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17 December, 2021 - 21:46 By Tony Quested

High glass as Cranfield University mirror technology heads for space

Cranfield University technology forms a key element of the most important space telescope to hit the skies since the Hubble began orbiting the Earth in 1990.

Due to be launched on December 22 on a European Ariane-5 rocket from French Guiana, the James Webb Space Telescope (JWST) is an unprecedented scientific instrument that will see further into the universe than anything ever built. 

The JWST has taken 30 years and $10 billion to develop. At seven times the size of the HST, which collects light using a main mirror of 2.4 metres, JWST has a primary mirror that's 6.5 metres in diameter. 

The light-collecting capability represents an unprecedented ability in sensitivity and promises to enable a step change in capability to observe and analyse the universe. 

Including all the associated equipment, the JWST is about the size of a tennis court and must be folded to fit inside its launch rocket. The rocket will send the telescope about 1.6 million km from Earth. 

It is tuned to detect infrared light that the Hubble is unable to. This light is invisible to the human eye, but it's the type of light in which the glow from the most distant objects in the universe will show up.

Unlike the HST, which has been orbiting the Earth since 1990, the JWST will orbit the sun one million miles from earth. It is fully robotic, highly complex and has around 570 mirror optical surfaces. 

The most important part of the telescope is the mirror. Almost half of the JWST mirrors are installed within its Mid-Infrared Instrument (MIRI). That’s where Cranfield zoomed in.

Paul Shore, director at Cranfield spin-out Loxham Precision Limited and head of engineering at the National Physical Laboratory, said: “Cranfield developed the manufacturing capability and produced all the MIRI spectrometer mirrors.

“This amounted to 132 flight mirrors on 24 substrate components together with a full set of flight spares. The development of the JWST MIRI optics, from initial samples through to the delivery, was performed by the Cranfield team within a three-year period.”

The JWST MIRI instrument was developed by the UK Astronomy Technology Centre in Edinburgh, who entrusted the Precision Engineering Institute at Cranfield University to manufacture the high-complexity image slicers and re-imager mirrors.  

More of the JWST mirrors were made in Cranfield than any other location. They were produced on an ultra-precision CNC machine tool designed and manufactured at the university.

Once operational, the telescope should see the light coming from the very first stars to shine in the Universe. The pioneer stars are thought to have switched on about 100-200 million years after the Big Bang, or a little over 13.5 billion years ago. 

JWST will be picking out groupings of these stars. They are so far away that their light, even though it moves at 300,000km per second, will have taken billions of years to travel the cosmos. JWST will have a fuel supply that should keep it stable in orbit for 10 years. 

It should be possible for JWST to detect a faint glow from the moment when the darkness ended and those first stars flickered into life. It will help us understand the origins of everything we see around us, and how planets form.

The Cranfield NION Nanocentre, the world’s most accurate CNC machine tool of its size in 2005, was used to manufacture all the MIRI image slicers and re-imagers. 

The NION machine was design and developed at Cranfield between 1988 – 1992. It was funded under the UK’s Department for Trade and Industry LINK National Initiative on Nanotechnology programme administered by the National Physical Laboratory.

• PHOTOGRAPH: Engineers conduct a “receiving inspection” of the James Webb Space Telescope’s Mid-Infrared Instrument at NASA’s Goddard Space Flight Center after its journey from the United Kingdom. Credit: NASA/Chris Gunn

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