Wednesday, January 19

Space. The James Webb Telescope’s heat shield fully deployed

It’s done ! The James Webb space telescope on Tuesday took a major step towards the success of its mission: its heat shield has been fully deployed, announced NASA.

This sun visor is made up of five layers each the size of a tennis court, intended to protect scientific instruments from the heat of our star. They have been carefully unfolded and stretched one by one since Monday. Too large to fit into a rocket, the telescope had to be folded on itself like an origami and requires deployment into space, an ultra-perilous procedure. Deploying this sunshade was one of the most difficult steps.

Deployment piloted from Baltimore

The most powerful space telescope ever designed, James Webb is eagerly awaited by astronomers around the world and must notably make it possible to observe the first galaxies, formed just a few hundred million years after the Big Bang.

The observatory took off a little over a week ago from French Guiana and is currently over 900,000 kilometers from Earth. It is still on its way to reach its final orbit, 1.5 million kilometers from us – four times the Earth-Moon distance. In this place, in the event of a problem, no repair mission can be envisaged. Its deployment, piloted from Baltimore, on the American east coast, must therefore be carried out without any missteps. More than a hundred engineers took turns 24 hours a day to make sure everything went according to plan.

Nasa broadcast the event live on the internet on Tuesday morning. As no aircraft on board can take photos of the observatory itself, the only images available were those of the operations control room, where the deployment teams cheered with joy after the announcement of the deployment. under tension of the fifth layer.

What is the composition of the heat shield?

The lens hood measures approximately 20 by 14 meters and is designed in the shape of a diamond. Its layers, as thin as a hair, were previously folded like an accordion, and are now spaced a few tens of centimeters from each other. They are made of kapton, a material chosen for its resistance to extreme temperatures: the face closest to the Sun can reach 125 ° C, and the furthest away -235 ° C.

Their deployment involved hundreds of pulleys and meters of cables to guide them, as well as motors to stretch each sail, from every corner of the diamond. A procedure repeated many times on Earth but that those in charge of the mission particularly feared. “When people ask me what keeps me awake at night is the deployment of the sun visor,” Bill Ochs, project manager for James Webb, said Monday just before operations began. “We’re all going to breathe a sigh of relief when we get to the fifth layer power-up. “

On Monday, the first three layers had been successfully unfolded and stretched. Tuesday morning, the teams did the same with the last two. Previously, the two “paddles” containing the solar shield had been released.

This heat shield is crucial because James Webb’s scientific instruments can only operate at very low temperatures and in darkness. The great novelty of this telescope is that it will indeed operate only in the near and middle infrared, wavelengths invisible to the naked eye. However, to be able to detect the weak light coming from the far reaches of the Universe, it must in no case be disturbed by the radiations of the Sun, or those returned by the Earth and the Moon.

The next step ?

The next step is the deployment of the mirrors: first the secondary mirror, smaller and placed at the end of a tripod. Then the iconic main mirror, covered with gold and measuring approximately 6.6 meters in diameter, and whose two sides will open one after the other.

Once in its final configuration, James Webb will arrive at its destination, known as the Lagrange 2 point. The instruments will still have to cool and be calibrated, and the mirrors very precisely adjusted. Six months after takeoff, the telescope will then finally be ready to go back to the origins of the Universe, but also to search for habitable environments, outside our solar system.

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