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 covers.  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 operating.       

     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.