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.
Bottom line: a structure well advanced into it’s functional lifespan and inadequate maintenance. With all of the infrastructure built around the telescope over the years and the fruits of the research carried out there, it really would be a good investment to rebuild the damage.
I doubt they have the expertise anymore. Hope they take that as a challenge and prove me wrong but I feel like if they tried to build that thing in the middle of the jungle in the 2020s instead of the 1960s it would run up billions of dollars in cost and they would be bogged down with inept committees and lack of enough real talent.
It was built in 1963 for 170 million, adjusted for inflation. Maybe if they contracted Musk, but they would rather drink drain-o than do that so I don’t see it.
Yeah he was very good at Hyperloop….
I think he lost interest once he decided he wasn’t going to be traveling between LA and SF anymore. It turns out its a tough problem too, and it doesn’t get us closer to mars. It s a convenience side project, not one that advanced the main goal. There are still smart people working on it though. It will probably happen eventually, but I suspect RT superconductors will be necessary to make it actually cost/energy effective.
You mean the project that was stifled at every turn by regulators swayed by activist lobbyists?
Dude just caught a 22 story building with chopsticks. He’s obviously inept.
Well, this was to be expected.
This “discovery” also seems to be come in handy to teny any responsibility for the collapse.
What’s also notable is that NASA had decreased fundings over the years.
The collapse was just the final result, in reality. We all were worried about Arecibo’s future for years.
Unfortunately, people in charge wanted to get rid of Arecibo for years.
The maintenance that was performed over the years is nothing to write home about.
It’s as if it was intentionally kept at minimum, to get rid of Arecibo, but the telescope still lasted longer than anticipated. Until that Hurricane.
Here at HaD we wrote comments about bad Arecibo support years ago.
“The collapse was just the final result, in reality.”
The collapse was just the final insult, in reality.
FTFY
Yeah… Budget is rough in those parts
I think this is a funding grab. The section on EP is written very wishy-washy, and admits there’s a lot they don’t know and cannot prove. However, given the destructive testing done originally, I’d expect at least a test rig to have been setup and at least measured temperature rise at multiple depths of the zinc, resistance measurements, and induced current flow measurements. (That’s really not asking for much!) But there’s none. I’ll stick with Occam’s razor here given the analysis of the sockets that did not fail. I would be interested in further testing though, which seems like exactly what this section was meant to do – get funding for additional testing, thus my opening line….because it worked on me :)
I’ve worked with 40-odd year old zinc socketed ropes, on severe duty cycle work, with never a moment of concern. They were hardier than any alternative.
This seems a reasonable theory for a failure with no other traceable cause. If you eliminate the impossible, the remaining however unlikely… to paraphrase A C Doyle’s famous detective.
if this is the case then you could have prevented this with a simple grounding strap on each cable. something to keep in mind when you build another one.
Yes, but no. You have to engineer that ‘simple’ strap so it will actually carry the current. We’re talking about RF currents here, and ‘a strap’ might be too much of an inductance. ‘Ground’ is also not ‘ground’ for everything RF. Perhaps some giant ferrite clamps would be an option to prevent the induced current from reaching the anchor points in the first place.
If it is RF currents, that’s not necessarily true. Though Wikipedia seems to suggest that electroplasticity is usually observed with DC currents.
Zinc oxide is a semiconductor. A layer of it can form a diode. Add high power RF currents and you’ve got DC.
https://en.wikipedia.org/wiki/Zinc_oxide#Electrical_and_optical_properties
so you could make the spelter sockets from a metal with a conductive oxide such as silver, or put an insulator at the ground end of the anchor to break the circuit through the zinc section.
why not just tie a knot in the cable on the other side of the socket? no need for zinc at all
not sure if troling, but I’d suggest you give it try and let us know how it went…that cable is a lot thicker and stiffer then you think
And as most riggers know, a knot is a weakness in a line.
