[meteorite-list] NASA's GRAIL-A Spacecraft 24 Hours Away From Moon

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 30 Dec 2011 19:14:43 -0800 (PST)
Message-ID: <201112310314.pBV3Eh81027588_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2011-397

NASA's GRAIL-A Spacecraft 24 Hours Away From Moon
Jet Propulsion Laboratory
December 30, 2011

PASADENA, Calif. -- NASA's Gravity Recovery And Interior Laboratory
(GRAIL)-A spacecraft is within 24 hours of its insertion burn that will
place it into lunar orbit. At the time the spacecraft crossed the
milestone at 1:21 p.m. PST today (4:21 p.m. EST), the spacecraft was
30,758 miles (49,500 kilometers) from the moon.

Launched aboard the same rocket on Sept. 10, 2011, GRAIL-A's mirror
twin, GRAIL-B, is also closing the gap between itself and the moon.
GRAIL-B is scheduled to perform its lunar orbit insertion burn on New
Year's Day (Jan. 1) at 2:05 p.m. PST (5:05 p.m. EST).

As they close in on the moon, both orbiters move toward the moon from
the south, flying nearly directly over the lunar south pole. The lunar
orbit insertion burn for GRAIL-A will take approximately 40 minutes to
complete and change the spacecraft's velocity by about 427 mph (687
kph). GRAIL-B's insertion burn - occurring 25 hours later -- will last
about 39 minutes and is expected to change its velocity by 430 mph (692
kph).

The insertion maneuvers will place each orbiter into a near-polar,
elliptical orbit with an orbital period of 11.5 hours. Over the
following weeks, the GRAIL team will execute a series of burns with each
spacecraft to reduce their period down to just under two hours. At the
start of the science phase in March 2012, the two GRAILs will be in a
near-polar, near-circular orbit with an altitude of about 34 miles (55
kilometers).

During the science phase, the moon will rotate three times underneath
the GRAIL orbit. The collection of gravity data over one complete
rotation (27.3 days) is referred to as a Mapping Cycle. When science
collection begins, the spacecraft will transmit radio signals precisely
defining the distance between them as they orbit the moon in formation.
Regional gravitational differences on the moon are expected to expand
and contract that distance. GRAIL scientists will use these accurate
measurements to define the moon's gravity field. The data will allow
mission scientists to understand what goes on below the surface of our
natural satellite. This information will help us learn more about how
the moon, Earth and other terrestrial planets formed.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the GRAIL
mission. The Massachusetts Institute of Technology, Cambridge, is home
to the mission's principal investigator, Maria Zuber. The GRAIL mission
is part of the Discovery Program managed at NASA's Marshall Space Flight
Center in Huntsville, Ala. Lockheed Martin Space Systems, Denver, built
the spacecraft. JPL is a division of the California Institute of
Technology in Pasadena.

More information about GRAIL is online at: http://www.nasa.gov/grail and
http://grail.nasa.gov .

The GRAIL press kit can be found online at:
http://www.jpl.nasa.gov/news/press_kits/graiLaunch.pdf .

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

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

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

2011-397
Received on Fri 30 Dec 2011 10:14:43 PM PST