JWST | MIRI and NIRSpec instruments tested at CSL (Centre Spatial de Liège)

We are involved through two of its four instruments, NIRSpec and MIRI, which also form ESA's part in the development of the instrumentation of this enormous telescope. These scientific instruments will analyse the radiation seen and captured by the JWST's gigantic 6.5-metre diameter primary mirror, making the JWST the largest and most powerful telescope ever put into orbit. The CSL had no involvement at all with the other two instruments, NIRISS-Fine Guiding Sensor, developed by the Canadian space agency, and NIRCam, developed by NASA.   

NIRSpec and MIRI were jointly developed by the United States (NASA, the Jet Propulsion Laboratory, the University of Arizona) and Europe (ESA and its contractors and partners, of which CSL is part as a 'facility', an ESA-approved centre). NIRSpec (Near Infrared Spectrograph) is a spectrograph that works in the near infrared, from 0.6 to 5 microns. It will help characterizing the mass, temperature or chemical composition of celestial objects observed. For this instrument, the Safran group company Reosc contacted us in 2006 to carry out cryogenic tests on small telescopes that they were developing. These are small telescopes of about 1m in length, called TMAs (Three-mirrors anastigmat). Each contains three mirrors. Safran has built three of these telescopes, the COL, the CAM and the FOR, with specific optical purposes. At CSL, we tested these telescopes in our FOCAL-2 vacuum chamber. We cooled them to cryogenic temperatures, close to -260°C. Once the telescopes had cooled down, we measured the optical quality of the images obtained at cold temperature using interferometric techniques, because a cryogenic environment distorts the images and we do not obtain the same images as at room temperature. Between 2008 and 2009, we carried out three tests and measurement campaigns with Safran, each lasting about one month. These three telescopes are now installed on the JWST. 

Yes, we were more involved than with NIRSpec. We tested, of course, but we also participated in the design and development of some key elements of MIRI (Mid-Infrared Instrument). MIRI will look at cold and distant objects (galaxies, stars, ...) in the mid-infrared, from 5 to 28 microns. The instrument is dedicated to faint objects, those objects whose luminosity is low or even extremely low, so that they can only be seen by their traces in the infrared. To achieve this goal, the JWST must capture as much light as possible, which is why it has a huge mirror with a diameter of 6.5 meters: a real photon funnel! All this captured light energy will be redirected to the various instruments.  

On MIRI, the CSL has worked more specifically on three elements. The first is the IOC, the Input Optics Calibration unit. It is like a periscope that captures the light passing through the main telescope and sends it to the instrument. This periscope was developed jointly with a Flemish company, OIP Space Instruments. The mirrors were manufactured by AMOS, and the CSL was involved in the surface coating. CSL also aligned this periscope within MIRI, which was a long and rather complicated job. Then we placed the periscope in a cryostat in order to check the performance of the IOC at cryogenic temperatures.  

The second element is a double prism, which separates the light into different wavelengths. The separated light enters a subsystem of MIRI, the MIRIM, which is the imager of MIRI. The prisms were developed by Amos, and CSL mainly carried out the surface coating, in addition to performance measurements.  

Finally, the third and last element, CSL was involved in the ICE, the Interface Control Electronics. This is the electronic box that controls and drives all the mechanisms of MIRI. In this case, the CSL worked closely with Thalès Belgium. We participated in the design and integration of the electronic cards of this box. It was our electronics laboratory at the CSL that carried out this technological feat with the teams from Thalès Belgium 

Because of our specific and internationally recognized skills! Indeed, over the years and through the projects, the CSL has developed a double expertise that ESA calls upon in the framework of Belgium's participation in the financing of the European Space Agency. On the one hand, there is cryogenics: the CSL has facilities that allow it to go down to extremely low temperatures, down to -269°C, and to conduct effective test campaigns with its specialists, who are among the best in the world in this field. And then there are the coatings: here too, our surface treatment laboratory enjoys a solid international reputation. The CSL is able to produce surface coatings with very specific properties by combining vacuum deposition techniques, laser treatments and micro-fabrication processes. For MIRI, a specific process has been developed to produce a gold coating that is both extremely resistant to the space environment and highly reflective in the infrared, the instrument's operating spectral range. 

Being involved in such a huge scientific project is really positive for CSL, the University of Liege and our region. This mission is a crazy challenge! To use Yaël Nazé's expression, it is a real space origami. And if a single mechanism doesn't work, that's it, the whole JWST won't work. So there are many single points of failure. But it is really a source of pride for the CSL to have contributed to the development and testing ten years ago of the real flight instruments, those that are now integrated into the JWST, which was launched on 22 December, and which will contribute, we all hope, in the coming months and years to major discoveries concerning the origin and development of our universe.