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The 2 Graces
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GRACE, twin satellites launched in March 2002, are making detailed measurements of
Earth's gravity field which will lead to discoveries about gravity and Earth's natural
systems. These discoveries could have far-reaching benefits to society and the world's
population.
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The GRACE mission combined with other existing sources of data will greatly improve
our understanding of:
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- Geodesy
- Glaciology
- Hydrology
- Oceanography
- Solid Earth Sciences
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Characteristics
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| Launch Date |
17 March 2002 |
| Mission Lifetime |
5 years |
| Orbit altitude |
450-500 km |
| Orbit Inclination |
89° |
| Mass |
487 kg 2x |
| Length |
3.1 m 2x |
| Launch Site |
Plesetsk, Russia |
| Launcher |
Rockot |
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GRACE - Gravity Recovery And Climate Experiment
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 The GRACE mission is a joint German-American project. The primary objective of the GRACE mission
is to obtain accurate global models for the mean and time variable components of the earth´s
gravity field. This goal will be achieved by measurements of the inter-satellite range between
2 co-planar, low altitude near-polar orbiting satellites. In addition, each satellite carries
a high accuracy accelerometer and a geodetic qualified GPS receiver to perform precise orbit
determination, recover gravity data and to estimate the gravity field.
The secondary task of the GRACE mission is to keep a daily record of several hundred globally
distributed profiles of the delay or inclination angle of GPS measurements. Both can be converted into a total
electron or refractivity by applying Atmospheric- and Ionospheric-Profiling.
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The Science Behind the GRACE Mission
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Gravity is the invisible force that pulls two masses together. The branch of science dealing with
obtaining precise measurements of the Earth, mapping points on the surface, and studying its
gravitational field is known as geodesy. Producing such a precise model of the changes in gravity
over the Earth's surface has proven to be a formidable task.
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Currently, data from several dozen satellites must be combined to produce a model of Earth's
gravitational field. These models do a good job at simulating the large-scale features of Earth's
gravitational field but cannot resolve finer-scale features. Adding data from ground-based
measurements and airborne altimeters allows for more precise measurement over large bodies
of water. The unique design of the GRACE mission (twin-satellites flying in formation) is
expected to lead to an improvement of several orders of magnitude in these gravity measurements
and allow much improved resolution of the broad to finer-scale features of Earth's gravitational
field over both land and sea.
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A secondary experiment that GRACE will perform is to examine how the atmosphere affects signals
from the Global Positioning System (GPS).
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