Keck Observatory Secondary Mirror

831B1F04-F304-BCC9-FCCE47D4B8C825CCWith a primary mirror of some 10 meters diameter, the Keck Observatory houses the largest telescope on earth.  The secondary mirror, positioned some 17.5 meters from the primary, was fabricated with beryllium by Brush Wellman, and machined by Axsys (Speed Ring), and optically figured on the LODTM at Lawrence Livermore Labs.  After rehearsing on an aluminum “pathfinder” blank, Epner Technology coated the actual beryllium mirror with 0.5 microns Laser Gold.

After some three years of deep space IR research in the Keck Observatory, ETI was asked to coat two more mirrors for the Keck II Observatory; an f25 and f40 aperture.

On one of his inspection trips to the summit, David Epner had the unique experience of observing a replacement of one of the hexagonal sectors in the primary mirror.  The whole operation seemed similar to a NASA docking.  And the trip was further enhanced by a view of the coating room, which displayed some mirrors that were waiting for coating and others that had their coating on them.

While exhibiting at the Kona Hawaii SPIE meeting of the worlds astronomers in 1998, David Epner was offered a VIP tour of the Keck I Observatory.  He was dismayed to see “his” mirror covered with condensate residue.  He was told by the technicians touching the gold surface was forbidden.  Epner replied, “The whole purpose of using Laser Gold was because it could be cleaned.”  Only after offering to re-coat the mirror at no charge if damaged by cleaning did the young technician agree to wipe down the mirror with alcohol, acetone or just detergent and DI water.

W.M. Keck Observatory Homepage