Zinc Creep And Electroplasticity: Why Arecibo Collapsed

November 5, 2024 by Dan Maloney 33 Comments

It’s been nearly four years since the Arecibo Telescope collapsed, an event the world got to witness in unprecedented detail thanks to strategically positioned drones. They captured breathtaking video of one of the support cables pulling from its socket as well as the spectacularly destructive results of 900 tons of scientific instruments crashing into the 300-meter primary reflector. But exactly why did those cable sockets fail?

A new report aims to answer that question, and in the process raises some interesting questions of its own. The proximate causes of the collapse have been known for a while, including the most obvious and visible one, the failure of the zinc “spelter sockets” that were cast around the splayed ends of the wire ropes to hold them in place. The new report agrees with this conclusion, at least in part, implicating “zinc creep,” or the tendency for zinc to deform over time under load. Where it appears to differ, though, is with the quality of workmanship on the sockets, finding no issues with the way the individual wires in the failed support cable were manually splayed within the socket before the molten zinc was poured. The report also points out that the collapse probably started when Hurricane Maria swept over Puerto Rico 39 months before the collapse, after which zinc creep in the sockets seemed to accelerate.

But why did the sockets fail? As the report points out, spelter sockets are commonly used to anchor cables that support heavy loads under conditions similar to the tropical climate at Arecibo. After ruling out every other cause, the committee was left with the conclusion that Arecibo itself may have been to blame for the accelerated zinc creep, thanks to electrical currents induced in the cables and sockets when the telescope’s powerful transmitters were used. They call this “long-term, low-current electroplasticity.” Electroplastic effects have been observed since the 1950s, and while far from certain that’s what happened here, the thought is that skin-effect currents induced in the support cables flowed to ground through the zinc sockets, increasing the plasticity of the metal and accelerating the zinc creep that ultimately led to collapse.

Case closed? Hardly. The electroplasticity mechanism for the Arecibo collapse offered by this report is almost a “diagnosis of exclusion” situation. It makes sense, though; since no other spelter sockets have ever failed this way in a century of use, there’s a good chance that the root cause was specific to Arecibo, and since it was once the world’s most powerful radio transmitter, it seems like a red flag that bears further investigation.

Hackaday Links: October 6, 2024

October 6, 2024 by Dan Maloney 22 Comments

Remember that time a giant cylindrical aquarium in a Berlin hotel bar catastrophically failed and left thousands of fish homeless? We sure do, and further recall that at the time, we were very curious about the engineering details of how this structure failed so spectacularly. At the time, we were sure there’d be plenty of follow-up on that score, but life happened and we forgot all about the story. Luckily, a faithful reader named Craig didn’t, and he helpfully ran down a few follow-up articles that came out last year that are worth looking at.

The first is from prosecutors in Berlin with a report offering three possibilities: that the adhesive holding together the acrylic panels of the aquarium failed; that the base of the tank was dented during recent refurbishment; or that the aquarium was refilled too soon after the repairs, leading to the acrylic panels drying out. We’re a little confused by that last one just from an intuitive standpoint, but each of these possibilities seems hand-wavy enough that the report’s executive summary could have been “Meh, Scheiße happens.”

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Hackaday Links: April 14, 2024

April 14, 2024 by Dan Maloney 10 Comments

The Great American Eclipse v2.0 has come and gone, sadly without our traveling to the path of totality as planned; family stuff. We did get a report from friends in Texas that it was just as spectacular there as expected, with the bonus of seeing a solar flare off the southwest limb of the disk at totality. Many people reported seeing the same thing, which makes us a bit jealous — OK, a lot jealous. Of course, this presented an opportunity to the “Well, ackchyually” crowd to point out that there were no solar flares or coronal mass ejections at the time, so what people saw wasn’t an exquisitely timed and well-positioned solar flare but rather a well-timed and exquisitely positioned solar prominence. Glad we cleared that up. Either way, people in the path of totality saw the Sun belching out gigatons of plasma while we had to settle for 27% totality.

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Blame It On The Sockets: Forensic Analysis Of The Arecibo Collapse

August 29, 2023 by Dan Maloney 58 Comments

Nearly three years after the rapid unplanned disassembly of the Arecibo radio telescope, we finally have a culprit in the collapse: bad sockets.

