A degree-100 lunar gravity model from the Chang’e 5T1 mission

Abstract

Context. Chinese lunar missions have grown in number over the last ten years, with an increasing focus on radio science investigations. In previous work, we estimated two lunar gravity field models, CEGM01 and CEGM02. The recently lunar mission, Chang’e 5T1, which had an orbital inclination between 18 and 68 degrees, and collected orbital tracking data continually for two years, made an improved gravity field model possible. Aims. Our aim was to estimate a new lunar gravity field model up to degree and order 100, CEGM03, and a new tidal Love number based on the Chang’e 5T1 tracking data combined with the historical tracking data used in the solution of CEGM02. The new model makes use of tracking data with this particular inclination, which has not been used in previous gravity field modeling. Methods. The solution for this new model was based on our in-house software, LUGREAS. The gravity spectrum power, post-fit residuals after precision orbit determination (POD), lunar surface gravity anomalies, correlations between parameters, admittance and coherence with topography model, and accuracy of POD were analyzed to validate the new CEGM03 model. Results. We analyzed the tracking data of the Chang’e 5T1 mission and estimated the CEGM03 lunar gravity field model. We found that the two-way Doppler measurement accuracy reached 0.2 mm s−1 with 10 s integration time. The error spectrum shows that the formal error for CEGM03 was at least reduced by about 2 times below the harmonic degree of 20, when compared to the CEGM02 model. The admittance and correlation of gravity and topography was also improved when compared to the correlations for the CEGM02 model. The lunar potential Love number k2 was estimated to be 0.02430±0.0001 (ten times the formal error). Conclusions. From the model analysis and comparison of the various models, we identified improvements in the CEGM03 model after introducing Chang’e 5T1 tracking data. Moreover, this study illustrates how the low and middle inclination orbits could contribute better accuracy for a low degree of lunar gravity field.

Review of the Precise Orbit Determination for Chinese Lunar Exploration Projects

“…The RMS value of the orbit overlap difference based on the GRGM660 gravity model was about 46 m, which agrees with our earlier processing results (J. Yan et al. 2020). The whole process on data collected from May of 2015 to December of 2016 can be read in J. Yan et al.…”

“…The whole process on data collected from May of 2015 to December of 2016 can be read in J. Yan et al. (2020). The orbit and Doppler data accuracy of the Chang’e 5T1 is similar to SELENE mission and LRO mission.…”

“…The LUGREAS software used in this analysis is proprietary to Wuhan University; however, the processing of the observables and estimation procedure is given in J. Yan et al, 2020.…”

“…We adopted our in‐house software, LUGREAS, to do the POD for the series of Chang’e missions. LUGREAS was written in Fortran 90 and designed to be a comprehensive and flexible system for executing the POD as well as estimating dynamic parameters to investigate the interior structure of the moon (e.g., Liu, Yan et al., 2020; J. Yan et al., 2020; Yan, Yang, Ping et al., 2018; Ye et al., 2016). We have strictly validated LUGREAS software with the well‐known planetary spacecraft POD and dynamical parameters software GEODYN II (Pavlis, 2001; Ye et al., 2016).…”

“…Based on the Chang’e 5T1 orbital tracking data collected in 2015 and 2016, J. Yan et al. (2020) solved a lunar gravity field model CEGM03 up to degree and order 100; the k 2 was estimated to be 0.02430 ± 0.0001 (10 times the formal error).…”