Celestial mechanics


Yesterday my new friends Holly and Dan took me (along with Dan’s family) to see the Discovery Channel Telescope, which is part of the Lowell Observatory. Or rather they took us to see the building the telescope will eventually be housed in, which is more interesting than you might think, given how huge and heavy the telescope is, and how vibrationally and thermally stable it has to be. Dan’s a software engineer, responsible for all the embedded systems that manage the huge shutter doors, rotating turret, etc., etc. I do embedded code myself, sometimes, and get nervous enough hitting RUN the first time a robot limb controller or whatever goes live. Imagine the tension the first time you let a little microcontroller loose on umpteen tons of precision steel!

The building reminds me of a Dutch windmill with no sails

The building reminds me of a Dutch windmill with no sails

The telescope is sited deep in the beautiful Coconino Forest, southeast of Flagstaff. The mirror is still awaiting polishing in Tucson, but eventually it will be stuffed into a padded envelope and mailed by UPS to the site, ready for silvering. Here’s a photo of the on-site vacuum chamber where it will be resilvered every two years. The bottom part will hold the mirror and slides out on tracks, from where it will be wheeled to the telescope. Rather them than me – I can’t be trusted with glass. “Down a bit. Left a bit… no hang on, I meant right, sorry… ooh…”

Holly and Dan in front of the vacuum chamber

Holly and Dan in front of the vacuum chamber

The mirror itself is 4.2 metres in diameter, and the telescope configuration has multiple focuses for both wide-field and high magnification use. According to my calculations it will gather more than 1700 times as much light as the little 4″ reflector I used to have! Dan says it’s optically perfect to within one wavelength across its diameter, and the silvering averages three atoms thick! Under and around the mirror are hundreds of pistons that keep it in shape (adjusted at 20Hz) as the glass tries to sag under its own weight when the telescope tilts and tracks.

Middle floor - where the telescope base will be

Middle floor - where the telescope base will be

The observatory building is on three levels and the base of the central mount is a massive concrete pillar and concrete cylinder, which have been aligned with the Earth’s radius by geostationary satellite. Everything’s carefully designed to minimise vibration and avoid temperature fluctuations across the metalwork.

Upper floor, facing the main shutters

Upper floor, facing the main shutters

The entire telescope and upper section rotates on these hefty rollers, with pressurised oil bearings.

Inch-thick steel track lying on one of the turret bearings

Inch-thick steel track lying on one of the turret bearings

It won’t be finished for at least another year, but it was fascinating to see it under construction. On the way back we went to Sedona and hit things just right for a perfect sunset. Then Dan and Holly kindly treated me to dinner. Climbing back up Oak Creek Canyon the stars were, of course, stunningly bright, Can’t wait to see them up close! Fascinating. Thanks guys!

Sedona 500


About stevegrand
I'm an independent AI and artificial life researcher, interested in oodles and oodles of things but especially the brain. And chocolate. I like chocolate too.

7 Responses to Celestial mechanics

  1. spleeness says:

    I love that you included so many details! I’m linking to your blog post from mine. Your pictures came out beautifully!

  2. When the project started, the dome was supposed to be a graceful sphere. After numerous budget cutbacks and redesigns it now looks like Liberace’s battleship turret but without a gun.

  3. Hi Steve,

    Nice article. 🙂

    I’m confused on how this telescope gathers light. Does part of the roof roll away or are the shutters on the main floor utilized in some way?

    • stevegrand says:

      Hey Richard,

      Those two big white shutters in the middle of the photo are essentially in the roof – i.e. the part that rotates, and they’re HUGE. In the photo you mostly see the vertical part of them, but if you look towards the top you can see that they also lie back at about 45 degrees and go up to the top of the roof. The photo is misleading because it’s so wide-angle that they look tiny in the distance. But they’re amply wide and tall to give a 4.2m mirror access to about 90 degrees of sky. The other, dark grey “blinds” are there to equalize the temperature across the telescope, I think.

  4. LOL,now I get it. I thought the gray “blinds” were the shutters as I didn’t notice the main white shutters in the center extending to the peak. Gathering light through the blinds would have been an interesting feat of magic. 🙂

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