High Resolution Gravitational Field of the Moon—Results from the Gravity Recovery and Interior Laboratory Mission

The Gravity Recovery and Interior Laboratory (GRAIL) mission utilized a dual-spacecraft system to produce a global gravitational field of the Moon to degree-and-order 420. The surface resolution from the recently completed three-month prime mission is ~13 km blocks. The primary observable is the inter-spacecraft range-rate via a 32 GHz high frequency microwave link, derived from dual spacecraft one-way range supplemented by Doppler tracking via the Deep Space Network. Advanced system calibrations lead to unprecedented data quality of better than 0.1 microns/sec. The error spectrum shows several orders of magnitude improvement for all wavelengths when compared to previous missions. Nearly uniform correlations with topography exist through higher harmonic degrees and are a good measure of field integrity. The mission’s scientific scientific objectives include determining the structure of the lunar interior from crust to core and advancing the understanding of the thermal evolution of the Moon. Specific investigations include mapping the structure of the crust and lithosphere, understanding the Moon’s asymmetric thermal evolution, determining the subsurface structure of impact basins and the origin of mascons, ascertaining the temporal evolution of the crustal brecciation and magmatism, and constraining deep interior structure from tides.