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Message 101817 - Posted: 27 Nov 2020, 18:17:27 UTC

Cross posting from the SETI main boards..
Streaming LIVE NOW (on Facebook): What happened to Arecibo? Join Space.com's Chelsea Gohd
The full video presentation will be viewable after the session is over also
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Message 101818 - Posted: 27 Nov 2020, 18:50:53 UTC

Did you know brown was dark orange?
Have you ever seen a brown light?

See https://www.youtube.com/watch?v=wh4aWZRtTwU
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Message 101878 - Posted: 1 Dec 2020, 20:50:14 UTC

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Message 101936 - Posted: 3 Dec 2020, 20:23:12 UTC - in response to Message 101878.  

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Les Bayliss
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Message 101939 - Posted: 3 Dec 2020, 23:18:35 UTC - in response to Message 101936.  

That was scary. And sad.
Vale Arecibo.
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Message 101962 - Posted: 5 Dec 2020, 2:21:40 UTC

Be careful what you tell your significant other what your computer actually is or this might happen to you
Lol.

Woman sells husband’s PlayStation 5 after she discovers it is not an air purifier
TAIPEI, Taiwan - A Taiwanese man who attempted to convince his wife that his PlayStation 5 was an air purifier was reportedly forced to sell the device after she discovered the ruse.
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Message 102037 - Posted: 8 Dec 2020, 16:52:45 UTC

Having watched the videos of the collapse I think everyone was extremely fortunate that they decided to do a drone survey before sending men into/onto the telescope. Wire strands were popping off, and when too many failed there was a massive release of energy and the whole of one of the towers gave way, closely followed by the failure of the remaining towers - cables about 100mm diameter were whipping around like bits of damp cotton - you may not value your life, but I'm sure few construction workers would want to be near that lot when the stored energy was released.
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Message 102052 - Posted: 9 Dec 2020, 19:20:01 UTC
Last modified: 9 Dec 2020, 19:22:54 UTC

Quite a few things went wrong at once - it is reported in some places that there was an earthquake shortly before the final failure; the cables had certainly been compromised by the earlier failure of the sockets where the cables were anchored to the pillars; and the actual pillars(which were reinforced concrete) appear to have been built to below today's standards. I doubt that anyone knew what state the cables were in, how many wires were failed and thus how many were actually working. The trouble with any of these wire cable structures is that unless continuously and correctly monitored it is not know if that wire that broke was the last one before cable failure or the first one ever to break and so there is plenty of margin left. (Hence the vast amounts of work being done to monitor the Forth, Humber and Severn suspension bridge cables - they don't want those structures to get into the "one more wire and bang" situation.)
Remember this collapse was during the "let's see what can be done to stop a collapse" phase and drones were probably the quickest and safest way of doing anything. One thing they did know was that the remaining cables were under a lot of strain, and had already been subject to a quite severe shock when the first one let go and I'm pretty certain they knew that wires were breaking, but didn't want to put men in the line of fire to see how many had broken.
If you want to hear a review of the video, and see the video from the drones during the collapse here's a link https://www.youtube.com/watch?v=vchDbyIRP44
[Edit to add:]
(One thing to note is that there is reference to towers 4, 8 & 12 - this refers the clock-face location of the three towers.)
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Message 102053 - Posted: 9 Dec 2020, 19:40:05 UTC

The reports also refer to the fallen instrument carrier weighing 900 tons. I haven't been able to find a corresponding weight for the platform as originally installed, but I'm pretty sure that a substantial amount of extra equipment was added over the years - like the 7-beam ALFA receiver that came into use while SETI@Home was active.
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Message 102055 - Posted: 9 Dec 2020, 20:29:20 UTC - in response to Message 102053.  

I dare say, like many objects it suffered "middle age spread" as it got older. More equipment was added and that meant more weight....... A few years ago there were some extra support cables added, I'm not sure if this was to cope with the additional weight of the added equipment or to mitigate for potential structural weakness - if one looks very carefully at the top of the tower as it fails one can see two very slightly different styles of securing which may be the ends of the original and added cables.
Where I'm sitting there are a lot of unknowns about the structure of the main Arecibo dish and towers. But let us not forget that the big dish was only one of the telescopes at the Arecibo site, and as far as I'm aware the others were not damaged by the collapse and will continue to operate.
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Message 102056 - Posted: 9 Dec 2020, 23:24:39 UTC - in response to Message 102053.  

I haven't been able to find a corresponding weight for the platform as originally installed

https://structurae.net/en/structures/arecibo-telescope quotes 820 tonnes being 900-short-ton.
http://articles.adsabs.harvard.edu//full/2002ASPC..278....1A/0000003.000.html from 2002 also reports 900 ton.

