An overview of JWST

The James Webb Space Telescope (JWST, formerly known as the Next Generation Space Telescope), which is being developed in a collaborative effort involving NASA, ESA, and the Canadian Space Agency (CSA), will be one of the prime astronomical facilities in the next decade. In this article we provide a short summary of the mission specifications. A more extensive overview can be found in Gardner et al. (2006), or at the Space Telescope Science Institute web site (

The Metal-rich Universe, eds. G. Israelian and G. Meynet. Published by Cambridge University Press. © Cambridge University Press 2008.

Figure 23.1. A schematic view of JWST, illustrating the main components of the observatory (credit: Northrop Grumman Space Technology).

JWST will be a 6.6-m-aperture deployable telescope, passively cooled to below 50 K, and optimized for near- and mid-IR observations. More specifically, JWST will observe in the wavelength range 0.6-28 |^m. The telescope is designed to deliver diffraction-limited image quality at 2 (i.e. angular resolution ~0".07) and, in terms of sensitivity, to be limited by the zodiacal light at k < 10 |^m.

JWST will be launched into orbit around the second Earth-Sun Lagrange point (L2), which provides a more stable environment and, most importantly, much less thermal emission from the Earth and the Moon, than any orbits around Earth. The launch is scheduled for 2013, on an Ariane 5 rocket. The minimum mission lifetime is 5 years, with the goal of lasting up to 10 years.

The primary mirror uses 18 semi-rigid segments made of beryllium with a thin gold coating (Figure 23.1), which will be phased periodically to maintain the required image quality. A sunshield is responsible for continuously keeping the telescope in the Sun's shade, thus allowing the required passive cooling. Six of the external mirror segments, the secondary mirror support, and the sunshield will be folded into the Ariane 5 rocket, and will be deployed during transfer to L2.

The Integrated Science Instrument Module (ISIM), located in the backplane of the primary mirror, will host four scientific instruments, which are described in the following.

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