Spring cleaning

The pre-dawn start this morning wasn't a welcome one. A call from the telescope in the very early hours woke me up and as usual I had trouble getting back to sleep and I find three or four hours sleep insufficient for a day at the summit, but that's the job...

Although I was on the mountain for another reason, today was cleaning day. Major observatories need to keep their telescope optics clean, in our case, being an infrared telescope, to reduce the emission from dust particles on the telescope mirror and the instrument's optics that are exposed to the atmosphere. The way that's done normally is to do what's known as a CO_{2 clean (}CO₂ being, of course, carbon dioxide). We can't just hose down the optics with soap and water, there a millions of dollars worth of instruments and associated electronics all over the place, so CO₂ is used instead as it sublimates almost instantly after it's released in a small jet.

Here one of our technicians is cleaning the instrument's field lense. It's quite a tricky job, he has to work on a crane and access is very difficult, but it's a vital job. The lense is close to the top of the dome, so is exposed to the elements when we observe. In wet and windy conditions dust sticks to the glass and we see that as out-of-focus doughnuts in our images. These imperfections can be dealt with in processing after the event, but as usual, it's best to avoid the problem in the first place.


This is the secondary mirror. It's in beautiful condition so no need to clean it today. That's good news as getting access to it is awkward!

The plumbing in this place is incredible. We have nitrogen, helium and glycol lines all over the place which are mainly used to keep our instruments cold and also to cool the primary mirror. They're fed by chillers and compressors in a dark and noisy room down below. All the lines have to be able to cope with a telescope that slews all over the sky without leaking, and it's a surprisingly difficult job. I think all telescopes around the world have had to deal with a leak from time to time. Add into this all the electrical cabling that's required and the need to avoid interference with the instruments' sensitive detectors (generally called "pickup") you can see that we need to employ excellent engineers and technicians in order to function. I think we've done well in this respect.

While the cleaning was going on I wasn't able to do the tests I was up for, so rather than just annoy everyone by taking photographs all day I thought I'd help with everyone's safety and stand close to the emergency "off" button just in case. I think I understood the instructions but I don't think my efforts were appreciated...

Finally, all spick and span. A beautifully clean primary mirror. Just in time as well, as we really do seem to be moving away from the recent terrible winter conditions and the real Mauna Kea astronomical weather is back with us.