Zinc creep in cable spelter sockets brought down the Arecibo telescope in 2020
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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.
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.
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.
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.
Sometimes with facilities like this you have to make the call that it's over.
Which is not to say it'd still be receiving operational funding, nor that its potential scientific contributions would be particularly worthwhile.
If the original builders had cared about the boring parts, then pre-WWII QC technology could easily have spotted the extremely shoddy workmanship in the zinc spelter sockets, while those were originally being fabricated.
Similar for designing larger safety margins into the whole cable system. Even PHB's can understand that "Hurricane Snaps Cables, Telescope Collapses" headlines could make them look really bad.
There is a lesson here to be ignored in the name of short-term personal gain.
Once failure is identified, it should be understood before deciding if you can delay remediation.
It seems once failing sockets were found they were considered to be random failures and not systematic failures that would accelerate.
>Watch the Arecibo Observatory's catastrophic collapse!
That seems a bit unlikely to me. As far as I know it was a radio telescope, receiving very weak signals, not transmitting them.
If it were such a major factor it would be present also in the guy wires of transmission towers, some of them emitting hundreds of kilowatts.
Other radio transmitters blast kilowatts and sometimes megawatts 24/7 for decades.
I don't really see it, I think this is just an excuse for total lack of maintenance.
https://www.seti.org/research/seti-101/project-phoenix/areci...
They used to use it to radar asteroids and sent a deep space message to try to contact aliens.
And I've seen a worrying number of those fail after decades too. In cases I've seen, the fact that load is uneven between the strands usually seems to play a part - some always start to snap or pull out before others.
Loop terminations aren't as strong and are generally more expensive.
So for the biggest structural strand the socket is the default, which is why Arecibo got so much attention: sockets that slipped and failed well below their rated load, not an inherently weak type of end.
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.
Repairing it would require extra funding, so it collapsed from the hurricane damage and it did not collapse due to cuts in funding.
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.
I presume we aren't using most bridges as interstellar antennas.
Likely won't matter in most cases, but there could be a few disasters waiting around.
any like area of metal will receive as much interstellar emissions but I guess they did run a MW transmitter sometimes.
It could track celestial positions for about 2.6 hours.
https://en.wikipedia.org/wiki/Arecibo_Telescope#Research_and...
Think about a radar round-trip of 2×12 light-hours; that is 86.57 AU, twice the distance from us to Pluto. Also, the Earth orbits the Sun aside from merely rotating. That radar round-trip would be one cosmic boomerang, looking at nearly nothing.
3 cm (10.0 GHz)–1 m (300 MHz)
While we are being helpful clarifying details perhaps to you could mention something about the difference between the wattage of the power supply used and the Terra watt figure arrived at when switching to EIRP.
As a newish ham I have at least seen the jargon but I fear many of out dear readers may be envisioning nuclear powered death rays with those numbers.
The telescope had three radar transmitters, with effective isotropic radiated powers (EIRPs) of 22 TW (continuous) at 2380 MHz,[12] 3.2 TW (pulse peak) at 430 MHz, and 200 MW at 47 MHz,[13] as well as an ionospheric modification facility operating at 5.1 and 8.175 MHz.[14]
“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.”
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).
I expect future bridges will design these joints even more conservatively because they were skating closer to the edge than they realized.