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William Atkins
Saturday, 10 February 2007 01:17
The Webb primary mirror will be 2.5 times larger than the Hubble mirror, although the overall mass of the Webb observatory is about one-half of Hubble’s mass.
While the Hubble mirror was made in one piece, the Webb mirror—a beryllium Cassegrain-style reflector—consists of 18 different hexagonal-shaped parts. The more complex design will allow the mirror to be folded up while being launched on a European Ariane 5 expendable rocket from Kourou, French Guiana, in 2013.
A Cassegrain reflecting mirror generally consists of two mirrors—a primary concave mirror and a secondary convex mirror that are both aligned symmetrically about their shared optical axis.
When unfolded after launch, the Webb mirror will be 6.6 meters (22 feet) in diameter—as opposed to the 2.4-meter (7.9-foot) diameter of the Hubble mirror. Upon beginning its operations from its stationary position 1.5 million kilometers (0.9 million miles) from the Earth, the 18 parts of the mirror will be individually moved by ground controllers with the use of micro-motors and a wave-front sensor to precisely align the mirror to maximize its performance. Although the mirrors can be moved after this initial alignment, it is not expected to be changed after this first calibration. At this point from the Earth—what is called the Lagrange point 2 (L2)—the telescope will remain stationary in an orbital configuration where it will be balanced between the Sun’s gravitational field and the Earth’s gravitational field. The Sun and the Earth are approximately 150 million kilometers (93 million miles) from each other.
The Webb Space Telescope, formerly called the Next Generation Space Telescope, will be operated by NASA (National Aeronautics and Space Administration), along with ESA (European Space Agency) and CSA (Canadian Space Agency). The increased size and accuracy of the Webb mirror will allow it to observe deeper into the universe than any other previous telescope—whether on the ground or in space. It will glean this information within the infrared (IR) region of the electromagnetic spectrum—primarily between 0.6 and 28 micrometers (mm) in wavelength.
Its intended launch will occur no earlier than June 2013. After an approximate six-month test period, the Webb will begin its minimum of five-year mission of exploring the universe. Its primary mission is to search for stars and galaxies that were formed in the early universe; to study the resulting formation and evolution of all types of galaxies; to analyze the formation of all types of stars and planetary systems, and to collect data on the origins of life, primarily from planetary systems.
The principal optical manufacturer is Ball Aerospace and Technologies Corporation (commonly called Ball Aerospace), a subcontractor for the prime Webb Telescope contractor Northrop Grumman Space Technology, which is managed by a federal contract from the NASA Goddard Space Flight Center, in Greenbelt, Maryland.
The home NASA Web page for the James Webb Space Telescope is: http://www.jwst.nasa.gov/.
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