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LSST E-News

LSST E-News

October 2009  •  Volume 2 Number 3  •  Archive

Mirror News

More than a year ago the LSST Primary/Tertiary (M1/M3) monolithic mirror blank emerged from the oven at the Steward Observatory Mirror Lab (SOML). Since that time the honeycomb structure has been cleaned out and moved into the large polishing area of the lab where the back surface has undergone months of loose abrasive grinding and then polishing, a process which finished up in early September. Over the next few months, hardware will be installed on the backside of the mirror blank in preparation for turning the blank over and placing it in the polishing cell for another two years of front surface grinding and optical polishing. As we follow this construction path, we gain an appreciation for mirror production as the longest lead time item in building the LSST. It really is a lot of work “just” to prepare a piece of glass to hold a few ounces of aluminum! Of course the hardware that holds the mirror is critical as well, and work on this important element began in earnest this past month. Senior Optical Engineer Bill Gressler describes work underway now in the LSST Mirror Support Hardware Lab.

LSST engineer Joe DeVries sets the air pressure on the pneumatic actuator test stand.

While the LSST M1/M3 mirror blank enters the final 2-year stage of front surface grinding and optical polishing at SOML, a parallel hardware engineering effort has begun at the Telescope and Site office at NOAO. There, the LSST Mirror Support Hardware Lab enables performance and environmental testing to assist with prototyping and final design selection of the M1/M3 support components. LSST plans to design, fabricate, assemble, and deliver qualified subassemblies for integration of the M1/M3 and telescope cell in early 2012.

The M1/M3 support system provides positioning of the mirror and surface figure control to remove bending modes and figure errors due to gravity and thermal fluctuations. Support forces are safely distributed through the mirror via 156 loadspreaders and 6 hardpoint wedges bonded onto the flat backplate. The M1/M3 support system consists of 6 hardpoint actuators that define the mirror’s position within the telescope and 156 axial support actuators. There are 52 single axis and 104 dual axis actuators, to total 260 axial actuators.

The baseline LSST axial actuator design is a pneumatic system incorporating successful features from LBT and Magellan. Specific tests of the cylinder types, valve control units, and load cells can be performed in the lab via a data recording test stand. Cylinder response (force vs. psi), resolution, repeatability, stiffness, and frequency response can all be charted for analysis. The stringent cadence requirements of the LSST (5 second slew and settle for an adjacent field move) mandate quick temporal response with minimal hysteresis and stiction. An alternate electro-mechanical approach based upon proven SOAR hardware will also be investigated.

The system development plan allows for analysis and comparison of competing designs to permit final component selection by mid 2010. This schedule enables fabrication and delivery of a mirror cell and support components for integration with the completed M1/M3 mirror, which is slated for delivery to LSST in early 2012.

Bill Gressler and Suzanne Jacoby 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; Columbia University; Drexel 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; 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 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 Team:

  • Suzanne Jacoby (Editor-in-Chief)
  • Anna Spitz (Writer at Large)
  • Mark Newhouse (Design & Production: Web)
  • Emily Acosta (Design & Production: PDF/Print)
  • Sidney Wolff (Editorial Consultant)
  • Additional contributors as noted

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.

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Copyright © 2009 LSST Corp., Tucson, AZ • www.lsst.org

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