Steel Wire Rope Failure...

[IRW]

Weeks after the announcement that the Arecibo radio telescope would be dismantled due to failure of two of the SWR lines holding the central platform up, it came down of it's own accord the other day- amazingly they had a drone up for an inspection flight, looking directly at the point of failure as it happened. Seems it was prudent not to 'get a man in' to go up and inspect!

 

 

 

[Jivemaster]

An example of rigging that was used then altered and used and altered and used until it failed. The original load was about 10% of the load that fell.

[Ynot]

That would have made a far more epic Bond movie scene!

Obviously the classic scene they used was a similar site to this one but I'm guessing nowhere near the actual damage done!

[timsabre]

The Bond scene was actually filmed at Arecibo...

 

Good assessment of the risk by their structural engineers, lots of people were saying that demolition was unnecessary but clearly it was right on the edge. It is presumably safe to work on now so will they rebuild it?

Edited December 4, 2020 by timsabre

[Jivemaster]

The clearance down to solid structure will likely cost more than the entire project cost. IF someone wants to spend a small country sized defence budget it could be rebuilt, with some expansion room in the support system. Does anyone have the money at the moment?

[alistermorton]

With Starlink et al cluttering the sky, it begs the question whether earth based observatories are worth it, these days.

[Andrew C]

With Starlink et al cluttering the sky, it begs the question whether earth based observatories are worth it, these days.

It would take quite lot of effort, and money, to build a 300m+ dish in orbit...

[bigclive]

The Bond scene was actually filmed at Arecibo...

 

Good assessment of the risk by their structural engineers, lots of people were saying that demolition was unnecessary but clearly it was right on the edge. It is presumably safe to work on now so will they rebuild it?

 

Perhaps they could build one in the UK?

 

Here's the plan:-

 

Strike while the iron's hot because of public emotion about the current collapse.

Award the contract to a building company with zero experience in that area, but owned by a lord.

Employ casual labour and qualify them as radio telescope experts with a one day slideshow and an orange boilersuit.

Make sure the labour is outnumbered by people in suits with white hats and clipboards, to prevent work being done.

Make sure the project repeatedly over-runs its budget by billions.

Announce that the project has sadly failed and brush it under the carpet.

[themadhippy]

Perhaps they could build one in the UK?

 

Here's the plan:-

 

copied almost word perfect from the governments handbook on awarding public contracts apart from one small error

 

Award the contract to a building company with zero experience in that area, but owned by a lord

 

The actually text in the handbook was amended in march 2020 and now reads

 

Award the contract to a company owned by a lord*¹⁴³ from a totally unrelated industry.

 

143-The term lord may be exchanged for party doner,fellow member of a private club or the brother of the aunty who advises the prime ministers cat groomer.

Edited December 4, 2020 by themadhippy

[alistermorton]

You forgot "Trebles all round", Clive.

[pscandrett]

With Starlink et al cluttering the sky, it begs the question whether earth based observatories are worth it, these days.

They're possibly not a problem due to the frequencies radio astronomers observe at and perhaps appearing 'invisible' due to their proximity to the apertures.

 

Moreover, Arecibo, because it had a spherical dish rather than parabolic (as well as its massive size) was also used for /transmissions/ - using it as a radar system to analyse planets and other objects in the solar system. Also, by using red/blue shift (ie doppler) it could work out how fast things were moving to a fairly high precision and accuracy. Handy if there's an asteroid heading our way.

 

It's been a while since I've done the physics of all this; it is true that Jodrell Bank has also been used for transmissions (bouncing signals off the moon, for example, and intercepting early transmissions of pictures taken by Russian probes). It was also used for tracking things like Sputnik as well as more nefarious things like possible missiles in the cold war, which helped with funding to get the thing built, so other instruments might be able to do this too. It's just that the /size/ of Arecibo was so large, with a huge collecting area; 300m diameter (compared to the Lovell at Jodrell at 76m, for example).

 

Even if there's the want to replace it, the funding just won't be there (unless someone can again tap into a defence budget somewhere). Scientific programmes are constantly under financial pressure and although Arecibo produced loads of great science, I suspect the case isn't there for building a replacement when other telescopes like Greenbank and Jodrell (itself 60+ years old) are still going strong - particularly as they're used together on things like VLBI, eMERLIN and other collaborations.

 

</off topic>

[ImagineerTom]

Having spent far too many years working festivals at jodrel bank one of the things I’ve learnt is that building single big dishes is a bad idea. Building a lot of tiny dishes spread out over a huge area (google the “square kilometre array” and MERLIN) bolted to some computing power enables much higher resolution scans to be taken, costs a fraction of the price, is more durable and adaptable... etc.

 

Aside from national pride/ego there hasn’t been a scientific need for massive single dishes to be built for 30 years.

 

....finally all those weeks hanging around with the geeks on site has paid off

[pscandrett]

Having spent far too many years working festivals at jodrel bank one of the things I’ve learnt is that building single big dishes is a bad idea. Building a lot of tiny dishes spread out over a huge area (google the “square kilometre array” and MERLIN) bolted to some computing power enables much higher resolution scans to be taken, costs a fraction of the price, is more durable and adaptable... etc.

 

The great thing about aperture synthesis using interferometry is that you get much higher resolutions that would be physically impossible otherwise (ie it's the size of the aperture - or essentially how far apart all the dishes are - that give you greater resolution). This can be then taken to the next level synthesising apertures the size of the Earth. One disadvantage is that the EM waves being detected by any telescope are /tiny/, and so a larger collecting area (and/or longer observation period) is vital to actually collect any signal at all. Interferometers are therefore good for looking at 'bright' things that you want to study in finer detail; large dishes are good for seeing fainter signals. (The unit used in radio astronomy for flux density is called the Jansky, and is of the order 10^-26 IIRC - W/m^2/Hz I think - which gives an idea of how tiny the signals are.) For this, a 300m Arecibo was great (but not moveable). But yes, the practicality of building lots of smaller dishes beats building movable large dishes hands down. I think the Lovell and other large telescopes that move have to account for hte shape of the dish changing under gravity, particularly when dealing with very short wavelengths/high frequencies, for example, and they're not terribly nimble.

 

Did you see all the correlators and signals coming in from MERLIN when working at Jodrell? I always found that fascinating; all the signals needed to be 'lined up' so the signals are analysed at precisely the same time. Since the update to eMERLIN the amount of data has increased - but then again so has the processing power got better over the past 50 years!

 

I have a soft spot for Jodrell Bank. As an undergraduate we did one of our lab experiments using the 7m telescope on site; others got to use the 42ft and, on one occasion when the 42ft was out of action, some students used the Lovell itself for their lab! The 7m we used wasn't originally built as a telescope - it was first installed on a missile range in Australia.

 

Dragging it back on topic a little - when it snows, they have to tip the dish of the Lovell telescope as it sort of fills up otherwise and puts extra weight on everything... and wind is a major enemy, too.

[IRW]

The great thing about aperture synthesis using interferometry...

 

:blink:

[Junior8]

The great thing about aperture synthesis using interferometry...

 

 

 

So I looked up interferometry and would I be right in thinking that it is something like tuning an organ where you tune one rank to a reference say a fork and others are tuned by sounding the same note on two ranks and using the resulting the resulting acoustic wobble you get as the indicator - when it disappears the two pipes are in tune. So the more out of tune they are the more information you get about the level of dissonance from the acoustic interaction of the two frequencies?

 

You understand I am trying to find a simple analogy I can grasp.

Edited December 5, 2020 by Junior8