SkyShed POD Review
When I first became seriously interested in astronomy, in my early teens, my Mum bought me a subscription to Sky and Telescope magazine.
Sky and Telescope is widely available over here now, but it wasn’t back then in the late Seventies. At that time the Atlantic seemed much wider than it does now: McDonalds was an exotic novelty that my girlfriend and I would travel to London or Milton Keynes to sample; Coach tours to the U.S. (I desperately wanted to see Yellowstone and The Grand Canyon) cost as much as they do now, 35 years of inflation later.
So my Sky and Telescope had to be delivered direct from the ‘States, complete with distinctive brown wrapper and USPS Airmail stamp. Every month I looked forward to it plopping heavily through the letterbox...
I loved Sky and Telescope magazine, loved the adverts for gear you couldn’t buy here (Unitron and Questar and Criterion), loved the Star Parties and the big home-built dob’s and weird folding refractors. But the thing I most hankered after was an observatory, which every Stateside astronomer seemed to have, usually on some desert ranch surrounded by snow-peaks.
So I developed a longing for my own observatory from an early age and always imagined it nestled in a pine forest under dark skies, a short trail-walk from my ranch house in the Utah mountains. Dream on.
Of course, I never got my observatory and pretty well gave up on the dream because I never lived anywhere with the space and sky views. I did once make a little angle measuring tool to survey the horizon from various points in the garden of the terrace where I grew up, but the inescapable conclusion was that there was nowhere suitable for an observatory.
In fact the whole observatory thing really only popped up again a few years ago after a few nasty incidents where I slipped carrying heavy chunks of mount or scope around my sloping lawn in the dark. What’s more, I was getting tired of re-aligning for every session.
Even then I delayed because I couldn’t find anything that suited my needs and budget. A wooden roll-off shed just seemed too flimsy and leaky to house expensive gear permanently. I wanted a proper eight-foot Sirius dome with motor-drive, but it cost many thousands too many. The seven-foot fibreglass dome made here was just that bit too small, the twelve-foot much too large. I also considered a fancy aluminium roll-off but worried it might not stand up to the Autumn gales that we get up here.
Then a friend suggested the then-very-new Sky Shed POD. The Promo film showed one being driven at speed on the back of a pick-up to prove the point that it could stand high winds. Heck, the script they used was just the same as the “Sky and Telescope” on the front of my Seventies magazines! It seemed like fate...
Location, Planning and Problems
Siting an observatory is never easy, unless you live on top of a hill. Unfortunately, the only possibility in my garden was right next to the road, to one side of my drive: not a perfect spot, but with good views of the ecliptic to the south for planets and the Moon.
A temporary structure like a POD is subject to much the same planning rules as a shed, but even so it technically shouldn’t be permanently anchored down and is subject to various restrictions about height and distance from boundaries. I would strongly advise checking with your local planning office before you start building any type of observatory.
If my house had been conventionally shaped it probably wouldn’t have been allowed where I put it, out in front, but as there is no clear front or side to my house I got away with it.
I say “Got away with it” because almost immediately I ran into trouble. Naively, perhaps, I imagined that because I live on a country lane, opposite fields and not directly overlooked by neighbours, there wouldn’t be any problem. Effectively the only people in a position to complain about my observatory were local dog walkers, but complain they did. I’m sympathetic, believe me: I can only imagine the distress caused by having to look at a white dome whilst waiting for your dog to finish crapping on my drive.
So inevitably I got a visit from the local planning officer, but he was very nice about it and gave me the all-clear without further ado. That, I hoped would be that. Errr... no.
For at least a year, crowds would gather next to my drive, pointing at the POD, shouting and rubbernecking at me and my family to see what kind of perverted weirdo puts that thing in their garden. I became increasingly irritable toward people who asked me (often rather aggressively) “What the hell is that thing?”
The planning officer admitted that the complainer had thought the POD to be a pagan temple and I had more than one complaint about the colour (“Does it have to be white?”). Another passer-by said he thought it was a huge composter.
Pagan temple or giant composter? The POD caused considerable local controversy.
The final act was one night at Easter when I woke in the small hours to find two drunks climbing on the POD and trying to prise it open. When I asked (amazingly politely, I thought) what it was they wanted, they ran off screaming “What the f**k is it? WHAT THE F**K IS IT?”
Since then (I hope) people seem to have got used to it and things have quietened down. Maybe the Mongolian Yurt that someone has erected in their garden nearby has directed local ire away from me.
I admit that I’m still amazed at how much fuss the POD caused. Perhaps where you live the natives are more enlightened, but local reaction is worth considering when siting any observatory.
