Keeping Dust out of RORO Observatory. Advice?

[samirkharusi (Samir)]

Hi, my first post here. I live in Oman (desert, hot, dusty, like some parts of Oz) and for my next observatory I wish to (1) keep dust out so that I do not have to drape cloths over equipment at 3am and (2) not use electrical cooling (air-conditioning) to keep the inside temperature not much higher than ambient.

Experiences to date with my current obs that has ample flow-through ventilation:

Our highest mid-summer, mid-day ambient temperatures of 45deg C do not damage my astro equipemt. I do not use the stuff when it goes over 30deg C anyway, but it would be a major nuisance to take away all the astro stuff for the summer and set it up all over again for winter.

There is far too much dust settling on the equipment, because of the current air flow-through design, to keep equipment undraped.

I suspect that there may be some people in this group who face similar issues. My plan for my next observatory is for a sealed RORO roof made of GI sheeting on a metal cage frame, similar to what I now have, but with a second sheet roof a couple of inches higher to act as a sunshade for the primary roof. There will be ample airflow between the two roofs. Consequently the inside of the sealed observatory should not heat up to more than a couple of degrees above ambient. Extra heat comes in mainly from the one wall exposed to the Sun at any one time (made of concrete breeze blocks). Any comments as to whether this double-roof idea has any chance of working? Since the lower, primary roof will always be at ambient, I expect that heat gain via the roof ought to be less than if I were to use heat insulation (fiberglass or 5cm polystyrene foam boards) under a single-sheet GI roof. An alternative could be a 3cm polyurethane spray-on foam on top the GI, but it would still transmit more heat into the observatory than if it were shaded and at ambient. Polyurethane is supposed to be a far better heat insulator than polystyrene so a thin application would be more effective than stapling 5cm polystyrene foam boards underneath a single GI sheet roof. Still unsure.

Any suggestions as to how to make the RORO roof seal when it slides into the closed position? Rubber seals, brushes, etc. What is likely to be trouble free? Thanks.

My existing observatory:
http://www.pbase.com/samirkharusi/planetary_perch

[Merlin66 (Ken)]

I've never been successful in keeping a RORO system dust tight!
The clearances need to allow the roof the freely roll are always an issue.
Maybe those brush strips you now see on the mudguards of lorries (to wipe the mud from the tyres) could be used - they would close the gap and cause minimum friction??
On my smaller TSO (Tin Shed observatory) I made the side weather seal a bit longer than usual (almost 200mm) to increase the overlap with the walls and the ends ( when the roof is closed) seal onto rubber tubes front and back. Certainly keeps the weather out - but the dust...Hmmm

[bmitchell82 (Brendan)]

if you can get it reasonably sealed you can use positive pressure to keep the air pushing out. its like water it wont flow up hill. Similar concept to a rally car, thats why they have the little bonnet scoop but mounted on the roof in the clear air.

Hope that helps

[GrampianStars (Rob)]

Originally Posted by samirkharusi

........
Any suggestions as to how to make the RORO roof seal when it slides into the closed position? Rubber seals, brushes, etc. What is likely to be trouble free? Thanks.
My existing observatory:
http://www.pbase.com/samirkharusi/planetary_perch

I have rubber molded on top of walls Nth/Sth, to seal the roof ends when open/closed.
along the rails there is foam strip seals.
and the rail open slots I use paint brush bristle.
85% dust free! the raised deck is open to allow ventilation from beneath.
(I 2 get HOT 45 in summer)
I still use a cotton sheet when not in use

[samirkharusi (Samir)]

Finally some encouragement! There are many situations of course. The first is if I am in the middle of taking a huge bunch of subexposures and the last thing I want to do is to dismantle the camera and wiring and have to re-set-up the next night to continue. Your encouragement there is noted, hugely. The second situation is when I have no clue when will I be using the equipment again, but probably in a week or two. So just putting on the OTA covers sounds like it would be adequate, provided I pay enough attention to the seals. Then there is the shutdown for the summer. I have no problems using drape cloths for that. Once per annum is not a huge chore.

Any idea how hot it gets inside your sealed observatory mid summer? 5deg C, 10deg C higher than ambient, or whatever?

[Merlin66 (Ken)]

Samir,
I was looking at my RORO roof this morning and thinking about the dust issue.
Sealing the ends is very straight forward with rubber tube being compressed as the roof closes - the real issue is the sides.
On my set up I have side strips about 200mm long which drop down from the roof and overlap the sides of the observatory. There's an obvious clearance gap - which you need to give free rolling of the roof -BUT
What if these side plates were hinged at the top and with a small spring could be "lifted" further way from the outer surface of the walls. The a seal strip - foam/ rubber etc could be fitted to the outer surafce of the walls just above the edge of the side strip....Making any sense?
Then as the roof closes a series of wedges (probably three per side) engage with similar on the outer surface of the side strips to gently force them in towards the walls - compressing the foam and giving a pretty good dust seal???????
I think this is a simple solution to try out???

[GrampianStars (Rob)]

Originally Posted by samirkharusi

.......

Any idea how hot it gets inside your sealed observatory mid summer? 5deg C, 10deg C higher than ambient, or whatever?

Now always 5deg C, Cooler ! than ambient (wood walls)
I am putting a raised 90% UV protection shade cloth 4" above the roof before the coming summer. Should then get hopefully get up to 8 deg C, Cooler ! than ambient with the airflow and NO sun striking the metal roof.