The forensic report on the failure of the cable sockets is at https://www.thorntontomasetti.com/sites/default/files/2022-0.... Unlike the linked article this includes detailed diagrams and discussion explaining how these sockets worked and how they failed.
My attempt at a quick summary: the Arecibo instruments were held up by heavy steel cables, which are composed of a bundle of 126 to 216 individual wire strands twisted together, where each wire strand is about 1/4 inch diameter. At the cable ends these were anchored in sockets. The socket is conical, widening out towards where the wire ends go. The wire strands of the cable would be separated in a "broom" shape to fill out that conical area, and then the whole thing filled in with molten zinc.
The failure mode of these zinc-filled sockets is for an inner core cylinder, about the same diameter as the cable body, to pull out from the socket while outer strands of the cable which are broomed out of that core either snap or pull free from the zinc plug.
This failure mode hadn't really been seen prior to the Arecibo collapse, partly because it is a long term process where the zinc slowly flows under stress over decades.
With competent engineering and construction, the (failed at Arecibo) zinc socket cable anchors can be very reliable. Unfortunately, Arecibo's engineering was so-so, and the construction quality was half-assed.
With annual inspections (by someone with a passable understanding of cable anchors) the problems at Arecibo could easily have been caught in time to correct. Unfortunately, Arecibo received no such inspections.
And this is roughly the pattern for most "sudden" failures of infrastructure.
> Unfortunately, Arecibo received no such inspections.
With or without the inspections, the problems Arecibo faced were of a more serious nature. They are hinted in one of the findings: the non-replacement, repair or bypass of the sockets where large slips were observed.
The telescope received minimal funding for maintenance over the two decades prior to the collapse despite signs of increasing damage observed in the various inspections. A lot of factors probably contributed to this (political climate, the dropping importance of Arecibo compared to other science instruments and missions, and so on) but the result was that the structure was left with slow but sure decay.
I met a couple of people who worked with the telescope including on location and they told me that the general feeling among the people who had this on their minds (most people who ever had anything to do with Arecibo cared about the science not the instrument) was that the decay was slow but certain and catastrophic failure was bound to happen sooner or later. Like a car receiving no maintenance despite the check engine light being on for a decade.
The telescope received minimal funding because stakeholders couldn't make a good case for more. The results the facility could produce weren't seen as justifying the expense. In that light, that it was operated at all was more than one might reasonably have expected. The alternative was to just shut it down earlier. They squeezed the last drops of output before the old thing was allowed to die.
Sometimes with facilities like this you have to make the call that it's over.
Yes-ish? Funding was far more plentiful when the telescope was being designed and built, and in its early decades. I know zero details about that era - but I strongly suspect it suffered from "just focus on the cool parts" syndrome. And if it'd been designed and built correctly, or the problem caught and corrected back then, it would very likely still be standing.
Which is not to say it'd still be receiving operational funding, nor that its potential scientific contributions would be particularly worthwhile.
It was built in the ‘60s and started losing its relevance and funding in the 2-3 decades before the collapse. A lot of time for issues to develop, be noticed, but not have enough money to fix.
Ah, so historically things were build with a lot of slop. It was just the traditional kind with sloppy design, sloppy construction, and sloppy maintenance.
There is a lesson here to be ignored in the name of short-term personal gain.
The pictures on page 25 seem to show how this socket design fails. First because they didn't evenly distribute the wires in the socket (seriously??)... And second, the shear on the zinc from the compressed wire bundle is essentially a narrow rectangle in the direction of the cable with almost all the force concentrated in a narrow forward bit, not really distributed evenly through the socket, because of the wire ends splaying outward and not being equally distributed. I guess the idea is the rest of the zinc towards the back provides a counter force on the front part, but there's a whole lot more zinc in the back pulling on a smaller amount in the front. The tight bundle and the conical shape is great for a tight install, but doesn't help distribution of load. Compare to the Golden Gate Bridge wire termination (https://c7.alamy.com/comp/2RY9PKW/golden-gate-bridge-plans-i...). The zinc creep is definitely bad, but it seems made worse by an uneven distribution of load in the socket, in addition to all the other problems...
tl;dr once the outer wires break in the socket (in part due to zinc creep, but also potentially more load on them), the "glue" keeping the wire bundle connected to the socket is broken, the former wedge keeping the core in place becomes a straight line, and you have a core ready to pop out.
