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An inexpensive, DIY, "gun turret" style 'dome' is definitely on the cards once I have finished the platform and mounting. A dome made absolutely no sense [at all] down on the ground in my heavily tree-shaded garden. On a raised platform it makes perfect sense. With panoramic views from NE to West right across the South above the minimum 30 degrees altitude generally accepted for reasonable 'seeing' conditions. Any lower and there is usually far too much 'boiling' atmosphere to spoil the view. Though being able to see such a low altitude object is often still well worth the effort for personal enjoyment.
The image was borrowed from the Hampshire Astronomical Group's 24" web page:24 inch Telescope - Hampshire Astronomical Group (HAG) - Clanfield Observatory
Is there any more sensible design for a home made "dome" than this? Every surface is curved in only one plane. None of the usual problems of working with spherical hemispheres and strangely shaped gores. Flat [waterproof] materials will roll easily into the necessarily gentle curves without stress or unsightly kinks. The design is easily built with lightweight aluminium and stiffened without resorting to involved 3D geometry.
The cost can be very modest indeed in comparison with commercial domes of similar or even, much smaller diameter. Moreover, there is much more more headroom when moving about inside. Wind problems and lift should be not much worse than a common dome. Hooked internal restraints are easily fashioned as is common with 'normal' hemispherical domes.
The shelter such a structure provides the observer should easily eclipse roll-off roofs or roll-off observatories. Thin, polished aluminium sheet for the roof will avoid solar gain and has very low heat capacity compared to the more common GRP domes. Opening the shutter should rapidly cool the interior to ambient. Having rapid access to an accurately, permanently set-up instrument sheltered form the cold wind means increased usage. Without any of the usual mental hurdles to carrying heavy equipment around and the inevitable time-wasting of pointing at the Pole and cool down of the optics.
Corrugated roofing sheets are readily available for the upright, cylindrical walls. These corrugations will reinforce the inherent stiffness and resistance to distortion which the cylindrical shape already enjoys. The choice of a white finish should avoid unwanted heat build up. A double wall with vertical, thermally induced ventilation on the south side makes sense. All aided and abetted by the corrugations to act as air channels.
The shutter and slit can be made wider than a hemispherical dome without seriously weakening the structure. A hemispherical dome loses strength rapidly as the slit eats into the integrity of the hemisphere's natural resistance to collapse. Usually requiring heavy reinforcement around the slit to maintain its structural strength. The shutters often begin to look top heavy as they overhang the smaller hemispherical dome.
Click on any image for an enlargement.
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