The Copernicus Sentinel-3B rocket at the top of the launch tower. The Copernicus Sentinel-3B satellite is scheduled for liftoff on 25 April 2018 from the Plesetsk cosmodrome in northern Russia. Its identical twin, Sentinel-3A, has been in orbit since February 2016. The two-satellite constellation offers optimum global coverage and data delivery for Europe’s Copernicus environment programme.