Post by: Star One on 09/21/2017 08:12 pm
Quote
Powerful Hurricane Maria struck Puerto Rico on Wednesday, wrecking buildings and disrupting power and communications across the island, home of the iconic Arecibo Observatory used for radio astronomy research.
Located on the northwestern part of the island, the observatory took a near-direct hit from Hurricane Maria as it trekked southeast-to-northwest as a Category 4 storm.
Officials with the Universities Space Research Association, or USRA, are working to assess and evaluate damage to the observatory, the organization said in a statement Thursday.
“Currently, we have no contact with the observatory,” USRA said in a statement. “One observatory staff member located in Arecibo Town contacted via short-wave radio reports that trees are down, power is out, houses damaged and roads impassable.”
USRA is part of a multi-institution team charged with operating Arecibo Observatory by the National Science Foundation.
“We have no reason to believe that staff sheltered at Arecibo Observatory are in immediate danger since they have generators, well water and plenty of food,” USRA said. “This is a rapidly changing situation, and we are trying to do the best we can to contact USRA employees and find out their status.”
https://astronomynow.com/2017/09/21/officials-await-damage-report-from-puerto-ricos-famed-arecibo-observatory/
Post by: catdlr on 09/22/2017 03:10 am
Quote
All staff at Puerto Rico's iconic Arecibo Observatory are safe after Hurricane Maria roared over the island.
SRI International, which helps manage the huge telescope, said Thursday night that they were able to make communication with the small team who weathered the storm there. There had been radio silence from the observatory since early Wednesday morning, hours before the eye of the storm passed over Arecibo, in Puerto Rico's northwest.
source: https://www.washingtonpost.com/news/speaking-of-science/wp/2017/09/20/arecibo-observatory-puerto-ricos-famous-radio-telescope-is-battered-by-hurricane-maria/?utm_term=.f6fe8fc16b23
Post by: jebbo on 09/22/2017 04:32 pm
Still no word on the majority of staff who sheltered at home. Hope they're all safe!
--- Tony
Post by: Star One on 09/22/2017 04:54 pm
http://newsroom.usra.edu/latest--usra--update-on-arecibo-observatory/
Still no word on the majority of staff who sheltered at home. Hope they're all safe!
--- Tony
Thoughts to them.
Post by: Blackstar on 09/23/2017 12:48 pm
That antenna, by the way, is where the final fight scene in the movie "Goldeneye" took place. Pierce Brosnan never actually went out to the antenna platform, however, because he is afraid of heights.
The news is bad in Puerto Rico right now. There is a risk of a major dam bursting and flooding thousands of homes. And millions of people are without power. Arecibo is a minor story in all of this.
Post by: Star One on 09/23/2017 12:54 pm
Post by: Rocket Science on 09/23/2017 01:53 pm
What’s their current status in relation to the US as far as aid is concerned as aren’t they in the process of becoming a state?No statehood status (US territory) yet all are US citizens just like those in Guam, D.C isn't a state either...
http://www.washingtonexaminer.com/puerto-rico-voters-overwhelmingly-choose-to-become-51st-state-but-no-change-expected/article/2625630
http://time.com/4296175/washington-dc-statehood-history/
Post by: Star One on 09/23/2017 07:52 pm
What’s their current status in relation to the US as far as aid is concerned as aren’t they in the process of becoming a state?No statehood status (US territory) yet all are US citizens just like those in Guam, D.C isn't a state either...
http://www.washingtonexaminer.com/puerto-rico-voters-overwhelmingly-choose-to-become-51st-state-but-no-change-expected/article/2625630
http://time.com/4296175/washington-dc-statehood-history/
Thank you for that.
Post by: catdlr on 09/26/2017 04:58 am
Quote
"So far, the only damage that's confirmed is that one of the line feeds on the antenna for one of the radar systems was lost," White says. That part was suspended high above the telescope's main 1,000-foot dish, which lost some panels when it shook loose and fell down.
source: http://www.npr.org/sections/thetwo-way/2017/09/25/553594041/puerto-ricos-arecibo-radio-telescope-suffers-hurricane-damage?utm_medium=RSS&utm_campaign=science
Post by: Star One on 09/26/2017 07:44 am
Post by: Star One on 09/28/2017 06:59 pm
Quote
ADELAIDE, Australia — The giant Arecibo radio telescope in Puerto Rico sustained less damage from Hurricane Maria than originally thought, and may have little effect on plans to transfer its operations, a National Science Foundation official said Sept. 27.
Ralphe Gaume, deputy division director for the NSF’s Divison for Astronomical Sciences, told a meeting of the Astronomy and Astrophysics Advisory Committee in Alexandria, Virginia, that major elements of the observatory appeared to survive the powerful hurricane last week that devastated the island.
“Despite the initial reports of significant damage, it turns out the damage is not anywhere near as serious as we thought,” he said.
http://spacenews.com/damage-to-arecibo-less-than-feared/
Post by: Blackstar on 09/28/2017 08:12 pm
Some staff have moved to the visitor's quarters because their homes were destroyed. I stayed at the visitor's quarters. They have what looks like a small hotel there with two levels of rooms. I'll have to post a picture, but the building was relatively sturdy. They also had small cabins up at a slightly higher elevation. I suspect those did less well than the dorm building. If you have seen the movie "Contact," Ellie stays in one of those cabins. The movie shows her cabin with a nice view of the dish, but in reality the cabins are not in view of the dish.
The article provides more details on the funding issues for the observatory, which are problematic. The people who pay most for the dish are not the people who use the dish all that much, so the whole thing is a bit precarious.
Post by: Star One on 11/17/2017 07:58 pm
Quote
Two months after escaping the destruction brought to Puerto Rico by Hurricane Maria, the famed Arecibo Observatory will get a new lease on life as the National Science Foundation seeks funding partners to keep the radio telescope aimed at the cosmos.
The NSF announced the decision Thursday, and astronomers enthusiastically welcomed the news.
“This important step concludes the agency’s decision-making process with respect to the general path forward for facility operations in a budget-constrained environment, and provides the basis for a future decision regarding a new collaborator,” the NSF said in a statement.
https://astronomynow.com/2017/11/16/arecibo-observatory-will-keep-scanning-the-skies/
Post by: eeergo on 08/11/2020 06:06 pm
https://www.ucf.edu/news/broken-cable-damages-arecibo-observatory/
Post by: FutureSpaceTourist on 08/17/2020 09:19 pm
Quote
NASA’s Lindley Johnson said he expects Arecibo to be out of service for at least several months; still working to asses the damage and find a root cause. (NASA uses Arecibo for a planetary radar.)
Post by: Blackstar on 08/18/2020 04:30 pm
Post by: Frogstar_Robot on 08/18/2020 04:57 pm
The University of Central Florida used the same image in it's report. https://www.ucf.edu/news/broken-cable-damages-arecibo-observatory/
I don't think there is any reason to doubt the image is of the most recent damage.
Post by: Star One on 08/18/2020 04:59 pm
https://youtu.be/4V3VCt24tkE
Post by: edzieba on 08/18/2020 05:25 pm
I heard a report yesterday that this image that was widely circulated showing the damage was actually from the previous hurricane damage. No public photos have been released of the current damage.If it is an old image, it was not posted on the Google-indexed portion of the internet prior to 2020/08/11.
Post by: Nomadd on 08/18/2020 05:29 pm
Post by: Frogstar_Robot on 11/02/2020 04:44 pm
Quote
ORLANDO, Fla., Nov. 2 (UPI) -- The Arecibo Observatory, the world's most powerful radio space telescope, is seeking $10.5 million to begin repairs after a disastrous cable break in August that damaged the facility in the mountains of Puerto Rico.
Observatory managers, based at the University of Central Florida in Orlando, Fla., made the funding request recently to the National Science Foundation, which owns the observatory.
The $10.5 million is only the first stage of funding that will be needed, and the request could be more than double that amount to make the facility fully functional again, said Ray Lugo, director of the university's Florida Space Institute.
Post by: Swedish chef on 11/08/2020 04:18 pm
https://twitter.com/Free_Space/status/1325456218140385280
Post by: Zed_Noir on 11/08/2020 09:17 pm
Post by: Sam Ho on 11/09/2020 03:38 am
https://www.ucf.edu/news/a-second-cable-fails-at-nsfs-arecibo-observatory-in-puerto-rico/
The thinking is that the loss of the auxiliary cable in August is overloading the other cables. The main cable that failed Friday had been seen sprouting broken wires.
There is also a lot of information on work done since the first cable failure, here.
https://www.ucf.edu/news/update-on-arecibo-observatory-facility-after-telescope-damage/
Post by: Star One on 11/10/2020 11:13 am
https://gizmodo.com/second-cable-fails-at-arecibo-causing-even-more-damage-1845619120
Post by: Blackstar on 11/13/2020 05:30 pm
Iconic radio telescope in Puerto Rico is at risk of collapsing
Arecibo Observatory, which has discovered planets, searched for alien life, and appeared in classic films, is in critical danger after two cables supporting the telescope failed.
PUBLISHED November 12, 2020
One of the world’s most venerable radio telescopes is on the brink of catastrophe, triggering a frantic race by engineers at the Arecibo Observatory in Puerto Rico to save it after two critical cables supporting a 900-ton equipment platform broke.
The platform, held aloft over a massive dish by cables strung to towers, must be quickly stabilized, or it could crash to the ground and destroy the telescope. With the loss of these two cables, the remaining cables are under increased strain, and it’s uncertain whether rescue efforts will be successful.
Post by: Blackstar on 11/13/2020 11:48 pm
Post by: Blackstar on 11/14/2020 04:02 pm
Apparently there are replacement cables heading there by ship. But I'm not optimistic. How can they make the repairs without putting people in great danger?
Post by: Star One on 11/14/2020 07:02 pm
https://www.nationalgeographic.com/science/2020/11/arecibo-observatory-in-puerto-rico-at-risk-of-collapsing/2020 strikes again.
Iconic radio telescope in Puerto Rico is at risk of collapsing
Arecibo Observatory, which has discovered planets, searched for alien life, and appeared in classic films, is in critical danger after two cables supporting the telescope failed.
PUBLISHED November 12, 2020
One of the world’s most venerable radio telescopes is on the brink of catastrophe, triggering a frantic race by engineers at the Arecibo Observatory in Puerto Rico to save it after two critical cables supporting a 900-ton equipment platform broke.
The platform, held aloft over a massive dish by cables strung to towers, must be quickly stabilized, or it could crash to the ground and destroy the telescope. With the loss of these two cables, the remaining cables are under increased strain, and it’s uncertain whether rescue efforts will be successful.
Post by: Orbiter on 11/14/2020 07:07 pm
Post by: Blackstar on 11/14/2020 08:49 pm
Losing Arecibo would be an incredibly sad loss. Disappointed more funds couldn't be allocated to the observatory to ensure proper maintenance over the years.
What I have heard is that they thought they were doing proper maintenance. The first cable break was apparently a big surprise, and they were trying to figure out why it happened given the fact that they had done inspections. I know somebody in the materials field who was being asked to look into this, because the metal in the cable had not behaved as expected. Now maybe they were not doing proper inspections, or maybe there was a hidden flaw, but I don't think they were aware of deferred maintenance that put them at risk.
Post by: Star One on 11/15/2020 10:10 am
I point the finger at the NSF over this as had they been more willing to fund the maintenance of the observatory over the years, they wouldn’t be looking at a more substantial bill now. That’s of course if they don’t just wash their hands of it deciding that it’s to costly a repair.Losing Arecibo would be an incredibly sad loss. Disappointed more funds couldn't be allocated to the observatory to ensure proper maintenance over the years.
What I have heard is that they thought they were doing proper maintenance. The first cable break was apparently a big surprise, and they were trying to figure out why it happened given the fact that they had done inspections. I know somebody in the materials field who was being asked to look into this, because the metal in the cable had not behaved as expected. Now maybe they were not doing proper inspections, or maybe there was a hidden flaw, but I don't think they were aware of deferred maintenance that put them at risk.
Post by: Frogstar_Robot on 11/15/2020 10:33 am
Obviously suspension cables are widely used, but Arecibo is a unique structure. It may come with unique problems. However, corrosion of cables can occur more quickly than expected. There is a trend to fit de-humidification systems to cables in suspension bridges. The Severn Bridge underwent a refit for his reason Severn Bridge corrosion revealed (https://www.newcivilengineer.com/archive/severn-bridge-corrosion-revealed-3-15-03-2007/)
I really hope this unique observatory is saved from disaster.
Post by: trm14 on 11/15/2020 11:28 am
I point the finger at the NSF over this as had they been more willing to fund the maintenance of the observatory over the years, they wouldn’t be looking at a more substantial bill now. That’s of course if they don’t just wash their hands of it deciding that it’s to costly a repair.Losing Arecibo would be an incredibly sad loss. Disappointed more funds couldn't be allocated to the observatory to ensure proper maintenance over the years.
What I have heard is that they thought they were doing proper maintenance. The first cable break was apparently a big surprise, and they were trying to figure out why it happened given the fact that they had done inspections. I know somebody in the materials field who was being asked to look into this, because the metal in the cable had not behaved as expected. Now maybe they were not doing proper inspections, or maybe there was a hidden flaw, but I don't think they were aware of deferred maintenance that put them at risk.
It's not like they have money just laying around. NSF astrophysics has been struggling to fund all its observatories for many years and it has tried to offload many of them to other organizations (universities and such). New, expensive facilities (ALMA, Vera C. Rubin Observatory) are coming up and since effective NSF/Astro budget has been flat or decreasing, something has to go.
Also, Arecibo's science return hasn't been that great for an observatory as expensive as it is.
Post by: Star One on 11/15/2020 02:11 pm
Looking on their website I am assuming the NSF are funded by the US federal government so that kind of tells me all I need to know as to why they are struggling for money.I point the finger at the NSF over this as had they been more willing to fund the maintenance of the observatory over the years, they wouldn’t be looking at a more substantial bill now. That’s of course if they don’t just wash their hands of it deciding that it’s to costly a repair.Losing Arecibo would be an incredibly sad loss. Disappointed more funds couldn't be allocated to the observatory to ensure proper maintenance over the years.
What I have heard is that they thought they were doing proper maintenance. The first cable break was apparently a big surprise, and they were trying to figure out why it happened given the fact that they had done inspections. I know somebody in the materials field who was being asked to look into this, because the metal in the cable had not behaved as expected. Now maybe they were not doing proper inspections, or maybe there was a hidden flaw, but I don't think they were aware of deferred maintenance that put them at risk.
It's not like they have money just laying around. NSF astrophysics has been struggling to fund all its observatories for many years and it has tried to offload many of them to other organizations (universities and such). New, expensive facilities (ALMA, Vera C. Rubin Observatory) are coming up and since effective NSF/Astro budget has been flat or decreasing, something has to go.
Also, Arecibo's science return hasn't been that great for an observatory as expensive as it is.
Post by: RonM on 11/15/2020 02:32 pm
Post by: meekGee on 11/15/2020 03:31 pm
Blackstar's post implies it wasn't a "save money by deferring maintenance" situation.Looking on their website I am assuming the NSF are funded by the US federal government so that kind of tells me all I need to know as to why they are struggling for money.I point the finger at the NSF over this as had they been more willing to fund the maintenance of the observatory over the years, they wouldn’t be looking at a more substantial bill now. That’s of course if they don’t just wash their hands of it deciding that it’s to costly a repair.Losing Arecibo would be an incredibly sad loss. Disappointed more funds couldn't be allocated to the observatory to ensure proper maintenance over the years.
What I have heard is that they thought they were doing proper maintenance. The first cable break was apparently a big surprise, and they were trying to figure out why it happened given the fact that they had done inspections. I know somebody in the materials field who was being asked to look into this, because the metal in the cable had not behaved as expected. Now maybe they were not doing proper inspections, or maybe there was a hidden flaw, but I don't think they were aware of deferred maintenance that put them at risk.
It's not like they have money just laying around. NSF astrophysics has been struggling to fund all its observatories for many years and it has tried to offload many of them to other organizations (universities and such). New, expensive facilities (ALMA, Vera C. Rubin Observatory) are coming up and since effective NSF/Astro budget has been flat or decreasing, something has to go.
Also, Arecibo's science return hasn't been that great for an observatory as expensive as it is.
They thought maintenance and inspections were adequate.
So either there was a design flaw, or something in the environment (including load environment) wasn't right.
Blaming the NSF and the USG is baseless right now.
Like other posters though I wonder how they'll approach repairs without risking lives. If the whole thing can go within weeks, and the cables are still not there, and they still don't understand how it happened - I'm not optimistic sadly.
Post by: Star One on 11/15/2020 07:11 pm
Blackstar's post implies it wasn't a "save money by deferring maintenance" situation.Looking on their website I am assuming the NSF are funded by the US federal government so that kind of tells me all I need to know as to why they are struggling for money.I point the finger at the NSF over this as had they been more willing to fund the maintenance of the observatory over the years, they wouldn’t be looking at a more substantial bill now. That’s of course if they don’t just wash their hands of it deciding that it’s to costly a repair.Losing Arecibo would be an incredibly sad loss. Disappointed more funds couldn't be allocated to the observatory to ensure proper maintenance over the years.
What I have heard is that they thought they were doing proper maintenance. The first cable break was apparently a big surprise, and they were trying to figure out why it happened given the fact that they had done inspections. I know somebody in the materials field who was being asked to look into this, because the metal in the cable had not behaved as expected. Now maybe they were not doing proper inspections, or maybe there was a hidden flaw, but I don't think they were aware of deferred maintenance that put them at risk.
It's not like they have money just laying around. NSF astrophysics has been struggling to fund all its observatories for many years and it has tried to offload many of them to other organizations (universities and such). New, expensive facilities (ALMA, Vera C. Rubin Observatory) are coming up and since effective NSF/Astro budget has been flat or decreasing, something has to go.
Also, Arecibo's science return hasn't been that great for an observatory as expensive as it is.
They thought maintenance and inspections were adequate.
So either there was a design flaw, or something in the environment (including load environment) wasn't right.
Blaming the NSF and the USG is baseless right now.
Like other posters though I wonder how they'll approach repairs without risking lives. If the whole thing can go within weeks, and the cables are still not there, and they still don't understand how it happened - I'm not optimistic sadly.
Not the point I was making in that post. The point I was making is if they don’t have enough budget then that’s the fault of the politicians who set their budget. But then you have a history of repeatedly misinterpreting what I am saying.
I am sure it’s even more tiresome for other posters than it is for me to go down this path again with you.
Post by: Blackstar on 11/15/2020 07:17 pm
Blaming the NSF and the USG is baseless right now.
He has a lot of opinions. Feel free to ignore them.
Post by: Frogstar_Robot on 11/15/2020 07:54 pm
Blackstar's post implies it wasn't a "save money by deferring maintenance" situation.Looking on their website I am assuming the NSF are funded by the US federal government so that kind of tells me all I need to know as to why they are struggling for money.I point the finger at the NSF over this as had they been more willing to fund the maintenance of the observatory over the years, they wouldn’t be looking at a more substantial bill now. That’s of course if they don’t just wash their hands of it deciding that it’s to costly a repair.Losing Arecibo would be an incredibly sad loss. Disappointed more funds couldn't be allocated to the observatory to ensure proper maintenance over the years.
What I have heard is that they thought they were doing proper maintenance. The first cable break was apparently a big surprise, and they were trying to figure out why it happened given the fact that they had done inspections. I know somebody in the materials field who was being asked to look into this, because the metal in the cable had not behaved as expected. Now maybe they were not doing proper inspections, or maybe there was a hidden flaw, but I don't think they were aware of deferred maintenance that put them at risk.
It's not like they have money just laying around. NSF astrophysics has been struggling to fund all its observatories for many years and it has tried to offload many of them to other organizations (universities and such). New, expensive facilities (ALMA, Vera C. Rubin Observatory) are coming up and since effective NSF/Astro budget has been flat or decreasing, something has to go.
Also, Arecibo's science return hasn't been that great for an observatory as expensive as it is.
They thought maintenance and inspections were adequate.
So either there was a design flaw, or something in the environment (including load environment) wasn't right.
Blaming the NSF and the USG is baseless right now.
Like other posters though I wonder how they'll approach repairs without risking lives. If the whole thing can go within weeks, and the cables are still not there, and they still don't understand how it happened - I'm not optimistic sadly.
Not the point I was making in that post. The point I was making is if they don’t have enough budget then that’s the fault of the politicians who set their budget. But then you have a history of repeatedly misinterpreting what I am saying.
I am sure it’s even more tiresome for other posters than it is for me to go down this path again with you.
If that is your point, it was not what you said, which may be why you think you were misinterpreted.
Regardless, there is no evidence that they didn't have enough money for maintenance, that remains your speculation.
Post by: Nomadd on 11/15/2020 11:15 pm
China seems to think it's worth it. As distasteful as it is to rely on "We must not allow a radio telescope gap" type motivation, whatever gets it built.
Post by: russianhalo117 on 11/16/2020 12:04 am
Would this facility ever be replaced is the worst comes to pass, or are array type setups a lot more practical now days?For analog based systems, the existing telescope could be replaced with a modernised version of what is there. Traditional analog array type systems are more complex in terms of meshing the grid together. For digital based active phased systems, an all/multiple band and all/multiple frequency digital multiple segment active phased array can be installed depending upon design selected at the existing telescopes bowl. Since the array segments themselves can be steered as well as their beams no towers and overhead transmitters and instrument structure is needed. If the arrays are curved to the same or similar shape of the current dish all sky viewing in all directions without steering to point is needed. For higher resolution the array segments that are in viewing range of the target can be steered to increase capability.
China seems to think it's worth it. As distasteful as it is to rely on "We must not allow a radio telescope gap" type motivation, whatever gets it built.
It boils down to cost and timeframe and funding.
Post by: Blackstar on 11/16/2020 11:33 am
Arecibo does several things: aeronomy (measuring properties of the Earth's upper atmosphere), radio astronomy, and planetary radar (which includes taking radar measurements of near Earth asteroids, which it can do with the Goldstone radar in California).
The aeronomy science community considers Arecibo to be very important, but they have very little money. (Aeronomy science is funded by the NSF.)
The astronomy community does not highly value radio astronomy (therefore Arecibo is low priority), and it has too many facilities to fund already and is looking for opportunities to shut some down, like Arecibo. (Ground astronomy is funded by the NSF.)
The planetary radar community considers Arecibo to be important, but they are a small segment of the overall planetary community, and NASA does not want to get stuck with the entire cost of operating Arecibo. (Planetary radar is funded by NASA.)
The short version: the science community that values Arecibo most is also the one with the least money.
For a long time now, one of the things keeping the observatory going was that the cost of dismantling it was considered to be much higher than the cost of maintaining it. There is an agreement with the PR government that the facility cannot be abandoned but must be dismantled. If it collapses, then the decision is forced upon the US government. I would guess that the cost of rebuilding is much greater than the cost of dismantling.
Post by: trm14 on 11/16/2020 12:24 pm
The astronomy community does not highly value radio astronomy (therefore Arecibo is low priority), and it has too many facilities to fund already and is looking for opportunities to shut some down, like Arecibo. (Ground astronomy is funded by the NSF.)
I strongly disagree with the statement that the astronomy community does not highly value radio astronomy. The issue is more that Arecibo is a rather old-fashioned instrument for doing that.
Post by: edzieba on 11/16/2020 12:38 pm
Post by: Swedish chef on 11/16/2020 06:28 pm
Back to mechanical issues: Is it even possible to lower the suspended structure to the crater floor (even accepting damage to the primary as "if it fell the primary would be damaged anyway")? Or was the suspended structure raised into position and the support cables permanently fixed at their current length?
I found this page which has some historical photographies from the construction.
https://www.naic.edu/history_gal/historicgal.html
To me it looks like they started with the towers, sprung the main bearing cables, and from there hoisted the main rotating structure up from the ground. Now I'm not a builder my self, but why should i let that stop me from speculating a bit. 8)
I'm guessing someone sooner or later has to risk his life by going up the structure with a small nylon rope. Connecting that to a pulley that needs to be installed. Then with the small rope they can pull a stronger steel wire from one tower out to the rotating structure. This would stabilize it a wee bit. Repeat that with more steel wires until it is reasonably safe to send out an larger construction crew that will swap out the main bearing cables.
A video showing what I'm thinking of.
https://www.youtube.com/watch?v=qOzpWk_ZKIg
Edit: Spelling
Post by: Zed_Noir on 11/17/2020 02:53 am
Back to mechanical issues: Is it even possible to lower the suspended structure to the crater floor (even accepting damage to the primary as "if it fell the primary would be damaged anyway")? Or was the suspended structure raised into position and the support cables permanently fixed at their current length?
If I understand how they build the Arecibo support structure correctly. It seems to be similar to support cables on bridges. So basically the cables are fixed in placed and can not be adjusted, however individual cable strands can be removed and replaced at some cost.
Post by: Star One on 11/17/2020 07:14 am
The policy background behind Arecibo is complicated, and that is one reason why replacing it would be difficult.
Arecibo does several things: aeronomy (measuring properties of the Earth's upper atmosphere), radio astronomy, and planetary radar (which includes taking radar measurements of near Earth asteroids, which it can do with the Goldstone radar in California).
The aeronomy science community considers Arecibo to be very important, but they have very little money. (Aeronomy science is funded by the NSF.)
The astronomy community does not highly value radio astronomy (therefore Arecibo is low priority), and it has too many facilities to fund already and is looking for opportunities to shut some down, like Arecibo. (Ground astronomy is funded by the NSF.)
The planetary radar community considers Arecibo to be important, but they are a small segment of the overall planetary community, and NASA does not want to get stuck with the entire cost of operating Arecibo. (Planetary radar is funded by NASA.)
The short version: the science community that values Arecibo most is also the one with the least money.
For a long time now, one of the things keeping the observatory going was that the cost of dismantling it was considered to be much higher than the cost of maintaining it. There is an agreement with the PR government that the facility cannot be abandoned but must be dismantled. If it collapses, then the decision is forced upon the US government. I would guess that the cost of rebuilding is much greater than the cost of dismantling.
I am a bit surprised it hasn’t been considered for World Heritage status as Jodrell Bank is already a World Heritage site.
Jodrell Bank is thriving even though it’s even older than Arecibo.
Post by: edzieba on 11/17/2020 11:11 am
Extremely helpful! That sadly rules out lowering the structure. The main support cables were strung on their own from the towers, and the suspended structure was lifted up onto them and then attached. To lower it would require extensive hands-on work on the suspended structure itself to attach new pulleys to the structure, and then to detach the structure form the support cables and transfer the load to the pulley attachments. With the structure as precarious as it is, even if you waved all hope of safety for the daredevils climbing onto it, the load shift when detaching the cable supports and shifting to the pulleys could itself trigger failure of the support cables. Even an IR-esque rescue attempt by stringing new support cables 'over the top' of the existing ones by placing extensions on top of the support towers and dragging the cables by helicopter (to avoid contacting the structure below) would be risky, as a cable failure that dropped the structure would likely cause one or more towers to also topple.Back to mechanical issues: Is it even possible to lower the suspended structure to the crater floor (even accepting damage to the primary as "if it fell the primary would be damaged anyway")? Or was the suspended structure raised into position and the support cables permanently fixed at their current length?
I found this page which has some historical photographies from the construction.
https://www.naic.edu/history_gal/historicgal.html
Mad ideas (beyond the bounds of likely available funding and good sense):
- String a net beneath the structure (without time to construct new pylons, it would be at best partway between the structure's location and the floor of the crater) anchored to shock absorbers, and use explosive cutters to simultaneously sever all support cables in a controlled manner (to minimise the chance of tower toppling) and hope damage to the structure on catching it is not too great.
- Perform all elevated works while suspended from a helicopter (similar to how powerline maintenance is done, but from a suspended basket rather than on a parallel platform), and hope nothing snags if the whole thing drops.
- Inflate giant airbag within crater, sever support cables, deflate airbag to lower structure to crater floor
Post by: DaveS on 11/19/2020 03:46 pm
William Harwood@cbs_spacenewsA very sad day for astronomy; the iconic Arecibo Observatory in Puerto Rico, once the largest single-aperture radio telescope in the world, is slated for demolition after cable failures that left its suspended 900-ton instrument platform in danger of catastrophic collapse
https://twitter.com/cbs_spacenews/status/1329463766308753414
William Harwood@cbs_spacenewsThe National Science Foundation says the structure cannot be safely repaired and that the only course of action is a controlled demolition to bring the instrument platform down without threatening lives or causing additional property damage
https://twitter.com/cbs_spacenews/status/1329464832295391232
Post by: Orbiter on 11/19/2020 04:00 pm
https://www.nsf.gov/news/news_summ.jsp?cntn_id=301674
Post by: Nomadd on 11/19/2020 04:41 pm
I'm guessing the method will be simultaneously blowing the guys and tower bases. Safe, fast and cheap. So, not much chance the reflector will be salvageable.
Post by: Blackstar on 11/19/2020 04:54 pm
https://www.nasa.gov/feature/nasa-statement-on-nsf-s-planned-controlled-decommissioning-of-arecibo-radio-telescope
Post by: eeergo on 11/19/2020 04:58 pm
EDIT: On second thought, why is it deemed unfeasible to release tension on the remaining cables in a controlled way so as to lower the structure to the ground a couple of meters under it, and then try to repair it rather than write it off?
Some more pics:
https://mobile.twitter.com/alexwitze/status/1329463808784404480 (https://mobile.twitter.com/alexwitze/status/1329463808784404480)
Post by: libra on 11/19/2020 05:08 pm
Then again, if it can't be repaired...
Post by: Nomadd on 11/19/2020 05:23 pm
EDIT: On second thought, why is it deemed unfeasible to release tension on the remaining cables in a controlled way so as to lower the structure to the ground a couple of meters under it, and then try to repair it rather than write it off?Because when things are failing sooner than they should be, how are you going be able to run the numbers to do the repair job? There's no way to know how much the remaining stuff can actually take while you're working on it. Even if it worked, the whole structure would be questionable. Was the steel below spec? Did corrosion sneak in where they didn't find it? Is fatigue greater than anticipated? Are friction fittings slipping?
If the structure gave way while they were working on it, the towers would probably collapse outward.
A complete renovation would uncover so many issues, take so long and cost so much, building a new one would almost surely be a much better plan.
It's just not a good bet.
Post by: whitelancer64 on 11/19/2020 05:41 pm
https://spacenews.com/nsf-to-decommission-arecibo-radio-telescope/
Post by: Frogstar_Robot on 11/19/2020 05:46 pm
EDIT: On second thought, why is it deemed unfeasible to release tension on the remaining cables in a controlled way so as to lower the structure to the ground a couple of meters under it, and then try to repair it rather than write it off?
[This appears to contradict the advice of five expert consultant engineer teams]?
[zubenelgenubi: Slight edit for "Be civil. Respect other members."]
Post by: Bananas_on_Mars on 11/19/2020 06:05 pm
The SKA telescope (s) will cost around 2 billion € for construction and the first 10 years of operation. As i understand it, it will be far more capable than Arecibo.EDIT: On second thought, why is it deemed unfeasible to release tension on the remaining cables in a controlled way so as to lower the structure to the ground a couple of meters under it, and then try to repair it rather than write it off?Because when things are failing sooner than they should be, how are you going be able to run the numbers to do the repair job. There's no way to know how much the remaining stuff can actually take while you're working on it. Even if it worked, the whole structure would be questionable. Was the steel below spec. Did corrosion sneak in where they didn't find it? Is fatigue greater than anticipated? Are friction fittings slipping?
If the structure gave way while they were working on it, the towers would probably collapse outward.
A complete renovation would uncover so many issues, take so long and cost so much, building a new one would almost surely be a much better plan.
It's just not a good bet.
https://en.wikipedia.org/wiki/Square_Kilometre_Array
Post by: racevedo88 on 11/19/2020 06:10 pm
Post by: trm14 on 11/19/2020 06:57 pm
The SKA telescope (s) will cost around 2 billion € for construction and the first 10 years of operation. As i understand it, it will be far more capable than Arecibo.EDIT: On second thought, why is it deemed unfeasible to release tension on the remaining cables in a controlled way so as to lower the structure to the ground a couple of meters under it, and then try to repair it rather than write it off?Because when things are failing sooner than they should be, how are you going be able to run the numbers to do the repair job. There's no way to know how much the remaining stuff can actually take while you're working on it. Even if it worked, the whole structure would be questionable. Was the steel below spec. Did corrosion sneak in where they didn't find it? Is fatigue greater than anticipated? Are friction fittings slipping?
If the structure gave way while they were working on it, the towers would probably collapse outward.
A complete renovation would uncover so many issues, take so long and cost so much, building a new one would almost surely be a much better plan.
It's just not a good bet.
https://en.wikipedia.org/wiki/Square_Kilometre_Array
SKA will be hugely more capable than Arecibo, when/if it gets built. Unfortunately it has been delayed repeatedly and the cost keeps growing.
Scientifically it would make no sense to rebuild Arecibo in its old form or location, but obviously scientific merit is not the only thing that would be considered.
Post by: rubicondsrv on 11/19/2020 07:23 pm
EDIT: On second thought, why is it deemed unfeasible to release tension on the remaining cables in a controlled way so as to lower the structure to the ground a couple of meters under it, and then try to repair it rather than write it off?Because when things are failing sooner than they should be, how are you going be able to run the numbers to do the repair job? There's no way to know how much the remaining stuff can actually take while you're working on it. Even if it worked, the whole structure would be questionable. Was the steel below spec? Did corrosion sneak in where they didn't find it? Is fatigue greater than anticipated? Are friction fittings slipping?
If the structure gave way while they were working on it, the towers would probably collapse outward.
A complete renovation would uncover so many issues, take so long and cost so much, building a new one would almost surely be a much better plan.
It's just not a good bet.
that would depend on how valuable the contents of the platform are. if they are costly and if you want to replace the telescope gambling worker safety on the unknown risks to salvage the contents could be the correct call.
either way the entire structure likely needs to be rebuilt, I doubt the maintence problems are confined to the cables.
If as I suspect NSF wants to be rid of the telescope the possibility of a catastrophic accident is a convenient excuse to ensure that they cannot be forced to continue operating the telescope.
the dish itself is likely fairly cheap, as is the structure of the platform. And given the state of the cables the platform structure is likely poorly maintained as well.
my guess is NSF is using safety as an excuse to rid themselves of the entire legacy platform in order to either get a complete replacement and higher budget, or if not to remove the costs for it entirely.
Post by: eeergo on 11/19/2020 07:35 pm
EDIT: On second thought, why is it deemed unfeasible to release tension on the remaining cables in a controlled way so as to lower the structure to the ground a couple of meters under it, and then try to repair it rather than write it off?
[This appears to contradict the advice of five expert consultant engineer teams]?
That's the reason I ask, I haven't found detailed technical evaluations.
In any case, turns out those same teams didn't appear to be able to foresee neither the first cable failure, in spite of recent damaging episodes fron earthquakes and most recently hurricanes, plus obvious accumulated wear and tear from exposure (as anybody who's seen it in person notes), nor the fallout from that first cable's snapping. From the Nature article:
Quote
the cable failures came as a surprise. After the first, engineering teams spotted a handful of broken wires on the second cable, which was more crucial to holding up the structure, but they did not see it as a major problem because the weight it was carrying was well within its design capacity. “It was not seen as an immediate threat,”
[...]
Over the years, external review committees have highlighted the ongoing need to maintain the telescope’s ageing cables.
Clearly not omniscient nor fortunate in their long- and near-term decisions.
Neverthless, as you surely know, in these kind of projects there's a substantial amount of political will behind, which will deem the (safe) repair worth the money or else. Unless it's materially impossible to repair it any way you cut it, in which case it'd probably would have been explicitly stated.
As for SKA, it looks like it will eventually fill some gaps, but:
Quote
Arecibo had been regularly upgraded, with several new instruments slated to be installed in the coming years. “The telescope is in no way obsolete,”
Meanwhile in China: http://english.www.gov.cn/news/topnews/202011/09/content_WS5fa87adec6d0f7257693f50a.html (http://english.www.gov.cn/news/topnews/202011/09/content_WS5fa87adec6d0f7257693f50a.html)
Post by: Kryten on 11/19/2020 08:07 pm
Neverthless, as you surely know, in these kind of projects there's a substantial amount of political will behind, which will deem the (safe) repair worth the money or else. Unless it's materially impossible to repair it any way you cut it, in which case it'd probably would have been explicitly stated.It has been explicitly stated. The NSF release says their first engineering consultants recommended controlled demolition and the others agreed safe repair was impossible.
Post by: rubicondsrv on 11/19/2020 08:21 pm
Neverthless, as you surely know, in these kind of projects there's a substantial amount of political will behind, which will deem the (safe) repair worth the money or else. Unless it's materially impossible to repair it any way you cut it, in which case it'd probably would have been explicitly stated.It has been explicitly stated. The NSF release says their first engineering consultants recommended controlled demolition and the others agreed safe repair was impossible.
what is the threshold for "safe" this is not a simple binary decision but one of acceptable risk. it is not uncommon to engage in construction activities where fatalities are highly likely to occur, but are considered an acceptable risk.
NSF is highly motivated to set risk thresholds as low as possible since they want to be rid of Arecibo.
the consultants work with the risk parameters given by the client, it is unlikely they would simply say impossible, but rather either give a level of risk or state that due to the questionable maintence a risk assessment is not feasible.
it is ultimately a judgment call for managers to decide how much risk is acceptable, and NSF management has been wanting to be rid of Arecibo for decades.
Post by: DistantTemple on 11/19/2020 08:22 pm
As for detailed technical evaluations, there is an inaccuracy or misunderstanding in your initial question:EDIT: On second thought, why is it deemed unfeasible to release tension on the remaining cables in a controlled way so as to lower the structure to the ground a couple of meters under it, and then try to repair it rather than write it off?
[This appears to contradict the advice of five expert consultant engineer teams]?
That's the reason I ask, I haven't found detailed technical evaluations.
In any case, turns out those same teams didn't appear to be able to foresee neither the first cable failure, in spite of recent damaging episodes fron earthquakes and most recently hurricanes, plus obvious accumulated wear and tear from exposure (as anybody who's seen it in person notes), nor the fallout from that first cable's snapping. From the Nature article:Quote
the cable failures came as a surprise. After the first, engineering teams spotted a handful of broken wires on the second cable, which was more crucial to holding up the structure, but they did not see it as a major problem because the weight it was carrying was well within its design capacity. “It was not seen as an immediate threat,”
[...]
Over the years, external review committees have highlighted the ongoing need to maintain the telescope’s ageing cables.
Clearly not omniscient nor fortunate in their long- and near-term decisions.
Neverthless, as you surely know, in these kind of projects there's a substantial amount of political will behind, which will deem the (safe) repair worth the money or else. Unless it's materially impossible to repair it any way you cut it, in which case it'd probably would have been explicitly stated.
As for SKA, it looks like it will eventually fill some gaps, but:QuoteArecibo had been regularly upgraded, with several new instruments slated to be installed in the coming years. “The telescope is in no way obsolete,”
Meanwhile in China: http://english.www.gov.cn/news/topnews/202011/09/content_WS5fa87adec6d0f7257693f50a.html (http://english.www.gov.cn/news/topnews/202011/09/content_WS5fa87adec6d0f7257693f50a.html)
Clarification; the item that would need lowering is the 900 Ton instrument platform.
Dimension: the height of the said instrument platform is about 150m above the dish. Not "a couple of meters under it,"
Lowering: There is almost certainly no provision for moving the cables in any way that could appreciably lower the platform. Any tampering/adjustment of the cables is likely to change the balance of forces in the cables likely precipitating another failure and dangerous collapse.
Safety observations: As more cables are considered at risk of immanent failure, it would be unsafe to have any person in any "fall zone". As well as underneath, this will likely include 'outside' the towers, where cables or tower parts may well recoil outwards. Even hanging above (from a helicopter) (e.g. adding cables) there may be a risk of cable ends or other debris flying upwards and threatening the helicopter etc, especially as close proximity would probably be needed for attachments. Any transitory weight of new cables could also trigger collapse.
The time factor, of a likely collapse, means that long complicated preparations could be pointless, and increase the risks from collapse (compared with demolition).
Post by: rubicondsrv on 11/19/2020 08:31 pm
Lowering: There is almost certainly no provision for moving the cables in any way that could appreciably lower the platform. Any tampering/adjustment of the cables is likely to change the balance of forces in the cables likely precipitating another failure and dangerous collapse.
lowering the platform has been done in the past. the structure is clearly in bad shape, but if the contents of the platform are sufficiently valuable risking workers to attempt salvage could still be a sound decision assuming the goal is to restore the telescope.
Post by: eeergo on 11/19/2020 08:37 pm
Neverthless, as you surely know, in these kind of projects there's a substantial amount of political will behind, which will deem the (safe) repair worth the money or else. Unless it's materially impossible to repair it any way you cut it, in which case it'd probably would have been explicitly stated.It has been explicitly stated. The NSF release says their first engineering consultants recommended controlled demolition and the others agreed safe repair was impossible.
What's "safe"? Is it tecnically impossible or, as it's legitimate to suspect, not economically feasible? If so, by how much, and how much would it cost? Why were the snaps such a big surprise, were safe inspections also impossible? Are such questions obvious, or so esoteric no question about some teams' decisions (twice incorrect lately) cannot be posed?
I'm not sure why discussion about possible alternatives to summarily destroying a unique, iconic, useful and regionally-critical facility is being quenched so with such hostility. Maybe if Boeing had built it...
Post by: matthewkantar on 11/19/2020 08:47 pm
Visited the gift shop and purchased the only souvenir Tee shirt I have ever bought.
Very sad to see such an interesting facility pass on, but best not let sentimentality get in the way of better gear down the road.
Post by: Frogstar_Robot on 11/19/2020 08:55 pm
Neverthless, as you surely know, in these kind of projects there's a substantial amount of political will behind, which will deem the (safe) repair worth the money or else. Unless it's materially impossible to repair it any way you cut it, in which case it'd probably would have been explicitly stated.It has been explicitly stated. The NSF release says their first engineering consultants recommended controlled demolition and the others agreed safe repair was impossible.
What's "safe"? Is it tecnically impossible or, as it's legitimate to suspect, not economically feasible? If so, by how much, and how much would it cost? Why were the snaps such a big surprise, were safe inspections also impossible? Are such questions obvious, or so esoteric no question about some teams' decisions (twice incorrect lately) cannot be posed?
I'm not sure why discussion about possible alternatives to summarily destroying a unique, iconic, useful and regionally-critical facility is being quenched so with such hostility. Maybe if Boeing had built it...