AFAIK cable brooming for spelter sockets is still not automated and relies on human skill, there's no tool to guarantee the necessary wire distribution. I wonder why it's hard to automate, these sockets are everywhere (along with wedge sockets) and are always safety-critical.
I did an apprenticeship in metalwork many..many years ago and I seem to recall the zinc is meant to be in compression. If a zinc plug pulled out, it was in shear. Sounds wrong to me.
Vincenti: https://en.wikipedia.org/wiki/What_Engineers_Know_and_How_Th...
Has a chapter on flush pop rivetting which discussed the loss of this kind of knowing.
Any bends or crimps in the wire create localized stress points which fail early. For crazy high loads you don't want any of that, so the zinc method is the standard. But I think this particular implementation will be rethought.
it had already been decommissioned prior to the collapse. Yes, decommissioning does indicate funding is being cut, but it was unrelated to the collapse.
> it had already been decommissioned prior to the collapse
The telescope was decommissioned one month before the collapse. The funding issues, lack of sufficient maintenance, and the inevitable decay that led to the collapse took a few decades more than that.
> Yes, decommissioning does indicate funding is being cut, but it was unrelated to the collapse.
The collapse was a direct consequence of the funding being cut. Maintenance was not performed on issues that were observed many years before exactly on the sockets that failed.
not good, not good at all, as this is how ALL bridges and towers are supported, the basic engineering bieng that any cable end will be stronger than the cable itself and will last longer than the cable itself, except now, when it isn't, not good, not easy to inspect, not easy to service.
> Long-term low-current electroplasticity, induced by the electromagnetic waves from the Arecibo telescope itself, may have sped up the zinc creep, it says.
I presume we aren't using most bridges as interstellar antennas.
The main paper goes into the detail on page 2. The cables were on beam path.
“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.
National Academies of Sciences, Engineering, and Medicine. 2024. Failure Analysis of the Arecibo Observatory 305-Meter Telescope Collapse. Washington, DC: The National Academies Press. https://doi.org/10.17226/26982.”
No, but there is a lot of potential for large structures to act like an accidental antenna and/or receive low level voltages from the environment or other equipment.
Likely won't matter in most cases, but there could be a few disasters waiting around.
They also mentioned that this is the first example of the unknown phenomena that caused the creep. This technology has been in use quite successfully for more than 100 years.
They were across the dish.
From the report:
“The Arecibo Telescope cables were suspended across the beam of “the most powerful radio transmitter on Earth””
The role of the cables was for supporting the equipment. The cables that failed, and are examined in the report, were designed to hold the equipment up, while it moved around. These cables weren't involved in carrying signals, data, or power.
There is no denying that energy was induced because of their placement at the focal length of the dish, but that was incidental to their purpose. The bundles of wires were spirally bound around a core. There were certainly ground connections and lightning arrestors involved. The EM effects and properties are discussed on pp 40–47 of the report.
anything, forgive the AI-sounding phrase, "load bearing" in terms of "the load is human lives" is very, very strictly regulated, with inspections mandated and consequences such as load limits and even closures being required when inspections flag issues.
However, even that is not foolproof. Here in Germany, we have had close calls (Rahmede bridge) as well as actual catastrophic failures (Carola bridge in Dresden).
50 comments:
The forensic report on the failure of the cable sockets is at https://www.thorntontomasetti.com/sites/default/files/2022-0.... Unlike the linked article this includes detailed diagrams and discussion explaining how these sockets worked and how they failed.
My attempt at a quick summary: the Arecibo instruments were held up by heavy steel cables, which are composed of a bundle of 126 to 216 individual wire strands twisted together, where each wire strand is about 1/4 inch diameter. At the cable ends these were anchored in sockets. The socket is conical, widening out towards where the wire ends go. The wire strands of the cable would be separated in a "broom" shape to fill out that conical area, and then the whole thing filled in with molten zinc.
The failure mode of these zinc-filled sockets is for an inner core cylinder, about the same diameter as the cable body, to pull out from the socket while outer strands of the cable which are broomed out of that core either snap or pull free from the zinc plug.
This failure mode hadn't really been seen prior to the Arecibo collapse, partly because it is a long term process where the zinc slowly flows under stress over decades.
I'd summarize it this way:
With competent engineering and construction, the (failed at Arecibo) zinc socket cable anchors can be very reliable. Unfortunately, Arecibo's engineering was so-so, and the construction quality was half-assed.
