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Now for a complete change of direction:
I have remembered a white dome I had seen on a local farm a couple of years ago. I stopped and asked the farmer how much it had cost him... and immediately dismissed it as an unlikely candidate for an observatory.
I have remembered a white dome I had seen on a local farm a couple of years ago. I stopped and asked the farmer how much it had cost him... and immediately dismissed it as an unlikely candidate for an observatory.
In my over-hasty judgement I had imagined it to be made of smooth, moulded, white plastic and the online drawings suggested a double roof. The lines were actually the two longitudinal seams. Now, thanks to further, and far more careful online research, it seems these things are made from sturdy GRP in three segments. The images borrowed from an online brochure show it is only a two man job to assemble.
Several European GRP silo manufacturers compete for the market for these calf rearing shelters. I contacted a couple of Danish dealers for pricing, earlier today. Not too terrifying for anybody in the market for such a thing. Expected lifespan is at least 20 years and they must be easily robust enough to survive a herd of 15-20 panicking and kicking calves! Moreover they [the domes, not the calves] have a solar reflective coating to inhibit solar heating. You couldn't ask for more!
These potential "domes" are about 4.5 meters in diameter! Were these complete astronomical observatories one could easily add a nought to the figure I was quoted over the telephone. 4.5m is about 14'6" in old money. With a height [naturally enough] of half that @ 2.2m meters or about 7'3" and change.Once modified into a "proper" observatory, with a rotating ring and wheels at the base and an up and over opening slit, the dome makes
Modification is certainly not a task for the faint hearted and will instantly trash the manufacturer's guarantee. But just think! You could swing a very serious refractor [or reflector] in there! And still have room for several Cats. 😉
It is very tempting, considering the cost of a bare 2.7m or 8' and something, astro dome. Not that I am comparing these items on cosmetic or even functional grounds. Not at all. That would be grossly unfair to observatory manufacturers. Their wares would be expected to be flawless on arrival and stay that way for quite a while. Or the word would soon go around the astro forums. But still, it does make one think furiously at the possibilities of these humble animal shelters.
Compare this to building a complete metal dome from scratch. You'd need a complex and sturdy framework first. Hours of sawing and mountains of sawdust and all that crap in your lungs.
This image shows the true height and scale better than the others.
Imagine handling huge sheets of razor sharp, unwieldy sheet metal in a gale from a tall and shaky stepladder. Now struggle to avoid kinks and wrinkles as you desperately try to accommodate three dimensions with flat sheet which knows of only two. Now add your disfiguring rivets or bolts or untidy flashing. Add an overcoat of fiberglass mat and resin followed by several decades of toxic sanding and hospitalization.
With a GRP dome you run a string of silicone along the seam. Then bolt the three segments together and it is immediately waterproof and stable. The manufacturer's claim only half an hour for two people to assemble.
Compare this to building a complete metal dome from scratch. You'd need a complex and sturdy framework first. Hours of sawing and mountains of sawdust and all that crap in your lungs.This image shows the true height and scale better than the others.
Imagine handling huge sheets of razor sharp, unwieldy sheet metal in a gale from a tall and shaky stepladder. Now struggle to avoid kinks and wrinkles as you desperately try to accommodate three dimensions with flat sheet which knows of only two. Now add your disfiguring rivets or bolts or untidy flashing. Add an overcoat of fiberglass mat and resin followed by several decades of toxic sanding and hospitalization.
With a GRP dome you run a string of silicone along the seam. Then bolt the three segments together and it is immediately waterproof and stable. The manufacturer's claim only half an hour for two people to assemble.
Sawing an observing slot in the center segment requires very careful internal support until the panel can be fully reinforced. By far the best idea is to reinforce it first. You will have to anyway. So why not do it before you break it? The dome would want to be complete before being touched with any cutting tool. Or it would distort at the first cut. The slit reinforcement replaces what was taken out of a carefully designed assembly of parts into a completely stable, self-supporting [hemispherical] form.
