The Steward Observatory Mirror Laboratory has completed the rough abrasive grinding of the 8.4-meter LSST M1/M3 mirror back surface (left). Technician Leslie Utley (right) carefully inspects the back surface of the monolithic mirror blank for imperfections. The back surface will undergo polishing over the next several weeks. Support hardware will then be bonded to the back surface and the mirror carefully turned so optical polishing of the front surface can begin later this year. PDF

Quality Assurance 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.

The LSST 8.4-meter mirror blank executed a couple of carefully choreographed turns and now rests horizontally in the large optical grinding area of the Steward Observatory Mirror Lab. Since October, when the mirror was lifted from the furnace hearth and installed vertically in the red handling ring, 16,000 kg of ceramic core material have been removed from the honeycomb structure. On the morning of January 13th, the 8.4-meter M1/M3 blank was moved forward, rotated vertically, moved back, and then carefully tilted so the back plate is now facing up; the face plate (with bonding pads still attached) lies on the underside of the horizontal glass monolith. In the large optics polishing area of the lab, the back plate and edges of the mirror blank will be ground down and polished in preparation for the next step - installation of load spreaders to the back plate. The mirror blank will then be placed in the polishing cell (with the face-plate up) before the multi-year polishing of the optical surface begins. The mirror is scheduled to be completed in January 2012, and will be the largest two-surface optical mirror ever made from a single substrate.

Today the perfectly cast 8.4-meter LSST primary/tertiary mirror blank was successfully lifted from the furnace hearth, put into the turning ring and tilted to the vertical position. The finished light weighted mirror will be 16,600 kg with the thickest outside edge (height of 0.92 meters) ever made at the UA Steward Observatory Mirror Lab. Once completed, this will be the largest two surface optical mirror made from one substrate in the world. The mirror is scheduled to be completed in January 2012.