LSST E-News |
LSST Secondary Mirror Substrate Fused
Bill Gressler
Technician Brian Todd unveils the LSST secondary (M2) mirror substrate recently fused at Corning's Canton, NY facility. After inspection and removal from the furnace, Corning will grind the 3.5-meter annulus and then return it to the oven for a controlled melt which helps define the final shape of the 100mm (3.9-inch) thick meniscus substrate. Delivery to the LSST Project is planned by the end of 2009.
Progress continues on fabrication of the LSST Secondary Mirror (M2) Substrate at Corning’s Canton, New York facility. Corning machined eight boules of ULE®, selected for coefficient of thermal expansion homogeneity and quality, into petal shapes and positioned in an annular arrangement inside Corning’s 8-meter furnace. The furnace’s burners ignited on March 9, 2009 starting off a gradual ramping of glass temperature to reach high temperature fusion seal firing (1800°C) on March 13th. At high temperature, the separate petal pieces fused together to create a contiguous substrate. The temperature was then stabilized around the annealing temperature (1000°C) before the controlled cool down cycle, which ended on March 15th.
After inspection workers will lift the substrate off the furnace. They will determine critical zone placement and will grind the mirror to oversize plano/plano in shape. Corning will then return the mirror to the furnace a second time where it will sit atop a convex contoured sag form. The mirror temperature will be elevated to 1500°C to enable the mirror to slump over the form to define its nominal 100 mm (3.9 inches) thick meniscus shape. Technicians will then generate the concave back and convex front surfaces and finally provide an acid etching to enable mirror support attachment, reduce residual stresses, and increase overall substrate integrity. Corning will deliver the M2 substrate to the LSST Project by the end of 2009.
LSST is a public-private partnership. Funding for design and development activity comes from the National Science Foundation, private donations, grants to universities, and in-kind support at Department of Energy laboratories and other LSSTC Institutional Members:
Brookhaven National Laboratory; California Institute of Technology; Carnegie Mellon University; Columbia University; Google, Inc.; Harvard-Smithsonian Center for Astrophysics; Johns Hopkins University; Kavli Institute for Particle Astrophysics and Cosmology - Stanford University; Las Cumbres Observatory Global Telescope Network, Inc.; Lawrence Livermore National Laboratory; National Optical Astronomy Observatory; Princeton University; Purdue University; Research Corporation for Science Advancement; Rutgers University; SLAC National Accelerator Laboratory; The Pennsylvania State University; The University of Arizona; University of California at Davis; University of California at Irvine; University of Illinois at Urbana-Champaign; University of Pennsylvania; University of Pittsburgh; University of Washington; Vanderbilt University
LSST E-News is a free email publication of the Large Synoptic Survey Telescope Project. It is for informational purposes only, and the information is subject to change without notice.
Subscribe | Unsubscribe
Copyright © 2009 LSST Corp., Tucson, AZ • www.lsst.org