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LSST Primary Mirror Build Begins with Spin CycleLarge Synoptic Survey Telescope to become operational by 2015 |
By Gabriel Gache, Science News Editor
8th of April 2008, 15:09 GMT
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When completed, the Large Synoptic Survey Telescope will have the ability of scanning the whole night sky every three days, thus keeping the track of asteroids that pass through the vicinity of Earth, observing supernova explosions and maybe even dark matter and dark energy. The observatory is due to be completed by 2015, at a cost of 400 million US dollars.
But you can't build a telescope without a mirror, can you? 24 tons of molten glass will be used to manufacture the 8.4-meter telescope, so that it would observe even the faintest starlight glow
to create images and share them amongst the scientific community around the world.
It starts with a spin
Aside of the 8.4 primary mirror, the LSST will also accommodate a secondary mirror right in the middle of the primary one, meaning that it will have to be much deeper than any of the previous primary mirror designs. It will have a thickness of a third of a meter towards the center, while the edges will measure one meter.
The building process began with the heating of the glass material at the University of Arizona's Steward Observatory Mirror Laboratory, turning it into molten glass with the consistency of heavy molasses. In order to give it the characteristic parabolic shape, the mold is spun, eliminating at the same time the extra 14 tons of rough material, which otherwise would be polished away.
The molten glass will then cool over a period of three month under the supervision of a computer controlled system, in order to remove the possibility of creating any stresses inside the glass.
Perfect finish
For now, the manufacturing process is going really well. "We'll only know for sure after it's down to room temperature. But everything looks very, very good; it's very unlikely that there will be a problem," says LSST Project Manager Don Sweeney.
So far, the mirror appears to be in good shape, according to LSST Project Manager Don Sweeney. With the mirror cooled, the final polishing stage may begin, as the mirror would have to be nearly exquisite and gather light perfectly. "That's quite a lot of testing there to make sure we get the curves right. The mirrors that we make now are way more difficult in testing than the Hubble mirror," said Sweeney.
Wide-field angle
Due to its unique design, incorporating a third mirror, the LSST will have a field of view about 40 times that of the apparent size of the Moon. However, very large pictures come with the wide-field angle. First of all, the LSST will need a digital camera with a focal plane at least 60 centimeters wide, with 10 micron pixels. Each nigh of investigation of the night sky will produce about 30 terabytes of information.
"Scientifically, it is the world's biggest database. You have to process all of that data as fast as it comes up, because if you get behind, you'll never catch up," said Sweeney.
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