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Thread: Broken Cable Damages Arecibo

  1. #31
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    Quote Originally Posted by Swift View Post
    While I really would like to see Arecibo replaced, I would hate for an important geological site like Meteor Crater be destroyed to accomplish that. I also can't believe it would make that much of a difference in cost.
    And there's already a perfectly good site that's not a unique geological formation and major tourist attraction. It's even already equipped to support radio telescope operations.

  2. #32
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    Quote Originally Posted by Roger E. Moore View Post
    The great telescope has collapsed as of today. Damage is severe.

    https://phys.org/news/2020-12-huge-p...telescope.html
    Quote Originally Posted by schlaugh View Post
    Makes me very sad. The tops of all three towers appear to have snapped off. The price of deferred maintenance.
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  3. #33
    Sums up 2020 perfectly.
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  4. #34
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    Ho-lee Cow, that is a terrible sad mess.

    https://www.universetoday.com/149029...has-collapsed/
    Do good work. —Virgil Ivan "Gus" Grissom

  5. #35
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    Quote Originally Posted by cjameshuff View Post
    And there's already a perfectly good site that's not a unique geological formation and major tourist attraction. It's even already equipped to support radio telescope operations.
    Exactly my thought. But it would cost $$$.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  6. #36
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    Scott Manley put together a quick video on the collapse:

    https://youtu.be/vchDbyIRP44

  7. #37
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    Twitter thread with some pictures:

    https://twitter.com/zonhei/status/13...s-collapsed%2F

    I got that from this article:

    https://arstechnica.com/science/2020...has-collapsed/


    It didn’t wait for the controlled demolition. *sigh*

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  8. #38
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    But it does show that demolition was the right call. It was just waiting to fall. Happily, it appears nobody was hurt. Now I wonder if there is any need for any more demolition, or just conventional removal procedures.

    "The problem with quotes on the Internet is that it is hard to verify their authenticity." — Abraham Lincoln

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  9. #39
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    Quote Originally Posted by Trebuchet View Post
    Exactly my thought. But it would cost $$$.
    As would the proposed Meteor Crater telescope.

  10. #40
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    So basically:
    the structure hung on 18 cables (6 cables in each of the 3 directions)
    when 1 of the 6 cables snapped after 50+ years, the structure was left standing for 3 month (August to November), but the remaining 5 cables, already weakened, were overloaded, so second cable snapped in early November and third cable 3 weeks after 4 cables of 6 had been left
    failure of 3rd cable out of 6 exceeded the margin of the safety of the remaining 3, so the structure collapsed immediately.

    What had been the contingency plan to replace 1 snapped cable out of 6, that they should have carried out in the 3 months after August but did not?
    What was supposed to be the contingency plan to replace cables without dropping them in the dish at all? What was the plan to detect weakening of cables, so they could be replaced before they ever snap and fall in the dish?

  11. #41
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    Quote Originally Posted by chornedsnorkack View Post
    What had been the contingency plan to replace 1 snapped cable out of 6, that they should have carried out in the 3 months after August but did not?
    On a telescope with a 900 ton suspended weight with decades of subpar maintenance? Nothing that I can think of would work especially since the budget would be next to nothing. New cables where ordered but the old ones collapsed much faster than it could ever been fixed.

  12. #42
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    I watched a Scott Manley video on it a couple of hours ago. He described the first two cable failures as being on "Tower 4". There are only three. What?
    Then he later referred to "Tower 8" and "Tower 12". Oh. It's a clock!
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  13. #43
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    There is some amazing video of the collapse at the following link:

    https://www.thedrive.com/the-war-zon...cope-collapsed
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  14. #44
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    Now that (most?) of the danger has passed, what about a central tower on the site?

    Most of the dish is intact---a central tower might be ringed with a hoop shaped feed horn that can be raised or lowered flagpole style?

    Not as good--but that might be something to salvage.

