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Design

At the start…

The initial design of the observatory was to be a Roll-off-Roof (ROR) design. This type of design has the roof on rollers that allow the roof to roll off thus opening the entire top of the building to the night sky. Like all things there are advantages and disadvantages of a ROR design. The main advantages to a ROR design is cost, while the main disadvantage is exposure to wind and the remote possibility of hitting the telescope with the roof. The initial design concept and objectives for the observatory looked for a pier and space accommodations for my existing 10″ Classic Meade LX200, with the possibility of upgrading to perhaps a more modern 14″ Schmidt Cassigrain Telescope (SCT). This called for a pier height above the floor of around 3′ with an additional 2′ below the floor to ground level. The total instrument weight would be around 100lbs max with a pier height above ground level 5′-6′. Preliminary designs looked like the following 3D CAD models.

ROR design foundation

3D view of the initial ROR design showing the foundation, footer and pier.

The original pier was a block of concrete approx 3’x3’x3′ with a 24″x2′ round column in the center.  The block/pier was to be rebar reinforced and weighed approximately 6000lbs.  There was a concern for how a scope and user would fit so an additional 3D model was constructed to show the walls, telescope and average person within the building.

3D model of ROR design

3D model with wedge mount, LX200 and ROR design concept

There can be a significant amount of wind in Overgaard.  The design for the roof was initially going to be a steel truss design both because of it’s strength and my son has his own metal fabrication shop, which means I could get a superior design at a wholesale price.

roll off roof design

Roll off roof design

 … but then things changed

The observatory actually started is life as simply some more construction that was added to an addition that my wife and I were adding to our Overgaard residence.  One thing kind of lead to another and we decided we should make the facility something that can be used with schools to assist in education.  We had some ties to a local astronomical research facility, which dovetailed nicely to our own plans.  In changing our objectives to be something far more than simply a hobby we decided that the facility needed to be a bit more robust.  While a ROR is fine in many applications, the two drawbacks mentioned above, open exposure to the environment and the possibility of hitting your instrument with the roof, were enough to change the design from a ROR to a full dome.  A dome costs more than a ROR and requires quite a bit more control electronics but they offer shielding to the environment and it is impossible to hit your instrument with a rotating dome.  The winds in Overgaard can easily be 10-15 Mph or more on some evenings. For a dome observatory this is not an issue and we can operate even up to 20Mph gusts without an issue.  For an open ROR design you would need to close things down when winds exceeded 5Mph.  (Note: OOO is strictly a photographic observatory.  For visual observing you can certainly operate at higher winds without much issue but for photographic facilities this is not the case.)

It would have been nice if the decision to change to a dome design had occurred before any construction had begun but that was unfortunately not the case.  Switching to a dome design caused a number of things to change.  First, the height of the pier needed to be raised from 5′ – 6′ above ground level to approximately 10′.  The mission of the observatory changed and in so doing we wanted to allow room for growth of the facility in terms of instrumentation.  This raised the maximum weight at the top of the pier from around 100lbs to a design maximum of 500lbs.  The exterior walls were completed at the time of the design change but it was a simple modification to change the top roof design to accommodate the dome that was chosen.

In keeping with the desire to accommodate larger instrumentation a number of CAD 3D models were built up in both Modo and Solidworks to investigate what the largest possible instrument that could be placed in the building.  The current instrument was a 10″ Meade SCT on a wedge/fork mount.  The possible candidates we looked at were Cassigrain designs (primarily from Planewave) up to  24″ in aperture.

lx100_in_observatory

This is the dome design with the current 10″ Meade LX200.  The top of the pier or bottom of the wedge is at a height equal to 10′ above ground level.

planewave_in_observatory1

This is the dome design with a 20″ Planewave on a GEM (German Equatorial Mount).

24_collision_left

For grins we looked at how a 24″ telescope might fit but the results pretty much speak for themselves.

It was shown that possibly an instrument as large as a 20″ Cassigrain could be mounted within the building.  An instrument of this size would need a substantial mount as well as large amount of counterweights assuming we used a GEM.  We did consider fork mounts but these have problems when it comes to the amount of space under the instrument.  We wanted to have the ability to add a spectrometer to the telescope and these require a foot or more of space under the instrument.  This pretty much eliminated the use of a fork type mount.

The dome chosen was a 10′ HomeDome from Technical Innovations.  This is a fiberglass dome that can be rotated 360 degrees with a 36″ wide shutter.  The shutter can open approximately 16″ past the zenith thus offering an unobtruded view directly above.

The pier was engineered and custom manufactured by my son at his fabrication facility.  The design of the pier was a considerable challenge, so much so, that it deserves it’s own page on our website.

The specific location of the observatory is in Overgaard Arizona.  A quick view from Google Maps shows the basic layout.

OOO_FromSpaceThere are some trees but for all practical purpose they block everything below about 20 degrees above the horizon, which is where you would never want to use a telescope anyway, so the foliage is really not an issue.  One thing we do have a lot of in this location is lightening.  During monsoon season in Arizona (July and August mostly) we have lots of sudden thunderstorms with many of these displaying impressive electrical fireworks.  This drove the decision to put up lightening rods both on our residence and at the observatory.  We used a local contractor located out of Payson Arizona, Classic Lightening Protection.  The observatory required a 30′ tower in order to adequately protect the structure.  My son’s shop came to the rescue again and they fabricated a custom 30′ aluminum tower that we bolted to the north side of the observatory.  While the tower does obstruct a small portion of the north sky this is an area that has the tallest trees and is already obstructed.  In addition, control software is such that the obstruction is in a fixed location that can be mapped out or dealt with fairly easy if something needs to be observed in that particular portion of the sky for an extended period of time.

Lightingrod2    ObservatoryTower

The rod being added to the observatory.  Check out the clouds on the picture to the left.  We did have a storm not too long after this picture was taken.  No lightening that day.  While it cannot be seen from these pictures, the concrete pylons that were originally embedded into the ground with the purpose of supporting the roll off roof are now use to support 2 of the 4 guy-wires used to support the lightning rod tower.  Classic Lightening Protection did an outstanding job and I’m happy to say, it has already been “field tested” and has passed with flying colors.

What we now have at the facility is an excellent building with an outstanding instrument capability.  We have the capability to do solar observing with our 90mm Cornado Solar Telescope, spectrographic observations using our L200 spectrograph hooked to our 10″ LX200 SCT and photographic observations with our various cameras connected to our 105mm Vixen.  All of this is driven by our AstroPhysics AP1600 GTO mount.