NASA's GRAIL Moon Twins Begin Extended Mission Science
NASA's twin, lunar-orbiting Gravity Recovery and Interior Laboratory  (GRAIL) spacecraft began data collection for the start of the mission's  extended operations.
PASADENA,  Calif. - NASA's twin, lunar-orbiting Gravity Recovery and Interior Laboratory  (GRAIL) spacecraft began data collection for the start of the mission's  extended operations.At  9:28 a.m. PDT (12:28 p.m. EDT) yesterday, while the two spacecraft were 19  miles (30 kilometers) above the moon's Ocean of Storms, the Lunar Gravity  Ranging System -- the mission's sole science instrument aboard both GRAIL twins  -- was energized."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," said Maria Zuber, principal investigator  for GRAIL from the Massachusetts Institute of Technology in Cambridge. "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  science phase of GRAIL's extended mission runs from Aug. 30 to Dec. 3. Its  goals are to take an even closer look at the moon's gravity field, deriving the  gravitational influence of surface and subsurface features as small as simple  craters, mountains and rilles. To achieve this unprecedented resolution, GRAIL  mission planners are halving the operating altitude - flying at the lowest  altitude that can be safely maintained.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). 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."Ebb  and Flow, and our mission operations team, are both doing great, which is  certainly notable considering all the milestones and challenges they have  experienced," said David Lehman, GRAIL project manager from NASA's Jet  Propulsion Laboratory in Pasadena, Calif. "The twins have endured the  lunar eclipse of June 4, 2012, and 26 rocket burns since arriving in lunar  orbit at the beginning of the year. Down here in our control room, with all the  planning and mission operations we have been doing, it feels as though we've  been riding right along with them. Of course, they have the better view."Science  data are collected when the Lunar Gravity Ranging System transmit radio signals  between the two spacecraft, precisely defining the rate of change of distance  between Ebb and Flow. The distance between the twins change slightly as they  fly over areas of greater and lesser gravity caused by visible features, such  as mountains and craters, and by masses hidden beneath the lunar surface.Mission  scientists calculated that even as the last data were downlinked, four of the  mission's six principal science measurement goals had already been achieved.  The objective of the GRAIL mission is to generate the most accurate gravity map  of the moon and from that derive the internal structure and evolution of  Earth's natural satellite.JPL  manages the GRAIL mission for NASA's Science Mission Directorate in Washington.  The GRAIL mission is part of the Discovery Program managed at NASA's Marshall  Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver  built the spacecraft.For  more information about GRAIL, visit:http://solarsystem.nasa.gov/grail/