The James Webb space telescope in 5 questions – Orange news

AFP, published on Friday, December 10, 2021 at 07:46 a.m.

The most powerful space telescope ever built, James Webb is due to take off at the end of December after more than 30 years of waiting. An engineering jewel, it will explore the Universe going back to some 13 billion years ago. Overview in five questions.

– What does it look like? –

Its centerpiece is its huge main mirror, measuring 6.6 meters in diameter and made up of 18 smaller, hexagonal mirrors. They are made of beryllium and coated with gold to better reflect the light captured from the far reaches of the Universe.

The observatory also has four scientific instruments: imagers for taking pictures of the cosmos, and spectrometers, which break down light to study the chemical and physical properties of the objects observed.

The mirror and the instruments are protected by a huge sun visor, made up of five superimposed layers. As big as a tennis court, they are as thin as a hair, and made of kapton, a material chosen for its resistance to extreme temperatures: one side will be over 110 ° C and the other at -235 ° C .

Also on board: a service module containing the propulsion and communication system … In total, the observatory weighs the equivalent of a school bus.

– Where is he going? –

The telescope will be placed in orbit 1.5 million kilometers from Earth, four times the distance of our planet from the Moon.

Unlike the Hubble telescope which revolves around the Earth, James Webb will be in orbit around the Sun. It will evolve in constant alignment with the Sun and the Earth, “behind” the latter. His mirror will constantly have his back to our star.

It will take about a month to reach this position, called the Lagrange point L2. At this distance, no manned mission of repair can be envisaged, as it had been the case for Hubble.

– How will it be deployed? –

Since the telescope was too large to fit into a rocket, it was folded over on itself. A technical constraint which generates the most complicated part of the mission: its deployment in space, the most perilous ever attempted by NASA.

About 30 minutes after take-off, the communications antenna and solar panels supplying it with energy will be deployed.

Then the deployment of the sun visor, hitherto folded like an accordion, will begin on the sixth day, well after having passed the Moon. Its thin membranes will be guided by a complex mechanism involving 400 pulleys and 400 meters of cable.

During the second week, the turn of the mirror will finally come.

Once in its final configuration, the instruments will need to cool and be calibrated, and the mirrors very precisely adjusted. After six months the telescope will be ready.

– What is he going to do? –

James Webb has two major science missions accounting for over 50% of the observation time. First, explore the early ages of the Universe, going back only a few hundred million years after the Big Bang. Scientists want to observe the first galaxies and the first stars …

Its second major mission will be to study exoplanets, that is to say planets around stars other than our Sun, in search of a habitable environment, in particular by studying their atmosphere.

The great novelty of James Webb is that he will only operate in the near and mid infrared. He will be able to see through clouds of dust impenetrable for Hubble, which has a small infrared capacity but operates mainly in visible light and ultraviolet.

Also planned are closer observations, in our solar system, of Mars or Europe, a moon of Jupiter.

– How long have we been waiting for him? –

The project was launched in the 1990s, and its construction began in 2004. Its take-off has been postponed many times, initially in 2007, then 2018 … in particular because of the complexity of its development.

The observatory is the result of an immense international collaboration, and integrates Canadian and European instruments. More than 10,000 people worked on the project, whose budget has exploded, at a cost ultimately approaching some 10 billion dollars.

It will operate for at least 5 years, and potentially up to more than 10 years.