Changing a Light Bulb

How many engineers does it take to change a light bulb?

Arc Lamp Bulb
An arc lamp bulb for the AO calibration source
Nearly every morning I begin the day with reading the nightlogs, a write-up of everything that went wrong in the night on both telescopes. Normally there is nothing I need worry about, or perhaps something to follow up on during the day. But occasionally, not very often, I find a nightlog that indicates I will be re-scheduling my whole day, dropping any previous plans and driving up the mountain.

This is one of those times. A nightlog coded as critical, the Keck 2 adaptive optics system has a slight problem, no output from the white light source, no calibrations, no science. Waiting until after 9am I call the support crew on the summit… Do you know how? No. I wrestle with the thought for a few moments. No avoiding it, I need to drive to the summit.

So how many engineers does it take to change a light bulb?

Just one.

OK, it is a really fancy light bulb, but a light bulb just the same. A wideband source that can be used to calibrate the adaptive optics system. Without this bulb there is no way to calibrate the AO system and no way to go on-sky that night. The bulb is an arc lamp that costs about $250 and is dangerous to look at directly while it is on. It must be carefully handled and installed correctly.

It takes me about 40 minutes to locate the replacement bulbs, head up into the AO enclosure and do the deed. The bulb is replaced. Then there is another half hour of returning to a computer, testing the bulb, responding to the nightlogs, then sending a few emails and a phone call to let everyone know that Keck 2 AO is back on-line. We will be able to observe with the system that night.

This particular bulb had lasted 14 months of operation, I last replaced it in June 2015 according to my notes. I look, there are three spares remaining for both AO systems. Before I leave I put in an order for four more, just another thousand dollars spent.

I hang out for a time while the support astronomer starts the AO system calibrations, just to make sure everything is well before I drive back down the mountain. All is well, except for the game of cribbage I lose, at least is was a good game. Then it is back down the mountain and to whatever I can salvage of my Sunday.

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on Mauna Kea, Hawai'i.

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