Physics – Optics
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21346022s&link_type=abstract
American Astronomical Society, AAS Meeting #213, #460.22; Bulletin of the American Astronomical Society, Vol. 41, p.370
Physics
Optics
Scientific paper
The LSST uses a modified Paul-Baker 3-mirror optical design with 8.4-m primary, 3.4-m secondary and 5-m tertiary mirrors feeding a 3 element refractive corrector to produce a 3.5-degree diameter field of view over a 64-cm flat focal surface in 6 spectral bands with excellent image quality. The proximity of the primary and tertiary surfaces enables fabrication of both mirrors from a single substrate. This unique design, referred to as the M1M3 monolith, offers significant advantages in the reduction of degrees of freedom during operational alignment and improved structural stiffness for the otherwise annular primary surface. The convex secondary will be the largest of its kind. As with all large optical elements, both of the LSST mirrors have long procurement times. In order to meet the LSST's first light schedule for the fall of 2014 we have started the fabrication process on both mirrors using private funding. The M1M3 monolith is being fabricated at the Steward Observatory Mirror Lab using their structured borosilicate spin casting technology. The M1M3 was successfully cast over the summer of 2008. The mold refractory cleanout process and detailed inspections are underway in preparation for back side processing. The casting includes special design features to enable the mirror to operate under the increased loads caused by the high accelerations needed by the LSST. The secondary mirror substrate is being made using Corning's Ultra Low Expansion (ULE) process, resulting in an annular meniscus mirror 100mm thick and a 1.8m diameter central hole. Glass selection for the secondary mirror has begun and the substrate will be fused late in 2008. Both mirrors are on schedule and their early start has substantially reduced risk within the LSST project.
Topics:
LSST Optics
Mirrors
Gressler William
Hileman Ed
LSST Collaboration
Neill Duff
Sebag Jacques
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