Design and Build
The POD is a fairly unique solution to the small home observatory problem. It is sort of a cross between a roll-off and a conventional dome. The dome rotates on wheels set into the top of the wall, just like a fibreglass dome, but instead of a slit, half of the dome flips up like the visor on a helmet. The advantage of this is that you get more protection from wind and stray light than with a roll-off, but a much larger sky view than with a slit.
The flip-up part of the dome rotates up or down on two large bolts running through the outer dome. A waterproof seal is provided by a rubber skirt between the visor and outer part of the dome. The visor has lugs that locate it with the walls when closed and two of these come with threads so you can “lock” it by screwing in two hand-wheeled bolts.
The dome rotates on small plastic wheels set into the top of the walls that run freely on plastic axles. I believe modern versions use an upgraded wheel system, though the early version is perfectly functional, albeit a little heavy and noisy to turn.
To open the dome, you lift the rim of the “visor” part from inside and push it open or pull it closed. The inner “visor” part slides in underneath the fixed outer dome when open. Handling the dome takes a reasonable amount of strength, especially to prevent it slamming when closing. For this reason I wouldn’t recommend the POD for children or the infirm.
Walls and Door
When my mate bought his seven-foot fibreglass dome he had to hire a removal van to collect it, because the walls and dome each come moulded in one piece. By comparison the POD is intentionally much more portable because the walls and dome break down into sections (four for the dome, six for the walls) which you then bolt together on site. Not only does this make delivery and setup easier at home, but you could in theory take the POD with you to star parties.
You can choose to replace one or more of the wall sections with useful alcoves that give more storage space. I didn’t have space to be able to do this, but I have to say that the damp problems I have encountered would prevent long term storage of books, clothing, or even computer equipment (more on the damp later).
The basic build material is polyethylene in a double wall moulding. This seems like a great choice, because it is light and tough and you can choose from various colours (I went for white and light gray). However, there is one obvious disadvantage compared to fibreglass (as well as a few less obvious one I’ll get back to): it’s thick. This means that the internal dimensions are significantly less than the outer, both in width and in height (especially in height, because the “visor” part of the dome runs inside the outer part). You should take this into account when planning your pier height and when working out what will and won’t fit in terms of OTAs and mounts.
I measured minimum internal clearance width and height of the inner dome as follows:
H 224cm W 187 cm (to an accuracy of +- 2 cm)
The inner dome is secured to the walls by metal brackets carrying wheels that can further reduce clearance on longer scopes, but because these attach to the outer dome, they fall within the 187cm figure given.
A moulded door is provided in one of the wall sections. The door fits against a seal, but in my POD the fit is only partial and blowing rain can leak in. The door is secured by sliding bolts top and bottom operated by the handle. The mechanism is a bit rudimentary and stiff.
Overall build quality of the POD is good, but the mouldings are a bit rough in places and a few plated ferrous parts (like the dome brackets and hinge bolts) would be better made from stainless.
You can (and I did) order the POD with the cavities filled with foam. If you go for this option, the walls and outer dome are filled, but the flip-up part isn’t because it would make it too heavy to lift. The foam makes the structure heavier, more robust, better insulated and more opaque, but on the downside the parts are heavier to move and assemble and the foam does go yellow over time, spoiling the colour of the plastic parts. Overall I wouldn’t recommend the foam option.
Will Your Scope Fit?
It’s very hard to be specific about what will and won’t fit in the POD. I reckon that like most small home observatories, it’s designed for the ubiquitous 8-12 inch SCT. Certainly, an 8” or 10” SCT would fit easily in the POD on an equatorial wedge. Larger SCTs might be a tighter fit, though SkyShed claim SCTs up to 14” will fit.
My 12” Dall-Kirkham fits in, but is a tight squeeze and requires manual slewing near the zenith (see left pic).
Longer refractors on German equatorials are more of an issue and larger mounts exacerbate the problem. You obviously need to ensure nothing hits any part of the POD during slewing, but you also need to allow enough space to look or image through the scope when it’s in use! Allow for racking out the focuser to accommodate long focal length eyepieces when planning.
I would strongly urge you to make detailed scale drawings to check that your scope and mount will fit, but even that is not a complete solution, because differences in balance points, accessories and even the way your mount slews will all change things. It’s almost impossible to allow for all the variables, unless you model everything in a CAD tool or similar (someone has written a program to do this and at the time of writing you could download it from Altair Astro’s website).
To give you an idea of what it’s possible to fit in the POD, my AP1200 mount fits in fine and a small 5” OTA, like an NP127 or an ED120, can be slewed around the entire sky without risk. My 7” TMB is really too large, but by weighting the focuser end to allow full retraction of the dewshield when slewing, it does fit... just. However, I often have to carefully slew it manually when pointing near the zenith to avoid hitting the dewshield on the dome. A shorter pier would help (I use a 42” pier), but would mean some very uncomfortable eyepiece positions. Clearance at the focuser end can be a problem too, especially around the brackets that hold the dome on.
