Astronomy: successful launch for the James-Webb space telescope



Lhe James-Webb Space Telescope (JWST), awaited for thirty years by astronomers around the world to examine the Universe with unparalleled means, successfully took off with an Ariane 5 rocket on Saturday to reach its observation post, at 1 , 5 million kilometers from Earth. The Ariane 5 rocket successfully injected the telescope on Saturday into its final orbit, which it will reach in a month, announced the director of launch operations at the Guyanese space center.

With the on-time flight at 12:20 GMT, JWST will become the most advanced cosmos-observing instrument ever to be sent to space. But it will take him another month to reach his final position.

With the ambition to shed more light on humanity on two questions that torment it: « Where do we come from? » And « Are we alone in the Universe? » « . And thus see the glimmers of « cosmic dawn », when the first galaxies began to light up the Universe since the big bang, 13.8 billion years ago. It will allow us to better understand the formation of stars and galaxies, and to observe exoplanets, of which astronomers are discovering more and more specimens, to perhaps identify other Earths one day. The James-Webb will follow in the footsteps of the Hubble telescope, which revolutionized the observation of the Universe: it is thanks to him that scientists discovered the existence of a galactic black hole at the center of all galaxies , or water vapor around exoplanets.

A technological feat

Imagined by NASA from the launch of Hubble in 1990, and built from 2004, with the collaboration of the European (ESA) and Canadian (CSA) space agencies, the JWST differs in more than one way. The size of its mirror, with a wingspan of 6.5 m, gives it a surface area and therefore a sensitivity seven times greater, sufficient to detect the thermal signature of a bumblebee on the Moon. Another difference: its mode of observation. Where Hubble observes space primarily in the domain of visible light, James-Webb ventures into a wavelength that eludes the eye: near and mid-infrared. A radiation that any body, star, human or flower, emits naturally. This light will be studied by four instruments, equipped with imagers and spectrographs to better dissect it. Their development mobilized a plethora of engineers and scientists, under the leadership of American and European laboratories and manufacturers.

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Thanks to this, « looking at the same objects (as with Hubble), we will see new things, » explained in Paris the astronomer Pierre Ferruit, co-scientific director of the telescope for ESA. For example, the first galaxies, objects whose remoteness turned their lights red. Or the young star colonies, which grow up hidden in the dust clouds of their nurseries. Or the atmosphere of exoplanets.

The prerequisite for the proper functioning of the JWST is an ambient temperature so low that it does not interfere with the examination of the light. Hubble is in orbit some 600 kilometers above Earth. At this distance, the JWST would be unusable, heated by the Sun and its reflection on the Earth and the Moon. It will be placed at the end of a one-month trip 1.5 million kilometers away. And will be protected from solar radiation by a thermal shield of five flexible sails which will dissipate the heat, lowering the temperature (which is 80 degrees) to – 233 degrees on the telescope side.

A delicate deployment

But before getting there, the machine and its designers will have to achieve a real feat: its flawless deployment, with a series of operations involving, for example, for the shield alone 140 opening mechanisms, 400 pulleys and almost 400 meters of cables. Because the observatory, with its 12 meters high and a shield equivalent to a tennis court, had to be folded to slip into Ariane 5’s cap. « The encapsulation » was carried out with laser guidance to avoid any damage to the instrument, the development of which cost some $ 10 billion. For these maneuvers, NASA also imposed draconian cleanliness measures to prevent any contamination of the telescope mirror, by particles or even charged breath …

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Finally, a tailor-made fairing depressurization system was installed by Arianespace so that, upon separation from the launcher, at an altitude of 120 kilometers, no sudden change in pressure would damage the beast. It will take several weeks to find out if the telescope is ready for use. With an official entry into service scheduled for June.


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