GRACE-FO

GRACE-FO
Name	GRACE-FO
Mission type	Earth observation
Operator	National Aeronautics and Space Administration / Deutsches Zentrum für Luft- und Raumfahrt
Launch date	2018-05-22
Launch vehicle	SpaceX Falcon 9 Full Thrust
Launch site	Vandenberg Space Force Base
Orbit reference	Geocentric orbit
Instruments	Microwave ranging system, Laser Ranging Interferometer, GPS receivers, accelerometers

GRACE-FO

GRACE-FO is a twin-satellite Earth science mission launched in 2018 to measure temporal variations in Earth's gravity field using inter-satellite ranging and positioning techniques. The mission builds on earlier missions and involves partnerships among NASA, Deutsches Zentrum für Luft- und Raumfahrt, Jet Propulsion Laboratory, University of Texas at Austin, and international science teams. Data from the mission support research in hydrology, glaciology, oceanography, and geophysics with applications for climate studies and resource management.

Overview

The mission employs two nearly identical spacecraft flying in a low Earth orbit tandem formation to map gravity-driven mass redistribution across continents and oceans. Hardware and algorithms trace their heritage to the earlier GRACE mission, while advances draw on technologies used in LISA Pathfinder, CHAMP (satellite), GOCE, and navigation systems like Global Positioning System and Galileo (satellite navigation). Science goals align with priorities by organizations such as the Intergovernmental Panel on Climate Change, World Meteorological Organization, and national agencies including NOAA. International science teams include investigators from institutions like California Institute of Technology, Massachusetts Institute of Technology, University of Colorado Boulder, GFZ German Research Centre for Geosciences, and CNES collaborators.

Mission and Objectives

Primary objectives are to quantify time-variable gravity signals from terrestrial water storage, cryospheric mass loss, and ocean bottom pressure. Specific aims include monitoring groundwater depletion in regions like India, California, and North China Plain; measuring ice mass changes in Greenland, Antarctica, and Alaska; and observing sea level and ocean circulation phenomena such as El Niño–Southern Oscillation and Indian Ocean Dipole. Objectives also support hazard assessment linked to earthquakes and volcanic eruptions by resolving mass redistribution associated with tectonic and magmatic processes. The mission provides continuity for long-term records sought by programs like the Global Climate Observing System and the Group on Earth Observations.

Spacecraft and Instruments

Each spacecraft carries a microwave inter-satellite ranging system descended from designs used on GRACE and augmented by a novel Laser Ranging Interferometer tested on LISA Pathfinder. Precision timing and orbit determination depend on dual-frequency GNSS receivers compatible with GPS and GLONASS and algorithms developed with inputs from Jet Propulsion Laboratory and European Space Agency. Non-gravitational acceleration is measured by electrostatic accelerometers influenced by heritage from GOCE instruments; attitude control and star sensing exploit technologies proven on Swarm (ESA mission) and Terra (satellite). The Laser Ranging Interferometer permits sub-nanometer sensitivity to inter-satellite displacement, enabling improved resolution for mass change signals when combined with microwave ranging and accelerometer data.

Operations and Data Processing

Ground operations are coordinated through NASA facilities and DLR centers with mission planning, command, and control informed by practices from Mission Control Center (Houston), Darmstadt, and international partner centers. Raw ranging, accelerometer, and GNSS tracking data undergo calibration and level-1 processing, followed by gravity field inversion techniques similar to those implemented for GRACE and refined using methods from Scripps Institution of Oceanography, University of Bonn, and NASA Goddard Space Flight Center. Time-variable gravity solutions are produced as monthly spherical harmonic coefficients and mascon products by teams at University of Texas at Austin, GFZ, CSR (Center for Space Research), and JPL. Data distribution follows protocols used by NASA Earthdata and is integrated into analysis frameworks employed by International Hydrographic Organization and regional agencies.

Scientific Results and Applications

GRACE-FO data have quantified groundwater depletion in major aquifers including the North China Plain, Central Valley (California), and Indus Basin, influencing water management by agencies like United States Geological Survey and Central Ground Water Board (India). Cryospheric studies using GRACE-FO have refined mass loss estimates for Greenland Ice Sheet, West Antarctic Ice Sheet, and mountain glaciers in the Himalayas and Andes, contributing to sea-level projections used by IPCC assessments and regional planners. Oceanographic applications include improved understanding of steric and mass-driven sea level changes related to ENSO events and ocean bottom pressure variability affecting El Niño, La Niña, and Indian Ocean Dipole phenomena. Geophysical analyses have resolved mass changes associated with large earthquakes such as the 2011 Tōhoku earthquake and tsunami and volcanic processes at sites like Mount St. Helens and Eyjafjallajökull. Hydrological and climate research groups at Columbia University, Princeton University, ETH Zurich, and Potsdam Institute for Climate Impact Research routinely incorporate GRACE-FO products into models for water resources and climate adaptation planning.

Mission History and Collaborations

GRACE-FO was selected as a partnership mission and launched aboard a SpaceX Falcon 9 from Vandenberg Space Force Base in May 2018, with mission operations coordinated by NASA JPL and scientific leadership shared with DLR and international teams. The project sustained collaborations with universities such as University of Texas at Austin, University of Colorado Boulder, University of Bonn, and research centers including GFZ, CNES, JPL, and NOAA. Technological collaborations leveraged developments from LISA Pathfinder, GOCE, and GNSS modernization efforts by European GNSS Agency. Continued international coordination with initiatives like Group on Earth Observations and data assimilation efforts at European Centre for Medium-Range Weather Forecasts and National Center for Atmospheric Research ensure integration of GRACE-FO results into operational and research applications.

Category:Earth observation satellites