Mission Overview
The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission continues the highly successful GRACE record of monitoring changes in Earth's gravity field. Launched in 2018, GRACE-FO measures the changing distribution of water, ice, oceans, and solid Earth mass by precisely tracking the distance between two satellites flying approximately 220 km apart in the same polar orbit. By extending the GRACE time series, GRACE-FO provides an uninterrupted record of global mass transport that supports studies of climate change, sea level rise, groundwater depletion, glacier and ice-sheet mass balance, droughts, floods, and solid Earth processes.
Mission Objectives
The primary objective of GRACE-FO is to produce accurate global models of both the static and time-varying components of Earth's gravity field. Like the original GRACE mission, these measurements are used to estimate monthly gravity field solutions that reveal changes in mass distribution across the Earth system.
A secondary objective is to demonstrate advanced laser interferometric ranging technology for future gravity missions. GRACE-FO also continues atmospheric observations through GPS radio occultation measurements, with these observations provided to U.S. and European weather prediction centers for use in operational weather forecasting products.
Instruments
Each GRACE-FO satellite carries a suite of precision geodetic instruments designed to measure the tiny variations in satellite separation caused by changes in Earth's gravity.
- K/Ka-band Microwave Ranging System (KBR): Measures changes in the distance between the two spacecraft with micrometer-level precision, providing the primary science measurement for gravity field recovery.
- Laser Ranging Interferometer (LRI): A technology demonstration that measures inter-satellite distance changes with substantially higher precision than the microwave ranging system, paving the way for future generations of gravity missions.
- GPS Receiver: Provides precise orbit determination and accurate time synchronization for both spacecraft.
- Accelerometer: Measures non-gravitational forces such as atmospheric drag and solar radiation pressure so they can be removed from the gravity measurements.
- Star Camera System: 3 star camera assemblies provide redundant, high-accuracy spacecraft attitude determination required for precise gravity measurements.
- Laser Retroreflector (LRR): Enables independent satellite laser ranging from ground stations for orbit validation and calibration.
International Partnership
GRACE-FO is a joint mission between the National Aeronautics and Space Administration (NASA) and the German Research Centre for Geosciences (GFZ). The mission is managed in the United States by NASA's Earth Science Division through the Earth Systematic Missions Program Office at NASA Goddard Space Flight Center, with the Jet Propulsion Laboratory responsible for project implementation on the U.S. side. The mission continues the successful international collaboration established by the original GRACE mission.