With annual inspections (by someone with a passable understanding of cable anchors) the problems at Arecibo could easily have been caught in time to correct. Unfortunately, Arecibo received no such inspections.
And this is roughly the pattern for most "sudden" failures of infrastructure.
> Unfortunately, Arecibo received no such inspections.
With or without the inspections, the problems Arecibo faced were of a more serious nature. They are hinted in one of the findings: the non-replacement, repair or bypass of the sockets where large slips were observed.
The telescope received minimal funding for maintenance over the two decades prior to the collapse despite signs of increasing damage observed in the various inspections. A lot of factors probably contributed to this (political climate, the dropping importance of Arecibo compared to other science instruments and missions, and so on) but the result was that the structure was left with slow but sure decay.
I met a couple of people who worked with the telescope including on location and they told me that the general feeling among the people who had this on their minds (most people who ever had anything to do with Arecibo cared about the science not the instrument) was that the decay was slow but certain and catastrophic failure was bound to happen sooner or later. Like a car receiving no maintenance despite the check engine light being on for a decade.
The telescope received minimal funding because stakeholders couldn't make a good case for more. The results the facility could produce weren't seen as justifying the expense. In that light, that it was operated at all was more than one might reasonably have expected. The alternative was to just shut it down earlier. They squeezed the last drops of output before the old thing was allowed to die.
Sometimes with facilities like this you have to make the call that it's over.
Budgets are limited and there was cooler science to do in space and the newer more modern (and in one case even larger) ground-based ones.
Yes-ish? Funding was far more plentiful when the telescope was being designed and built, and in its early decades. I know zero details about that era - but I strongly suspect it suffered from "just focus on the cool parts" syndrome. And if it'd been designed and built correctly, or the problem caught and corrected back then, it would very likely still be standing.
Which is not to say it'd still be receiving operational funding, nor that its potential scientific contributions would be particularly worthwhile.
It was built in the ‘60s and started losing its relevance and funding in the 2-3 decades before the collapse. A lot of time for issues to develop, be noticed, but not have enough money to fix.
Ah, so historically things were build with a lot of slop. It was just the traditional kind with sloppy design, sloppy construction, and sloppy maintenance.
There is a lesson here to be ignored in the name of short-term personal gain.
Thanks for the quick summary
The pictures on page 25 seem to show how this socket design fails. First because they didn't evenly distribute the wires in the socket (seriously??)... And second, the shear on the zinc from the compressed wire bundle is essentially a narrow rectangle in the direction of the cable with almost all the force concentrated in a narrow forward bit, not really distributed evenly through the socket, because of the wire ends splaying outward and not being equally distributed. I guess the idea is the rest of the zinc towards the back provides a counter force on the front part, but there's a whole lot more zinc in the back pulling on a smaller amount in the front. The tight bundle and the conical shape is great for a tight install, but doesn't help distribution of load. Compare to the Golden Gate Bridge wire termination (https://c7.alamy.com/comp/2RY9PKW/golden-gate-bridge-plans-i...). The zinc creep is definitely bad, but it seems made worse by an uneven distribution of load in the socket, in addition to all the other problems...
tl;dr once the outer wires break in the socket (in part due to zinc creep, but also potentially more load on them), the "glue" keeping the wire bundle connected to the socket is broken, the former wedge keeping the core in place becomes a straight line, and you have a core ready to pop out.
AFAIK cable brooming for spelter sockets is still not automated and relies on human skill, there's no tool to guarantee the necessary wire distribution. I wonder why it's hard to automate, these sockets are everywhere (along with wedge sockets) and are always safety-critical.
In case you didn't see the video of collapse at the time (don't miss the drone footage which starts at 0:55):
>Watch the Arecibo Observatory's catastrophic collapse!
https://www.youtube.com/watch?v=u34uwFOCM-4
Huh interesting. They expected the whole thing to fall apart so they actually had cameras up on a drone to inspect it. Very cool.
When those cables go... dang that's a lot of tension.
There is a Practical Engineering video [1] discussing the failure. (Just saw that it is not a new one discussing the report, sorry)
[1] https://www.youtube.com/watch?v=3oBCtTv6yOw
I did an apprenticeship in metalwork many..many years ago and I seem to recall the zinc is meant to be in compression. If a zinc plug pulled out, it was in shear. Sounds wrong to me. Vincenti: https://en.wikipedia.org/wiki/What_Engineers_Know_and_How_Th... Has a chapter on flush pop rivetting which discussed the loss of this kind of knowing.
