GRACE
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| GRACE | |
|---|---|
| Name | GRACE |
| Mission type | Earth observation |
| Operator | NASA / German Aerospace Center |
| Mission duration | 2002–2017 |
| Launch date | 2002-03-17 |
| Launch vehicle | Rockot (rocket) |
| Launch site | Plesetsk Cosmodrome |
| Manufacturer | Jet Propulsion Laboratory / German Research Centre for Geosciences |
GRACE The Gravity Recovery and Climate Experiment was a joint NASA and German Aerospace Center satellite mission that mapped Earth's gravity field to unprecedented spatial and temporal resolution. Operating from 2002 to 2017, the mission provided continuous measurements that linked mass redistribution in the Cryosphere, Hydrosphere, and Solid Earth to climate variability, sea level rise, and tectonic processes. Data from the mission underpinned studies involving major events and institutions such as the Indian Ocean earthquake and tsunami, the Antarctic ice sheet, and the Intergovernmental Panel on Climate Change.
Overview
GRACE consisted of twin spacecraft flying in tandem in low Earth orbit to measure minute variations in the geopotential caused by mass redistribution. The mission produced monthly gravity field solutions used by researchers at organizations like the National Oceanic and Atmospheric Administration, the European Space Agency, and the United States Geological Survey to study phenomena ranging from groundwater depletion in California Central Valley to glacial mass loss in Greenland ice sheet. GRACE’s measurements complemented datasets from missions such as TOPEX/Poseidon, Jason-1, and ICESat.
Mission and Objectives
Primary objectives included determining time-variable gravity to quantify mass transport within and between the Hydrosphere, Cryosphere, and Solid Earth. Specific science goals targeted changes in continental water storage affecting regions like the Ganges–Brahmaputra Delta, sea level budget contributions from the Antarctic Peninsula and West Antarctic Ice Sheet, and post-seismic deformation following events including the 2004 Indian Ocean earthquake and the 2010 Chile earthquake. The mission also aimed to improve models used by agencies such as the World Meteorological Organization and to provide observational constraints for climate assessments by the Intergovernmental Panel on Climate Change.
Spacecraft and Instruments
The mission architecture paired two nearly identical satellites in the same orbit separated by about 220 km. The critical instrument was a high-precision K-band ranging system developed with contributions from institutions like the Jet Propulsion Laboratory and the GFZ German Research Centre for Geosciences; additional sensors included star cameras and accelerometers with heritage from the Gravity Probe B program. Other onboard systems derived from technologies tested on projects such as CHAMP and supported by organizations like the Deutsches Zentrum für Luft- und Raumfahrt. The inter-satellite ranging enabled detection of micrometer-scale changes in separation linked to gravity anomalies beneath regions like the Amazon Basin and the Sahara.
Data Processing and Products
Raw measurements were processed into monthly gravity field solutions and degree/order spherical harmonic coefficients by science teams at institutions including University of Texas at Austin, University of Bonn, and the NASA Jet Propulsion Laboratory. Products included mascon solutions, gridded mass anomaly maps, and level-2 datasets used in hydrology and glaciology. Agencies such as the National Aeronautics and Space Administration and the German Aerospace Center distributed datasets that fed assimilation systems at the European Centre for Medium-Range Weather Forecasts and databases maintained by the Paleoclimatology Program.
Scientific Contributions and Applications
GRACE transformed quantitative understanding of continental water storage, revealing significant groundwater depletion in regions like the Indus Basin, the Central Valley (California), and the North China Plain. The mission quantified ice mass loss in the Greenland ice sheet and the West Antarctic Ice Sheet, influencing sea level rise projections used by the IPCC and national agencies in Netherlands coastal planning. Geophysical applications included resolving post-glacial rebound signatures in Fennoscandia, mapping hydrologically driven surface loading in the Amazon Basin, and detecting coseismic mass redistributions after the Sumatra earthquake and the Tohoku earthquake and tsunami. GRACE data supported interdisciplinary research involving universities such as Massachusetts Institute of Technology, Harvard University, and ETH Zurich and informed policy discussions at bodies like the United Nations Framework Convention on Climate Change.
Development, Launch, and Operations
Development traced collaborations among the NASA Jet Propulsion Laboratory, GFZ Potsdam, and contractors experienced with launch systems like Rockot (rocket). The twin satellites launched from the Plesetsk Cosmodrome on 17 March 2002 into near-polar orbit. Operations and calibration relied on international ground networks including tracking stations affiliated with the European Space Agency and data centers at the University of Bonn and JPL. The mission achieved extended operations beyond its nominal lifetime, with successful continuous operation until gradually reduced functionality led to mission end in 2017.
Legacy and Successors
GRACE established a measurement paradigm continued by follow-on missions such as GRACE Follow-On and complementary programs including Swarm and ICESat-2. The mission’s datasets remain integral to contemporary studies by institutions like the International Centre for Integrated Mountain Development and the World Bank for water resource management and climate adaptation planning. Its technical innovations in inter-satellite ranging informed technology demonstrations on projects supported by DARPA and the European Commission, and its scientific legacy endures in ongoing citations across journals published by societies such as the American Geophysical Union.