Lack of long term investment in decaying infrastructure?
(that'll be my bet until evidence suggests otherwise)
The remaining cables supporting a 900-ton platform hanging over America’s largest radio telescope are struggling to take the load, threatening the 1,000-ft wide reflector dish. The Arecibo Observatory instrument, located in a national forest in Puerto Rico, was the largest radio telescope of its kind in the world until 2016 …
On boats, shrouds (the wires holding the mast up) in steel are only insurable for around 10 years (out of tropical climates). they are much finer, and usually now made from Stainless (stronger, and corrosion resistant). 1960's and r older 19th/20th C rigging was traditional steel, varnished regularly with Stockholm tar and linseed oil to protect it against rust.
Point is, we know how steel wire reacts under stress for extended periods. Its shocking to require '3 engineering companies' to assess this for months before coming to a bloody obvious conclusion...
And since Puerto Rico is an island in the Caribbean it stands to reason the telescope cables were exposed to a LOT of salt spray.
From the article: An official investigation into what caused the cables to break away was launched in August,
I can already tell you what did it: chloride embrittlement and corrosion in general, combined with cyclic stress fatigue with continuous tensile stress. *SNAP*
Certain kinds of stainless steel are affected by chloride embrittlement, and though you may not see corrosion, you might STILL see pitting on the metal, and with constant tensile stress it causes microfractures into which the chlorides (from salty air and hurricanes and stuff like that) embrittle it (if I remember correctly). This is also somewhat the case for copper conductors and "just plain steel". Salty air is bad for them, yeah.
You would generally need to paint and/or coat all cables with some kind of anti-corrosion paint (or other coating) that typically has chromates or some similar material in it, and possibly use sacrificial anodes [if even possible] to limit galvanic corrosion. As far as chloride stress corrosion goes, you might not be able to stop it if the material is susceptible.
Also 'work hardening' due to cyclic stresses can also result in cracking and even total failure. 50-something years of hanging there through hurricanes might explain that, yeah. If you bend soft metal back/forth enough times, it cracks and breaks. Same idea.
And when a stress crack forms, the physical properties of it (along with salty air) form corrosion that just makes it worse.
There is such a thing as corrosion fracture. This is where corrosion causes pits in the metal surface, and those defects form the focal points of cracks. This then reduces the metal fatigue rating of the structure. I imagine that the supporting cables for the telescope are subject to considerable varying forces, due to the effects of wind. The rust retarding products I have looked into, such as grease, have a limited lifetime. The product I worked on only needed three year's working life, and a single application of rust retarding grease provided that.
If the cables are stainless steel, then maybe corrosion is not the problem. It could just be metal fatigue.
"I can already tell you what did it: chloride embrittlement and corrosion in general, combined with cyclic stress fatigue with continuous tensile stress. *SNAP*"
Yup. Here in North we've had, not one but two swimming hall roof collapses in last 10 years. Neither of those was more than 20 years old.
The steel beams& cables were sturdy enough to stand snow on the roof when new, but they weren't painted well/at all so rust hit and that eats the strength in single years: Large swimming pools produce a lot of chlorides.
Then comes a winter and 10 inches of wet snow on the roof: *SNAP* says a cable and whole thing collapses like a house of cards.
There is a possibility that the management in charge of maintaining the structure were hoping to find an engineering company that gave the "right" answer, which would mean not spending any money. So they asked one company after another.
I find that when manglement types ask a question, and you do not give the "right" answer, they will ask the same question again, but phrased differently, and keep doing this, in the hope that you eventually change your mind. This is of course how incompetent and dishonest firms are awarded contracts, rather than competent and trustworthy firms.
"...[if] you do not give the "right" answer, they will ask the same question again, but phrased differently, and keep doing this, in the hope that you eventually change your mind."
Oh, I thought it was just retail customers who did that.
The Forth Road bridge suffered from fraying cables until it had to be closed to heavy traffic. The weight and amount of heavy goods vehicles hadn't been anticipated when it was built in 1964.
Likewise when the Arecibo Observatory was built in 1960 the engineers couldn't have anticipated the massive fast radio bursts it now has to cope with.
"... working vigorously to understand why this industrial failure occurred."
Really don't know?
In August last year I noted that due to the lack of federal aid, a great deal of Puerto Rico's basic infrastructure was still in ruins after hurricanes Irma and María (both in 09/2017) devastated the island, all made worse by an earthquake in January of this year.
The lack of basic federal aid in the wake of two important hurricanes (two weeks apart) undoubtedly affected not only Arecibo's maintenance schedules but also its funding, if any at that point in The Orange Asshole's™ tenure as occupant of the White House.
Really no need to be asking why, it's quite obvious.
Unfortunately, I don't see Arecibo getting any help before January 20th. 2021, so who knows if it will survive 2020.
I'm no fan of nutjob Trump, but unfortunately this is not unusual and probably can't be blamed on him, see my other post.
