[meteorite-list] NASA's GRAIL Moon Twins Begin Extended Mission Science

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 31 Aug 2012 10:52:10 -0700 (PDT)
Message-ID: <201208311752.q7VHqAdY017480_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2012-273

NASA's GRAIL Moon Twins Begin Extended Mission Science
Jet Propulsion Laboratory
August 31, 2012

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/

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

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

2012-273
Received on Fri 31 Aug 2012 01:52:10 PM PDT