Funny, when we are talking about impacts of satellite constellations, you tell us to "trust the experts in the field". Now you are saying "I don't trust the experts..." Bit of a double standard there ::)
Anyway, you are asking the wrong people. You should be asking NSF/UCF, although they are not obliged to answer.
Post by: Frogstar_Robot on 11/19/2020 08:59 pm
Neverthless, as you surely know, in these kind of projects there's a substantial amount of political will behind, which will deem the (safe) repair worth the money or else. Unless it's materially impossible to repair it any way you cut it, in which case it'd probably would have been explicitly stated.It has been explicitly stated. The NSF release says their first engineering consultants recommended controlled demolition and the others agreed safe repair was impossible.
what is the threshold for "safe" this is not a simple binary decision but one of acceptable risk. it is not uncommon to engage in construction activities where fatalities are highly likely to occur, but are considered an acceptable risk.
In 2020 USA, no one is gambling with worker's lives, and this is not Chernobyl.
It's on the brink of collapse. Pieces could go in any direction. The only question now is whether it will collapse before it can be demolished.
Post by: DistantTemple on 11/19/2020 09:02 pm
OK I had a quick search, and didn't know it had (edit: ever) been lowered. (maybe its in this thread, I haven't read it all) I assume its just the "Gregorian Dome" that has been lowered.
Lowering: There is almost certainly no provision for moving the cables in any way that could appreciably lower the platform. Any tampering/adjustment of the cables is likely to change the balance of forces in the cables likely precipitating another failure and dangerous collapse.
lowering the platform has been done in the past. the structure is clearly in bad shape, but if the contents of the platform are sufficiently valuable risking workers to attempt salvage could still be a sound decision assuming the goal is to restore the telescope.
Any current lowering would have to be (almost) completely controlled remotely. ... Is that possible? Is lowering gear in place, and adequately in commission?
And any structure for it (900t) to land on would have to be robotically installed.... as that is in the main danger zone..... It looks like very many-too-many difficult challenges, all with a ticking clock!
Post by: rubicondsrv on 11/19/2020 09:04 pm
In 2020 USA, no one is gambling with worker's lives, and this is not Chernobyl.
It's on the brink of collapse. Pieces could go in any direction. The only question now is whether it will collapse before it can be demolished.
workers lives are gambled on every job every day, it is just a question of the risk threshold. nothing is risk free
Post by: russianhalo117 on 11/19/2020 09:33 pm
That's devastating, especially for Puerto Rico after all the hurricane devastation and neglect from the "freely associated state". Such a shame, let's just hope just bad luck and no negligence was also to blame for this.with the way the guy wires are anchored that is not easily or safely achievable .
EDIT: On second thought, why is it deemed unfeasible to release tension on the remaining cables in a controlled way so as to lower the structure to the ground a couple of meters under it, and then try to repair it rather than write it off?
Some more pics:
https://mobile.twitter.com/alexwitze/status/1329463808784404480 (https://mobile.twitter.com/alexwitze/status/1329463808784404480)
Post by: RonM on 11/19/2020 09:34 pm
In 2020 USA, no one is gambling with worker's lives, and this is not Chernobyl.
It's on the brink of collapse. Pieces could go in any direction. The only question now is whether it will collapse before it can be demolished.
workers lives are gambled on every job every day, it is just a question of the risk threshold. nothing is risk free
OSHA has standards and the contractors have legal obligations. I'm pretty sure the people involved know more about this than we do.
Post by: Sam Ho on 11/19/2020 09:35 pm
Quote
The second broken cable was unexpected -- engineering assessments following the auxiliary cable failure indicated the structure was stable and the planning process to restore the telescope to operation was underway. Engineers subsequently found this 3-inch main cable snapped at about 60% of what should have been its minimum breaking strength during a period of calm weather, raising the possibility of other cables being weaker than expected.
Inspections of the other cables revealed new wire breaks on some of the main cables, which were original to the structure, and evidence of significant slippage at several sockets holding the remaining auxiliary cables, which were added during a refit in the 1990s that added weight to the instrument platform.
Thornton Tomasetti, the engineering firm of record hired by UCF to assess the structure, found that given the likelihood of another cable failing, repair work on the telescope -- including mitigation measures to stabilize it for additional work -- would be unsafe. Stress tests to capture a more accurate measure of the remaining cables' strength could collapse the structure, Thornton Tomasetti found. The firm recommended a controlled demolition to eliminate the danger of an unexpected collapse.
https://www.nsf.gov/news/news_summ.jsp?cntn_id=301674
Post by: russianhalo117 on 11/19/2020 09:41 pm
scheduling to remove all remaining instruments and and aerial mounted antennae are in coordination with the respective science teams. They will likely not themselves be allowed to conduct the physical retrieval which is likely to be delegated to the closeout team. Removing power already already occurred shortly after the cable failure per a triggered safety protocol.
In 2020 USA, no one is gambling with worker's lives, and this is not Chernobyl.
It's on the brink of collapse. Pieces could go in any direction. The only question now is whether it will collapse before it can be demolished.
workers lives are gambled on every job every day, it is just a question of the risk threshold. nothing is risk free
OSHA has standards and the contractors have legal obligations. I'm pretty sure the people involved know more about this than we do.
Post by: Star One on 11/19/2020 10:04 pm
Also reporting vague noises about replacing it.
Quote
In a press conference, reps for the NSF were very careful to say that they intend to work with the Puerto Rico and scientific communities, and Congress, to continue the observatory itself even as the 305-meter is shut down. In other words, hopes are that a new telescope will be built to replace it. Arecibo provides a lot of economic support for the citizens of the island, as well as STEM support for both teachers and students. Keeping the observatory running with a new 'scope is an important mission.
https://www.syfy.com/syfywire/the-giant-arecibo-radio-telescope-to-be-decommissioned-due-to-damage
Post by: russianhalo117 on 11/19/2020 10:09 pm
This article raises an interesting point in that they have to be careful how they decommission it as a lot of wildlife including some endangered species live under the dish.A study is proposed regarding at site replacement versus switching to other existing or new locations. PR government is to meet about it next years during their legislative session.
Also reporting vague noises about replacing it.QuoteIn a press conference, reps for the NSF were very careful to say that they intend to work with the Puerto Rico and scientific communities, and Congress, to continue the observatory itself even as the 305-meter is shut down. In other words, hopes are that a new telescope will be built to replace it. Arecibo provides a lot of economic support for the citizens of the island, as well as STEM support for both teachers and students. Keeping the observatory running with a new 'scope is an important mission.
https://www.syfy.com/syfywire/the-giant-arecibo-radio-telescope-to-be-decommissioned-due-to-damage
Post by: rubicondsrv on 11/19/2020 11:17 pm
scheduling to remove all remaining instruments and and aerial mounted antennae are in coordination with the respective science teams. They will likely not themselves be allowed to conduct the physical retrieval which is likely to be delegated to the closeout team. Removing power already already occurred shortly after the cable failure per a triggered safety protocol.
If the more expensive feed antenna components can be removed there is not likely much else to bother to salvage. the structure itself is clearly in need of replacement due to prolonged neglect.
Post by: catdlr on 11/20/2020 01:51 am
Arecibo Uncut: First Visit to the Platform & Dome with Dana Whitlow
https://youtu.be/N3lCL5oPVwo
Arecibo Uncut: Second visit to Platform & Dome with Dana Whitlow
https://youtu.be/ZpoHOnVdHdc
The Entire Playlist for the facility.
Arecibo Radio Observatory (ISEE-3 Reboot) - Uncut (https://www.youtube.com/playlist?list=PLPmwwVknVIiUlPbkfBUY1ebP_8hA_4q8j)
Post by: matthewkantar on 11/20/2020 04:07 am
scheduling to remove all remaining instruments and and aerial mounted antennae are in coordination with the respective science teams. They will likely not themselves be allowed to conduct the physical retrieval which is likely to be delegated to the closeout team. Removing power already already occurred shortly after the cable failure per a triggered safety protocol.
If the more expensive feed antenna components can be removed there is not likely much else to bother to salvage. the structure itself is clearly in need of replacement due to prolonged neglect.
No need to get all scoldy. Arecibo was a one of a kind, 57 year old outdoor facility. It owed its existence to a one time military need for information about radar signatures from warheads in the ionosphere. It produced stacks of papers for decades, but it was not designed to last forever.
Failure to fully understand an exotic construct situated in a jungle is not so surprising.
Unless there is specific evidence of neglect, claiming so is a disservice to all the folks who worked hard to keep it in service and update its instruments.
Post by: Eric Hedman on 11/20/2020 05:23 am
Post by: faramund on 11/20/2020 07:13 am
Once this radio telescope is gone, does it make sense to build anything to replace it in it's current location that would be capable of doing everything it had been capable of and more from a technical, financial and scientific return perspective? I think that should the criteria. Just because we have had a telescope there for nearly six decades is not a reason to replace it. As sad as it is to lose this facility, I think it should only be rebuilt albeit with modern technology if it would cost effectively adds to a scientific return versus other more modern facilities. I suspect that will be a hard argument to make.Well, China thought it was. Isn't the China Sky Eye just Arecibo only bigger? Of course China might have just done it to one-up Arecibo, who knows if besides that its justified.
Post by: Star One on 11/20/2020 07:22 am
Once this radio telescope is gone, does it make sense to build anything to replace it in it's current location that would be capable of doing everything it had been capable of and more from a technical, financial and scientific return perspective? I think that should the criteria. Just because we have had a telescope there for nearly six decades is not a reason to replace it. As sad as it is to lose this facility, I think it should only be rebuilt albeit with modern technology if it would cost effectively adds to a scientific return versus other more modern facilities. I suspect that will be a hard argument to make.Because it was more than just another radio telescope.
As the article I posted above points out it was the home to endangered species, it was a boon for the local economy and people, it performed public outreach etc etc. You can’t just consider the facility and site within the narrow bands of radio astronomy alone. Jodrell Bank in the U.K. is more than just another radio telescope and so can’t be looked at in the same narrow way hence the new visitor centre there.
Post by: eeergo on 11/20/2020 08:12 am
Neverthless, as you surely know, in these kind of projects there's a substantial amount of political will behind, which will deem the (safe) repair worth the money or else. Unless it's materially impossible to repair it any way you cut it, in which case it'd probably would have been explicitly stated.It has been explicitly stated. The NSF release says their first engineering consultants recommended controlled demolition and the others agreed safe repair was impossible.
What's "safe"? Is it tecnically impossible or, as it's legitimate to suspect, not economically feasible? If so, by how much, and how much would it cost? Why were the snaps such a big surprise, were safe inspections also impossible? Are such questions obvious, or so esoteric no question about some teams' decisions (twice incorrect lately) cannot be posed?
I'm not sure why discussion about possible alternatives to summarily destroying a unique, iconic, useful and regionally-critical facility is being quenched so with such hostility. Maybe if Boeing had built it...
Funny, when we are talking about impacts of satellite constellations, you tell us to "trust the experts in the field". Now you are saying "I don't trust the experts..." Bit of a double standard there ::)
Anyway, you are asking the wrong people. You should be asking NSF/UCF, although they are not obliged to answer.
Oh, so you're basing your biting attempts at quenching legitimate discussion on some wildly off-topic vendetta? Are you trying to sabotage this thread too so that it goes into moderation to never return? Good to know.
Funny the experts in the field have been spot on with their detailed, reasoned and open-for-scrutiny studies regarding the other topic you mention. Funny in in this case the "experts" have strepitously failed at least twice in the last few months to foresee, or even prepare for, a catastrophic failure that has brought this facility from operational to demolition status in a few short weeks. Not quite the same "experts", although in both cases the precaution principle (to preserve something valuable, if that's indeed the aim) is ignored.
Indeed NSF/UCF would be the ones with answers, yet as far as I've seen no detailed accounts on the difficulties and costs have been published. So far, even Nature has had to ask for satellite imagery on their own to illustrate their story, so transparency for such an important facility has been less than ideal. Some members here have provided partial insight into some of the reasons, thankfully.
Post by: John Kerslake on 11/20/2020 08:30 am
Post by: daedalus1 on 11/20/2020 08:51 am
Post by: catdlr on 11/20/2020 09:54 am
SETI Institute and National Radio Astronomy Observatory Team Up for SETI Science at the Very Large Array (https://www.seti.org/seti-institute-and-national-radio-astronomy-observatory-team-up-for-seti-science-at-very-large-array)
Post by: edzieba on 11/20/2020 12:14 pm
That space RADAR capability is lost unless a new facility is constructed.
Post by: Crispy on 11/20/2020 12:48 pm
Post by: Blackstar on 11/20/2020 02:30 pm
Astonishing how easy another piece of U.S. technological lead is handed to China. Don't get me wrong I'm all for as many countries as possible to do cutting-edge astronomical research, but it seems that the U.S. is abandoning this with ease. To my distant observation at least.
It's way more complicated than that. There are many different areas of space science. The US (NASA, NSF) chooses to emphasize some more than others based upon what the scientific communities say are the priorities. So you could point to one and say "China is ahead," but even if that is true, does it matter if the US is ahead in a whole bunch of other areas?
Post by: Star One on 11/20/2020 02:32 pm
It appears too matter to a lot of US politicians.Astonishing how easy another piece of U.S. technological lead is handed to China. Don't get me wrong I'm all for as many countries as possible to do cutting-edge astronomical research, but it seems that the U.S. is abandoning this with ease. To my distant observation at least.
It's way more complicated than that. There are many different areas of space science. The US (NASA, NSF) chooses to emphasize some more than others based upon what the scientific communities say are the priorities. So you could point to one and say "China is ahead," but even if that is true, does it matter if the US is ahead in a whole bunch of other areas?
Post by: Nomadd on 11/20/2020 04:13 pm
Astonishing how easy another piece of U.S. technological lead is handed to China. Don't get me wrong I'm all for as many countries as possible to do cutting-edge astronomical research, but it seems that the U.S. is abandoning this with ease. To my distant observation at least.As deplorable as that attitude is, it's real and the basis for getting a lot of things built, so you take what you can get. Fundraising for any scientific endeavor is hardly ever pretty, but if it's a choice of putting up with the smell or losing the science, your sense of distaste isn't really important.
Post by: rubicondsrv on 11/20/2020 05:08 pm
Funny the experts in the field have been spot on with their detailed, reasoned and open-for-scrutiny studies regarding the other topic you mention. Funny in in this case the "experts" have strepitously failed at least twice in the last few months to foresee, or even prepare for, a catastrophic failure that has brought this facility from operational to demolition status in a few short weeks. Not quite the same "experts", although in both cases the precaution principle (to preserve something valuable, if that's indeed the aim) is ignored.
Indeed NSF/UCF would be the ones with answers, yet as far as I've seen no detailed accounts on the difficulties and costs have been published. So far, even Nature has had to ask for satellite imagery on their own to illustrate their story, so transparency for such an important facility has been less than ideal. Some members here have provided partial insight into some of the reasons, thankfully.
only 2 of the 3 engineering firms consulted recommended demolition. the 3rd proposed a plan to stabilize the structure while controlling (but not eliminating) the risks to crews.
If they wanted to try and keep the telescope as it is they could have selected that companies proposal.
Post by: Frogstar_Robot on 11/20/2020 05:12 pm
only 2 of the 3 engineering firms consulted recommended demolition. the 3rd proposed a plan to stabilize the structure while controlling (but not eliminating) the risks to crews.
If they wanted to try and keep the telescope as it is they could have selected that companies proposal.
What is your source for that?
Post by: rubicondsrv on 11/20/2020 05:14 pm
only 2 of the 3 engineering firms consulted recommended demolition. the 3rd proposed a plan to stabilize the structure while controlling (but not eliminating) the risks to crews.
If they wanted to try and keep the telescope as it is they could have selected that companies proposal.
What is your source for that?
https://media.telemundopr.com/2020/11/EMBARGOED-NSF-Arecibo-call-materials.pdf
WJE was willing to continue the work, the other consultants thought it was too risky. NSF and UCF management sided with the more risk averse companies.
It is not unusual to have multiple differing risk analysis's and to pick the one that allows the desired activity to continue even when a minority opinion.
Post by: su27k on 11/21/2020 03:24 am
Quote
We will work with @NSF and @UCF to save #AreciboObservatory if at all possible. @RepJenniffer and I are asking Congress and federal agencies to help salvage this iconic structure, & its mission to view distant worlds & identify meteors that threaten earth.
https://twitter.com/RepJenniffer/status/1329894249182208000
Quote
Sent a letter w/ @RepStephMurphy & @RepDarrenSoto to the House & Senate Appropriations Committee requesting the necessary funds to safely stabilize the Arecibo telescope, a valuable scientific asset treasured by all Puerto Ricans & I'm committed to continuing work to preserve it.
Post by: libra on 11/21/2020 09:37 am
The scientists have said, so far that a) they need a strong scientific argument to b) get enough money to repair it.
Strictly from this point of view, it seems to be : GAME OVER.
Now,
- If people, from Puerto Rico and elsewhere, and politicians, and private funding, can be mobilized for what they consider a national / SETI / whatever - symbolical and valuable asset
- If a pile of money big enough can be found this way,
- and if it can be repaired without endangering and/or killing people,
(well that's a LOT of IF !)
Then why not repair it ? On technical grounds, can it be repaired ?
Post by: Frogstar_Robot on 11/21/2020 10:36 am
Then why not repair it ? On technical grounds, can it be repaired ?
tldr; If 3 out of 4 engineering firms say that it can not be repaired safely, then it appears no.
I would also add "Can it be repaired before it collapses anyway?". There is now no redundancy, the next cable break will cause collapse. The man cable broke at 60% capacity in calm conditions, safety factor on remaining cables is as low as 1.32.
The rescue plan outlined by WJE has 5 Immediate Priority tasks to stabilize the structure and establish a 10% load margin, by using helicopters and operations where workers are not present to avoid undue risk. They recognize that these steps may cause a collapse.
Having done those Immediate tasks, they say "limited and controlled access onto the platform and space below the reflector
dish will be permitted", and another 5 Additional Tasks are performed. After that,
Quote from: WJE
"With the additional tasks completed, we are confident the stability of the structure will no longer be
compromised by the failure of an additional M4 main cable. Restoration and investigative work can then
safely proceed with the original plan."
However, the other consultants disagree that the Additional Tasks can be performed safely. In particular, they that the factor of safety can not be reliably determined, and that WJE's Immediate Priority tasks are not sufficient to allow workers near the structure.
Quote from: WSP
At this time, WSP believes that
there is no course of action that can be taken to confidently verify the structural integrity of the existing
cables/structure. WSP strongly advises against allowing personnel on the platform or towers, or
anywhere in their immediate physical vicinity in case of potential sudden structural failure.
Quote from: TT
It has been suggested that proof-loading the structure for a period of time – to demonstrate that
the critical structural elements can sustain forces approximately 10% more than the predicted
forces in these elements during the implementation of any remedial work – will provide a
calculable margin of safety over some duration, and that repeated proof-loading could provide
the means to ensure safety throughout the duration of work. However, we believe that even if
proof loading does not cause collapse or further failure of an element, it will cause damage and
reduce reserve capacity, making the structure less safe. If we accept collapse to be an
acceptable outcome, we need to understand the collapse mechanism to reduce risk. Collapse
from a proof-testing event will not be predictable and hence creates undue risk.
NSF brought in a fourth firm (unnamed) to review the first 3 reports:
Quote from: NSF
After receiving the contracted assessments, NSF brought in an independent engineering firm and the
Army Corps of Engineers to review the findings. The firm NSF hired concurred with the
recommendations of Thornton Tomasetti and expressed concern about significant danger from
uncontrolled collapse.
It's not stated if the Army Corps of Engineers expressed an opinion regarding the repair plan.
Edit: add a rather important "not"
Post by: rubicondsrv on 11/21/2020 11:16 am
Then why not repair it ? On technical grounds, can it be repaired ?
tldr; If 3 out of 4 engineering firms say that it can not be repaired safely, then it appears no.
1 of 4 or 1 of 100 is good enough to proceed if the desire is there, the dissenters are just fodder for the lawsuits that will occur if a fatal accident occurs, such a lawsuit would likely only cost in the low tens of millions and mostly be paid by WJE.
Given the reaction from the above mentioned congresscritters it appears the report may have accomplished its real goal regardless of if the telescope as it stands collapses or not. If they throw enough money at it NSF gets a new telescope without all the accumulated maintence problems.
Post by: Frogstar_Robot on 11/21/2020 11:54 am
1 of 4 or 1 of 100 is good enough to proceed if the desire is there, the dissenters are just fodder for the lawsuits that will occur if a fatal accident occurs, such a lawsuit would likely only cost in the low tens of millions and mostly be paid by WJE.
Your viewpoint is so bizarre it's almost beyond rational argument.
I had a friend who wanted to jump out of plane without a parachute. All the jumping instructors he went to said it was too dangerous, and refused to help. After 99 rejections, he found an instructor who said "Hmm, you might get lucky, and land on a haystack. A few people have survived falling out of a plane without a parachute, so let's give it a shot!".
He was very excited to finally get to jump without a parachute. I said, "what about those other 99 who say it is too dangerous?". "Oh, they are just dissenters for the lawsuits that will follow when I die".
https://edition.cnn.com/2020/02/22/us/science-channel-mike-hughes-dead/index.html (https://edition.cnn.com/2020/02/22/us/science-channel-mike-hughes-dead/index.html)
So I guess it's true. If you want to do something that will get you killed, eventually you can find someone to go along with it.
Post by: rubicondsrv on 11/21/2020 12:55 pm
1 of 4 or 1 of 100 is good enough to proceed if the desire is there, the dissenters are just fodder for the lawsuits that will occur if a fatal accident occurs, such a lawsuit would likely only cost in the low tens of millions and mostly be paid by WJE.
Your viewpoint is so bizarre it's almost beyond rational argument.
What is bizarre about considering risking a loss of life event to be potentially acceptable as long as the payoff is sufficient and measures are taken to limit the harm as much is practical while still accomplishing the objective?
I assume you consider marine salvage and wreck removal to be truly bizarre as well given the risks involved?
The dissenters do not say a collapse will occur if repairs are attempted, only that it might and they are unwilling to attempt to determine the odds.
WJE agrees, but is willing to take the risk and take measures to limit the risk exposure but also to accept that some is necessary to accomplish the job.
The only dispute between the reports is which contractors are willing to accept the potential liability from an accident. If collapse was all but guaranteed the structure would have likely collapsed within hours of the cable breaking.
The missing part that we cannot know here is how costly is salvage and rebuild vs complete replacement, if the costs are close it is not worth it, but if not it very well could be. That is the truly important part for a sane discussion of the merits of accepting a risk, and is not likely to be publically available.
also none of this matters if congresscritters start throwing huge amounts of money around.
and as far as mike Hughes goes, he was a bit nutty, but there was no reason to try and stop him, he knew the risks involved.
Post by: DistantTemple on 11/21/2020 01:53 pm
Having read the whole of the released/(was embargoed) document quoted above... https://media.telemundopr.com/2020/11/EMBARGOED-NSF-Arecibo-call-materials.pdf
Funny the experts in the field have been spot on with their detailed, reasoned and open-for-scrutiny studies regarding the other topic you mention. Funny in in this case the "experts" have strepitously failed at least twice in the last few months to foresee, or even prepare for, a catastrophic failure that has brought this facility from operational to demolition status in a few short weeks. Not quite the same "experts", although in both cases the precaution principle (to preserve something valuable, if that's indeed the aim) is ignored.
Indeed NSF/UCF would be the ones with answers, yet as far as I've seen no detailed accounts on the difficulties and costs have been published. So far, even Nature has had to ask for satellite imagery on their own to illustrate their story, so transparency for such an important facility has been less than ideal. Some members here have provided partial insight into some of the reasons, thankfully.
only 2 of the 3 engineering firms consulted recommended demolition. the 3rd proposed a plan to stabilize the structure while controlling (but not eliminating) the risks to crews.
If they wanted to try and keep the telescope as it is they could have selected that companies proposal.
TL/DR - unless you have an armchair, a Scotch and a spare afternoon!
It does not look like a matter of the balance of opinion between 3 companies, but one of intent, possible outcome and risk management. WJE seems to provide a fairly safe path to rescue. (although even they repeatedly qualify their plan with risks) This plan doesn't put people directly in harms way until a margin of 10% has been achieved on tower 4 main cables by releasing and moving weights, and adding a cable.
I do not know how on-going degradation of the tower 4 cables progresses, but it is noted to be taking place! To me this is the one fatal element to saving Arecibo, but some of this is visible with external wire breaks, and the structure is being (this is implied in the document) carefully monitored for movement (by laser at many points).
The Nov 6th break of the M4-4 cable appears to have taken 8 minutes, suggesting (to me) that there could be an alarm triggered, with 10's of seconds warning before another major failure. This would possibly allow a scenario where a helicopter could release (drop) lines and begin to fly clear) during a collapse.
Controlled Demolition is said to reduce the risks of an uncontrolled collapse, or one precipitated by load-testing. However, WHAT are the risks of uncontrolled collapse? Are other parts of the site, or other properties at risk?
Since M4-4 failed at "60%" of its believed breaking strain, what else is inferior through degradation or original materials and workmanship? How much does this increase the cost of rescue and refurbishment?
As others have said, what is the benefit of saving Arecibo? Can it in a safe or refurbished form produce sufficiently valuable science.
Would it "in-any-case" need massive investment and upgrades? Are there more (than the cables) crucial parts that are coming to end of life? Would the cost of emergency rescue be better spent towards a new instrument, in the same location? Is the location fit for purpose going forward?
How much would a new instrument cost? Could this be a flagship for science astronomy and a boost for Puerto Rico? I guess it would deliver great science for a couple of decades...... however AIUI a space based instrument will be vastly superior, and I would guess possible in 10 years, with Starship etc!
Edit; comma after "intent" on my fourth written line.
Post by: DistantTemple on 11/21/2020 02:04 pm
I looked for a numerical analysis in your reply, or a reasoned argument. I could find neither. You gave an example of risk with one statistic "99%" but it was unclear if this had a factual source or was an euphemism.1 of 4 or 1 of 100 is good enough to proceed if the desire is there, the dissenters are just fodder for the lawsuits that will occur if a fatal accident occurs, such a lawsuit would likely only cost in the low tens of millions and mostly be paid by WJE.
Your viewpoint is so bizarre it's almost beyond rational argument.
I had a friend who wanted to jump out of plane without a parachute. All the jumping instructors he went to said it was too dangerous, and refused to help. After 99 rejections, he found an instructor who said "Hmm, you might get lucky, and land on a haystack. A few people have survived falling out of a plane without a parachute, so let's give it a shot!".
He was very excited to finally get to jump without a parachute. I said, "what about those other 99 who say it is too dangerous?". "Oh, they are just dissenters for the lawsuits that will follow when I die".
https://edition.cnn.com/2020/02/22/us/science-channel-mike-hughes-dead/index.html (https://edition.cnn.com/2020/02/22/us/science-channel-mike-hughes-dead/index.html)
So I guess it's true. If you want to do something that will get you killed, eventually you can find someone to go along with it.
You failed to present an argument that the scenario you presented is analogous to the fate of workers on Arecibo, without which,
It remains to quote a learned source above: "Your viewpoint is so bizarre it's almost beyond rational argument."
Edit: grammar - strikethrough.
Post by: Blackstar on 11/21/2020 02:21 pm
Maybe posters could try adding more information and fewer opinions?
Post by: rubicondsrv on 11/21/2020 02:29 pm
Would it "in-any-case" need massive investment and upgrades? Are there more (than the cables) crucial parts that are coming to end of life? Would the cost of emergency rescue be better spent towards a new instrument, in the same location? Is the location fit for purpose going forward?
this is likely a safe bet. if the cables were neglected until catastrophic failures started to occur it is highly likely that the remainder of the structure has also been neglected. unless there was some documented reason the cables were ignored while the rest of the structure was maintained the safe bet prior to inspection to confirm condition is the entire structure requires extensive repairs and in some cases replacement.
as far as the prior comments that assuming neglect is not fair, engineered structures that have been standing for decades do not usually suffer major structural failures that are not due to either large load changes, outside damage, or the type of age related deterioration that maintence programs are intended to detect and repair.
It can happen, but without additional information deferred and negligent maintence is a safe bet until disproven.
Post by: matthewkantar on 11/21/2020 05:36 pm
Would it "in-any-case" need massive investment and upgrades? Are there more (than the cables) crucial parts that are coming to end of life? Would the cost of emergency rescue be better spent towards a new instrument, in the same location? Is the location fit for purpose going forward?
this is likely a safe bet. if the cables were neglected until catastrophic failures started to occur it is highly likely that the remainder of the structure has also been neglected. unless there was some documented reason the cables were ignored while the rest of the structure was maintained the safe bet prior to inspection to confirm condition is the entire structure requires extensive repairs and in some cases replacement.
as far as the prior comments that assuming neglect is not fair, engineered structures that have been standing for decades do not usually suffer major structural failures that are not due to either large load changes, outside damage, or the type of age related deterioration that maintence programs are intended to detect and repair.
It can happen, but without additional information deferred and negligent maintence is a safe bet until disproven.
Sure, guilty until proven innocent. If only the boobs in charge here had looked at the best practices of the many thousands of other 57 year old, thousand foot radio dishes with catenary/cable suspended foci.
Post by: Swedish chef on 11/22/2020 12:42 am
https://www.youtube.com/watch?v=IEe4Wlc5Vp0
Since the money ran out fifteen years ago for proper maintenance Im guessing its faith is sealed now. So no need for speculation on how to save the structure.
Post by: darkenfast on 11/22/2020 08:19 am
Post by: Dizzy_RHESSI on 11/22/2020 11:34 am
https://www.nsf.gov/mps/ast/env_impact_reviews/arecibo/eis/DEIS.pdf
It will be sad to see Arecibo go as a piece of astronomical and cultural heritage, and I'm sure it will be particularly tragic for the locals. However, NSF has a very small budget for astronomy which has not grown in the way people would want. If legacy facilities are not decommissioned in a timely fashion then new projects are stalled and science will suffer. NSF already has a backlog of things that astronomers prioritised but it couldn't afford (e.g. supporting the ELTs and CCAT). Some have said that impact beyond science should be considered but NSF astronomy is charged with doing research, not supporting jobs or tourism. Radio astronomers have submitted a very ambitious concept for a next generation VLA to the 2020 Decadal Survey, it would be capable of opening up new science rather than just replacing an old facility. I do hope that politicians don't insert themselves into this process and start dictating what radio astronomers really want. If politicians want to support astronomy, then they can support the NSF budget and offer funds for decommissioning. If they want to help the locals, then they can invest in diversifying the local economy.
Post by: Johnnyhinbos on 11/22/2020 12:54 pm
Post by: Star One on 11/22/2020 07:10 pm
It’s too bad that the richest person in the world, with literally hundreds of billions in personal wealth, isn’t interested in space...Fourth richest.
Post by: lrk on 11/22/2020 07:52 pm
It’s too bad that the richest person in the world, with literally hundreds of billions in personal wealth, isn’t interested in space...Fourth richest.
Pretty sure he's referring to Bezos, not Musk. Bezos has a lot more cash sitting around that he has previously used in projects of a historical nature like picking up the Apollo F-1 engines from the sea floor.
Post by: freddo411 on 11/22/2020 08:16 pm
It’s too bad that the richest person in the world, with literally hundreds of billions in personal wealth, isn’t interested in space...
Seriously ... have you tried to fit a collectable NSF 300 meter Radio Telescope in your office? It's just not practical
Post by: Star One on 11/23/2020 06:26 am
Hard to tell as that description more or less applies to both of them.It’s too bad that the richest person in the world, with literally hundreds of billions in personal wealth, isn’t interested in space...Fourth richest.
Pretty sure he's referring to Bezos, not Musk. Bezos has a lot more cash sitting around that he has previously used in projects of a historical nature like picking up the Apollo F-1 engines from the sea floor.
Post by: Dalhousie on 11/23/2020 11:15 pm
Hard to tell as that description more or less applies to both of them.It’s too bad that the richest person in the world, with literally hundreds of billions in personal wealth, isn’t interested in space...Fourth richest.
Pretty sure he's referring to Bezos, not Musk. Bezos has a lot more cash sitting around that he has previously used in projects of a historical nature like picking up the Apollo F-1 engines from the sea floor.
Why would either of them spend that amount of money on something that does not advance their personal space vision?
Post by: Star One on 11/24/2020 07:42 am
Largesse. And doing something for the common good.Hard to tell as that description more or less applies to both of them.It’s too bad that the richest person in the world, with literally hundreds of billions in personal wealth, isn’t interested in space...Fourth richest.
Pretty sure he's referring to Bezos, not Musk. Bezos has a lot more cash sitting around that he has previously used in projects of a historical nature like picking up the Apollo F-1 engines from the sea floor.
Why would either of them spend that amount of money on something that does not advance their personal space vision?
Post by: Star One on 11/24/2020 07:49 am
https://www.change.org/p/united-states-national-science-foundation-nsf-repair-the-arecibo-observatory-do-not-decommission-it
Post by: pochimax on 11/24/2020 09:24 am
I think it's important to remember the context. NSF has been looking at divesting from Arecibo for years. Arecibo has unique capabilities but it's scientific output has been in a long term decline, its current output is low given its running costs. NSF conducted an environmental impact study in 2016, which included options for mothballing and decommissioning the observatory. NSF knew that decommissioning would be expensive, this very probably extended its operational life. Even if a pile of money were found to repair it now and there was no risk to anyone, NSF would still be lumped with the running costs and they would be talking about decommissioning again in 5 or 10 years. It's also clear that rebuilding a similar facility is a bad investment, we know that from Arecibo's output alone.I don' t know exactly, but in the High Sensivity Array Arecibo was very important in order to obtain good sensitivities for the longest VLBI baselines.
https://www.nsf.gov/mps/ast/env_impact_reviews/arecibo/eis/DEIS.pdf
It will be sad to see Arecibo go as a piece of astronomical and cultural heritage, and I'm sure it will be particularly tragic for the locals. However, NSF has a very small budget for astronomy which has not grown in the way people would want. If legacy facilities are not decommissioned in a timely fashion then new projects are stalled and science will suffer. NSF already has a backlog of things that astronomers prioritised but it couldn't afford (e.g. supporting the ELTs and CCAT). Some have said that impact beyond science should be considered but NSF astronomy is charged with doing research, not supporting jobs or tourism. Radio astronomers have submitted a very ambitious concept for a next generation VLA to the 2020 Decadal Survey, it would be capable of opening up new science rather than just replacing an old facility. I do hope that politicians don't insert themselves into this process and start dictating what radio astronomers really want. If politicians want to support astronomy, then they can support the NSF budget and offer funds for decommissioning. If they want to help the locals, then they can invest in diversifying the local economy.
https://science.nrao.edu/facilities/vlba/docs/manuals/oss/vlba-plus/hsa (https://science.nrao.edu/facilities/vlba/docs/manuals/oss/vlba-plus/hsa)
http://www2.naic.edu/~astro/aovlbi/ (http://www2.naic.edu/~astro/aovlbi/)
It is very strange for me to read that USA wants a next generation VLA and, at the same time, losing probably the most sensitive piece of it or of any other global or space VLBI observation. Plus, Arecibo was a good bridge in VLBI observations between USA and America.
Post by: daedalus1 on 11/24/2020 09:36 am
Put exlposives on the base of cables at two of the towers. Chop the cables at the third tower and as the receiver swings to the dish edge blow the explosives. Then mount a new receiver, after some damage repair. No danger to people and it should be good for decades more.
Post by: SimonFD on 11/24/2020 11:04 am
Abandoning it because it is too dangerous to send people up to reprare the cables.
Put exlposives on the base of cables at two of the towers. Chop the cables at the third tower and as the receiver swings to the dish edge blow the explosives. Then mount a new receiver, after some damage repair. No danger to people and it should be good for decades more.
What? Is there enough clearance to miss the dish or does your "some damage repair" refer to the complete rework of the reflector?
Post by: Zed_Noir on 11/24/2020 09:03 pm
Abandoning it because it is too dangerous to send people up to reprare the cables.
Put exlposives on the base of cables at two of the towers. Chop the cables at the third tower and as the receiver swings to the dish edge blow the explosives. Then mount a new receiver, after some damage repair. No danger to people and it should be good for decades more.
This idea will most likely have the 820 tonne receiver platform fall more or less straight down and take down the other two towers. ::)
Post by: Nomadd on 11/24/2020 11:18 pm
I used some pretty interesting tricks to get radio towers down that were too close to powerlines and such, but I can't think of any practical way to get this thing disassembled without dropping everything, including the towers, into the dish. Not when things are giving out that shouldn't be giving out.Abandoning it because it is too dangerous to send people up to reprare the cables.This idea will most likely have the 820 tonne receiver platform fall more or less straight down and take down the other two towers. ::)
Put exlposives on the base of cables at two of the towers. Chop the cables at the third tower and as the receiver swings to the dish edge blow the explosives. Then mount a new receiver, after some damage repair. No danger to people and it should be good for decades more.
Before I'd give much credit to any firm who says the job could be done, I think I'd have a look at the contract terms they'd want.
Post by: Johnnyhinbos on 11/25/2020 01:44 am
https://www.wcvb.com/article/trapped-under-the-sea/8036178
Post by: baldusi on 11/25/2020 02:06 am
So this is way off topic, but the discussion of repair, and the potential dangers to the humans who would be tasked with any (futile) repairs reminds me of the disaster under Boston Harbour that cost the lives of two divers and in which I had a really distant connection to (really distant). But it’s a tragic and cautionary tale...
https://www.wcvb.com/article/trapped-under-the-sea/8036178
I had a similar story, when I was a teenager I had a friend of my dad come to have dinner a few times. He was also a diver and died in a cleanup operation in the docks. As much as I'm appalled at Arecibo's fate, I don't think people should be risking other people's life so lightly in their arguments. If many experts stated that it can't be repaired without putting the technician's life at risk, I think that argument is kinda final.
Post by: Dizzy_RHESSI on 11/25/2020 05:45 pm
I don' t know exactly, but in the High Sensivity Array Arecibo was very important in order to obtain good sensitivities for the longest VLBI baselines.
https://science.nrao.edu/facilities/vlba/docs/manuals/oss/vlba-plus/hsa (https://science.nrao.edu/facilities/vlba/docs/manuals/oss/vlba-plus/hsa)
http://www2.naic.edu/~astro/aovlbi/ (http://www2.naic.edu/~astro/aovlbi/)
It is very strange for me to read that USA wants a next generation VLA and, at the same time, losing probably the most sensitive piece of it or of any other global or space VLBI observation. Plus, Arecibo was a good bridge in VLBI observations between USA and America.
If you look at publications which use the High Sensitivity Array the vast majority do not use Areicibo, 14 of 18 (of those that specified antennas). My search will not be complete as they don't keep a list but it should be unbiased. It's very limited in declination range and in the time they can observe for, longer observations mean better imaging as the Earth rotates.
Arecibo just isn't used in most VLBI observations. Over 15 years I can only find about 40 VLBI papers in Arecibo's publication list. There actually aren't really any VLBI stations in South America at these frequencies (if that's what you meant), just some small antennas. ALMA and APEX in Chile only observe at high frequencies, beyond the range of Arecibo. VLBI is quite niche science, few objects are bright and compact enough to be studied. NSF has also been studying divesting from the VLBA for years, which is far more significant to VLBI than Arecibo.
Space VLBI is dead for now with the demise of RadioAstron. Most of the concepts for the future of space VLBI look to higher frequencies, in the range of Event Horizon Telescope, beyond that of Arecibo.
People are not proposing ngVLA as just a VLBI station, it will be a transformational observatory. ngVLA will extend the work done at the VLA with greater resolution, sensitivity, image fidelity and frequency coverage. The VLA only spends a fraction of its time during VLBI with other telescopes. ngVLA actually puts a lot of emphasis on having lots of short baselines as well as long ones, without short ones an interferometer isn't sensitive to diffuse emission. Arecibo can't actually observe most of the frequency range that ngVLA would cover. In the full concept ngVLA would place 3 new antennas at the Arecibo site. It may be that ngVLA will spare the VLBA also, either upgrading or replacing it entirely.
VLBI is just not a strong case to keep Arecibo, it not often used for it. Arecibo's strongest science case by far is pulsar timing to detect very low frequency gravitational waves. This is science that FAST, ngVLA and SKA can replace however.
Post by: libra on 11/25/2020 06:53 pm
So this is way off topic, but the discussion of repair, and the potential dangers to the humans who would be tasked with any (futile) repairs reminds me of the disaster under Boston Harbour that cost the lives of two divers and in which I had a really distant connection to (really distant). But it’s a tragic and cautionary tale...
https://www.wcvb.com/article/trapped-under-the-sea/8036178
Sorry, this content is not available in your region.
Then go FRACK yourself, you SOB jingoistic website ! >:( >:( >:(
Post by: AnalogMan on 11/25/2020 07:29 pm
So this is way off topic, but the discussion of repair, and the potential dangers to the humans who would be tasked with any (futile) repairs reminds me of the disaster under Boston Harbour that cost the lives of two divers and in which I had a really distant connection to (really distant). But it’s a tragic and cautionary tale...
https://www.wcvb.com/article/trapped-under-the-sea/8036178
Sorry, this content is not available in your region.
Then go FRACK yourself, you SOB jingoistic website ! >:( >:( >:(
See if this works:
https://webcache.googleusercontent.com/search?q=cache:c_5WHCJyG1sJ:https://www.wcvb.com/article/trapped-under-the-sea/8036178
Post by: eeergo on 12/01/2020 11:35 am
Almost four months to the day since the first major consequence of post-hurricane and earthquake neglect.
Eager to see the beautiful science substitutes freed up from its decades-old chains. Not to mention the opportunities for Puerto Rico. /s
https://twitter.com/DeborahTiempo/status/1333741751069192195 (https://twitter.com/DeborahTiempo/status/1333741751069192195)
Post by: Hobbes-22 on 12/01/2020 12:00 pm
Post by: Frogstar_Robot on 12/01/2020 12:04 pm
Was it demolished, or catastrophic failure?
It collapsed by itself. So at least the engineering consultants called that right.
Post by: baldusi on 12/01/2020 12:12 pm
Was it demolished, or catastrophic failure?
It collapsed by itself. So at least the engineering consultants called that right.
It was pretty much what the technicians and engineers predicted after the second cable failed. It was clear that if the cables were failing at 2.0 their failure margin, at 1.0 they would collapse pretty fast. That's what "too much risk" meant.
