You’re not supposed to be there!

I recently found a collection of very short stories, imitating Hemingway’s 6-word story about baby shoes. My favourites were:

– We kissed. She melted. Mop please!
– Computer, did we bring batteries? Computer?
– The baby’s blood type? Human, mostly.
– whirl. Help! Caught in a time –

Since then I’ve been thinking a lot in sets of 6-words or less. I know this sounds strange, but –

Well, ULTRASPEC was so nearly fixed. After my last post, we had the cryostat open again, as we tested some tiny fiddly cables for electrical shorting. This was incredibly tedious, as it meant checking each of the 30 cables with each of the other cables, twice. I felt like the worst operation theatre nurse ever – passing all manner of tools to my supervisor, and unable to keep my hands steady at the most important times. But we did find a problem! The ‘output gate’ cable was short circuit-ing with cable “B”. Oops. We replaced the entire set of cables, checked all the springs and screws and thermal contacts and put it all back together. This really was our last attempt, and we went home praying all would be well when we pumped and cooled it down after the weekend. Was it? Of course not.

This screw was almost ready to fall out! It must have caused the loss of thermal contact.

This screw was almost ready to fall out! It must have caused the loss of thermal contact.

Actually, it was almost completely perfect – all the electronics seemed to be working absolutely fine, without any weird streaks or patterns – hurray! But unfortunately the chip itself didn’t seem to be able to cool below 230K (-40°C), but it should have no problem cooling down to 150K (-120°C) with the help of liquid Nitrogen. So what was wrong? We’d broken the thermal contact between the LN2 canister and the aluminium plate which held the chip. Doh!

Last week I had three days out of the office on a first aid course, and whilst I was away my two supervisors took the cryostat apart, again (third time lucky?). They found a loose screw which was supposed to be pinning down a copper cable conducting heat away from the plate. After tightening this screw, and checking for any other potential problems, they closed up and we tried again to cool the detector. This time the chip cooled down as normal, and everything genuinely seemed to be working OK. Phewf!

Over the weekend I had to come in about ten times to run more dark current tests, but these are now finally finished, and thus a first draft of a first chapter of my thesis is more or less complete.

Ten weeks in, first milestone reached.

ULTRASPEC almost finished - connected more or less as it would be on the telescope.

ULTRASPEC almost finished – connected more or less as it would be on the telescope.

So yesterday we spent the entire afternoon setting up ULTRASPEC to the next level – bolting things together, attaching cables, and lifting heavy things around. This morning I turned it all on, and checked that everything was working. And it was! Everything seemed absolutely fine, except for a sort of shaded region on the left of the images. I figured this was this the out-of-focus shape of the bubble-wrap covering the filter wheel, and thought nothing of it. My supervisor however, knows better.

Dark regions on the left side - a shadow perhaps?

Dark regions on the left side – a shadow perhaps?

He found there was a spring sitting in the light path, on the inside of the lens! That means, inside the vacuum, and only millimeters away from the chip! It must have come loose and fallen into this space while we were moving it around and bolting it on to the frame. We were incredibly lucky it didn’t fall on to the chip itself – it probably would have ruined it, at a cost of more than £100,000…

Cheeky little spring, literally 'chilling' in the lightpath, in the vacuum on the other side of the lens.

Cheeky little spring, literally ‘chilling’ in the lightpath, in the vacuum on the other side of the lens.

You wouldn’t believe it if you couldn’t see it! This is the sort of goofy mistake that astronomy engineers will tell their grandchildren. Anyway, it looks like we’ll need to open up again tomorrow, to fish out the spring. I really hope that’s the last of our problems. Each one has been more and more menial and frustrating, and I can’t think of anything more so than this one! With the meeting in Paris next week I’ve got plenty other things to worry about for the time being.

Come on man, let’s do science!

Nothing much else to report, except that keeping track of these local peregrine falcons as they prepare for their first flights is probably a major factor in keeping me sane. That and my imminent, inevitable breakdown. Woo!

If in doubt, eat ice-cream.

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