James Webb Space Telescope
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| Image:JWST.jpg | |
| Organization | NASA, ESA, CSA |
|---|---|
| Wavelength regime | Infrared (IR) |
| Orbit height | 1.5×106 km from Earth (L2 Lagrangian point) |
| Orbit period | 1 year |
| Launch date | (June 2013) |
| Deorbit date | (2018 - 2023) |
| Mass | 6,200 kg |
| Other names | Next Generation Space Telescope |
| Webpage | http://www.jwst.nasa.gov |
| Physical characteristics | |
| Telescope style | (refractor, Newtonian reflector, etc.) |
| Diameter | ~6.5 m |
| Collecting area | 25 m2 |
| Focal length | (m, ft) |
| Instruments | |
| NIRCam | Near IR Camera |
| NIRSpec | Near IR Spectrograph |
| MIRI | Mid IR Instrument |
| FGS | Fine Guidance Sensors |
The James Webb Space Telescope (JWST) is a planned space infrared observatory, intended to be a significant improvement on the aging Hubble Space Telescope. It will be jointly constructed and operated by NASA, ESA, and CSA. Formerly called the Next Generation Space Telescope (or NGST), it was renamed after NASA's second administrator, James E. Webb, in 2002. The telescope's launch is planned for no earlier than June 2013.
Contents |
Mission
The JWST's primary scientific mission has four main components: to search for light from the first stars and galaxies which formed in the Universe after the Big Bang; to study the formation and evolution of galaxies; to understand the formation of stars and planetary systems; and to study planetary systems and the origins of life. Due to a combination of redshift, dust obscuration, and the intrinsically low temperatures of many of the sources to be studied, the JWST must operate at infrared wavelengths, spanning the wavelength range from 1 to 27 micrometres. In order to ensure that the observations are not hampered by infrared emission from the telescope and instruments themselves, the entire observatory must be cold, well-shielded from the Sun so that it can radiatively cool to roughly 50 kelvins (−220 °C, −370 °F). To this end, JWST will incorporate a large metallized fanfold sunshield, which will unfurl to block infrared radiation from the Sun, as well as from the Earth and Moon. The telescope's location at the Sun-Earth L2 Lagrange point (see below) ensures that the Earth and Sun occupy roughly the same relative position in the telescope's view, and thus make the operation of this shield possible. The observatory is due to be launched no earlier than June 2013. After a commissioning period of approximately 6 months, the observatory will begin the science mission, which will be required to last a minimum of 5 years. The potential for extension of the science mission beyond this period exists, and the observatory is being designed accordingly.
Optics
Although JWST has a planned mass half that of the Hubble, its primary mirror (a 6.5 meter diameter beryllium reflector) has a collecting area which is almost 6 times larger. As this diameter is much larger than any current launch vehicle, the mirror is composed of 18 hexagonal segments, which will unfold after the telescope is launched. Sensitive micromotors and wavefront sensor 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 using active optics to overcome the effects of gravitational loading and wind loading.
Current status
The JWST program is in its detailed design phase. In January 2007 the program is scheduled to undergo a non-advocate review in order to determine if the proposed designs and technologies are sufficiently mature to begin the major construction phase. Prior to that major milestone in April 2006 the program will be reviewed following a replanning phase begun in August 2005. That replanning was necessitated by the cost growth revealed in Spring 2005. The primary outcomes of the replanning are significant changes in the integration and test plans, a 22-month launch delay (from 2011 to 2013), and elimination of system level testing for observatory modes at wavelength shorter than 1.7 micrometres. Other major features of the observatory are unchanged following the replanning efforts.
Construction & engineering
NASA's Goddard Space Flight Center in Greenbelt, Maryland is leading the management of the observatory project. The project scientist for the James Webb Space Telescope is Dr. John Mather. Northrop Grumman Space Technology serves as the primary contractor for the development and integration of the observatory. They are responsible for developing and building the Spacecraft, which includes both the spacecraft bus and sunshield. Ball Aerospace has been subcontracted to develop and build the Optical Telescope Element (OTE). Goddard Space Flight Center is also responsible for providing the Integrated Science Instrument Module (ISIM).
The ISIM contains four science instruments and a fine guidance sensor. The primary science instrument of the observatory is the NIRCam (Near InfraRed Camera), which will have a spectral coverage ranging from the edge of the visible (0.6 micrometres) through the near IR (5 micrometres). The NIRCam will also serve as the observatory's wavefront sensor, which is required for wavefront sensing and control activities. The NIRCam is being built by a team led by the University of Arizona, with Principal Investigator Dr. Marcia Rieke. The industrial partner is Lockheed-Martin's Advanced Technology Center located in Palo Alto, California.
In addition to the near IR imaging capabilities of the NIRCam, the observatory will also perform spectrography over this range with the NIRSpec (Near InfraRed Spectrograph). NIRSpec is being built by the European Space Agency at ESTEC in Noordwijk, Holland, leading a team involving Astrium GmbH, Ottobrun, Germany, and the Goddard Space Flight Center: the NIRSpec project scientist is Dr. Peter Jakobsen. The mid-IR wavelength range will be measured by the MIRI (Mid InfraRed Instrument), which contains both a mid-IR camera and spectrometer that has a spectral range extending from 5 to 27 micrometres. MIRI is being developed as a collaboration between NASA and a consortium of European countries, and is co-led by Dr. George Rieke (University of Arizona) and Dr. Gillian Wright (UK Astronomical Technology Centre, Edinburgh, part of the Particle Physics and Astronomy Research Council). The FGS (Fine Guidance Sensor), led by the Canadian Space Agency under project scientist Dr. John Hutchings (Dominion Astrophysical Observatory, Victoria), is used to stabilize the line-of-sight of the observatory during science observations and also includes a Tunable Filter module for astronomical narrow-band imaging in the 1.5 to 5 micrometres wavelength range. The infrared detectors for both the NIRCam and NIRSpec modules are being provided by the Imaging Division of Rockwell Scientific Company.
See also
External links
General project information
- JWST homepage at NASA
- JWST homepage at STScI
- JWST homepage at ESA
- Cost overruns put squeeze on Hubble’s successor
Science instrument teams
- NIRCam homepage at Arizona
- MIRI homepage at Arizona
- MIRI homepage at UK Astronomy Technology Centrede:James Webb Space Telescope
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