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Sitelle – Here at Last

Posted by Tom Benedict on 08/07/2015

A little over four years ago I posted a rendering to Flickr.

Cryogenic Detector Internals

I’d been tasked with designing and building new internals for a pair of matched cameras. The rendering was what I thought would be the final design of these parts. I try to save my Flickr stream for photos, but it was an important milestone in my professional life. It was also visual, aesthetically pleasing, and geeky, so I figured it was fair game.

I was wrong, of course. Shortly after posting that rendering I was told we couldn’t use the cryostats I’d design these to fit into, so I had to design two entire cameras. I kept most of the internals the same, but the outer part was completely new. Over the course of several months the rest of the camera design took shape.

Sitelle Camera September, 2012

We held a final design review, I got the go-ahead to start cutting metal, and a few months after that we had our first prototype camera.

Sitelle Camera Pumping

Early in the project we decided to build three cameras. The first was the prototype. The other two were the final cameras. This let work continue on the prototype as the final cameras were manufactured and finished. As each part of the prototype camera tested out ok, we made those parts for the final pair of cameras.

Sitelle Parts

Once we had complete sets of parts, they all went off to be anodized. Marc, the guy designing and building the electronics for the cameras, liked gold. So gold they became.

CFHT Sitelle Parts Anodized

Since it’s a porous surface, anodizing doesn’t work well in vacuum. So the insides of the camera bodies were machined clean and polished. The internal components were never anodized at all.

CFHT Sitelle Camera Assembly

Two internal components went through a number of revisions along the way: the cold strap and the getter – the cryosorb pump that maintains vacuum while the cameras are in use. We went through a number of designs for each of these. The first generation is shown above. We went through two more before we finalized the design for the getters, and almost that many cold strap designs. In addition to the box of unused getters and cold strap assemblies we now have in our clean room, we eventually wound up with two fully functioning cameras.

Two For Sitelle

We boxed the cameras up and shipped them off to Quebec for integration with the rest of the instrument. We had a number of issues that still needed to be addressed, the largest of which was that the hermetic space-rated connectors we used for the feed-throughs leaked once they were potted. We’re still dealing with this, though we’ve got what I hope is a real solution for the next generation of feed-throughs.

The cameras lived in Quebec for almost two years. A little over a month ago the team building Sitelle bid it farewell, loaded it into an airplane, and shipped it to Hawaii. After several weeks of unpacking, re-assembly, and testing, we finally put Sitelle on the telescope.

One Instrument - Two Cameras

And there at the end of each beam of the instrument is one of the cameras Marc and I built, beginning with that early design of the internals a little over four years ago. Designing and building the cameras was an exciting, if exhausting, process. But seeing them installed as part of a new instrument is indescribable.

Home At Last

As one might guess, I did a bunch of photography of the installation for first light. Toward the end, after balancing, after checkout, while we were testing the long instrument limits on the telescope, Marc and a number of other people involved in the project stood, watching the clearance between the instrument and the south bearing. I was struck how similar it was to the final scene of Ocean’s Eleven. I had to smile as I tripped the shutter. It seemed a fitting end to a wonderful caper.

Sitelle's Eleven

And the beginning of an even better one. Sitelle had a successful first light last night. Marc and the rest of the team are taking it through its commissioning tests, which will take several more nights. After that it will be unleashed on the sky, taking four million spectra at a time.

I can’t wait!

– Tom

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