GRAIL Moon Mission Begins Science Phase
September 2, 2012

Scientific Phase Of NASA’s GRAIL Moon Mission Begins

redOrbit Staff & Wire Reports - Your Universe Online

The data collection phase for NASA's pair of lunar-orbiting Gravity Recovery and Interior Laboratory (GRAIL) spacecraft has officially commenced, the US space agency announced on Friday.

The lone scientific instrument on board the GRAIL orbiters was activated Thursday at 12:28pm EDT (9:28am PDT), when the twin vehicles were located 19 miles (30 kilometers) above the Ocean of Storms, according to officials from NASA's California-based Jet Propulsion Laboratory (JPL).

That device, the Lunar Gravity Ranging System, will be used during the science phase of GRAIL's mission, which will run until December 3 and will analyze the moon's gravitational field. The satellites will attempt to derive the gravitational influence of craters, mountains, and other surface and subsurface features, and in order to do so at the highest possible resolution, mission planners are planning to lower the altitude of the probes by half -- to the lowest levels that can be safely maintained, according to JPL officials.

"The data collected during GRAIL's primary mission team are currently being analyzed and hold the promise of producing a gravity field map of extraordinary quality and resolution," Maria Zuber, principal GRAIL investigator at the Massachusetts Institute of Technology (MIT), said in a statement. "Mapping at a substantially lower altitude during the extended mission, and getting an even more intimate glimpse of our nearest celestial neighbor, provides the unique opportunity to globally map the shallow crust of a planetary body beyond Earth."

The overall objective of the GRAIL mission is to create the most accurate gravity map of the moon to date, and from that to derive its internal structure and evolution. Scientists report that four of that mission's six principle scientific measurement goals had already been reached, as the Lunar Gravity Ranging System collects data when the two GRAIL vehicles transmit radio signals from one to the other.

"During the prime mission, which stretched from March 1 to May 29, the two GRAIL spacecraft, named Ebb and Flow, orbited at an average altitude of 34 miles (55 kilometers)," officials from JPL said. "The average orbital altitude during extended mission will be 14 miles (23 kilometers), which places the GRAIL twins within five miles (eight kilometers) of some of the moon's higher surface features."

David Lehman, the GRAIL project manager at JPL, said that both GRAIL spacecrafts were doing "great," especially in light of the multiple challenges they have faced since their September 2011 launch. Those obstacles included a lunar eclipse in June of this year, as well as more than two dozen rocket burns since arriving in lunar orbit in early 2012.

On the mission's official website, NASA personnel reported that the mission, upon completion, will improve scientists' understanding of near-side moon gravity by 100 times and of far-side gravity by 1,000 times. They also noted that this mission marks the first time any space agency had attempted to maneuver a pair of robotic spacecraft in the same, precise orbit around any celestial body other than Earth.