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The end of the line for the Arecibo radio telescope
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Ian.M:
Its also a matter of access.   You'd need to get heavy lifting equipment in place to relieve the load on the cables.  I suspect the nearest >1000 tonne mobile cranes are in the USA or Mexico and even assuming you could get three big enough cranes on the quay in San Juan with enough time to do the work (there's only seven months till the next hurricane season), getting them up the road to the observatory (Highway 625) and emplaced just outside the rim of the dish between the towers, avoiding the danger zone would be a challenge in itself.

You'd also need to design a method of grappling or getting slings on the antennae platform that doesn't put the workers at unacceptable risk.
Nauris:

--- Quote from: David Hess on November 27, 2020, 03:42:03 pm ---Photographs show that the remaining cables have already had strands break due to excessive strain.

--- End quote ---
That must be from corrosion/fatigue or past overload. If there were strands breaking from static load it would already be on the ground

--- Quote --- The structure could collapse at any time.

--- End quote ---
But why would it collapse at any time? I think it most probably comes down when there is some small extra stress acting on it like a gust of wind. So if it survived a windy day it is unlikely to come down following calm day and that is exactly the moment repair crew should be working on it.


--- Quote ---It would take too much time, and cost too much considering available funds.

--- End quote ---
I don't think it takes more than a week or two. Few kilometers of steel rope and a group of brave spanish men in Puerto Rico getting things done cost way less than those worry worry engineers and managers currently overanalyzing it and making straightforward things sound impossible. After all it is still up just needs some cables reinforced.
Gyro:

--- Quote from: Nauris on November 27, 2020, 07:29:46 pm ---But why would it collapse at any time? I think it most probably comes down when there is some small extra stress acting on it like a gust of wind. So if it survived a windy day it is unlikely to come down following calm day and that is exactly the moment repair crew should be working on it.

--- End quote ---

It does seem pretty unlikely that, with a static load of 900 tonnes, stretched out at an angle too, the additional weight of a couple of people going out to attach the end of an emergency support cable would trigger a sudden collapse.

The crew could maybe be on safety lines from a helicopter too.


P.S. Mind you, I'm sitting in an armchair!
Ian.M:
Due to the geometry, there's far more than 900 short tons (approx 820 metric tonnes) load on the cables.   You can find some details of the geometry here: https://www.naic.edu/~astro/aotms/performance/StructureDynamics.pdf


One of the problems is a cable under tension will whip violently if it breaks, and anyone in the way of a steel one as large as the Arecibo platform uses when it lets go would most likely end up as a chunky bloody splatter, and any helicopter could be swatted out of the sky.   

Also, if the cables have been weakened enough that there is insufficient remaining redundancy, its no longer possible to slack off one cable at a time and replace it to the same anchor points, so cable replacement becomes vastly more complex, putting more people in the high danger zone for longer.
David Hess:

--- Quote from: Nauris on November 27, 2020, 07:29:46 pm ---
--- Quote from: David Hess on November 27, 2020, 03:42:03 pm ---Photographs show that the remaining cables have already had strands break due to excessive strain.
--- End quote ---

That must be from corrosion/fatigue or past overload. If there were strands breaking from static load it would already be on the ground.
--- End quote ---

The strands were broken from the two recent overload events.


--- Quote ---
--- Quote ---The structure could collapse at any time.
--- End quote ---

But why would it collapse at any time? I think it most probably comes down when there is some small extra stress acting on it like a gust of wind. So if it survived a windy day it is unlikely to come down following calm day and that is exactly the moment repair crew should be working on it.
--- End quote ---

It could collapse because the remaining cables are damaged and in an uncertain condition.


--- Quote ---[A] Few kilometers of steel rope and a group of brave spanish men in Puerto Rico getting things done cost way less than those worry worry engineers and managers currently overanalyzing it and making straightforward things sound impossible.
--- End quote ---

The physics and engineering are straightforward.  The weights are known and the geometry can be measured from a distance to calculate the strains involved.  Photographs show that the remaining cables have been stressed beyond their safe limit.

"Management" is who allowed deterioration of the structure to proceed over the past 13 years of no maintenance.
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