the development of lunar exploration projects in China. At present, the lunar libration parameters is calculated by the ephemeris method, but this method cannot guarantee the positioning accura‐ cy of the lander. Methods: We first establish the expressions of the very long baseline interferometry (VLBI) time delay and delay rate with the changes of the lander����s position, velocity, then based on VLBI technique, the lunar physical libration parameters are calculated by using weighted least square adjustment method.Results: Compared with the interpolation results of the DE421 ephemeris, the improvements of the Euler angles Ω, i and μ are compensated to -0.692 4″, 0.009 6″ and -0.009 7″ respectively.Based on the lunar physical libration parameters ,the position and velocity of the lander were solved, the results show that the positioning accuracy of the lander can be improved in X,Y,Z directions by 24.204 m, 0.405 m, 1.996 m respectively. The estimation accuracy of the velocity error is also improved by 0.010 6 m/s, 0.013 5 m/sand 0.007 2 m/s in X,Y,Z directions.Conclusions: This paper provides strong reference for the related research on the calculation of the physical libration parameters in the future.