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March 17, 2002
Scientists Say 'Grace' as Water-Sensing Satellites Lift Off
NASA and the German Center for Air and Space
Flight today successfully launched the Gravity
Recovery and Climate Experiment, or "Grace,"
mission into Earth orbit at 1:21:27 a.m. Pacific time
from Russia's Plesetsk Cosmodrome. The mission,
comprised of identical twin satellites, will precisely
measure Earth's shifting water masses and map their
effects on Earth's gravity field.
The five-year Grace mission-the first launch of
NASA's Earth System Science Pathfinder program-will
be a scientific boon to researchers who study Earth
with space-based instruments. The monthly gravity
maps generated by Grace will be up to 1,000 times
more accurate than those currently in use,
substantially improving the accuracy of many techniques used by oceanographers,
hydrologists, glaciologists, geologists and other scientists to study phenomena that influence
climate. These phenomena range from shallow and deep ocean currents, water movement
on and beneath Earth's surface, and the movement and changing mass of ice sheets, to
sea-level heights, sea-level rise and changes in the structure of the solid Earth.
Under partly cloudy, cold skies, the Grace twins lifted off on a Russian Rockot launch
vehicle. Riding nearly 160,000 kilograms (approximately 350,000 pounds) of thrust, the
rocket headed northward over the Arctic Ocean and Alaska, then south across the Pacific
Ocean and Antarctica before heading north again over Africa and Europe. At 85 minutes,
38 seconds into the mission-or 2:47 a.m. Pacific time-the satellites separated from the
launch vehicle's third stage above Africa into a polar orbit 500 kilometers (311 miles) above
Earth.
Ground controllers successfully acquired the spacecraft's signal from the German Space
Operations Center's ground tracking station in Weilheim, Germany at 2:49 a.m. Pacific time.
Initial telemetry reports received by the Grace team show both satellites to be in excellent
health.
Following separation, the leading Grace satellite began pulling away from the trailing
satellite at a relative speed of about 0.5 meters (1.6 feet) per second. Over the course of the
next four days, the satellites will be spaced 220 kilometers (137 miles) apart- a little more
than the distance between Los Angeles and San Diego.
As they race around the globe 16 times a day, the satellites will sense minute variations
in Earth's surface mass below and corresponding variations in Earth's gravitational pull.
Regions of slightly stronger gravity will affect the lead satellite first, pulling it slightly away
from the trailing satellite. By measuring the constantly changing distance between the two
satellites using an extremely sensitive microwave ranging system and combining that data
with precise positioning measurements from Global Positioning System instruments,
scientists will be able to construct a precise Earth gravity map.
During the next two and a half weeks, basic satellite operations will be established.
During a subsequent three-week commissioning phase, Grace's science instruments and
supporting systems will be powered up, evaluated and calibrated. The performance of the
Grace system for measuring Earth gravity will then be validated over the following six
months. The mission then enters its observational phase, during which routine operational
data products will be made available to scientists.
Additional information about the Grace program is available on the Internet at:
Grace is a joint partnership between NASA and the German Center for Air and Space
Flight (Deutsches Zentrum fur Luft und Rumfahrt, or DLR). NASA's Jet Propulsion
Laboratory, Pasadena, Calif., manages the U.S. portion of the project for NASA's Office of
Earth Science, Washington. Science data processing, distribution, archiving and product
verification are managed under a cooperative arrangement between JPL and the University
of Texas' Austin-based Center for Space Research in the United States and Germany's
Earth Research Center (or GeoForschungsZentrum).
JPL is a division of the California Institute of Technology in Pasadena.
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Contacts:
JPL/Alan Buis (818) 354-0474
NASA Headquarters/David E. Steitz (202) 358-1730
NASA Goddard Space Flight Center/Lynn Chandler (301) 286-2806
German Center for Air and Space Flight/Vanadis Weber +49 (0) 2203/601-3068
University of Texas Center for Space Research/Margaret Baguio (512) 471-6922
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Launch of GRACE
The Gravity Recovery and Climate Experiment (GRACE) was launched from Plesetsk Cosmodrome in Russia on 17 March 2002. Shown here is the ROCKOT as it lifts off the pad carrying GRACE.
Preparation of GRACE
This photograph shows the two GRACE satellites mounted on the multisatellite dispenser, which is placed inside the third stage of the launch vehicle.
(Credit: University of Texas Center for Space Research)
Artist's Concept of GRACE
Once in space, the two satellites separate from the launch vehicle and are positioned approximately 220 km apart from one another.
Related Link
GRACE Fact Sheet
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