The Gravity Recovery and Climate Experiment (GRACE) was a joint mission of NASA and the German Aerospace Center (DLR). Twin satellites took detailed measurements of Earth's gravity field anomalies from its launch in March 2002 to the end of its science mission in October 2017. The GRACE Follow-On (GRACE-FO) is a continuation of the mission on near-identical hardware, launched in May 2018. By measuring gravity anomalies, GRACE showed how mass is distributed around the planet and how it varies over time. Data from the GRACE satellites is an important tool for studying Earth's ocean, geology, and climate. GRACE was a collaborative endeavor involving the Center for Space Research at the University of Texas at Austin, NASA's Jet Propulsion Laboratory, the German Aerospace Center and Germany's National Research Center for Geosciences, Potsdam. The Jet Propulsion Laboratory was responsible for the overall mission management under the NASA ESSP (Earth System Science Pathfinder) program. The principal investigator is Byron Tapley of the University of Texas Center for Space Research, and the co-principal investigator is Christoph Reigber of the GeoForschungsZentrum (GFZ) Potsdam. The two GRACE satellites, GRACE-1 and GRACE-2, were launched from Plesetsk Cosmodrome, Russia, on a Rockot (SS-19 + Breeze upper stage) launch vehicle on 17 March 2002. The spacecraft were launched to an initial altitude of approximately 500 km at a near-polar inclination of 89°. During normal operations, the satellites were separated by 220 km along their orbit track. This system was able to gather global coverage every 30 days. GRACE far exceeded its 5-year design lifespan, operating for 15 years until the decommissioning of GRACE-2 on 27 October 2017. Its successor, GRACE-FO, was successfully launched on 22 May 2018. In 2019, a glacier in West Antarctica was named after the GRACE mission. Discoveries and applications The monthly gravity anomalies maps generated by GRACE are up to 1,000 times more accurate than previous maps, substantially improving the accuracy of many techniques used by oceanographers, hydrologists, glaciologists, geologists and other scientists to study phenomena that influence climate. From the thinning of ice sheets to the flow of water through aquifers and the slow currents of magma inside Earth, mass measurements provided by GRACE help scientists better understand these important natural processes. Oceanography, hydrology, and ice sheets GRACE chiefly detected changes in the distribution of water across the planet. Scientists use GRACE data to estimate ocean bottom pressure (the combined weight of the ocean