Sophie Hebden, a project scientist for the National Centre for Earth Observation who is based at the University of Leicester, went to the European Space Research and Technology Centre (ESTEC) in the Netherlands to celebrate the launch of the latest satellite in the Copernicus Sentinel programme. She tells us about the satellite, the instrument it carries – and the party!

Air pollution is a huge and growing challenge facing society today. Researchers estimate that half a million people in Europe die prematurely each year because of poor air quality due to burning fossil fuels for transport, industry and heating.

The European Space Agency’s new Sentinel-5P satellite will monitor the pollutants in the air we breathe much more accurately than currently possible. The measurements made by its Tropomi instrument will cover the entire world every day in ten times more detail than currently possible from space.  I’ll explain more about this special sensor further down, but first the fun of the launch party!

I wasn’t expecting to go to the launch on 13 October 2017, but two days beforehand my colleague discovered she had mumps and was homebound ‘on doctor’s orders’. When we found she would have to cancel her trip, I offered to take her place and was lucky to get last-minute permission to join the #Sentinerds: the group of social media enthusiasts invited to promote the launch.

Preparations for space

On arrival, the #Sentinerds were given bright orange T-shirts so we could identify other members of the pack. Over coffee and biscuits, we had a briefing from ESA on things that could stop the rocket launch.  The list of ‘what could go wrong’  included faulty communications, the nitrogen feed on the rocket getting stuck and adverse weather conditions.

With a better appreciation of the seriousness of the day, we followed staff for a tour of ESTEC’s satellite test facilities. Tests are an important part of preparing a satellite for space, and all of the Sentinel satellites are thoroughly tested before they go on their rocket trips. We rushed along long, wide corridors – floors polished to a shine – that were dotted with space agency artefacts: I saw old landing vehicles with their parachutes strewn out and signed by the astronauts whose lives depended on them, and lots of glass cabinets containing mini-models of famous spacecraft, such as Rosetta, which recently explored the comet 67P/Churyumov-Gerasimenko.

We were under strict instructions not to take photographs in working areas: commercial satellites are sent here to test their space-worthiness, so any leaks of test outcomes or processes could compromise them. We were, however, allowed to photograph the large space simulator – the largest vacuum testing facility in Europe. Inside its main chamber, spacecraft are subjected to the coldest and hottest temperatures  a satellite must be able to withstand in orbit. To simulate the heating effect of the sun, there is an intense radiation facility that  uses a bank of the world’s most powerful lamps, focusing mirrors and a moving robotic arm to spin the spacecraft.

Next we viewed the vibration test facility, which tests whether a satellite can withstand the  shaking forces – of various angles and frequencies – that it could experience during launch and in space. The spacecraft are mounted onto a platform, covered in sensors, and then literally shaken, both vertically and horizontally, using pistons beneath the platform. Data from the sensors enables the experts at ESA to see any weak spots on the spacecraft.

Suspense and celebration

An hour before launch we were led to the party venue to join a crowd of VIPs: directors from the space industry and people directly involved in developing Sentinel-5P. NCEO’s director, Professor John Remedios, was one of about twenty-five people invited to speak not just to those of us gathered at ESTEC, but to thousands of people across the world watching the launch on ESA-TV. Professor Remedios explained the importance of  Sentinel-5P, linking it to the serious issue of air quality which affects us all.

As launch time (9:27 GMT) approached, the whole room quietened down for the take-off sequence. Video from the launch headquarters in Plesetsk, Russia, was live-streamed onto a big screen behind the stage. The satellite was built by Airbus Defence and Space UK in Stevenage, so had already had quite a few journeys before its big journey into space.

The rocket was dwarfed by the big blue launch tower, surrounded by the browns and greens of the Siberian boreal forest, and blanketed in thick morning mist. I caught a glimpse of fire and billowing smoke from the rocket during countdown at about ‘four’ or ‘three’, but then ‘two, one, lift-off’ seemed surprisingly fast! We cheered as the rocket set off into orbit, and then mingled for lunch while awaiting for an answer to the crucial question: would the satellite get into orbit safely and be detected by the first ground station it was due to fly over?

We assembled once again to watch live-streamed video from launch headquarters and a computer screen at the ground station in Kiruna, Norway, awaiting the signal – due 93 minutes after launch – with bated breath. Suddenly, a spikey waveform showed on the screen and was met with a cheer of relief. ESTEC staff in front of me hugged one another in joy.

Being there for this special moment helped me to appreciate the relief all those who spend years working to make a world-class satellite feel on a successful launch .

How Tropomi works

Tropomi stands for TROPOspheric Monitoring Instrument, and it is the most advanced instrument of its kind. It is a spectrometer that will detect sunlight scattered back to space by the Earth’s surface and atmosphere, spreading the light out into a spectrum. By comparing the spectra of the scattered light and the incoming sunlight, Tropomi will be able to determine the concentrations of various gases in our atmosphere. Each gas has a distinctive signature that shows up in the ultraviolet, visible, near-infrared and shortwave infrared parts of the electromagnetic spectrum. Because it can make measurements in all of these bands, Tropomi can detect a wide range of harmful pollutants, such as nitrogen dioxide, ozone, formaldehyde, sulphur dioxide, methane and carbon monoxide. It has a maximum resolution of  7 km × 3.5 km, which means it could see enough detail to detect air pollution over individual cities. Tropomi should begin full operation in Spring 2018.

All photographs by Sophie Hebden.

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