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The James Webb Telescope is packing up its lens hood to prepare for launch

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The size of a tennis court, the sun visor of the James Webb Telescope has been folded up one last time. This important step, which requires incredible meticulous work, brings us closer to its launch scheduled for October.

A huge parasol

The James Webb Telescope, one of the most anticipated space observatories, will be entirely focused on infrared wavelengths. These lengths are ideal for probing the early Universe. But to detect weak heat signals from very distant objects, you need to make sure that there is an almost total absence of stray heat sources.

To carry out its mission, the telescope will therefore be positioned around the point of Lagrange L2, 1.5 million kilometers from the Earth on the side opposite the Sun. To protect it from our star, NASA engineers have also imagined a sun visor of 22 meters long by 11 meters wide, composed of five very thin layers of extremely reflective materials.

This incredible structure should keep the telescope’s mirror (the structure in yellow) in the shade, at temperatures around -223 ° C. Note that some of the instruments on board will also be kept cool (-258 ° C) thanks to an active cooling system.

That being said, engineers at Northrop Grumman in Redondo Beach, Calif., Recently successfully folded and packaged this famous sun visor. The goal: that it can fit into the fairing of the Ariane 5 rocket, responsible for freeing the observatory in space. The structure had obviously been specially designed to fold around the two sides of the telescope and fit within the limits of its launcher (5.4 meters in diameter).

Incredible meticulous work

“There is nothing quite analogous to folding a sun visor the size of a tennis court, but it is quite similar to packing a parachute.”, says Jeff Cheezum, who oversaw the design of the structure. “Just like a skydiver needs their parachute to be properly packed to open perfectly, Webb will need their sun visor to be neatly stowed to ensure it opens normally and maintains its shape.”.

It took engineers a full month to fold this incredible structure. The process began by laying the five layers as flat as possible, details the NASA. Then the layers were lifted vertically and propped up on special support equipment so that they could be properly held for folding. A team then carefully folded each layer in a zigzag fashion to create stacks of accordion membranes on either side of the telescope.

The first layer of the sun visor has a thickness of only 0.005 cm, while the other four layers are half the thickness. Folding over such thin layers was therefore another challenge. The process also had to take into account the 90 different voltage cables of the sunshade, which must be stowed in a specific way to ensure the correct deployment of the sunshade.

Credit: NASA / Chris Gunn

Finally, one of the more complex aspects of the folding process involved the alignment of the membrane stacks. Each of the layers of the sun visor has hundreds of holes arranged in such a way as to prevent light and heat from passing to the optical elements of the telescope. These holes had to be aligned during bending so that technicians could insert “pins” through. These pins (there are 107 of them) will help hold the layers together for launch, but also unfold the sun visor once in space.

Over the next three months, engineers and technicians will finish storing and securing the sun visor. It will remain in this form until launch, and will only unfold once in space.



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