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The Meteosat Third Generation Sounder (MTG-S1) satellite, which is hosting the instrument for the Copernicus Sentinel-4 mission, has been placed inside the nose cone of the Falcon 9 launch rocket and is ready for the scheduled liftoff at 23:03 CEST on Tuesday, 1 July.

Last week saw the final flurry of pre-launch activities and checks. It marked a significant landmark for the teams involved, including the satellite's encapsulation within the fairing, which was the last time the satellite could be seen and that engineers could manually interact with it.

First of all, MTG-S1 was attached to the flight adapter, a structure that connects the satellite to the rocket and provides a secure mount during launch. The adapter will help to separate the satellite from the second stage of the launcher when they reach the right altitude.

During these activities, the satellite keeps its solar arrays in a folded position, like a moth inside its cocoon. The two science instruments on board—both the Infrared Sounder, which is the primary mission instrument, and the Copernicus Sentinel-4 ultraviolet, visible and near-infrared (UVN) imaging spectrometer—were kept switched off during this time.

James Champion, ESA's MTG Project Manager, said, "The mating to the flight adapter is a critical step and it involves a physical and electrical connection of the satellite to the adapter, which will interface with the rocket.

"These operations require extreme precision and a high level of expertise to orient the crane position correctly so as to lower the satellite onto the adapter with the aid of guiding tools to ensure the perfect alignment and mechanical attachment," he noted.

Safety and functional checks concluded the attachment of MTG-S1 to its flight adapter.

The satellite and its flight adapter were then encapsulated inside the tip of the rocket, known as the fairing, where the cone-shaped structure provides a protective case during the initial phase of the launch ascent. This encapsulated assembly, with the MTG-S1 satellite inside, is then mated with the rocket after its transportation to the hangar at the launch pad.

Loading propellant on the satellite already took place about two weeks before the scheduled launch date. This was a very hazardous activity that required the highest safety measures.

The MTG-S1 satellite was loaded with two types of propellant liquid: first with MON3, a red fuming liquid that is a mixture of nitrogen tetroxide and nitric oxide and then with Monomethylhydrazine, or MMH, which is a highly toxic, volatile and flammable liquid.

Because fuel loading is so hazardous, it is done by experts wearing the protective Self-Contained Apparatus Protective Ensemble (SCAPE) suits.

They are tasked with entering the loading hall to physically handle the barrels of propellant and perform the loading activities, while two colleagues remain in a dedicated safe control room in case of an emergency.

James explained, "Propellant loading is a critical operation which must be handled exclusively by only a few experts to reduce the number of personnel involved in this extremely hazardous activity to the absolute minimum.

"The propellant is extremely toxic and has the significant risk of spontaneous ignition or corrosion under the right conditions if released inadvertently in the air."

With these last pre-launch activities now concluded, MTG-S1, with the Copernicus Sentinel-4 instrument on-board, is ready for launch and its journey to geostationary orbit where observations of severe storms and air pollution over Europe and northern Africa will be performed in a way that has not been possible until now.

MTG-S1 will observe:

• a profile of temperature and moisture at different altitudes over Europe every 30 minutes; and
• data on aerosols, ozone, nitrogen dioxide and sulfur dioxide over Europe and Africa every 60 minutes.

And Copernicus Sentinel-4 will measure pollution every 60 minutes with a level of detail and precision that will transform how we predict air quality across Europe.

Both these world-class Earth observation missions, developed by the European Space Agency (ESA) with European partners, will address scientific and societal challenges. They will contribute data that will enable better preparations for extreme weather events and more accurate warnings on air pollution that damages our health.

ESA's Director of Earth Observation Programs, Simonetta Cheli, said, "I'm extremely grateful to the teams across ESA, in dozens of European companies and at our European partners, who have contributed to the MTG-Sounder satellite and the Copernicus Sentinel-4 mission.

"These instruments are indeed going to provide new and exciting ways to forecast and understand our atmosphere. I'm looking forward to launch and to seeing how these Earth observation missions will benefit society, enabling us to prepare ahead of severe weather and to mitigate the risks of air pollution."