Effectively, at least for the radio astronomy sites, NSF sites get lavish initial fundings, it's state of the art and there's plenty of spare parts. But after that, in business terms they effectively get funding for opex (operating expenditures) that cover operations and they did good inspection and maintenance; but near-zero capex (capital expenditures) so if anything out-of-the-ordinary needed repair, no money to do it; no money for spares, so (even with them doing board-level repair to repair lightning-blasted components, blown caps, etc. to preserve spares) they were down to 1-2 spares for some boards and such (not per-site, total among about a dozen sites). The NRAO site I've been to, it was installed in 1985, and it's state-of-the-art 1985-era equipment, so it's simply wearing out.
"In any normal accounting regime, maintenance and repairs (including cost of replacement components) is not capital expenditure."
Repairing anything is an investment, i.e. capital expenditure. Spare parts definitely are.
Possibly applies only to government accounting though, but equipment is assumed to last for ever and never need spare parts. If you need either it's an investment to "aging equipment", i.e. throwing money away, and in general not allowed.
Arsenoise is lacking in so many ways, yet I doubt he even knows Arecibo exists. For one thing, he'd have to understand that the word "telescope" doesn't necessarily mean a long tube with lenses in it, parrot, cutlass and eyepatch optional...
Neglect, pure and simple. Any competent metallurgist will take one glance at that picture and declare expansion and friction assisted metal fatigue in a nanosecond¹. This is a compound failure, recognised with the benefit of hindsight, to allocate resources over more than half a century. Hanlon's Razor applies.
¹ The various wires in those cables expand and contract at different rates as they heat and cool by layers. It's not much movement but, given 57 years, it all adds up. At this point, replacement is needed as the visible effects mean the invisible damage is already past the point of no return.
Agreed. I'd imagine the uncertanty limits mitigation efforts (that's a scary amount of weight that could let loose at any moment)
I'm picturing energency cribbing under the tower. You might be fine just offloading a portion of the weight for a while. You'd have to loose part of the reflector dish to make room for cribbing, but you're probably much better off with a controlled removal of the middle vs an uncontrolled crash.
Adding or replacing any cables looks problematic as there's no place to attach them apart from on the existing towers and apparently no spare attachment points, but the real killer is that it looks to be very difficult to do anything without damaging the main dish reflector: drop anything and another gash is made. Putting up netting strong enough to protect the dish risks causing major damage and may well require making holes in the dish for supporting the protective structure.
IOW, does the main mirror need to be removed while the cables supporting the stuff at the prime focus are replaced?
I am surprised that there's apparently nothing on t'net that describes the construction sequence of the Arecibo Radio Telescope, i.e. that says whether the main mirror was present while, the stuff at the focus was being hung up there or whether it was put in last.
"I am surprised that there's apparently nothing on t'net that describes the construction sequence of the Arecibo Radio Telescope"
This might help: https://www.naic.edu/ao/photos ... takes a while to load, but it has some good pictures that might help people visualize the scale of this thing. It is not a toy. Scroll down to see B&W pics of it being built.
For the lazy, clicky-clicky.
> An official investigation into what caused the cables to break away was launched in August, and the observatory has been closed since. Three engineering firms have been hired to probe the structure, and a socket holding a auxiliary cable was shipped off to NASA's Kennedy Space Center for forensic analysis
Much of the construction was done in mid air before the reflector below was finished. There does not appear to be any method of safely lowering or supporting the overhead structure as it stands. If the cables can not be replaced in situ then the only other option that I could see would be to dismantle the overhead structure lowering the individual pieces to the ground then finally lower the triangle to the ground then replace all the cables then raise it again and rebuild the overhead structure and repair the reflector surface - Arecibo would be out of action for years if this was done.
The people doing the dismantling would also deserve hazard pay - if one of the three main cables fails then the structure will plummet to the ground.
I'd be quite shocked if it hadn't been considered & dismissed for whatever reasons*, but, instead of the suggestions of ways to reinforce the remaining cables and such, what about ripping out as much of it as possible to lighten the load they still have to support? It could at least be done promptly, maybe just in time, without having to engineer & produce whatever longer-term solution might allow it to carry the full load again, if it's doable at all.
* Two that come to mind right away:
They can't safely go out to access its contents and remove them.
No significant part of its mass is removable over the catwalks or with available cranes that are tall enough.
I have been to one of the NRAO radio observatory sites; it was installed in the mid-1980s. The dish has a single railroad rail style thing at the base on a several foot tall concrete "wall", with several wheels running on it, these wheels are then powered to rotate the dish. Last I was there, they'd been reporting for several years that the cement under some sections of the rail had crumbled away, the railroad rail was sagging 1/2" to 1" from the weight when the wheel was over these sections, at which point of course the electric motor was drawing extra current, extra wear on the motor bearings, and so on. No budget even for just slapping some concrete under this thing.
