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Engineering – From CAD to Camera

Posted by Tom Benedict on 26/09/2012

It’s a good week for projects coming together. First I had the successful flight of my new panoramic KAP rig. Today I closed our prototype camera for the first time and put it on the vacuum pump.

The last time I wrote about this project the picture I posted was a CAD rendering of the camera design as it stood that day.

Sitelle Camera September, 2012

This time I can actually show off the camera!

Sitelle Camera Pumping

Some parts are missing in this photo – namely the cryo cooler isolators and hose support, and the pre-amplifier box. Those parts are done, mind you. They’re just not installed because they’re not part of this test. Except for some of the internals, the cameras are just about complete. (And yes, those internals are what I’m working on now. More pictures and stories to come!)

This photo also represents a new idea we’re trying with this instrument: a prototype. Normally everything we build is a prototype because we only ever build one of them. This instrument calls for two cameras. In the old way of doing things we’d build precisely that: two cameras. This time we decided to build three. It came down to timing: building three was faster.

Yeah… that requires some explanation.

In almost every way these cameras are a new approach to a problem. It’s a detector we’ve never worked with before. We’re using a new pre-amplifier design. None of our existing cameras fit in the space we had available, so the form-factor is a new design. It’s the first camera we’ve designed around the Polycold PCC cryocooler rather than retrofitting at a later date. And it’s our first instrument to use this kind of vibration damping on the cryocooler. Because of some space constraints even the cold strap and cold foot are new. Any time you have even one new thing in an instrument, it pays to test test test. But testing takes time. Finding out your initial design didn’t work takes even longer.

Early on we realized having a prototype camera we could hack on would let us test each idea as it was integrated while still allowing development on the two production cameras to proceed. Lessons learned could be rolled into the final design as we went. It also let us do time-intensive tasks – like anodizing all the parts for the production cameras – while development and testing work was still being done.

As a result the anodizing is happening at the same time the electronics development is being done. All of that is being done in parallel with testing of the cryocooler and cold strap. And that is being done in parallel with the machining of the camera internals. No one task has to wait for any other. As a result, the cameras are being developed in much less time than it would have taken if we’d only built two. See? Building three was faster!

To add icing to the cake, the camera pumped down fine the first time. It has no leaks (a first for me on a first-pump!) a nice fast pump rate, and at just under 10kg fully built, it’s easy to handle. If the rest of the project goes as smoothly as this, I might actually get to take some time off to fly a kite at some point. I can only hope.

– Tom

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