Thursday, January 15, 2009

More Mirror Lab Activity

A few more images of the Steward Observatory Mirror Lab where we are making the biggest telescope mirrors in the world. The other day the casting crew moved the LSST(Large Synoptic Survey Telescope) primary from it's vertical position (horizon-pointing during mold clean out) to horizontal (nadir-pointing) in preparation for transport to the polishing lab next door. So while it looks like a new volleyball court, it is the rear surface of our newest mirror project!

I mentioned the other day that the holes in the back plate are a by-product of the casting process. The mirror is cast into a mold, the hexagonal structure of which is anchored with cylinders of refractory. When the mold material and refractory is removed from the glass interior, a cylindrical hole remains in the back plate. These honeycomb hollows give the mirror substrate it's stiffness, and also is responsible for the mirror to be only a fourth of the weight if it were a solid mirror. Temperature-controlled air can also be blown into the mirror while it is in the telescope to actively control the mirror temperature, tracking the nighttime air temperature to minimize thermal distortions of the incoming light.

So while the back plate holes are a necessary part of the process, they are currently a nuisance for the generating, grinding and polishing of the back plate. So we are currently working on plugging all 1600 holes to keep the interior of the mirror from being flooded or contaminated. The red plastic plugs fit snugly into the holes. The next step will be to fill the plugs with a blue castable modeling RTV that will provide a waterproof seal, yet will be easily removable without leaving any traces.

The polishing crew has a lot of work in the next few weeks as diamond generating starts. From left here is Jordan, Kevin, Pat and Kirk. With me added in, nearly 45 years of experience in mechanics and optics. And don't forget that there are other fabrication tasks going on at the moment. Stay tuned and you will see!

1 comment:

Andrew Cooper said...

Thanks for the update! Glad to see this unique facility is not idle after the completion of the LBT mirrors.