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Communications

Arecibo Collapsed Because of Engineering Failures That Inspectors Failed To Spot (behindtheblack.com) 61

An anonymous reader quotes a report from Behind the Black: According to a new very detailed engineering analysis into the causes of the collapse of the Arecibo radio telescope in Puerto Rico in 2020, the failure was caused first by a surprising interaction between the radio electronics of Arecibo and the traditional methods used to anchor the cables, and second by a failure of inspections to spot the problem as it became obvious.

The surprising engineering discovery is illustrated [here (PNG)]. The main antenna of Arecibo was suspended above the bowl below by three main cables. The figure shows the basic design of the system used to anchor the cable ends to their sockets. The end of the cable bunches would be inserted into the socket, spread apart, and then zinc would be poured in to fill the gap and then act as a plug and glue to hold the cables in place. According to the report, this system has been used for decades in many applications very successfully.

What the report found however was at Arecibo over time the cable bunch and zinc plug slowly began to pull out of the socket, what the report labels as "zinc creep." This was noted by inspectors, but dismissed as a concern because they still believed the engineering margins were still high enough to prevent failure at this point. In fact, this is exactly where the structure failed in 2020, with the first cable separating as shown in August 2020. The second cable did so in a similar manner in November 2020.

The report concluded that the "only hypothesis the committee could develop that provides a plausible but unprovable answer to all these questions and the observed socket failure pattern is that the socket zinc creep was unexpectedly accelerated in the Arecibo Telescope's uniquely powerful electromagnetic radiation environment. The Arecibo Telescope cables were suspended across the beam of 'the most powerful radio transmitter on Earth.'"

Arecibo Collapsed Because of Engineering Failures That Inspectors Failed To Spot

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  • How? How do these radio waves affect the zinc filler in the socket? What happens?

    • It probably heats up the zinc? Maybe?

    • The two mechanisms I can think of would be that either it heats it up, or it causes things to vibrate and slowly work loose. It would only have to be a tiny effect, it happened over decades after all.

    • by SandorZoo ( 2318398 ) on Thursday October 31, 2024 @08:10AM (#64908581)

      Long-term, low-current electroplasticity. The radio waves induced a current in the cables, which ended up grounding through some of the sockets. Or something like that. The report says:

      The only hypothesis the committee developed that could possibly explain the measured patterns and ultimate effects of the observed socket zinc creep acceleration was the effect of electroplasticity (EP). EP is "the reduction in flow stress of a material undergoing deformation on passing an electrical pulse through it." EP was first discovered by Eugene S. Machlin, who reported in 1959 that making a 6 kV (dc) closed circuit with NaCl crystals made them weaker and more ductile. Later, in 1963, Troitskii and Likhtman reported the same EP effect in zinc crystals. In 2020, Baumgardner et al. reported the following:

      A low-energy electroplastic effect in aluminum alloys at an ultra-low current density threshold between 0.035 and 0.1 A/mm2 that resulted in EP-assisted reduction in hardness of 10% and increases in creep rate up to 38% over a range in temperatures from 25C to 100C. Systematic experiments and ab initio calculations showed that Mg-Zn alloying elements in Al7050 were the origin of the EP effect.

      "To date, the theories of Joule-heating, electron-wind force, and de-pinning from paramagnetic obstacles are the most commonly invoked explanations for instances of EP observed in different materials."

      You can get the whole report ftom here [nationalacademies.org]

    • by Rei ( 128717 )

      They attract aliens, which beam down and steal the zinc for their saucers' corrosion protection systems.

    • How? How do these radio waves affect the zinc filler in the socket? What happens?

      The radio waves would have induced electrical currents in the entire structure. And any mechanical metal-to-metal junctions would have been subject to ingress of water and contaminants. I'm just guessing here, but I suspect that at these points the current flow would be destructive in the same way that an electroplating process sometimes sacrifices one of the electrodes used.

      Note that such junctions can become de-facto batteries in any structure where different metals com into contact. The resulting current

  • I'm sure having (ex) OO agents running around conducting firefights on the array back in the 90s didn't help matters either, along with converting it into an easily drained and refilled lake to avoid aerial detection.

  • For a long time there was talk of closing down Arecibo, so letting it collapse is the safest way to stop funding it.
    Closing it down would involve saving the most expensive parts, the detectors in the hub suspended above the reflector.
    This will also result in the expensive parts being stored for use in a future radio telescope.
    The collapse and their destruction solved that problem too.

  • Not to trash them but they have a bad history with maintaining infrastructure.
  • by Pibroch(CiH) ( 7414754 ) on Thursday October 31, 2024 @08:39AM (#64908655)

    Come back zinc!! Come baaaaack!!!

  • Data point (Score:4, Informative)

    by ElizabethGreene ( 1185405 ) on Thursday October 31, 2024 @09:40AM (#64908795)

    Those poured-zinc-in-socket joints are called "Spelter Sockets", and they are ludicrously strong.

    Here's a video that shows a Spelter socket being poured.
    https://www.youtube.com/watch?... [youtube.com]

    This technology has been in use for a very long time, so there had to be something very odd in this application for it to have failed unexpectedly.

    • Cool video.

      Aren't these used all the time on cable-stayed radio transmission towers out West?

      Was Arecibo still in operation after the first cable failed?

      If so did they not see where the first cable failed and then inspect that point at other cables?

      If the socket was majorly deformed on the first cable did the inspector not know what to look for?

      Their theory on zinc migration is interesting but that shouldn't have any impact on rigging inspection, except as an academic footnote.

      This seems like something insu

      • Insufficient data to answer. My exposure to spelter sockets is from a brief hyperfixation (unsuccessfully) trying to find a cheap 3d printable mechanism for strongly attaching braided monofilament to plastic components in such a way that the line would not saw through the plastic.

  • It's a telescope, so it's a receiver. Why - and, indeed, what - was it transmitting?

  • ...than to prop up Arecibo any longer. Nothing lasts forever.
  • Next time, maybe use welding or something. Instead of glue. Also, if you do use glue, maybe replace the glue entirely on a schedule instead of gluing the cracked glue back together. Also, maybe use welding or something. Instead of glue.
  • by ElitistWhiner ( 79961 ) on Thursday October 31, 2024 @11:24AM (#64909095) Journal

    Creep was inspected, noted and documented

    Inspectors have neither the technical background to adjudge the degree of safety margin engineered into the fastener system nor physics that would explain it in the first instance.

    Inspected, noted, documented Arecibo management, policy and procedures failed science. Its a simple process if ignored invalidates all means to capturing a problem before it cascades into collapse.

    That no one lost a job over the loss of structure and telescope tells that leadership was too big to fail on the management team. Public-facing unsubstantiated conjecture masquerading as fact is paraded instead for blank check acquiescence. Gone is the science, the mission and any hope for the public investment. Clearly it is noted. People had all the reason to act. But failed imagination bias for the greatest telescope vulnerability cost everyone involved their jobs.

    Dumb

  • Inspectors were surprised when Arecibo collapsed because they missed something that led to the collapse.

    Really? That's newsworthy? Of course they missed the cause of the collapse, if they caught the cause before it collapsed, they wouldn't have been surprised when it collapsed!

    Now, if they saw the flaw and ignored it, THAT would be newsworthy...

  • ...Rico. Arecibo antenna is now garbage.

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