In case you somehow missed it, back in 2020 we started getting ominous reports that the cables supporting the 900-ton instrument platform above the 300-meter primary reflector of what was at the time the world’s largest radio telescope were slowly coming undone. From the first sign of problems in August, when the first broken cable smashed a hole in the reflector, to the failure of a second cable in November, it surely seemed like Arecibo’s days were numbered, and that it would fall victim to all the other bad luck we seemed to be rapidly accruing in that fateful year. The inevitable finally happened on December 1, when over-stressed cables on support tower four finally gave way, sending the platform on a graceful swing into the side of the natural depression that cradled the reflector, damaging the telescope beyond all hope of repair.

The long run-up to the telescope’s final act had a silver lining in that it provided engineers and scientists with a chance to carefully observe the failure in real-time. So there was no real mystery as to what happened, at least from a big-picture perspective. But one always wants to know the fine-scale details of such failures, a task which fell to forensic investigation firm Thornton Tomasetti. They enlisted the help of the Columbia University Strength of Materials lab, which sent pieces of the failed cable to the Oak Ridge National Laboratory’s High Flux Isotope reactor for neutron imaging, which is like an X-ray study but uses streams of neutrons that interact with the material’s nuclei rather than their electrons.

The full report (PDF) reveals five proximate causes for the collapse, chief of which is “[T]he manual and inconsistent splay of the wires during cable socketing,” which we take to mean that the individual strands of the cables were not spread out correctly before the molten zinc “spelter socket” was molded around them. The resulting shear stress caused the zinc to slowly flow around the cable strands, letting them slip out of the surrounding steel socket and — well, you can watch the rest below for yourself.

As is usually the case with such failures, there are multiple causes, all of which are covered in the 300+ page report. But being able to pin the bulk of the failure on a single, easily understood — and easily addressed — defect is comforting, in a way. It’s cold comfort to astronomers and Arecibo staff, perhaps, but at least it’s a lesson that might prevent future failures of cable-supported structures.

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Books You Should Read: Why Buildings Fall Down

November 23, 2022 by Dan Maloney 35 Comments

People with long commutes usually come up with tricks to stay focused and alert and avoid the dangerous tendency to zone out during the drive. One trick I used to use was keeping mental track of the various construction projects I’d pass by on my way to work, noticing which piers on a new highway overpass were nearing completion, or watching steelworkers put together the complex rebar endoskeletons of a new stretch of roadway.

One project I loved to watch back in the 80s was a new high-rise going in right next to the highway, which fascinated me because of the construction method. Rather than putting together a steel frame, laying out decking, and covering each floor with concrete, the workers seemed to be fabricating each floor at ground level and then jacking them up on the vertical steel columns. I was fascinated by this because every time I passed by the floors were in a different position, spreading out vertically as the building grew.

And then one day, it just wasn’t there anymore. Where there had been columns stretching nine stories into the city sky with concrete slabs lined up ready to be jacked up into their final positions, there was just an enormous hole in the ground with a ghastly gray cloud of concrete dust rising from it. It was April 23, 1987, and what was once going to be a luxury apartment building called L’Ambience Plaza in Bridgeport, Connecticut lay pancaked into the ground, entombing the bodies of 28 construction workers.

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Hackaday Links: July 4, 2021

July 4, 2021 by Dan Maloney 9 Comments

With rescue and recovery efforts at the horrific condo collapse in Florida this week still underway, we noted with interest some of the technology being employed on the site. Chief among these was a contribution of the Israeli Defense Force (IDF), whose secretive Unit 9900 unveiled a 3D imaging system to help locate victims trapped in the rubble. The pictures look very much like the 3D “extrusions” that show up on Google Maps when you zoom into a satellite view and change the angle, but they were obviously built up from very recent aerial or satellite photos that show the damage to the building. The idea is to map where parts of the building — and unfortunately, the building’s occupants — ended up in the rubble pile, allowing responders to concentrate their efforts on the areas most likely to hold victims. The technology, which was developed for precision targeting of military targets, has apparently already located several voids in the debris that weren’t obvious to rescue teams. Here’s hoping that the system pays off, and that we get to learn a little about how it works.

Radio enthusiasts, take note: your hobby may just run you afoul of authorities if you’re not careful. That seems to be the case for one Stanislav Stetsenko, a resident of Crimea who was arrested on suspicion of treason this week. Video of the arrest was posted which shows the equipment Stetsenko allegedly used to track Russian military aircraft on behalf of Ukraine: several SDR dongles, a very dusty laptop running Airspy SDR#, an ICOM IC-R6 portable communications receiver, and various maps and charts. In short, it pretty much looks like what I can see on my own desk right now. We know little of the politics around this, but it does give one pause to consider how non-technical people view those with technical hobbies.

