NASA's GRAIL Moon Twins Begin Extended Mission Science

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE 818-354-5011
http://www.jpl.nasa.gov

DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle@jpl.nasa.gov

Caroline McCall 617-253-1682
Massachusetts Institute of Technology, Cambridge
cmcall5@mit.edu

News release: 2012-273 August 31, 2012

NASA's GRAIL Moon Twins Begin Extended Mission Science

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-273&cid=release_2012-273

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/

-end-

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