Post by: eeergo on 12/01/2020 12:23 pm
https://twitter.com/DeborahTiempo/status/1333747356605571072
Post by: edzieba on 12/01/2020 12:26 pm
Post by: eeergo on 12/01/2020 02:38 pm
https://twitter.com/ruperto1023/status/1333791522269978626
Post by: edzieba on 12/01/2020 02:40 pm
Post by: Star One on 12/01/2020 02:43 pm
Edit to add:
https://twitter.com/ruperto1023/status/1333794746054033410
Post by: eeergo on 12/01/2020 02:44 pm
Looks like the cable opposite the support buildings went first, and the structure swung into the side of the depression before the rest of the cables/towers failed.
Yes, there's quite a separation between the remains of the Gregorian Dome and the support truss. Maybe even the dome detached from the truss first and the structure, still swinging as a pendulum, went further out before crashing onto the valley side.
Post by: Star One on 12/01/2020 02:47 pm
Post by: eeergo on 12/01/2020 02:51 pm
Post by: eeergo on 12/01/2020 03:32 pm
Unmitigated f*cking disaster, and I don't really believe I should include that asterisk. The cables on the two towers that supported the pendulum motion were able to sustain the huge structure's swing, probably even withstanding the detachment of the dome halfway through it, plus allowing the support truss to swing all the way until its hard stop onto the opposite wall, making those two towers fail *sideways* - but they couldn't have supported an emergency strengthening of the damaged third tower's cable bundle during the four months that it had to wait and see.
I hope NSF will find some use for the pearls it was clutching and at least have the decency of cleaning up the mess.
Fate loves the irony that it gave way just as certain events were unfolding on our satellite.
Post by: Mammutti on 12/01/2020 03:34 pm
Post by: Mark S on 12/01/2020 03:42 pm
More photos: https://www.noticel.com/galeria/20201201/imagenes-aereas-exclusivas-del-colapso-del-observatorio-de-arecibo/
It looks like the cables did do significant damage to some of the observatory buildings.
Post by: eeergo on 12/01/2020 03:54 pm
Post by: jeffreycornish on 12/01/2020 03:56 pm
I guess the joke is that funding to maintain and upgrade the facility was never allocated (because it's more important to build <insert whatever government program you think is wasteful>) much less consistently fund operations.
The joke is that Arecibo was always on the chopping block in the NSF's budget. Please refer to https://en.wikipedia.org/wiki/Arecibo_Observatory#Funding_reductions (https://en.wikipedia.org/wiki/Arecibo_Observatory#Funding_reductions)
The joke is that someone not to different from you would ask why money is being 'spent' on that thing.
How would you tell a congressperson in less than two minutes why funding should go to an aging Cold War era radio research facility in Puerto Rico?
Also, the Chinese facility is receive only, it cannot transmit like Arecibo could.
Post by: eeergo on 12/01/2020 03:56 pm
Yes they did - and they were lucky the main tower didn't fall on the underlying building.More photos: https://www.noticel.com/galeria/20201201/imagenes-aereas-exclusivas-del-colapso-del-observatorio-de-arecibo/ (https://www.noticel.com/galeria/20201201/imagenes-aereas-exclusivas-del-colapso-del-observatorio-de-arecibo/)
It looks like the cables did do significant damage to some of the observatory buildings.
Post by: Blackstar on 12/01/2020 03:59 pm
Post by: Star One on 12/01/2020 04:05 pm
Post by: eeergo on 12/01/2020 04:07 pm
Arecibo was over 50 years old. It is lamentable, but not unexpected.
[...]
How would you tell a congressperson in less than two minutes why funding should go to an aging Cold War era radio research facility in Puerto Rico?
50 years is not a whole lot for such a structure if even approximately maintained in a proper way. Or should we expect, I don't know, the Brooklyn bridge to collapse too? I agree it was not unexpected, but not from inexorable principles.
Vocal and talented professional activists exist who tried to make themselves heard, in the US and elsewhere.
Quote
Also, the Chinese facility is receive only, it cannot transmit like Arecibo could.
Indeed, and that means humanity's most capable single instrument for hazardous asteroid detection and characterization, among many other uses, has been let into disrepair and collapse without a proper substitute.
Post by: edzieba on 12/01/2020 04:10 pm
The cables on the two towers that supported the pendulum motion were able to sustain the huge structure's swing, probably even withstanding the detachment of the dome halfway through it, plus allowing the support truss to swing all the way until its hard stop onto the opposite wall, making those two towers fail *sideways* - but they couldn't have supported an emergency strengthening of the damaged third tower's cable bundle during the four months that it had to wait and see.No, they could not.
The truss that had lost a main cable was not the one that failed first. That means that all cables were WELL below design load capability. There were no 'good' cables able to hold up the structure while emergency repairs were carried out, they were all bad and on the verge of failure on a hair trigger. This wasn't a failure under storm conditions, multiple cables failed in a situation where they should have had enormous remaining margin. They did not. They ALL did not.
Arecibo was on borrowed time before the first secondary cable slipped from the anchor block. Emergency cable replacement work started then (you need to manufacture the cables and figure out how to get them up there, this isn't and of-the-shelf part or a scheduled maintenance item), and the time just wasn't available.
Post by: zubenelgenubi on 12/01/2020 04:12 pm
Re: tone of discussion. "Do unto others," etc.
Post by: eeergo on 12/01/2020 04:24 pm
The cables on the two towers that supported the pendulum motion were able to sustain the huge structure's swing, probably even withstanding the detachment of the dome halfway through it, plus allowing the support truss to swing all the way until its hard stop onto the opposite wall, making those two towers fail *sideways* - but they couldn't have supported an emergency strengthening of the damaged third tower's cable bundle during the four months that it had to wait and see.No, they could not.
The truss that had lost a main cable was not the one that failed first. That means that all cables were WELL below design load capability. There were no 'good' cables able to hold up the structure while emergency repairs were carried out, they were all bad and on the verge of failure on a hair trigger. This wasn't a failure under storm conditions, multiple cables failed in a situation where they should have had enormous remaining margin. They did not. They ALL did not.
Arecibo was on borrowed time before the first secondary cable slipped from the anchor block. Emergency cable replacement work started then (you need to manufacture the cables and figure out how to get them up there, this isn't and of-the-shelf part or a scheduled maintenance item), and the time just wasn't available.
We shall see the report that undoubtedly comes out of this. I obviously can't provide a detailed assessment based on solid figures, but I find it impossible to believe while seeing the images that show how the failure progressed, that cables (all cables as you say) with such damage could have supported such a pendulum motion all the way through, plus held on -with huge loads on them- until the towers themselves failed *away* from the dish.
I certainly could understand if *just* the cables on the tower that appears to have failed first were suspect and unsafe, as indeed it was there where the previous failure had taken place - but then the case against attempting to lay a single backup cable from there to the central truss, or even just lowering it to the ground, would be much weaker.
As for time being available... if you neglect maintenance and wait until catastrophic failure is inevitable after several hurricanes and earthquakes, it follows time doesn't allow for a safe repair. But that's a syllogism.
Post by: Dizzy_RHESSI on 12/01/2020 04:25 pm
Indeed, and that means humanity's most capable single instrument for hazardous asteroid detection and characterization, among many other uses, has been let into disrepair and collapse without a proper substitute.
Radar isn't actually useful for detecting asteroids. The most capable instruments for finding hazardous asteroids are small optical telescopes like Panstarrs and the Catalina telescopes.
https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png
Post by: edzieba on 12/01/2020 04:31 pm
The loads on the cables during the 'pendulum' are below those experienced by them supporting the structure statically. If you are familiar with climbing jargon, the suspended truss is at the bottom of an exceptionally wide angle 'American death triangle'. The static loads on the trusses are far, far above the naïve 1/3 of total structure mass that would be expected, and are instead above 1x the load of the structure mass (PER truss, i.e. total load experienced on all three trusses is more than triple the load from the mass of the structure if it were to be suspended purely vertically). But when swinging, the two remaining trusses would not even be attempting to support the load of the structure (as it would be falling), instead just be taking a small component of the lateral load. More damage would be done to the concrete towers from the cable recoil than from the swinging of the structure.
By the time the first secondary slipped, it was already far too late to save Arecibo.
Post by: Frogstar_Robot on 12/01/2020 04:47 pm
As for time being available... if you neglect maintenance and wait until catastrophic failure is inevitable after several hurricanes and earthquakes, it follows time doesn't allow for a safe repair. But that's a syllogism.
There is still no evidence that maintenance was neglected. And absolutely no one thought failure was inevitable until after the second cable broke.
I can't find what the expected lifetime of the telescope was. The actual lifetime may have been less than planned. These things happen in construction, particularly for unique structures. We have been building bridges for centuries and they still collapse unexpectedly. Compare this with the Genoa bridge collapse (https://www.theguardian.com/cities/2019/feb/26/what-caused-the-genoa-morandi-bridge-collapse-and-the-end-of-an-italian-national-myth) or the Miami bridge (https://eu.usatoday.com/story/news/nation/2019/10/22/design-error-blamed-florida-international-university-pedestrian-bridge-collapse/2449316001/) which collapsed before it was even opened. At least at Arecibo, no one was killed.
I am baffled by people's sense of entitlement over this. We should be thanking the US government for the research opportunity Arecibo provided, which they were not obliged to fund. If the USG have other spending priorities, that is up them and the people who vote for them.
Post by: eeergo on 12/01/2020 04:50 pm
Indeed, and that means humanity's most capable single instrument for hazardous asteroid detection and characterization, among many other uses, has been let into disrepair and collapse without a proper substitute.
Radar isn't actually useful for detecting asteroids. The most capable instruments for finding hazardous asteroids are small optical telescopes like Panstarrs and the Catalina telescopes.
https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png (https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png)
That's... not very true? Unless you're specifically talking about actually discovering them for the first time.
https://www.planetary.org/articles/planetary-society-arecibo-reaction (https://www.planetary.org/articles/planetary-society-arecibo-reaction)
https://www.space.com/arecibo-observatory-hunting-asteroids-for-nasa.html (https://www.space.com/arecibo-observatory-hunting-asteroids-for-nasa.html)
https://www.space.com/arecibo-observatory-loss-for-planetary-defense-asteroids (https://www.space.com/arecibo-observatory-loss-for-planetary-defense-asteroids)
Quote
Arecibo never played a role in discovering asteroids; that task is much more easily completed by a host of telescopes that see large swaths of the sky in visible and infrared light [...] But larger asteroids with orbits that might bring them too close for comfort get additional study, and often, that work has been Arecibo Observatory's. [...]
The same telescopes that identify asteroids in the first place can also give scientists the data they need to track a space rock's orbit, but when planetary radar can spot the object, it completes the same work more quickly.
Post by: Star One on 12/01/2020 04:56 pm
You know very well people are hardly going to be voting for a US federal government and or president on the basis of science spending. Let alone the spending on such a specific topic as radio astronomy.
As for time being available... if you neglect maintenance and wait until catastrophic failure is inevitable after several hurricanes and earthquakes, it follows time doesn't allow for a safe repair. But that's a syllogism.
There is still no evidence that maintenance was neglected. And absolutely no one thought failure was inevitable until after the second cable broke.
I can't find what the expected lifetime of the telescope was. The actual lifetime may have been less than planned. These things happen in construction, particularly for unique structures. We have been building bridges for centuries and they still collapse unexpectedly. Compare this with the Genoa bridge collapse (https://www.theguardian.com/cities/2019/feb/26/what-caused-the-genoa-morandi-bridge-collapse-and-the-end-of-an-italian-national-myth) or the Miami bridge (https://eu.usatoday.com/story/news/nation/2019/10/22/design-error-blamed-florida-international-university-pedestrian-bridge-collapse/2449316001/) which collapsed before it was even opened. At least at Arecibo, no one was killed.
I am baffled by people's sense of entitlement over this. We should be thanking the US government for the research opportunity Arecibo provided, which they were not obliged to fund. If the USG have other spending priorities, that is up them and the people who vote for them.
Post by: Nomadd on 12/01/2020 05:02 pm
A replacement will no doubt be budgeted for by politicians who wouldn't know a photon from a hole in the ground, but money is money and I'm really looking forward to seeing the proposals. A large low rf noise zone is getting pretty hard to come by and shouldn't be wasted.
Post by: Blackstar on 12/01/2020 05:04 pm
Indeed, and that means humanity's most capable single instrument for hazardous asteroid detection and characterization, among many other uses, has been let into disrepair and collapse without a proper substitute.
Radar isn't actually useful for detecting asteroids. The most capable instruments for finding hazardous asteroids are small optical telescopes like Panstarrs and the Catalina telescopes.
https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png (https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png)
That's... not very true? Unless you're specifically talking about actually discovering them for the first time.
No, it's totally true. The radar can only be used when you know where the asteroid is in the first place. The asteroid has to be detected by other means. The reason is that the beam is pretty narrow, and you have to point it to where the asteroid will be when the radar reaches that point.
The radar was used for characterizing asteroids--determining their properties. But it was still limited in this capability. It could only be pointed at a few asteroids per year (I don't know the number, but it was not dozens of them). Now there were lots of limitations on how many asteroids it could be pointed at, including which asteroids were in the field of view, but also observing time and cost. I seem to remember that one of the issues back in 2009 was that the radar required a lot of power that was generated on site, meaning they had to fire up a diesel generator to turn on the radar (they were not getting power off the local electricity grid). That was expensive.
When I took my group there in 2009 we were specifically interested in the radar capabilities. We were there because of a major study of government-supported work on near Earth objects. I have attached a photo I took of the Klystron generator for the radar. This was in one of the structures out there on the tower.
Goldstone also has radar capabilities, and it could be added to other dishes. There are pros and cons to doing this at any facility, which was true of Arecibo.
Post by: eeergo on 12/01/2020 05:05 pm
As for time being available... if you neglect maintenance and wait until catastrophic failure is inevitable after several hurricanes and earthquakes, it follows time doesn't allow for a safe repair. But that's a syllogism.
There is still no evidence that maintenance was neglected. And absolutely no one thought failure was inevitable until after the second cable broke.
I can't find what the expected lifetime of the telescope was. The actual lifetime may have been less than planned. These things happen in construction, particularly for unique structures. We have been building bridges for centuries and they still collapse unexpectedly. Compare this with the Genoa bridge collapse (https://www.theguardian.com/cities/2019/feb/26/what-caused-the-genoa-morandi-bridge-collapse-and-the-end-of-an-italian-national-myth) or the Miami bridge (https://eu.usatoday.com/story/news/nation/2019/10/22/design-error-blamed-florida-international-university-pedestrian-bridge-collapse/2449316001/) which collapsed before it was even opened. At least at Arecibo, no one was killed.
I am baffled by people's sense of entitlement over this. We should be thanking the US government for the research opportunity Arecibo provided, which they were not obliged to fund. If the USG have other spending priorities, that is up them and the people who vote for them.
Good for you to have chosen the Genova bridge as an example of clear lack of maintenance (through which the operating company narrowly escaped having its nation-wide highway contract revoked, and only because of immediate lack of technical means elsewhere), or the Miami walkway as a chain of gross negligences.
Among the community, the fact the facility was neglected is vox populi. Without the engineering reports, of course, it's impossible to claim that with absolute authority. It is telling cables fail "mysteriously" under their design load, endless analysis and lead times are quoted as valid reasons to do nothing, just as infrastructure woes happen all over the island, coinciding with a huge regional economic crisis, several major natural disasters hit where relief is scantly provided, and there's a well-known declared intention from the owner to reduce as much funding going to the facility as possible.
As for the entitlement... I guess we're stuck with accepting everything as is unless we personally are stakeholders on something, and even then. Maybe it would be nice to review the history of Arecibo to understand why the USG was "nice enough" to fund it - which in any case I agree it was, and should have continued to be.
Post by: eeergo on 12/01/2020 05:07 pm
Indeed, and that means humanity's most capable single instrument for hazardous asteroid detection and characterization, among many other uses, has been let into disrepair and collapse without a proper substitute.
Radar isn't actually useful for detecting asteroids. The most capable instruments for finding hazardous asteroids are small optical telescopes like Panstarrs and the Catalina telescopes.
https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png (https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png)
That's... not very true? Unless you're specifically talking about actually discovering them for the first time.
The radar was used for characterizing asteroids--determining their properties. But it was still limited in this capability. It could only be pointed at a few asteroids per year (I don't know the number, but it was not dozens of them). Now there were lots of limitations on how many asteroids it could be pointed at, including which asteroids were in the field of view, but also observing time and cost. I seem to remember that one of the issues back in 2009 was that the radar required a lot of power that was generated on site, meaning they had to fire up a diesel generator to turn on the radar (they were not getting power off the local electricity grid). That was expensive.
Goldstone also has radar capabilities, and it could be added to other dishes. There are pros and cons to doing this at any facility, which was true of Arecibo.
With respect, knowing that you worked there and how familiar you are with these facilities, that's what I referenced to in the links provided, and what the quoted text explained. As for Goldstone, there's comments about how far/close that facility is to replacing Arecibo's capabilities.
Post by: Frogstar_Robot on 12/01/2020 05:12 pm
You know very well people are hardly going to be voting for a US federal government and or president on the basis of science spending. Let alone the spending on such a specific topic as radio astronomy.
Of course. The petition to "save Arecibo" gathered a paltry 60,000 signatures. By comparison "Call for Investigations Into The 'Bill & Melinda Gates Foundation' For Medical Malpractice & Crimes Against Humanity" has gathered 675,000 signatures.
There seems to be an attitude that US voters are apathetic about science, therefore concerned parties are entitled to tell the USG how to spend their taxpayers' money. How or why US citizens vote is entirely up to them and no business of any other nation. If US citizens don't express an preference, do you really think the USG will pay much attention to non-citizens?
Post by: Frogstar_Robot on 12/01/2020 05:24 pm
Good for you to have chosen the Genova bridge as an example of clear lack of maintenance (through which the operating company narrowly escaped having its nation-wide highway contract revoked, and only because of immediate lack of technical means elsewhere), or the Miami walkway as a chain of gross negligences.
The Genova bridge needed a lot of maintenance because of design and construction flaws. In that case, the flaws were easily visible, and the need for maintenance obvious. At Arecibo, the flaws were hidden inside the cables, and so the need for maintenance can only be deduced with hindsight.
The Miami bridge was an example of a novel design, which was flawed, but that was not apparent until the structure was put in place. There was no chain of gross negligence. When physical flaws became obvious, restorative maintenance was almost immediately applied, during which the bridge collapsed.
Arecibo is very similar. There were flaws in design or construction. When the flaws become physically obvious, it was race against time to fix them before collapse.
The examples I quoted may or may not be informative to the open minded. But regardless, I repeat, there is absolutely no evidence that lack of maintenance or funding led to the collapse of Arecibo observatory.
Post by: Blackstar on 12/01/2020 05:26 pm
With respect, knowing that you worked there and how familiar you are with these facilities
I didn't work there. I visited. I took a group of experts (mostly scientists) there as part of a congressionally-mandated National Academy of Sciences study on near Earth objects. I'm not an expert on radar, nor am I an expert on NEOs. I have, however, run two major studies on NEOs. (My expertise is running science policy studies.) The second one was last year. Here are the covers of our 2009 interim report, our 2010 final report, and a 2019 study we did on using space-based telescopes to detect and track NEOs.
Post by: leovinus on 12/01/2020 05:29 pm
Indeed, and that means humanity's most capable single instrument for hazardous asteroid detection and characterization, among many other uses, has been let into disrepair and collapse without a proper substitute.
Radar isn't actually useful for detecting asteroids. The most capable instruments for finding hazardous asteroids are small optical telescopes like Panstarrs and the Catalina telescopes.
https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png (https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png)
That's... not very true? Unless you're specifically talking about actually discovering them for the first time.
[snip]
The radar was used for characterizing asteroids--determining their properties. But it was still limited in this capability. It could only be pointed at a few asteroids per year (I don't know the number, but it was not dozens of them). Now there were lots of limitations on how many asteroids it could be pointed at, including which asteroids were in the field of view, but also observing time and cost. I seem to remember that one of the issues back in 2009 was that the radar required a lot of power that was generated on site, meaning they had to fire up a diesel generator to turn on the radar (they were not getting power off the local electricity grid). That was expensive.
[snip]
Goldstone also has radar capabilities, and it could be added to other dishes. There are pros and cons to doing this at any facility, which was true of Arecibo.
Indeed, for example Arecibo was used to characterize asteroid 99942 Apophis (2004 MN4) which we keep a close eye on. From Goldstone Radar Observations Planning: 99942 Apophis in 2021 (https://echo.jpl.nasa.gov/asteroids/Apophis/apophis.2021.goldstone.planning.html) it says
Quote
Apophis was discovered in June of 2004, observed briefly, and then lost until it was serendipitously
recovered in December of 2004. Apophis has been observed with radar in January 2005 (Arecibo), August 2005 (Arecibo),
August 2006 (Arecibo), and from December 2012-March 2013 (Goldstone and Arecibo).
Post by: Dizzy_RHESSI on 12/01/2020 05:37 pm
Indeed, and that means humanity's most capable single instrument for hazardous asteroid detection and characterization, among many other uses, has been let into disrepair and collapse without a proper substitute.
Radar isn't actually useful for detecting asteroids. The most capable instruments for finding hazardous asteroids are small optical telescopes like Panstarrs and the Catalina telescopes.
https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png (https://en.wikipedia.org/wiki/Catalina_Sky_Survey#/media/File:Neo-chart.png)
That's... not very true? Unless you're specifically talking about actually discovering them for the first time.
Yes I do mean discovery, which is what I thought you meant. If instead you mean literally just detecting known asteroids (which is a slightly odd boast), then it's probably not the most capable either. Optical telescopes can detect asteroids at huge distances, radar is much more limited because you have the inverse square law both ways in the return signal (1/R^4). You can also factor in its inability to observe most of the sky. Apologies for the confusion.
Post by: meekGee on 12/01/2020 05:42 pm
This is not what cable bundles all teetering on the edge of failure do to a reinforced concrete tower after swinging 1.33x their design load across half the valley.
There's no way that all cables deteriorated equally. Some weak points developed, probably a function of environment, geometry, etc. Those failed at well below design loads. The rest of the cable were ok, but a structure like that doesn't have a bunch of alternate load paths, so once a couple of weak points went, it swung and caused the damage that you saw.
Post by: Sam Ho on 12/01/2020 06:00 pm
So this is way off topic, but the discussion of repair, and the potential dangers to the humans who would be tasked with any (futile) repairs reminds me of the disaster under Boston Harbour that cost the lives of two divers and in which I had a really distant connection to (really distant). But it’s a tragic and cautionary tale...
https://www.wcvb.com/article/trapped-under-the-sea/8036178
Sorry, this content is not available in your region.
Then go FRACK yourself, you SOB jingoistic website ! >:( >:( >:(
See if this works:
https://webcache.googleusercontent.com/search?q=cache:c_5WHCJyG1sJ:https://www.wcvb.com/article/trapped-under-the-sea/8036178
The above digression has since been overtaken by current on-topic events, but for completeness, the video mentioned is an interview with Neil Swidey on his book Trapped Under the Sea: One Engineering Marvel, Five Men, and a Disaster Ten Miles Into the Darkness.
https://www.neilswidey.com/books
Excerpt: https://www.bostonglobe.com/magazine/2014/02/09/tragedy-beneath-boston-harbor-the-crime-scene-miles-below/uyUoaQWX3ybPhxyvqfO6EN/story.html
Post by: mrhuggy on 12/01/2020 06:30 pm
https://www.youtube.com/watch?v=vchDbyIRP44
Post by: ccdengr on 12/01/2020 06:46 pm
Quote
To support the additional weight of the Gregorian dome considerable work was needed to stiffen the platform and support the 50% increase in the suspended weight. Two additional main and backstay cables with new anchors were installed at each tower.
Post by: Star One on 12/01/2020 06:46 pm
Quote
The NSF’s decision to decommission the telescope didn’t stop scientists and Puerto Ricans, for whom the telescope holds cultural as well as scientific value, to rally in support of the observatory. For decades, the facility has been a source of pride and inspiration for the island, and it has served as a crucial resource for local communities during natural disasters. Now, the crumpled telescope leaves a large, dangerous mess to clean up—and, perhaps, a site upon which to rebuild.
Anne Virkki, who leads the planetary radar team at the observatory, writes in an email: “We’ll need to start campaigning for rebuilding from today.”
https://www.nationalgeographic.com/science/2020/12/arecibo-radio-telescope-in-puerto-rico-collapses/
Post by: Blackstar on 12/01/2020 07:07 pm
Indeed, for example Arecibo was used to characterize asteroid 99942 Apophis (2004 MN4) which we keep a close eye on. From Goldstone Radar Observations Planning: 99942 Apophis in 2021 (https://echo.jpl.nasa.gov/asteroids/Apophis/apophis.2021.goldstone.planning.html) it saysQuoteApophis was discovered in June of 2004, observed briefly, and then lost until it was serendipitously
recovered in December of 2004. Apophis has been observed with radar in January 2005 (Arecibo), August 2005 (Arecibo),
August 2006 (Arecibo), and from December 2012-March 2013 (Goldstone and Arecibo).
It was also possible to use both Goldstone and Arecibo (although I don't remember how) to do a radar observation of an asteroid. There were strengths and weaknesses to both of them. Goldstone is pretty old too, although I don't know the status of the equipment there.
I think that for the very small radar astronomy community, if they had their wish, they would prefer another radar in the southern hemisphere rather than continued operation of Arecibo. So you may see some kind of push for that now. But if my grandma had wheels she'd be a wagon.
Post by: jgoldader on 12/01/2020 08:15 pm
It was also possible to use both Goldstone and Arecibo (although I don't remember how) to do a radar observation of an asteroid. There were strengths and weaknesses to both of them. Goldstone is pretty old too, although I don't know the status of the equipment there.
I also remembered hearing that some time ago. I did some searching, and they have indeed been used together for bistatic radar, with one the transmitter (Goldstone, in one reference I found) and the other (Arecibo) the receiver.
Post by: zubenelgenubi on 12/01/2020 09:10 pm
Re: what have we got now or nearest future to perform asteroid characterization or other fun active RF stuff: Let's keep that here unless we need to splinter-thread a burgeoning discussion.
Post by: eeergo on 12/01/2020 09:30 pm
Quote
When it comes to planetary defense, there's nothing like it. "There's been statements in the media that, 'Oh we have other systems that can kind of replace what Arecibo is doing,' and I don't think that's true," Anne Virkki, who leads the planetary radar team at Arecibo Observatory, told Space.com. "It's not obsolete and it's not easily replaceable by other existing facilities and instruments."
[...]
Radar can more quickly offer other details about a space rock that can inform planetary defense, including such vital information as whether an asteroid is actually a single object or a pair of objects in disguise.
[...]
Arecibo wasn't the only radar facility, but it's a rare capacity given how expensive the technology involved is. With its demise, the only remaining radar transmitter is at the Goldstone Deep Space Communications Center in California, run by NASA's Jet Propulsion Laboratory. But this facility has a host of additional responsibilities — it's part of the Deep Space Network that manages communication with spacecraft throughout the solar system and it has military responsibilities as well.
[...]
Goldstone's radar system is also about 20 times less sensitive than Arecibo's was, and the two systems could see different subsets of space. [...] Virkki said there are plans in the works to add radar capability at the Green Bank Observatory in West Virginia, but here again, it won't be able to take over Arecibo's work [...] You now don't have any redundancy in your system, it's a single-point failure with the Goldstone radar. So if it breaks at the wrong time, you don't get what you need."
I'm not basing this take on just this article though, this is a handy one I found when documenting my claims. There have been ample commentary along these lines in Twitter during the last couple of months by qualified professionals, they're not hard to track down.
This is not what cable bundles all teetering on the edge of failure do to a reinforced concrete tower after swinging 1.33x their design load across half the valley.There's no way that all cables deteriorated equally. Some weak points developed, probably a function of environment, geometry, etc. Those failed at well below design loads. The rest of the cable were ok, but a structure like that doesn't have a bunch of alternate load paths, so once a couple of weak points went, it swung and caused the damage that you saw.
Sure, but in the three failures, including the final and catastrophic one, everything that failed was in the same tower. It could have been environmental or otherwise, I don't know. But it certainly paints a very different picture of the telescope's status than had been floated around with little detail, and calls into question the inevitability of letting it wait weeks for a very particular replacement cable or collapse as the only safe option, when the most (only?) affected cables were all in the same area.
The explanation about the remaining cables being perhaps as weak, given by edzieba and referenced below, does not stand when confronted with the direct quotes from the very experienced gentleman in the video, who witnessed the collapse (and was the first to check on the telescope after hurricane Maria): it took 30 seconds and the pendulum swinging was under significant tension from the remaining two towers, whose cables indeed supported the weight without failing, transporting the truss until its mountain side hard stop, and allowing the instrumented dome to detach due to the dynamics involved while not failing themselves too.
https://twitter.com/nadiamdrake/status/1333838393294385154 (https://twitter.com/nadiamdrake/status/1333838393294385154)
The loads on the cables during the 'pendulum' are below those experienced by them supporting the structure statically. [...]when swinging, the two remaining trusses would not even be attempting to support the load of the structure (as it would be falling), instead just be taking a small component of the lateral load. More damage would be done to the concrete towers from the cable recoil than from the swinging of the structure.
Post by: Blackstar on 12/01/2020 09:43 pm
-radio astronomy
-aeronomy
-radar astronomy
Post by: Blackstar on 12/01/2020 09:52 pm
Collapsed Arecibo Radio Telescope Was Originally Built For Ballistic Missile Defense Research
The destroyed telescope, best known for other scientific research, including attempts to contact extraterrestrials, was born out of the Cold War.
By Joseph TrevithickDecember 1, 2020
Post by: Asteroza on 12/01/2020 09:59 pm
Post by: launchwatcher on 12/01/2020 10:01 pm
-aeronymyaeronomy?
Post by: launchwatcher on 12/01/2020 10:22 pm
This might be a dumb question, but for telescope designs like Arecibo, do they normally not have a means of moving the center platform away from the dish for normal maintenance work? I understand that requires greater tower offsets from the dish to allow landing the platform onto some sort of maintenance support rig beyond the lip of the dish, and complicates the design as you need some means of releasing the wires from the anchors and winching them (or a wire extension on a winch and some sort of hard stopper on the wire that slots into the anchor). The main benefit would be an unloaded system during maintenance (or retracting when a major storm is coming), though retensionings and recalibrating the platform position would be a pain.Earlier in this thread I learned that this was not possible.
Arecibo's massive central platform was hoisted up to the cables from the valley floor before the reflector was installed. (One source I found says the original mass was 550 metric tons, increasing to 815 metric tons in the 1997 upgrade).
The only other similar installation on the earth is the much newer FAST in China, which apparently uses a skycam-like cable robot to "fly" the receiving antenna to the desired location inside the dish.
Post by: Frogstar_Robot on 12/01/2020 10:30 pm
Quote from: https://spacenews.com/nasa-weighing-options-for-future-planetary-radar-capabilities-after-arecibo/
Johnson argued that the closure of Arecibo presents an opportunity to examine the future of planetary radar systems. “It’s really time to be looking at the next generation of planetary radar capabilities,” he said. That’s likely to use arrays of smaller dishes rather than one monolithic dish, like Arecibo.
Old facilities, he added, are “high maintenance” and difficult to keep operate. “Technology has moved on from 30 years ago,” when Arecibo first got planetary radar capabilities, he said. “We need to take advantage of the new technologies.”
Any future planetary radar system would likely be done in partnership with other organizations. With few exceptions, notably the Infrared Telescope Facility observatory in Hawaii, NASA does not operate ground-based telescopes, focusing instead on space-based observatories.
Given funding and a blank sheet of paper, rebuilding Arecibo as it was does not seem likely. An opportunity to build something better.
Post by: robertross on 12/02/2020 02:23 am
Article by Jeff Foust, published today but written before news of collapse:Quote from: https://spacenews.com/nasa-weighing-options-for-future-planetary-radar-capabilities-after-arecibo/Johnson argued that the closure of Arecibo presents an opportunity to examine the future of planetary radar systems. “It’s really time to be looking at the next generation of planetary radar capabilities,” he said. That’s likely to use arrays of smaller dishes rather than one monolithic dish, like Arecibo.
Old facilities, he added, are “high maintenance” and difficult to keep operate. “Technology has moved on from 30 years ago,” when Arecibo first got planetary radar capabilities, he said. “We need to take advantage of the new technologies.”
Any future planetary radar system would likely be done in partnership with other organizations. With few exceptions, notably the Infrared Telescope Facility observatory in Hawaii, NASA does not operate ground-based telescopes, focusing instead on space-based observatories.
Given funding and a blank sheet of paper, rebuilding Arecibo as it was does not seem likely. An opportunity to build something better.
Well theoretically as soon as a facility is commissioned it is obsolete. No different than many computer systems.
In my opinion, if they (really the taxpayers) are serious about building any sort of infrastructure, there needs to be funds allocated from the start to maintain it on an annual basis, until it's no longer able to function as intended. That doesn't even begin to address its decommissioning.
(also voicing my dismay at the constant neglect of so much infrastructure, scientific and otherwise).
So sad to see this scientific instrument go to waste.
Post by: John-H on 12/02/2020 02:48 am
John
Post by: Eric Hedman on 12/02/2020 03:11 am
https://www.dailymail.co.uk/sciencetech/article-9004341/Australian-telescope-maps-deep-space-record-speed.html (https://www.dailymail.co.uk/sciencetech/article-9004341/Australian-telescope-maps-deep-space-record-speed.html)
Post by: Star One on 12/02/2020 07:53 am
Post by: faramund on 12/02/2020 08:23 am
There might be an answer to this, but I haven't heard/seen it, I mean there must be some reason why China built the Sky-eye, and if that's a rational reason, i.e. as opposed to a political one-upmanship one, then it might give another reason for why it should be rebuilt, but maybe I'm just grasping at straws.
PS the only reason I said (Western-allied) is that if there is a good reason for Sky-eye, then it could still be valid, even though Sky-eye could do the same thing.
Post by: Star One on 12/02/2020 08:25 am
I understand the emotional case for Arecibo, but those who support rebuilding it haven't built a rational case, i.e. if Aredibo was rebuilt, even in a more modern fashion, what could it do that other (Western-allied) telescopes couldn't do?It’s a bit off just describing the concerns of scientists and the people in Puerto Rico as emotional. I am sure back in the colonial days there was much use of such terminology to dismiss such concerns.
There might be an answer to this, but I haven't heard/seen it, I mean there must be some reason why China built the Sky-eye, and if that's a rational reason, i.e. as opposed to a political one-upmanship one, then it might give another reason for why it should be rebuilt, but maybe I'm just grasping at straws.
PS the only reason I said (Western-allied) is that if there is a good reason for Sky-eye, then it could still be valid, even though Sky-eye could do the same thing.
Post by: Hobbes-22 on 12/02/2020 08:55 am
There might be an answer to this
Arecibo has 2 unique features:
1. powerful planetary radar, useful for studying asteroids. The only other radar system in the US is the one on Goldstone DSS-14. This is a 70-m dish, with a lower-power transmitter (500 kW vs. 1000 for Arecibo), making it less sensitive. DSS-14 also has other duties (it's part of the DSN).
2. lots of collection area (more than any array of smaller dishes), which results in a sensitive receiver.
Whether that's enough to warrant a replacement, is the question. Arecibo's scientific output has been declining. The fixed dish made it less flexible than radio telescopes with steerable dishes. The observation platform could be moved around to steer the beam, but the beam angle was limited.
This made the telescope less useful for e.g. VLBI because targets can only be observed briefly.
Post by: faramund on 12/02/2020 09:14 am
And yet, this doesn't give a reason. Isn't it a huge problem with NASA (well and many other organisations) that it gets diverted into political decisions of where and what to spend money on. I get that people in an area want money to be spent in their area, but that's not really a reason for people in other areas to agree to it.I understand the emotional case for Arecibo, but those who support rebuilding it haven't built a rational case, i.e. if Aredibo was rebuilt, even in a more modern fashion, what could it do that other (Western-allied) telescopes couldn't do?It’s a bit off just describing the concerns of scientists and the people in Puerto Rico as emotional. I am sure back in the colonial days there was much use of such terminology to dismiss such concerns.
There might be an answer to this, but I haven't heard/seen it, I mean there must be some reason why China built the Sky-eye, and if that's a rational reason, i.e. as opposed to a political one-upmanship one, then it might give another reason for why it should be rebuilt, but maybe I'm just grasping at straws.
PS the only reason I said (Western-allied) is that if there is a good reason for Sky-eye, then it could still be valid, even though Sky-eye could do the same thing.
Maybe saying emotional was wrong, a cold focus on self-interest can appear the same.
Post by: edzieba on 12/02/2020 11:36 am
The explanation about the remaining cables being perhaps as weak, given by edzieba and referenced below, does not stand when confronted with the direct quotes from the very experienced gentleman in the video, who witnessed the collapse (and was the first to check on the telescope after hurricane Maria): it took 30 seconds and the pendulum swinging was under significant tension from the remaining two towers, whose cables indeed supported the weight without failing, transporting the truss until its mountain side hard stop, and allowing the instrumented dome to detach due to the dynamics involved while not failing themselves too.No.
Remember how I mentioned the cable angle? The dramatic change in cable angle between the 3-spancase (where load is 'down' relative to the tower-to-tower span) and the 2-span pendulum-fall case where the load is 'down' relative to the current angle between load and ground (so at the start of the swing, that would be horizontal)? The two-span case has a much lower load per cable due to the change in angle, even missing one cable.
See the attached images (I'm actually overestimating the angle in the 3-span case from that photo, reality is an even more acute angle): For the 3-span case, the span angle form horizontal is ~8°, so the 'bottom angle' (angle between spans at the point of load if they were to meet at a point) is 164°. For the 2-span case, the span angle form horizontal is ~25°, so the 'bottom angle' is 130°.
Force on the span = Weight/ (2*Cos(ThetaB/2).
Force on the a span in the 3-span case = Weight / (2*Cos(82) = Weight / 0.278 = 3.6 * Weight
Force on the a span in the 2-span case = Weight / (2*Cos(65) = Weight / 0.845 = 1.2 * Weight
Or in other words: when the first span failed, the other two spans were subject to 1/3 of the load they were previously asked to carry.
Post by: Hobbes-22 on 12/02/2020 01:01 pm
No, it's totally true. The radar can only be used when you know where the asteroid is in the first place. The asteroid has to be detected by other means. The reason is that the beam is pretty narrow, and you have to point it to where the asteroid will be when the radar reaches that point.
Does that apply to the Arecibo radar in particular, or to planetary radar in general? On Earth, radar is pretty useful for first detection of objects: the narrow beam gets swept across a search volume either mechanically by moving the antenna, or electronically (phased array radar).
Arecibo's fixed dish made sweeping the beam difficult. But e.g. Goldstone could do this, albeit slowly because you have to wait for the return signal before you can move the dish. Does that limitation make the Goldstone radar useless to find asteroids?
Post by: Alpha_Centauri on 12/02/2020 01:51 pm
No, it's totally true. The radar can only be used when you know where the asteroid is in the first place. The asteroid has to be detected by other means. The reason is that the beam is pretty narrow, and you have to point it to where the asteroid will be when the radar reaches that point.
Does that apply to the Arecibo radar in particular, or to planetary radar in general? On Earth, radar is pretty useful for first detection of objects: the narrow beam gets swept across a search volume either mechanically by moving the antenna, or electronically (phased array radar).
Arecibo's fixed dish made sweeping the beam difficult. But e.g. Goldstone could do this, albeit slowly because you have to wait for the return signal before you can move the dish. Does that limitation make the Goldstone radar useless to find asteroids?
Yes, radar is not optimized for asteroid detection. The search volume you are talking about is vast compared to terrestrial applications.
Asteroids are observationally effectively blackbody objects so you can make use of the peak in the reflected/emitted light which occurs in the optical.
All the major NEO search projects are small optical survey telescopes with large fields of view, or less commonly IR. It is far more efficient.
Post by: Mark S on 12/02/2020 01:53 pm
I see there has been absolutely no discussion on here as to what this loss means to the scientists of Puerto Rico or even the people of that country. It’s this kind of narrow focus without considering the country these facilities are based in that has contributed to issues like the troubles around the building of The Thirty Metre telescope in Hawaii.
"That country"? You mean like, the United States? As far as I can tell, this will have zero impact on the lives of average US citizens. This scientific catastrophe barely rated a footnote on popular news outlets. I doubt this will even have a major impact on the lives of average Puerto Ricans, who by the way are US citizens living in a US territory.
Oddly enough, Hawaii is also part of the United States, and was granted statehood in 1959.
The impact on the science, the scientists and technicians is undeniable, and some of the scientific functionality of Arecibo will not be available until some kind of replacement is built. I understand your point about the impact on local residents. However, on the one hand you are lamenting the impact of this failure on the locals in PR, and on the other, also lamenting that the locals are opposing the TMT in Hawaii. These two positions seem to be in opposition. If the TMT opponents in Hawaii are successful in blocking its construction, they will be preemptively creating their own negative impact.
This may be a major event in the scientific community, but the average US citizen has no clue that any of this is going on.
Post by: Star One on 12/02/2020 01:58 pm
I am well aware they are all US citizens. I didn’t say I was supporting the protests in Hawaii more that not taking the local population along with them in Hawaii through engagement may have contributed to the protests. That when making these decisions you can’t just focus on the scientific arguments.I see there has been absolutely no discussion on here as to what this loss means to the scientists of Puerto Rico or even the people of that country. It’s this kind of narrow focus without considering the country these facilities are based in that has contributed to issues like the troubles around the building of The Thirty Metre telescope in Hawaii.
"That country"? You mean like, the United States? As far as I can tell, this will have zero impact on the lives of average US citizens. This scientific catastrophe barely rated a footnote on popular news outlets. I doubt this will even have a major impact on the lives of average Puerto Ricans, who by the way are US citizens living in a US territory.
Oddly enough, Hawaii is also part of the United States, and was granted statehood in 1959.
The impact on the science, the scientists and technicians is undeniable, and some of the scientific functionality of Arecibo will not be available until some kind of replacement is built. I understand your point about the impact on local residents. However, on the one hand you are lamenting the impact of this failure on the locals in PR, and on the other, also lamenting that the locals are opposing the TMT in Hawaii. These two positions seem to be in opposition. If the TMT opponents in Hawaii are successful in blocking its construction, they will be preemptively creating their own negative impact.
This may be a major event in the scientific community, but the average US citizen has no clue that any of this is going on.
Post by: Blackstar on 12/02/2020 02:38 pm
Does that apply to the Arecibo radar in particular, or to planetary radar in general?
