GRACE (Gravity Recovery And Climate Experiment) was a completed NASA-led Earth-observation program launched on 17 March 2002 in partnership with Germany’s DLR. Its twin spacecraft measured tiny changes in the distance between them to map Earth’s changing gravity field and reveal the movement and storage of water, ice, ocean mass, groundwater, and solid-Earth mass. GRACE science operations concluded in October 2017, establishing a foundational mass-change record continued by GRACE-FO.