Arkaroola Remote Observatory - South Australia
Observatory Design - April to August 2011
Section view of planned observatory
With our minds made up and fully automated 3m diameter domes ordered from Scopedome in Poland, we began the design phase of the project. A model of the dome and the major telescope components was created, and the still to be built pieces such as the pier, floor, riser and footing were designed to suit. The design criteria for all the custom made observatory components was that they had to be constructed in Adelaide, disassembled and easily reassembled at the remote site. The first major decision was the addition of an octagonal riser platform for the dome. We choose an octagonal shape for ease of fabrication, transportation (8 manageable sections) and installation (simply bolted together). The riser gave us better clearance to see over the solar panel array on the northern extent of the ridge, and more importantly allowed us to have a floor above the concrete pad. The floor served 3 crucial functions.
1) Create a flat surface clear of any obstacles that could snag the shutter umbilical cable that sweeps across when the dome rotates.
2) Insulation against heat exchange between the telescope area and the concrete slab.
3) Storage area for all the electronics and cabling with access via a hatch.
The inner walls of the riser were also insulated with fiberglass batting to minimize heating of the concrete. Only the small exposed outer surface of the footing could receive direction solar radiation and the area under the floor actually remains quite cool. The heated air inside the dome is easily equilibrated when the shutter is opened. The steel riser, fiberglass dome and wooden floor have low heat capacity and cool quite quickly after sunset. The thickness of the concrete pad was set to 100mm under the load bearing areas and 50mm in the gap. This was possible since we were building on what is really a solid rock outcrop with a light coating of red dust. The minimization of the volume of concrete required was essential to reduce the thermal loading in the dome, reduce the mass concrete mix to be transported to such a remote location, and the amount of mixing required in the middle of nowhere!
Technical drawing of observatory riser and floor
Steel riser platform components being welded
Prefabricated timber forms for concrete footings
As mentioned previously the site had no available power. Therefore a solar power station had to be designed, built and installed at the site. Solar panels with aluminium mounting rails were easily obtainable, however we needed continuous power to operate at night. So the power collected during the day needed to be stored in batteries for use at night and to keep the communications equipment functioning during overcast days. We were planning on two domes with shared internet communications and quickly realized that a single large battery bank with an industrial inverter would be the most robust and cheapest solution. A computer model was created to simulate the collected energy from the solar panels, the stored energy in the batteries and the power drain from the equipment. The model allowed us to predict the optimum battery bank size and number of solar panels required for the site conditions and our budget. Additionally we wanted a very modest depth of discharge to maximize the battery lifetime.
Solar panel and battery bank capacity model
We found that 12 x 185W monosilicon panels and 20 x 100 AHr would be sufficient for even the worst case of 5 overcast days in a row, a very rare event at that location.
Skeleton of battery box