James Webb Space Telescope
The James Webb Space Telescope (JWST) is a planned orbital infrared observatory, intended (in part) to replace the aging Hubble Space Telescope. Formerly called the Next Generation Space Telescope (NGST), it was renamed after NASA's second administrator, James E. Webb, in 2002. The telescope's launch is planned for sometime between 2009 and 2011.
Mission
The JWST's primary mission is to examine the infrared remant of the big bang, and thus to make observations of an earlier state of the universe earlier than is possible today. To achieve this, sensors of unparalleled sensitivity will be used, which in turn requires that the entire spacecraft be particularly cold, and that major sources of IR interference (notably the Sun, the Earth, and the Moon) be blocked. To this end, JWST will be accompanied by a large metalized fanfold sunshield, which will unravel to block infrared radiation from these sources. The telescope's lagrangian orbit (see below) ensures that the Earth and Sun occupy the same relative position in the telescope's view, and thus make the operation of this shield possible.
Orbit
In order to keep the Earth and Sun at the same location in the telescope's "sky", it will be placed in orbit at the L2 lagrangian point point. This location, around 1.5 million km from Earth, is considerably beyond the maximum altitude achievable using the Space Shuttle, so JWST will probably be placed in orbit using a European Ariane 5 launcher. This distance also means that, unlike Hubble, it will not be possible to repair or upgrade the observatory during its 5-10 year design life. Although the L2 point is well outside the orbit of the Moon, JWST will still need a sunshade to avoid the faint heat of reflected moonlight.
Optics
Although JWST has a planned weight half that of the Hubble, its primary mirror (a 6.5 meter beryllium reflector) is more than 5 times larger. As this diameter is much larger than any current launch vehicle, the mirror is composed of 18 segments, which will unfold after the telescope is launched. Sensitive micromotors and wavefront sensors will position the mirror segments in the correct location, but subsequent to this initial configuration they will only rarely be moved; unlike terrestrial telescopes like the Keck which continually adjust their mirror segments to overcome atmospheric scintillation.
See also: telescope, space telescope.
External link
Referenced By
1 E9 m | 1e9 m | 1e9 metres | Astronomical satellite | E9 m | Hubble Space Telescope | Hubble Telescope | Hubble space telescope/temp | Lagrange Points | Lagrange point | Lagrangian Point | Langrangian point | NASA | National Aeronautic and Space Administration | National Aeronautics and Space Administration | National Aeronautics and Space Agency | Space observatory | Trojan point
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