Countdown to launch — Sentinel-6 Michael Freilich

Sentinel-6 Michael Freilich illustration

Exciting times lay ahead in the world of satellites, as the newest Ocean observation spacecraft is scheduled to launch from the Vandenberg Air Force Base in less than a month. The satellite will be carried by no other than SpaceX’s remarkable Falcon 9 vehicle and it commemorates a historic partnership between Europe and the United States.

A bit of history

The Copernicus Programme

European Union's Copernicus roots can be traced back to late 20th century Italy, where a group of experts have signed a document proposing the development of a European monitoring programme. The document is known as the Baveno Manifesto and it was signed on May the 19th of 1998 in the beautiful city of Baveno, located in the northern part of Italy.

The programme was named GMES, an acronym standing initially for ‘Global Monitoring for Environmental Security, which later changed to ‘Global Monitoring for Environment and Security’. As of 2012, GMES is renamed Copernicus, after the renowned Polish astronomer Nicolaus Copernicus, who has revolutionised the world of astronomy in 1543 by introducing a model of a heliocentric Universe with the Sun at the heart of the Universe instead of the Earth.

Another defining year in the History of the Copernicus Programme is 2013, when the European Union adopted a Regulation that became a trademark characteristic of the entire programme: the full, free and open data policy, granting free and open access to all environmental Sentinel data. This has allowed users around the world to make use of the satellite imagery and develop their own ground-breaking applications, which proved beneficial to multiple local economies.

It is important to mention that Earth observation satellites are not the only tool collecting data within the Copernicus Programme, as in-situ, airborne and seaborne sensors are also used to complement the datasets. These, together with the spacecrafts, provide valuable information for six thematic services addressed by the European programme: atmosphere monitoring, climate change, marine environment monitoring, emergency management, land monitoring and security.

7 Satellites and over 28 TB of downloaded data later, Copernicus continues to provide valuable information for a variety of value chains, from ocean and land monitoring, to the oil and gas industry. Today, more than 70% of the Earth Observation companies within Europe are using Copernicus data, and almost 40% are exploiting Copernicus services, such as the Copernicus Atmosphere Monitoring Service implemented by the European Centre for Medium-Range Weather Forecasts.

The Sentinels - past and future

In order to briefly sum up about 22 years of Copernicus history, let’s take a look at all the previous missions one by one, and simply divide them by a few determining factors such as their operation timeline, objectives and deployed technology.

The first thing to remember is that in order to provide comprehensive space-borne datasets, attain a high revisit frequency and meet the coverage requirements, each Sentinel mission uses a twospacecrafts constellation. And this is where things get a bit complicated, as not all Sentinel missions have dedicated satellites, Sentinel-6 is about to be launched, while Sentinel-4 is scheduled to be deployed 3 years from now. But let’s not get ahead of ourselves and start with the beginning.

Sentinel-1 represents the first ESA mission developed for the Copernicus Programme and it focuses on acquiring C-band SAR imagery incoming from two polar-orbiting Sentinels, launched in April, 2014 (Sentinel-1A) and April, 2016 (Sentinel-1B) respectively. The objective is to provide continuous day and night data for land, emergency management and ocean applications, no matter the weather conditions. The satellites are expected to be operational for at least 7 years, but have enough fuel on board to allow for a total of 12 years of operations.

Sentinel-2 provides high-resolution multi-spectral images to complement the collection of data acquired by the SPOT satellites and the LANDSAT Thematic Mapper (TM) instrument, as the simultaneously-operating twin-satellites are equipped with a MultiSpectral instrument (MSI), which passively registers reflected sunlight from the Earth in 13 spectral bands. Sentinel-2A was successfully launched in June 2015 and Sentinel-2B followed less than two years later in March 2017. The main services aided by Sentinel-2 data are land monitoring, climate change, emergency management and security. Similar to the Sentinel-1 spacecrafts, their lifespan is estimated at around 7 years, with enough propellant to last for 12 years.

Sentinel-3 mission carries multiple instruments for both land and ocean monitoring, having multiple objectives such as the measurement of sea surface topography, sea and land surface temperature, or ocean and land surface colour among others. The data acquired provides continuity to missions such as ENVISAT for ocean measurements and SPOT for land observations. The main instruments carried on board are as follows: an Ocean and Land Colour Instrument (OLCI), a Sea and Land Surface Temperature Instrument (SLSTR), a SAR Radar Altimeter (SRAL) and a Microwave Radiometer (MWR). Both satellites, launched in February 2016 (Sentinel-3A) and April 2018 (Sentinel-3B), are operated cooperatively by ESA and EUMETSAT. In the same manner as the previous missions, the spacecrafts are designed to be operational for 7 years, with the possibility of continuing the mission for up to 12 years.

