The following excerpt is from the NASA website:
“WASHINGTON -- 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 8:15 p.m. EST (5:15 p.m.
PST). During this mission phase, the spacecraft will transmit radio
signals precisely defining the distance between them. 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, the distance between the two spacecraft will change
slightly. 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)."
Previously named GRAIL A and B, the names Ebb and Flow were the result
of a nation-wide student contest to choose new names for the
spacecraft. 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.”
