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The goal of the Gravity Recovery And Climate Experiment (GRACE) space mission is to obtain accurate global and high-resolution determination of both the static and the time-variable components of the Earth's gravity field.

GRACE maps variations in the Earth's gravity field over its five-year lifetime (extended to eight years in 2005) 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 + Breeze upper stage) launch vehicle, on March 17, 2002.

The two satellites constantly maintain a two-way microwave-ranging link between them, as well as measuring their own movements using accelerometers and star cameras and by listening to GPS satellite broadcasts. All of this information is then downloaded to ground stations. The GRACE vehicles also have optical corner reflectors 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. Also data on Ocean and deep sea currents as well on tectonics are derived from the data.

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. The instrument computer along with a highly precise GPS system has been provided by JPL in Pasadena. The highly precise accelerometer that is needed to separate atmospheric and solar wind effects from the gravitation data has been manufactured by ONERA.

The data so far obtained by GRACE is the most precise gravimetric data yet recorded: it has been used to re-analyse data obtained from the LAGEOS experiment to try to measure the relativistic frame-dragging effect.

In 2006 a team of researchers led by Ralph von Frese and Laramie Potts used GRACE data to discover the 480 km (300 miles) wide Wilkes Land crater in Antarctica, which probably formed about 250 million years ago.^[1]

GRACE data has also been used to analyze the shifts in the Earth's crust caused by the earthquake that created the 2004 Indian Ocean tsunami. ^[2]

1. ^ Gorder, Pam Frost (June 1, 2006). Big Bang in Antarctica -- Killer Crater Found Under Ice. Research News.
2. ^ Chang, Kenneth (August 8, 2006). Before the ’04 Tsunami, an Earthquake So Violent It Even Shook Gravity. New York Times.

• GRACE mission home page (Primary Investigator)
• GRACE mission home page (co Primary Investigator) (language: German)
• 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 [1]