Sentinel-3 is a mission with wide-swath low-medium resolution visible and infrared radiometers and a radar altimeter package, and part of GMES space component. Sentinel-3 is a low-Earth-orbiting mission providing fast revisit land and ocean monitoring on a global basis. In order to meet the GMES requirements and in particular the Ocean and Land (global) Fast Track Services, two operational satellites are envisaged in-orbit to provide a one-day (land) and two-day (ocean) revisit time. Additional satellites are then required to provide the sustained operational services over a minimum operational period of twenty years following the first satellite launch. Artistic drawing of Sentinel-3.