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Observatory Construction


Cassel Observatory is a 15.5' domed structure built in 1990. All observatory functions including door and dome movement, lighting, alarm system, CCD imaging, and telescope tracking are computer controlled. Two Pentium-based computers provide the processing power necessary to run the observatory. Disk Storage is maintained by a Windows 2000 server maintained in the residence on the property.


The following are a sequence of pictures taken during the construction process along with a brief description: (Click on the thumbnail for the full size picture).


con1.jpg (64137 bytes)Construction began with excavation of a 10' deep hole. This provided the foundation for the telescope pier seen here in the picture. A circular foundation was dug, a concrete footer was poured, and the foundation wall of 10" concrete blocks were laid. The inside corners of the blocks were chipped away to allow the circular wall to be formed. You can see that the observatory was constructed in the middle of what used to be a vegetable garden. The top of the concrete pier that you see is the heighth of the finished observatory floor.


con2.jpg (48617 bytes)After the wall was complete, a sealer was applied to the exterior surface and bolts were set in concrete to provide a secure place to fasten the wall base plate. A concrete floor was later poured.



con3.jpg (39469 bytes) The walls are constructed of standard 2x6's. The base and top rings were made by cutting arcs from 3/4" plywood, and then gluing and screwing them together to achieve the 15' circle. Holes were drilled in the lower ring to match the bolts in the foundation. This picture also shows the entrance door in place.


con4.jpg (48638 bytes)This photo shows the walls after the 1/4" plywood was applied. In order to allow bending, the wood was soaked with water and curved over the structure while still wet.


con5.jpg (48192 bytes)

Standard white vinyl soffit was used to side the structure. The upper and lower trim moldings were curved and applied as the soffit was installed. 



con6.jpg (42067 bytes)Another laminated plywood ring was made to support the dome. Here the dome is partially assembled on the ring. Note the plywood skirt which will later be covered with soffit. The actual dome is a new silo roof! I decided to use this after finding the price of commercially available domes to be astronomical (no pun intended).


con7.jpg (33514 bytes)My father's farm tractor and front-end loader were used to place the dome on the observatory. You can see the industrial casters that were mounted on the building to support the dome. After the dome was in place, I was pleased to see that it could be rotated with one hand. Additional casters were later installed to prevent lateral movement of the dome.


con8.jpg (18745 bytes)After the dome was in place, the opening for the shutter doors was cut and framed with 3/4" plywood. As with the plates used on the walls, the plywood was laminated with glue and screws.



con9.jpg (44631 bytes)This photo shows the drive motor used to rotate the dome. It is a inflated rubber tire mounted on a bi-directional slow speed geared motor. The tire is held against the dome ring by a spring mechanism. Activating the motor rotates the dome at approximately 1 r.p.m in either direction



con10.jpg (47573 bytes)This is an example of one of the relay boxes used to control the observatory functions. Several of these devices mounted in the crawl space allow computer control of the dome drive, shutter doors, all interior and exterior lighting, and the alarm system.



con11.jpg (38788 bytes)This is the crawl space mounted interface between the relay boxes (pictured above) and the low voltage relay cards in the control computer.




con12.jpg (42430 bytes)The telescope is mounted on a custom pier fabricated by a local machine shop. You can see the pier in this photo along with the telescope drive corrector and CCD camera control box. Also, the wood observing floor is visible in this picture.



con13.jpg (36870 bytes)Here are the two computers used in the observatory. Pentium computers control the observatory functions, telescope tracking and the CCD imaging camera and tracking system. This photo was taken before the drywall was installed.

A Microsoft Windows NT® server in the residence supports the observatory computers. An Ethernet Lan serves as the network communication backbone.


c14.jpg (42609 bytes)This is the Celestron C-14 telescope mounted in the observatory. The_Sky® software from Software Bisque is used to track the telescope movement. A Meade 2045 SCT is mounted to the main scope with a tangent assembly and is used for tracking and astrophotography. A SBIG ST-4 is used for autoguiding and imaging.





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Copyright © 2009 Calvin L Cassel Jr
Last modified: March 13, 2009