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The Giant Magellan Telescope

Back in Feb of 2015 my wife, Robyn, and I got to go take a private tour of the building of the mirrors for the Giant Magellan Telescope, known as the GMT at the University of Arizona. I know a couple of the engineers involved with it through the Minibuggy.net forum. I've met a lot of really fascinating people there.

Gonna cheat a bit and plagiarize from wikipedia:
The telescope will use seven of the world's largest mirrors as primary mirror segments, each 8.417 m (27.61 ft) in diameter. These segments will then be arranged with one mirror in the center and the other six arranged symmetrically around it.

We got to see two of the mirrors in process.

This is where the mirrors are made. This entire structure spins. As I recall, the outside edge had a speed close to 25 mph. (don't hold me to that number, I was there years ago...)

Once out of the centrifugal casting oven they have to turn the mirror over. It's held inside a giant cage and flipped. We're standing beside it for size reference.

Bad shot of the structure that's on the back side of the frame.

Getting ready for polishing. My friend Bruce's wife, Lenslie was in charge of this. (I nicknamed her Lenslie, as her name is actually Leslie and it seemed fitting.)

Another shot of the polishing setup.

This is a measuring tower. It actually floats on air bearings. The accuracy of this is just insane. It measures in millionths of an inch

They were packing one of the mirrors to send off to Chile while we were there.

One of the fascinating aspects of the mirrors is that they have to be hollow otherwise the weight of the glass would warp it. To do this they made a sort of honey-comb patterned hollow sections. Each section is EXACTLY the same volume, although not the same shape.

Each one of the hollow sections is then pressurized while the grinding and polishing is done to the other side. This pressurization eliminates any stress and/or flex that would be introduced during the finishing process.

This ensures that these giant mirrors are PERFECTLY flat when done.

Thank you Bruce and Lenslie for the tour!