The Calotte dome with aperture pointing at the horizon. THE DOME KEY FEATURES
The Madawaska Highlands Observatory dome is an advanced design using the
latest materials, topologies and created primarily as an extension
of the Optical Tube Assembly. The core function of the dome is
to protect the telescope and yet not deteriorate the seeing. The
dome features a Calotte design. This has circular aperture and
offers many performance advantages over more traditional topologies,
such has better air flow and resistance to snow accumulation.
The dome is elevated from the ground level by over 3 metres.
This serves three important functions:
First to elevate the telescope from the ground
turbulence. This can improve the local seeing by almost 0.5".
Second to permit a smooth air flow below and
around the dome. The idea is to minimize the air disturbance and
thereby improve the seeing by perhaps 0.25".
Third to eliminate the insulating effect caused
by placing a facility at ground level. Heat accumulated during
the day will radiate up through such observatories. Elevating
the dome allows very rapid ambient temperature tracking by having
the entire dome exposed to the air instead of just the top and
sides.
The shape of the dome is a 3/4 sphere. This shape
was chosen because it presents the lowest air resistance thus
improving air flow and seeing.
The dome is made of carbon fibre sandwich core,
which is light and absorbs very little heat. It has excellent
dimensional stability over temperature which will ensure stable
azimuth and slit movements. The dome features significant venting
from the bottom, which will improve the thermal tracking.
The Calotte dome design has several performance
advantages over traditional designs.
- A smoother air flow due a smoother profile. The Calotte topology
has no external protrusions thus air turbulence will be minimized
around the dome.
- A circular aperture will minimize wind buffeting and stray
star starlight from bright stars.
- The Circular hatch is much more immune to snow accumulation
due the the fact the the aperture door when closed presents
a smooth face.
- The Calotte design is mechanically simpler and thus more reliable.
The end result will be better dome seeing.
The dome is supported by 6 legs that join into a tripod at ground
level. This will give the support needed and facilitate the dome
leveling.
The pier is designed to minimize the thermal footprint and is
composed of a 48" diameter concrete cylinder with a 36"
hollow core. All power, control and communications are passed
down the pier.
Dome characteristics include:
- Three Quarter sphere for smoother air flow.
- Constructed of Carbon Fibre Sandwich Core for light weight
and low thermal expansion.
- Continuous observing crossing the zenith. No interruption
during a long exposure crossing the zenith
- Calotte design. A smooth profile to air flow will improve
seeing.
- Elevated (3-m) off the ground to minimize ground turbulence
and faster ambient air temperature tracking.
- Back-up solar power and controls to ensure fail-safe operation.
- 48" pier with 36" hollow core for minimum thermal
mass.
- 3 pad footing design and 6 legged dome attachment.
- 1.5 m aperture.
This 3D CAD drawings shows the 3/4 sphere shape of the dome. The
48" hollow pier is off to one side of the dome. A six leg
support structure that merges into a 3 pad support at ground level.
Top view of the dome with aperture open.
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