  15. #45
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    Puerto Rico's Arecibo Observatory 'not closing' after collapse

    QUOTE: Ralph Gaume, director of the US National Science Foundation's division of astronomical sciences, said "the NSF is not closing the Arecibo Observatory... The NSF is deeply saddened by the situation," he told reporters, adding that the agency "has a very well-defined process for funding and constructing large-scale infrastructure including telescopes... it's very early for us to comment on the replacement."

    https://phys.org/news/2020-12-puerto...-collapse.html
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  16. #46
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    Puerto Rican scientists want Arecibo to be rebuilt.

    https://www.nbcnews.com/news/latino/...build-n1249666
    Do good work. —Virgil Ivan "Gus" Grissom

  17. #47
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    Quote Originally Posted by Roger E. Moore View Post
    Puerto Rican scientists want Arecibo to be rebuilt.

    https://www.nbcnews.com/news/latino/...build-n1249666
    Good. So do I. Like the Six Million Dollar man, let's make it better!
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  18. #48
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    Quote Originally Posted by Trebuchet View Post
    Good. So do I. Like the Six Million Dollar man, let's make it better!
    I don’t know about faster, but stronger would be good.
    I may have many faults, but being wrong ain't one of them. - Jimmy Hoffa

  19. #49
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    If nothing else, maybe a pilot rectenna for SPSS.

    A decade or two back, I saw art of disk shaped AESA Radar blimps.

    I wonder if such a disk could be raised/lowered here. Soft robotics and print-on circuits and all.

    Deflate before storms...

  20. #50
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    Quote Originally Posted by Trebuchet View Post
    I confess I haven't looked, but have they said WHY the cables failed? My first guess would be corrosion. That should have been preventable.
    I just watched the drone footage. When we learn about multistrand cables like those, the failure of one strand is a very serious event because total failure is not far behind. Obviously the cable is designed within safe load and, I would think, fatigue limit, which for steel is about half the proof load, which is the elastic limit.

    So a single strand should not fail. Corrosion is a possible cause but I suspect slippage or creep at the end where the cable is expanded and locked together with Zinc. The idea is that all strands are equally loaded but if the centre strands start to creep through the zinc block, the outers get overloaded. To some degree the load sharing is benign, but once one strand goes there is the domino effect.

    Unfortunately, the weight load cannot be removed so failure is inevitable unless another cable can be introduced. So it might not be a failure of maintenance but a built in obsolescence due to creep in the cable ends. Those cables are old and in the 60s creep was just being discovered and researched. Creep of steel inside a zinc block might not even have been discovered.

    It is thought that creep will occur at all loads but takes longer, obviously, as load decreases. Metals basically do not creep in their crystalline form but when you have an interface, the bond is not necessarily crystalline and you have the hard to analyse interface of two metals with different Youngs Modulus. Basic testing will have established a safe proof load at the time, but creep was too new to be considered or to have design parameters.

    That’s just my speculation, I studied creep in the 60s. It was not in the syllabus at that time.
    Last edited by profloater; 2020-Dec-08 at 02:26 PM. Reason: Corrected increase to decrease
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  21. #51
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    Nice explanation profloater.

    I also wonder if dynamic loads could have been higher than anticipated, such as from the several hurricanes that Puerto Rico has had, accelerating the slippage over time.
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  22. #52
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    Maybe lightning strikes annealed some of the metal? Vibrations alone would work the metal like spoonbenders do.

  23. #53
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    Quote Originally Posted by Swift View Post
    Nice explanation profloater.

    I also wonder if dynamic loads could have been higher than anticipated, such as from the several hurricanes that Puerto Rico has had, accelerating the slippage over time.
    Yes that is also a major factor, the wind load could start vibrations too. When I was at Bristol university the Severn bridge was being built and not only did I visit regularly to watch progress, I was lectured by the team dealing with that problem. At a critical wind speed, the cables go into higher modes of vibration, the Aeolian harp effect. The answer then , in 1966, was peanut shaped weights strapped to the cables at the nodes of the higher frequencies. Their angular inertia damped those. Without them there was a risk of failure above a certain wind speed through resonance. That also stresses the outer fibres more. Thanks for the thought, I had not considered higher wind speeds as I should have done. It also loads the ends more.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  24. #54
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    https://c8.alamy.com/comp/2B5E9GR/de...uk-2B5E9GR.jpg
    In this photo the added weights can just be made out on the vertical cables . From memory some were at a quarter, second mode while others were lower for even higher modes on longer cables.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  25. #55
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    Congress asks for report on Arecibo radio telescope collapse. The observatory is not closing, according to the National Science Foundation. The request comes as the observatory's supporters continue to rally on the facility's behalf, including a successful public petition calling for White House support of rebuilding at the site and a decision by the island's governor to allocate $8 million to the effort.

    https://www.space.com/arecibo-observ...o-funding.html
    Do good work. —Virgil Ivan "Gus" Grissom

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