Dwayne Brown
Headquarters, Washington
202-358-1726
dwayne.c.brown@nasa.gov
DC Agle
Jet Propulsion Laboratory, Pasadena,
Calif.
818-393-9011
agle@jpl.nasa.gov
Caroline McCall
Massachusetts Institute of Technology,
Cambridge
617-253-1682
cmccall5@mit.edu
WASHINGTON -- A NASA mission to study
the moon from crust to core has completed its prime mission earlier than
expected. The mission team of NASA's Gravity Recovery and Interior Laboratory
(GRAIL) mission, with twin probes named Ebb and Flow, is now preparing for
extended science operations starting Aug. 30 and continuing through Dec. 3,
2012.
The GRAIL mission has gathered
unprecedented detail about the internal structure and evolution of the moon.
This information will increase our knowledge of how Earth and its rocky
neighbors in the inner solar system developed into the diverse worlds we see
today.
Since March 8, the spacecraft have
operated around the clock for 89 days. From an orbit that passes over the lunar
poles, they have collected data covering the entire surface three times. An
instrument called the Lunar Gravity Ranging System onboard each spacecraft
transmits radio signals that allow scientists to translate the data into a
high-resolution map of the moon's gravitational field. The spacecraft returned
their last data set of the prime mission today. The instruments were turned off
at 1 p.m. EDT when the spacecraft were 37 miles (60 kilometers) above the Sea
of Nectar.
"Many of the measurement objectives
were achieved from analysis of only half the primary mission data, which speaks
volumes about the skill and dedication of our science and engineering
teams," said Maria Zuber, principal investigator of GRAIL at the
Massachusetts Institute of Technology in Cambridge. "While there is a
great deal of work yet to be done to achieve the mission's science, it's
energizing to realize that what we traveled from Earth to the moon for is right
here in our hands."
"GRAIL delivered to Earth over
99.99 percent of the data that could have been collected, which underscores the
flawless performance of the spacecraft, instrument and the Deep Space
Network," said Zuber.
Both spacecraft instruments will be
powered off until Aug. 30. The spacecraft will have to endure a lunar eclipse
on June 4. The eclipse and the associated sudden changes in temperature and the
energy-sapping darkness that accompanies the phenomena were expected and do not
concern engineers about the spacecraft's health.
"Before launch, we planned for all
of GRAIL's primary mission science to occur between lunar eclipses," said
David Lehman, project manager of GRAIL from NASA's Jet Propulsion Laboratory
(JPL) in Pasadena, Calif. "But now that we have flown Ebb and Flow for a
while, we understand them and are confident they can survive these eclipses in
good shape."
The extended mission goal is to take an
even closer look at the moon's gravity field. To achieve this, GRAIL mission
planners will halve their current operating altitude flying at the lowest
altitude that can be safely maintained.
"Orbiting at an average altitude of
14 miles (23 kilometers) during the extended mission, the GRAIL twins will be
clearing some of the moon's higher surface features by about 5 miles (8
kilometers)," said Joe Beerer, GRAIL's mission manager. "If Ebb and
Flow had feet, I think by reflex they'd want to pull them up every time they
fly over a mountain."
Along with mission science, GRAIL's
MoonKAM (Moon Knowledge Acquired by Middle school students) education and
public outreach program is also extended. To date over 70,000 student images of
the moon have been obtained. The MoonKAM program is led by Sally Ride,
America's first woman in space, and her team at Sally Ride Science in
collaboration with undergraduate students at the University of California in
San Diego.
The GRAIL mission is managed by JPL for
NASA's Science Mission Directorate in Washington. The mission is part of the
Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville,
Ala. NASA's Deep Space Network is an international network of antennas that
supports interplanetary spacecraft missions and radio and radar astronomy
observations for the exploration of the solar system and the universe. The
network also supports selected Earth-orbiting missions. Lockheed Martin Space
Systems in Denver built the spacecraft.
For more information about GRAIL, visit http://www.nasa.gov/grail.
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