If you could choose a superpower to suddenly have, it really would take some careful consideration. Sure, it would be handy to shoot spider webs or burst into flames, but the whole idea of some kind of goo shooting out of your wrists seems gross, and what a nuisance to have to keep buying new clothes after every burn. Maybe just teaching yourself a new sense, like echolocation, would be a better place to start. And as it turns out, it’s not only possible for humans to echolocate, but it’s actually not that hard to learn. Researchers used a group of blind and sighted people for the test, ranging in age from 21 to 79 years, and put them through a 10-week training program to learn click-based echolocation. After getting the basics of making the clicks and listening for the returns in an anechoic chamber, participants ran through a series of tasks, like size and orientation discrimination of objects, and virtual navigation. The newly minted echolocators were also allowed out into the real world to test their skills. Three months after the study, the blind participants had mostly retained their new skill, and most of them were still using it and reported that it had improved their quality of life.

As with everything else he’s involved with, Elon Musk has drawn a lot of criticism for his Starlink satellite-based internet service. The growing constellation of satellites bothers astronomers, terrestrial ISPs are worried the service will kill their business model, and the beta version of the Starlink dish has been shown to be flakey in the summer heat. But it’s on equipment cost where Musk has taken the most flak, which seems unfair as the teardowns we’ve seen clearly show that the phased-array antenna in the Starlink dish is being sold for less than it costs to build. But still, Musk is assuring the world that Starlink home terminals will get down in the $250 to $300 range soon, and that the system could have 500,000 users within a year. There were a couple of other interesting insights, such as where Musk sees Starlink relative to 5G, and how he’s positioning Starlink to provide backhaul services to cellular companies.

Well, this is embarrassing. Last week, we mentioned that certain unlucky users of an obsolete but still popular NAS device found that their data had disappeared, apparently due to malefactors accessing the device over the internet and forcing a factory reset. Since this seems like something that should require entering a password, someone took a look at the PHP script for the factory restore function and found that a developer had commented out the very lines that would have performed the authentication:

    function get($urlPath, $queryParams=null, $ouputFormat='xml'){
//        if(!authenticateAsOwner($queryParams))
//        {
//            header("HTTP/1.0 401 Unauthorized");
//            return;
//        }

It’s not clear when the PHP script was updated, but support for MyBook Live was dropped in 2015, so this could have been a really old change. Still, it was all the hacker needed to get in and wreak havoc; interestingly, the latest attack may be a reaction to a three-year-old exploit that turned many of these devices into a botnet. Could this be a case of hacker vs. hacker?

NSF Releases Video Of Arecibo’s Final Moments

December 3, 2020 by Tom Nardi 82 Comments

Today the National Science Foundation released a pair of videos that document the collapse of the Arecibo Observatory with incredible detail. A wide shot, apparently taken from the Visitors Center, shows the 900 ton instrument platform breaking free and swinging on the remaining support cables until it smashes into the edge of the dish. The second clip, recorded by an airborne drone, is focused directly on the cables as they failed. Both can be seen in the video embedded below.

Together, they produce an invaluable visual record of what finally brought the iconic radio telescope down. As was predicted by engineers earlier in the month, the failure of another support cable on tower 4 triggered a chain reaction that brought the entire platform crashing down onto the 305 meter reflector. Footage from a drone observing the top of tower 4 shows that the entire sequence, from the first visual wire break to the remaining cables being torn from their mounts, only took five seconds. While some initially doubted the NSF’s determination that it was too dangerous to repair Arecibo, this footage seems to prove just how tenuous the structural integrity of the Observatory really was.

A drone captured the critical cable failure.

These videos will hopefully help investigators who still need to determine why the cables failed in the first place. The cable in August didn’t snap, it simply pulled lose from its mount. It was suspected that the cable may have been incorrectly installed, but as it was only a backup, the situation was not seen as critical. But when the second cable failed in November it was found to have snapped at just 60% of its minimum breaking strength.

This immediately called into question the condition of the remaining cables, and ultimately lead to the decision by the NSF to proceed with a controlled demolition of the Observatory that would preserve as much of the scientific equipment as possible. Unfortunately, the remaining cables didn’t last long enough to put that plan into action.

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