A leap forward for astronomical observation.
After numerous postponements and years behind schedule, the JAMES WEBB telescope has taken to space aboard an Ariane 5 rocket from the Kourou space launch center in French Guiana.
James Webb, HUBBLE's long-awaited replacement.
In order to better realize the technological evolution brought by the JWST, it is necessary to speak about its predecessor, HUBBLE.
The American Congress votes the implementation of the Large Space Telescope project, allocating the funds necessary for its construction in 1983. The LST takes the name of a renowned astronomer, Edwin Hubble (1889-1953).
Launched in 1990, Hubble is a massive telescope: its primary mirror measures 2.4 meters in diameter. The set weighs 11 tonnes and is made up of various instruments such as cameras (Wide Field Camera 3, Advanced Camera for Surveys or the Space Telescope Imaging Spectrograph camera-spectrometer) or spectrometers (Near Infrared Camera and Multi-Object Spectometer for infrared and Cosmic Origins Spectrograph for ultraviolet).
Equipment that allows the HUBBLE telescope to provide highly detailed images of the space objects it observes.
An evolution for its time, being placed in orbit, the observations were therefore no longer subject to light and atmospheric pollution.
What are the changes made by JWST?
James Webb has at his disposal a power 100 times greater than that of Hubble. It will be able to see further and with more precision than any other observation instrument before it.
Unlike HUBBLE, JWST will not be put into orbit, but will reach the second Lagrange point (say P2), located 1,500,000 kilometers from Earth in the opposite direction to that of the Sun.
A disadvantage for potential repairs to be made, Hubble being only 570 km from the earth.
Thanks to this short distance, the Hubble telescope has benefited from numerous repairs throughout its 30 years of good and loyal service, thus exceeding 2005, the date of end of service initially planned.
Let's take a closer look at the different observation instruments, although Hubble and James Webb are both telescopes, they were not designed to carry out the same missions.
Hubble is designed to make its observations in the visible light field (Visible spectrum), although throughout its life some instruments have been added in particular to study the near infrared radiation field, in 2009.
James Webb, for his part, was specifically designed to observe space in the very particular field of infrared light, invisible to the human eye.
With longer wavelength coverage and greatly improved sensitivity, JWST will allow to see further, to the beginning of time and to search for the unobserved formation of the first galaxies, but also to look inside the clouds of dust where stars and planetary systems are formed.
Looking at the weight and size characteristics, one may be surprised that the JWST mirror is less heavy than the Hubble one, while it is larger.
Since 1990, the year Hubble was created, technology has evolved enormously.
The weight saving comes from the material used for the mirror, indeed Hubble was equipped with a thick glass mirror while that of the JWST is composed of beryllium divided into 18 thin and light pieces which have been assembled.
Beryllium is a light metal which is extremely resistant to any deformation in a very wide range of temperatures. It is an excellent conductor of electricity, but not magnetic. As, in its pure state, beryllium is a very dangerous metal to handle and breathe, it is more precisely one of its oxides which is used: a fine powder called O-30.
To ensure the good reflectivity of the mirrors, they will therefore be covered with a layer of gold. This coating must be thick enough to completely cover the mirror, but also thin enough so that it does not deform when the temperature varies.
In the case of both telescopes, the shape of the mirror must be extremely precise (the variation from the "ideal" shape of the mirror must be even smaller than the thickness of a hair).
A high-risk setup
Sending a telescope into space is no mean feat.
Unlike its predecessor Hubble, which was put into orbit by the space shuttle Discovery, JWST will be sent by an Ariane 5 rocket, curled up in its fairing.
A perilous operation, indeed, there is no “second JWST”.
It is a 10 billion dollar project, a state-of-the-art instrument, surely the most complex ever developed by Man.
The installation should last 3 weeks, with more than 180 maneuvers necessary.
The pressure on the shoulders of the NASA teams is enormous, being located 1,500,000 million kilometers from the earth, it is not possible to have recourse to human maintenance.
A thought to the Hubble telescope which once in orbit in 1990 produced blurred images.
After human maintenance, 5 spacewalks, 50% chance of success, and many sleepless nights, everything was back to normal in 1993.
This is also why the expected lifetime for JWST is much less than that achieved by Hubble.
Originally planned for 15 years, with the help of maintenance and surely a little luck, Hubble is still active today more than 30 years after its launch.
In order to meet the scientific objectives set, JWST was designed to operate for at least 5 years.
