GRACE (satellite)

GRACE (satellite)
Name	GRACE
Names list	Gravity Recovery and Climate Experiment
Mission type	Earth science
Operator	NASA / German Aerospace Center
Cospar id	2002-043A
Satcat	27558
Manufacturer	Jet Propulsion Laboratory / NASA Goddard Space Flight Center / German Research Centre for Geosciences
Launch date	17 March 2002
Launch vehicle	Rockot
Launch site	Plesetsk Cosmodrome
Orbit reference	Geocentric
Orbit type	Low Earth orbit
Mission duration	2002–2017 (primary)

GRACE (satellite) was a twin-satellite mission that mapped temporal changes in Earth's gravity field by tracking relative motion between two spacecraft. A joint project of NASA and the German Aerospace Center, the mission delivered unprecedented observations of mass redistribution in the hydrosphere, cryosphere, and solid Earth that informed studies spanning climatology, glaciology, hydrology, and geophysics.

Overview

The mission flew two identical spacecraft in a low, near-polar orbit separated by roughly 220 kilometers to measure time-variable gravity via inter-satellite ranging. Built through collaboration among the Jet Propulsion Laboratory, NASA Goddard Space Flight Center, and the German Research Centre for Geosciences, GRACE produced monthly gravity field solutions that quantified mass change for features such as the Greenland ice sheet, Antarctic ice sheet, major river basins like the Amazon River basin, and groundwater systems under the Indo-Gangetic Plain.

Mission concept and objectives

GRACE's core objective was to monitor Earth's gravity field and its temporal variations to infer mass transport. The mission design exploited precise ranging and accelerometry to separate gravitational signals from non-gravitational forces. Specific science goals included measuring ice mass loss from polar ice sheets including contributions to sea level rise, detecting terrestrial water storage variations under the Ganges–Brahmaputra, Murray–Darling basin, and Mississippi River systems, resolving post-glacial rebound across regions such as Fennoscandia and Hudson Bay, and improving global models used by institutions like the Intergovernmental Panel on Climate Change and the World Climate Research Programme.

Spacecraft and instruments

Each spacecraft carried a microwave ranging system, a K-band ranging instrument, a SuperSTAR accelerometer, a star camera suite, and a GPS receiver. The K-band ranging system measured variations in inter-satellite distance to micrometer precision, while the SuperSTAR accelerometer characterized non-gravitational forces such as atmospheric drag and solar radiation pressure. Attitude and orbit determination relied on GPS data processed with models used by the International GNSS Service and attitude sensors comparable to those on missions like CHAMP and GRACE Follow-On. Spacecraft buses incorporated components from the Astrium heritage and were integrated with payloads tested at EADS Astrium facilities.

Launch, operations, and data processing

Launched from Plesetsk Cosmodrome on a Rockot vehicle, GRACE entered a near-polar orbit and began routine science operations shortly thereafter. Mission operations were conducted jointly by NASA/JPL and the German Research Centre for Geosciences, with ground stations such as those operated by the European Space Agency and the German Space Operations Center supporting data downlink. Data processing pipelines produced Level-1 to Level-3 products distributed to scientific users at institutions including the University of Texas at Austin, the University of Colorado Boulder, NASA Goddard, and the GFZ German Research Centre for Geosciences. Algorithms leveraged techniques developed in missions like TOPEX/Poseidon and the Jason series for orbit determination and gravity inversion, and made use of software from the Goddard Earth Sciences Data and Information Services Center.

Scientific results and applications

GRACE revolutionized quantification of continental water storage changes, providing direct observations of groundwater depletion beneath regions such as the Central Valley (California), the Nile Basin, and the Indus Basin. The mission detected accelerating mass loss from the Greenland ice sheet and the West Antarctic Ice Sheet, and constrained ice dynamics in outlet glaciers like Jakobshavn Isbræ and Pine Island Glacier. In geophysics, GRACE measured post-seismic gravity changes after events such as the 2004 Indian Ocean earthquake and the 2010 Chile earthquake, and refined models of glacial isostatic adjustment used in sea-level studies by groups at the National Oceanic and Atmospheric Administration and the University of Tasmania. Applications extended to operational hydrology and water management by the World Bank and national agencies, climate studies informing the Intergovernmental Panel on Climate Change, and improvements to global geoid models used by the International Association of Geodesy.

Successors and legacy

GRACE's success led to the GRACE Follow-On mission, continued work by projects at NASA, GFZ, CNES, and the European Space Agency, and stimulated new missions such as SWOT for ocean and surface water monitoring. The GRACE data record established a benchmark for detecting anthropogenic impacts on Earth's mass balance and influenced policies on water resources and climate mitigation discussed at forums including the United Nations Framework Convention on Climate Change. The legacy persists in improved gravity-field models used by the International Hydrographic Organization, hydrologic forecasting centers, and in follow-up studies by universities such as MIT, Caltech, ETH Zurich, and Columbia University.

Category:Earth observation satellites Category:NASA spacecraft Category:German space program