GRAVITY RECOVERY AND INTERIOR LABORATORY (GRAIL) MISSION: MISSION STATUS AND APPLICATIONS TO LUNAR GEOLOGY

The Gravity Recovery and Interior Laboratory (GRAIL) Mission is a component of the NASA Discovery Program. GRAIL is a twin-spacecraft lunar gravity mission that has two primary objectives: to determine the structure of the lunar interior, from crust to core; and to advance understanding of the thermal evolution of the Moon. GRAIL launched successfully from the Cape Canaveral Air Force Station on September 10, 2011, executed a low-energy trajectory to the Moon, and inserted the twin spacecraft into lunar orbit on December 31, 2011 and January 1, 2012. A series of maneuvers brought both spacecraft into low-altitude (55-km), near-circular, polar lunar orbits, from which they perform high-precision satellite-to-satellite ranging using a Ka-band payload along with an S-band link for time synchronization. Precise measurements of distance changes between the spacecraft are used to map the lunar gravity field. GRAIL completed its primary mapping mission on May 29, 2012, collecting and transmitting to Earth >99.99% of the possible data. Spacecraft and instrument performance were nominal and has led to the production of a high-resolution and high-accuracy global gravity field, improved over all previous models by two orders of magnitude on the nearside and nearly three orders of magnitude over the farside. GRAIL’s high spatial resolution provides the opportunity to study geologic features with geophysical methods that will elucidate coupled surficial and interior processes that occurred early in the evolution of the Moon and terrestrial planets.

GRAIL Science Team members: David E. Smith, Sami W. Asmar, Alexander S. Konopliv, Frank G. Lemoine, H. Jay Melosh, Gregory A. Neumann, Roger J. Phillips, Sean C. Solomon, Michael M. Watkins, Mark A. Wieczorek and James G. Williams.