The NP127/AP1200 are an easy fit: you can use GOTO anywhere, even with the dome shut.
Preparing a Base
I went for a concrete slab with a damp-proof membrane. I did the digging, then had the concrete laid professionally. The builder got it very flat and level. I then bolted the POD onto the slab using big anchors drilled into the concrete and screwed through the holes provided through the flange at the base of the POD walls. After much thought I decided against a permanent pier, as a moveable one allows me to “tune” the position of the pier within the POD (I have settled with it offset southwards to give me a bit more space behind the scope in its most common position).
You often see PODs mounted on decking with the pier protruding through and in retrospect that might have been a better option. The reason is that waterproofing around the solid base is an ongoing problem because the POD flexes slightly with use, loosening any sealing compound you put around the base to prevent water running under it. A decking base would collect and channel water less than solid concrete.
A comprehensive video is provided and I found the POD fairly straightforward to assemble. For a step-by-step account of assembly, see the Sky Shed website. Assembly took the best part of a day and would need at least two people and preferably more.
Most of the required parts and materials are provided, like rubber sealing strips, but you will need to buy a staple gun to attach the draught excluder seals around the dome hinges.
You start by assembling the dome into its two halves. This requires a certain amount of perseverance, as the mouldings aren’t perfect. You have to put a waterproof strip in each of the joints. I did this very carefully, but have had to back it up with a bead of silicone that needs regular replacement because the plastic is greasy and thermal contraction loosens the sealant over time.
Fixing the rubber-curtain sealing strip to the outer dome requires considerable care. Do this when you’re fresh and allow plenty of time to get it right. If you don’t, you’ll get kinks in the rubber and the seal won’t be good, allowing water to get in between the outer and inner dome segments.
Having assembled the dome segments, you then bolt the walls together, which is easy enough to do. The dome outer is then lifted onto the walls, followed by the inner opening part, and the two are bolted together. You need to leave the walls loose and unfixed until you’ve done this, as running the dome around forces the wall segments into a perfect circle.
Finally, you attach the brackets that keep the dome on, after which the POD can be bolted down (or not, depending on how permanent you want the installation to be).
The POD doesn’t come with electrics. I just drilled a hole through the walls, then ran in an armoured cable from an RCD in my garage. You could go as far as having a separate fused circuit added to the main junction box, but I haven’t yet got around to this.
Inside the POD, I wired in a waterpoof twin socket for the mount and accessories and a switch, designed for garden pond lighting, to operate the red and white lights. I found that the polyethylene construction of the POD walls makes drilling and subsequent fixing of electrical fittings quite easy.
Pond-lighting switch installed. Note the dome-locking handle to the upper right.
For lighting I used a cheap bulkhead lamp for a white light and a set of red-LED Christmas lights secured around the base to provide red lighting. I wired both of these into separate switches.
Sketching Jupiter using the 7”: It’s a tight squeeze, even for a 12 year old.
The POD is easy to use, which is good because that is what an observatory is all about. Getting out and observing is amazingly easy with a permanently set up and aligned mount and scope:
A typical observing session sees me grab the POD keys and a few eyepieces, stuff them in the pockets of my duvet jacket and walk out of the front door. I then have to walk across 10m of lawn, unlock the door and twist the handle, reach around and switch the white light on, duck and walk in. I flip the switch on the mount and (if I have a smaller scope installed) just select the object I want to view from the GOTO menu before opening up. As the scope is slewing, I undo the two handles that lock the dome and then push it open to reveal the night sky, turning it if required. By then the scope is usually settled on my first target, so all I have to do is put in an eyepiece (I keep a diagonal in the scope), pull the stool around and start observing.
The only complication to this routine arises if the dome is snowed or iced up. I recommend removing snow during the day and before it gets icy, because ice on the inner dome can rip and damage the rubber sealing strip when you flip the dome open. De-icing the dome with buckets of hot water at -15 in the small hours is no fun, believe me.
I found that the door lock ices up in very cold weather. WD40 helped, but the real fix was a squirt of something called ACF 50, which is a creeping lubricant designed for the military and much used by motorcyclists.
Closing the dome is similarly easy, except that I have to carefully rotate and lower it back into the lugs on the walls. Letting the dome slam shut isn’t a good idea, as that tends to loosen seals around the base and dome segments.