This has been answered already. But I'll just add that planetary radar in general is a rather esoteric art. Keep in mind that the signal that gets sent out spreads out (and therefore is weaker). Then when it gets reflected back, that spreads out and gets weaker still. So the signal that comes back is far weaker than what you sent out. Also, you have to consider where the object will be when the signal eventually reaches that spot, and also consider where the receiver will be when the signal eventually comes back. And if your target is rotating (like Mercury) that will also affect the signal as well as its velocity away or toward the Earth.
It gets really complex and weird. I had people explain it to me several times and I didn't understand it. It's not like the big radars at airports. It's a rather unique set of parameters.
Post by: eeergo on 12/02/2020 04:27 pm
The explanation about the remaining cables being perhaps as weak, given by edzieba and referenced below, does not stand when confronted with the direct quotes from the very experienced gentleman in the video, who witnessed the collapse (and was the first to check on the telescope after hurricane Maria): it took 30 seconds and the pendulum swinging was under significant tension from the remaining two towers, whose cables indeed supported the weight without failing, transporting the truss until its mountain side hard stop, and allowing the instrumented dome to detach due to the dynamics involved while not failing themselves too.No.
Remember how I mentioned the cable angle? The dramatic change in cable angle between the 3-spancase (where load is 'down' relative to the tower-to-tower span) and the 2-span pendulum-fall case where the load is 'down' relative to the current angle between load and ground (so at the start of the swing, that would be horizontal)? The two-span case has a much lower load per cable due to the change in angle, even missing one cable.
See the attached images (I'm actually overestimating the angle in the 3-span case from that photo, reality is an even more acute angle): For the 3-span case, the span angle form horizontal is ~8°, so the 'bottom angle' (angle between spans at the point of load if they were to meet at a point) is 164°. For the 2-span case, the span angle form horizontal is ~25°, so the 'bottom angle' is 130°.
Force on the span = Weight/ (2*Cos(ThetaB/2).
Force on the a span in the 3-span case = Weight / (2*Cos(82) = Weight / 0.278 = 3.6 * Weight
Force on the a span in the 2-span case = Weight / (2*Cos(65) = Weight / 0.845 = 1.2 * Weight
Or in other words: when the first span failed, the other two spans were subject to 1/3 of the load they were previously asked to carry.
Thanks for the explanation, I see the point you're trying to make but I also see several issues there that invalidate the conclusion - maybe I'm reflecting wrongly on it so I appreciate your clarifications.
First, you say the static load under 3 points on each cable bundle is higher than the dynamic one when the load is falling under tension from two cables. That's correct at a very specific moment in time: at T+0s from failure the antenna assembly.
At that time, each cable would transition from:
- the static situation seeing a static tension of Tstatic=m·g·sin(A) on each cable bundle, being A the angle between horizontal and the cable bundle (approximately 35 degrees in both towers 4 and 12 from this paper (https://www.naic.edu/~astro/aotms/performance/StructureDynamics.pdf), i.e. Tstatic=0.57w, being w=mg the weight of the suspended load)...
- to just having a reactionless horizontal component pulling it towards the bisector of the two towers, with each cable providing T' = Tstatic*cos(B/2), with B the angle subtended by the two cables, let's say 120º for the sake of simplicity (don't really know where you pull 130º from), i.e. half of the original tension.
That tension would be all but released almost instantly anyway once the third cable bundle snapped, the other two managing to pull the assembly closer to them, leaving the remaining cables essentially free from loads. This is roughly the situation I understand you referenced in your first post, even if our numbers don't fully coincide because you're forgetting to account for 2D projections you're making on your diagrams on the 3-point span case in your effort to convert it to an "American death triangle" situation, which it is not. See my diagrams for clarification.
That situation, however, would not last long once the receiver assembly started to fall and re-tension the intact cables providing a centripetal force pulling the load away from a free fall, which you're neglecting.
Then, the load would become a positively-sloped function of the receptor's height/speed, both being equivalent metrics in this case (v2 = 2·g·L(1-sin(35)), where h is the cable length of around 150 m, per conservation of energy mg(L-h0)=mv2/2, where h0 is the initial "negative height" from level with the towers, equal to L·sin(35)).
Like a swing, this load would be maximal at the lowest point of the oscillation, where it would equal the static weight of the load plus the centripetal force (1.85·m·g, or 1.85x the platform's weight per the above, when the centripetal force is entirely kynetic energy), projected on each cable. That position would never be reached in this case because of the obvious physical impediments of the wall. But it can be easily demonstrated the load on the remaining cables would surpass Tstatic = 0.57·m·g approximately after slightly increasing
You're by the way underestimating the angle in the second picture, being the plane between the two cables inclined with respect to the image's: the angle between horizontal and the cables on the T4 and T16 towers (surviving ones) is 35 deg in both, so in reality what you label as the "bottom angle" is 120º.
Post by: eeergo on 12/02/2020 04:37 pm
No, it's totally true. The radar can only be used when you know where the asteroid is in the first place. The asteroid has to be detected by other means. The reason is that the beam is pretty narrow, and you have to point it to where the asteroid will be when the radar reaches that point.
Does that apply to the Arecibo radar in particular, or to planetary radar in general? On Earth, radar is pretty useful for first detection of objects: the narrow beam gets swept across a search volume either mechanically by moving the antenna, or electronically (phased array radar).
Arecibo's fixed dish made sweeping the beam difficult. But e.g. Goldstone could do this, albeit slowly because you have to wait for the return signal before you can move the dish. Does that limitation make the Goldstone radar useless to find asteroids?
Yes, radar is not optimized for asteroid detection. The search volume you are talking about is vast compared to terrestrial applications.
Asteroids are observationally effectively blackbody objects so you can make use of the peak in the reflected/emitted light which occurs in the optical.
All the major NEO search projects are small optical survey telescopes with large fields of view, or less commonly IR. It is far more efficient.
Again, this is only true for NEO discovery. Why are some members here systematically ignoring authoritative quotes on the matter, from trustworthy outlets, in order to baselessly play down Arecibo's importance? Regarding characterization of asteroids, radiotelescopes are more efficient, and particularly high-transmit-power, large dishes like Arecibo, for which there's no substitute, either existent or in work, and only a non-redundant, overbooked comparable facility (Goldstone).
Post by: eeergo on 12/02/2020 04:42 pm
I see there has been absolutely no discussion on here as to what this loss means to the scientists of Puerto Rico or even the people of that country. It’s this kind of narrow focus without considering the country these facilities are based in that has contributed to issues like the troubles around the building of The Thirty Metre telescope in Hawaii.
"That country"? You mean like, the United States? As far as I can tell, this will have zero impact on the lives of average US citizens. This scientific catastrophe barely rated a footnote on popular news outlets. I doubt this will even have a major impact on the lives of average Puerto Ricans, who by the way are US citizens living in a US territory.
Oddly enough, Hawaii is also part of the United States, and was granted statehood in 1959.
The impact on the science, the scientists and technicians is undeniable, and some of the scientific functionality of Arecibo will not be available until some kind of replacement is built. I understand your point about the impact on local residents. However, on the one hand you are lamenting the impact of this failure on the locals in PR, and on the other, also lamenting that the locals are opposing the TMT in Hawaii. These two positions seem to be in opposition. If the TMT opponents in Hawaii are successful in blocking its construction, they will be preemptively creating their own negative impact.
This may be a major event in the scientific community, but the average US citizen has no clue that any of this is going on.
It is entirely appropriate to consider Puerto Ricans a separate nationality, as recognized by their double US/PR citizenship, most recently ratified in 2009: https://en.wikipedia.org/wiki/Puerto_Rican_citizenship#United_States_recognition_of_Puerto_Rican_citizenship
As for having "zero impact on the lives of US citizens", you could say that of any major science project suddenly going south. The ISS? Nobody needs that, other than those actually working on it (like in Arecibo). It *would* have an impact for US citizens, Puerto Ricans and mostly every living organism on the planet, and quite a major one, if it was needed for planetary defense before an equivalent alternative is (if ever) available.
Post by: Star One on 12/02/2020 04:46 pm
Well said. Can I hold my hands up and say as a U.K. citizen I was genuinely ignorant of the finer details of Puerto Rico in relation to the US.I see there has been absolutely no discussion on here as to what this loss means to the scientists of Puerto Rico or even the people of that country. It’s this kind of narrow focus without considering the country these facilities are based in that has contributed to issues like the troubles around the building of The Thirty Metre telescope in Hawaii.
"That country"? You mean like, the United States? As far as I can tell, this will have zero impact on the lives of average US citizens. This scientific catastrophe barely rated a footnote on popular news outlets. I doubt this will even have a major impact on the lives of average Puerto Ricans, who by the way are US citizens living in a US territory.
Oddly enough, Hawaii is also part of the United States, and was granted statehood in 1959.
The impact on the science, the scientists and technicians is undeniable, and some of the scientific functionality of Arecibo will not be available until some kind of replacement is built. I understand your point about the impact on local residents. However, on the one hand you are lamenting the impact of this failure on the locals in PR, and on the other, also lamenting that the locals are opposing the TMT in Hawaii. These two positions seem to be in opposition. If the TMT opponents in Hawaii are successful in blocking its construction, they will be preemptively creating their own negative impact.
This may be a major event in the scientific community, but the average US citizen has no clue that any of this is going on.
It is entirely appropriate to consider Puerto Ricans a separate nationality, as recognized by their double US/PR citizenship, most recently ratified in 2009: https://en.wikipedia.org/wiki/Puerto_Rican_citizenship#United_States_recognition_of_Puerto_Rican_citizenship
As for having "zero impact on the lives of US citizens", you could say that of any major science project suddenly going south. The ISS? Nobody needs that, other than those actually working on it (like in Arecibo). It *would* have an impact for US citizens, Puerto Ricans and mostly every living organism on the planet, and quite a major one, if it was needed for planetary defense before an equivalent alternative is (if ever) available.
Post by: eeergo on 12/02/2020 04:56 pm
Well said. Can I hold my hands up and say as a U.K. citizen I was genuinely ignorant of the finer details of Puerto Rico in relation to the US.I see there has been absolutely no discussion on here as to what this loss means to the scientists of Puerto Rico or even the people of that country. It’s this kind of narrow focus without considering the country these facilities are based in that has contributed to issues like the troubles around the building of The Thirty Metre telescope in Hawaii.
"That country"? You mean like, the United States? As far as I can tell, this will have zero impact on the lives of average US citizens. This scientific catastrophe barely rated a footnote on popular news outlets. I doubt this will even have a major impact on the lives of average Puerto Ricans, who by the way are US citizens living in a US territory.
Oddly enough, Hawaii is also part of the United States, and was granted statehood in 1959.
The impact on the science, the scientists and technicians is undeniable, and some of the scientific functionality of Arecibo will not be available until some kind of replacement is built. I understand your point about the impact on local residents. However, on the one hand you are lamenting the impact of this failure on the locals in PR, and on the other, also lamenting that the locals are opposing the TMT in Hawaii. These two positions seem to be in opposition. If the TMT opponents in Hawaii are successful in blocking its construction, they will be preemptively creating their own negative impact.
This may be a major event in the scientific community, but the average US citizen has no clue that any of this is going on.
It is entirely appropriate to consider Puerto Ricans a separate nationality, as recognized by their double US/PR citizenship, most recently ratified in 2009: https://en.wikipedia.org/wiki/Puerto_Rican_citizenship#United_States_recognition_of_Puerto_Rican_citizenship
As for having "zero impact on the lives of US citizens", you could say that of any major science project suddenly going south. The ISS? Nobody needs that, other than those actually working on it (like in Arecibo). It *would* have an impact for US citizens, Puerto Ricans and mostly every living organism on the planet, and quite a major one, if it was needed for planetary defense before an equivalent alternative is (if ever) available.
I can hold my hand up to being a Spanish citizen and being utterly ignorant on most of Puerto Rico's history until I actually made some friends from the island relatively recently, which is IMO much worse. Kind of off-topic, but the island has an entirely different history, society and culture than the vast majority of US territories, even the unincorporated ones, and ignoring that is not doing their mutual relationship any favors - which is also true concerning the Arecibo observatory.
Post by: whitelancer64 on 12/02/2020 04:57 pm
No, it's totally true. The radar can only be used when you know where the asteroid is in the first place. The asteroid has to be detected by other means. The reason is that the beam is pretty narrow, and you have to point it to where the asteroid will be when the radar reaches that point.
Does that apply to the Arecibo radar in particular, or to planetary radar in general? On Earth, radar is pretty useful for first detection of objects: the narrow beam gets swept across a search volume either mechanically by moving the antenna, or electronically (phased array radar).
Arecibo's fixed dish made sweeping the beam difficult. But e.g. Goldstone could do this, albeit slowly because you have to wait for the return signal before you can move the dish. Does that limitation make the Goldstone radar useless to find asteroids?
In general. Aside from the narrow field of view, and the other excellent points raised by others, radar data is very noisy. If you look at animations of radar data of asteroids, you see all sorts of noise in the background. You need a strong signal return to be sure you're hitting something. On Earth radar sweeps work well because we already know there's nothing in the air other than airplanes and birds, so spurious noise can be ignored.
Another point, if we did want to have many large banks of radar arrays looking for asteroids, we would have to constantly send out very strong signals in order to do that. That would unintentionally be signaling to the stars that we exist and are here. If you are among those that thing active SETI is a bad idea, you wouldn't like to do that either.
Post by: whitelancer64 on 12/02/2020 05:08 pm
No, it's totally true. The radar can only be used when you know where the asteroid is in the first place. The asteroid has to be detected by other means. The reason is that the beam is pretty narrow, and you have to point it to where the asteroid will be when the radar reaches that point.
Does that apply to the Arecibo radar in particular, or to planetary radar in general? On Earth, radar is pretty useful for first detection of objects: the narrow beam gets swept across a search volume either mechanically by moving the antenna, or electronically (phased array radar).
Arecibo's fixed dish made sweeping the beam difficult. But e.g. Goldstone could do this, albeit slowly because you have to wait for the return signal before you can move the dish. Does that limitation make the Goldstone radar useless to find asteroids?
Yes, radar is not optimized for asteroid detection. The search volume you are talking about is vast compared to terrestrial applications.
Asteroids are observationally effectively blackbody objects so you can make use of the peak in the reflected/emitted light which occurs in the optical.
All the major NEO search projects are small optical survey telescopes with large fields of view, or less commonly IR. It is far more efficient.
Again, this is only true for NEO discovery. Why are some members here systematically ignoring authoritative quotes on the matter, from trustworthy outlets, in order to baselessly play down Arecibo's importance? Regarding characterization of asteroids, radiotelescopes are more efficient, and particularly high-transmit-power, large dishes like Arecibo, for which there's no substitute, either existent or in work, and only a non-redundant, overbooked comparable facility (Goldstone).
Planetary radar is excellent for characterizing the shape and rough surface structure, and quickly and very accurately determining the orbit of an already-discovered asteroid. Nobody here has said otherwise.
It isn't good at detection or discovery of asteroids, as everyone who has weighed in on this has said, including yourself.
Describing its capabilities and limitations is hardly disparaging Arecibo's importance.
Post by: John-H on 12/02/2020 05:09 pm
John
Post by: Mark S on 12/02/2020 05:21 pm
The explanation about the remaining cables being perhaps as weak, given by edzieba and referenced below, does not stand when confronted with the direct quotes from the very experienced gentleman in the video, who witnessed the collapse (and was the first to check on the telescope after hurricane Maria): it took 30 seconds and the pendulum swinging was under significant tension from the remaining two towers, whose cables indeed supported the weight without failing, transporting the truss until its mountain side hard stop, and allowing the instrumented dome to detach due to the dynamics involved while not failing themselves too.No.
Remember how I mentioned the cable angle? The dramatic change in cable angle between the 3-spancase (where load is 'down' relative to the tower-to-tower span) and the 2-span pendulum-fall case where the load is 'down' relative to the current angle between load and ground (so at the start of the swing, that would be horizontal)? The two-span case has a much lower load per cable due to the change in angle, even missing one cable.
See the attached images (I'm actually overestimating the angle in the 3-span case from that photo, reality is an even more acute angle): For the 3-span case, the span angle form horizontal is ~8°, so the 'bottom angle' (angle between spans at the point of load if they were to meet at a point) is 164°. For the 2-span case, the span angle form horizontal is ~25°, so the 'bottom angle' is 130°.
Force on the span = Weight/ (2*Cos(ThetaB/2).
Force on the a span in the 3-span case = Weight / (2*Cos(82) = Weight / 0.278 = 3.6 * Weight
Force on the a span in the 2-span case = Weight / (2*Cos(65) = Weight / 0.845 = 1.2 * Weight
Or in other words: when the first span failed, the other two spans were subject to 1/3 of the load they were previously asked to carry.
Thanks for the explanation, I see the point you're trying to make but I also see several issues there that invalidate the conclusion - maybe I'm reflecting wrongly on it so I appreciate your clarifications.
First, you say the static load under 3 points on each cable bundle is higher than the dynamic one when the load is falling under tension from two cables. That's correct at a very specific moment in time: at T+0s from failure the antenna assembly.
At that time, each cable would transition from:
- the static situation seeing a static tension of Tstatic=m·g·sin(A) on each cable bundle, being A the angle between horizontal and the cable bundle (approximately 35 degrees in both towers 4 and 12 from this paper (https://www.naic.edu/~astro/aotms/performance/StructureDynamics.pdf), i.e. Tstatic=0.57w, being w=mg the weight of the suspended load)...
- to just having a reactionless horizontal component pulling it towards the bisector of the two towers, with each cable providing T' = Tstatic*cos(B/2), with B the angle subtended by the two cables, let's say 120º for the sake of simplicity (don't really know where you pull 130º from), i.e. half of the original tension.
That tension would be all but released almost instantly anyway once the third cable bundle snapped, the other two managing to pull the assembly closer to them, leaving the remaining cables essentially free from loads. This is roughly the situation I understand you referenced in your first post, even if our numbers don't fully coincide because you're forgetting to account for 2D projections you're making on your diagrams on the 3-point span case in your effort to convert it to an "American death triangle" situation, which it is not. See my diagrams for clarification.
That situation, however, would not last long once the receiver assembly started to fall and re-tension the intact cables providing a centripetal force pulling the load away from a free fall, which you're neglecting.
Then, the load would become a positively-sloped function of the receptor's height/speed, both being equivalent metrics in this case (v2 = 2·g·L(1-sin(35)), where h is the cable length of around 150 m, per conservation of energy mg(L-h0)=mv2/2, where h0 is the initial "negative height" from level with the towers, equal to L·sin(35)).
Like a swing, this load would be maximal at the lowest point of the oscillation, where it would equal the static weight of the load plus the centripetal force (1.85·m·g, or 1.85x the platform's weight per the above, when the centripetal force is entirely kynetic energy), projected on each cable. That position would never be reached in this case because of the obvious physical impediments of the wall. But it can be easily demonstrated the load on the remaining cables would surpass Tstatic = 0.57·m·g approximately after doubling the initial cable angle (i.e. after swinging down approximately 35º, due to the ever-increasing centripetal force). That's clearly within the swing range that took place before the crash against the mountainside, again without cable breakage.
You're by the way underestimating the angle in the second picture, being the plane between the two cables inclined with respect to the image's: the angle between horizontal and the cables on the T4 and T16 towers (surviving ones) is 35 deg in both, so in reality what you label as the "bottom angle" is 120º.
I'm not an engineer, so unfortunately I can't really follow your math. But all of this talk about angles during the fall seems moot. Keep in mind that the support towers were not carrying the full tensile load of the cables. The towers elevated the cables, but that load was mostly vertical. The tension from the cables was transmitted to the cable anchors, which were embedded in the ground some ways back from the towers. When the cables to the first tower failed, and the platform started swinging down, the load imposed on the two remaining towers would have been at an increasing angle to the anchor cables. This would have put a sideways load on the towers that they were not designed to withstand.
Post by: Alpha_Centauri on 12/02/2020 05:27 pm
No, it's totally true. The radar can only be used when you know where the asteroid is in the first place. The asteroid has to be detected by other means. The reason is that the beam is pretty narrow, and you have to point it to where the asteroid will be when the radar reaches that point.
Does that apply to the Arecibo radar in particular, or to planetary radar in general? On Earth, radar is pretty useful for first detection of objects: the narrow beam gets swept across a search volume either mechanically by moving the antenna, or electronically (phased array radar).
Arecibo's fixed dish made sweeping the beam difficult. But e.g. Goldstone could do this, albeit slowly because you have to wait for the return signal before you can move the dish. Does that limitation make the Goldstone radar useless to find asteroids?
Yes, radar is not optimized for asteroid detection. The search volume you are talking about is vast compared to terrestrial applications.
Asteroids are observationally effectively blackbody objects so you can make use of the peak in the reflected/emitted light which occurs in the optical.
All the major NEO search projects are small optical survey telescopes with large fields of view, or less commonly IR. It is far more efficient.
Again, this is only true for NEO discovery. Why are some members here systematically ignoring authoritative quotes on the matter, from trustworthy outlets, in order to baselessly play down Arecibo's importance? Regarding characterization of asteroids, radiotelescopes are more efficient, and particularly high-transmit-power, large dishes like Arecibo, for which there's no substitute, either existent or in work, and only a non-redundant, overbooked comparable facility (Goldstone).
Yes...because the post I was answering was asking about NEO discovery.
I'm sorry that not every comment can be about making out how wonderful Arecibo was.
Post by: meekGee on 12/02/2020 05:43 pm
I see there has been absolutely no discussion on here as to what this loss means to the scientists of Puerto Rico or even the people of that country. It’s this kind of narrow focus without considering the country these facilities are based in that has contributed to issues like the troubles around the building of The Thirty Metre telescope in Hawaii.
You have it backwards.
Thinking about global science priorities as a whole is "wide focus".
Mixing it in about "think about the local scientists" is "narrow focus".
Everyone's local to somewhere.
And in fact, if you consider the non-scientists of the country, then (exactly as in Hawaii) they may not even want the project in their country.
Post by: electricdawn on 12/02/2020 05:51 pm
I've read somewhere that people were surprised by the sudden cable failures, that were supposed to withstand twice the stress.
My thoughts (and I'm by no means an adept of physics) could be that wear and tear over the decades (wind, rain and atmospheric conditions) have weakened the material to a point that the cables were no longer able to withstand the acting forces on them.
I'm specifically interested if wind applied shear forces onto the cable, weakening the materials over the decades of Arecibo's existence. Not sure if that makes sense, since there are other structures out there with steel cables that have probably lived longer than that without breaking.
I'm interested in your thoughts.
Post by: eeergo on 12/02/2020 07:08 pm
The explanation about the remaining cables being perhaps as weak, given by edzieba and referenced below, does not stand when confronted with the direct quotes from the very experienced gentleman in the video, who witnessed the collapse (and was the first to check on the telescope after hurricane Maria): it took 30 seconds and the pendulum swinging was under significant tension from the remaining two towers, whose cables indeed supported the weight without failing, transporting the truss until its mountain side hard stop, and allowing the instrumented dome to detach due to the dynamics involved while not failing themselves too.No.
Remember how I mentioned the cable angle? The dramatic change in cable angle between the 3-spancase (where load is 'down' relative to the tower-to-tower span) and the 2-span pendulum-fall case where the load is 'down' relative to the current angle between load and ground (so at the start of the swing, that would be horizontal)? The two-span case has a much lower load per cable due to the change in angle, even missing one cable.
See the attached images (I'm actually overestimating the angle in the 3-span case from that photo, reality is an even more acute angle): For the 3-span case, the span angle form horizontal is ~8°, so the 'bottom angle' (angle between spans at the point of load if they were to meet at a point) is 164°. For the 2-span case, the span angle form horizontal is ~25°, so the 'bottom angle' is 130°.
Force on the span = Weight/ (2*Cos(ThetaB/2).
Force on the a span in the 3-span case = Weight / (2*Cos(82) = Weight / 0.278 = 3.6 * Weight
Force on the a span in the 2-span case = Weight / (2*Cos(65) = Weight / 0.845 = 1.2 * Weight
Or in other words: when the first span failed, the other two spans were subject to 1/3 of the load they were previously asked to carry.
Thanks for the explanation, I see the point you're trying to make but I also see several issues there that invalidate the conclusion - maybe I'm reflecting wrongly on it so I appreciate your clarifications.
First, you say the static load under 3 points on each cable bundle is higher than the dynamic one when the load is falling under tension from two cables. That's correct at a very specific moment in time: at T+0s from failure the antenna assembly.
At that time, each cable would transition from:
- the static situation seeing a static tension of Tstatic=m·g·sin(A) on each cable bundle, being A the angle between horizontal and the cable bundle (approximately 35 degrees in both towers 4 and 12 from this paper (https://www.naic.edu/~astro/aotms/performance/StructureDynamics.pdf), i.e. Tstatic=0.57w, being w=mg the weight of the suspended load)...
- to just having a reactionless horizontal component pulling it towards the bisector of the two towers, with each cable providing T' = Tstatic*cos(B/2), with B the angle subtended by the two cables, let's say 120º for the sake of simplicity (don't really know where you pull 130º from), i.e. half of the original tension.
That tension would be all but released almost instantly anyway once the third cable bundle snapped, the other two managing to pull the assembly closer to them, leaving the remaining cables essentially free from loads. This is roughly the situation I understand you referenced in your first post, even if our numbers don't fully coincide because you're forgetting to account for 2D projections you're making on your diagrams on the 3-point span case in your effort to convert it to an "American death triangle" situation, which it is not. See my diagrams for clarification.
That situation, however, would not last long once the receiver assembly started to fall and re-tension the intact cables providing a centripetal force pulling the load away from a free fall, which you're neglecting.
Then, the load would become a positively-sloped function of the receptor's height/speed, both being equivalent metrics in this case (v2 = 2·g·L(1-sin(35)), where h is the cable length of around 150 m, per conservation of energy mg(L-h0)=mv2/2, where h0 is the initial "negative height" from level with the towers, equal to L·sin(35)).
Like a swing, this load would be maximal at the lowest point of the oscillation, where it would equal the static weight of the load plus the centripetal force (1.85·m·g, or 1.85x the platform's weight per the above, when the centripetal force is entirely kynetic energy), projected on each cable. That position would never be reached in this case because of the obvious physical impediments of the wall. But it can be easily demonstrated the load on the remaining cables would surpass Tstatic = 0.57·m·g approximately after doubling the initial cable angle (i.e. after swinging down approximately 35º, due to the ever-increasing centripetal force). That's clearly within the swing range that took place before the crash against the mountainside, again without cable breakage.
You're by the way underestimating the angle in the second picture, being the plane between the two cables inclined with respect to the image's: the angle between horizontal and the cables on the T4 and T16 towers (surviving ones) is 35 deg in both, so in reality what you label as the "bottom angle" is 120º.
I'm not an engineer, so unfortunately I can't really follow your math. But all of this talk about angles during the fall seems moot. Keep in mind that the support towers were not carrying the full tensile load of the cables. The towers elevated the cables, but that load was mostly vertical. The tension from the cables was transmitted to the cable anchors, which were embedded in the ground some ways back from the towers. When the cables to the first tower failed, and the platform started swinging down, the load imposed on the two remaining towers would have been at an increasing angle to the anchor cables. This would have put a sideways load on the towers that they were not designed to withstand.
I really didn't apply more than freshman physics but I remember having a tough time with trigonometry and pendular motion at the time, so don't fret over the math. I did take into account the point you make - in fact, that's mostly the point I was trying to make since the beginning: the cables on towers T4 and T12 (the ones that supported the pendulum) could not have been as weak as the initially failed ones, when the towers fell inwards after the full motion range supporting the whole load was covered. My calculation just attempted to show tensions would have been above nominal during said motion, even discounting the vigorous dynamics involved (vibrations, shocks). The towers might have snapped due to lateral loads, but the cables supported such a motion until the former gave way - apparently shortly before or just after the truss crashed on the mountain side.
Post by: eeergo on 12/02/2020 07:16 pm
No, it's totally true. The radar can only be used when you know where the asteroid is in the first place. The asteroid has to be detected by other means. The reason is that the beam is pretty narrow, and you have to point it to where the asteroid will be when the radar reaches that point.
Does that apply to the Arecibo radar in particular, or to planetary radar in general? On Earth, radar is pretty useful for first detection of objects: the narrow beam gets swept across a search volume either mechanically by moving the antenna, or electronically (phased array radar).
Arecibo's fixed dish made sweeping the beam difficult. But e.g. Goldstone could do this, albeit slowly because you have to wait for the return signal before you can move the dish. Does that limitation make the Goldstone radar useless to find asteroids?
Yes, radar is not optimized for asteroid detection. The search volume you are talking about is vast compared to terrestrial applications.
Asteroids are observationally effectively blackbody objects so you can make use of the peak in the reflected/emitted light which occurs in the optical.
All the major NEO search projects are small optical survey telescopes with large fields of view, or less commonly IR. It is far more efficient.
Again, this is only true for NEO discovery. Why are some members here systematically ignoring authoritative quotes on the matter, from trustworthy outlets, in order to baselessly play down Arecibo's importance? Regarding characterization of asteroids, radiotelescopes are more efficient, and particularly high-transmit-power, large dishes like Arecibo, for which there's no substitute, either existent or in work, and only a non-redundant, overbooked comparable facility (Goldstone).
Yes...because the post I was answering was asking about NEO discovery.
I'm sorry that not every comment can be about making out how wonderful Arecibo was.
Fine, as referenced by whitelancer above, we're violently agreeing then. But the opening discussion was -mistakenly, I believe- disagreeing with such argument (and there were posts before that one arguing there hadn't really been capability loss), hence my reminder. Apologies for wording it as antagonizing to you.
It's not about defending Arecibo as manna from heaven, but rather calling out misconceptions around "this is no big deal", "it was unavoidable", "it wasn't useful anyway".
Post by: Mark S on 12/02/2020 07:45 pm
I really didn't apply more than freshman physics but I remember having a tough time with trigonometry and pendular motion at the time, so don't fret over the math. I did take into account the point you make - in fact, that's mostly the point I was trying to make since the beginning: the cables on towers T4 and T12 (the ones that supported the pendulum) could not have been as weak as the initially failed ones, when the towers fell inwards after the full motion range supporting the whole load was covered. My calculation just attempted to show tensions would have been above nominal during said motion, even discounting the vigorous dynamics involved (vibrations, shocks). The towers might have snapped due to lateral loads, but the cables supported such a motion until the former gave way - apparently shortly before or just after the truss crashed on the mountain side.
Cool, thanks. So if I understand the physics, the first tower should have fallen outward, due to the pull of its anchor cables. And the other two towers should have fallen inward, or more likely sideways, towards the fallen truss structure. Or maybe they also got pulled outward by their anchor cables. I'll have to go back and look at the photos again.
Post by: demorcef on 12/02/2020 08:08 pm
Post by: mn on 12/02/2020 08:58 pm
... could not have been as weak as the initially failed ones, when the towers fell inwards after the full motion range supporting the whole load was covered. My calculation just attempted to show tensions would have been above nominal during said motion, even discounting the vigorous dynamics involved (vibrations, shocks). The towers might have snapped due to lateral loads, but the cables supported such a motion until the former gave way - apparently shortly before or just after the truss crashed on the mountain side.
Ok, I'm certainly not an engineer so this is most certainly a dumb question, but here goes anyway, (gotta learn something today).
How much time elapsed from when the last cable snapped and the 'swing' hit the mountainside?
Perhaps the cables are not as strong as you are calculating, they just didn't have time to fail before the load 'failed' (or the top of the tower failed from lateral load, effectively releasing the load on the cables).
Post by: eeergo on 12/02/2020 09:55 pm
... could not have been as weak as the initially failed ones, when the towers fell inwards after the full motion range supporting the whole load was covered. My calculation just attempted to show tensions would have been above nominal during said motion, even discounting the vigorous dynamics involved (vibrations, shocks). The towers might have snapped due to lateral loads, but the cables supported such a motion until the former gave way - apparently shortly before or just after the truss crashed on the mountain side.
Ok, I'm certainly not an engineer so this is most certainly a dumb question, but here goes anyway, (gotta learn something today).
How much time elapsed from when the last cable snapped and the 'swing' hit the mountainside?
Perhaps the cables are not as strong as you are calculating, they just didn't have time to fail before the load 'failed' (or the top of the tower failed from lateral load, effectively releasing the load on the cables).
The whole failure took around 30 seconds as per direct witnesses on record (see account a few posts upthread). The swing would have overloaded the cables 24º under the nominal inclination as per my simple calculation above, not taking into account dynamic loads like vibrations, shocks etc (so realistically, a bit earlier, let's say 20º). Look at a side view photograph of the working observatory, or even better, a cross-sectional diagram. The "swing" would reach almost 90º (say 80º conservatively) before contacting the wall, well beyond that overload angle, by around 30º, with a rapidly increasing centripetal load. Take into account such a pendulum falling free from such height would withstand ~2x the static load when reaching verticality.
Moreover, now check out the resting location of the upper support truss in aftermath pictures: it's actually *beyond* the straight line joining the two "swing" towers. The gashes on the reflector caused by the fallen "swing" cables (completely dissimilar to the ones caused by the first failing cables) are approximately on that line. The "swing" towers' top sections have fallen slightly canted outward with respect to the reflector, and the bent rebar supports that deflection. The gregorian dome and lower truss actually either broke free before that impact or had an orientation such that it contacted the ground first.
This is all evidence pointing in the same direction: the cables in the T8 and T12 towers didn't yield at the slightest disturbance or even overload: they supported a >20 second dynamic, violent event surpassing nominal tension early into its unfolding.
Post by: mn on 12/02/2020 10:19 pm
... could not have been as weak as the initially failed ones, when the towers fell inwards after the full motion range supporting the whole load was covered. My calculation just attempted to show tensions would have been above nominal during said motion, even discounting the vigorous dynamics involved (vibrations, shocks). The towers might have snapped due to lateral loads, but the cables supported such a motion until the former gave way - apparently shortly before or just after the truss crashed on the mountain side.
Ok, I'm certainly not an engineer so this is most certainly a dumb question, but here goes anyway, (gotta learn something today).
How much time elapsed from when the last cable snapped and the 'swing' hit the mountainside?
Perhaps the cables are not as strong as you are calculating, they just didn't have time to fail before the load 'failed' (or the top of the tower failed from lateral load, effectively releasing the load on the cables).
The whole failure took around 30 seconds as per direct witnesses on record (see account a few posts upthread). The swing would have overloaded the cables 24º under the nominal inclination as per my simple calculation above, not taking into account dynamic loads like vibrations, shocks etc (so realistically, a bit earlier, let's say 20º). Look at a side view photograph of the working observatory, or even better, a cross-sectional diagram. The "swing" would reach almost 90º (say 80º conservatively) before contacting the wall, well beyond that overload angle, by around 30º, with a rapidly increasing centripetal load. Take into account such a pendulum falling free from such height would withstand ~2x the static load when reaching verticality.
Moreover, now check out the resting location of the upper support truss in aftermath pictures: it's actually *beyond* the straight line joining the two "swing" towers. The gashes on the reflector caused by the fallen "swing" cables (completely dissimilar to the ones caused by the first failing cables) are approximately on that line. The "swing" towers' top sections have fallen slightly canted outward with respect to the reflector, and the bent rebar supports that deflection. The gregorian dome and lower truss actually either broke free before that impact or had an orientation such that it contacted the ground first.
This is all evidence pointing in the same direction: the cables in the T8 and T12 towers didn't yield at the slightest disturbance or even overload: they supported a >20 second dynamic, violent event surpassing nominal tension early into its unfolding.
Thanks, I missed that part from the witness about it taking 30 seconds.
Post by: eeergo on 12/03/2020 06:14 am
'Who would have thunk' for NSF, which continues its glorious path on this issue.
https://mobile.twitter.com/ruperto1023/status/1334184780192223232
Post by: Star One on 12/03/2020 07:07 am
https://youtu.be/b7cU0vBX_Ac
Post by: Moskit on 12/03/2020 08:18 am
My thoughts (and I'm by no means an adept of physics) could be that wear and tear over the decades (wind, rain and atmospheric conditions) have weakened the material to a point that the cables were no longer able to withstand the acting forces on them.Another contributing factor might be earthquakes - Scott Manley mentioned that the fall coincided with an earthquake wave going through the site.
I'm specifically interested if wind applied shear forces onto the cable, weakening the materials over the decades of Arecibo's existence. Not sure if that makes sense, since there are other structures out there with steel cables that have probably lived longer than that without breaking.
https://youtu.be/vchDbyIRP44?t=97
Post by: chewi on 12/03/2020 08:49 am
Quote
Multiple sources confirm that the NSF will have a press conference tomorrow. It seems like they will be releasing the video of the collapse of the Arecibo Radio Telescope. The people who have seen it tell me it’s a devastating blow and a very intense sequence. @SaveTheAO
Quote
Meeting is at 11 am AST.
Post by: Hobbes-22 on 12/03/2020 08:59 am
My thoughts (and I'm by no means an adept of physics) could be that wear and tear over the decades (wind, rain and atmospheric conditions) have weakened the material to a point that the cables were no longer able to withstand the acting forces on them.
I'm specifically interested if wind applied shear forces onto the cable, weakening the materials over the decades of Arecibo's existence. Not sure if that makes sense, since there are other structures out there with steel cables that have probably lived longer than that without breaking.
AFAIK, regular maintenance (incl repainting the structure) was done until about a decade ago. This would have kept the cables in good condition. When the maintenance budget was cut, it looks like the cables were allowed to corrode (paint deteriorates, water gets into the cable, corrosion starts).
Wind shear is not a significant factor: wind loads have been taken into account in the design.
The observatory is about 15 km from the coast, so saltwater wouldn't have been a big issue. But it is in a hot, humid climate.
Earthquakes and hurricanes will stress the structure. Again, this would have been taken into account in the design. But once corrosion starts weakening the structure, this eats into the structural margins you have to withstand those.
Post by: edzieba on 12/03/2020 09:06 am
1) The '30 seconds' eyewitness has not been clarified to mean '30 seconds of the platform swinging about' or '30 seconds since I heard the start of what was alter clear to be the failure' or anything in-between. It's not a hugely useful measure of duration.... could not have been as weak as the initially failed ones, when the towers fell inwards after the full motion range supporting the whole load was covered. My calculation just attempted to show tensions would have been above nominal during said motion, even discounting the vigorous dynamics involved (vibrations, shocks). The towers might have snapped due to lateral loads, but the cables supported such a motion until the former gave way - apparently shortly before or just after the truss crashed on the mountain side.
Ok, I'm certainly not an engineer so this is most certainly a dumb question, but here goes anyway, (gotta learn something today).
How much time elapsed from when the last cable snapped and the 'swing' hit the mountainside?
Perhaps the cables are not as strong as you are calculating, they just didn't have time to fail before the load 'failed' (or the top of the tower failed from lateral load, effectively releasing the load on the cables).
The whole failure took around 30 seconds as per direct witnesses on record (see account a few posts upthread). The swing would have overloaded the cables 24º under the nominal inclination as per my simple calculation above, not taking into account dynamic loads like vibrations, shocks etc (so realistically, a bit earlier, let's say 20º). Look at a side view photograph of the working observatory, or even better, a cross-sectional diagram. The "swing" would reach almost 90º (say 80º conservatively) before contacting the wall, well beyond that overload angle, by around 30º, with a rapidly increasing centripetal load. Take into account such a pendulum falling free from such height would withstand ~2x the static load when reaching verticality.
Moreover, now check out the resting location of the upper support truss in aftermath pictures: it's actually *beyond* the straight line joining the two "swing" towers. The gashes on the reflector caused by the fallen "swing" cables (completely dissimilar to the ones caused by the first failing cables) are approximately on that line. The "swing" towers' top sections have fallen slightly canted outward with respect to the reflector, and the bent rebar supports that deflection. The gregorian dome and lower truss actually either broke free before that impact or had an orientation such that it contacted the ground first.
This is all evidence pointing in the same direction: the cables in the T8 and T12 towers didn't yield at the slightest disturbance or even overload: they supported a >20 second dynamic, violent event surpassing nominal tension early into its unfolding.
2) You can see the cable impacts are well below the impact point of the structure, so the structure detached from the cables before its ultimate impact point. From the final position of the cables, support structure, and gregorian dome, it can be surmised that as well as swinging about the tower apexes the structure itself pivoted about the axis of the remaining two upper attachment points. As the structure started to rotate, the gregorian dome and track was sheared off and fell just off centre, the structure continued to rotate and detached from the cables (and/or the cables snapped during this portion of the event), and continued to rotate as it fell and flew sideways (due to the velocity imparted from the swing about the tower apexes) to hit the side of the dome 'base-on'. Hopefully there were cameras operating on-site that will allow engineers to study the failure dynamics once they are recovered.
3) After the first span failed, the cables would no longer be under pure tensile load: much of the energy of the swinging system would instead have gone into crushing of the concrete in the support towers as they twisted and snapped.
Post by: eeergo on 12/03/2020 09:36 am
1) The '30 seconds' eyewitness has not been clarified to mean '30 seconds of the platform swinging about' or '30 seconds since I heard the start of what was alter clear to be the failure' or anything in-between. It's not a hugely useful measure of duration.... could not have been as weak as the initially failed ones, when the towers fell inwards after the full motion range supporting the whole load was covered. My calculation just attempted to show tensions would have been above nominal during said motion, even discounting the vigorous dynamics involved (vibrations, shocks). The towers might have snapped due to lateral loads, but the cables supported such a motion until the former gave way - apparently shortly before or just after the truss crashed on the mountain side.
Ok, I'm certainly not an engineer so this is most certainly a dumb question, but here goes anyway, (gotta learn something today).
How much time elapsed from when the last cable snapped and the 'swing' hit the mountainside?
Perhaps the cables are not as strong as you are calculating, they just didn't have time to fail before the load 'failed' (or the top of the tower failed from lateral load, effectively releasing the load on the cables).
The whole failure took around 30 seconds as per direct witnesses on record (see account a few posts upthread). The swing would have overloaded the cables 24º under the nominal inclination as per my simple calculation above, not taking into account dynamic loads like vibrations, shocks etc (so realistically, a bit earlier, let's say 20º). Look at a side view photograph of the working observatory, or even better, a cross-sectional diagram. The "swing" would reach almost 90º (say 80º conservatively) before contacting the wall, well beyond that overload angle, by around 30º, with a rapidly increasing centripetal load. Take into account such a pendulum falling free from such height would withstand ~2x the static load when reaching verticality.