They were running the original 1985-era hardware (due to lack of funds for upgrades), in some cases down to having 1 or 2 spares left for some of the equipment that gets damaged by lightning strikes and such (1-2 total among about a dozen sites, not 1-2 per site...) To maintain the spares inventory, my friend (who is now retired) was regularly giving his voltmeter a real workout and replacing components with his soldering iron. They were still running some VMEbus hardware (with the problem being that Motorola sold their spares supply some years back, and the purchasers marked up the remaining equipment by about 10-fold, so now far out of budget for them to buy any remaining bits of this they needed), there was still a PC/XT up there running as a replacement for a dead VT-100. Last I know, they were still running everything to reel-to-reel tape and mailing it to the central office; to their misfortune, they replaced the tape-based functionality with a stack of IBM Deskstars, it turned out it was when all those faulty Deskstars came out; no budget to buy a second set of drives, so they went back to reel-to-reel tape.
Last time I was there (a few years back) I was like "Hey, you got some new hardware!"... nope, it was not for the dish, it was a USGS-run environmental sensor that got their in-building computer upgraded.
It's unfortunate, because these NRAO-sites truly are state-of-the-art (in so far as the newer equipment would not have improved RF performance over what they had) but NSF has the most shoestring of budgets for these places, in normal business terms they have just enough to cover opex (operating expenses) but zero for capex (capital expenses, i.e. maintenance and replacing hardware that's worn out.)
What about sending a balloon or an airship above the central structure and hooking it up to provide some lift? Yeah, I suppose the numbers don't check out. A quick search on the net puts the lifting capacity of hydrogen at 68 pounds per 1000 cu. ft. with helium even lower (can't be arsed to convert that to proper units). So offloading the cables in any meaningful way would require something much larger than the largest airships ever built.
Alternatively, repair crews could be lowered from an airship to work on the platform without the risk of falling down with it (well, a lower risk in any case). A helicopter could be used for that scenario as well, being somewhat less sensitive to windy conditions... but I wouldn't want to be on that repair crew in any case.
One other idea involving bags of air is to set up an airbag under the platform so that the damage to the mirror is at least somewhat reduced once the platform does fall. I'm afraid, though, that the mirror is far too sensitive even for that.
900,000m3, works out to be a ~120m diameter balloon, quite big. Which raises the question, maybe you could just (...) stuff an airbag beneath it instead?
(The cables are quite horizontal, which means they're carrying quite a few times the weight of the observatory, I guess somebody has thought about the tradeoff. Maybe it's jerk versus relatively static force that's part of the issue?)
If all anyone does is to set out to try and fix the existing structures and cables, then the first thing to accept is that the entire structure must be at end of life; that every part of the support structure will have to be replaced new. As another has already mentioned, that would necessitate a close down of some years. Turning to the 900 ton platform, would it not be a better solution to completely re-design the structure using light weight composites, and then re-design the support structures to account for the new loading? It may well be that the re-design would end up the cheaper solution; as well as creating a longer life for the resulting structure. Much better to start again with a clean sheet of paper and work out a design that will last to the end of the century.
> Rebuild the entire structure is the best solution
Obviously, especially since repairing it would most likely require tearing it partly down (remove the dish so you can lower the suspended structure and change the cables and whatever else has rotted away).
The remaining question is, is there a budget to (re)build the Arecibo Observatory, especially with all the Covid-19 expenses, given it's not a status symbol anymore? Yes, it's needed for science (and planetary safety), but we'd had noticed if Science was a priority.
Given the obscene profits being squirreled away by the big US tech giant they could do something philanthropic and just get some loose change out of their pockets.
The likes of Google, Apple, Facebook & Amazon would not even notice the amount to rebuild it with 21st century tech.
One can but dream.........
> One can but dream.........
One can, but meanwhile back in reality their propaganda teams will explain that observatories are the reason a honest, hard-working bloke can't have a cool beer after work, and that all those stoopid observatories should be banned, being an useless commie hippie plot to waste taxpayers' money.
Yes, sounds like I'm laying it on quite thick, but I've actually already heard this, in very much those terms. And indeed, what use are observatories to somebody who would lose an argument to a potted plant and the only star constellation he's heard of are the Kardashians?...
ref Register Report - I note:
1: 'Three engineering firms have been hired to probe the structure,'
Therein lies a finger pointing escape route for all if they're not kept separated - and that will be very difficult!
2: 'and a socket holding a auxiliary cable was shipped off to NASA's Kennedy Space Center for assessment '
Q: Is that where (ie. retaining anchor / socket cable end area) the cables are failing ?
If that be first area/prevalent area where cable failure found,
I do venture, without the facility of recourse to dtld as built dwgs:
.1: Failure be due to lack of free movement for articulation of cable at/near anchor point.
Lack of ability to move at socket/anchor would impose much bending stress at times on cable immediately adjacent anchor point.
.2: Single gripping to looped cables around eyes/posts gives over concentration of force
"... nobody has mentioned replacing the snapped cable nor replacing the remaining cables is very telling!"
It was mentioned, only not directly. The problem is that the central structure, 900 tons of steel, can fall at any moment.
It's really hard to attach cables from one end. Also, you'd need money to do that and they don't have any.
Same reason for replacing: You'd need to remove old one first and you can't do that, it will drop immediately.
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