Wednesday, January 7, 2009

Mirror Lab Activity - Jan 7th

With the holiday shutdown at the University of Arizona over and the new year begun, the Lab is again buzzing with activity. While grinding a big mirror project can seem interminably slow, there has been major progress in the mirror for the Large Synoptic Survey Telescope (LSST). When I last posted a few pictures and talked about the project, interestingly nearly exactly one month ago, the cast mirror was still having the mold removed with high-pressure water.

Today, the washout stand was in the last stages of removal. So the sound of impact wrenches, and steelwork being disassembled filled the air. After the mold was removed in mid-December, leaving the future mirror a lightweight honeycomb substrate, it was allowed to dry over the shutdown. Washout occurs, or more properly causes nearly 100% humidity in the enclosure, so slow drying over a couple weeks prevents any thermal shocks to the mirror.

A good percentage of the Mirror Lab activities are to prepare for the start of optical processing of LSST. First up as it moves into the polishing lab is backplate generating using diamond tools. Worked face down, over a quarter inch of glass will be machined off, then the back ground and polished to relieve stress. Here Kevin prepares plastic plugs to seal the backplate holes during the liquids of generator coolant and grinding/polishing slurry. I forgot what we were discussing at the moment, but here was a happy Mirror Lab employee!

Later in the day, after a hardhat was no longer needed in the casting lab, Pat and Delayne took pictures to go with the procedures being prepared, in this case, for hole-plugging. Most every process is having a procedure documented, so that the old semi-retired "salts" like me can pass along experience to the next generation of optical workers. The LSST mirror is our standard-size 8. 4 meter mirror, which will make it tied for the largest diameter single-piece glass telescope mirror in the world (with the Large Binocular Telescope and Giant Magellan Telescope segments). In these shots, you can see the backplate, and the holes leading to the hexagonal hollows that make the mirror "light". It will only weigh about 20 tons, about 1/4 the weight it would be if solid. It is hard to comprehend how large it is until you have a couple figures standing next to it for reference!

Here is an interesting-looking shot down one of the hex core hollows, towards the faceplate of core number D15 (you can see the core number written on the inside surface of the faceplate - originally scratched onto the core, then transferred onto the glass when it was molten).

Not all optics is "light work" (an inside optician's joke). Here the primary members of the casting crew (Jim, Phil, John and Damon - only supervisor Randy is missing) are working on shoveling out "the pit", the solids left over from mold cleanout and backplate glass grinding in the settling tank. Not only was it backbreaking work, but the smell was quite memorable as well!

With all this activity, there will be lots to update as generating starts up - Stay tuned!

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