This paper discusses an initial gravity science results from the Gravity Recovery And Interior Laboratory (GRAIL) mission. The inter-satellite and ground-based Doppler measurements during the three-month prime science phase were processed and a 420th degree and order spherical harmonics lunar gravity field, called GL0420A, was computed. The root-mean-square of measurement residuals were 0.1 mm/s for the ground-based Doppler data (10-s count time) and 0.05 micron/s for the inter-satellite data (5-s count time), respectively. The ground-based Doppler data was fitted to the expected noise level whereas the inter-satellite data has not reached the expected noise floor of 0.03 microns/s, indicating that there exists higher order gravity signal (n＞420). Overall, the result shows that the lunar gravity field has improved by 3-5 orders of magnitude over knowledge from pre-GRAIL gravity field.
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