Just as an odd aside... bicycle cables are made this way. The little fitting at the end of the cable is molded from zinc.
Why are wire ends like this not using a loop? Would the loop be too huge?
https://www.mazzellacompanies.com/learning-center/wire-rope-...
Loop terminations aren't as strong and are generally more expensive.
Any bends or crimps in the wire create localized stress points which fail early. For crazy high loads you don't want any of that, so the zinc method is the standard. But I think this particular implementation will be rethought.
[flagged]
Well, that and the reductions in funding.
it had already been decommissioned prior to the collapse. Yes, decommissioning does indicate funding is being cut, but it was unrelated to the collapse.
> it had already been decommissioned prior to the collapse
The telescope was decommissioned one month before the collapse. The funding issues, lack of sufficient maintenance, and the inevitable decay that led to the collapse took a few decades more than that.
> Yes, decommissioning does indicate funding is being cut, but it was unrelated to the collapse.
The collapse was a direct consequence of the funding being cut. Maintenance was not performed on issues that were observed many years before exactly on the sockets that failed.
That's... kind of the point. Catastrophic failures usually have non-technical contributory causes as well, and we ignore that at our peril.
(2024). Here's the report 'Failure Analysis of the Arecibo Observatory 305-Meter Telescope Collapse'
https://www.nationalacademies.org/read/26982/chapter/1#vi
Much better, AI generated "summary" pages are not a good link for this story.
This is the better link. The meat is on page 2.
[dead]
not good, not good at all, as this is how ALL bridges and towers are supported, the basic engineering bieng that any cable end will be stronger than the cable itself and will last longer than the cable itself, except now, when it isn't, not good, not easy to inspect, not easy to service.
> Long-term low-current electroplasticity, induced by the electromagnetic waves from the Arecibo telescope itself, may have sped up the zinc creep, it says.
I presume we aren't using most bridges as interstellar antennas.
The main paper goes into the detail on page 2. The cables were on beam path.
“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. National Academies of Sciences, Engineering, and Medicine. 2024. Failure Analysis of the Arecibo Observatory 305-Meter Telescope Collapse. Washington, DC: The National Academies Press. https://doi.org/10.17226/26982.”
> I presume we aren't using most bridges as interstellar antennas.
any like area of metal will receive as much interstellar emissions but I guess they did run a MW transmitter sometimes.
MW as in Mega Watts? (I read it as Medium Wave the first time)
Yeah it was a radar that could collect the echo on the next rotation of Earth.
Arecibo didn’t know it was a telescope. Every wire in the world is an antenna.
No, but there is a lot of potential for large structures to act like an accidental antenna and/or receive low level voltages from the environment or other equipment.
Likely won't matter in most cases, but there could be a few disasters waiting around.
That’s what the government (… and most rational people) wants you to think.
how could the government control the birds without using bridges as antennas?!
They also mentioned that this is the first example of the unknown phenomena that caused the creep. This technology has been in use quite successfully for more than 100 years.
My guess is the safety factor here was lower than typical, causing the failure mode to occur.
I expect future bridges will design these joints even more conservatively because they were skating closer to the edge than they realized.
Bridges probably shouldn't be subject to the same electromagnetic radiation that gets focused by the telescope though so ideally not a problem there.
Where the cables were there’s nothing focused, just wires, it was outside of the dish.
They were across the dish. From the report: “The Arecibo Telescope cables were suspended across the beam of “the most powerful radio transmitter on Earth””
The role of the cables was for supporting the equipment. The cables that failed, and are examined in the report, were designed to hold the equipment up, while it moved around. These cables weren't involved in carrying signals, data, or power.
There is no denying that energy was induced because of their placement at the focal length of the dish, but that was incidental to their purpose. The bundles of wires were spirally bound around a core. There were certainly ground connections and lightning arrestors involved. The EM effects and properties are discussed on pp 40–47 of the report.
This would predict that we should be seeing far more mystery collapses than we do though
anything, forgive the AI-sounding phrase, "load bearing" in terms of "the load is human lives" is very, very strictly regulated, with inspections mandated and consequences such as load limits and even closures being required when inspections flag issues.
However, even that is not foolproof. Here in Germany, we have had close calls (Rahmede bridge) as well as actual catastrophic failures (Carola bridge in Dresden).