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The investigation into why a cable mysteriously broke on the Arecibo Observatory has begun 9

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WKTaylor

WKTaylor

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I have seen flight control cable failures under high tensile load... especially during crashes... but nothing like this failure...

Failure obviously occurred under high tensile load... wire strands unwinding/splaying about... but the break appears almost straight across all the wires at one discrete location. This is going to be an interesting failure analysis...

The investigation into why a cable mysteriously broke on the Arecibo Observatory has begun
Officials at the Arecibo Observatory in Puerto Rico still don't know what caused a cable failure that severely damaged the facility's iconic radio telescope this week, forcing it to shut down temporarily.

On Monday (Aug. 10), an auxiliary cable supporting a platform that is suspended above the 1,000-foot-wide (300 meters) radio dish broke and crashed into the telescope's reflector panels, creating a gash in the dish measuring about 100 feet (30 m) long.
… …
From the article... A photo of the support cable that broke on Aug. 10, 2020. (Image credit: University of Central Florida)


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Oh no!
What a crushing event for the astronomers.

It looks to me like the break may have happened by pulling the cable out of a swaged fitting. There appears to be some deformation of the last few inches of the cable, and they remain tightly bundled, as if they were still compressed together. I suggest this would be the appearance of a cable end that pulled out of the fitting it was swaged into. The progress of that failure, beginning with perhaps some threads before others could then explain the unravelling of the rest of the cable.
BUT.
This cable construction is not a kind I'm used to working with. On aircraft, I work with stuff smaller than 1/2" so naturally this cable about 2" diameter is going to look different. It seems to have many counter-wound layers in it. The strands that seem to have failed are all in the outer layer. The next inner layer seems completely intact. Is that a clue to the mechanism of failure?

Arecibo_Broken_Cable_2020-Aug_sedqu2.jpg


FYI: Swaging of fittings onto the ends of wire rope, like this type used in bridge anchors:

Bridge_Cable_Anchor_az5ehu.jpg



 
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From the limited data available it looks more like a cable to fixture failure and not a cable failure per se.

Would need to see the other end to be sure and figure out what failed.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
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You can see what appears to be some material stuck to the wires at the end with the flat cut. This is likely the remains of the "spelter" used to anchor the wire to a Spelter Socket. Old school was to use Zinc as the spelter compound, In service inspection is nearly impossible.

Several standards require proof testing of spelter sockets at assembly to 2x or 2.5x, which is not possible if field assembled. See the attached crosby manual starting at page 58
The cable type is a type of strand. The lays in opposite directions indicate it is rotation resistant.
 
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The guy here confirms - "It didn't really break it just kind of slipped out of it's socket...."
I suspect it failed at the outer support and fell suspended from the centre hence the gash in the reflector starts part way in and descends into the centre.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
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I worked on a very successful project terminating Kevlar into titanium sockets (taper pin, taper socket). We routinely achieved > 90% efficiency, more typically 98%. This whole gum it up with goo and stick it in a hole and squish it approach is a bit 18th century. Admittedly our rig was not suitable for field deployment, but I see no particular reason why cables cannot be assembled off site.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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The Empire [tiefighter] finally tired of NSA evesdropping.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"
 
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"I see no particular reason why cables cannot be assembled off site"

When you're dealing with huge fabricated structures hundreds of feet across, and the associated tolerances of that construction, exact lengths of cables to the 1/8" are impossible to know.
 
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I like what this channel presented on the damage. Although he doesn't have any additional information on the damage the snapped cable caused, he does go a little into the technical details about how the suspended gegorian dome corrects for the spherical shape of the main dish. The suspended dome also sustained some damage.
 
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Definitely a failed spelter socket, I work on cranes regularly where these type of fixtures are used extensively. Molten zinc or epoxy is typically used to secure the rope in the socket. I cant say I have ever seen one fail.
wirelock epoxy
 
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And it was such a great prop in the movie 'Contact', not quiet as important to the plot-line as was the 'Very Large Array' in New Mexico, but still pretty cool.

John R. Baker, P.E. (ret)
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That's terrible news!

While the even-bigger Chinese Five-hundred-metre Aperture Spherical Telescope (FAST) is still a working option, according to the linked article, FAST can't do "active radar" work, so it can’t take Arecibo’s place in imaging asteroids and determining their orbits.

And in any case - nobody seems to be getting on very well with China these days ...

 
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Damaged Arecibo Telescope To Be Dismantled
Pierce Brosnan?
He has the experience.
Maybe he will be willing to do it again. (grin)

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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