James-Webb: 12 questions to understand the mission of the space telescope

The James-Webb Space Telescope (JWST) must soon leave the mainland, in order to observe the premises of our Universe. Here’s everything you need to know about the mission of Hubble’s worthy successor.

Its launch into space is eagerly awaited by astronomers. The James Webb Space Telescope (JWST) is developed by NASA, with the participation of the European Space Agency (ESA) and the Canadian Space Agency (CSA). This immense observatory should soon join the stars, to begin its scientific activities.

Here’s everything you need to know about the colossal JWST’s mission.

What will the James-Webb telescope be used for?

This observatory was designed to advance research in four main areas:

  • Detect the light of the first galaxies, which appeared shortly after the Big Bang,
  • To study the formation and evolution of galaxies,
  • Better understand the birth of the stars,
  • As well as exoplanets.

For this, the JWST observes in the infrared domain (that is, the radiation between visible light and microwaves) and in space. Thus, the observatory will be able to go back far into the past of the Universe, to see the first galaxies in formation – “Baby galaxies” – and inspect the interior of the dust clouds in which the stars and planets have formed.

A (adorable) design inspired by the JWST mission. // Source: Flickr / CC / Pooja Mulmuley Nibandhe

What are the instruments of the James-Webb telescope?

The observatory has four scientific instruments on board:

  • A near infrared camera, NIRCam (for “Near-InfraRed Camera”), which will allow, among other things, to detect stars that have appeared after the Big Bang, to search for supernovæ, to measure distorted light due to dark matter,
  • a near infrared spectrometer, the NIRSpec (“Near-Infrared Spectrometer”), which will, for example, make it possible to study chemical elements in distant galaxies or clusters of young stars,
  • a medium infrared instrument, the MIRI (“Mid Infrared Instrument”), with which it will be possible in particular to observe brown dwarfs, exoplanets and the evolution of stars and protoplanetary systems,
  • And one near infrared imager and slitless spectrograph, says NIRISS (“Near Infrared Imager and Slitless Spectrograph”), which will help study distant exoplanets and galaxies.

Why does the James-Webb telescope have a segmented mirror?

The sumptuous primary mirror of the James Webb telescope, with a diameter estimated at 6.5 meters, does not go unnoticed with its golden coloring and its 18 assembled hexagonal segments. In astronomy, we say that the mirror is segmented. This is not a technical choice, because it would have been possible to build it in a single block.

There is a logistical motivation behind this choice: it would have been impossible to fit a mirror of this size made up of a single block in the rocket that will launch the JWST into space. For the first time, therefore, it was decided to launch a telescope with a segmented mirror in space.

Will the James-Webb telescope replace Hubble?

It would not be entirely correct to say that the James-Webb Space Telescope is intended to replace Hubble. It should be seen more as a successor. Admittedly, the JWST exceeds a limit of Hubble, which proves to be unable to see beyond the near infrared (it thus goes back less far in the past than will do the JWST). It is also more imposing than Hubble in size.

But the day Hubble stops working, the James-Webb telescope will not have the means to completely replace it. Currently, Hubble is the only telescope capable of observing in the ultraviolet, and the JWST is not equipped to do the same.

“Yep James, you can never really replace me.” “// Source: Nino Barbey for Numerama

When will the James-Webb telescope be launched?

The James-Webb space telescope was initially to be launched on December 18, 2021. Finally, the departure cannot take place before December 22, at the earliest: an incident exposed the space telescope to possible damage.

Where will the James-Webb telescope be launched from?

It will take off from the Kourou space center in French Guiana, transported aboard an Ariane 5 ECA rocket. The observatory had to be transported by boat from California to reach its launch base.

How much does the James-Webb telescope cost?

The total cost of the telescope is estimated $ 9.7 billion, or 8.2 billion euros. Since the start of the project, this budget has been regularly revised upwards.

NASA mentions participating in the total cost of JWST up to $ 7.998 billion. She estimates that the first five years of operating the observatory, plus the two years it takes to exploit its data, will result in an additional cost of $ 8.835 billion – knowing that the JWST may be able to operate for longer.

Why was the launch of the James Webb telescope postponed?

The flight of the JWST into space was many times rejected. In 2003, the date envisaged for his departure in space was 2011. However, that year, the schedule had to be readjusted due to regular problems and the increase in budget. Representatives of the US Congress have even considered canceling the project, become too expensive. However, the launch was postponed until 2018.

And since then, take-off has been continuously postponed. The covid-19 pandemic has changed the pace of work even more, forcing the launch date to be further postponed to the end of 2021.

Why is the name of the James-Webb telescope controversial?

At the start of the project, the telescope was given the temporary designation « Next Generation Space Telescope » (NGST, for “New Generation Space Telescope”). It was named so to symbolize the continuity of its activities, compared to those of Hubble.

The JWST received its official name on September 10, 2002, referring to James Webb (1906-1992), NASA’s second administrator. He is known to have led Apollo. However, this choice of name is questioned by many scientists, because James Webb would have favored a policy of exclusion of LGBTQI + people within the space agency. NASA does not intend to rename it, however.

Why does the James-Webb telescope need to be sent into space?

It was necessary to make the JWST a space telescope, and not a terrestrial one, because this observatory requires very specific observation conditions. The Earth’s atmosphere would risk blurring the images obtained by the telescope, because it is almost opaque and glows in the infrared wavelengths in which the James-Webb will observe. The technologies used in terrestrial telescopes do not currently allow this problem to be circumvented.

This need to send it into space makes the mission all the more complex: all the JWST mechanisms must work perfectly, despite the hundreds of dangers that await the telescope in space.

Where will the James-Webb telescope be placed in space?

It will take about a month for the telescope, after launch, to reach its intended location: the Lagrange point L2, located approximately 1.5 million kilometers of our planet. It is essential to place the JWST very far, because it needs a low temperature to function correctly (-223 ° C). Its shield will help keep it cold, by blocking the light emitted by the Sun, the Earth and the Moon (it would risk, by heating the telescope, to distort its observations).

But in addition to the shield, the position of the space telescope plays a role: it will be placed behind the Earth, relative to the Sun. The JWST will thus be aligned at all times with our planet and the Sun.

This is the first time that a telescope will be positioned at the Lagrange L2 point. At such a distance, no repair can be considered in space, like the maintenance missions that take place with Hubble.

How long should the James-Webb telescope mission last?

From its launch, the telescope was designed to last its mission at least 5 and a half years (including the first six months of its commissioning). The objective would rather be that its lifespan is greater than 10 years. Unlike the Hubble telescope, it is not so much the functioning of its various components that is likely to be a problem over time. Rather, it is the quantity of fuel loaded by the observatory to maintain its orbit that will be decisive. The JWST therefore transports fuel in sufficient quantity to be functional for ten years.

Article originally published on September 19, 2021 and updated on November 24, 2021

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