The NASA/German Space Agency (DLR) Gravity Recovery and Climate Experiment/GRACE Follow-on (GRACE and GRACE-FO) platforms each consist of two identical satellites that act in unison as the primary instrument. The two satellites comprising each mission orbit one behind the other in the same orbital plane at an approximate distance between the two satellites of 220 km (137 miles). 

As the satellite pair circles Earth, areas of slightly stronger gravity affect the lead satellite first, pulling it toward the planet and away from the trailing satellite. As the satellites continue along their orbital path, the trailing satellite passes over the gravity anomaly and is pulled toward the lead satellite. An extremely precise ranging system aboard both GRACE and GRACE-FO detects minute changes in the distance between the satellite pairs.

The GRACE-FO satellite mission successfully completed its nominal five-year prime mission phase in May 2023, and is currently in its extended mission phase. GRACE-FO continues the unique essential climate data record of mass change in the Earth system initiated in 2002 by the GRACE mission (2002-2017).

The combined GRACE & GRACE-FO data records now span over 24 years and provide foundational observations of monthly to decadal global mass changes and transports in the Earth system derived from temporal variations in the Earth’s gravity field.  

In parallel, a continuity mission called GRACE-Continuity (GRACE-C) scheduled for launch in 2028 is being developed in partnership between NASA (US) and DLR (Germany), leveraging heritage elements considerably in the design.  One departure from heritage, is that the primary ranging instrument on GRACE-C will be a higher precision laser interferometer, capitalizing on the successful demonstration of this technology on GRACE-FO.