First of NASA's Grail Spacecraft Enters Moon Orbit

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

Dwayne Brown 202-358-1726
Headquarters, Washington
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Caroline McCall 617-253-1682
Massachusetts Institute of Technology, Cambridge
cmcall5@mit.edu

News release: 2011-398 December 31, 2011

First of NASA's Grail Spacecraft Enters Moon Orbit

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-398&cid=release_2011-398

PASADENA, Calif. – The first of two NASA spacecraft to study the moon in unprecedented detail
has entered lunar orbit.

NASA's Gravity Recovery And Interior Laboratory (GRAIL)-A spacecraft successfully completed
its planned main engine burn at 2 p.m. PST (5 p.m. EST) today. As of 3 p.m. PST (6 p.m. EST),
GRAIL-A is in an orbit of 56 miles by 5,197 miles (90 kilometers by 8,363 kilometers) around the
moon that takes approximately 11.5 hours to complete.

"My resolution for the new year is to unlock lunar mysteries and understand how the moon, Earth and
other rocky planets evolved," said Maria Zuber, GRAIL principal investigator at the Massachusetts
Institute of Technology in Cambridge. "Now, with GRAIL-A successfully placed in orbit around the
moon, we are one step closer to achieving that goal."

The next mission milestone occurs tomorrow when GRAIL-A's mirror twin, GRAIL-B, performs its
own main engine burn to place it in lunar orbit. At 3 p.m. PST (6 p.m. EST) today, GRAIL-B was
30,018 miles (48,309 kilometers) from the moon and closing at a rate of 896 mph (1,442 kilometers
per hour). GRAIL-B's insertion burn is scheduled to begin tomorrow, Jan. 1, at 2:05 p.m. PST (5:05
p.m. EST) and will last about 39 minutes.

"With GRAIL-A in lunar orbit we are halfway home," said David Lehman, GRAIL project manager
at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Tomorrow may be New Year's everywhere
else, but it's another work day around the moon and here at JPL for the GRAIL team."

Once both spacecraft are confirmed in orbit and operating, science work will begin in March. The
spacecraft will transmit radio signals precisely defining the distance between them as they orbit the
moon in formation. As they fly over areas of greater and lesser gravity caused by both visible
features, such as mountains and craters, and masses hidden beneath the lunar surface, the distance
between the two spacecraft will change slightly.

Scientists will translate this information into a high-resolution map of the moon's gravitational field.
The data will allow scientists to understand what goes on below the lunar surface. This information
will increase knowledge of how Earth and its rocky neighbors in the inner solar system developed
into the diverse worlds we see today.

JPL manages the GRAIL mission for NASA's Science Mission Directorate at the agency's
headquarters 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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