Seven hundred tons of steel and aluminum, thirty meters diameter. The dome represents a huge piece of machinery critical to the operation of the observatory.
Controlling everything is a PLC, a programmable logic controller, twenty year old technology from another era. Operation is critical, if the dome or shutter fail at the wrong time the telescope could be left exposed to the elements causing untold damage.
Despite, or perhaps because of, their huge mass the domes move with stately grace. I never seem to tire of hitting the button and listening to the rumble, of riding the huge structure as it smoothly rotates.
Every time something breaks it is a chance to learn. In this case it is an inclinometer, a simple angle measurement sensor that allows the system to read out the position of the shutter. Tests from the control panel show that it is simply not talking, I will have to get at the device itself, deep inside the structure of the shutter.
I feared that accessing the inclinometer would be difficult. The reality was somewhat easier, just drop the lower shutter all the way down, and climb into a hatch at the top.
Inside the first chamber is found much of the cabling and the inclinometer. There are even a few lights available so I am not working in the dark. Still, it is a bit eerie to be working inside a big aluminum box, a box that moves.
