James Webb Space Telescope

Two decades to launch

Planning for a successor to Hubble began in the 1990s, as the Next Generation Space Telescope; in 2002 it was named for James E. Webb, NASA's administrator during the Apollo era. The telescope is a partnership of NASA, the European Space Agency and the Canadian Space Agency, and the Space Telescope Science Institute operates it. It was launched on 25 December 2021 from Kourou, French Guiana, on an Ariane 5.

Its development was long and costly, with budgets and schedules that rose repeatedly, and the launch followed more than 300 single points of failure that had to work.

Unfolding and arriving

In the month after launch, the telescope unfolded its sunshield of five layers and its mirror, in a sequence that could not be tested fully on the ground, and it arrived at the second Sun–Earth Lagrange point, L2, in January 2022. The first full-colour images and spectra were released on 12 July 2022.

In August 2022 NASA announced the first clear detection of carbon dioxide in the atmosphere of an exoplanet, WASP-39 b, by observing starlight filtered through its atmosphere as it passed in front of its star. Webb has since found galaxies at redshifts above ten, formed within a few hundred million years of the Big Bang.

Operating at L2

Webb sits where the gravity of the sun and the Earth balance the centrifugal force, so it keeps the Sun, Earth and Moon on one side behind its sunshield and its instruments stay at about 40 kelvin, which is needed to see faint infrared light. Fuel for station keeping was conserved so well by a precise launch that it is expected to last for 20 years or more. Observing proposals are open to astronomers worldwide, and the data enter the public archive after a proprietary period, which is zero for some large programmes.

The cost of being unrepairable

Unlike Hubble, Webb is too far away to be repaired, so every system was tested to a higher standard and many have redundancy. The price was years of delay and billions of dollars, and the telescope's mission is limited by its fuel rather than by its instruments. The programme's experience has influenced later planning, including the discussions of servicing for future space telescopes. Webb's early success also shows that an extremely complex deployment can work if the design allows for testing at every stage and if the team can rehearse the sequence many times.

Instruments and technologies

• Segmented beryllium mirror Eighteen hexagonal segments, 1.3 metres across, coated in gold and adjustable by actuators on seven axes after unfolding.
• NIRCam and NIRSpec An infrared camera and a multi-object spectrograph working from 0.6 to 5 micrometres.
• MIRI A mid-infrared camera and spectrograph cooled to about 7 kelvin by a cryocooler.

The people

• James E. Webb NASA Administrator from 1961 to 1968, for whom the telescope is named.

Timeline

• 2002 Next Generation Space Telescope renamed for James E. Webb.
• 2021 Launched on 25 December from Kourou, French Guiana.
• 2022 Reaches L2 in January; first full-colour images released on 12 July.
• 2022 First clear detection of carbon dioxide in an exoplanet atmosphere (WASP-39 b), announced in August.

Key lessons for observation today

• Deployment risk is the programme risk Hundreds of single points of failure had to work once. Test what can be tested and design out what cannot.
• Cold is a capability Passive cooling made the instruments sensitive. Thermal design is part of the sensor.
• Open archives return value Data enter an open archive and have been reanalysed by thousands. Open access amplifies the investment.

Sources

• Wikipedia, James Webb Space Telescope
• Wikipedia, Timeline of the James Webb Space Telescope
• University of Bristol, NASA's Webb detects carbon dioxide in exoplanet atmosphere
• Wikipedia, James E. Webb