Sentinel-4 is designed to obtain hourly atmospheric composition measurements, largely used for air quality purposes. Unlike the preceding missions, Sentinel-4 does not have any dedicated satellites. Instead, the mission consists of two Ultraviolet-Visible-Near-Infrared (UVN) light imaging spectrometer instruments, that will be accommodated by two state-of-the-art Meteosat Third Generation (MTG-S) geostationary spacecrafts, operated by EUMETSAT. The satellites have an expected operational lifetime of 15.5 years and are estimated to be launched in 2023.

Sentinel-5P or Sentinel-5 Precursor, is a filler mission dedicated to atmosphere composition monitoring, designed to reduce the gap in Air Quality data left by the loss of the ENVISAT in 2012. It was launched in October 2017 and will be replaced by Sentinel-5 after its launch in 2021. The single low Earth orbit (LEO) satellite carries a passive grating imaging spectrometer called TROPOMI, or the Tropospheric Monitoring Instrument, which identifies unique gas traces in various parts of the electromagnetic spectrum.

Sentinel-5 is very similar to the Sentinel-4 mission, as it consists of an atmospheric composition monitoring payload that will be carried on-board a weather EUMETSAT satellite, the MetOp-SG A. However, unlike the fourth mission, Sentinel-5 comprises of a single high-resolution UV-VIS-NIRSWIR spectrometer system and will be residing on a low Earth orbit. The satellite is estimated to be launched in 2021 and has an operational life expectancy of 7.5 years with a 2-year possible extension.

Sentinel-6 is where we are today and it represents the sixth Sentinel operation within the Copernicus Earth Observation Programme. The mission returns to the original dedicated twosatellite constellation format, and the Sentinel-6 Michael Freilich spacecraft is the first of the duo to be launched later this month. Its twin, Sentinel-6B, is scheduled to follow in 2025. The satellites will focus on marine monitoring and climate studies, carrying a Poseidon-4 Radar Altimeter and an Advanced Microwave Radiometer (AMR-C), the spacecraft will be able to obtain the most accurate measurements for sea level rise monitoring to date. The collected data will provide continuity to missions such as Sentinel-3, TOPEX/Poseidon and Jason-1, 2, and 3.

A memorable partnership

Not only that Sentinel-6 Michael Freilich is next on our countdown-to-launch clock, but the mission also represents a historic partnership between the U.S. and Europe, as it is the first cooperative NASA-ESA effort in a scientific Earth satellite mission. What is more, the joint mission is also the first international involvement in the Copernicus Programme, as until now it was an entirely European effort. The outstanding partnership able to deliver the latest ocean-monitoring tools consists of the U.S. National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), the European Commission, the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), Centre National d'Etudes Spatiales (CNES), Airbus and the U.S. National Oceanic and Atmospheric Administration (NOAA).

Another key point to mark the importance of the partnership is the renaming of the satellite from Sentinel-6A/Jason-CS to Sentinel-6 Michael Freilich in January of this year. The spacecraft is named after Dr Michael H. Freilich, the director of NASA’s Earth Sciences Division between 2006-2019, whose ongoing contributions towards advancing Earth science worldwide made this mission possible, as Josef Aschbacher (ESA’s Director of Earth Observation Programmes) commented at the renaming ceremony held in Washington earlier this year:

Our suggestion to rename the satellite to ‘Sentinel-6 Michael Freilich’ is an expression of how thankful we are to Mike. Without him, this mission as it is today would not have been possible.

And the latest ocean monitoring technology

Once in orbit, Sentinel-6 Michael Freilich will become the state-of-the-art instrument of Ocean monitoring and climate research, as each sentinel will track over 90% of the world’s oceans down to the centimetre. Able to observe the seas and coastlines at an unprecedented resolution, the spacecraft was described as “a milestone for sea level measurements” by NASA's Jet Propulsion Laboratory Project Scientist, Josh Willis.

Sentinel-6 Michael Freilich arrived at the California launch site on September the 24th, from where it is to be integrated on-board a SpaceX’s Falcon 9 rocket. The launch is scheduled to take place from Vandenberg Air Force Base's Space Launch Complex 4E on November the 10th at 18:31 UTC/GMT.

Set your alarm, stay tuned and watch some space history in the making!


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