Our observatory is a Parabam
Astrodome. The observatory is 10 feet in diameter and overall
height is 11.5 feet. The aperture or width of the hatch
opening is 76 inches. It opens 14 degrees beyond zenith.
The aperture is enclosed by a solid laminate fiberglass frame and is
covered by an overhead sliding door (hatch) and 2 lower horizon
The horizon covers are put on separately to block light and wind.
The dome structure is fabricated using sandwich type
construction. Two skins of polyester impregnated fiberglass
cloth are bonded to a thermal insulating core. The dome is
mounted on a roller system which rests on the upper flange of the
base ring to allow the dome to rotate. The dome rides on 3 sets of wheels.
Each set consists of one wheel pointing up for the dome to ride on
and one wheel pointing out to keep the dome spinning in a
circle. The base ring serves as a track and slide for the
guiding rollers and support rollers. A skirt angle at the base
of the dome seals underneath the upper flange of the base cylinder
to provide a weatherproof, dustproof seal. A cable operated
latch system is mounted on the aperture frame. This has hooks
that seal the hatch and horizon covers to the dome for
weatherproofing and security.
The observatory sits on a round slab that's 12 feet in diameter.
The wind load for this dome is 130 MPH non operating and 50 MPH
The cylinder (base) is approx.
4 feet high and is made of 1/4 inch steel
plate. The inside of the base was originally lined with 2 inch
thick cork covered with canvas. We removed the cork because of
its poor condition. There is a flange on the top and the
bottom of the cylinder. The bottom flange has holes to bolt it
to the cement. It has a weatherproof, dustproof personnel door
for access to the dome.
There is a large roller chain connected
all around the outside
of the dome. A 12v wireless remote control winch motor spins
the dome in either direction. It makes one revolution in under
15 seconds. There is no power at the observatory site, so
everything runs on 12v batteries.
These Astrodomes are used by the
military to track missiles at test ranges. The military uses
cinetheodolites instead of telescopes. This observatory was
built for the military in 1969. The military had a hydraulic motor to spin this
dome. It made one revolution in 6
seconds! We have slowed it down a bit.
When we bought the dome,
the drive systems were completely inoperable. The support
wheels and guide rollers needed replacement, along with the guide
roller bearings. We now have the dome spinning
under its own power but the hatch motor is not working yet.
The dome will have to be disassembled one more time for paint
preparation. We will be replacing all the seals for the
observatory after it is painted.