Tuesday, December 9, 2008

Large Synoptic Survey Telescope (LSST)

I know there has been a lot of astronomy postings lately, but with the return to Tucson a month ago and my being back to work at the Mirror Lab, they seem to come more naturally than "normal" posts!

Anyway, the Tucson Amateur Astronomy Association had their monthly meeting last Friday, and the invited speaker was Victor Krabbendam, project manager for the LSST telescope and site. It was a great talk - I love the technical side of projects and Victor did a good job of explaining the details as finely as you wanted them!

This is a really cool project! I invite you to go to their home page and check out the specs. In short, they are building a 3 mirror wide-field 8.4 meter diameter telescope (Hmmm, wonder who is making that for them?), combined with a 3.2 GIGApixel (!) camera 64cm diameter providing a 3.5 degree field of view (about 7 widths of the full moon), it reaches 24th magnitude in a 15 second exposure! The camera, weighing nearly a ton and a half (including corrective lenses) will generate a peak data flow of 3 Gbytes/second, totalling an estimated 20-30 Tbytes of data per night. The plan is to cover the entire sky in 3 nights, each field being imaged twice over some interval, looking for things that move or vary in brightness. It is expected to generate 100,000 alerts/night of things that change!

This telescope is different in that there are no astronomers per se - all data is made public as soon as it is taken. Most people do not know that Hubble data, for instance, is the property of the astronomer for 6 months to a year before release to public domain. You can sit at your home computer, watching the data streaming out. Or you can subscribe to whatever alerts you would like to see (asteroids, variable stars, ???) and be the first to see the images after the computer. Interestingly, Victor was saying that in the early part of the evening the data will be close to "live", but even with supercomputers and fiber cables connecting the United States to South America (Observatory will be in Chile), it won't keep up to the data flow, needing about 24 hours per night of data reduction.

The telescope mirror, made by the Mirror Lab in Tucson (Yea!) will be the first large mirror that will have 2 curvatures on the primary (the primary curvature, plus the R3 tertiary surface as well). It should be a challenging project, particularly with the strong aspheric of the tertiary surface...

The mirror, in fact, has been under construction for some time. The mold for the lightweight primary was constructed the end of 2007 (you can see the two curvatures in the cores here), finished in January, and the glass loaded in March for the 29 March casting. The oven was opened in July, and as of today, the mold material is being removed using high-pressure water similar to that of a carwash. The fellows that do that job wear wetsuits in the 100% humidity and forced-air respirators to minimize inhalation of the refractory material. That task will be finished tomorrow, and after a final rinse and allowing it to dry out over the Christmas break, it will be inspected in January and delivered to the polishing lab the end of January, 2009 to start work on the backplate.

So I'll get a chance to get my hands on it early in '09 when the casting crew finishes up. Melinda and I are only here to 1 May or so, and it seems realistic to finish diamond generating and get into the grinding and perhaps polishing before then. In any case, with LSST and GMT going strong, it will be a busy winter and spring!


Tuguldur said...

thanks for posting! very informative.

but the secondary is 5m in diameter blocking lots of light, so would that mean the actual collecting area of this scope is similar to of 6.8m mirror?

Dean said...

With light baffles too, I've heard 6.5 meter equivalent, but at F/1.2 still collects a LOT of light!

Tuguldur said...

I can imagine. at this much of aperture, f/1.2 is just lightning fast piece of rig.