This is a build log for a dome “annex” to an existing ROR. It is offered here to help others who may want to embark on a similar journey. It will be posted in two parts. This is part 1.
First, why do this? My setup was a side-by-side installation of an AP 130mm Starfire GTX used for DSO imaging and a CFF 300mm classic Cassegrain used for visual, EAA, and planetary imaging.
Adding a dome to my existing ROR addresses allows me to split up this setup and solves several issues. First, the side-by-side arrangement makes it more complicated to view over the sides of the ROR for the telescope on the “down” side. Second, there are times I want to have the GTX off imaging and I want to look at different stuff with the CFF. Finally, putting the imaging setup in a remotely controlled and automated dome allows for the possibility of longer imaging sessions while I sleep.
Linking my dome with the existing ROR allowed me to share power and data already linked to the ROR. I can also have a common work and storage area (in the ROR) to run both observatories. It also avoided the need for a new building permit. While the buildings are linked, they are also structurally independent: they share no load-bearing walls.
It made sense to place the annex on the east of the existing ROR. The roof of the ROR will block the view to the west from the dome (though I can move it if needed), and the dome will block the view of the ROR to the east. However, those views are already compromised by trees. I can place the dome close to the ROR because I do not plan to open the lower shutter due to light pollution, poor seeing at low altitudes and trees blocking the western horizon. However, if I need to, I can always open the ROR to allow for unrestricted opening and rotation.
Height management became the vital issue in the design of the dome observatory. I wanted to have six feet of clearance for walking in the annex, but I wanted to minimize overall height of the dome. My architect/builder designed a post-and-beam system using pressure-treated 4x6 timbers that minimizes the height of the roof structure. The height necessitated a high concrete pier 26” above the rough floor (and five feet below it). We decided to do the concrete pour in two phases to allow for precise height measurement once the dome was installed.
On top of the concrete pier I installed a 54” high 10” diameter ATS steel pier. In total, the base of the telescope in the park-4 position is 93” above the rough floor. This gives me access to all altitudes above 24° to 27° across about 90% of the horizon and from 27° to 33° around the rest.
I considered several dome options but ultimately chose an ExploraDome with the full MaxDome II automation setup.
The dome annex is a 10’x10’ building supported by eight 4x6” pressure-treated posts on concrete footers with a concrete pier base that extends three feet below ground and about a foot above it, with rebar extending several feet further up to allow us to tie in the second concrete pour for the base.
Exterior walls are Hardie planks that match the current ROR. All of the trim is Azek – no wood is exposed to the element except the pressure-treated timbers.
A circular platform supports the base ring for the ExploraDome.
The roof is white TPO. It was important to have good flashing into the existing ROR structure. The only potential issue will be snow, which is relatively rare in this area. I might have to brush off the snow in the section between the buildings.
We cut a passageway between the new annex and the existing ROR. We also removed a small air conditioner from the ROR and installed a slightly larger unit in the annex, opposite the passageway. There is a window above my desk in the ROR that allows me to see the dome telescope. This setup allows cool air to circulate between the structures in the hot summertime. I can also control the new air conditioner via my iPhone.
Dome Installation -- Structure
The aluminum base ring and the ring on top that supports the dome were straightforward to install. A fair amount of time was spend using a laser level to insure it was all level.
We installed the dome itself using only three people (but it would have been easier with 4). The next step was to install the hold-down rings on the inside of the dome skirt. There were small gaps between the underlying wooden ring and the dome ring – these were filled with expanding foam. Overall, dome installation was not that difficult and took three people about two hours.
Dome Electrical / Mechanical Systems
Some challenges emerged around the dome’s electrical and mechanical systems. Most fundamental is a complete lack of any documentation on how to install the various motors, brackets, battery housing, pre-assembled controller units, electrical connectors, etc. that come with the ExploraDome and full automation kit. This is because ExploraDome just switched from the Foster System to the MaxDome II system. I needed to sit back and work from first principles – look at each piece and figure what it must be for and what it must connect to. I also got excellent advice from fellow CN’ers who have been through this. Here are some of the specific challenges that emerged.
First, if you get the dome pre-assembled with shutter opening systems installed, you need to be able to close the shutter (the dome is shipped with the shutter open) and you can only do that using the motor. The wiring connections used by ExploraDome are Molex connectors with 14-20 AWG .093" pins. It is helpful to prepare a cable in advance that you can use to connect the shutter motor to a battery to open and (by reversing polarity) close it.
Second the bracket for holding the rotation motor shipped with the automation kit was in my case improperly specified – the mounting holes misplaced by 1 ½”. It was also improperly assembled when shipped. There was no way to mount the motor in that configuration.
The gap meant the rotating gear teeth would not contact the mount rotation ring.
ExploraDome immediately shipped a modified bracket of an earlier design that worked fine.
Data and Power
Power and data cables are routed been under the floor of the observatory and up into the concrete pier.
There are four 20A circuits serving the existing ROR. Two of these are extended into the annex, one to power the mount, cameras, and other devices on the pier and the other for lights (one red and one white) and receptacles. I checked all of the loads and it will work fine. All receptacles and light fixtures are rated for wet conditions – just in case.
A managed POE switch in the new annex connects via fiber to the existing switch in the ROR, itself feeding back into main switch 800 feet away via fiber. The switch will connect to the mount’s CP5, the rain/cloud sensor, a weather station, and some other devices. Powered USB hubs will connect cameras and other devices on the pier to the computer workstation in the ROR. I also took this opportunity to (finally) upgrade my GTOCP3 controller on the existing 1100 mount to the GTOCP4 controller that has been sitting in a box for over a year.
All of the electrical AND data connections have inline surge protectors, primarily to protect against nearby lightning ground strikes.
A SkyAlert-E is installed for weather detection and automation shutter closure should circumstances warrant. An air conditioner is installed – it gets hot here in the summer – for those cloudy days when daytime work inside the observatory is required. Four surveillance cameras monitor the inside and outside of the observatory, complementing the other three already installed in the existing structure. The observatory has its own weather station.
It was now time to install the mount and telescope (part 2 in the next post)...