Observatory on bedrock

[GilesB]

I am fortunate to have a site for an observatory that is on sandstone bedrock.

I am thinking of a 2.7m dome with the floor supported from the circular edge.

And the pier bolted directly to the bedrock.

Or is there a better way?

[michael8554]

The norm is that a dome attached to a circular concrete floor requires the pier to be isolated from the concrete.

Are you sure that the dome and pier attached to the same lump of rock gives the pier the necessary isolation from vibrations ?

Michael

[GilesB]

No, I am not sure.    

Also considering adding six or more rubber anti-vibration truck engine mounts around the periphery on which to build the floor and dome.

Concerns about that are a) securing the dome against occasional very high winds, b) earthing the dome.

[AstroKeith]

You have over a metre between the building and floor fixings and the pier. I doubt you will have a problem.

You are right to worry about securing the structure and dome against wind. If the dome support doesnt come with a suitable retaining mechanism then it is fairly easy to add something. You won't be observing in such winds, so just 'tie it down'.

Is the dome metal? Protection against lightening strike is complicated. Is it very exposed?

[saac]

If you are using the observatory for visual then the vibration concerns should not really be as much a concern as when imaging.  I think sometimes we can over analyse these issues and certainly over engineer solutions to perceived problems. One of the easiest ways to minimise transmitted vibrations is to avoid moving around excessively during the image run - can you set up with a remote operation?  At the end of the day, your structure will ultimately communicate to the bedrock so I wouldn't worry overly about it. I think your proposal to float your sub floor on isolation pads is reasonable, I would imagine a sheet rubber (matt) material would suffice, and perhaps similar between the pier and the bedrock should you wish.  I just moved my own pier to accommodate a larger telescope in my obsy and this time i didn't bother with isolation, I tend to run the imaging remotely c=vacating the obsy once the run starts. 

Jim 

Edited July 3, 2023 by saac

[Henrik_er]

Hi! 

I am about to tackle the same challenge on bedrock in Norway. I have around 20 sqm of bare mountain. I was planning to create the slab for the pier first, and then a separate slab for the dome, with a rubber or air gap between them. Not sure if it makes any difference though when it is all stood on the same piece of bedrock? Any thoughts are most welcome. I did read the thread where there were vibration issues, but I understood that was placed in soil?

 

Best regards,

Henrik

[900SL]

I would decouple the floor from the pier, and the bedrock. Most vibration comes from footfalls (walking) near to the pier, so isolating the floor using a separation joint and resilient floor covering is advisable 

Bolting the observatory to the bedrock shouldn't cause major issues. The mass of the bedrock greatly exceeds that of the observatory. 

I did some design on a facility for Tokyo Electron years ago. They built wafer fab machines and the restriction on floor vibration in the clean room was the most onerous I have ever seen. Aircraft passing over could create enough vibration to exceed tolerance.

Mass damping was the key. 

 

[inFINNity Deck]

On 03/07/2023 at 09:37, GilesB said:

No, I am not sure.    

Also considering adding six or more rubber anti-vibration truck engine mounts around the periphery on which to build the floor and dome.

Concerns about that are a) securing the dome against occasional very high winds, b) earthing the dome.

Yes, you could use those to mount the observatory and fixate them to the bedrock using chemical anchors. If you use the M10 male to female versions, you could use M10 anchors, cut them to size and then mount the vibration dampers. I use these dampers for the motor that drives my dome. The motor now can turn several degrees on its base without affecting too much the observatory, while not transmitting any sound from the motor to it (see fig.2 in https://www.dehilster.info/astronomy/dome_automation.php).

Nicolàs