Sentinel-3
Sentinel-3 is an Earth observation satellite series developed by the European Space Agency as part of the Copernicus Programme. It currently (as of 2020) consists of 2 satellites: Sentinel-3A and Sentinel-3B. After initial commissioning, each satellite was handed over to EUMETSAT for the routine operations phase of the mission. Two recurrent satellites— Sentinel-3C and Sentinel-3D— will follow in approximately 2024 and 2028 respectively to ensure continuity of the Sentinel-3 mission. The Sentinel-3 mission's objectives are to measure topography, temperature, marine ecosystems, water quality, pollution, and other features for ocean forecasting and environmental and monitoring. Overview. On 14 April  2008, the European Space Agency and Thales Alenia Space signed a contract to build the first GMES Sentinel-3 in its Cannes Mandelieu Space Center. Bruno Berruti led the team that was responsible for delivering the Copernicus Sentinel-3 satellites from the drawing board into orbit. The satellite platform was delivered to France for final integration in 2013. The communications systems were completed by Thales Alenia Space España in early 2014. Sentinel-3A was subsequently launched on 16 February 2016 on a Rokot vehicle from the Plesetsk Cosmodrome, located near Arkhangelsk, Russia. This first launch was followed by the launch of Sentinel-3B on  25 April 2018, also aboard a Rokot. The Sentinel-3 mission's main objective is to measure sea-surface topography, land- and sea-surface temperature, and land- and ocean-surface colour with accuracy in support of ocean forecasting systems, and for environmental and climate monitoring. Sentinel-3 builds directly on the heritage pioneered by ERS-2 and Envisat satellites. Near-real time data will be provided for ocean forecasting, sea-ice charting, and maritime safety services on the state of the ocean surface, including surface temperature, marine ecosystems, water quality and pollution monitoring. A pair of Sentinel-3 satellites will enable a short revisit  time of less than two days for the OLCI instrument and less than one day for SLSTR at the equator. This will be achieved using both Sentinel-3A and Sentinel-3B satellites in conjunction. The satellite orbit provides a 27-day repeat for the topography package, with a 4-day sub-cycle. Objectives. Mission objectives are: Instruments. Sentinel-3 will make use of multiple sensing instruments: Satellite operation and data flow. Sentinel-3 is operated by the European Space Operations Centre (ESA) and Eumetsat. The in-orbit operations for Sentinel-3 are coordinated by Eumetsat in Darmstadt, Germany. This includes monitoring the health of the  satellite and the instruments, and coordinates housekeeping telemetry and commands at the main flight control center in Darmstadt, Germany. ESA maintains a backup flight control center at a ground station in Kiruna, Sweden. In addition, the ESA operates an x-band core station in Svalbard, Norway. This station is responsible for receiving the data collected by Sentinel-3. The data is then analysed by the Sentinel Collaborative Ground Segment and compiled into the Copernicus Space Component (CSC). The CSC is an earth observation program run by the ESA with the objective of providing high quality continuous monitoring of the earth. Applications . The applications of Sentinel-3 are diverse. Using the collection of sensors on-board Sentinel-3 is able to detect ocean and land temperature and colour change. The Ocean and Land Color Instrument (OLCI) has a resolution with 21 distinct bands allowing global coverage in less than four days. This sensor can then be used to by researches to do water quality and land-monitoring research. The satellite also has the ability to monitor the temperature of the sea, land and ice through the Sea and Land Surface Temperature Radiometer (SLSTR). Sentinel-3 also had the ability to detect changes in sea-surface  height and sea-ice using the synthetic aperture radar altimeter and the microwave radiometer, two of the most complex sensors on the satellite. The observations acquired by the mission will be used to in conjunction with other ocean-observing missions to contribute to the Global Ocean Observing System (GOOS) which aims to create a permanent system of ocean observation.