|  | Artist's impression of JWST | |
Mission
JWST is the successor to the Hubble Space Telescope, and it will be almost three times the size of Hubble. JWST has been designed to work best at infrared wavelengths. This will allow it to study the very distant Universe, looking for the first stars and galaxies that ever emerged.
Compared to existing or planned observatories, JWST will have the unique advantage of combining superb image quality, a relatively large field of view and low background light with a highly stable operating environment. All of these are very important characteristics for the infrared observations JWST will need to carry out to see the first stars and galaxies. JWST should operate for at least five years and possibly even for as long as ten.
What’s special?
JWST will have a primary mirror with a diameter of 6.5 metres - more than twice that of Hubble’s - giving it much more light-gathering capability.
Even though Hubble only has about 1/15 the collecting area of today's largest ground-based telescopes, its images are much sharper, making it possible for Hubble to detect fainter objects than is possible from the ground. As a space-based observatory, JWST will share this unique ability.
The sharpness of images from both Hubble and JWST is due to the absence of any atmosphere between the astronomical objects and the telescope. The turbulence of the Earth's atmosphere blurs images from Earth-based telescopes and causes the naked eye to see stars twinkle on clear nights.
One of the biggest technical challenges of JWST though has been the packing of an 6.5-metre spacecraft into a small rocket with a diameter of only 5 metres. This has been described by JWST scientists as ‘a bit like designing a ship in a bottle’.
| | Artist's view of the JWST space observatory | |
Spacecraft
The JWST space observatory consists of a telescope and its four associated scientific instruments, mounted on the telescope itself:
NIRCam, a Visible/Near Infrared Camera: dedicated to the detection of light from the first stars, star clusters or galaxy cores; the study of very distant galaxies seen in the process of formation; detection of light distortion due to dark matter; the discovery of supernovae in remote galaxies; studies of the stellar population in nearby galaxies, young stars in the Milky Way and the Kuiper Belt objects in our Solar System.
NIRSpec, a Near-Infrared Multi-Object Dispersive Spectrograph: sensitive over a wavelength range that matches the radiation from the most distant galaxies and capable of observing more than 100 objects simultaneously. The key scientific objectives of this instrument are: studies of star formation and chemical abundances of young distant galaxies; tracing the creation of the chemical elements back in time; and exploring the history of the intergalactic medium (the gaseous material that fills the vast volumes of space between the galaxies).
MIRI, a Mid-Infrared Camera-Spectrograph, essential for the study of: the old and distant stellar population; regions of obscured star formation; hydrogen emission from previously unthinkable distances; the physics of protostars; and the sizes of Kuiper Belt objects and faint comets.
The FGS, a Fine Guidance Sensor will provide high-precision pointing error signals to the observatory to enable stable pointing at the milli-arcsecond level. It will also support star field identification via correlation with a star catalogue as well as spatial and radiometric calibrations.
Journey
For JWST to be able to make precise infrared observations it is necessary that the telescope and its instruments are cooled. This is to avoid that their own infrared emission would overwhelm the faint signals from the astronomical objects being observed. For this reason, the JWST orbit will be 1.5 million km away from Earth, at a special point in space called Lagrange Point 2, or ‘L2’. JWST has to be extremely reliable, even though it is using new and innovative technology. Once in orbit, it will be too far away for astronauts to perform servicing missions.
History
The James Webb Space Telescope was formerly known as the Next Generation Space Telescope (NGST). It is due to be launched in 2014 on an Ariane 5 and will follow on the successful footsteps of the Hubble Space Telescope. ESA has participated actively in both Hubble and JWST from the very beginning, thereby not only bringing huge scientific benefits to European astronomers, but also promoting competitiveness and cross-border collaboration within European science as a whole. NASA and ESA, joined by the Canadian Space Agency, have collaborated on JWST since 1997.
Partnerships
JWST is a partnership between ESA, NASA and the Canadian Space Agency.
Last update: 14 October 2009 | 