The POD makes observing much more comfortable: the dome helps shield you from the frost and the walls keep wind and stray light out. Observing in a proper snug little “room” with a floor, light and power is hugely pleasurable if you are used to a frosty or muddy lawn. Even using a small scope or binoculars is nicer in the POD, as it gives you privacy and a break from lights and cold winds. Having almost half the sky in view means you don’t have to turn the dome unless you start observing in a completely different part of the sky.
The ease and quickness of opening and closing the POD dome mean you can observe during short breaks in the weather without risk of getting your scope rained on – a key benefit in our climate.
One small issue is that the dome design doesn’t allow viewing at the zenith.
Viewing near the zenith isn’t possible with larger scopes. Here you can see why.
Overall, the POD is such a cosy and relaxing environment that I have fallen asleep at the eyepiece on several occasions during early morning planetary vigils!
The biggest problem with the POD, in my two years of experience with it, is that of leaks. The wall segments don’t seem to let water in, so the problem areas are the dome joints, the base and (worst of all) the areas around the dome hinge-bolts.
The polyethylene is greasy and silicone sealant loosens away from it over time, so I have to renew the sealing along the dome segments every six to twelve months, but if I do this the dome remains watertight.
Silicone sealant loosens over time.
Flexing of the walls means any sealing around the base always starts leaking with time, but again renewing this yearly keeps things under control. I have found a combination of foam gap sealer and regularly-renewed silicone to be the best sealant.
The main problem area, though, is the seals around the hinges. This area isn’t covered by the rubber strip and you need to fix extra bits of rubber around them to help keep rain out (instructions and extra seal material are provided for this). These often get caught and folded in when I close the dome so I usually have to take a minute to re-seat them with a thin stick every time I close up.
This area is the main source of leaks: note the patched seal which gets trapped, kinked and torn easily here.
However carefully I re-seat the rubber seals, a few cupfuls of water get through every time it rains and I keep drip trays permanently in place to cope with this. Even so, after wet weather I usually have to go in and mop up a litre or so of water from the floor, then turn on a de-humidifier for an hour or two. The latter is a great addition to any observatory where cold metal parts get wet in high humidity; I have a Mitsubishi unit that works very well.
Keeping on top of water and dampness is an ongoing chore, but a much less time consuming one than dragging equipment in and out. Fail to do it, though, and you could end up with problems and even corrosion of your mount and scope. I have seen a horribly rusty Takahashi EM500 (a £10000 mount) in an observatory with poor waterproofing – don’t let that happen to you!
In many ways the Sky Shed is an excellent and unique product that has allowed me to fulfil my observatory dream.
The Sky Shed is relatively easy to transport and assemble, unlike many fibreglass domes, and it can fairly simply be taken down and re-built for home moves and even star parties. The flip-opening works much better than a slit for many amateurs and broadens the scope of the Sky Shed to include a huge range of observers (there’s an argument for one of these even if all you do is keep a deckchair in it to use with binos). The flip-opening not only allows you to see a much broader swathe of sky and requires much less dome-turning, it also allows you to house a bigger scope and mount than a conventional dome of the same size. The POD has proved very ruggedly constructed and has stood up to some savage storms.
There are a few minor negatives, like the noisy wheels (fixed on recent models); the sticky door catch (fixed with WD40, or better ACF50); the fact that the thickness of the mouldings makes the interior smaller than the external dimensions; the yellow discolouration of the (optional) foam filling over time. But these are very minor gripes.
However, two years on I have to tell you that my POD has two fairly significant issues:
· The main one highlights the reason I started this website: whilst the POD is doubtless adequately waterproof for continental U.S. conditions, in the rainy northern UK it just plain leaks too much, despite endless efforts to seal it. The problem is inherent in its modular design. Careful assembly and regular re-sealing of the seams with silicone goo will help, but on very wet days you’ll probably need to do some drying up and mopping out.
· The zenith is a bit of a no-go zone for POD users, because the lip of the fold-up part of the dome overhangs and obscures it. Big OTAs and mounts exacerbate this problem.
All in all, though, the best thing about the POD that the niggles can’t spoil is that it’s an observatory: a permanent setup for your gear. I just can’t overstate how wonderful it is to be able to pop-out at midnight for a quick look or a few images, then close-up and walk away within minutes. You’ll do ten times more observing with a proper, permanently aligned rig in this (or any other) decent observatory.
An observatory is the best thing you can buy to make this hobby more enjoyable and productive. On that basis, even given its drawbacks, the Sky Shed POD gets my highest recommendation. It’s cheaper and easier to transport than a fibreglass dome and offers a snugger environment (and more robustness) than a roll-off. The only real disadvantages are leaks and the heavy dome which makes it unsuitable for the weak or infirm.