Maintenance Trip Feb 2014 Part 1: Ice, snow and operating the telescope

We have now returned to the UK from our first maintenance trip of 2014. The maintenance trip will be memorable for us for a number of reasons. A lot happened on the trip so instead of a single round up post, I will spread the news over a number of posts in the coming weeks.

In the first of these posts I am going to talk about operating the telescope in the winter months and how the cold disrupts our operation.

When snow and ice strike there are lots of visible signs of its presence at the observatory. From the ice build ups visible on the web camera images through to the wildly varying graphs of wind speed, in the days following a winter storm it is very clear why the system is not operating.

In the days that follow the ice melts away, the web cam images return to normal and the weather station charts take on a familiar pattern. Everything appears to return to normal, but the telescope still isn't operating. This is the point at which we start getting lots of contact about why this is the case.

The recent maintenance visit to the observatory coincided with the end of a winter storm, so we have been given a rather unique opportunity to visually show what we never normally get to see.. the striking difference between what we can see on our web cams and the actual state of the site.

21/02/14: Conditions on site appear to be returning to normal

By the time we had managed to reach the observatory (there will probably be another post about this) on the 21st, the weather conditions appeared to have greatly improved on site. On the dome camera the ice had entirely melted and the system looked ready for operation.

Our observatory is located at the western extremity of the OT site, with our dome located at the north western end of our building. There are no buildings beyond our observatory, so we can only have cameras pointed at the southern side of the building.

As we approached the northern aspect of our building it became clear that out of direct sunlight the ice was taking far longer to melt.

21/02/14: Fallen ice covers the ground on the northern side of the building

The image above shows a considerable amount of ice resting on the path outside of the building. What is not clear from the image is that all of the larger blocks of ice have a neatly corrugated side, revealing that the ice was originally attached to the building. (The image also doesn't show that I had spent the last thirty minutes clearing ice so that the doors would be accessible.)

As we moved around the building to the north west side the extent of the ice remaining on the dome was surprising even to us.

21/02/2014: Large amounts of ice remain on the hidden NW side of the dome

When the ice rule triggers on the weather station we watch the weather data and try to guess when we think that the ice will have cleared. At this point there is no way to know if the ice has released the dome or not, so we gingerly try to operate the dome. We watch a video feed from a web cam which allows us to see and listen to the dome drive wheel in real time, allowing us to see if the dome can be turned. Using command line tools, first we ask the dome to home. If we can see from the video feed that the dome isn't turning we quickly have to kill the command to stop the drive wheel. If the dome does home, we then rotate the dome through a few full revolutions to make sure everything is free. We can then use the external dome cam to check the shutter for ice, and test the shutter operation.

When we do these tests we generally don't tell the users unless the tests are all successful. When everything is working again, the ice rule in the weather station is reset and the telescope is allowed to resume operation.