Gravity Recovery And Climate Experiment

GRACE will map variations in the Earth's gravity field over its five-year lifetime with its two identical spacecraft flying about 220 kilometers apart in a Polar Orbit 500 kilometers above the Earth. The twin GRACE satellites were launched from Plesetsk Cosmodrome , Russia on a Rockot (SS-19) launch vehicle, on March 17 , 2002 .

The two satellites constantly maintain a two-way radio-ranging link between them, as well as measuring their own movements using Accelerometer s and Star Camera s and by listening to GPS satellite broadcasts. All of this information is then downloaded to ground stations.
The GRACE vehicles also have optical Corner Reflector s to enable Laser Ranging from ground stations.

GRACE is intended to enable precise measurement of Earth's shifting water masses by detecting their effects on our planet's gravity field, allowing the study of global climatic issues by enabling a better understanding of ocean surface currents and heat transport, measuring changes in sea-floor pressure, watching the mass of the oceans change, and by monitoring changes in the storage of water and snow on the continents.

The data so far obtained by GRACE is the most precise experiment to try to measure the relativistic Frame-dragging effect.

The spacecraft were manufactured by Astrium of Germany . The microwave RF systems, and attitude determination and control system algorithms were provided by Space Systems/Loral .

EXTERNAL LINKS

GRACE mission home page

''Science@NASA'' article about GRACE

''Weighing Earth's Water from Space'' Estimating ground water using GRACE (written for non-scientists)

Report by BBC showing early results

''An early version of this article was adapted from public domain text at {Link without Title} ''

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Gravity Recovery And Climate Experiment