James Webb Space Telescope prepares to unfold another mirror

NASA’s James Webb is preparing to unfold the second wing of its primary mirror on Saturday, marking the final major deployment in its ’29 days on the edge’ journey.

Due to its size, about half as large as a 737 aircraft, Webb had to be folded up for launch on December 25, so it would fit inside the Ariane 5 rocket. 

It has been slowly unfolding, part-by-part, as it makes the million mile journey to the second lagrange point, a gravitationally stable point between the sun and Earth.

The final milestone in the preparation of the $10 billion observatory is the deployment of the primary mirror — happening in two stages, finishing tomorrow.

The primary mirror is made up of 18 individual segments, split into two three-segment side panels which need to be unfolded for the telescope to work. 

They will unfold the first of these panels, the Port Primary Mirror Wing, at some point today, finishing tomorrow with the Starboard Primary Mirror Wing.

The NASAWebb team tweeted: ‘It’s what we’ve all been waiting for: The James Webb Space Telescope will soon spread its primary mirror wings! 

‘Today we begin with the mirror wing on the port (left) side of the observatory. This process should take a few hours.’

This isn’t automated, with NASA engineers able to reschedule to unfolding if they feel the time isn’t right or would pose a risk to the observatory.

The team is beginning today with the mirror wing on the port (left) side of the observatory. 

‘Engineers must first release mechanisms that held the wing in place for launch, in order to allow the wing to deploy,’ NASA wrote in a blog post on the unfolding.

‘The panel then rotates into position, a motor-driven process that takes about five minutes. 

‘Once the wing is extended, engineers begin a meticulous, two-hour process to securely latch it into place.’

The second part of this process will begin on Saturday and work in the same way, according to NASA. 

The telescope is a joint project of NASA, ESA and the Canadian Space Agency and is expected to reach L2 by the end of this month, where engineers will begin a series of calibrations, before the first images are revealed in June 2022.

Webb launched on Christmas Day atop a European Space Agency funded, Ariane 5 rocket from the Arianespace port in French Guiana.    

With its liftoff, a spokesperson for NASA said, ‘Webb will usher in a new era of astronomy’, and four days later, Webb began the unfolding its massive sunshield.

It has been gradually morphing into its final form ever since, with the secondary mirror unfolded on Wednesday, and the primary mirror ready tomorrow. 

The final parts of the mirror will begin unfolding around 14:00 GMT (9:00 ET) on Saturday, with NASA broadcasting live as the team monitors the data coming in from the telescope.

This doesn’t mean Webb will be ready to begin observing the universe, as it isn’t scheduled to reach its final destination — the second Legrange point — until the end of this month, after which the mirrors and instruments have to be calibrated.

However, NASA has declared the unfolding of the primary mirror as the last major milestone in the telescopes ’29 days on the edge’ journey to L2. 

The secondary mirror, measuring 2.4 feet wide, located on the tips of three long booms, finished unfolding on Wednesday — this is the second surface that light from the cosmos hits on its path to the telescope.

It is supported by three shallow carbon fibre tubes, or struts, that extend out from the large primary mirror, which is comprised of 18 hexagonal segments. 

‘Another banner day for JWST,’ said Bill Ochs, Webb project manager at NASA’s Goddard Space Flight Center, at the Mission Operations Center near Baltimore.

‘This is unbelievable…We’re about 600,000 miles from Earth, and we actually have a telescope.’

NASA said the ‘secondary mirror is one of the most important pieces of equipment on the telescope, and is essential to the success of the mission.’

The mirror now sits out in front of Webb’s primary mirror to collect light from Webb’s 18 mirrors into a focused beam.

That beam is then sent down into the tertiary and fine steering mirrors, and finally to Webb’s four powerful scientific instruments.

Lee Feinberg, optical telescope element manager for Webb at NASA’s space center in Greenbelt, Maryland, said in a 2019 statement: ‘The proper deployment and positioning of its secondary mirror is what makes this a telescope — without it, Webb would not be able to perform the revolutionary science we expect it to achieve.

‘This successful deployment test is another significant step towards completing the final observatory.’

This is the second milestone Webb has completed this week. On Tuesday, it deployed its 70-foot sunshield.

‘All five layers of the sunshield are fully tensioned,’ said an announcer at 11:59am ET at the observatory’s control centre in Baltimore, where team members cheered.

It took just one and a half days to tighten the ultra-thin layers using motor-driven cables, half the expected time.

The sunshield — about the size of a tennis court at full size — was folded to fit inside the payload area of an Arianespace Ariane 5 rocket’s nose cone prior to launch, which took place on Christmas Day.

The shield is designed with small plastic sheets, each of which are about as thin as a human hair and coated with reflective metal, providing protection on the order of more than SPF 1 million.

The five-layered sunshield will protect the telescope from the light and heat of the sun, Earth and moon, but keeping its scientific instruments below -380 degrees Fahrenheit. 

The telescope is now more than two thirds of the way to Lagrange Point 2 (L2), an area of balanced gravity between the sun and the Earth, where it will spend more than a decade exploring the universe in infrared.