The second Copernicus Sentinel-3 satellite, Sentinel-3B, lifted off on a Rockot from the Plesetsk Cosmodrome in northern Russia at 17:57 GMT (19:57 CEST) on 25 April 2018. Sentinel-3B joins its twin, Sentinel-3A, in orbit. The pairing of identical satellites provides the best coverage and data delivery for Europe’s Copernicus programme – the largest environmental monitoring programme in the world. The satellites carry the same suite of cutting-edge instruments to measure oceans, land, ice and atmosphere. Feeding a new generation of data products, the Sentinel-3 mission is at the heart of operational oceanography. For example, it provides measurements to monitor aquatic biological productivity and marine pollution, to map sea-level change and to forecast the sea state for efficient and safe ship routeing. As well as measuring the oceans, the mission also delivers unique and timely information about changing land cover, vegetation, urban heat islands, and for tracking wildfires.