The Copernicus Sentinel-6 is taking on the role of radar altimetry reference mission, continuing the long-term record of measurements of sea-surface height started in 1992 by the French–US Topex Poseidon and then the Jason series of satellite missions. While Sentinel-6 is one of the European Union’s family of Copernicus satellite missions, its implementation is the result of a unique cooperation between ESA, Eumetsat, NASA and NOAA. The Copernicus Sentinel-6 mission comprises two identical satellites launched five years apart. The first, Sentinel-6 Michael Freilich, launches on 21 November 2020 from the Space Launch Complex 4 East at the Vandenberg Air Force Base near the city of Lompoc in California, US.