Ah...
https://www.naic.edu/~astro/aotms/performance/StructureDynamics.pdf
Page 3: In the original configuration, the triangular platform had a mass of 550 tons, and was suspended by 12 main cables (each of 3 inch diameter - braided steel) from 3 towers.
Page 5: The second Arecibo upgrade, completed in 1997, was the implementation of the new Gregorian system (receiver/transmitter), whose weight and additional structure increased the total mass of the platform form 550,000 kg to 815,000 kg. [2]. To support this much heavier platform, using the same three towers, additions to the number of cables were made: 6 auxiliary mainstay cables (each of 413 inch diameter) were added from the tower tops (2 per tower) to the platform and 6 auxiliary backstay cables (each of 853 inch diameter) were added from the tower tops to the ground.
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Message 102061 - Posted: 10 Dec 2020, 5:26:06 UTC - in response to Message 102044.  
Last modified: 10 Dec 2020, 5:26:38 UTC

Or were the wires rusting and long overdue replacement?
After having found the cable attach ends were not made to spec, a prudent engineer would assume the cable itself wasn't made to spec. Spec would include corrosion prevention, flaws in manufacture, and ability to prevent metal fatigue.

While sending men in to prevent a reactor issue may be prudent, having the dish fail isn't going to cause potential harm to millions located around the globe. Not having been built to set the instrument platform on the ground, once the first failure occurred it was just a matter of time until a cascade event took place.

If there is political will to spend the money to rebuild, I would expect a much higher quality main mirror and a much lighter carbon fiber observation platform as a replacement. One could perhaps envision a dish with a active surface control able to counter wind loading and keep figure to say 300GHz. With the issues of RFI from the airport and ship radars perhaps its replacement might not even be sighted on Puerto Rico but in a much more radio quiet area. However this ignores phased array technology, which easily could deliver a more steerable signal and do so with a flat "dish" area potentially of many square kilometers.
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Message 102063 - Posted: 10 Dec 2020, 9:21:43 UTC - in response to Message 102056.  
Last modified: 10 Dec 2020, 9:22:03 UTC

To support this much heavier platform, using the same three towers, additions to the number of cables were made: 6 auxiliary mainstay cables (each of 413 inch diameter) were added from the tower tops (2 per tower) to the platform and 6 auxiliary backstay cables (each of 853 inch diameter) were added from the tower tops to the ground.
Those would be some cables!

The original has 'three and a quarter inches' and 'three and five eighths inches' respectively (88.5 mm : 92 mm). Another triumph for the US adherence to imperial measurements in a technical setting. NASA would be proud. And another triumph for Word-PDF conversion - it transposes the digits when I try to copy-paste them, too.
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Message 102068 - Posted: 10 Dec 2020, 14:49:18 UTC - in response to Message 102063.  

(each of 413 inch diameter)
(each of 853 inch diameter)
No, that's 3 1/4 inch and 3 5/8 inch.

I was already going... uh, cables of 10 and 21 meter thick? They themselves weigh several kilotons already per meter. But it's the way the notation was in the original text.
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Message 102069 - Posted: 10 Dec 2020, 15:28:58 UTC

The thesis is a fascinating read, and in some respects shows how far structural analysis has come on in the last decade or so.
One thing I did notes is that the cables are described as "braided", but in the pictures and videos they appear to be wrapped-layered cables. A subtle difference and probably not relevant until one gets into analysing the failure mechanics of a cable.
For the uninitiated a braided cable is one in which each layer of the cable comprises what appears to be a woven tube of wire, while a wrapped-layer cable is one in which each layer is wound in turn. The former tend to use much finer wires than the latter, and the surface looks like one of those old fabric covered mains flex. Braided cables tend to be a bit better when it comes to abrasion resistance and are harder to produce when the cable diameter gets over about 50-80mm.

Corrosion?
Most certainly an issue. Nowhere on the island is that far from the sea, it's also in the middle of a rain forest, so very humid in a salt-rich with salt-rich water. Then add the fact that we are near the equator, so lots of UV which makes life hard for any surface coating. Over the years there have been vast improvements in surface coatings, but I think they just went for the "more of the same" approach - every few years slap on another coat of paint having chipped off the obviously loose stuff. I don't know if they ever did a proper strip off all the old paint, inspect and prime the surface (including the inter-strand surfaces) then applying a modern high performance coating as used on things like deep-sea rigs or very tall communications towers.
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Message 102070 - Posted: 10 Dec 2020, 15:53:25 UTC

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Message 102071 - Posted: 10 Dec 2020, 17:56:38 UTC

Interesting. I know little about cables and the relative strengths of different types of cable. What I do know from my time spent around circuses is that a 50ml braided rope has virtually no bounce for drops compared with a traditionally laid rope. With cables I would guess there is also a difference in elasticity which will affect things like resonance as well as differential changes in length if one cable is in sunlight another in shadow etc.
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