Moreover, now check out the resting location of the upper support truss in aftermath pictures: it's actually *beyond* the straight line joining the two "swing" towers. The gashes on the reflector caused by the fallen "swing" cables (completely dissimilar to the ones caused by the first failing cables) are approximately on that line. The "swing" towers' top sections have fallen slightly canted outward with respect to the reflector, and the bent rebar supports that deflection. The gregorian dome and lower truss actually either broke free before that impact or had an orientation such that it contacted the ground first.
This is all evidence pointing in the same direction: the cables in the T8 and T12 towers didn't yield at the slightest disturbance or even overload: they supported a >20 second dynamic, violent event surpassing nominal tension early into its unfolding.
2) You can see the cable impacts are well below the impact point of the structure, so the structure detached from the cables before its ultimate impact point. From the final position of the cables, support structure, and gregorian dome, it can be surmised that as well as swinging about the tower apexes the structure itself pivoted about the axis of the remaining two upper attachment points. As the structure started to rotate, the gregorian dome and track was sheared off and fell just off centre, the structure continued to rotate and detached from the cables (and/or the cables snapped during this portion of the event), and continued to rotate as it fell and flew sideways (due to the velocity imparted from the swing about the tower apexes) to hit the side of the dome 'base-on'. Hopefully there were cameras operating on-site that will allow engineers to study the failure dynamics once they are recovered.
3) After the first span failed, the cables would no longer be under pure tensile load: much of the energy of the swinging system would instead have gone into crushing of the concrete in the support towers as they twisted and snapped.
1- Obviously the latter, a 150-meter pendulum doesn't have a 2-minute period. It means the remaining cables were subject to vibrations, shocks and finally off-nominal loads for around 30 seconds. Notice I conservatively shortened that to 20 s in my comment, since I assumed it took some time for the cables failing to the other cables seeing major off-nominal loads, but in reality it makes no difference.
2- I have already noted before how the lower truss and gregorian dome appear to have either detached (consequence of the large forces near maximum centripetal load, which nevertheless didn't snap the cables) or just impacted the rock wall earlier, due to its orientation. It is pretty far away from center, approximately halfway to the reflector rim.
The cables couldn't have snapped at that point, even despite the forces involved in such crash/detachment at that angle, because (a) their gashes are higher up, (b) the upper truss structure of the support platform ended up *higher* than them as you note (which I speculate can mean it first crashed against the wall still attached to the towers, which then broke their top while the cables were recoiling to fall slightly behind the truss remains) and (c) moreover the top of the towers fell *outwards*, suggesting again an outward inertia the platform couldn't have provided, having already reached the wall - inertia which then only the detached cables could provide before falling flailing into the dish. The exact chain of events is speculative and I agree on your hope of seeing footage to clarify that, but the evidence is clear and redundant.
3- That's incorrect, the cable span between the tower apex and the attach point with the truss would be entirely under tensile load. The "concrete crushing" (which by the way didn't take place: the tower just snapped sideways at a junction) would have just added shocks and anomalous load paths. I have proven exactly how the load progressed, when it exceeded design load and how much it would have increased before impact, showing how your initial assessments were quite wrong and anyway applicable only to a precise instant, with quite simple arithmetic - because it's really mostly a simple system. If you so desire, please show alternative math, not handwaving attempts at finding (minor, and irrelevant) dissipation hypotheses.
Post by: edzieba on 12/03/2020 10:23 am
If the cables failed after the structure impacted, they would have been dragged upwards of the structure's impact point by the collapse of the towers' upper sections and the inertia of the cables themselves (both recoil forces and their mass, which is not inconsiderable). Instead, they impacted the dish well below the structure (you can even see the cable to the tower nearest the on-site buildings that the cable impacted further down the dish, and was dragged up by the tower collapse, meaning both it failed before the tower collapse completed and that it failed further down the dish than its current resting place). For that to occur, they could have needed to have some force imparted to them after impact to push them back down the dish.1) The '30 seconds' eyewitness has not been clarified to mean '30 seconds of the platform swinging about' or '30 seconds since I heard the start of what was alter clear to be the failure' or anything in-between. It's not a hugely useful measure of duration.... could not have been as weak as the initially failed ones, when the towers fell inwards after the full motion range supporting the whole load was covered. My calculation just attempted to show tensions would have been above nominal during said motion, even discounting the vigorous dynamics involved (vibrations, shocks). The towers might have snapped due to lateral loads, but the cables supported such a motion until the former gave way - apparently shortly before or just after the truss crashed on the mountain side.
Ok, I'm certainly not an engineer so this is most certainly a dumb question, but here goes anyway, (gotta learn something today).
How much time elapsed from when the last cable snapped and the 'swing' hit the mountainside?
Perhaps the cables are not as strong as you are calculating, they just didn't have time to fail before the load 'failed' (or the top of the tower failed from lateral load, effectively releasing the load on the cables).
The whole failure took around 30 seconds as per direct witnesses on record (see account a few posts upthread). The swing would have overloaded the cables 24º under the nominal inclination as per my simple calculation above, not taking into account dynamic loads like vibrations, shocks etc (so realistically, a bit earlier, let's say 20º). Look at a side view photograph of the working observatory, or even better, a cross-sectional diagram. The "swing" would reach almost 90º (say 80º conservatively) before contacting the wall, well beyond that overload angle, by around 30º, with a rapidly increasing centripetal load. Take into account such a pendulum falling free from such height would withstand ~2x the static load when reaching verticality.
Moreover, now check out the resting location of the upper support truss in aftermath pictures: it's actually *beyond* the straight line joining the two "swing" towers. The gashes on the reflector caused by the fallen "swing" cables (completely dissimilar to the ones caused by the first failing cables) are approximately on that line. The "swing" towers' top sections have fallen slightly canted outward with respect to the reflector, and the bent rebar supports that deflection. The gregorian dome and lower truss actually either broke free before that impact or had an orientation such that it contacted the ground first.
This is all evidence pointing in the same direction: the cables in the T8 and T12 towers didn't yield at the slightest disturbance or even overload: they supported a >20 second dynamic, violent event surpassing nominal tension early into its unfolding.
2) You can see the cable impacts are well below the impact point of the structure, so the structure detached from the cables before its ultimate impact point. From the final position of the cables, support structure, and gregorian dome, it can be surmised that as well as swinging about the tower apexes the structure itself pivoted about the axis of the remaining two upper attachment points. As the structure started to rotate, the gregorian dome and track was sheared off and fell just off centre, the structure continued to rotate and detached from the cables (and/or the cables snapped during this portion of the event), and continued to rotate as it fell and flew sideways (due to the velocity imparted from the swing about the tower apexes) to hit the side of the dome 'base-on'. Hopefully there were cameras operating on-site that will allow engineers to study the failure dynamics once they are recovered.
3) After the first span failed, the cables would no longer be under pure tensile load: much of the energy of the swinging system would instead have gone into crushing of the concrete in the support towers as they twisted and snapped.
1- Obviously the latter, a 150-meter pendulum doesn't have a 2-minute period. It means the remaining cables were subject to vibrations, shocks and finally off-nominal loads for around 30 seconds. Notice I conservatively shortened that to 20 s in my comment, since I assumed it took some time for the cables failing to the other cables seeing major off-nominal loads, but in reality it makes no difference.
2- I have already noted before how the lower truss and gregorian dome appear to have either detached (consequence of the large forces near maximum centripetal load, which nevertheless didn't snap the cables) or just impacted the rock wall earlier, due to its orientation. It is pretty far away from center, approximately halfway to the reflector rim.
The cables couldn't have snapped at that point, even despite the forces involved in such crash/detachment at that angle, because (a) their gashes are higher up, (b) the upper truss structure of the support platform ended up *higher* than them as you note (which I speculate can mean it first crashed against the wall still attached to the towers, which then broke their top while the cables were recoiling to fall slightly behind the truss remains) and (c) moreover the top of the towers fell *outwards*, suggesting again an outward inertia the platform couldn't have provided, having already reached the wall - inertia which then only the detached cables could provide before falling flailing into the dish. The exact chain of events is speculative and I agree on your hope of seeing footage to clarify that, but the evidence is clear and redundant.
In addition, if they had remained intact until the dish impacted the side, then there is no reason for them to have subsequently failed in the no load state. If they were to have been snapped by the tower failure subsequent to structure impact, then the collapse of the towers would have dragged them up the dish from the structure impact location. This did not occur.
Quote
3- That's incorrect, the cable span between the tower apex and the attach point with the truss would be entirely under tensile load. The "concrete crushing" (which by the way didn't take place: the tower just snapped sideways at a junction) would have just added shocks and anomalous load paths. I have proven exactly how the load progressed, when it exceeded design load and how much it would have increased before impact, showing how your initial assessments were quite wrong and anyway applicable only to a precise instant, with quite simple arithmetic - because it's really mostly a simple system. If you so desire, please show alternative math, not handwaving attempts at finding (minor, and irrelevant) dissipation hypotheses.The concrete must have crushed (and rebar snapped) in order for he towers to snap. While they may look toothpick like in distance shots, they are not insubstantial structures and their failure will absorb a significant amount of energy.
You've also yet to actually post your math. You concluded with
Quote
But it can be easily demonstrated the load on the remaining cables would surpass Tstatic = 0.57·m·g approximately after slightly increasing doubling the initial cable angle (i.e. after swinging down approximately 24º35º,(edit: reviewed mistaken result) due to the ever-increasing centripetal force).But skipped over the actual 'easily demonstrate' bit.
You also mistakenly used the 35° backstay cable angle from that linked paper, not the angle of the support cables from horizontal (necessary to calculate the bottom angle). The linked paper did not provide that angle, and indeed assumes that angle to be so acute that the horizontal case is used instead:
Quote from: from paper
As an approximation, the angle that the mainstay cables make with the horizontal plane of motion of the tower-tops is not taken into account. In reality, the angles at equilibrium are in fact small (i.e. less than 10 degrees), the cosine of the angle is always greater than 0.98, and we make the assumption it is approximately 1.0.Their 'less than 10°' figure jives with the ~8° measured from the photos attached to my previous post.
Post by: eeergo on 12/03/2020 12:41 pm
If the cables failed after the structure impacted, they would have been dragged upwards of the structure's impact point by the collapse of the towers' upper sections and the inertia of the cables themselves (both recoil forces and their mass, which is not inconsiderable). Instead, they impacted the dish well below the structure (you can even see the cable to the tower nearest the on-site buildings that the cable impacted further down the dish, and was dragged up by the tower collapse, meaning both it failed before the tower collapse completed and that it failed further down the dish than its current resting place). For that to occur, they could have needed to have some force imparted to them after impact to push them back down the dish.
We'll know soon enough, they should release video of the failure today. But in your reasoning you're ignoring the upper truss is actually halfway out the reflector. If the cables snapped early, why isn't it resting approximately at their midpoint, or next to the lower part? You're making lots of assumptions about the complex dynamics at the time of impact, that are no more than that.
Quote
In addition, if they had remained intact until the dish impacted the side, then there is no reason for them to have subsequently failed in the no load state. If they were to have been snapped by the tower failure subsequent to structure impact, then the collapse of the towers would have dragged them up the dish from the structure impact location. This did not occur.
You're ignoring the small, almost negligible transient of the truss slamming against a granite wall at near maximum velocity with 2 times its weight pulling on the supports due to centripetal loads. Then you make another assumption of where they should be resting. I have another speculation, but I labeled it as such, and IMO it's at least as likely as yours.
Quote
Quote3- That's incorrect, the cable span between the tower apex and the attach point with the truss would be entirely under tensile load. The "concrete crushing" (which by the way didn't take place: the tower just snapped sideways at a junction) would have just added shocks and anomalous load paths. I have proven exactly how the load progressed, when it exceeded design load and how much it would have increased before impact, showing how your initial assessments were quite wrong and anyway applicable only to a precise instant, with quite simple arithmetic - because it's really mostly a simple system. If you so desire, please show alternative math, not handwaving attempts at finding (minor, and irrelevant) dissipation hypotheses.The concrete must have crushed (and rebar snapped) in order for he towers to snap. While they may look toothpick like in distance shots, they are not insubstantial structures and their failure will absorb a significant amount of energy.
Regardless of how much the crushing/snapping process dissipates (and it will have been little, by the relatively intact looks of the battered tower top remains), it's insubstantial to the fact that the cables will be supporting the full tensile load derived from the pendular motion until they detached and started to fall (they wouldn't have supported a pendular motion otherwise), as I stated.
Quote
You've also yet to actually post your math. You concluded withQuoteBut it can be easily demonstrated the load on the remaining cables would surpass Tstatic = 0.57·m·g approximately after slightly increasing doubling the initial cable angle (i.e. after swinging down approximately 24º35º,(edit: reviewed mistaken result) due to the ever-increasing centripetal force).But skipped over the actual 'easily demonstrate' bit.
Because I described the formula with words to avoid posting a long symbolic string, and assumed it to be trivial. But fine, here it is:
Tstatic = Tpendulum + mv2/R;
0.57·m·g = sin(W)·m·g·cos(B) + mv2/R; (v2 ≈ gR; this approximation doesn't hold when the angle is very small, i.e. at large deviations from verticality, and you'd need to insert a sinusoidal dependence to approximate, which actually simplifies the math)
Solve for W and take into account it's made up of the original static angle, plus the sought-for angle increment in the pendular motion: 24 degrees in these idealized conditions, smaller when introducing real-life conditions such as vibrations, shocks, the cable's self-weight...
Quote
You also mistakenly used the 35° backstay cable angle from that linked paper, not the angle of the support cables from horizontal (necessary to calculate the bottom angle). The linked paper did not provide that angle, and indeed assumes that angle to be so acute that the horizontal case is used instead.Yet you failed to realize a smaller angle brings the pendular motion to fuller completion, leaving the analysis unchanged in shape but increasing the centripetal contribution, reinforcing my point. That's what the h0 in my original analysis took care of. Try bringing it to zero (starting position at 90º to vertical): the static load increases marginally (trigonometrically for small angles), the centripetal force shoots up quadratically, bringing the maximum load at verticality from the approximately 1.85x I derived to the theoretical maximum of 3x.
Bottom line: a more acute angle makes stresses worse as soon as you deviate from the rupture point.
Quote
Their 'less than 10°' figure jives with the ~8° measured from the photos attached to my previous post.
Your number was based on wrong projections from pictures. You got the 8 degrees looking at an almost-side-on image, failing to compensate for the projection due to the camera inclination. Then you redid it with another one, getting a patently incorrect 130º as the value for a third of a circle's angle. In any case, it's pointless: if it was 8º, it would further reinforce the point.
Post by: edzieba on 12/03/2020 01:22 pm
Your number was based on wrong projections from pictures. You got the 8 degrees looking at an almost-side-on image, failing to compensate for the projection due to the camera inclination. Then you redid it with another one, getting a patently incorrect 130º as the value for a third of a circle's angle. In any case, it's pointless: if it was 8º, it would further reinforce the point.You appear to have fundamentally missed the point: the two images measure two entirely different angles. The first is the angle of force distribution in the static case (structure supported by suspended cables), and the second angle is the force distribution for the dynamic case (pendulum motion). Go back and reread my previous comment, because those two different angles are very important in determining the actual load experienced by the cables.
Post by: eeergo on 12/03/2020 01:32 pm
Your number was based on wrong projections from pictures. You got the 8 degrees looking at an almost-side-on image, failing to compensate for the projection due to the camera inclination. Then you redid it with another one, getting a patently incorrect 130º as the value for a third of a circle's angle. In any case, it's pointless: if it was 8º, it would further reinforce the point.You appear to have fundamentally missed the point: the two images measure two entirely different angles. The first is the angle of force distribution in the static case (structure supported by suspended cables), and the second angle is the force distribution for the dynamic case (pendulum motion). Go back and reread my previous comment, because those two different angles are very important in determining the actual load experienced by the cables.
I have derived the whole framework for the calculation, including diagrams to illustrate/minimize ambiguity, based on freshman-level physics entirely applicable to such a system as a best-case simplification and trivial derivations (including the one used for the well-known result that a pendulum's maximum tension is equal to 3x the bob's weight).
I additionally pointed out why this dynamic situation isn't equivalent to an "American death triangle" as you claimed, showed why your angular estimates were wrong because you neglected to account for several projections (even if I misapplied a reference for said angles, fortunately yielding an overbenign result), and explained why a more acute starting angle only reinforces my conclusion, with explicit (basic) formulation that allows anyone to check the claims, or insert any value they would like.
I really think you should address those concerns or show failings with the model provided before asking others to study your sketch from 20 messages ago.
Post by: edzieba on 12/03/2020 02:10 pm
I additionally pointed out why this dynamic situation isn't equivalent to an "American death triangle" as you claimedNo, you have not. The geometry is the geometry.
You have again missed the point: The change in bottom angle between the two cases means that, for a load X applied where the structure is, the cable tension in the static case is 1/3 (1.2/3.6) that in the dynamic case. The two calculations of force multiplication are independent of the load (i.e. they are the factor you apply to the load to get the cable tension). That means that if the load in the static case is the mass of the structure accelerated by gravity (as it should be), the force applied during pendulum must be 3x that in order for cable tension during pendulum motion just to equal the tension in the static case.
Post by: joncz on 12/03/2020 02:31 pm
Post by: eeergo on 12/03/2020 02:55 pm
I additionally pointed out why this dynamic situation isn't equivalent to an "American death triangle" as you claimedNo, you have not. The geometry is the geometry.
You have again missed the point: The change in bottom angle between the two cases means that, for a load X applied where the structure is, the cable tension in the static case is 1/3 (1.2/3.6) that in the dynamic case. The two calculations of force multiplication are independent of the load (i.e. they are the factor you apply to the load to get the cable tension). That means that if the load in the static case is the mass of the structure accelerated by gravity (as it should be), the force applied during pendulum must be 3x that in order for cable tension during pendulum motion just to equal the tension in the static case.
In the static case, you have an m·g load translated into a tension on the cables of m·g·sin(A), with A being the cables' deflection angle (be it 35º, 10º or whatever).
In the dynamic case, you have a pendulum with two tethers. You can reduce the treatment of the problem to a single tether, and just apply the scaling factor of cos(B), B being the half-angle between the cables (60º in this case, which means the scaling factor is 0.5), to find the actual tension on each cable. The "bottom angle", if you're referring to the opening angle between support cables as I understand it, doesn't change between both cases because the towers are fixed and 3 equal sectors of a circle sum up to 360º.
The tension on a single-tethered pendulum is m·g·sin(D), being D the instantaneous angle with respect to horizontal at each point in the trajectory, plus the centripetal tension (approximately m·g·sin(D) too, when considering large enough swings, like in this case). This is time-variable because of D, and is the reason why I say this situation is not like an American death triangle, but whatever, that's terminology.
The angle at which the static load is consequently surpassed by the swinging two-string pendulum as shown in the final step in the derivation I spelled out at your request in my previous message, and is of course trivially load mass independent: m·g·sin(initial angle) ≤ m·g·sin(dynamic angle)·cos(B) + mv2/R or, cancelling out terms on both sides of the inequality: sin(initial angle) ⪅ (3/2)*sin(X) -> X ≳ asin(2·sin(A)/3), be A the opening angle what it may, 10º, 35º, whatever.
As is obvious intuitively, if the initial angle from horizontal is too large you will never satisfy the inequality for non-complex angles, because the bob is too close from equilibrium to acquire enough speed to increase its centrifugal acceleration by enough, and consequently the tether's centripetal tension reaction. Conversely, the closer to horizontal you raise the load, the sooner you'll surpass the initial static load due to the rapid build-up of speed as it falls while the tethers pull it inward: basics of circular motion. You can even derive the tension at the lowest point of the swing as per my initial calculation, for any initial opening angle A, or equivalently initial height from horizontal, as I also spelled out.
I have sketched these situations clearly. I have shown they are consistent with the academic, well-know limit case of 0º-90º simple pendulum result where the tension is 3x the bob's weight, a derivation possible with high-school level algebra and conservation of energy, from start to finish. You can even intuitively feel it in your hand if you hold a bag of potatoes, slide it off a table and let it oscillate - but have instead pulled numbers out of thin air handwaving superficial similarities with a static rule of thumb from climbing.
Post by: eeergo on 12/03/2020 02:56 pm
https://twitter.com/DJSnM/status/1333954898858184704
Precisely. Glad KSP agrees.
Post by: eeergo on 12/03/2020 03:26 pm
https://twitter.com/DeborahTiempo/status/1334530900655304706 (https://twitter.com/DeborahTiempo/status/1334530900655304706)
The cables DID NOT give way until wall impact, withstanding the immense shock of the gregorian dome + lower truss detaching (at a significant angle that I roughly estimate is more than twice the initial cable angle). They were even strong enough to rip out the access bridge on their wake.
QED.
EDIT for observations:
- The trigger of the final collapse was near the apex of the background tower that hosted the only weakened cables.- That tower took its sweet time to be pulled back and snap from the remaining tension in the ground anchors, its top falling off after the pendulum had collapsed.- The entire free swing of the pendulum took about 10 seconds, with secondary collapses happening afterwards.- The foreground tower (Visitor Center's hosting the bridge) collapsed just as the upper truss impacted the reflector dish, or a split second before, judging from the flailing of the cables and an estimate of how long it would take for it to detach and fall to the first impact point before rolling down the mountain.
- The main cables supported the full swing and ended up falling on the forest beyond the reflector: the gash on the reflector is due to the secondary. Had the towers not fallen, they would probably still be attached to the truss. Never been sadder to see a calculation confirmed by reality.
Post by: mrhuggy on 12/03/2020 03:30 pm
Video from drone is on here - https://www.nsf.gov/news/special_reports/arecibo/
https://twitter.com/DeborahTiempo/status/1334530900655304706
Post by: Naito on 12/03/2020 03:34 pm
edit: that B-Roll footage is even more terrifying. How remarkable to capture essentially "the moment of death" of this great observatory. Incredibly sad.
Post by: mrhuggy on 12/03/2020 03:34 pm
https://youtu.be/nejO4BmzCd0?t=50
Post by: FutureSpaceTourist on 12/03/2020 03:38 pm
https://twitter.com/thesheetztweetz/status/1334536726975574016
Quote
Here's the view from a drone at the top of one of the Arecibo towers that was monitoring the condition of the support cables:
Post by: eeergo on 12/03/2020 03:44 pm
This the footage of the collapse from a drone next to one of the towers. Drone footage begins at 0:50
https://youtu.be/nejO4BmzCd0?t=50
My God. Prior to this I'd only seen similar footage in Hollywood movies.
Truly heart-sinking.
Allowing such a telescope (the one that Humanity sent out its first message to the stars with, no less) to disappear suffer this undignified violent death because of penny-pinching, neglecting repairs for a decade and then dragging feet for FOUR months while increasingly critical failures accumulated, is repulsive.
Hope the relentless apologists will at least scratch their heads after watching this footage.
Post by: meekGee on 12/03/2020 03:53 pm
Aaand here's the final proof:I think it's a lot more complex than that.
https://twitter.com/DeborahTiempo/status/1334530900655304706 (https://twitter.com/DeborahTiempo/status/1334530900655304706)
The cables DID NOT give way until wall impact, withstanding the immense shock of the gregorian dome + lower truss detaching (at a significant angle that I roughly estimate is more than twice the initial cable angle). They were even strong enough to rip out the access bridge on their wake.
QED.
EDIT for observations: The trigger of the final collapse was near the apex of the background tower that hosted the only weakened cables.
- That tower took its sweet time to be pulled back and snap from the remaining tension in the ground anchors, its top falling off after the pendulum had collapsed.- The entire free swing of the pendulum took about 10 seconds, with secondary collapses happening afterwards.- The foreground tower (Visitor Center's hosting the bridge) collapsed just as the upper truss impacted the reflector dish, or a split second before, judging from the flailing of the cables and an estimate of how long it would take for it to detach and fall to the first impact point before rolling down the mountain.
EDIT2 after drone footage: Indeed, the cables fell on the dish after allowing the full pendular motion until the truss crashed on the reflector's edge, swayed mostly load-free *AND* came back forward to fall on the reflector as the towers fell outwards. Had the towers not collapsed, the cables would probably still be attached. Just unbelievable, never been sadder to have a calculation proven right by reality.
Once the first cable goes, load on the other two cables will first decrease, and they'll unstretch, pulling the load towards them.
This is a small motion but it has a large effect on loads.
Then the swing take over, but it doesn't start from equilibrium anymore, so loads will increase again partway through the swing, and you have no way of knowing whether it hit the ground before or after that.
There's no way you can ascertain from this whether the other cables were damaged or not.
Post by: Star One on 12/03/2020 04:04 pm
But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.This the footage of the collapse from a drone next to one of the towers. Drone footage begins at 0:50
https://youtu.be/nejO4BmzCd0?t=50
My God. Prior to this I'd only seen similar footage in Hollywood movies.
Truly heart-sinking.
Allowing such a telescope (the one that Humanity sent out its first message to the stars with, no less) to disappear suffer this undignified violent death because of penny-pinching, neglecting repairs for a decade and then dragging feet for FOUR months while increasingly critical failures accumulated, is repulsive.
Hope the relentless apologists will at least scratch their heads after watching this footage.
Post by: eeergo on 12/03/2020 04:08 pm
Aaand here's the final proof:I think it's a lot more complex than that.
https://twitter.com/DeborahTiempo/status/1334530900655304706 (https://twitter.com/DeborahTiempo/status/1334530900655304706)
The cables DID NOT give way until wall impact, withstanding the immense shock of the gregorian dome + lower truss detaching (at a significant angle that I roughly estimate is more than twice the initial cable angle). They were even strong enough to rip out the access bridge on their wake.
QED.
EDIT for observations: The trigger of the final collapse was near the apex of the background tower that hosted the only weakened cables.
- That tower took its sweet time to be pulled back and snap from the remaining tension in the ground anchors, its top falling off after the pendulum had collapsed.- The entire free swing of the pendulum took about 10 seconds, with secondary collapses happening afterwards.- The foreground tower (Visitor Center's hosting the bridge) collapsed just as the upper truss impacted the reflector dish, or a split second before, judging from the flailing of the cables and an estimate of how long it would take for it to detach and fall to the first impact point before rolling down the mountain.
EDIT2 after drone footage: Indeed, the cables fell on the dish after allowing the full pendular motion until the truss crashed on the reflector's edge, swayed mostly load-free *AND* came back forward to fall on the reflector as the towers fell outwards. Had the towers not collapsed, the cables would probably still be attached. Just unbelievable, never been sadder to have a calculation proven right by reality.
Once the first cable goes, load on the other two cables will first decrease, and they'll unstretch, pulling the load towards them.
This is a small motion but it has a large effect on loads.
Then the swing take over, but it doesn't start from equilibrium anymore, so loads will increase again partway through the swing, and you have no way of knowing whether it hit the ground before or after that.
There's no way you can ascertain from this whether the other cables were damaged or not.
Please review my analysis and don't revert to the old adage of "it's too complicated".
The real-world dynamics are certainly not exactly represented by an ideal pendulum, an ideal static load, ideally-rigid massless cables and the whole lot. But the approximation is pretty darn accurate at this scale.
The load release because of cable elasticity is only applicable (if at all) during the first milliseconds after third tower failure. After that, it's a simple pendulum (with the load shared between two symmetric points) to the second decimal point. As I mentioned, there *is* a real-world shock to the cables as they are under nominal load, then they relax to near-zero load, then increase again due to rapidly increasing (sinusoidally from that near-zero) centripetal loads and projection of the gravitational inertial mass on the cable axis.
The video (and common sense) shows the truss hitting the mountainside well after the pendular motion began (around 10 seconds to be exact). Where do you think the centripetal force to move the load in a pendular motion comes in the first place, other than tension on the cables?
It is fully clear the cables supported continuous loads >2x their design capacity, with the added stresses from vibrations, shocks, ripping through the access bridge and platform impact, snapping the towers laterally and slightly outwards, without yielding. What's with this lazy, baseless, blind denial?
Post by: eeergo on 12/03/2020 04:12 pm
But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.This the footage of the collapse from a drone next to one of the towers. Drone footage begins at 0:50
My God. Prior to this I'd only seen similar footage in Hollywood movies.
Truly heart-sinking.
Allowing such a telescope (the one that Humanity sent out its first message to the stars with, no less) to disappear suffer this undignified violent death because of penny-pinching, neglecting repairs for a decade and then dragging feet for FOUR months while increasingly critical failures accumulated, is repulsive.
Hope the relentless apologists will at least scratch their heads after watching this footage.
I'm honestly flabbergasted, and worried.
Denial of obviousness was first only found in "flexible" politics topics (even if clear cut), then it became mainstream with the pandemic, but this level of reducing everything uncomfortable to one's view to esoteric unknowable mysteries, even about an approachable well-documented problem and in face of intuitive graphic evidence on a technical forum, is something to behold.
All this when the prediction for what we'd see in the video was provided hours if not days before said footage was released, and other's were proven wrong!
Post by: Frogstar_Robot on 12/03/2020 04:20 pm
But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
Post by: Eric Hedman on 12/03/2020 04:38 pm
I completely agree. It collapsed and nothing will change that. The debate should be, is there enough value in rebuilding a new radio telescope in Arecibo. I think that will be a hard argument to make.But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
Post by: eeergo on 12/03/2020 04:54 pm
But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
I have provided a step by step derivation, with clarifications upon request, which predicted the outcome before being shown on video. Others have contented themselves with confounding the issue over quibbles about minor perturbative effects and handwaved, generally inapplicable, qualitative misconceptions.
Certainly if proper maintenance and/or swift reinforcing had taken place during the years of widespread, documented and denounced corner-cutting, the outcome *might possibly* been different, don'ttya think? What are you even claiming? Improper maintenance is equal to proper maintenance?
As for the emotional upset: so far the ones that have constantly polluted this thread with wrong predictions based on falsified rule-of-thumb "calculations" at best, or fact-impermeable foregone conclusions most of the time, are the ones that are now asking, in the face of evidence, for very specific proof that only those with access to internal documentation could possibly have. While ignoring the actual facility staff denouncing it, and NSF's declared aim of defunding the facility. While providing NO objective backing to their claims themselves, moving their goalposts at light speed and *acting offended* when the mere concept is brought up.
But the emotional response is always on the other side, ain't it?
Post by: Star One on 12/03/2020 04:54 pm
Well according to the Twitter thread posted up thread you would appear to be mistaken in that belief. Let alone as I keep repeating on this thread that this is bigger than just the science arguments.I completely agree. It collapsed and nothing will change that. The debate should be, is there enough value in rebuilding a new radio telescope in Arecibo. I think that will be a hard argument to make.But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
Post by: eeergo on 12/03/2020 05:02 pm
I completely agree. It collapsed and nothing will change that. The debate should be, is there enough value in rebuilding a new radio telescope in Arecibo. I think that will be a hard argument to make.But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
That argument is being howled by the community after the budget cuts, after the first failures, after the decision to decomission it, and right now as we speak, with plenty of technical rationale as partly quoted in this thread.
Is the rest of the comment anyway an argument to just do away with the burgeois nicety of failure investigation and correction? It certainly sounds like it.
Post by: eeergo on 12/03/2020 05:05 pm
But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
I have provided a step by step derivation, with clarifications upon request, which predicted the outcome before being shown on video. Others have contented themselves with confounding the issue over quibbles about minor perturbative effects and handwaved, generally inapplicable, qualitative misconceptions.
Certainly if proper maintenance and/or swift reinforcing had taken place during the years of widespread, documented and denounced corner-cutting, the outcome *might possibly* been different, don'ttya think? What are you even claiming? Improper maintenance is equal to proper maintenance?
As for the emotional upset: so far the ones that have constantly polluted this thread with wrong predictions based on falsified rule-of-thumb "calculations" at best, or fact-impermeable foregone conclusions most of the time, are the ones that are now asking, in the face of evidence, for very specific proof that only those with access to internal documentation could possibly have. While ignoring the actual facility staff denouncing it, and NSF's declared aim of defunding the facility. While providing NO objective backing to their claims themselves, moving their goalposts at light speed and *acting offended* when the mere concept is brought up.
But the emotional response is always on the other side, ain't it?
Were any of your tax dollars spent on this project?
Again, I certainly appreciate your experience and insight in many topics, but I must point out the inappropriateness of the retort. The soundness of my arguments, or lack thereof, is not dependent upon my fiscal residence.
But since you ask: yes they were, I was employed by NSF for 7 years.
Post by: eeergo on 12/03/2020 05:22 pm
But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
I have provided a step by step derivation, with clarifications upon request, which predicted the outcome before being shown on video. Others have contented themselves with confounding the issue over quibbles about minor perturbative effects and handwaved, generally inapplicable, qualitative misconceptions.
Certainly if proper maintenance and/or swift reinforcing had taken place during the years of widespread, documented and denounced corner-cutting, the outcome *might possibly* been different, don'ttya think? What are you even claiming? Improper maintenance is equal to proper maintenance?
As for the emotional upset: so far the ones that have constantly polluted this thread with wrong predictions based on falsified rule-of-thumb "calculations" at best, or fact-impermeable foregone conclusions most of the time, are the ones that are now asking, in the face of evidence, for very specific proof that only those with access to internal documentation could possibly have. While ignoring the actual facility staff denouncing it, and NSF's declared aim of defunding the facility. While providing NO objective backing to their claims themselves, moving their goalposts at light speed and *acting offended* when the mere concept is brought up.
But the emotional response is always on the other side, ain't it?
Were any of your tax dollars spent on this project?
Again, I certainly appreciate your experience and insight in many topics, but I must point out the inappropriateness of the retort. The soundness of my arguments, or lack thereof, is not dependent upon my fiscal residence.
But since you ask: yes they were, I was employed by NSF for 7 years.
Since you worked for the NSF, then presumably you can provide proof that the maintenance budget was cut, right? I mean, that's been alleged here. Can we see some proof?
I was paid by NSF and paid my US taxes (at least twice, actually, since not everything NSF paid went to my pocket), I wasn't part of the agency staff nor did I ever have access to internal facility assessments, even my own. Neither did I feel inclined to go dig outside my turf, to be honest.
But thought the issue was whoever hadn't paid US taxes was summarily forbidden from showing analysis here, let alone commenting. Well, as mentioned, I did - and a healthy sum. Does my opinion count more now? Or is tax seniority also needed?
Pretty disheartening you're bringing this to a personal attack, but go ahead, I don't believe in secrecy and have no problema to continue answering.
Do you have proof to the contrary to authoritatively dismiss the testimony of dozens of insiders? Can we see it? Even better would be reports showing the stable, or even increased, non-parchwork maintenance for the last ten years, particularly around earthquake and hurricane events.
Post by: apollo16uvc on 12/03/2020 05:37 pm
An unique and irreplaceable instrument made more than 50 years ago, and we could not take proper care of it. Pity,
Post by: leovinus on 12/03/2020 05:42 pm
Post by: Eric Hedman on 12/03/2020 05:48 pm
If there wasn't enough maintenance due to budget cuts, that ultimately comes back to Congress and we know they don't take responsibility for failures like this. Even if they say "My bad." it won't change anything. I think there should be a failure investigation. But if there is a detailed explanation of the cause of the failure and blame to affix, it still won't change anything because we don't build telescopes like these anymore.I completely agree. It collapsed and nothing will change that. The debate should be, is there enough value in rebuilding a new radio telescope in Arecibo. I think that will be a hard argument to make.But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
That argument is being howled by the community after the budget cuts, after the first failures, after the decision to decomission it, and right now as we speak, with plenty of technical rationale as partly quoted in this thread.
Is the rest of the comment anyway an argument to just do away with the burgeois nicety of failure investigation and correction? It certainly sounds like it.
Post by: eeergo on 12/03/2020 05:59 pm
If there wasn't enough maintenance due to budget cuts, that ultimately comes back to Congress and we know they don't take responsibility for failures like this. Even if they say "My bad." it won't change anything. I think there should be a failure investigation. But if there is a detailed explanation of the cause of the failure and blame to affix, it still won't change anything because we don't build telescopes like these anymore.
And that's a tautology, so?
In any case, the 'fault' cannot only be abscribed to Congress, seeing how many are eager to publicly jump in the "problem? what problem? nothing to see here" bandwagon, here and elsewhere.
Post by: Blackstar on 12/03/2020 05:59 pm
I've included a few photos from the lower structure as well, including one from inside the dome. The dome was a reflecting device that bounced the signals and concentrated them onto collectors.
I'll also post some photos from underneath the dish.
Post by: Blackstar on 12/03/2020 06:02 pm
They had a crane inside the tower for lifting equipment up from the floor of the crater. The scale of the telescope was pretty amazing.
Post by: freddo411 on 12/03/2020 06:13 pm
This could become the latest vid that captures the vibe of the "tacoma narrows bridge collapse" ..
https://twitter.com/inbarspace/status/1334544217293643776?s=20
Post by: ccdengr on 12/03/2020 06:14 pm
Who knows if the handover to UCF for the support contract helped or hurt the situation.
Post by: Dizzy_RHESSI on 12/03/2020 07:04 pm
I completely agree. It collapsed and nothing will change that. The debate should be, is there enough value in rebuilding a new radio telescope in Arecibo. I think that will be a hard argument to make.Well according to the Twitter thread posted up thread you would appear to be mistaken in that belief. Let alone as I keep repeating on this thread that this is bigger than just the science arguments.
Which twitter thread exactly? I've looked over a lot of these "rebuild AO" pages and there's very little discussion of the actual science case.
People are free to believe that this discussion should be wider than just the science, but repeating that opinion doesn't mean everyone else has to agree. NSF astronomy has had a terrible decade in funding, with facilities taking up more and more of the budget squeezing grants and mid-scale programs. There isn't room in the budget to be squandered on facilities which are a bad investment.
Post by: Sam Ho on 12/03/2020 07:23 pm
https://www.nsf.gov/news/special_reports/arecibo/
Post by: meekGee on 12/03/2020 07:44 pm
If there wasn't enough maintenance due to budget cuts, that ultimately comes back to Congress and we know they don't take responsibility for failures like this. Even if they say "My bad." it won't change anything. I think there should be a failure investigation. But if there is a detailed explanation of the cause of the failure and blame to affix, it still won't change anything because we don't build telescopes like these anymore.
And that's a tautology, so?
In any case, the 'fault' cannot only be abscribed to Congress, seeing how many are eager to publicly jump in the "problem? what problem? nothing to see here" bandwagon, here and elsewhere.
There are always those eager to place blame, usually bringing old axes to grind.
Allocating funds between instruments all over the world will always leave someone short. Pretty much by definition.
That said, you're totally wrong on your cable analysis... But that's a separate post...
Post by: darkenfast on 12/03/2020 07:58 pm
So, first: Did the original design allow for the maintaining and repair of the original cables?
Second: Was there ever a proposal developed during the next 50+ years to repair or replace the cables?
Until these questions are answered, I don't see the point in all the finger-pointing at those alleged to have allowed this to happen by withholding maintenance funding.
Post by: meekGee on 12/03/2020 09:16 pm
Will someone please explain to me how deteriorating cables were to be maintained, repaired, or replaced? The period leading up to the collapse showed that cables were failing well below their design load and that interior strands within the cables were failing (as seen in one of the Scott Manly videos). The whole structure above the bowl was in tension and was supporting a center weight of 800 tons that could not be removed.There's an argument floating around that lack of cable maintenance such as painting is to blame.
So, first: Did the original design allow for the maintaining and repair of the original cables?
Second: Was there ever a proposal developed during the next 50+ years to repair or replace the cables?
Until these questions are answered, I don't see the point in all the finger-pointing at those alleged to have allowed this to happen by withholding maintenance funding.
Maybe.
But I haven't heard anyone ever yell from Arecibo that it's going to collapse and we need to paint the cables.
So maybe they didn't understand the state of the cables either.
...If that whole painting thing is really real anyway.
...
Post by: mn on 12/03/2020 09:22 pm
Edit: on 2nd thought, it seems that a cable that snaps leaves some cloud of (something??) in place visible to the camera, and that cloud just took time to dissipate? makes sense?
Post by: eeergo on 12/03/2020 09:32 pm
Quote from: meekGee link=topic=43786.msg2161813#msg2161813
That said, you're totally wrong on your cable analysis... But that's a separate post...
Pretty adventurous claim considering your prior armwaving at esoterism and the zero math you provide. Until you're ready to prove it objectively, I (and probably others) will ignore your comments as trolling.
Post by: eeergo on 12/03/2020 09:34 pm
In video of the failure, I'm trying to understand what is the horizontal cable which seems to remain horizontal during the failure? what is that cable attached to that is not in motion?
Edit: on 2nd thought, it seems that a cable that snaps leaves some cloud of (something??) in place visible to the camera, and that cloud just took time to dissipate? makes sense?
Paint and fragments. You can see the same effect on the foreground just after the access bridge is ripped apart, by a snapping cable leaving such a cloud.
Post by: Swedish chef on 12/03/2020 09:37 pm
Will someone please explain to me how deteriorating cables were to be maintained, repaired, or replaced?
Well I guess you start with installing an extra cable, then you could replace one existing cable at a time. Finish with uninstalling the extra cable.
Post by: eeergo on 12/03/2020 09:52 pm
Will someone please explain to me how deteriorating cables were to be maintained, repaired, or replaced? The period leading up to the collapse showed that cables were failing well below their design load and that interior strands within the cables were failing (as seen in one of the Scott Manly videos). The whole structure above the bowl was in tension and was supporting a center weight of 800 tons that could not be removed.
So, first: Did the original design allow for the maintaining and repair of the original cables?
Second: Was there ever a proposal developed during the next 50+ years to repair or replace the cables?
Until these questions are answered, I don't see the point in all the finger-pointing at those alleged to have allowed this to happen by withholding maintenance funding.
1st: Yes: https://www.planetary.org/articles/0409-arecibo-observatory-earthquake-repairs
https://books.google.it/books?id=Z1oHVlRS6a4C&pg=PA25&lpg=PA25&dq=arecibo+cable+replacement+operation+-break+-snap+-collapse&source=bl&ots=b4plsIH16H&sig=ACfU3U2bJKy24_pYKF3JeB8d1KayfEUBdg&hl=it&sa=X&ved=2ahUKEwiMlZTq8bLtAhWPsBQKHcGfAso4ChDoATAJegQIBxAC#v=onepage&q=arecibo%20cable%20replacement%20operation%20-break%20-snap%20-collapse&f=false
2nd: Yes, actuated, see above.
It's obvious such an operation was foreseen - otherwise, as soon as it was built, the whole thing would be expected to collapse as soon as the cables were old enough. Most recently, when the first cable snapped in August, a (slow) operation was initiated to replace it and reinforce the weakened structure.
