Star Gully Construction 2
The roof is covered with PVC roof panels with silicone caulking at the joints. I put a layer of Tyvek under the PVC as a barricade against any moisture that might make it through. The roof splits at the ridgeline, so a aluminum flashing ridgecap is attached to one side; when the roof is closed it covers seam between the two panels, keeping water out. To open, the roof panels simply fold out to the East and to the West. They are supported by short lengths of chain bolted to the main walls. I've placed small eyehooks on the frame that will let me open the roof, but not lower the panels completely -- this will afford me some protection from light mostly, but also any cold winter breezes I might be observing in!
I constructed all the walls and roof panels in my garage (since we were getting toward winter, the days were kind of nasty outside). We had a clear sunny day in mid-November, and I put it all up at once.
The interior is "cozy" -- barely enough room for the scope to lay horizontal diagonally (generally the mirror toward the NW and the eyepiece toward the SE). Most of the work inside consisted of laying down foam interlocking flooring (to make standing a bit more comfortable, provide a bit of insulation from the cold, and to protect dropped equipment), and management of the ropes that held the roof in place hwen it was open (mostly connect points and loops for keeping them out of my way).
The scope went in on 22 Nov 2009, and survived the first snow later that night!
Once I started observing inside, I added small thin plywood panels to the roof panels to serve as atlas tables. I have one on each side, so I have plenty of space to put my observing guides and logbooks when I am out at night.
The counterweights were a late addition. I had originally intended to simply lift the roof panels up and down from inside the observatory, but in the end I couldn't get enough leverage to do it. My dad and I fiddled around with it over Thanksgiving 2009, and settled on a scheme to lever the walls up and down with a long hook from the outside, but it still required some effort. But then I was perusing this post and this post at Cloudy Nights and saw Peter Talmage's small observatory that he counterweighted using external weights (he described this in detail in three articles for the Astromonical Society of Northern New England: Article 1, Article 2, and Article 3).
I had always known about counterweighting systems, but was thinking in terms of pulleys and cables lifting hanging weights; this solution was brilliant and elegant! A quick torque calculation suggested I only needed about 45 lbs of weight on each corner, so I purchased some Olympic free weights from a local sports store, and made the modifications. It could have been built into the super structure a bit more elegantly if I had started with this in mind from the beginning, but it works pretty well! I can open and close from inside as I wanted to, and I always have control of the panels!
Each corner weight is provided by 45 lbs of Olympic free-weights with 2" central openings. The lever arms are simply long boards screwed down onto the original face of the observatory ridgelines. The mounts for the weights are simply pipe flanges, with 6" lenghts of pipe (threaded on both ends) and a pipe cap to keep the weights from coming off.
It works so well, I'm seriously considering this as an option for the larger Starlight Basin Observatory, thereby removing the need for a large roof run! The problem in the case of a LARGE roof is going to be the amount of mass needed at each corner.