James Webb Space Telescope unfurls giant sunshade

The $10bn telescope was launched at Christmas. It is already more than halfway towards its destination approximately one million miles from Earth.

The 6.1-tonne telescope is so large that its sunshield and now-iconic primary gold-plated mirror had to be folded for launch for opening up in space.

Its sunshield protects the telescope’s IR sensing instrumentation from solar radiation with five thin, reflective layers of different shapes and sizes, keeping it below its maximum temperature of -233°C. It is necessary to keep the telescope this cool to prevent its instruments being overwhelmed by its own IR signal. The shield, designed by Northrop Grumman, is intended to transmit just 23mW of 300kW of incident solar radiation. 

It is especially unwieldy, kite-shaped, and spans 21.1m by 14.6m when fully spread. When fully open, the layers are opened wider at the edges to help reflect heat outwards. The sunshield has proved a technical challenge, with tears appearing in 2018 and contributing to JWST’s delayed launch, while at another point dozens of fasteners fell off during a vibration test.

The success is a relief for Nasa scientists, particularly as nothing like this has been attempted before in the zero-gravity space environment – despite many trials on the ground – and the complex design with many moving parts was certain to prove challenging.

The unfolding process involves separating the five layers and then tightening them. Ground controllers cheered and exchanged fist bumps after the fifth and final layer of the sunshield was secured. Tightening the ultra-thin layers of the sunshield via motor-driven cables took a day and a half, half the time expected. Engineer Alphonso Stewart told media: “First time and we nailed it!”

“This is a really big moment,” project manager Bill Ochs told the control team, based in Baltimore. “We’ve still got a lot of work to do, but getting the sunshield out and deployed is really, really big.”

The next part of the telescope to be prepared is the mirror array, which will be released from its folded-up configuration later this week.

JWST is the largest and most powerful observatory ever launched. It is 100 times more powerful than its predecessor, the Hubble space telescope, which is nearing the end of its operational life at 31 years old. JWST is equipped with technologies that will allow it to look deeper into the universe and thus, further back in time towards the Big Bang. It will attempt to search for longer wave light from the universe’s first stars and galaxies, from 3.7 billion years ago.