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LSST Gets Real

Loading and evenly spreading 51,900 pounds of glass into a gigantic rotating furnace—by hand—marked the initial steps in the mirror fabrication process for the world’s most powerful survey telescope, the Large Synoptic Survey Telescope (LSST). The process, performed by workers at the Steward Observatory Mirror Laboratory (SOML) in Tucson, Arizona, is not simple by any means; the mirror fabrication will take five years from start to finish.

Private donations in the neighborhood of $40 million enabled the mirror fabrication as well as research and development of other key components.

"We've been the recipient of generous private funding," said Steve Kahn, Director of Particle Physics and Astrophysics at SLAC and LSST deputy director. "Seeing this project move forward has been exciting."

For three days, chunks of glass were spun and gradually heated in a large rotating furnace on top of customized ceramic hexagonal inserts. The inserts, which will account for mirrors' final honeycomb texture, filled with glass as it began to melt at about 900 degrees Fahrenheit. Spinning the 39-foot-diamter apparatus seven times a minute caused centrifugal force to pull molten material outward, resulting in a crescent shape—close to the final desired curve—along the glass's surface.

In the process, the temperature topped out at 2,150 degrees Fahrenheit. This so-called "high fire" event occurred a few weeks ago. Over the next months, the carefully monitored cooling process will take place before the combined 85,000 pounds of glass and 1,650 ceramic inserts are extracted and flipped over so the inserts can be separated from the mirror—along with 16,000 pounds of glass—during the final stages of fabrication.

Workers at SOML are not the only ones with their hands full. The Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) is leading the research and development of the telescope's six-foot tall, 3.2 billion-pixel camera detector. The detector, which is the largest of its kind, will enable scientists worldwide to see an enormous portion of the night sky.

The LSST collaboration has started to receive bids from companies interested in building the main sensors of the camera. Researchers are also exploring the sensor configuration and bandwidth filters for the telescope's broad spectral range, which will sweep the night sky from the limits of visual light to infrared.

The LSST is scheduled to be built on Cerro Pachón, an 8,800-foot Chilean peak in the Andes Mountains, in 2011 and is expected to begin operations in 2014 or 2015.

Matt Cunningham, SLAC Today, April 16, 2008

Above image: Workers at the University of Arizona Steward Observatory Mirror Laboratory load the glass that will become the primary and tertiary mirrors of the LSST.