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January 2010  •  Volume 2 Number 4

LSST’s M1/M3 Mirror Set for Generation and Polishing

The steeply curved M1/M3 surface is prepared for polishing. Dec. 17, 2009

Steward Observatory’s Mirror Lab (SOML) team performed the LSST primary/tertiary (M1/M3) mirror’s final rotation and integration with its polishing cell in November, and has since moved the 8.4-meter mirror to the Large Optical Generator to begin generation and polishing of the M1/M3 surfaces. SOML technicians will remove an excess of 234-mm of glass over the M3 surface—equal to 2.3 cubic meters or 11,000 pounds of material—using fixed abrasive wheels and then ever more delicate loose abrasive polishing with stress lap tools until they produce the specified mirror figure.

This rotation is the culmination of eleven months of painstaking work. Since January 2009 when initial rear surface processing began, the SOML team of technicians, engineers and scientists has performed a sequence of well-defined steps. They centered the outer and inner diameters around the cast core geometry and finished it to specs. They polished the 25-mm thick back plate with additional core hole polishing at 24 hardpoint locations to increase load capacity. The team attached six hardpoint wedges to allow mirror positioning and interface with the cell. They assembled and bonded loadspreaders to the backplate to support and distribute bending forces safely throughout the mirror. And they bonded 146 precision theromocouples to the mirror front, back and mid-plane locations to guide polishing and on-telescope thermal control.

For the next two years, SOML staff will generate and polish, test and measure, refine and perfect. Updates will keep us informed until the M1/M3 surfaces are complete—scheduled for January 2012.

Bill Gressler contributed to this article.


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; Chile; Cornell University; Drexel University; Google Inc.; Harvard-Smithsonian Center for Astrophysics; Institut de Physique Nucléaire et de Physique des Particules (IN2P3); Johns Hopkins University; Kavli Institute for Particle Astrophysics and Cosmology at Stanford University; Las Cumbres Observatory Global Telescope Network, Inc.; Lawrence Livermore National Laboratory; Los Alamos National Laboratory; National Optical Astronomy Observatory; Princeton University; Purdue University; Research Corporation for Science Advancement; Rutgers University; SLAC National Accelerator Laboratory; Space Telescope Science Institute; The Pennsylvania State University; The University of Arizona; University of California, Davis; University of California, Irvine; University of Illinois at Urbana-Champaign; University of Pennsylvania; University of Pittsburgh; University of Washington; Vanderbilt University

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