Indeed, I notice an interesting cognitive dissonance among those who continue to insist this is no big deal. On the one side, maintenance wasn't defective and everything was kept in impeccable working order. On the other, all supporting cables were extremely weakened (contrary to what a simple mathematical analysis and videographic evidence shows). It seems to me the only way to reconcile the two is to invoke an arcane, mysterious magic swiftly and hopelessly corroding the cables in spite of spotless maintenance.
Post by: russianhalo117 on 12/03/2020 10:05 pm
For point 2: epoxy sealed cables would have extended their lifespan. Painting doesn't seal well enough unless every strand at every winding step in the process is coated right then and there. In mining hoist and winch cables continually get shorter as the ends are cut off for annual destructive testing and analysis. The observatory was not designed to do this as the ends were permanently terminated.Will someone please explain to me how deteriorating cables were to be maintained, repaired, or replaced? The period leading up to the collapse showed that cables were failing well below their design load and that interior strands within the cables were failing (as seen in one of the Scott Manly videos). The whole structure above the bowl was in tension and was supporting a center weight of 800 tons that could not be removed.
So, first: Did the original design allow for the maintaining and repair of the original cables?
Second: Was there ever a proposal developed during the next 50+ years to repair or replace the cables?
Until these questions are answered, I don't see the point in all the finger-pointing at those alleged to have allowed this to happen by withholding maintenance funding.
1st: Yes: https://www.planetary.org/articles/0409-arecibo-observatory-earthquake-repairs
https://books.google.it/books?id=Z1oHVlRS6a4C&pg=PA25&lpg=PA25&dq=arecibo+cable+replacement+operation+-break+-snap+-collapse&source=bl&ots=b4plsIH16H&sig=ACfU3U2bJKy24_pYKF3JeB8d1KayfEUBdg&hl=it&sa=X&ved=2ahUKEwiMlZTq8bLtAhWPsBQKHcGfAso4ChDoATAJegQIBxAC#v=onepage&q=arecibo%20cable%20replacement%20operation%20-break%20-snap%20-collapse&f=false
2nd: Yes, actuated, see above.
It's obvious such an operation was foreseen - otherwise, as soon as it was built, the whole thing would be expected to collapse as soon as the cables were old enough. Most recently, when the first cable snapped in August, a (slow) operation was initiated to replace it and reinforce the weakened structure.
Indeed, I notice an interesting cognitive dissonance among those who continue to insist this is no big deal. On the one side, maintenance wasn't defective and everything was kept in impeccable working order. On the other, all supporting cables were extremely weakened (contrary to what a simple mathematical analysis and videographic evidence shows). It seems to me the only way to reconcile the two is to invoke an arcane, mysterious magic swiftly and hopelessly corroding the cables in spite of spotless maintenance.
Post by: Nomadd on 12/03/2020 10:12 pm
Lots of suspension bridges have corrosion problems because of improper galvanization of cables. Lack of maintenance didn't help, but it's hard to make a cable vapor proof with paint, so moisture will usually find a way in.
Indeed, I notice an interesting cognitive dissonance among those who continue to insist this is no big deal. On the one side, maintenance wasn't defective and everything was kept in impeccable working order. On the other, all supporting cables were extremely weakened (contrary to what a simple mathematical analysis and videographic evidence shows). It seems to me the only way to reconcile the two is to invoke an arcane, mysterious magic swiftly and hopelessly corroding the cables in spite of spotless maintenance.
Just hope the NTSB isn't doing the investigation.
Post by: ccdengr on 12/03/2020 10:18 pm
It's obvious such an operation was foreseen - otherwise, as soon as it was built, the whole thing would be expected to collapse as soon as the cables were old enough.I've never seen any explicit statement of what the design lifetime was supposed to be, have you?
The initial construction with its too-short spliced cable on day one doesn't suggest building for the ages.
Post by: eeergo on 12/03/2020 10:38 pm
It's obvious such an operation was foreseen - otherwise, as soon as it was built, the whole thing would be expected to collapse as soon as the cables were old enough.I've never seen any explicit statement of what the design lifetime was supposed to be, have you?
The initial construction with its too-short spliced cable on day one doesn't suggest building for the ages.
No, I haven't, but I did find a reference to a study performed on the occasion of the 1981 cable replacement to determine the remaining lifetime on the cables: https://books.google.it/books?id=COAdAAAAMAAJ&pg=PA553&lpg=PA553&dq=arecibo+%221981%22+cable+replacement+-collapse+-break+-snap+-break&source=bl&ots=cU6ayWhek5&sig=ACfU3U3DTejhOPEIyC2yzgtFxlUU5dEdBQ&hl=it&sa=X&ved=2ahUKEwibmp-h-7LtAhXzDmMBHcSsBMoQ6AEwB3oECAcQAg#v=onepage&q=arecibo%20%221981%22%20cable%20replacement%20-collapse%20-break%20-snap%20-break&f=false. A pretty good answer as to the projected lifetime and how to extend it should be there. I failed to find that report though, seems not to be indexed or use other set of keywords.
OTOH, it's not a matter of building for the ages. Either you have a way of repairing/replacing the cables to keep it going, or you have a way to release tension and decommission it once their lifetime is expired (which implies you can also replace them)... or just wait for the whole thing to collapse by itself as per-design end-of-life "strategy".
Post by: eeergo on 12/03/2020 10:45 pm
Lots of suspension bridges have corrosion problems because of improper galvanization of cables. Lack of maintenance didn't help, but it's hard to make a cable vapor proof with paint, so moisture will usually find a way in.
Indeed, I notice an interesting cognitive dissonance among those who continue to insist this is no big deal. On the one side, maintenance wasn't defective and everything was kept in impeccable working order. On the other, all supporting cables were extremely weakened (contrary to what a simple mathematical analysis and videographic evidence shows). It seems to me the only way to reconcile the two is to invoke an arcane, mysterious magic swiftly and hopelessly corroding the cables in spite of spotless maintenance.
Just hope the NTSB isn't doing the investigation.
Thanks for the insight, that's an interesting point I hadn't heard before.
I'd argue that'd still classify as improper maintenance though, since cable replacement is a non-overly-extraordinary possibility and they've had diagnostic tools to determine unacceptable degradation since the early days of the facility, see reference in my replies to darkenfast and ccdengr. It may be unpreventable corrosion from the perspective of not being able to avoid it through any amount of ordinary maintenance, but it can be quantified and planned for before the whole thing snaps away from control.
As for all cables being exceedingly weakened, the T4/T12 cables beg to differ with their pendulum shenanigans.
Post by: ulm_atms on 12/03/2020 10:49 pm
But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
I have provided a step by step derivation, with clarifications upon request, which predicted the outcome before being shown on video. Others have contented themselves with confounding the issue over quibbles about minor perturbative effects and handwaved, generally inapplicable, qualitative misconceptions.
Certainly if proper maintenance and/or swift reinforcing had taken place during the years of widespread, documented and denounced corner-cutting, the outcome *might possibly* been different, don'ttya think? What are you even claiming? Improper maintenance is equal to proper maintenance?
As for the emotional upset: so far the ones that have constantly polluted this thread with wrong predictions based on falsified rule-of-thumb "calculations" at best, or fact-impermeable foregone conclusions most of the time, are the ones that are now asking, in the face of evidence, for very specific proof that only those with access to internal documentation could possibly have. While ignoring the actual facility staff denouncing it, and NSF's declared aim of defunding the facility. While providing NO objective backing to their claims themselves, moving their goalposts at light speed and *acting offended* when the mere concept is brought up.
But the emotional response is always on the other side, ain't it?
Were any of your tax dollars spent on this project?
Do we get a choice? Wouldn't that affect who gets the money distribution in the budget? That would be an interesting social experiment....letting the tax payers decide ;D but I digress.
Guys, seriously...do we have to do the blame game on here? It's a sad day...so lets argue over what ifs till the cows come home? ???
I can tell that eeergo is very upset at what happened (any science loss is bad in my book) but this snipping at each other....we are better then that guys...we really are. There is no need for snipping.
All we can do now is learn all the lessons of why/how this happened and put that knowledge to use to make other things safer/better in the future.
And I did say very bad words when it collapsed...Arecibo was on my bucket list to visit...that place always looked so cool from the pictures up close. Lets remember it for the good....not for arguments on who's fault it was..
Post by: LouScheffer on 12/03/2020 10:55 pm
There are many radio telescopes that could do what Arecibo does, more or less, for receiving. They can also access wider frequency ranges and much more of the sky. Therefore the hardest to replace function of Arecibo is the giant honking radar transmitter, which could generate a 20 TW EIRP beam by combining a large (1 MW) transmitter with a high antenna gain (about 20,000,000). The only other facility that's even close is the transmitter at the 70 meter antenna at Goldstone, but it has lots of other work to do for DSN and is hard to schedule. The FAST telescope in China, built like Arecibo, can't do this since their focal structure was not designed to support a large, heavy transmitter.
But building another Arecibo may not be the right way to approach this. As a conceptual example, imagine a flat concrete slab 120 meters on a side covered with StarLink antennas. Each Starlink can generate an EIRP of 38.4 dbW (according to FCC specs) which is about 6600 watts. They are about 0.5 meter on a side so it would take 240*240 = 57,600 of them to cover the slab. If all phased up properly (and this should mostly be a matter of software) this would generate an EIRP of 6600*5760^2 or about 22 TW, similar to Arecibo. If the antennas cost $1000 each (as many have suggested) the total cost is less then $60M, way less than for Arecibo. And everything is at ground level and trivial to service. The beam can be steered at least 50o from zenith, much better than Arecibo.
Alternatively, you could add a 1MW X-band transmitter to an existing 100 meter telescope such as Greenbank or Effelssburg. As at Goldstone, the higher frequency means higher antenna gain, making them comparable to Arecibo.
These are just a hypothetical examples, but the reasoning holds more generally. You can probably do better for the same amount of money than building a replica of the old Arecibo.
Post by: illectro on 12/03/2020 11:08 pm
In video of the failure, I'm trying to understand what is the horizontal cable which seems to remain horizontal during the failure? what is that cable attached to that is not in motion?
Edit: on 2nd thought, it seems that a cable that snaps leaves some cloud of (something??) in place visible to the camera, and that cloud just took time to dissipate? makes sense?
That cable is one of the supports for the waveguide and walkway up to the platform, it's not carrying anywhere near the load of the other cables so lasts until the platform swinging down smashes this structure.
Post by: ulm_atms on 12/03/2020 11:16 pm
snip...
These are just a hypothetical examples, but the reasoning holds more generally. You can probably do better for the same amount of money than building a replica of the old Arecibo.
The transmit part aside....Why did China build a bigger version of Arecibo then? I guess what I am asking is what can a receiver like Arecibo/China's do better then something else like a array type setup? There has to be something it does better then anything else...otherwise why do it in the first place?
Post by: ccdengr on 12/03/2020 11:17 pm
imagine a flat concrete slab 120 meters on a side covered with StarLink antennas.It took a while, but even this thread worked around to Elon having the answer! :)
I have no idea if your idea is practical, but I suspect it's not as easy as you think.
Post by: LouScheffer on 12/03/2020 11:48 pm
Well, I wrote about this scheme in 2005 (https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005RS003243) (in the pre-Elon era) and it passed peer review at that time. So perhaps it's not completely crazy. The main reason to cite StarLink is not for the technology, but for the cost estimate.imagine a flat concrete slab 120 meters on a side covered with StarLink antennas.It took a while, but even this thread worked around to Elon having the answer! :)
I have no idea if your idea is practical, but I suspect it's not as easy as you think.
Clearly the Starlink transmitters match phase across their face - that's how they point. The only new part is matching the phases between the separate dishes. But sending absolute phase references across a 100 meter distance is a problem radio telescopes have solved for years.
Post by: meekGee on 12/03/2020 11:53 pm
Quote from: meekGee link=topic=43786.msg2161813#msg2161813That said, you're totally wrong on your cable analysis... But that's a separate post...
Pretty adventurous claim considering your prior armwaving at esoterism and the zero math you provide. Until you're ready to prove it objectively, I (and probably others) will ignore your comments as trolling.
I'll be gentle.
Your own words:
Quote
The real-world dynamics are certainly not exactly represented by an ideal pendulum, an ideal static load, ideally-rigid massless cables and the whole lot.
Let's start with "ideally rigid".
In the starting conditions, since the cables are well above 45-degrees, the tension in them is higher than the mg of the load. So right there already, once a cable is disconnected, the acceleration in the direction into the remaining cables is higher than the acceleration downwards. Since additionally, downward motion doesn't stretch the cables 1:1 (again because of the angle), then it's obvious that initially the remaining cables will untension.
So with that assumption (ideally-rigid), you already robbed the system of probably it's most important trait. Your house of cards of the previous 10 posts is already on shaky foundations.
Then, we're talking about real-world cables. Once tension reduces, they begin to unwind. You have no idea what's going on at that point. Your calculation is not even wrong, it's just, well - of a different system.
Third, you assume "mass-less" cables. Are they? The payload weighs about 800 tons. How much do the cables weigh? It looks like there are 4 cables coming down from the tower towards the center, each 3-4 inches in diameter, about 150 m each, very roughly - heh, 800 tons. Give or take. So massless, they aren't.
So this other assumption pulls you even further from the system you're trying to calculate.
Then you conclude:
Quote
But the approximation is pretty darn accurate at this scale.
And I'm the one that's hand-waiving?!
--
Methinks you QED'ed much too early.
Post by: launchwatcher on 12/03/2020 11:59 pm
FAST has a bowl-shaped reflector similar to Arecibo, but it does not have a massive 800+-ton truss structure at the focus.
snip...
These are just a hypothetical examples, but the reasoning holds more generally. You can probably do better for the same amount of money than building a replica of the old Arecibo.
The transmit part aside....Why did China build a bigger version of Arecibo then? I guess what I am asking is what can a receiver like Arecibo/China's do better then something else like a array type setup? There has to be something it does better then anything else...otherwise why do it in the first place?
Instead it uses a much lighter weight "cable robot" driven by winches on six towers around the perimeter. The FAST paper (https://arxiv.org/pdf/1105.3794.pdf) doesn't appear mention the full weight of the feed cabin, though it does mention that the stabilizer for the receiver has a payload capacity of about 3 tons.
A similar lightweight design would make sense in an Arecibo rebuild. I wonder if something could be rapidly prototyped based on the existing flying camera systems often found in sports stadiums.
Post by: LouScheffer on 12/04/2020 12:06 am
The transmit part aside....Why did China build a bigger version of Arecibo then? I guess what I am asking is what can a receiver like Arecibo/China's do better then something else like a array type setup? There has to be something it does better then anything else...otherwise why do it in the first place?There are two advantages. One is a very large collecting area for the price, and the need for only one receiver, but this comes with the restriction of a limited view of the sky and a lower top frequency limit. The area can be equaled by other arrangements (the next generation VLA is planning an array of 244 dishes of 18 meters each). This is the same as a 281 meter single dish, but has a much wider frequency range, can point anywhere, can use subset for different projects, has much much higher resolution (since this is set by the separation of the dishes, not the size of a single dish). But it's much more costly.
Another advantage is a lower low-frequency limit. An antenna needs to be several 10s of wavelengths across to get a decent beam, so arrays of smaller antennas can't do lower frequencies very well. This is important for some particular astronomy problems - in particular the OH lines can get red-shifted down to where arrays can't handle them well. But on the other hand, these lower frequencies don't go through the atmosphere and ionosphere well anyway - in fact one of the main original uses of Arecibo was to investigate the ionosphere with radar. Also there are huge numbers of human made transmitters at these frequencies.
Post by: tpw2 on 12/04/2020 04:04 am
The transmit part aside....Why did China build a bigger version of Arecibo then? I guess what I am asking is what can a receiver like Arecibo/China's do better then something else like a array type setup? There has to be something it does better then anything else...otherwise why do it in the first place?Another advantage is a lower low-frequency limit. An antenna needs to be several 10s of wavelengths across to get a decent beam, so arrays of smaller antennas can't do lower frequencies very well. This is important for some particular astronomy problems - in particular the OH lines can get red-shifted down to where arrays can't handle them well. But on the other hand, these lower frequencies don't go through the atmosphere and ionosphere well anyway - in fact one of the main original uses of Arecibo was to investigate the ionosphere with radar. Also there are huge numbers of human made transmitters at these frequencies.
LOFAR uses, and SKA is planning to use, simple dipole antennas for the low frequency part.
The big thing at low frequencies is studying the 21 cm hydrogen line at high redshifts and that is actually one of the main science drivers for SKA (though 18 cm OH lines are also observed sometimes)
Post by: edzieba on 12/04/2020 09:51 am
The "bottom angle", if you're referring to the opening angle between support cables as I understand it, doesn't change between both cases because the towers are fixed and 3 equal sectors of a circle sum up to 360º.That's the fundamental mistake you're making: The two cases are NOT the same.
In the static case, the load is distributed entirely in the horizontal plane (because the only load is purely vertical, and the cables are stationary). The angle used to calculate load distribution is that of the cable offset from horizontal.
In the swinging case, the cables are no longer restrained. The force distribution plane is now coincident with the plane formed by the two remaining cables, and moves as the cables swing. There is no load tangential to the cables, as the cables are no longer restrained from moving (i.e. any twisting loads simple flex the cables, they do not tension them). This is why the angle used to calculate the load distribution is measured in a different plane.
This is why the tension in the cables is 3x higher in the static case than the swinging case (for the same point loading).
You can also see this as the structure swings: the cables visibly de-tension and begin to flex as soon as the third span fails. Rather than their tensile load on the cables increasing after the third span fails, it decreases.
As we can also see in the new drone footage, the cables at the top of the tower were in a very poor state of repair. There seems to be no evidence that the cables on this tower were all on the verge of an unforced failure, but the cables on the other towers were all pristine and untouched. Why would the cables of tower be uniquely different from the others?
Post by: eeergo on 12/04/2020 10:32 am
That said, you're totally wrong on your cable analysis...
In the starting conditions, since the cables are well above 45-degrees, the tension in them is higher than the mg of the load. So right there already, once a cable is disconnected, the acceleration in the direction into the remaining cables is higher than the acceleration downwards. Since additionally, downward motion doesn't stretch the cables 1:1 (again because of the angle), then it's obvious that initially the remaining cables will untension.
So with that assumption (ideally-rigid), you already robbed the system of probably it's most important trait. Your house of cards of the previous 10 posts is already on shaky foundations.
Then, we're talking about real-world cables. Once tension reduces, they begin to unwind. You have no idea what's going on at that point. Your calculation is not even wrong, it's just, well - of a different system.
Third, you assume "mass-less" cables. Are they? The payload weighs about 800 tons. How much do the cables weigh? It looks like there are 4 cables coming down from the tower towards the center, each 3-4 inches in diameter, about 150 m each, very roughly - heh, 800 tons. Give or take. So massless, they aren't.
So this other assumption pulls you even further from the system you're trying to calculate.
Then you conclude:QuoteBut the approximation is pretty darn accurate at this scale.
And I'm the one that's hand-waiving?! Methinks you QED'ed much too early.
Have you ever had to rough-order-of-magnitude estimate loads, or actually any quantity in a physical system? From your post you don't seem to understand how to roughly approximate the behavior of a simplified system -which a real-life one never is, even a small countertop pendulum has major deviations from ideal- without appealing to a full-fledged simulation or in-depth study.
I do that every day in my work, and the bare minimum is to check back-of-the-envelope calculations agree with the real system, accounting for corrections. You again have not provided ANY numbers (but then accuse me of handwaving when I mention a neglected second-order correction), and just nitpick at deviations from ideal, while condescendingly "being gentle".
You're saying you're completely unable to roughly calculate the loads on those cables (which contradicts edzieba's wrong, but at least quantitative, approach), and furthermore it's impossible to reach that estimate... and that's, to put it "gently", incorrect.
In any case, just to set the record straight:
- Massive cables just add to the tensions. I did hint to that when referring to their inertia on the towers once the platform had crashed. That is, the case with the massless cables is a lower limit of tensions from that point of view. This is a concept from high-school-level physics.
- You appeal to the tension release when the opposing cables snap. This is actually NOT the behavior of the real system, as can be seen from the video, and is just approximated that way to avoid calculating a transient that doens't really affect the final result.
* The opposing cable isn't one: it's at least 3 as can be seen from the video, that snap at different times.
* The tension isn't released instantaneously: the two-string pendulum is released during an extended, finite amount of time. This means tension buildup from the platform falling will quickly catch up with the tension release from the failing cables, not allowing them to unstretch much, and certainly not "start to unwind". This major "unwinding" is also unsupported from imagery: there should be a cloud of flecked paint around them if they did that, as visible when they snap. That effect, if there at all, is minute.
* You're neglecting the 800-ton platform reorientation visible in the video. As soon as the opposing cables start to fail, that end of the platform starts to rotate, keeping a moderate amount of tension on the surviving cables, through inertia and displacement. Yet you ignore this MAJOR load, and bicker about corrections from ideal rigid, massless cable behavior. In fact, a major contributor I ignored for the sake of simplicity and to provide a lower possible limit, is the rotation inertia of the platform load, which almost reached verticality before shedding part of its weight (the dome).
* I took this transient into account in my posts, in any case, and it would moreover cause vibrations/shocks that would overexert the cables beyond my simplified calculations. If they'd lost structural integrity due to unwinding, which they mostly did not, this argument would be even stronger. So, again, these are a best-case lower limit of the tensions those cables saw.
* Finally, this "loadless" transient (if it ever existed due to the aforementioned effects) wouldn't take more than a fraction of a second, both from the platform rotation and its downward motion, retensioning the cables immediately to (to the second decimal point) 0.5·m·g·sin(W) as derived.
- I did forget to account for a factor of 3 in the static load calculation (m·g = 3·Tu, Tu being the upward component of each cable's tension), which means the initial load is indeed higher than that estimated initially, as you correctly point out. For the 35º case I first derived, it doesn't matter (serendipitously cancels out) - but for the real angle of 10º it does.
However, the difference isn't so great as to overcome the mounting centripetal effect, which reaches (ignoring cable self-weight and platform inertia, which will just add to that) around 3 times the suspended weight just before the crash. Instead of at 24º beyond the static position, the initial load will be surpassed at 54º - again neglecting real-world factors that only increase loads, so realistically this would be more 45º-50º.
In hindsight, that's both a more reasonable result (one would expect tremendous loads near the bottom of the trajectory for a quadratically-increasing quantity, if after only 10º of displacement nominal loads were exceeded, not just 3 times the weight) - but still results in exceeding nominal loads significantly earlier than the position actually reached by the platform during its swing, and neglects major dynamic weakening factors such as vibrations and shocks. So yeah, QED again.
Post by: Star One on 12/04/2020 10:35 am
All the more reason then surely to take the site’s future away from the NSF I would have thought?I completely agree. It collapsed and nothing will change that. The debate should be, is there enough value in rebuilding a new radio telescope in Arecibo. I think that will be a hard argument to make.Well according to the Twitter thread posted up thread you would appear to be mistaken in that belief. Let alone as I keep repeating on this thread that this is bigger than just the science arguments.
Which twitter thread exactly? I've looked over a lot of these "rebuild AO" pages and there's very little discussion of the actual science case.
People are free to believe that this discussion should be wider than just the science, but repeating that opinion doesn't mean everyone else has to agree. NSF astronomy has had a terrible decade in funding, with facilities taking up more and more of the budget squeezing grants and mid-scale programs. There isn't room in the budget to be squandered on facilities which are a bad investment.
Post by: Dizzy_RHESSI on 12/04/2020 10:35 am
The transmit part aside....Why did China build a bigger version of Arecibo then? I guess what I am asking is what can a receiver like Arecibo/China's do better then something else like a array type setup? There has to be something it does better then anything else...otherwise why do it in the first place?Another advantage is a lower low-frequency limit. An antenna needs to be several 10s of wavelengths across to get a decent beam, so arrays of smaller antennas can't do lower frequencies very well. This is important for some particular astronomy problems - in particular the OH lines can get red-shifted down to where arrays can't handle them well. But on the other hand, these lower frequencies don't go through the atmosphere and ionosphere well anyway - in fact one of the main original uses of Arecibo was to investigate the ionosphere with radar. Also there are huge numbers of human made transmitters at these frequencies.
LOFAR uses, and SKA is planning to use, simple dipole antennas for the low frequency part.
The big thing at low frequencies is studying the 21 cm hydrogen line at high redshifts and that is actually one of the main science drivers for SKA (though 18 cm OH lines are also observed sometimes)
Indeed. Arecibo's current lowest frequency receiver is 327 MHz, while LOFAR covers 10 to 240 MHz. I don't think Areicbo has ever really pushed low frequencies. The reason it's unattractive for this is the beam size. At 50 MHz the Arecibo beam is 1.5 degrees, which is just miserable resolution. You aren't going to be detecting high redshift galaxies with terrible angular resolution, because the signal is diluted by the beam. Another problem with an Arecibo like design is field of view, you're only going to get one independent beam given the small field of view. That means you only have one resolution element (one pixel), which makes mapping slow. Interferometric arrays can have large numbers of resolution elements, because the beam is much larger than the resolution of the array. This is why arrays are much more attractive at low frequencies, you can have area, FoV and resolution. Dipoles also have the feature that their collecting area increases with decreasing frequency.
Post by: Star One on 12/04/2020 10:39 am
You need to learn from the mistakes of the past so as to not repeat them. If maintenance issues were caused by funding issues then it’s best they are uncovered.But we keep being told on this thread that there was nothing wrong with the funding and upkeep, and that the NSF’s hands are ‘clean’ in this matter.
Let's say for the sake of argument that NSF failed to pay for maintenance. Does that change anything? Nope.
But no one has been able to identify any specific maintenance item that was requested, and not funded. It's all just hand waving, and an odd competition to see who is most emotionally upset by this event.
I have provided a step by step derivation, with clarifications upon request, which predicted the outcome before being shown on video. Others have contented themselves with confounding the issue over quibbles about minor perturbative effects and handwaved, generally inapplicable, qualitative misconceptions.
Certainly if proper maintenance and/or swift reinforcing had taken place during the years of widespread, documented and denounced corner-cutting, the outcome *might possibly* been different, don'ttya think? What are you even claiming? Improper maintenance is equal to proper maintenance?
As for the emotional upset: so far the ones that have constantly polluted this thread with wrong predictions based on falsified rule-of-thumb "calculations" at best, or fact-impermeable foregone conclusions most of the time, are the ones that are now asking, in the face of evidence, for very specific proof that only those with access to internal documentation could possibly have. While ignoring the actual facility staff denouncing it, and NSF's declared aim of defunding the facility. While providing NO objective backing to their claims themselves, moving their goalposts at light speed and *acting offended* when the mere concept is brought up.
But the emotional response is always on the other side, ain't it?
Were any of your tax dollars spent on this project?
Do we get a choice? Wouldn't that affect who gets the money distribution in the budget? That would be an interesting social experiment....letting the tax payers decide ;D but I digress.
Guys, seriously...do we have to do the blame game on here? It's a sad day...so lets argue over what ifs till the cows come home? ???
I can tell that eeergo is very upset at what happened (any science loss is bad in my book) but this snipping at each other....we are better then that guys...we really are. There is no need for snipping.
All we can do now is learn all the lessons of why/how this happened and put that knowledge to use to make other things safer/better in the future.
And I did say very bad words when it collapsed...Arecibo was on my bucket list to visit...that place always looked so cool from the pictures up close. Lets remember it for the good....not for arguments on who's fault it was..
Post by: eeergo on 12/04/2020 10:47 am
The "bottom angle", if you're referring to the opening angle between support cables as I understand it, doesn't change between both cases because the towers are fixed and 3 equal sectors of a circle sum up to 360º.That's the fundamental mistake you're making: The two cases are NOT the same.
In the static case, the load is distributed entirely in the horizontal plane (because the only load is purely vertical, and the cables are stationary). The angle used to calculate load distribution is that of the cable offset from horizontal.
In the swinging case, the cables are no longer restrained. The force distribution plane is now coincident with the plane formed by the two remaining cables, and moves as the cables swing. There is no load tangential to the cables, as the cables are no longer restrained from moving (i.e. any twisting loads simple flex the cables, they do not tension them). This is why the angle used to calculate the load distribution is measured in a different plane.
This is why the tension in the cables is 3x higher in the static case than the swinging case (for the same point loading).
You can also see this as the structure swings: the cables visibly de-tension and begin to flex as soon as the third span fails. Rather than their tensile load on the cables increasing after the third span fails, it decreases.
As we can also see in the new drone footage, the cables at the top of the tower were in a very poor state of repair. There seems to be no evidence that the cables on this tower were all on the verge of an unforced failure, but the cables on the other towers were all pristine and untouched. Why would the cables of tower be uniquely different from the others?
In my analysis I did account for an (anyway intuitive) release of tension when the opposing cables snapped, but I did also neglect a factor of 3 in my static estimate - see the last point in my response to meekGee for the explanation. Nevertheless, as you can see there, it doesn't invalidate the conceptual conclusion (just delays it to halfway through the trajectory instead of almost at the beginning of it), and the fact that your prior analysis was ignoring the dynamic behavior when paralleling it to a (static) American death triangle.
As for your last question: in principle, I agree they should all be in the approximate same state of disrepair - but they demonstrably weren't. First, from the fact all failures happened on the same tower; and second, because of what they withstood prior to failing during the pendulum swing, as per my calculation plus all the major intermediate shocks visible in teh video. Being objective, I gather part of the disrepair seen in the drone footage must certainly have been caused by debris from the prior two snaps (even if it's increasingly clear lack of proper maintenance is most certainly the main reason for this collapse), but if anything that comment of yours also would detract from the arguments of those claiming upkeep was impeccable.
EDIT: Rather than focusing on which angle exactly was reached before the tensile load was excessive though, at this point I would however think we should be focusing on how come the main cables you predicted were the ones causing the reflector gashes were actually thrown into the forest behind after guiding the truss all the way to the wall and beyond, the towers gave way laterally and outwards after the crash instead of prior as you claimed, the dome detached when almost vertical due to the acceleration, the cables withstood not only the pendular motion but also ripping through a bridge... or just how come, ignoring all the analysis and hypothesizing all cables were exactly in as bad shape as the failed ones, that was an unpreventable outcome.
Post by: Dizzy_RHESSI on 12/04/2020 11:38 am
All the more reason then surely to take the site’s future away from the NSF I would have thought?
And where is the money going to come from for construction, operations and upgrades? Note that the NSF were looking for partners to support operations at Arecibo for years, there is no way UCF has pockets deep enough.
Post by: LouScheffer on 12/04/2020 01:01 pm
Congrats on your first post, which was helpful, informative, and correct. Welcome to the forum!LOFAR uses, and SKA is planning to use, simple dipole antennas for the low frequency part.
Another advantage is a lower low-frequency limit. An antenna needs to be several 10s of wavelengths across to get a decent beam, so arrays of smaller antennas can't do lower frequencies very well.
The big thing at low frequencies is studying the 21 cm hydrogen line at high redshifts and that is actually one of the main science drivers for SKA (though 18 cm OH lines are also observed sometimes)
You are completely correct. I should have said an array of smaller *dishes*, as in VLA, does not work as well as Arecibo at low frequencies. An array of dipoles (or other simple antennas such a CHIME uses), as you point out, works much better than Arecibo.
Basically, Arecibo is getting squeezed from both ends of the frequency spectrum. At the high end, an array of dishes works much better - full sky, high frequencies, much better resolution (based on array size, not antenna size). At the low end, an array of dipoles (or other simple, cheap antennas) works much better - full sky, lower frequencies, much better resolution. Both array solutions require lots of computing power, not available when Arecibo was built, but possible now.
Arecibo's (and FAST's) niche is a very large collecting area with a single focal point at mid frequencies. But the single focal point advantage for receiving has become a bad tradeoff with array computing technologies. Yes, you need fewer physical receivers (an advantage if they are cryogenic), but you lose resolution and full sky coverage. For transmitters, there are no big phased array transmitters yet, but here too an array would be much more versatile and likely cheaper than re-building Arecibo.
Post by: SimonFD on 12/04/2020 03:04 pm
Given the discussion on here I can't see any good reason for a full repair that can be funded for the long term.
It's very sad to see this collapse. I feel very very lucky that I and my family were able to visit Arecibo in 2003 (I bought a mug, obvs) and had thought to return in the future (when funds increase and human malware decreases). Maybe we'll visit the museum...
Post by: rubicondsrv on 12/04/2020 03:16 pm
EDIT: Rather than focusing on which angle exactly was reached before the tensile load was excessive though, at this point I would however think we should be focusing on how come the main cables you predicted were the ones causing the reflector gashes were actually thrown into the forest behind after guiding the truss all the way to the wall and beyond, the towers gave way laterally and outwards after the crash instead of prior as you claimed, the dome detached when almost vertical due to the acceleration, the cables withstood not only the pendular motion but also ripping through a bridge... or just how come, ignoring all the analysis and hypothesizing all cables were exactly in as bad shape as the failed ones, that was an unpreventable outcome.
the survival of the cables through the swing is hardly a statement on the remaining margin in the cables. that can only be conclusively determined by inspecting the cables.
It is often possible to dramatically overload a structural element beyond the normal failure point without it breaking as long as the loads are applied for a short time. basically it takes time for the material to yield and then break, and if the overload is sufficiently short in duration the deformation will not have time to progress to failure.
nothing can be said conclusively about the remaining strength in the cables until they are retrieved and examined.
Post by: edzieba on 12/04/2020 03:23 pm
and the fact that your prior analysis was ignoring the dynamic behavior when paralleling it to a (static) American death triangle.You have yet to show this, and have repeatedly fundamentally misunderstood the forces and angles involved.
Quote
the towers gave way laterally and outwards after the crash instead of prior as you claimedRe-watch the videos. The towers had failed (or the cables at the top of the towers) before the base of the structure had hit the wall, and well before the top had reached it. Step through the footage from the drone: it pans over the structure just at the moment of nadir impact, and the support cables are already slack when they come into view.
Post by: FutureSpaceTourist on 12/04/2020 03:33 pm
Post by: eeergo on 12/04/2020 03:38 pm
EDIT: Rather than focusing on which angle exactly was reached before the tensile load was excessive though, at this point I would however think we should be focusing on how come the main cables you predicted were the ones causing the reflector gashes were actually thrown into the forest behind after guiding the truss all the way to the wall and beyond, the towers gave way laterally and outwards after the crash instead of prior as you claimed, the dome detached when almost vertical due to the acceleration, the cables withstood not only the pendular motion but also ripping through a bridge... or just how come, ignoring all the analysis and hypothesizing all cables were exactly in as bad shape as the failed ones, that was an unpreventable outcome.
the survival of the cables through the swing is hardly a statement on the remaining margin in the cables. that can only be conclusively determined by inspecting the cables.
It is often possible to dramatically overload a structural element beyond the normal failure point without it breaking as long as the loads are applied for a short time. basically it takes time for the material to yield and then break, and if the overload is sufficiently short in duration the deformation will not have time to progress to failure.
nothing can be said conclusively about the remaining strength in the cables until they are retrieved and examined.
The argument that spawned these derivations was that not just the failing cable set, but *all* structural cables were ready to yield at the slightest perturbation (while at the same time claiming poor maintenance was not to blame, but that's another story).
This was so much so, as to not allow for any workable "safe" (what that means isn't clear, especially when one contractor disagreed) graceful payload lowering, or reinforcement, plan to minimize damage or save the instrumentation. I would say not just the overload from the swing dynamics discussed here during the last few days, but also the violent shocks, jolts and vibrations throughout the 30-second event visible in the videos now available -which nevertheless allowed the cable bundles to survive even visible secondary bending under tension, induced by the access bridge until the tower tops snapped, beyond the straight line joining the towers- at the very least would make inquiring minds question that conclusion.
I agree the post-mortem report about the condition of the different cables will be interesting, if it's made public. Hopefully they will determine exactly what brought the weakest ones to that disrepair too.
Post by: eeergo on 12/04/2020 04:14 pm
and the fact that your prior analysis was ignoring the dynamic behavior when paralleling it to a (static) American death triangle.You have yet to show this, and have repeatedly fundamentally misunderstood the forces and angles involved.
I did not related to the climbing arrangement you mentioned (which is fundamentally a STATIC arrangement, that's the whole point, you're ignoring centripetal tension), and I accepted + corrected the necessary points in my calculation the moment you pointed them out to me, which showed how the updated values only worsened the outcome.
Quote
Quotethe towers gave way laterally and outwards after the crash instead of prior as you claimedRe-watch the videos. The towers had failed (or the cables at the top of the towers) before the base of the structure had hit the wall, and well before the top had reached it. Step through the footage from the drone: it pans over the structure just at the moment of nadir impact, and the support cables are already slack when they come into view.
Please do step through the footage yourself, I did that very carefully already. Although no high-res view of the top of the "swing" towers exists, you can make out pretty clearly their cables did not snap in the drone video, falling with their tops. In fact, the only cable that definitively snapped prior to the platform hitting the wall, apart from the far tower's, was a secondary which got grossly overpulled by the platform's rotation (being anchored to its far angle), rubbed against the access bridge.
As for the towers failing, you can clearly see from the ground footage when that happens from the foreground cables detensioning: at 7:53:57 in the video, just after the secondary snapped and the mains ripped through the bridge, recovering from the overstress bending it briefly made them follow. That's about a quarter second before the truss starts hitting the wall, at maximum overload - and the towers yield first, I speculate from the shock induced by the detachment of the dome.
The remaining tower's cables are tensioned a bit longer, which on one go probably explains the slight rightside leaning of the crashed truss on the wall, and that tower snapping in half instead of just at the top, reaching the ground later.
Anyway, you'd asserted (1) the mains had opened the gashes on the reflector, which is false, (2) the mains could never have reached beyond the reflector edge, even transiently while swinging, because they'd failed much earlier, which is also false as the mains resting on the forest attest, (3) the structure "fell sideways" into the wall, when it's clearly visible it had little to none downward motion at the time of impact, as is expected from a pendular motion near verticality, and (4) the towers had failed (and the cables detensioned) much earlier than the end of the pendular motion, even as early as when the dome started detaching, while at most it was a fraction of a second earlier for the first failure at the Visitor Center's tower.
But since you go on refusing to acknowledge even the glaring conceptual errors and predictions you committed in most of your posts, I think I'll stop beating the dead horse and let the reader figure out whose arguments are more solidly backed, in the interest of letting the thread breathe a bit.
Post by: meekGee on 12/04/2020 04:31 pm
That said, you're totally wrong on your cable analysis...
In the starting conditions, since the cables are well above 45-degrees, the tension in them is higher than the mg of the load. So right there already, once a cable is disconnected, the acceleration in the direction into the remaining cables is higher than the acceleration downwards. Since additionally, downward motion doesn't stretch the cables 1:1 (again because of the angle), then it's obvious that initially the remaining cables will untension.
So with that assumption (ideally-rigid), you already robbed the system of probably it's most important trait. Your house of cards of the previous 10 posts is already on shaky foundations.
Then, we're talking about real-world cables. Once tension reduces, they begin to unwind. You have no idea what's going on at that point. Your calculation is not even wrong, it's just, well - of a different system.
Third, you assume "mass-less" cables. Are they? The payload weighs about 800 tons. How much do the cables weigh? It looks like there are 4 cables coming down from the tower towards the center, each 3-4 inches in diameter, about 150 m each, very roughly - heh, 800 tons. Give or take. So massless, they aren't.
So this other assumption pulls you even further from the system you're trying to calculate.
Then you conclude:QuoteBut the approximation is pretty darn accurate at this scale.
And I'm the one that's hand-waiving?! Methinks you QED'ed much too early.
Have you ever had to rough-order-of-magnitude estimate loads, or actually any quantity in a physical system? From your post you don't seem to understand how to roughly approximate the behavior of a simplified system -which a real-life one never is, even a small countertop pendulum has major deviations from ideal- without appealing to a full-fledged simulation or in-depth study.
Stop condescending towards everyone already.
Your analysis is flawed. It is not a rough-order-of-magnitude analysis, it is simply wrong since the setup is wrong.
You're ignoring forces and traits that are first-order important, and then you go analyze the flawed system in great detail.
You're also ignoring common sense - the cables are flexible and in equilibrium, and once one of them is cut, the initial response will be a considerable transient slackening of tension. You don't know how long the transient lasts, and you don't know what these cables do once tension is relaxed.
It's what I told you before - it's a dynamic system and much more complex then you think it is. It is not a simple swinging pendulum starting at equilibrium.
Post by: Hobbes-22 on 12/04/2020 04:49 pm
The argument that spawned these derivations was that not just the failing cable set, but *all* structural cables were ready to yield at the slightest perturbation (while at the same time claiming poor maintenance was not to blame, but that's another story).
This was so much so, as to not allow for any workable "safe" (what that means isn't clear, especially when one contractor disagreed) graceful payload lowering, or reinforcement, plan to minimize damage or save the instrumentation. I would say not just the overload from the swing dynamics discussed here during the last few days, but also the violent shocks, jolts and vibrations throughout the 30-second event visible in the videos now available -which nevertheless allowed the cable bundles to survive even visible secondary bending under tension, induced by the access bridge until the tower tops snapped, beyond the straight line joining the towers- at the very least would make inquiring minds question that conclusion.
I think it's pretty clear from the collapse video where the risk was. Any work on the towers or cables to install new cables would place personnel and equipment in the vicinity of the existing cables. If a cable were to break during operations, the snapped cable would whiplash violently through nearby structures. Not to mention the concrete towers breaking up and obliterating everything underneath.
There was no way to relieve the load on the cables quickly. To achieve that, you'd need to:
1. dismantle the center section of the main dish.
2. build a tower capable of handling 800 tons, with a height of at least 450 ft, on a foundation strong enough to handle the combined weight.
3. Put hydraulics on that tower to lift the antenna platform.
This would take several months of ferrying specialized equipment to the site, building foundations, erecting the tower. All with an 800-ton Sword of Damocles hanging overhead.
When the antenna platform is jacked up, the main load is off the cables and they can be replaced one by one.
Quote
especially when one contractor disagreed
There's going to be a lot of headscratching, if not heads rolling, at that particular contractor, for misjudging the situation this badly.
Post by: ccdengr on 12/04/2020 04:52 pm
If people have hard evidence of anything different, I'd like to see it.
Post by: Blackstar on 12/04/2020 05:12 pm
Personally I think the site should become a museum. Clear out the wreckage and salvage key parts (if possible) for display; repair the dish and open to the public.
Unfortunately, it's in the middle of nowhere. I got lost heading out there (at one point my GPS was telling me to turn left at a point on the side of a mountain where there was no road and left would have sent me careening down into the forest). I don't think it makes much sense as a museum. Maybe a hiking trail. But I can almost guarantee that they will tear everything down and block the road and let nature reclaim it.
