How to send a satellite abroad and prepare it for launch

The first of the European Sentinel-3 Earth-observation satellites, Sentinel-3A, will be shot into Earth orbit tomorrow from the Plesetsk Cosmodrome in Russia. The mission's main objective is to measure sea surface height along with land and ocean temperature in real time, to help weather forecasters and environmental monitoring.

But Sentinel-3A wasn't built in Russia. It was put together in Thales Alenia Space in Cannes, France, 4,000 kilometres away. So how do you transport a €305 million, 1,250-kilogram satellite across a continent, then get it ready for lift-off? 

We tagged along on the satellite's final few months on Earth.

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ESA / A. Le Floc’h

Sentinel-3A sitting in the cleanroom at Thales Alenia Space in Cannes, France, above. That metallic cone is a special thermal blanket installed on the satellite's antenna, but it is transparent to electromagnetic waves to allow transmission back to Earth.

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ESA / Stephane Corvaja, 2015

The satellite's solar wings will keep it powered for 7.5 years – the mission duration.

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ESA / J.F. Flamand

Then, in November 2015, Cannes engineers said goodbye as the dormant satellite was carefully wrapped and tucked away in a container for the first leg of its journey. 

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After being loaded on a truck, the container was driven to Nice airport and popped in a waiting Antonov aircraft … only to sit on the tarmac for an entire week, as bad weather in Russia delayed the plane's departure.

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ESA / Sentinel-3 team

The aircraft finally took off from Nice airport on 27 November, bound for a stopover in Moscow to clear paperwork, before heading to snowy Arkhangelsk (Archangel) airport, in Russia's northwest. It landed on 28 November.

The delicate process to unload the satellite took more than three hours, but once it disembarked, a convoy of trucks carried it and its support equipment to Plesetsk train station.

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ESA / Sentinel-3 team

Finally, en route to its last Earthly home before blast-off.

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In transit, the dormant satellite lay horizontally in the container. Upon arrival to the cosmodrome, it haad to be mounted on a tilting dolly which rotated it 90 degree to stand up in its vertical position. Engineers held their breath as the satellite was switched on.

And everything was fine. Software, thrusters, electrics – it all worked. 

After being checked out, the satellite went back to sleep, horizontally in its container, for the Christmas break.

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After being woken and spun round to its vertical position on 11 January 2016, Sentinel-3A was popped onto its fuelling platform. But then came a bit of a wait. Delays by the Russian Khrunichev State Research and Production Space Centre, which produced the "Rockot" rocket carrying Sentinel-3A, needed to complete further testing. Most of the Sentinel team members stayed at the launch site to "babysit" their satellite until they were given the green flag.

Fuelling finally started on 2 February and took two days. That orange tank is full of hydrazine, which was first used during World War II, and commonly used in rocket fuel today. Needless to say, it's very dangerous. During fuelling, only the bare minimum staff are on site, plus a doctor, security staff, and ambulance and fire engine. Everyone else works from the hotel.

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ESA / S. Corvaja

Once fuelled up, the satellite was "mated" to flight and launch components and the Rockot. 

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One week before launch, on 9 February, two halves of the protective casing, or "fairing", were closed around Sentinel-3A. The satellite is the largest ever tranported on a Rockot. There's only four or five centimetres between the satellite and the fairing, so it was a tight fit.

The process of closing and sealing the fairing can take up to 13 hours, as engineers check components, lock them and check again. It's then painted white.

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The Sentinel-3A will be Rockot launch number 25, so the constellation Libra, which traces a line connecting 25 bright stars, was painted on.

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The team was allowed to write their own messages wishing their satellite well on its journey on the fairing – even signing the very tip of its nose.

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And now, it's ready to roll. But once it's safely in orbit, it's not the end of the story. Its sister, Sentinel-3B, is slated for launch in 18 months.


Related reading:
Timeline: a stroll through 50 years of weather satellites

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