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Scientists
Say 'Grace' as Water-Sensing Satellites Lift Off
NASA
and the German Center for Air and Space Flight successfully launched the Gravity
Recovery and Climate Experiment, or "Grace," mission into Earth orbit
at 1:21:27 a.m. Pacific time March 17, 2002 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.
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).
AMAZING
GRACE - THE BEST LOOK YET AT EARTH'S INVISIBLE GRAVITY FIELD
Gravity - it's the unseen hand that roots humanity firmly to the ground and helps
control the motion of the oceans. It's a force of nature like no other, working
to pull two masses together. Just like the life it plants on the surface of the
Earth, gravity is ever changing. When mass moves within the planet's atmosphere,
ocean, land, or frozen surface (cryosphere), the gravity field moves as well.
NASA's Gravity Recovery and Climate Experiment (GRACE), launching in March 2002,
will give scientists around the globe the most accurate look yet at the face of
gravity and how it shapes our world. Amazing
GRACE
GRACE
is actually two identical spacecraft that will fly about 200 kilometers apart,
connected only by a microwave signal. As they orbit the Earth, the spacecraft
are pulled by areas of higher and lower gravity and will move in relation to one
another. As the front satellite approaches an area of higher gravity, it will
be pulled toward that higher gravity and speed up, increasing the distance between
the two spacecraft. As GRACE straddles the area of higher gravity, the trailing
satellite will speed up but the front satellite will slowdown. HAIRS, the high
accuracy intersatellite ranging system will measure the distance changes between
the spacecraft. New maps of Earth's gravity field will be produced every thirty
days based on distance measurements between the two spacecraft.
TRT:
SUPER:NASA GRACE
in Action - Click
here for animation
We
don't reside on a flat planet as we perceive from our daily activities. Earth
appears neat and round from space, but take a look at the planet from GRACE's
perspective. The bumps and lumps seen in the next animation are the result of
an uneven distribution of mass inside the Earth. Mass varies between mountains,
valleys, oceans, and caverns, which means gravity varies in these areas as well.
GRACE will map out the precise location of these lumps, enabling greater understanding
of the structure of the Earth. TRT:
SUPER: NASA, USFS Taking
Our Lumps - Click
here for animation
GRACE
gravity data will provide scientists a monthly view of Earth that looks like the
following animation. Land features like mountains and valleys cause differences
in the gravity field, but they are not the only creators of this bumpy view of
Earth. Changes in the ocean, like El Nino events, runoff and ground water storage
on land masses, exchanges between ice sheets, glaciers, and the oceans and many
other subtle changes can alter the gravity field. Understanding gravity better
might help us predict changes in our planet. TRT:
SUPER:NASA, USFS
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