NASA's Twin GRAIL Spacecraft Begin Collecting Lunar Science Data

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

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
Dwayne.c.brown@nasa.gov

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

News release: 2012-061 March 7, 2012

NASA's Twin GRAIL Spacecraft Begin Collecting Lunar Science Data

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-061&cid=release_2012-061

PASADENA, Calif. -- NASA's Gravity Recovery And Interior Laboratory (GRAIL) spacecraft
orbiting the moon officially have begun their science collection phase. During the next 84 days,
scientists will obtain a high-resolution map of the lunar gravitational field to learn about the moon's
internal structure and composition in unprecedented detail. The data also will provide a better
understanding of how Earth and other rocky planets in the solar system formed and evolved.

"The initiation of science data collection is a time when the team lets out a collective sigh of relief
because we are finally doing what we came to do," said Maria Zuber, principal investigator for the
GRAIL mission at the Massachusetts Institute of Technology in Cambridge, "but it is also a time
where we have to put the coffee pot on, roll up our sleeves and get to work."

The GRAIL mission's twin, washing-machine-sized spacecraft, named Ebb and Flow, entered lunar
orbit on New Year's Eve and New Years Day. GRAIL's science phase began yesterday at 5:15 p.m.
PST (8:15 p.m. EST). During this mission phase, the spacecraft will transmit radio signals precisely
defining the rate of change of distance between the two. The distance between the spacecraft will
change slightly as they fly over areas of greater and lesser gravity caused by visible features such as
mountains, craters and masses hidden beneath the lunar surface. Science activities are expected to
conclude on May 29, after GRAIL maps the gravity field of the moon three times.

"We are in a near-polar, near-circular orbit with an average altitude of about 34 miles (55 kilometers)
right now," said David Lehman, GRAIL project manager from NASA's Jet Propulsion Laboratory
(JPL) in Pasadena, Calif. "During the science phase, our spacecraft will orbit the moon as high as 31
miles (51 kilometers) and as low as 10 miles (16 kilometers). They will get as close to each other as
40 miles (65 kilometers) and as far apart as 140 miles (225 kilometers)."

The two spacecraft were previously named GRAIL A and B. The names Ebb and Flow were the
result of a nationwide student contest to choose new names for them. The winning entry was
submitted by fourth graders from the Emily Dickinson Elementary School in Bozeman, Mont. Nearly
900 classrooms with more than 11,000 students from 45 states, Puerto Rico and the District of
Columbia, participated in the contest.

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://www.nasa.gov/grail .

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