34th Meeting of the AAS Division on Dynamical Astronomy, May 2003
7 Space Missions, Astrometry, and Observables
Oral, Tuesday, May 6, 2003, 8:30-10:50am,

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[7.01] The GRACE Mission: Status and Early Results

B. D. Tapley (The University of Texas at Austin, Center of Space Research), C. Reigber (GeoForschunzgsZentrumn, Potsdam), J. C. Ries (The University of Texas at Austin, Center of Space Research)

The Gravity Recovery and Climate Experiment (GRACE) is a dedicated satellite mission whose objective is to map the global gravity field with unprecedented accuracy over a spectral range from 500 km to 40,000 km. The measurement precision will support gravity field solutions in this frequency range that are between 10 and 1000 times better than our current knowledge. The mission profile calls for a gravity field solution with this accuracy every thirty days, which will allow studies of the gravitational signals associated with the mass exchange between the Earths solid, ocean and atmospheric system components. The primary measurement provided by the High Accuracy Inter-satellite Ranging System (HAIRS) is the range change between two satellites orbiting one behind the other at an approximate distance of 200 km. The range change will be measured with a precision better than 10 microns over a ten second averaging interval. A highly accurate three-axis accelerometer, located at the satellite mass center, will be used to measure the surface force and attitude control induced accelerations. Satellite GPS receivers will position the satellites over the earth with centimeter level accuracy. With this set of measurements, GRACE will provide highly accurate measurements of the global gravity field once every thirty days. The two satellites were launched on March 17, 2002 and were designed to operate for a period of five years. The satellites will fly in coplanar nearly polar orbits, at an altitude between 500 and 300 km, separated by approximately 200 km along track. The mission, which is one of the first NASA Earth System Pathfinder Missions, is implemented through a collaborative arrangement by NASA and DLR. The presentation will summarize the mission structure, the early satellite and instrument performance, the data system and ancillary data requirements and will describe some of the early analysis results.

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Bulletin of the American Astronomical Society, 35 #4
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