The James Webb Space Telescope (JWST), awaited for thirty years by astronomers around the world to examine the Universe with unequalled resources, took off on an Ariane 5 rocket on Saturday to reach its observation station. It was successfully injected into its final orbit, announced the director of launch operations at the Guiana Space Centre.
"Good separation Webb telescope, Go Webb", announced Jean-Luc Boyer from the control centre in Kourou. After 27 minutes of flight, the upper stage of the Ariane rocket released the telescope, which will now take around a month to reach its observation post 1.5 million km from Earth.
His ambition: to shed light on the creation of the universe
The JWST will become the most advanced instrument ever sent into space to observe the cosmos. Its ambition is to shed more light on the two questions that plague humanity: "Where do we come from? and "Are we alone in the universe? And to catch a glimpse of the "cosmic dawn", when the first galaxies began to illuminate the universe from the Big Bang, 13.8 billion years ago.
It will enable us to better understand the formation of stars and galaxies, and to observe exoplanets, of which astronomers are discovering more and more specimens, with a view to perhaps one day identifying other Earths.
In the footsteps of Hubble
The James Webb will follow in the footsteps of the Hubble telescope, which revolutionised observation of the universe: it was thanks to the telescope that scientists discovered the existence of a galactic black hole at the centre of all galaxies, or water vapour around exoplanets.
Conceived by NASA when Hubble was launched in 1990, and built from 2004 onwards in collaboration with the European Space Agency (ESA) and the Canadian Space Agency (CSA), the JWST is different in more ways than one.
The size of its mirror, with a span of 6.5 metres, 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 is the way it is observed. Whereas Hubble observes space mainly in the visible light range, James Webb ventures into a wavelength that the eye cannot see: the near- and mid-infrared. This radiation is emitted naturally by all bodies, stars, humans and flowers.
This light will be studied by four instruments, equipped with imagers and spectrographs to better dissect it. Their development has mobilised a plethora of engineers and scientists, under the leadership of American and European laboratories and manufacturers.
Need cold to see clearly
The imperative condition for the JWST to function properly is an ambient temperature so low that it does not interfere with the examination of the light. Hubble is in orbit some 600 km above the Earth. At this distance, the JWST would be unusable, heated by the Sun and its reflection off the Earth and Moon. It will therefore be placed 1.5 million km away. And it will be protected from solar radiation by a heat shield made up of five flexible sails that will dissipate the heat, lowering the temperature (which is 80°C) to -233 degrees on the telescope side.
But before that could happen, the machine and its designers had to achieve a real feat: its flawless deployment, with a series of operations involving, for example, 140 opening mechanisms, 400 pulleys and almost 400 metres of cable for the shield alone. The observatory, 12 metres high and with a shield the size of a tennis court, had to be folded to fit inside the Ariane 5 fairing. The "encapsulation" was carried out using laser guidance to avoid any damage to the instrument, which cost some ten billion dollars to develop.
Absolutely clean
For these manoeuvres, NASA has also imposed draconian cleanliness measures to avoid any contamination of the telescope's mirror by particles or even contaminated breath. Finally, Arianespace has installed a customised fairing depressurisation system to ensure that no sudden change in pressure will damage the beast when it separates from the launcher at an altitude of 120 km. "An ESA official in Kourou explained on Thursday that "exceptional 'customers' require exceptional measures".
It will be several weeks before we know whether the telescope is ready for operation. Official commissioning is scheduled for June.
FR 
EN 
DE