James Webb Space Telescope

Mission facts

Date: 25 December 2021
Agency: National Aeronautics and Space Administration (NASA)
Launcher: Ariane
Mission: James Webb Space Telescope

#NASA#ESA#CSA#space telescope#infrared astronomy#Sun–Earth L2#Ariane 5

Contents · 12

01Mission timeline
02Overview and partnership
03Mirror and sunshield
04Instruments and orbit
05Launch and deployment
06Commissioning and science
07Mission in numbers
08Did you know?
09Gallery
10Related articles
11Sources
12Connections

Mission timeline

3 chapters

Select a phase to read what happened. Every chapter has its own detailed page.

The Ariane 5 carrying Webb clears the launch tower at the Guiana Space Centre, 25 December 2021.

25. 12. 2021

Launch on Ariane 5

Webb left Kourou on Christmas Day 2021 aboard an Ariane 5 provided by ESA.

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Overview and partnership

The James Webb Space Telescope (JWST, or Webb) is a space observatory optimised for infrared light. The mission is led by NASA in an international partnership with the European Space Agency (ESA) and the Canadian Space Agency (CSA) [1, 6]. Observing in the infrared allows Webb to detect light from the earliest stars and galaxies, which has been redshifted into the near- and mid-infrared part of the spectrum [1].

ESA provided the launch vehicle and launch services, the Near-Infrared Spectrograph (NIRSpec), and – together with a consortium of European countries – the Mid-Infrared Instrument (MIRI). The CSA provided the Fine Guidance Sensor/Near-Infrared Imager and Slitless Spectrograph (FGS/NIRISS) [1]. Science and flight operations are run from the Science and Operations Center at the Space Telescope Science Institute (STScI) in Baltimore, Maryland [1].

Mirror and sunshield

Webb's primary mirror is approximately 6.5 m (21.3 ft) across, about 2.75 times the diameter of Hubble's mirror and roughly six times its collecting area [1]. It consists of 18 thin, lightweight beryllium segments held in shape and position by actuators on a stiff backing frame; the mirrors are coated with gold to optimise their reflectivity in the infrared [1]. Because the mirror is too large to fit inside a rocket fairing, it was folded for launch and deployed in space [1, 3].

The largest structure of the observatory is a five-layer sunshield made of Kapton membranes, roughly the size of a tennis court [1, 3]. It shields the telescope from the Sun, Earth and Moon, so that the near-infrared instruments can cool passively to about 39 K (−234 °C); MIRI is cooled further to about 7 K (−266 °C) by a helium cryocooler [1].

Instruments and orbit

The observatory carries four science instruments: the Near-Infrared Camera (NIRCam), NIRSpec, MIRI and FGS/NIRISS [1]. NIRCam was built by the University of Arizona with Lockheed Martin [1].

Unlike Hubble, which orbits about 600 km above Earth, Webb operates around the second Sun–Earth Lagrange point (L2), about 1.5 million km from Earth [1]. Webb does not sit at L2 itself but circles it in a large loop, and the location allows the sunshield to block the Sun, Earth and Moon at all times; the journey there took about a month [1]. At that distance the telescope is beyond the reach of servicing missions, a trade-off studied and accepted early in the project [1].

The assembled telescope, with its 18 gold-coated primary mirror segments and the secondary mirror on its support struts, seen face-on through the observation window of the cleanroom at NASA's Goddard Space Flight Center.

Launch and deployment

Webb lifted off on an Ariane 5 from Europe's Spaceport in Kourou, French Guiana, at 12:20 UTC (7:20 a.m. EST) on 25 December 2021 [2, 3]. The observatory separated from the rocket about 27 minutes after launch at an altitude of roughly 1,400 km and unfolded its solar array about 30 minutes after launch [2]. The first mid-course correction, 12.5 hours after launch, fired the main thruster for 64 minutes and added about 20 m/s [3].

Over roughly two weeks the observatory went through nearly 50 major deployments [3]. Sunshield deployment began on 28 December; on 4 January 2022 the fifth layer was tensioned, a sequence that used 139 of Webb's 178 release mechanisms, 70 hinge assemblies, eight deployment motors, about 400 pulleys and 90 cables [3, 4]. The secondary mirror and the two primary-mirror wings followed, and on 8 January 2022 Webb was fully deployed [3]. A 297-second burn on 24 January 2022 placed the telescope into its halo orbit around L2 [5].

Commissioning and science

After about six months of mirror alignment and instrument calibration, commissioning was completed on 10 July 2022; NASA reported that the instruments' sensitivity was substantially better than predicted before launch [3]. On 11 July 2022 the first full-colour image, Webb's First Deep Field of the galaxy cluster SMACS 0723, was presented, and the full set of first images followed on 12 July [6]. Webb was designed for at least five years of operation with a goal of ten; because of the accurate launch and efficient course corrections, NASA estimates enough propellant for more than 20 years of science operations [1, 3].

Early results include what NASA described as the first clear evidence of carbon dioxide in the atmosphere of an exoplanet, the hot gas giant WASP-39 b, measured with NIRSpec [7]. In May 2024 the JADES team reported a spectroscopic redshift of 14.32 for the galaxy JADES-GS-z14-0, corresponding to less than 300 million years after the Big Bang; at the time of the announcement it was the most distant known galaxy [8]. Such records are provisional and continue to be revised as observations accumulate.

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Mission in numbers

primary mirror diameter: 6,5 m (18 segmentů)
distance from Earth (L2 region): asi 1,5 milionu km
estimated propellant lifetime: přes 20 let

Did you know?

Webb's mirrors are coated with gold to improve their reflectivity in the infrared; NASA estimates the total amount of gold at about the mass of a golf ball [1].
Unfolding and tensioning the sunshield used 139 of the observatory's 178 release mechanisms and 90 cables totalling roughly a quarter of a mile (about 400 m) [4].
The final course correction on 24 January 2022 changed Webb's speed by only about 1.6 m/s – roughly walking pace [5].
Webb's First Deep Field was assembled from 12.5 hours of exposures and covers a patch of sky about the size of a grain of sand held at arm's length [6].