Tuesday, July 14, 2009

Meanwhile, Back in Tucson...

I was on the road all day today - but made it the 650 miles to Oklahoma City in about 11 hours. A little warmer down here - 70s in Iowa, about 100 here in Oklahoma! That leaves about 210 miles for tomorrow morning. Melinda flies into Dallas tomorrow evening for the last leg across Texas.

Meanwhile, I've not posted about the Mirror Lab in a long time. No, I'm not thinking too much about work, but they did call me while I was driving today to get my opinion on something. And I've got these pictures from June 23rd, the day before leaving Tucson that I never posted, so it makes for an easy blog entry!

There are three main projects in which Steward Observatory Mirror Lab is heavily involved. I've posted about the LSST and SPM Telescopes recently, but there has been lots of progress lately, so will update those as well. In this uppermost shot of the Polishing Lab, you can see both the GMT mirror at left, and the LSST mirror across the room.

Mostly I've been helping out on the LSST (Large Synoptic Survey Telescope) finishing the backplate generating and edging this Spring, but now we are using a 2 meter diameter grinding tool to get through the loose abrasive grinding and polishing to fully stress-relieve the backplate. We had just started the grinding on the flat rear of the mirror. As shown in earlier posts, the backplate has a hole over each core that is temporarily plugged to keep the mirror interior clean. You can see a PVC arm holding an array of brushes that sweep up the grit out of the holes to recycle the abrasive grit. Leslie is rinsing off the edge of the 8.4 meter diameter mirror.

Across the room, the GMT (Giant Magellan Telescope) has just started the polishing process on the front surface. I've not posted about GMT since my earliest Mirror Lab post last winter, and really need to describe it in more detail. It has a complicated surface figure - unlike most mirrors that are parabolic, or just rotationally symmetric for that matter, this mirror, designed to be mounted in the telescope with 6 other 8.4 meter mirrors is actually an off-axis parabola, the largest one in the world that has ever been attempted by far. Here Bill keeps an eye on the Stressed Lap Polisher - which changes to the ideal mirror shape, as the operation continues. As the mirror surface becomes more polished, we can start optical testing, but the testing is complicated by the off-axis shape.

The first part of the test setup, is a 4 meter "Foldsphere" now permanently mounted in the top of our new test tower. The Foldsphere was the last mirror I finished before "retiring" over a year ago, and in the interim, it has been aluminized and lifted to the highest point in the lab. Note that the image of my Canon camera pointed into the test tower is reversed in the mirror. My camera is very near the center of curvature of the concave sphere, so is magnified greatly. The center of curvature is also where an interferometer will be permanently mounted to monitor the shape of the Foldsphere during GMT testing. The main interferometer test of the GMT will bounce off this Foldsphere and will contribute the majority of the aspheric correction of the GMT mirror. Will include some diagrams and further discussion at a later point!

Also since my last post, the casting crew has finished the mold for the 6.5 meter diameter San Pedro Martir Telescope. They really worked hard and finished mold construction in a record 4 or 5 weeks (I lost count). In this image from 23 June, Damon and Phil were using the dust collection system, and dowel rods to plug the rib gaps of the mold to generate enough air flow through the backplate gap to vacuum up dust and contaminants. While I've been gone, they have started a mold prefire to "set" the mold. After cooling and another inspection, the mold will be ready for glass loading and a mirror casting in early Fall. You are now as up to date as I am!

1 comment:

Anonymous said...

Nice work keep it up. I am working on large optics. like to have interactions.