Cutting-edge objectives

O

n a clear, starry night, if you happen to spot a satellite in the sky, there’s a good chance that an engineer from the CSL (Centre Spatial de Liège) is thoroughly familiar with its instruments. This is because, whether it's the Sentinel observation satellites, the Hubble and Euclid telescopes, or the renowned James Webb telescope, all house instruments that have been tested, and sometimes even designed, at the CSL. This expertise is a source of pride for its director, Professor Serge Habraken: "We are renowned at the European and even global level for our tests in space environments of all optical instruments on board satellites, as well as for their calibration, and sometimes even their design."

The Space Centre has come a long way since 1964, the year instruments for the first rockets intended to study the Northern Lights were developed. "The building that now houses our facilities was constructed in 1984, and the centre underwent a major expansion in 1994 with the development of the X-ray telescope XMM-Newton, a project of immense scope," recounts the director.

Thanks to such projects, the centre has developed real expertise, making it an indispensable partner for many players in space exploration. Its mission: to ensure that the instruments sent into space function perfectly. "Most observation satellites carry extremely sensitive optical instruments," Serge Habraken emphasises. "Space, due to the vacuum and temperatures close to absolute zero, is an extreme environment. It is therefore essential to ensure that the instruments can withstand the journey, and that once up there, the images they capture remain true to reality."

READY FOR SERVICE

To this end, the CSL has enormous vacuum chambers several metres in diameter, specifically designed to accommodate these instruments. They simulate the vacuum and temperatures the instruments will encounter in orbit or deep space, testing their functionality in these harsh conditions: "This is done using various light sources that simulate the radiation the satellite is expected to capture, whether it be visible light, infrared, or even UV and X-rays. Increasingly, these light sources are designed directly here at the CSL." This stage, known as calibration, is crucial for the success of the mission. "It's not just about observing a planet or a star. The observations must also be reliable. By recreating the observation conditions and radiation fluxes here, we ensure that the image sent to Earth is usable," explains the professor.

Once these tests are successfully completed, the instruments are placed on vibration pads to test their resistance to the launch conditions of a rocket. "These vibrations are extremely violent and hard to endure," he notes. After further checks to confirm their proper functioning, the instruments are finally ready to be installed on a satellite.

Given the number of satellites deployed today, the CSL "operates like a company, with staff working 24/7." For several months now, the clean rooms have been housing instruments that will be used in future weather satellites for EUMETSAT. One of these instruments is designed for real-time monitoring of the Earth's ocean surface temperature and vegetation, in direct relation to the study of climate change. "These satellites have become a significant part of our activity, particularly in terms of calibration," notes Serge Habraken.

In another laboratory, several scientists are turning their gaze towards other stars. "We are currently testing the PLATO telescope, scheduled for launch in 2026, with the objective of discovering even more exoplanets." Unlike traditional telescopes, PLATO is made up of 26 high-resolution cameras that will observe a vast area of the sky with unmatched precision. "Each camera is assembled here and then undergoes a full test, which represents over two years of work," estimates the director of CSL.

KEEPING FEET ON THE GROUND

As exciting as these missions are, Serge Habraken does not hide his true aspiration: "The ultimate goal lies elsewhere." What truly excites the scientists at the CSL is the design of measuring instruments themselves, at the rate of one or two per decade. "The images of the Sun that we saw during the recent solar flares, which caused the Northern Lights to be visible even in Belgium, were obtained thanks to an instrument we designed and which is aboard Solar Orbiter," he proudly explains. "This satellite is on its way to the Sun and is already providing us with absolutely remarkable images. In previous years, all images of the Sun came from Proba-2, a nearly 100% Belgian satellite."

The CSL’s 60th anniversary will also be an opportunity to celebrate the October launch of its "little sister," the Proba-3 probe, which represents a world-first in technological innovation. "Designed to observe the Sun, and specifically its corona, Proba-3 is actually composed of two parts. In space, they will be positioned 150 metres apart. The first will serve to eclipse the solar disk, allowing only the corona to be visible, which will be studied by the second," summarises the director.

In the near future, alongside its usual missions, the CSL will keep its feet firmly planted on Earth. Thanks to substantial investments from the Walloon and federal governments, the centre will expand to house a new chamber, the largest in Europe. "This chamber, seven metres in diameter, will be used to accommodate next-generation instruments, which are becoming increasingly large, and will secure our leadership for the next two decades!" the scientist exclaims.

Finally, through a strengthened collaboration with engineers at ULiège, the CSL is positioning itself to test technologies for the future Einstein telescope. Unlike traditional telescopes, the Einstein telescope will be buried 250 metres underground, shielded from worldly disturbances. Designed to detect gravitational waves—those tiny ripples in spacetime caused by cosmic cataclysms—it will be made up of three mirrors arranged in a triangle, spaced ten kilometres apart. The CSL is currently developing "a revolutionary technique for cooling the mirrors." Detecting the slightest tremors in the universe requires these mirrors to be free from any vibration. Since temperature is merely a measure of the energy resulting from molecular vibrations, the mirrors must be cooled as close as possible to absolute zero. "Once validated, our technique will allow us to remain competitive for a long time, even after the Einstein telescope is constructed, when other countries will begin building similar telescopes," Serge Habraken hopes. All of which points to a bright future for the Centre Spatial de Liège.