High-accuracy gravity acceleration measurements at the Moon from the GRAIL mission

The over-arching objective of the Gravity Recovery and Interior Laboratory (GRAIL) mission is to understand the structure of the Moon from crust to core. The mission's stringent science measurement requirements were achievable due to the very high-accuracy gravitational accelerations measured by GRAIL and the very high-accuracy topography obtained by the laser altimeter on the Lunar Reconnaissance Orbiter (LRO) mission. The measurement quality of gravitational accelerations achieved by the GRAIL spacecraft exceeded any planetary mission past or present. GRAIL was a satellite-to-satellite tracking mission that determined the acceleration of gravity by measuring the rate of change of distance between two spacecraft in the same lunar orbit but separated by several tens of km to over 200 km during two three-month periods in 2012. The mission improved the accuracy of the Moon's low-degree gravity field by more than 3 orders of magnitude and obtained the most precise measurement of the product of the mass and gravitational constant and low-degree gravity of any planetary body.