The James Webb Space Telescope (JWST) will be a partial replacement for the Hubble Space Telescope, with a much larger mirror (6.5 meters (21.3 feet) in diameter, versus 2.4 meters/7.9 feet for Hubble) but optimized for a different range of radiation wavelengths. Hubble observes primarily in visible light, with some coverage in the ultraviolet and infrared, but the JWST is designed mainly for infrared observations. The reason for this is that infrared radiation penetrates interstellar dust better than visible light does, allowing better views of developing stars and planetary systems as well as observations of the formation and evolution of distant galaxies.

To observe at infrared wavelengths, the telescope has to remain at a very low temperature, which means shielding it from infrared radiation from the sun and Earth. For this reason, the JWST will not be placed in Earth orbit; instead, it will be in an orbit around the L2 Lagrange point, an area of gravitational stability roughly 1.5 million kilometers (940,000 miles) from Earth in the direction opposite the sun. There, a large heat shield will block both the sun and Earth from JWST's view, allowing the telescope to operate at the lowest temperature possible.

JWST is currently scheduled for launch in 2014.

http://upload.wikimedia.org/wikipedia/commons/2/28/Jwst_front_view.jpg

http://upload.wikimedia.org/wikipedia/commons/3/37/Jwst_back_view.jpg
Source(s):
http://www.jwst.nasa.gov/
http://en.wikipedia.org/wiki/James_Webb_Space_Telescope
http://hubble.nasa.gov/


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