GRACEFO

GRACE-FO, or Gravity Recovery and Climate Experiment Follow-On, is a joint United States–German space mission designed to map Earth's gravity field and its time-dependent variations. It continues the time-variable gravity data record established by the original GRACE mission (2002–2017) and is intended to advance understanding of mass redistribution on and within the planet.

The mission consists of two identical satellites operating in a near-polar orbit at about 500 kilometers altitude, separated by roughly 200 kilometers. By precisely measuring how the distance between the satellites changes as they travel over the Earth, scientists infer variations in the Earth's gravity field caused by moving masses such as oceans, ice sheets, and groundwater. The mission provides a flowing, monthly view of gravity field changes that reflect global hydrological and geophysical processes.

GRACE-FO carries a microwave inter-satellite ranging system to track distance changes between the spacecraft. In addition, a Laser Ranging Interferometer (LRI) was included as a technology demonstrator to test higher-precision laser interferometry for inter-satellite ranging, potentially enhancing gravity measurements in the future.

Data products from GRACE-FO include time-variable gravity field models and associated applications that help quantify changes in ice mass, groundwater storage, soil moisture, and ocean mass. These data support climate and water-resource research, natural hazard assessment, and sea-level studies.

The mission is a collaboration led by NASA and the German Research Centre for Geosciences (GFZ), with contributions from the German Aerospace Center (DLR) and other partners. It was launched on May 22, 2018, from Vandenberg Air Force Base aboard a SpaceX Falcon 9 rocket. As of the mid-2020s, GRACE-FO continues to operate and release data, maintaining an ongoing record of Earth's evolving gravity field.