Addendum: go find it on Google Maps and look at it in satellite view, then pull out and look around. There's not much around there.
Post by: Frogstar_Robot on 12/04/2020 05:29 pm
Quoteespecially when one contractor disagreed
There's going to be a lot of headscratching, if not heads rolling, at that particular contractor, for misjudging the situation this badly.
To be fair, that contractor did not guarantee it could be safely repaired, since they recognized that collapse could occur anytime or even as a result of the remedial actions. Their proposal was more of a "there is a chance of success and we would like to try".
But I think you are right, they will be glad it's a contract they didn't win.
Post by: rubicondsrv on 12/04/2020 05:44 pm
But I think you are right, they will be glad it's a contract they didn't win.
That depends on how they wrote the contract. High risk contracts are often written to ensure payment for all work up until the failure.
as long as there was not a fatality in the failure, a collapse would not necessarily leave the contractor with a financial loss.
Post by: eeergo on 12/04/2020 06:06 pm
That said, you're totally wrong on your cable analysis...
In the starting conditions, since the cables are well above 45-degrees, the tension in them is higher than the mg of the load. So right there already, once a cable is disconnected, the acceleration in the direction into the remaining cables is higher than the acceleration downwards. Since additionally, downward motion doesn't stretch the cables 1:1 (again because of the angle), then it's obvious that initially the remaining cables will untension.
So with that assumption (ideally-rigid), you already robbed the system of probably it's most important trait. Your house of cards of the previous 10 posts is already on shaky foundations.
Then, we're talking about real-world cables. Once tension reduces, they begin to unwind. You have no idea what's going on at that point. Your calculation is not even wrong, it's just, well - of a different system.
Third, you assume "mass-less" cables. Are they? The payload weighs about 800 tons. How much do the cables weigh? It looks like there are 4 cables coming down from the tower towards the center, each 3-4 inches in diameter, about 150 m each, very roughly - heh, 800 tons. Give or take. So massless, they aren't.
So this other assumption pulls you even further from the system you're trying to calculate.
Then you conclude:QuoteBut the approximation is pretty darn accurate at this scale.
And I'm the one that's hand-waiving?! Methinks you QED'ed much too early.
Have you ever had to rough-order-of-magnitude estimate loads, or actually any quantity in a physical system? From your post you don't seem to understand how to roughly approximate the behavior of a simplified system -which a real-life one never is, even a small countertop pendulum has major deviations from ideal- without appealing to a full-fledged simulation or in-depth study.
Stop condescending towards everyone already.
Your analysis is flawed. It is not a rough-order-of-magnitude analysis, it is simply wrong since the setup is wrong.
You're ignoring forces and traits that are first-order important, and then you go analyze the flawed system in great detail.
You're also ignoring common sense - the cables are flexible and in equilibrium, and once one of them is cut, the initial response will be a considerable transient slackening of tension. You don't know how long the transient lasts, and you don't know what these cables do once tension is relaxed.
It's what I told you before - it's a dynamic system and much more complex then you think it is. It is not a simple swinging pendulum starting at equilibrium.
Fine: you wish to continue appealing to knowledge being esoteric when the system is clearly analyzable (heck, videogames like KSP can simulate its dynamics accurately without applying those factors, and I actually *predicted* the outcome seen in the video before it was released), at the same time claiming I'm going into too much detail, without actually providing any corrections or alternative input yourself, other than disparaging comments and now also snappy personal attacks?
Have a good one, believe what you will and enjoy it, I'm done - but please refrain from pontificating certainties when you assert you can't even begin to roughly analyze the system.
Post by: SimonFD on 12/05/2020 01:20 am
Personally I think the site should become a museum. Clear out the wreckage and salvage key parts (if possible) for display; repair the dish and open to the public.
Unfortunately, it's in the middle of nowhere. I got lost heading out there (at one point my GPS was telling me to turn left at a point on the side of a mountain where there was no road and left would have sent me careening down into the forest). I don't think it makes much sense as a museum. Maybe a hiking trail. But I can almost guarantee that they will tear everything down and block the road and let nature reclaim it.
Addendum: go find it on Google Maps and look at it in satellite view, then pull out and look around. There's not much around there.
I know. We drove there, driving on the wrong side of the road on the wrong side of the car that only had two pedals! I didn’t have sat nav, I had a paper map so of course took a wrong turn or two. Saved by my wife who has a much better sense of direction than I do.
Actually the Camuy caves are not too far away from there and they were well worth the visit too.
Also the landscape is incredible!
So don’t give me “there’s not much round there”! ::)
Post by: Blackstar on 12/05/2020 03:09 am
I know. We drove there, driving on the wrong side of the road on the wrong side of the car that only had two pedals! I didn’t have sat nav, I had a paper map so of course took a wrong turn or two. Saved by my wife who has a much better sense of direction than I do.
Actually the Camuy caves are not too far away from there and they were well worth the visit too.
Also the landscape is incredible!
So don’t give me “there’s not much round there”! ::)
Well, if you like forest, and unpaved roads, and abandoned cars, it's great.
Post by: Frogstar_Robot on 12/05/2020 09:39 am
Quote from: https://www.nationalacademies.org/our-work/decadal-survey-on-astronomy-and-astrophysics-2020-astro2020
The Astronomy and Astrophysics Decadal Survey (Astro2020) will develop a comprehensive research strategy and vision for a decade of transformative science at the frontiers of astronomy and astrophysics. Astro2020 continues to make progress in the era of COVID-19. The Steering Committee is holding all of its meetings virtually and has been engaging in a vigorous schedule of weekly telecons and multi-day meetings to continue its deliberative work. The rest of its meetings will be held in closed session. The goal remains to deliver the report in Spring 2021.
Post by: tpw2 on 12/05/2020 09:56 am
Anyone know what projects Astro2020 are considering? I guess an "Arecibo replacement" is not one of them.Quote from: https://www.nationalacademies.org/our-work/decadal-survey-on-astronomy-and-astrophysics-2020-astro2020The Astronomy and Astrophysics Decadal Survey (Astro2020) will develop a comprehensive research strategy and vision for a decade of transformative science at the frontiers of astronomy and astrophysics. Astro2020 continues to make progress in the era of COVID-19. The Steering Committee is holding all of its meetings virtually and has been engaging in a vigorous schedule of weekly telecons and multi-day meetings to continue its deliberative work. The rest of its meetings will be held in closed session. The goal remains to deliver the report in Spring 2021.
Anyone can (or could; the deadline has passed) submit whitepapers for consideration. You can find those under "Community Input". Of course, not all of the proposals are very widely supported or even technically feasible. The most relevant proposal for the future of radio astronomy in the US is probably the Next Generation VLA: http://surveygizmoresponseuploads.s3.amazonaws.com/fileuploads/623127/5043187/137-fe4771da409a7413465c9bb1cb579ae7_McKinnonMarkM.pdf
For space-based flagships there's a predetermined shortlist of four projects that are being studied in detail, but I don't think there's anything similar for ground-based ones.
Post by: Dizzy_RHESSI on 12/05/2020 12:57 pm
Anyone know what projects Astro2020 are considering? I guess an "Arecibo replacement" is not one of them.Quote from: https://www.nationalacademies.org/our-work/decadal-survey-on-astronomy-and-astrophysics-2020-astro2020The Astronomy and Astrophysics Decadal Survey (Astro2020) will develop a comprehensive research strategy and vision for a decade of transformative science at the frontiers of astronomy and astrophysics. Astro2020 continues to make progress in the era of COVID-19. The Steering Committee is holding all of its meetings virtually and has been engaging in a vigorous schedule of weekly telecons and multi-day meetings to continue its deliberative work. The rest of its meetings will be held in closed session. The goal remains to deliver the report in Spring 2021.
There's a searchable list of the 307 submitted APC white papers here:
https://jermity.gitlab.io/samples/astro2020_apc_white_papers.html
Not all of them are proposing new facilities or missions. Note that even though a white paper for a replacement will not have been submitted, a few of the white papers have mentioned the need for Arecibo because some communities were still trying to rescue it from NSF divestment. Aside from the ambitious ngVLA there was also a proposal for DSA-2000, which is much more modest. It would basically be a survey array but it would be very good a pulsar timing, which is probably the most significant area which will feel the loss of Arecibo.
Post by: meekGee on 12/05/2020 03:26 pm
That said, you're totally wrong on your cable analysis...
In the starting conditions, since the cables are well above 45-degrees, the tension in them is higher than the mg of the load. So right there already, once a cable is disconnected, the acceleration in the direction into the remaining cables is higher than the acceleration downwards. Since additionally, downward motion doesn't stretch the cables 1:1 (again because of the angle), then it's obvious that initially the remaining cables will untension.
...
Have you ever had to rough-order-of-magnitude estimate loads, or actually any quantity in a physical system? From your post you don't seem to understand how to roughly approximate the behavior of a simplified system -which a real-life one never is, even a small countertop pendulum has major deviations from ideal- without appealing to a full-fledged simulation or in-depth study.
...
You're ignoring forces and traits that are first-order important, and then you go analyze the flawed system in great detail.
You're also ignoring common sense - the cables are flexible and in equilibrium, and once one of them is cut, the initial response will be a considerable transient slackening of tension. You don't know how long the transient lasts, and you don't know what these cables do once tension is relaxed.
...
Fine: you wish to continue appealing to knowledge being esoteric when the system is clearly analyzable (heck, videogames like KSP can simulate its dynamics accurately without applying those factors, and I actually *predicted* the outcome seen in the video before it was released), at the same time claiming I'm going into too much detail, without actually providing any corrections or alternative input yourself, other than disparaging comments and now also snappy personal attacks?
Have a good one, believe what you will and enjoy it, I'm done - but please refrain from pontificating certainties when you assert you can't even begin to roughly analyze the system.
Well, I finally got around to watching Scott Manley's video with 1/4 speed video. (https://www.youtube.com/watch?v=59WQIRvezzI)
There is no doubt that during the collapse, the two remaining main cable groups (4 cables each) go slack.
They are not straight at all! Start at 8:40. The cable group on the right develops large amplitude waves in it, and the cable group on the left runs into the walkway and easily forms an angle, indicating very low tension, until it breaks the walkway and bounces back.
This leaves no doubt that the motion was as far from a pendulum swing as can be, and that the cable tension decreased, at least through most of the downward path.
Also, since the payload was such a large rigid body, even if the cables ever got tensioned again, the effect would be to spin the rigid body about itself, not to create a simple pendulum motion.
This means that your analysis is not a "simplification". The collapse was more of a slingshot than a pendulum. Two elastic members in tension, a third one releasing suddenly.
The elasticity of the cables if further accentuated by the fact that they are very far from "massless" - they tend to form a catenary arc that pulls the ends towards each other, essentially making the cables more "elastic".
--
Scott's analysis agrees btw: "As the platform begins to fall and is pulled sideways by the cable tension" (8:50)
Post by: Frogstar_Robot on 12/05/2020 04:24 pm
There is no doubt that during the collapse, the two remaining main cable groups (4 cables each) go slack.
They are not straight at all! Start at 8:40. The cable group on the right develops large amplitude waves in it, and the cable group on the left runs into the walkway and easily forms an angle, indicating very low tension, until it breaks the walkway and bounces back.
This leaves no doubt that the motion was as far from a pendulum swing as can be, and that the cable tension decreased, at least through most of the downward path.
Yes, I think your analysis is correct. It seems obvious to me that the remaining cables should reduce in tension when the first set breaks, although I appreciate it may be counter-intuitive. The KSP simulation shows it, the video of the actual collapse shows it. There's no need to rely on some faulty freshman physics here.
It's also an easy experiment to perform. You just need four soft mattresses, three pieces of rope, two willing colleagues, and a heavy weight. You will all fall backwards, once one of you let's go of the rope.
I hope there will be a forensic analysis of the cables, to see what was the cause of failure, as well as the residual strength. I guess it is possible that one set of cables was faulty, but it seems likely whatever the issue, it is was present in all the cables.
Post by: Blackstar on 12/05/2020 05:00 pm
"The closure of Arecibo, he said, will have “a slight negative impact” on NASA’s planetary defense work. NASA has another radar system at the Goldstone Observatory in California that can also be used for observing near Earth asteroids and other objects. The Goldstone radar is back in operation after recently installing a new klystron.
The Goldstone radar has some advantages over Arecibo, including being able to see more of the sky and finer resolution. However, Arecibo’s more powerful radar has a greater range, allowing it to observe more distant objects.
Another disadvantage for Goldstone is that it is located near restricted military airspace, which requires coordination for radar observations that can make it difficult to use for time-sensitive studies. Johnson said that process has improved somewhat.
Johnson argued that the closure of Arecibo presents an opportunity to examine the future of planetary radar systems. “It’s really time to be looking at the next generation of planetary radar capabilities,” he said. That’s likely to use arrays of smaller dishes rather than one monolithic dish, like Arecibo.
Old facilities, he added, are “high maintenance” and difficult to keep operate. “Technology has moved on from 30 years ago,” when Arecibo first got planetary radar capabilities, he said. “We need to take advantage of the new technologies.”
Post by: Eric Hedman on 12/05/2020 06:03 pm
https://spacenews.com/nasa-weighing-options-for-future-planetary-radar-capabilities-after-arecibo/Another interesting part of the article is this:
"The closure of Arecibo, he said, will have “a slight negative impact” on NASA’s planetary defense work. NASA has another radar system at the Goldstone Observatory in California that can also be used for observing near Earth asteroids and other objects. The Goldstone radar is back in operation after recently installing a new klystron.
The Goldstone radar has some advantages over Arecibo, including being able to see more of the sky and finer resolution. However, Arecibo’s more powerful radar has a greater range, allowing it to observe more distant objects.
Another disadvantage for Goldstone is that it is located near restricted military airspace, which requires coordination for radar observations that can make it difficult to use for time-sensitive studies. Johnson said that process has improved somewhat.
Johnson argued that the closure of Arecibo presents an opportunity to examine the future of planetary radar systems. “It’s really time to be looking at the next generation of planetary radar capabilities,” he said. That’s likely to use arrays of smaller dishes rather than one monolithic dish, like Arecibo.
Old facilities, he added, are “high maintenance” and difficult to keep operate. “Technology has moved on from 30 years ago,” when Arecibo first got planetary radar capabilities, he said. “We need to take advantage of the new technologies.”
"WASHINGTON — With the Arecibo radio telescope to be decommissioned, NASA is beginning to consider options for future planetary radar capabilities, including potential cooperation with the U.S. Space Force."
Post by: Star One on 12/05/2020 06:48 pm
Well they’ve talked about that for the Arecibo site.https://spacenews.com/nasa-weighing-options-for-future-planetary-radar-capabilities-after-arecibo/Another interesting part of the article is this:
"The closure of Arecibo, he said, will have “a slight negative impact” on NASA’s planetary defense work. NASA has another radar system at the Goldstone Observatory in California that can also be used for observing near Earth asteroids and other objects. The Goldstone radar is back in operation after recently installing a new klystron.
The Goldstone radar has some advantages over Arecibo, including being able to see more of the sky and finer resolution. However, Arecibo’s more powerful radar has a greater range, allowing it to observe more distant objects.
Another disadvantage for Goldstone is that it is located near restricted military airspace, which requires coordination for radar observations that can make it difficult to use for time-sensitive studies. Johnson said that process has improved somewhat.
Johnson argued that the closure of Arecibo presents an opportunity to examine the future of planetary radar systems. “It’s really time to be looking at the next generation of planetary radar capabilities,” he said. That’s likely to use arrays of smaller dishes rather than one monolithic dish, like Arecibo.
Old facilities, he added, are “high maintenance” and difficult to keep operate. “Technology has moved on from 30 years ago,” when Arecibo first got planetary radar capabilities, he said. “We need to take advantage of the new technologies.”
"WASHINGTON — With the Arecibo radio telescope to be decommissioned, NASA is beginning to consider options for future planetary radar capabilities, including potential cooperation with the U.S. Space Force."
Post by: eeergo on 12/06/2020 10:51 am
There is no doubt that during the collapse, the two remaining main cable groups (4 cables each) go slack.
They are not straight at all! Start at 8:40. The cable group on the right develops large amplitude waves in it, and the cable group on the left runs into the walkway and easily forms an angle, indicating very low tension, until it breaks the walkway and bounces back.
This leaves no doubt that the motion was as far from a pendulum swing as can be, and that the cable tension decreased, at least through most of the downward path.
Yes, I think your analysis is correct. It seems obvious to me that the remaining cables should reduce in tension when the first set breaks, although I appreciate it may be counter-intuitive. The KSP simulation shows it, the video of the actual collapse shows it. There's no need to rely on some faulty freshman physics here.
It's also an easy experiment to perform. You just need four soft mattresses, three pieces of rope, two willing colleagues, and a heavy weight. You will all fall backwards, once one of you let's go of the rope.
I hope there will be a forensic analysis of the cables, to see what was the cause of failure, as well as the residual strength. I guess it is possible that one set of cables was faulty, but it seems likely whatever the issue, it is was present in all the cables.
Popping in to stop willful misinterpretations of my words right there: the INITIAL release in tension is mentioned (and obvious, and transient, and irrelevant) in my analysis, and is one of the points I've clarified over and over. No need to appeal to strawmen, no "faulty" physics at play, since the overloads would happen when the pendular motion is well established, peaking near its end - just before the "waves" develop on the cables, which only form once the towers give, beyond the bisector line between the two towers, i.e. when the dome has already detached and the upper truss is starting to contact the dish.
It's also interesting how it's concluded the cables were slack but the rigid-body platform got rotated to vertical and the dish fell off it. My freshman physics must be really faulty.
It's trivial to calculate what horizontal velocity an instantaneous acceleration equal to the two sets of cables' initial tension would effect on the 800-tonne platform (which anyway would be mostly absorbed by the truss', and tower's, elasticity), and see a "slingshot" effect is preposterous to propose.
It seems this thread has been taken over by an agenda, not bothering to address the points presented or provide alternative calculations, just conceptual esoterism and video "interpretation" - but please, go on agreeing with your foregone conclusions; as I said before, I'm done. Just quit ignoring the content in my posts, which I wrote as detailedly and unambiguously as possible, to then refer to them.
Post by: eeergo on 12/06/2020 08:53 pm
https://twitter.com/LIGO/status/1335586098458865667
Post by: eeergo on 12/23/2020 11:58 am
https://twitter.com/FYIscipolicy/status/1341166030694080516
Meanwhile the WH petition to rebuild the facility has surpassed the 100000-signatures mark.
Post by: captainoverboard on 12/23/2020 12:24 pm
I realize there would be difficulties, but surely as with Hubble, JWST and so forth, we ought to be able to solve them.
https://satelliteobservation.net/2017/09/24/a-radiotelescope-in-the-sky-the-usa-202-orion-satellite/
Post by: donaldp on 12/23/2020 12:52 pm
I'm very sad we have lost Arecibo, but I wonder if it's not time to move on from Earth bound radio telescopes. We have moderately large antennas on Satellites now. This article seems to show COTS antenna in the 50 Meter range. While I'm familiar with the inverse square law and I know that the Arecibo 300 meter antenna is a very important feature, it would seem to me that if we can get 50 meters regularly in space, we could, either by launching a few 50 meters and operating them at L1/l2 in a formation, or by scaling up whatever we do for 50 meters to 500 meters, have a more sensitive device that is actually not attenuated by atmosphere.
I realize there would be difficulties, but surely as with Hubble, JWST and so forth, we ought to be able to solve them.
https://satelliteobservation.net/2017/09/24/a-radiotelescope-in-the-sky-the-usa-202-orion-satellite/
I'm fairly certain that you don't need large space based radio telescopes for astronomy or even large dish radio telescopes on earth. With current technology the way to go is to use large arrays of smaller dishes such as the very large array https://public.nrao.edu/telescopes/vla/
The link you have seems to be related to spy satalites where you do need a large array to pick up weak signals on earth from space.
You only really need large optical telescopes in space as it's then that the atmosphere causes real issues. With the possible era of starship it may well become much cheaper to launch large optical telescopes into space without going to the hugh expense of the James Webb Telescope. https://www.nasa.gov/mission_pages/webb/main/index.html
Post by: Hobbes-22 on 12/23/2020 12:53 pm
There's been some speculation about very large parabolic antennas on some SIGINT satellites (50-100 m range).
Putting an antenna array in space has its own problems (the distance between the antennas becomes variable, making it harder to do phase matching between the antennas).
For the time being, putting stuff into space is vastly more expensive than building the same capability on Earth. An additional problem to building an Arecibo-class observatory in space is that Arecibo had a 1-MW radar transmitter, it's difficult to generate that much power in a satellite.
Post by: Cherokee43v6 on 12/23/2020 01:10 pm
I'm very sad we have lost Arecibo, but I wonder if it's not time to move on from Earth bound radio telescopes. We have moderately large antennas on Satellites now. This article seems to show COTS antenna in the 50 Meter range. While I'm familiar with the inverse square law and I know that the Arecibo 300 meter antenna is a very important feature, it would seem to me that if we can get 50 meters regularly in space, we could, either by launching a few 50 meters and operating them at L1/l2 in a formation, or by scaling up whatever we do for 50 meters to 500 meters, have a more sensitive device that is actually not attenuated by atmosphere.
I realize there would be difficulties, but surely as with Hubble, JWST and so forth, we ought to be able to solve them.
https://satelliteobservation.net/2017/09/24/a-radiotelescope-in-the-sky-the-usa-202-orion-satellite/
I'm fairly certain that you don't need large space based radio telescopes for astronomy or even large dish radio telescopes on earth. With current technology the way to go is to use large arrays of smaller dishes such as the very large array https://public.nrao.edu/telescopes/vla/
The link you have seems to be related to spy satalites where you do need a large array to pick up weak signals on earth from space.
You only really need large optical telescopes in space as it's then that the atmosphere causes real issues. With the possible era of starship it may well become much cheaper to launch large optical telescopes into space without going to the hugh expense of the James Webb Telescope. https://www.nasa.gov/mission_pages/webb/main/index.html
I'd put one caveat on that.
Placing radiotelescopes on the Lunar Farside would be effective. Namely because the bulk of the Moon would then block most Earth based signal interference.
Post by: edzieba on 12/23/2020 02:14 pm
Post by: Nomadd on 12/23/2020 03:47 pm
Placing radiotelescopes on the Lunar Farside would be effective. Namely because the bulk of the Moon would then block most Earth based signal interference.People do tend to forget that reducing the N is just as important as increasing the S. With some of the ludicrously low noise front ends they have now, blocking out Earth noise could get some nice results.
Post by: Blackstar on 12/23/2020 04:02 pm
Arecibo was irreplaceable in its capability as a space RADAR system.
It was not "irreplaceable"
There are other ways to do it. Goldstone already has a radar, and there are other concepts that have been proposed. There are tradeoffs to any option.
Post by: Star One on 12/23/2020 04:05 pm
Still not as effective as placing it on the lunar far side. Which I believe is also an ideal site if you doing SETI related work.Placing radiotelescopes on the Lunar Farside would be effective. Namely because the bulk of the Moon would then block most Earth based signal interference.People do tend to forget that reducing the N is just as important as increasing the S. With some of the ludicrously low noise front ends they have now, blocking out Earth noise could get some nice results.
Post by: libra on 12/23/2020 04:40 pm
FWIW, Appropriations Bill contains language to study rebuilding at the site and a field a report on the "causes and extent of the damage", hopefully will be made public.
https://twitter.com/FYIscipolicy/status/1341166030694080516
Meanwhile the WH petition to rebuild the facility has surpassed the 100000-signatures mark.
After Notre Dame de Paris went up in smoke 18 months ago (seems to be two centuries ago) President Macron said
"Cette cathédrale, nous la reconstruirons"
also applies to Arecibo "That cathedral for astronomy, we will rebuild it"."
Post by: Alpha_Centauri on 12/23/2020 05:00 pm
We've already established that Arecibo is a technology of the past that would be done differently today, nor would it sufficiently address current scientific priorities to justify the expense. We should not throw good money after bad for the sake of sentiment.
Post by: Nomadd on 12/23/2020 05:37 pm
There is no place for sentiment in science. You move forward by building the best instrument to address current or anticipated scientific problems. It's not a jobs programme, or a cultural monument, it is a tool of scientific inquiry.
We've already established that Arecibo is a technology of the past that would be done differently today, nor would it sufficiently address current scientific priorities to justify the expense. We should not throw good money after bad for the sake of sentiment.
Except for the minor fact that many if not most scientific endeavors now days wouldn't exist if not for sentiment and jobs programs. The money is procured by people, most of whom wouldn't know a photon from a hole in the ground.
Failing to get a project off the ground because of refusal to acknowledge the motivations of the people who pay for it doesn't advance anything.
Post by: Mark K on 12/23/2020 06:01 pm
There is no place for sentiment in science. You move forward by building the best instrument to address current or anticipated scientific problems. It's not a jobs programme, or a cultural monument, it is a tool of scientific inquiry.
We've already established that Arecibo is a technology of the past that would be done differently today, nor would it sufficiently address current scientific priorities to justify the expense. We should not throw good money after bad for the sake of sentiment.
Except for the minor fact that many if not most scientific endeavors now days wouldn't exist if not for sentiment and jobs programs. The money is procured by people, most of whom wouldn't know a photon from a hole in the ground.
Failing to get a project off the ground because of refusal to acknowledge the motivations of the people who pay for it doesn't advance anything.
I agree and to add my opinion - science is nothing BUT a "cultural monument.". Humans do not need scientific research to live. Purely Bible flat earthers or other anti-science hard liners can have a very functional and perhaps "more successful" society than one that spends a lot on scientific research. It can help us live better and to paraphrase Leon Lederman among others it helps make life worth living. Thus emotional reasons to spend money on research are essential.
Post by: Alpha_Centauri on 12/23/2020 06:21 pm
Except for the minor fact that many if not most scientific endeavors now days wouldn't exist if not for sentiment and jobs programs.
Which current scientific endeavour are you talking about that has nothing to do with the science but is just rebuilding something for the sake of it/jobs? I'm struggling to think of one.
The money is procured by people, most of whom wouldn't know a photon from a hole in the ground.
Yes, that's why we have scientific advisors to inform leaders about what our current priorities are.
Failing to get a project off the ground because of refusal to acknowledge the motivations of the people who pay for it doesn't advance anything.
What project is not getting off the ground because we're not going to rebuild something at great cost for relatively little scientific benefit?
Post by: Star One on 12/23/2020 06:45 pm
It’s partly the attitude you’re displaying here that explains why politicians don’t always listen to their scientific advisors. It’s not just the message but how it’s delivered. And delivery is all about going beyond pure science.Except for the minor fact that many if not most scientific endeavors now days wouldn't exist if not for sentiment and jobs programs.
Which current scientific endeavour are you talking about that has nothing to do with the science but is just rebuilding something for the sake of it/jobs? I'm struggling to think of one.The money is procured by people, most of whom wouldn't know a photon from a hole in the ground.
Yes, that's why we have scientific advisors to inform leaders about what our current priorities are.Failing to get a project off the ground because of refusal to acknowledge the motivations of the people who pay for it doesn't advance anything.
I'm sorry, what project is not getting off the ground because we're not going to rebuild something at great cost for relatively little scientific benefit?
Post by: Alpha_Centauri on 12/23/2020 06:50 pm
It’s partly the attitude you’re displaying here that explains why politicians don’t always listen to their scientific advisors. It’s not just the message but how it’s delivered. And delivery is all about going beyond pure science.
So in other words you can't actually answer my reasonable questions.
Post by: Eric Hedman on 12/23/2020 07:43 pm
It’s partly the attitude you’re displaying here that explains why politicians don’t always listen to their scientific advisors. It’s not just the message but how it’s delivered. And delivery is all about going beyond pure science.There is another reason politicians don't listen to their science advisors. Several years ago when Jim Sensenbrenner was chairman of the house science committee he told me something I'll never forget. He said that on almost every issue they dealt with a group of three or four experts would come in and testify on a science issue the government needed to address. These people would each have one or more PhD from a prestigious university. They would have a stack of books and articles they had published on the issue and tell them what they should do. When they would leave another group with equally impressive credentials would come in and tell them the exact opposite of what the first group had told them. He said this would cover things like the validity or the priority of the issue. Scientists can be as political as everyone else.
Post by: whitelancer64 on 12/23/2020 08:22 pm
It’s partly the attitude you’re displaying here that explains why politicians don’t always listen to their scientific advisors. It’s not just the message but how it’s delivered. And delivery is all about going beyond pure science.There is another reason politicians don't listen to their science advisors. Several years ago when Jim Sensenbrenner was chairman of the house science committee he told me something I'll never forget. He said that on almost every issue they dealt with a group of three or four experts would come in and testify on a science issue the government needed to address. These people would each have one or more PhD from a prestigious university. They would have a stack of books and articles they had published on the issue and tell them what they should do. When they would leave another group with equally impressive credentials would come in and tell them the exact opposite of what the first group had told them. He said this would cover things like the validity or the priority of the issue. Scientists can be as political as everyone else.
Ugh, sadly true. You can cobble together a group of 5 "distinguished scientists" that don't believe in "X thing" and have them make a convincing-sounding argument to a group of politicians. Nevermind the 10,000 other scientists that know "X thing" is happening. This happens for so many different topics.
Post by: whitelancer64 on 12/23/2020 10:00 pm
It’s partly the attitude you’re displaying here that explains why politicians don’t always listen to their scientific advisors. It’s not just the message but how it’s delivered. And delivery is all about going beyond pure science.There is another reason politicians don't listen to their science advisors. Several years ago when Jim Sensenbrenner was chairman of the house science committee he told me something I'll never forget. He said that on almost every issue they dealt with a group of three or four experts would come in and testify on a science issue the government needed to address. These people would each have one or more PhD from a prestigious university. They would have a stack of books and articles they had published on the issue and tell them what they should do. When they would leave another group with equally impressive credentials would come in and tell them the exact opposite of what the first group had told them. He said this would cover things like the validity or the priority of the issue. Scientists can be as political as everyone else.
Ugh, sadly true. You can cobble together a group of 5 "distinguished scientists" that don't believe in "X thing" and have them make a convincing-sounding argument to a group of politicians. Nevermind the 10,000 other scientists that know "X thing" is happening. This happens for so many different topics.
Yeah. It's too bad that there's no way that the science community forms a consensus on science priorities that is then provided to the government.
For NASA, they kinda do. The Decadal Survey. Granted, not everything proposed by the Survey is accepted or acted upon by Congress, but that could be a model for other areas of goverance... Also, it would take a lot of work to get that kind of framework in place for other agencies. Most aren't anywhere nearly as science-focused as NASA is.
I fear this is veering off-topic though.
Post by: Zed_Noir on 12/24/2020 02:00 am
Post by: tpw2 on 12/24/2020 06:13 am
It’s partly the attitude you’re displaying here that explains why politicians don’t always listen to their scientific advisors. It’s not just the message but how it’s delivered. And delivery is all about going beyond pure science.There is another reason politicians don't listen to their science advisors. Several years ago when Jim Sensenbrenner was chairman of the house science committee he told me something I'll never forget. He said that on almost every issue they dealt with a group of three or four experts would come in and testify on a science issue the government needed to address. These people would each have one or more PhD from a prestigious university. They would have a stack of books and articles they had published on the issue and tell them what they should do. When they would leave another group with equally impressive credentials would come in and tell them the exact opposite of what the first group had told them. He said this would cover things like the validity or the priority of the issue. Scientists can be as political as everyone else.
Ugh, sadly true. You can cobble together a group of 5 "distinguished scientists" that don't believe in "X thing" and have them make a convincing-sounding argument to a group of politicians. Nevermind the 10,000 other scientists that know "X thing" is happening. This happens for so many different topics.
Yeah. It's too bad that there's no way that the science community forms a consensus on science priorities that is then provided to the government.
For NASA, they kinda do. The Decadal Survey. Granted, not everything proposed by the Survey is accepted or acted upon by Congress, but that could be a model for other areas of goverance... Also, it would take a lot of work to get that kind of framework in place for other agencies. Most aren't anywhere nearly as science-focused as NASA is.
I fear this is veering off-topic though.
Decadal survey is not NASA only. It also gives recommendations for ground-based astronomy. The problem is that the budget for NSF/Astro, which is the main (public) funding source for ground-based astronomy in the US, has been flat or declining for a long time. Out of the recommended list in the last decadal, only the Vera C. Rubin Observatory (LSST) has been able to get any significant funding from NSF.
Outside of astronomy, I think that some sort of long-term planning process with extensive community input is also used in HEP.
Post by: Star One on 12/24/2020 06:41 am
Of course they can. It was certainly the case at my university that you could almost tell someone’s politics by their discipline. I think in some cases we’ve seen that this year in various countries of politicians disengaging from their advisors for both these reasons, plus others and unfortunately that’s come with a heavy and more than academic cost.It’s partly the attitude you’re displaying here that explains why politicians don’t always listen to their scientific advisors. It’s not just the message but how it’s delivered. And delivery is all about going beyond pure science.There is another reason politicians don't listen to their science advisors. Several years ago when Jim Sensenbrenner was chairman of the house science committee he told me something I'll never forget. He said that on almost every issue they dealt with a group of three or four experts would come in and testify on a science issue the government needed to address. These people would each have one or more PhD from a prestigious university. They would have a stack of books and articles they had published on the issue and tell them what they should do. When they would leave another group with equally impressive credentials would come in and tell them the exact opposite of what the first group had told them. He said this would cover things like the validity or the priority of the issue. Scientists can be as political as everyone else.
Post by: Star One on 12/28/2020 04:02 pm
Quote
NASA recently gave out a new round of grants for its favourite up and coming innovative space projects. One of which is a plan to fit a 1 km radio telescope inside a crater on the far side of the Moon, the largest radio telescope in the Solar System https://buff.ly/2xaypqJ
https://www.nasa.gov/directorates/spacetech/niac/2020_Phase_I_Phase_II/lunar_crater_radio_telescope/
Post by: eeergo on 12/28/2020 05:11 pm
Post by: RoadWithoutEnd on 12/28/2020 05:36 pm
It was not "irreplaceable"
There are other ways to do it. Goldstone already has a radar, and there are other concepts that have been proposed. There are tradeoffs to any option.
This is a very important thing to say. I'm bothered by the learned helplessness of so much of the commentary surrounding Arecibo's demise. People don't talk about it like a tool made in living memory, they talk about it like a pyramid built by some mysterious and impossibly lavish ancient civilization. Meanwhile it's a rounding error in the cost overruns of programs that shall remain nameless.
As far as I'm concerned, the proper response to "What should replace Arecibo?" is "Five."
Or at least, that's the proper attitude.
Post by: Frogstar_Robot on 12/28/2020 06:34 pm
It was not "irreplaceable"
There are other ways to do it. Goldstone already has a radar, and there are other concepts that have been proposed. There are tradeoffs to any option.
This is a very important thing to say. I'm bothered by the learned helplessness of so much of the commentary surrounding Arecibo's demise. People don't talk about it like a tool made in living memory, they talk about it like a pyramid built by some mysterious and impossibly lavish ancient civilization. Meanwhile it's a rounding error in the cost overruns of programs that shall remain nameless.
As far as I'm concerned, the proper response to "What should replace Arecibo?" is "Five."
Or at least, that's the proper attitude.
Indeed, I find it hugely ironic that Arecibo is equated to a cathedral, as if we built a monument to the Gods of Science, and they blessed us with their Scientific Wisdom. Maybe the Gods of Science became angry, because our worship was insufficient, and now we must build bigger monuments and worship more!
The Arecibo Telescope was a tool we built for a purpose. Whether we still need such a tool or whether the money is better spent elsewhere should be subject of rational discussion, not sentiment.
Post by: Blackstar on 12/28/2020 07:44 pm
However, what you should keep in mind is that the decadal surveys prioritize science, not instruments. They start from the premise that certain scientific questions are the highest priorities, and then proceed to the issue of how to answer those questions. So they will be asking those questions that were related to the work that Arecibo did, and then they'll be coming up with ways of answering those questions that may not require a device like Arecibo but some different instrument entirely. To give you an example, one of the limitations of radar astronomy for characterizing near Earth objects is that the US had two radars (Goldstone and Arecibo) in the northern hemisphere and none in the southern hemisphere. This limited how much sky can be observed.* So if the question for radar astronomy is "What is the best way to conduct it to achieve science goals X, Y, and Z," the implementation may suggest that a planetary radar in Australia is a better way to do it than another one (like Arecibo) in the northern hemisphere.
Now there are all kinds of related political and policy issues. For instance, is there another government agency that is willing to pay some money for that capability? What are their priorities? A hypothetical is that maybe Space Force wants a radar too, but wants it in the southern hemisphere. That may tip the scale in favor of that solution.
*Caveat: radar astronomy for NEO characterization is more of an application (to planetary defense) than a science question. But for the sake of this example, we'll pretend that it's a science question
Post by: Lee Jay on 12/28/2020 08:10 pm
I'm very sad we have lost Arecibo, but I wonder if it's not time to move on from Earth bound radio telescopes. We have moderately large antennas on Satellites now. This article seems to show COTS antenna in the 50 Meter range. While I'm familiar with the inverse square law and I know that the Arecibo 300 meter antenna is a very important feature, it would seem to me that if we can get 50 meters regularly in space, we could, either by launching a few 50 meters and operating them at L1/l2 in a formation, or by scaling up whatever we do for 50 meters to 500 meters, have a more sensitive device that is actually not attenuated by atmosphere.
I realize there would be difficulties, but surely as with Hubble, JWST and so forth, we ought to be able to solve them.
One of those difficulties is the 1 megawatt radar transmitter formally on Arecibo.
http://www.naic.edu/~nolan/radar/
Kind of hard to do in space. Not impossible but that's a big solar array to launch and have to point at the sun. For reference, that's about 10 times as much solar as is on ISS.
Post by: Nomadd on 12/28/2020 10:25 pm
ISS is about 240kw of solar cells and radar power is peak, not average. I don't know the specifics of Arecibo, but a 1MW radar usually puts out about 1KW average rf, or only has a 1/1000 duty cycle. The most efficient radar I've known, assuming they scale linearly, would take about 2KW input to put out 1MW pulses. Less than a clothes dryer.I'm very sad we have lost Arecibo, but I wonder if it's not time to move on from Earth bound radio telescopes. We have moderately large antennas on Satellites now. This article seems to show COTS antenna in the 50 Meter range. While I'm familiar with the inverse square law and I know that the Arecibo 300 meter antenna is a very important feature, it would seem to me that if we can get 50 meters regularly in space, we could, either by launching a few 50 meters and operating them at L1/l2 in a formation, or by scaling up whatever we do for 50 meters to 500 meters, have a more sensitive device that is actually not attenuated by atmosphere.
I realize there would be difficulties, but surely as with Hubble, JWST and so forth, we ought to be able to solve them.
One of those difficulties is the 1 megawatt radar transmitter formally on Arecibo.
http://www.naic.edu/~nolan/radar/
Kind of hard to do in space. Not impossible but that's a big solar array to launch and have to point at the sun. For reference, that's about 10 times as much solar as is on ISS.
Arecibo used lower frequency and I don't know how long the pulses were, what the duty cycle was or if it had big capacitor banks, but steady state input had to be quite a bit under peak power in any case.
Post by: AnalogMan on 12/28/2020 11:40 pm
430 MHz Radar
Max total peak pulse output power at transmitter output 2.5 MW
Max duty factor 6%
Max average power at transmitter output 150 KW
Klystron efficiencies 44% - 48%
Power supply max output rating 120,000 V @ 4.4A (528 kW) (37.2µF capacitor bank!)
ERIP: 2 MW with 62dB antenna gain = 3.2 TW peak, or max average @ 6% duty cycle of 224,000 MW
Beamwidth 0.13 degrees
S-Band 2.380 GHz Radar
Peak and Average power output of transmitter 1 MW
EIRP: 1 MW with 74dB antenna gain = 25 TW
Beamwidth 0.032 degrees
46.8 MHz Radar
Transmitter max output 40 kW peak and 2 kW average
EIRP 40 KW with 37dB antenna gain = 200,000 kW peak, 10,000 kW average
Beamwidth 1.2 degrees
Post by: Lee Jay on 12/29/2020 04:08 pm
S-Band 2.380 GHz Radar
Peak and Average power output of transmitter 1 MW
EIRP: 1 MW with 74dB antenna gain = 25 TW
Beamwidth 0.032 degrees
I assume they also used this for warming up frozen dinners. Quickly.
Post by: edzieba on 12/30/2020 01:49 pm
In a budgetary sense, it's not so easy. Funds just to keep Arecibo operating were always slim and had been shrinking for decades, and it got built in the first place because of a weird and transient confluence of need for and budget for a re-entry aeronomy observatory and enough people linked to that project who also had astronomy background and sufficient influence to dual-purpose the facility. Even a naïve adjust-for-inflation estimate for rebuilding Arecibo would be on the order of $100m, not counting clearing up the existing debris or any desired design changes.
Post by: LouScheffer on 01/02/2021 12:24 am
the implementation may suggest that a planetary radar in Australia is a better way to do it than another one (like Arecibo) in the northern hemisphere.Furthermore, the implementation may suggest a phased array transmitter instead of a giant dish. In this case, the siting requirements would be quite different - best would be a large flat area in a mostly dry region, as opposed to an existing crater in a rain forest.
Post by: Blackstar on 01/02/2021 02:41 am
area in a mostly dry region, as opposed to an existing crater in a rain forest.
When I was at Arecibo I was surprised to find out that it's not a rain forest. It doesn't meet the definition in terms of precipitation. Not a jungle either. Just a forest.
Post by: LouScheffer on 01/02/2021 03:38 am
I once talked to a radar technician who was working in the far north. He said they would warm their hands by sticking them in the transmit horn.S-Band 2.380 GHz RadarI assume they also used this for warming up frozen dinners. Quickly.
Peak and Average power output of transmitter 1 MW
EIRP: 1 MW with 74dB antenna gain = 25 TW
Beamwidth 0.032 degrees
Post by: vjkane on 01/02/2021 01:34 pm
I once talked to a radar technician who was working in the far north. He said they would warm their hands by sticking them in the transmit horn.From Wikipedia: "In 1925, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a chocolate bar he had in his pocket. The first food deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters."
Post by: Star One on 01/07/2021 03:33 pm
https://youtu.be/uY7hpdc8Xso
Post by: Dalhousie on 01/07/2021 09:14 pm
I once talked to a radar technician who was working in the far north. He said they would warm their hands by sticking them in the transmit horn.From Wikipedia: "In 1925, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a chocolate bar he had in his pocket. The first food deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters."