The whole thing needs to be safely protected against any flexure or damage until the slit and shutter work is complete. Epoxy bonding, as well as securely screwing the necessary [plywood] arcs, seems like a very good idea. Internal trestles with curved dome supports are easily out together out of wood. The weigh of the supported center segment is not enormous. Actually, each segment weighs about 160lbs!
The brochure and assembly instructions specifically warn against allowing the panels to flex until the dome is completely assembled. It has a strong steel hoop to reinforce the door arc. I think I'd be closing the open door area with reinforced plywood and very well attached. You don't want to be struggling with a massive GRP 'spinnaker' in a gale. Not unless you are hoping for a new Guinness free flight record!
This afternoon, in a snowstorm, I laid out battens 4.4 meters along along the ground and stood up a stepladder to suggest the expected height. Then I laid out some rope in an arc to show the circumference. This thing is absolutely terrifying in its sheer scale! It will need to be very safely restrained with sturdy hooks to anchor it down at all times. Letting strong winds get inside with the observing slit wide open could be an expensive and potentially lethal mistake. Common sense is obviously required to attack and complete such a project successfully.
I'm now asking myself whether I have enough common sense to take on such a thing at my age. Having it sited down on the ground seems like a necessity rather than trying to lift it onto a raised platform. But where could it go without losing most of the sky to all the tall trees and hedges?
Perhaps I am simply exaggerating the problems. The brochure mentions fitting a lifting eye at the top of the dome. So a tractor, or loader, can move it easily around the farm. There are even online videos of this happening. They can't be very fragile if farmers can abuse them for years on end under all working and weather conditions. Not to mention their being placed at random orientations to the wind and weather. Always with that large, half-moon door wide open, so that frisky and hefty animals can rush in and out.
If I could place one of these domes on the ground, on low supporting walls, I would not hesitate to use one for an observatory.
All images were borrowed from Holm & Laue's online brochures.
The whole thing needs to be safely protected against any flexure or damage until the slit and shutter work is complete. Epoxy bonding, as well as securely screwing the necessary [plywood] arcs, seems like a very good idea. Internal trestles with curved dome supports are easily out together out of wood. The weigh of the supported center segment is not enormous. Actually, each segment weighs about 160lbs!
The brochure and assembly instructions specifically warn against allowing the panels to flex until the dome is completely assembled. It has a strong steel hoop to reinforce the door arc. I think I'd be closing the open door area with reinforced plywood and very well attached. You don't want to be struggling with a massive GRP 'spinnaker' in a gale. Not unless you are hoping for a new Guinness free flight record!This afternoon, in a snowstorm, I laid out battens 4.4 meters along along the ground and stood up a stepladder to suggest the expected height. Then I laid out some rope in an arc to show the circumference. This thing is absolutely terrifying in its sheer scale! It will need to be very safely restrained with sturdy hooks to anchor it down at all times. Letting strong winds get inside with the observing slit wide open could be an expensive and potentially lethal mistake. Common sense is obviously required to attack and complete such a project successfully.
I'm now asking myself whether I have enough common sense to take on such a thing at my age. Having it sited down on the ground seems like a necessity rather than trying to lift it onto a raised platform. But where could it go without losing most of the sky to all the tall trees and hedges?
Perhaps I am simply exaggerating the problems. The brochure mentions fitting a lifting eye at the top of the dome. So a tractor, or loader, can move it easily around the farm. There are even online videos of this happening. They can't be very fragile if farmers can abuse them for years on end under all working and weather conditions. Not to mention their being placed at random orientations to the wind and weather. Always with that large, half-moon door wide open, so that frisky and hefty animals can rush in and out.
If I could place one of these domes on the ground, on low supporting walls, I would not hesitate to use one for an observatory.
All images were borrowed from Holm & Laue's online brochures.
Click on any image for an enlargement.
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