James Webb Space Telescope

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James Webb Space Telescope

(JWST) A next-generation space observatory optimized for infrared astronomy that NASA plans to launch in August 2011 as the successor to the Hubble Space Telescope. It was named to commemorate a former NASA administrator, James E. Webb, who served from 1961 to 1968 during the time of the Apollo missions. The observatory actually began its development as the Next Generation Space Telescope (NGST) following an initial proposal for such an instrument in 1996. The new name was adopted in 2002.

The chief goal of the JWST is to look across time and space 90% of the way back to the Big Bang in order to explore the era when stars and galaxies started to form out of primeval gas and dust clouds. Radiation from this very remote region is redshifted so much that many spectral lines are moved into the infrared. Viewing the heavens in the infrared waveband also allows astronomers to penetrate dust and gas. For this reason, the JWST will have detectors that are highly sensitive to the infrared part of the spectrum, with some capability in the visible part. Its observing position will also be as stable and as isolated from unwanted background interference as possible, orbiting the Lagrangian point L2, well beyond the Moon's orbit at a location about 1.5 million kilometers from the Earth in the cold darkness of interplanetary space. The JWST's mission is scheduled to last between five and ten years.

The total mass of the JWST spacecraft is expected to be 6.2 tonnes, housing the telescope with its 6.5-meter 18-segment beryllium primary mirror (nearly three times the diameter of that of the Hubble Space Telescope but only about one-third as heavy, and foldable so that it can be carried conveniently within the spacecraft before being deployed). In the focal plane of the telescope, also known as the Optical Telescope Element (OTE), there will be an Integrated Science Instrument Module (ISIM), consisting of a cryogenic instrument module containing the infrared detectors linked into the telescope and to computers and software in the relatively warm part of the spacecraft. The science instruments within this module will be a Near-Infrared Camera (NIRCam), a Near-Infrared Spectrometer (NIRSpec), a Mid-Infrared Instrument (MIRI), and the telescope's Fine Guidance System (FGS). To help maintain the operating temperature of the detectors at less than 50 K, they will be permanently in the shadow of a sun shield about the size of a tennis court (22 m × 10 m), which will be deployed between them and the Sun to screen out light, heat, and other solar radiation. The sun shield will turn as the spacecraft orbits. Like the primary mirror, the sun shield will be folded until the JWST is on station. The remaining part of the JWST spacecraft houses attitude and other control mechanisms and supplies electrical power and communications facilities to the science instruments and onboard computers.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006
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