Indeed though a splice is not (done properly anyway). So I suppose the concept could be done with a spliced eye around the anchor socket. That said this scale I don’t think there is really any better choice than the one used, or a variation of it. Can’t claim to have ever tried it on anything nearly this large but splicing and knotting the thickest stuff I’ve ever played with was sufficiently challenging.
I’ve spliced many lines for sailboats etc it isn’t bad if it’s the regular hemp or sissel (sp?) and it’s fun and decorative. I’ve spliced a 1/8″ metal line (cable) and it was miserable. You have to do it around an eye too. The way you splice metal vs natural/synthetic “regular” rope is totally different too. It can be done in larger metal cables but requires hammers and big fids and stuff. By larger I mean like 1″. Since the article claims this is the first know failure of a poured metal socket it’s hard for me to imagine why one would ever use an eye splice in huge load bearing cables. I’m unsure if even with machines you could splice one if you wanted to- my limited experience so take it w a grain of salt.
One variation I know (used in railway applications) is to put a thorn in the cable instead of the zinc. When the cable creeps, it pulls in the thorn, increasing pressure on all strands (ideally equally distributed), until the creep stops. Seems to work flawless on cables around 5 mm diameter, but I’m not sure about scalability.
For once let it be Aliens please.
Yes, of course it’s aliens. But first, they cover their tracks very well, and second, even if there is proof, people hide it in fear of being laughed at, and third, they have agents in place to organize coverups. Just like with the 300 feet telescope in the Green Banks Observatory in 1988.
I got tired of that dish looking at my significant other while she was in the bathroom!
Earth perverts!
Having been professionally engaged in modeling mechanics of porous media in the oil industry, I dread seeing the constitutive equations for electroplasticity.
When you add the water like attributes of microwaves, it is bound to get really weird.
Yep. And then factor in that the thing was almost as old as Bonanza. Also, substitute the oil industry budget for a forgotten-project NASA budget.
I was fortunate enough to visit Arecibo in 2000. Being a kid who grew up in the 90s, and a huge nerd, I was excited to be at the iconic location featured in Contact and Goldeneye. Didn’t get to chase Sean Bean across the girders, but it was easily the highlight of my trip to Puerto Rico.
couldn’t galvanic reduction be a factor? (I’m asking, as I don’t know)
between rain, fatigue/stress/time, electricity and huge RF, couldn’t that turn the zinc/steel to a galvanic battery of a sort that just dissolved itself over time until failure?
While reading this, my mind wandered to thinking about how to do ultra-long term maintenance on this type of termination.
The best thing I can come up with at the moment is to re-melt the plug on a regular schedule.
Each end has multiple wire ropes terminated at the location.
Unload 1 wire rope.
Melt Zink plug. Pull rope back into place if it crept out.
Let plug cool.
Load rope.
Move to another wire rope.
You could integrate resistive/inductive coils into the mount for each plug.
No electronics needed. Have those on a cart that can get plugged into the dumb coil at each plug.
You could also have a drain on each plug to remove the Zonc each time and do some sort of inspection before pouring it back in.
I have no doubt that it wouldn’t be that simple.
What obvious flaw am I missing?
there’s a zillion things you can do but the problem is if you wait until it’s already failing then the process of rigging it so you can detension a cable has to be done in the context of expecting the thing to fall on your head. makes it much more expensive and/or dangerous. as i understand it, that’s why they didn’t do anything when the first cable failed.
presumably they could have detected that failure sooner and done some maintenance like what you’re describing. i would guess cable replacement is more plausible than melting-in-place but there’s lots of possibilities, if they can rig it to their needs
I meant doing it often enough that the Zinc creap doesn’t damage the rope strands, so they don’t need replacement.
Surely unloading a wire rope in-place for a few hours is simpler than replacing one.
Of course, they wouldn’t do it because of costs, but to “over build” by by one additional cable for each tower to allow a cable to be replaced/ repaired as needed. 20/20 hindsight