People work working with high powered microwave radar in 1925?
Post by: pochimax on 01/07/2021 09:36 pm
I think it is very important to mantain this current location because we will loose an importante VLBI point (with bridge VLBI baselines between North America and Europe and between North and South)the implementation may suggest that a planetary radar in Australia is a better way to do it than another one (like Arecibo) in the northern hemisphere.Furthermore, the implementation may suggest a phased array transmitter instead of a giant dish. In this case, the siting requirements would be quite different - best would be a large flat area in a mostly dry region, as opposed to an existing crater in a rain forest.
Post by: Frogstar_Robot on 01/07/2021 09:47 pm
I once talked to a radar technician who was working in the far north. He said they would warm their hands by sticking them in the transmit horn.From Wikipedia: "In 1925, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a chocolate bar he had in his pocket. The first food deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters."
People work working with high powered microwave radar in 1925?
Yeah that's a typo, should be 1945. :)
Post by: tpw2 on 01/14/2021 04:24 pm
The plan for a replacement sounds ambitious, to put it nicely.
Post by: Star One on 01/15/2021 03:34 pm
I know this is a military project but this is the kind of thing I am talking about.
https://www.newscenter1.tv/b-21-industry-forum-held-for-local-construction-manufacturing-businesses/pic/458488/
Post by: Frogstar_Robot on 01/15/2021 04:57 pm
I’d rather a system be developed where proposers of such projects don’t just have to demonstrate their science benefits but also the benefits to the areas where they are located.
I completely disagree - with the following exception - if the developers of multi-billion dollar social or economic projects are required to demonstrate what benefits to science their project has.
It's bad enough that science has to compete for funds with billion dollar social programs, without jumping through further hoops.
I'm pretty sure most people only regard the former Arecibo telescope as "iconic" since it appeared in a couple of big movies. Without those movies, virtually no one would have heard of it, nor would they care about it.
Post by: eeergo on 01/15/2021 06:58 pm
I’d rather a system be developed where proposers of such projects don’t just have to demonstrate their science benefits but also the benefits to the areas where they are located.
I completely disagree - with the following exception - if the developers of multi-billion dollar social or economic projects are required to demonstrate what benefits to science their project has.
It's bad enough that science has to compete for funds with billion dollar social programs, without jumping through further hoops.
I'm pretty sure most people only regard the former Arecibo telescope as "iconic" since it appeared in a couple of big movies. Without those movies, virtually no one would have heard of it, nor would they care about it.
Virtually nobody would care for it being the place:
- where Humanity's first message to the stars was beamed from.
- which detected the first solid evidence from.GWs.
- which found the first exoplanet.
- which cartographed asteroids and even Venus' surface with unprecedended detail, in most cases unmatched.
- which advanced the currently red-hot field of FSBs.
Among the other myriad of less 'wowing' topics it uniquely researched on that professionals en-masse do not care about in the slightest.
As for the socioeconomic factors, it sure must be nice up there in the ivory tower. Surprising how "science" is so important in your statements now, when the lost science because of this debacle was just an unfortunate collateral victim a few weeks ago.
Post by: Star One on 01/15/2021 07:10 pm
I’d rather a system be developed where proposers of such projects don’t just have to demonstrate their science benefits but also the benefits to the areas where they are located.
I completely disagree - with the following exception - if the developers of multi-billion dollar social or economic projects are required to demonstrate what benefits to science their project has.
It's bad enough that science has to compete for funds with billion dollar social programs, without jumping through further hoops.
I'm pretty sure most people only regard the former Arecibo telescope as "iconic" since it appeared in a couple of big movies. Without those movies, virtually no one would have heard of it, nor would they care about it.
I don’t think if you asked the average person from Puerto Rico they would be so sanguine about not considering the economic and social benefits
Post by: Alpha_Centauri on 01/15/2021 08:05 pm
A long article on Science: https://www.sciencemag.org/news/2021/01/how-famed-arecibo-telescope-fell-and-how-it-might-rise-again
The plan for a replacement sounds ambitious, to put it nicely.
Clearly the thing to do when a difficult-to-maintain instrument spontaneously goes kaput is to design a massive hydraulic bench to replace it. :o
Quote
The extreme tilt was designed to bring an important target within view: the supermassive black hole that sits in the galactic center.
This kind of emphasises Blackstar's point from earlier; one issue with a replacement at Arecibo is that it's simply in the wrong place from a scientific standpoint.
Post by: tpw2 on 01/16/2021 06:39 am
A long article on Science: https://www.sciencemag.org/news/2021/01/how-famed-arecibo-telescope-fell-and-how-it-might-rise-again
The plan for a replacement sounds ambitious, to put it nicely.
Clearly the thing to do when a difficult-to-maintain instrument spontaneously goes kaput is to design a massive hydraulic bench to replace it. :o
But it would look great. Definitely good potential to become iconic.
Post by: Blackstar on 01/16/2021 12:54 pm
A long article on Science: https://www.sciencemag.org/news/2021/01/how-famed-arecibo-telescope-fell-and-how-it-might-rise-again
The plan for a replacement sounds ambitious, to put it nicely.
A nice graphic from that article.
https://science.sciencemag.org/content/sci/371/6526/225/F1.large.jpg
Post by: vjkane on 01/16/2021 06:14 pm
https://www.nationalacademies.org/event/01-20-2021/planetary-science-and-astrobiology-decadal-survey-2023-2032-panel-on-small-solar-system-bodies-meeting-seven (https://www.nationalacademies.org/event/01-20-2021/planetary-science-and-astrobiology-decadal-survey-2023-2032-panel-on-small-solar-system-bodies-meeting-seven)
Post by: Dizzy_RHESSI on 01/18/2021 04:22 pm
A long article on Science: https://www.sciencemag.org/news/2021/01/how-famed-arecibo-telescope-fell-and-how-it-might-rise-again
The plan for a replacement sounds ambitious, to put it nicely.
Clearly the thing to do when a difficult-to-maintain instrument spontaneously goes kaput is to design a massive hydraulic bench to replace it. :o
Indeed. I think a massive moving platform is a non-starter, it represents a huge technical risk. There have been a few small Stewart platform telescopes, like the Hexapod Telescope, but nothing like this. The largest such telescope is AMiBA, which is just a 6 meter platform. A few CMB and far infrared concepts have flirted with Stewart platforms, but went no further. If they're just talking about having the platform move north-south, then the same increase in sky access can be done with simple single axis mounts in a system like the PUMA study. Going with a single mount for many antennas just seems backwards. It also seems odd to restrict the baseline to the original 300 meters at the cost of science, but I guess this is driven by their choice of mount. It's hard to tell because the white paper doesn't seem to be public, but it does appear that these odd design choices are being driven so that it has the same form factor as Arecibo. Trading form over function is a bad deal.
https://www.puma.bnl.gov/
NSF didn't want to continue funding just the operations of Arecibo, it doesn't seem like this proposal takes that to heart as it will certainly be more expensive to maintain a huge mechanism in the humid climate. With the NSF astronomy budget in it's current state it's very unlikely to be funded. At the end of the day it seems like a very expensive incremental facility.
Post by: Nomadd on 01/18/2021 04:36 pm
Post by: Blackstar on 01/18/2021 05:52 pm
I volunteer to wander around Ecuador, lugging an overpriced signal strength analyzer, looking for the perfect rf conditions for a new site. Actually did something like that in Congo-Brazzaville in the 90s.
Make sure to bring a bullwhip, a fedora, and a monkey.
Post by: Robotbeat on 01/19/2021 12:22 am
Green Bank Telescope is 100m and fully steerable. Let's do 300m. Let us never dream small dreams. :)A long article on Science: https://www.sciencemag.org/news/2021/01/how-famed-arecibo-telescope-fell-and-how-it-might-rise-again
The plan for a replacement sounds ambitious, to put it nicely.
Clearly the thing to do when a difficult-to-maintain instrument spontaneously goes kaput is to design a massive hydraulic bench to replace it. :o
Indeed. I think a massive moving platform is a non-starter, it represents a huge technical risk. There have been a few small Stewart platform telescopes, like the Hexapod Telescope, but nothing like this. The largest such telescope is AMiBA, which is just a 6 meter platform. A few CMB and far infrared concepts have flirted with Stewart platforms, but went no further. If they're just talking about having the platform move north-south, then the same increase in sky access can be done with simple single axis mounts in a system like the PUMA study. Going with a single mount for many antennas just seems backwards. It also seems odd to restrict the baseline to the original 300 meters at the cost of science, but I guess this is driven by their choice of mount. It's hard to tell because the white paper doesn't seem to be public, but it does appear that these odd design choices are being driven so that it has the same form factor as Arecibo. Trading form over function is a bad deal.
https://www.puma.bnl.gov/
NSF didn't want to continue funding just the operations of Arecibo, it doesn't seem like this proposal takes that to heart as it will certainly be more expensive to maintain a huge mechanism in the humid climate. With the NSF astronomy budget in it's current state it's very unlikely to be funded. At the end of the day it seems like a very expensive incremental facility.
Post by: Lee Jay on 01/19/2021 02:45 pm
Green Bank Telescope is 100m and fully steerable. Let's do 300m. Let us never dream small dreams. :)
Can someone explain to me why the VLA's approach isn't even better? I mean, you can have almost arbitrary collection area and you can adjust your effective aperture over a huge range (IIRC up to 36km or so). And then there's this: https://ngvla.nrao.edu/page/about
So, why is that approach not a natural replacement for Arecibo?
Post by: Robotbeat on 01/19/2021 02:49 pm
Curse of the thinned array. Not good for transmitting, which is needed for radar.Green Bank Telescope is 100m and fully steerable. Let's do 300m. Let us never dream small dreams. :)
Can someone explain to me why the VLA's approach isn't even better? I mean, you can have almost arbitrary collection area and you can adjust your effective aperture over a huge range (IIRC up to 36km or so). And then there's this: https://ngvla.nrao.edu/page/about
So, why is that approach not a natural replacement for Arecibo?
Post by: Dizzy_RHESSI on 01/19/2021 05:19 pm
Curse of the thinned array. Not good for transmitting, which is needed for radar.
Based on what exactly? I'm not sure this is the case, as far as I'm aware it's just a matter of gain and in a phased array the gain related to the total area. This white paper from the Planetary decadal makes the case that arrays are the future of planetary radar:
http://surveygizmoresponseuploads.s3.amazonaws.com/fileuploads/623127/5489366/18-347ff7e4fdba7f8e6fcafb91d6f05c7e_LazioJoseph.pdf
Radar imaging with transmitting arrays has been demonstrated over baselines of 250 m. This paper also lists some strengths of arrays over single apertures.
https://ui.adsabs.harvard.edu/abs/2017amos.confE..82G/abstract
For receiving widely spread arrays benefit from better resolution. It was noted that Goldstone-ngVLA would rival the sensitivity of Arecibo, but wtih greater sky access.
http://aspbooks.org/publications/517/113.pdf
Post by: Lee Jay on 01/20/2021 02:50 am
Curse of the thinned array. Not good for transmitting, which is needed for radar.Green Bank Telescope is 100m and fully steerable. Let's do 300m. Let us never dream small dreams. :)
Can someone explain to me why the VLA's approach isn't even better? I mean, you can have almost arbitrary collection area and you can adjust your effective aperture over a huge range (IIRC up to 36km or so). And then there's this: https://ngvla.nrao.edu/page/about
So, why is that approach not a natural replacement for Arecibo?
Even if that were true, the dishes are in rails and can be all crammed together in the center anyway.
Post by: Robotbeat on 01/20/2021 05:05 am
Doesn’t work like that.Curse of the thinned array. Not good for transmitting, which is needed for radar.Green Bank Telescope is 100m and fully steerable. Let's do 300m. Let us never dream small dreams. :)
Can someone explain to me why the VLA's approach isn't even better? I mean, you can have almost arbitrary collection area and you can adjust your effective aperture over a huge range (IIRC up to 36km or so). And then there's this: https://ngvla.nrao.edu/page/about
So, why is that approach not a natural replacement for Arecibo?
Even if that were true, the dishes are in rails and can be all crammed together in the center anyway.
Post by: Robotbeat on 01/20/2021 05:06 am
You lose most of the energy in side lobes transmitting with a thinned array.Curse of the thinned array. Not good for transmitting, which is needed for radar.
Based on what exactly? I'm not sure this is the case, as far as I'm aware it's just a matter of gain and in a phased array the gain related to the total area. This white paper from the Planetary decadal makes the case that arrays are the future of planetary radar:
http://surveygizmoresponseuploads.s3.amazonaws.com/fileuploads/623127/5489366/18-347ff7e4fdba7f8e6fcafb91d6f05c7e_LazioJoseph.pdf
Radar imaging with transmitting arrays has been demonstrated over baselines of 250 m. This paper also lists some strengths of arrays over single apertures.
https://ui.adsabs.harvard.edu/abs/2017amos.confE..82G/abstract
For receiving widely spread arrays benefit from better resolution. It was noted that Goldstone-ngVLA would rival the sensitivity of Arecibo, but wtih greater sky access.
http://aspbooks.org/publications/517/113.pdf
Post by: Lee Jay on 01/20/2021 10:28 am
Doesn’t work like that.Curse of the thinned array. Not good for transmitting, which is needed for radar.Green Bank Telescope is 100m and fully steerable. Let's do 300m. Let us never dream small dreams. :)
Can someone explain to me why the VLA's approach isn't even better? I mean, you can have almost arbitrary collection area and you can adjust your effective aperture over a huge range (IIRC up to 36km or so). And then there's this: https://ngvla.nrao.edu/page/about
So, why is that approach not a natural replacement for Arecibo?
Even if that were true, the dishes are in rails and can be all crammed together in the center anyway.
What doesn't? I know for a fact the dishes can all be crammed together in a densified array at the VLA.
Post by: Hobbes-22 on 01/20/2021 12:10 pm
Post by: Dizzy_RHESSI on 01/20/2021 12:55 pm
You lose most of the energy in side lobes transmitting with a thinned array.
I don't think that can be true as a general statement. The primary beam is also narrower for a more widely spread array, an effect which would have to be included.
Post by: LouScheffer on 01/21/2021 05:57 pm
That's not the problem. The main beam is just as strong (through narrower) if you set the phases right. It's just the vector sum of all the waves, which (if phased properly) is exactly the same, spread or compact.Curse of the thinned array. Not good for transmitting, which is needed for radar.You lose most of the energy in side lobes transmitting with a thinned array.
The problem is figuring out the correct phase. With a sparse array, each antenna is looking through a different patch of atmosphere, giving a different random phase contribution. When receiving you can calibrate this out (basically look for a phase for each antenna that maximizes the correlation with the other antennas), in a process called phase closure. When you are transmitting, on the other hand, you are running open loop.
So you could get the same equivalent power with a sparse or dense array, if you knew exactly how to set the phase. But for transmitting you don't know this.
Post by: baldusi on 01/24/2021 02:32 am
Post by: tpw2 on 01/24/2021 06:26 pm
How do AESA radar's solve this? How big is the transmission lobe? Because big visual telescopes use a laser to probe the atmosphere. And I wonder if you couldn't use something similar, like a balloon with a target.
At radio frequencies the Fried parameter is large, so unless your baselines are very long (like in astronomical interferometers), the different patches of atmosphere don't cause that different phase shifts.
Post by: baldusi on 01/25/2021 03:51 pm
How do AESA radar's solve this? How big is the transmission lobe? Because big visual telescopes use a laser to probe the atmosphere. And I wonder if you couldn't use something similar, like a balloon with a target.
At radio frequencies the Fried parameter is large, so unless your baselines are very long (like in astronomical interferometers), the different patches of atmosphere don't cause that different phase shifts.
I must have done the numbers wrong because I get an r0 around 126km at 2380Mhz.
Post by: LouScheffer on 02/03/2021 03:50 am
The baselines does not have to be very long to cause problems. From Uplink array concept demonstration with the EPOXI spacecraft (https://ieeexplore.ieee.org/document/4839372), trying to combine 3 elements at X band (8 GHz) with a max 500m baseline:How do AESA radar's solve this? How big is the transmission lobe? Because big visual telescopes use a laser to probe the atmosphere. And I wonder if you couldn't use something similar, like a balloon with a target.
At radio frequencies the Fried parameter is large, so unless your baselines are very long (like in astronomical interferometers), the different patches of atmosphere don't cause that different phase shifts.
Quote
differential phase build-up due to the troposphere was found to be insignificant above 30 degrees elevation, leading at most to 20 degrees over the DSS-24/25 baseline(so likely significant below 30 degrees elevation)
Quote
As described in the insert in Fig. 5a, on the part of the power/phase curve corresponding to approximately 100 degrees of differential phase error, the combined power fluctuates near the single-antenna power level −103 dBm, likely due to differential tropospheric delay fluctuations on the order of 1 mm over the 258m baseline.
Likewise, the paper Field Demonstration of Coherent Uplink from a Phased Array of Widely Separated Antennas: Steps Toward A Verifiable Real-Time Atmospheric Phase Fluctuation Correction for a High Resolution Radar System (https://www.researchgate.net/publication/275272070_Field_Demonstration_of_Coherent_Uplink_from_a_Phased_Array_of_Widely_Separated_Antennas_Steps_Toward_A_Verifiable_Real-Time_Atmospheric_Phase_Fluctuation_Correction_for_a_High_Resolution_Radar_System), Figure 4, shows good correlation between antennas a few hundred meters apart but much worse correlation from one a few km away.
These two papers show the two different ways of compensating for this. In the first paper, the target is a spacecraft which can report the received power. These reports are then used to optimize the transmit phase. The second requires some astrophysical source quite close to the target (the paper says within the primary beam, but I'd guess this restriction can be relaxed. You just need close enough and nod the antennas...). You then used the measured received phases to estimate the atmospheric contribution, which you adjust for on transmit.
Post by: tpw2 on 02/03/2021 08:33 am
The baselines does not have to be very long to cause problems. From Uplink array concept demonstration with the EPOXI spacecraft (https://ieeexplore.ieee.org/document/4839372), trying to combine 3 elements at X band (8 GHz) with a max 500m baseline:How do AESA radar's solve this? How big is the transmission lobe? Because big visual telescopes use a laser to probe the atmosphere. And I wonder if you couldn't use something similar, like a balloon with a target.
At radio frequencies the Fried parameter is large, so unless your baselines are very long (like in astronomical interferometers), the different patches of atmosphere don't cause that different phase shifts.Quotedifferential phase build-up due to the troposphere was found to be insignificant above 30 degrees elevation, leading at most to 20 degrees over the DSS-24/25 baseline(so likely significant below 30 degrees elevation)
I think 30 degrees was just the lowest elevation that they tried. A site/weather would have to be very bad for phase errors at 8 GHz to become a serious problem with baselines of a few hundred meters (in that case even the largest single dishes would start suffering from bad seeing). But at baselines of a couple of kilometers or so, it can certainly become an issue.
Post by: Blackstar on 02/03/2021 02:45 pm
http://www.naic.edu/ao/ngat
Post by: Lee Jay on 02/03/2021 06:42 pm
White paper proposing a replacement:
http://www.naic.edu/ao/ngat
The was apparently written by scientists and not engineers. Give an engineer (like me) the challenge of constructing a 314m diameter plate (bigger than a football stadium, and taller too) that has to be stiff and tiltable to ~45 degrees, and we'll ask for some serious cubic money (billions, probably, not including the instruments) and time. And steel - lots and lots of steel. Maybe a couple million yards of concrete too.
Post by: matthewkantar on 02/03/2021 06:59 pm
Post by: Frogstar_Robot on 02/03/2021 07:01 pm
White paper proposing a replacement:
http://www.naic.edu/ao/ngat
The was apparently written by scientists and not engineers. Give an engineer (like me) the challenge of constructing a 314m diameter plate (bigger than a football stadium, and taller too) that has to be stiff and tiltable to ~45 degrees, and we'll ask for some serious cubic money (billions, probably, not including the instruments) and time. And steel - lots and lots of steel. Maybe a couple million yards of concrete too.
With a maximum deflection of 8mm, if I read that right. The estimate of $454 million may be a a little low...
Post by: Blackstar on 02/03/2021 09:28 pm
My question is: “Why would such an instrument be built on a hilly area in a jungle?”
I may be wrong on this, but I don't think that technically the area where Arecibo is qualifies as a jungle. It's a forest, and not even a rain forest, just a forest someplace that gets hot.
Post by: matthewkantar on 02/03/2021 09:39 pm
My question is: “Why would such an instrument be built on a hilly area in a jungle?”
I may be wrong on this, but I don't think that technically the area where Arecibo is qualifies as a jungle. It's a forest, and not even a rain forest, just a forest someplace that gets hot.
I googled it, seems a forest's undergrowth is passable while a jungle's is not? The description of the foliage notwithstanding, the site of Arecibo seems ill suited to the proposed design.
Hopefully the jungle/forest debate is not the new explosion/deflagration debate.
Post by: LouScheffer on 02/04/2021 01:08 am
To avoid the antennas shadowing each other, you can just space them a diameter or so apart. That makes the array perhaps twice as big, but finding a flat spot for a 600 meter wide array should not be hard.
Next, the VLA estimated costs for a whole bunch of 18m antenna mounts. See table 10-3 of document ngVLA Memo 27: Various Suitable Mounts for an 18m Antenna (https://library.nrao.edu/public/memos/ngvla/NGVLA_27.pdf). Here they estimate a cost of about $1M/mount. You would need 287 18-meter antennas to equal one 305 meter one, so that's a total mount cost of about $287M. It's not obvious to me the giant tilting slab would be much cheaper. Plus if each mount is independent you can break the array into sub-arrays when you do not need the full aperture, which you cannot do with one giant plate.
Plus if you built it this way, you'd have a much wider frequency range (on the low end since the dishes are bigger, and on the high end since you don't need to worry about deformation in the platform). In fact you could simply copy whatever the VLA comes up with, add a transmitter module to each antenna, and you'd have a fantastic facility.
Post by: tpw2 on 02/04/2021 09:16 am
The giant tilting platform has two advantages: the dishes do not obstruct each other's field of view, and you don't need a mount for each antenna. It's not obvious to me that these advantages hold up compared to an array of dishes on flat ground.
To avoid the antennas shadowing each other, you can just space them a diameter or so apart. That makes the array perhaps twice as big, but finding a flat spot for a 600 meter wide array should not be hard.
Next, the VLA estimated costs for a whole bunch of 18m antenna mounts. See table 10-3 of document ngVLA Memo 27: Various Suitable Mounts for an 18m Antenna (https://library.nrao.edu/public/memos/ngvla/NGVLA_27.pdf). Here they estimate a cost of about $1M/mount. You would need 287 18-meter antennas to equal one 305 meter one, so that's a total mount cost of about $287M. It's not obvious to me the giant tilting slab would be much cheaper. Plus if each mount is independent you can break the array into sub-arrays when you do not need the full aperture, which you cannot do with one giant plate.
Plus if you built it this way, you'd have a much wider frequency range (on the low end since the dishes are bigger, and on the high end since you don't need to worry about deformation in the platform). In fact you could simply copy whatever the VLA comes up with, add a transmitter module to each antenna, and you'd have a fantastic facility.
The example configurations given in the white paper are 400 15 metre dishes or 1112 9 metre dishes. The cost estimates seem extremely optimistic. For example, I think ASKAP cost about $100 million for 36 12 metre dishes.
The mechanical challenges of building the huge tilting platform are obvious, but the white paper also says almost nothing about how it would be used as an interferometer. Just the correlator for 1000+ dishes would be a very significant piece of hardware. The $17 million cost estimate for backend signal processing, data storage and public data archive seems to be from some different reality altogether.
Post by: Don2 on 02/05/2021 03:30 am
It is worrying that engineering firms convinced themselves that the telescope was not about to fall. It should have been obvious, given the cable breaks that were happening on a daily basis, that the structure was rapidly degrading and would fail in the near future. Were the engineers under pressure to produce a politically correct answer?
Rather than trying to design a tilting dish to look towards the galactic center, it would be smarter to build in another part of the world where the galactic center passes directly overhead. Northern Chile has a number of large copper mines which might provide a suitable hole for an Arecibo clone.
Post by: edzieba on 02/05/2021 01:41 pm
Post by: Paul451 on 02/06/2021 08:02 am
It's not obvious to me that these advantages hold up compared to an array of dishes on flat ground.
To avoid the antennas shadowing each other, you can just space them a diameter or so apart. That makes the array perhaps twice as big, but finding a flat spot for a 600 meter wide array should not be hard.
AIUI (which is not well), other than direct shadowing, the main issue is that as you change the angle of the dishes, the orientation and planar-distance changes in ways that make the interferometry harder to do. That change includes during simple tracking against the Earth's rotation during a single observation. Their design is meant to avoid that. A lot of long-baseline interferometer dishes were mounted on rail lines to let them adjust their spacing (I presume east/west).
However, if you are building a 300m steerable plate, is it really harder or more expensive to use the same frame and mount for a 300m monolithic steerable dish?
Post by: edzieba on 02/06/2021 11:26 am
Post by: Nomadd on 02/06/2021 03:24 pm
Post by: Dizzy_RHESSI on 02/07/2021 12:29 am
AIUI (which is not well), other than direct shadowing, the main issue is that as you change the angle of the dishes, the orientation and planar-distance changes in ways that make the interferometry harder to do. That change includes during simple tracking against the Earth's rotation during a single observation. Their design is meant to avoid that. A lot of long-baseline interferometer dishes were mounted on rail lines to let them adjust their spacing (I presume east/west).
The fact that projected east-west baselines are shorter doesn't really make interferometry harder, it just lowers the resolution. But this would be more than made up for by the longer baselines of a 600 m array. The tracks used in interferometers like the VLA are not used during observations, they are just used to change between compact and dispersed configurations. It's not necessary to keep the baseline fixed during an observation, if it was intercontinental VLBI would be impossible.
However, if you are building a 300m steerable plate, is it really harder or more expensive to use the same frame and mount for a 300m monolithic steerable dish?
A huge monolithic telescope also goes back to the old problems of Arecibo: a) small field of view and b) limited to lower frequencies.
Post by: LouScheffer on 02/07/2021 02:39 am
Getting a little out of my depth here. Would a Cassegrain setup be inappropriate for a Arecibo type spherical dish?Not inappropriate at all. That's what the Arecibo upgrade did in the mid-90s. For practical reasons, they used a Gregorian and not a Cassegrainian configuration (the two are similar, but the Cassegrain uses a convex secondary, a Gregorian a concave). This also had the huge advantage that they could shape the Gregorian reflector to compensate for the spherical primary. This gave a single point focus which was a big advantage over the line feeds they used before.
The Gregorian configuration was not obvious since the last mirrors were all inside a large housing attached to the suspended platform. If you google for Arecibo upgrade you can find lots of information about it, such as this NASA document (https://history.nasa.gov/SP-4218/ch9.htm).
Post by: tpw2 on 02/07/2021 08:17 am
AIUI (which is not well), other than direct shadowing, the main issue is that as you change the angle of the dishes, the orientation and planar-distance changes in ways that make the interferometry harder to do. That change includes during simple tracking against the Earth's rotation during a single observation. Their design is meant to avoid that. A lot of long-baseline interferometer dishes were mounted on rail lines to let them adjust their spacing (I presume east/west).
The fact that projected east-west baselines are shorter doesn't really make interferometry harder, it just lowers the resolution. But this would be more than made up for by the longer baselines of a 600 m array. The tracks used in interferometers like the VLA are not used during observations, they are just used to change between compact and dispersed configurations. It's not necessary to keep the baseline fixed during an observation, if it was intercontinental VLBI would be impossible.
And changing (projected) baselines due to Earth's rotation actually help because you get a better uv-coverage for "free".
Post by: Star One on 03/09/2021 10:57 am
Quote
A report by the National Science Foundation estimates it will cost up to $50 million to clean up the damage from the collapsed Arecibo radio telescope, but that it is still too soon to determine whether or how to rebuild the famous observatory.
Quote
NSF added that it is planning a “community workshop” in April to discuss potential options for the site. “The development costs of potential projects coming out of this stakeholder engagement are unknown,” it stated.
https://spacenews.com/nsf-report-estimates-arecibo-cleanup-cost-at-up-to-50-million/
Post by: eeergo on 03/09/2021 11:34 am
QuoteA report by the National Science Foundation estimates it will cost up to $50 million to clean up the damage from the collapsed Arecibo radio telescope, but that it is still too soon to determine whether or how to rebuild the famous observatory.
Overall operating costs were <$10M/year, of which $2M were to be provided by NSF under the new funding scheme - so no net savings for the next five or six years (upwards of twenty-five for the NSF).
Of course, this is ignoring:
- the continued costs from the surviving facilities that won't be saved anyway,
- the huge capability loss ($???M) for most probably upwards of a decade, and
- the destruction of probably tens of millions of dollars worth of state-of-the-art receiver equipment, deemed a "complete loss for scientific purposes".
The cleanup is probably also going to severely affect the -protected- wildlife living under the reflector, as can be seen from the bare ground under the cleaned-up area.
Interesting tidbit buried in a non-descript footnote of the report:
Quote
The cable that pulled loose was not the cable for which a replacement had been planned [due to a construction defect] as part of the Hurricane repair appropriation.Attached are the three pre-collapse engineering reports that are buried at the bottom of the NSF Arecibo media page: https://www.nsf.gov/news/special_reports/arecibo/index.jsp
FYI, WJE's is the one that wasn't just suggesting capitulation, and started by proposing two immediate actions -reducing backstay tension- that would involve no significant risk but would reduce the loads by about 4% (!!) - plus some trivial ones that could, and should, have been quickly performed during the Fall after the first cable failed, as the further 4% load reduction by removing... 45 thousand pounds of lead ballast! Thornton Tomasetti, in their more quantitative report, also shows the benign reduction, even if their conclusion falters in uncertainty, paradoxically while stressing inaction would invariably lead to sudden -and certainly not risk-free- collapse.
Post by: edzieba on 03/09/2021 12:58 pm
Quote from: WJE
The key element in pursuing this path is reducing structural uncertainty to acceptable levels byThe failure occurring in one of the 'good' strands - and in normal conditions rather than a storm event, or an earthquake, or other external factor that would have significantly increased loads - makes it clear that it is extraordinarily unlikely the remaining cables would have the capacity to achieve the necessary 10% margin, even with such high risk measures such as their proposed:
demonstrating that key elements have the capacities needed to support the work that must be done.
[...]
Of course, if the requisite capacity cannot be successfully
demonstrated at any time, risks to occupants would be excessive and repair efforts would cease, leaving
demolition as the only option.
Quote from: WJE
An attempt will be made to throw the lead from the azimuth using workers positioned from a helicopter.I don't think anyone could claim with a straight face that the observed failure would have been amenable to survival of any helicopter-lifted crew working inside the suspended structure at that time, as the counterweights are located on the same track the Gregorian Dome moves along.
The other engineering firms agree:
Quote from: Thornton
With the loss of two cables, there are now three original cables (of four) and one auxiliary cable
(of two) connecting the platform to Tower 4. Should another of these three original cables fail,
the two remaining original cables will undergo static force demands at or above the specified
minimum breaking strength. A catastrophic failure would be very likely. These cables are not
capable of handling the required dynamic demands of a sudden failure of an adjacent cable.
[...]
We have noted wire breaks on the three remaining 3-inch-diameter original cables from Tower
4, which occurred during the November event. We continue to monitor the structure and
continue to note wire breaks since the failure last week. Furthermore, there is no evidence that
the existing original cables can achieve the specified minimum breaking strength and certainly
evidence to the contrary, since one failed at 62% of this strength.
[...]
It has been suggested that proof-loading the structure for a period of time – to demonstrate that
the critical structural elements can sustain forces approximately 10% more than the predicted
forces in these elements during the implementation of any remedial work – will provide a
calculable margin of safety over some duration, and that repeated proof-loading could provide
the means to ensure safety throughout the duration of work. However, we believe that even if
proof loading does not cause collapse or further failure of an element, it will cause damage and
reduce reserve capacity, making the structure less safe.
[...]
Now that we have witnessed two cables fail, one from the original set of cables and one from
the auxiliary cables, both at tension forces significantly below their design strengths, it would
appear that remediation will require replacement of all of the cables. This factor needs to be
considered, as does the timing of the replacement program.
We believe the structure will collapse in the near future if left untouched. Controlled demolition,
designed with a specific collapse sequence determined and implemented with the use of
explosives, will reduce the uncertainty and danger associated with collapse. Although it saddens
us to make this recommendation, we believe the structure should be demolished in a controlled
way as soon as pragmatically possible. It is therefore our recommendation to expeditiously plan
for decommissioning of the observatory and execute a controlled demolition of the telescope.
Quote from: WSP
The current stability of the structure is unknown, and we cannot quantify the structure’s factor of
safety. Wiss, Janney, Elstner (WJE) has proposed using a proof load test to quantify the current factor
of safety. WSP does not recommend performing a proof load test on the system for the following
reasons:
1. Due to the compromised state and additional damage being observed in the remining cables from
Tower 4, the maximum capacity of the remaining cables is unknown, and the additional load
could cause additional cable failures.
2. It is not recommended to put the structure through additional load cycles due to the additional
degradation that can occur by adding load to the system through proof loading.
3. The proof load proves capacity at that moment in time and it is unknown if the cables can support
that load again in the future.
After the fact, we can indeed confirm that not only would additional loading of the cables have led to collapse, but that even completely normal loading led to collapse in short order, and in a manner that would very likely have led to loss of life of any crews working on or near the towers or suspended structure.
It is abundantly clear that the cable damage that led to the collapse was well beyond rectification though 'simple' external measures (like running additional cables or removing structural mass) long before the first secondary cable slid out of its mount. The time for the complete replacement of all cabling needed was also prior to then: by the time the second (main) cable failed, the collapse was effectively already over but for the noise.
Whether the cables were in that state due to wilful neglect (knowledge through surveys that had degraded well below design load but that knowledge ignored), neglect out of ignorance (surveys not conducted), or incompetence (surveys failing to identify degradation, or requests for surveys denied due to non-budgetary reasons), or the unlikely event of some brand new never-before-encountered failure mode, and whether that neglect and/or ignorance of the problem was due to incompetence or simply lack of sufficient budget is completely moot: the time to 'save Arecibo' was long before August 2020.
Post by: eeergo on 03/09/2021 01:22 pm
Those reports were released last year [...] Whether the cables were in that state due to wilful neglect (knowledge through surveys that had degraded well below design load but that knowledge ignored), neglect out of ignorance (surveys not conducted), or incompetence (surveys failing to identify degradation, or requests for surveys denied due to non-budgetary reasons), or the unlikely event of some brand new never-before-encountered failure mode, and whether that neglect and/or ignorance of the problem was due to incompetence or simply lack of sufficient budget is completely moot: the time to 'save Arecibo' was long before August 2020.
Hadn't caught them at the time, thanks for the note and the attachment. The (admittedly significantly uncertain, but indicative) numbers in the TT presentation show margins were significant (≳2) in all cables but M4, where it was slim and obviously decreased even more in November. The rest of the cables were not suspect and supported a highly dynamic event with large non-static loads (see both the swinging and the amplitude excursions recorded in page 9 for the much less powerful event of the main snap), supporting a large pendular movement and ripping through structure, as discussed.
Post by: edzieba on 03/09/2021 02:28 pm
Regardles, once the 4 tower let go, the loads in the remaining cables would reduce rather than increase. You can see on p.15 of the engineering analysis that the load in the cables from pre-tensioning is well above the load imparted by the platform itself: once tower 4 failed, that tensioning is gone and you have purely the load imparted by the swinging platform, which is well below that pre-tension load. This has been discussed earlier in the thread.
Post by: Robotbeat on 03/09/2021 02:39 pm
Post by: SteveU on 03/09/2021 03:40 pm
Post by: eeergo on 03/09/2021 04:22 pm
The other cables were suspect (and indeed one set already scheduled for replacement prior to the first socket slip event).
Regardles, once the 4 tower let go, the loads in the remaining cables would reduce rather than increase. You can see on p.15 of the engineering analysis that the load in the cables from pre-tensioning is well above the load imparted by the platform itself: once tower 4 failed, that tensioning is gone and you have purely the load imparted by the swinging platform, which is well below that pre-tension load. This has been discussed earlier in the thread.
I've -roughly- proven this not to be the case once the swing is under effect, but I'm not going down that rabbit hole again - the analysis is there waiting for a minimally rigorous counterproof, as the only dissenting arguments have been claiming it's unknowable / impossible to calculate easily, focusing on fudging factors that are just corrections but are treated as dominant (or ignored if they increase loads), and a colorful "slingshot" hypothesis based on fantasy.
I disagree. Even a small amount of reinforcement would have drastically reduced probability of immediate failure, allowing later and better reinforcement.
I fully agree, and there were demonstrably trivial ways to at least try.
A full 4% of trivial load reduction (through the backstays detensioning) could have taken place already in September, possibly prolonging the main cable's life beyond the foot-dragging planned schedule for more durable reinforcements in Nov/Dec. Even after rupture of the main, it might have bought enough time to perform more involved tasks or reduce uncertainty as to the load capacity in the damaged cables, to better characterize the system and better assess eventual risk to workers.
But if you defer crucial maintenance of cables *known* to have decades-old issues (i.e. M8), being more engaged in saving a few bucks that would be spent anyway, multiplied by ten, when a failure finally occurred, plus don't even recognize prone-to-failure cables (i.e. the failed ones, which weren't even on a special watchlist, which means proper characterization wasn't performed when a cable that stayed intact until the bitter end was known to have issues deemed serious enough), and throw your hands up in the air considering all cables as equally beyond hope (when only one was truly dicey) while paralyzed by analysis for months waiting for manna to fall from the sky...
Post by: Frogstar_Robot on 03/09/2021 04:28 pm
Post by: Nomadd on 03/09/2021 08:45 pm
Hindsight solves all problems.How exactly is saying that they shouldn't have ignored known issues "hindsight"? Is deciding that someone shouldn't have stood under a falling piano while declaring his right not to acknowledge gravity "hindsight" too?
Post by: Lee Jay on 03/09/2021 10:22 pm
Hindsight solves all problems.How exactly is saying that they shouldn't have ignored known issues "hindsight"? Is deciding that someone shouldn't have stood under a falling piano while declaring his right not to acknowledge gravity "hindsight" too?
In hindsight, I'm not sure I'd have put people in harm's way to adjust the tension on or reinforce the cables. In hindsight, a failure resulting in the tops of the towers falling to the ground could have put people in mortal danger.
Post by: eeergo on 03/10/2021 08:37 am
Hindsight solves all problems.How exactly is saying that they shouldn't have ignored known issues "hindsight"? Is deciding that someone shouldn't have stood under a falling piano while declaring his right not to acknowledge gravity "hindsight" too?
In hindsight, I'm not sure I'd have put people in harm's way to adjust the tension on or reinforce the cables. In hindsight, a failure resulting in the tops of the towers falling to the ground could have put people in mortal danger.
Assessed in the studies linked upthread: detensioning of the backstays wouldn't have resulted in significant danger increase - the towers are quite a distance away. Proper monitoring would have avoided surprises too. There were already people around the towers in other settings after the main cable failure. Prior to that, the danger was even lower.
Post by: tpw2 on 03/10/2021 11:07 am
Hindsight solves all problems.How exactly is saying that they shouldn't have ignored known issues "hindsight"? Is deciding that someone shouldn't have stood under a falling piano while declaring his right not to acknowledge gravity "hindsight" too?
In hindsight, I'm not sure I'd have put people in harm's way to adjust the tension on or reinforce the cables. In hindsight, a failure resulting in the tops of the towers falling to the ground could have put people in mortal danger.
Assessed in the studies linked upthread: detensioning of the backstays wouldn't have resulted in significant danger increase - the towers are quite a distance away. Proper monitoring would have avoided surprises too. There were already people around the towers in other settings after the main cable failure. Prior to that, the danger was even lower.
I thought they said in the press conference after the collapse that they had detensioned the backstays. Or am I imagining things?
Post by: eeergo on 03/10/2021 12:41 pm
Hindsight solves all problems.How exactly is saying that they shouldn't have ignored known issues "hindsight"? Is deciding that someone shouldn't have stood under a falling piano while declaring his right not to acknowledge gravity "hindsight" too?
In hindsight, I'm not sure I'd have put people in harm's way to adjust the tension on or reinforce the cables. In hindsight, a failure resulting in the tops of the towers falling to the ground could have put people in mortal danger.
Assessed in the studies linked upthread: detensioning of the backstays wouldn't have resulted in significant danger increase - the towers are quite a distance away. Proper monitoring would have avoided surprises too. There were already people around the towers in other settings after the main cable failure. Prior to that, the danger was even lower.
I thought they said in the press conference after the collapse that they had detensioned the backstays. Or am I imagining things?
Almost positive no action was taken prior to the collapse, especially major cable operations.
Post by: FutureSpaceTourist on 03/16/2021 09:19 am
Quote
#GF-2 satellite image collected on March 13 shows the cleanup of iconic #AcreciboObservatory in #PuertoRico, which collapsed last December. The cleaning up could cost 30-50 million USD, according to the National Science Foundation, USA. #infrastructuremonitoring
Post by: Blackstar on 04/04/2021 11:44 pm
The Collapse of Puerto Rico’s Iconic Telescope
The uncertain future of the Arecibo Observatory, and the end of an era in space science.
By Daniel Alarcón
March 29, 2021
Just before eight in the morning on December 1st of last year, Ada Monzón was at the Guaynabo studios of WAPA, a television station in Puerto Rico, preparing to give a weather update, when she got a text from a friend. Jonathan Friedman, an aeronomer who lives near the Arecibo Observatory, about an hour and a half from San Juan, had sent her a photo, taken from his sister-in-law’s back yard, of the brilliant blue Caribbean sky and the green, heavily forested limestone hills. In the picture, a thin cloud of dust hovered just above the tree line; the image was notable not for what it showed but for what was missing. On a normal day—on any day before that one, in fact—a shot from that back yard would have captured Arecibo’s nine-hundred-ton radio-telescope platform, with its massive Gregorian dome, floating improbably over the valley, suspended from cables five hundred feet above the ground. Accompanying the photo was Friedman’s message, which read, simply, “Se cayó ”—“It fell.”
Post by: catdlr on 10/12/2021 11:11 am
Quote
On the morning of December 1st, 2020, one of the most iconic astronomical instruments in the world collapsed. The Arecibo Telescope was not only one of the largest radio telescopes in the world, it was also a fascinating problem in structural engineering. Its loss was felt across the world. This video provides a quick lesson on radio telescopes, a summary of the failure, and some discussion about the engineering lessons learned in the wake of the event. I hope that eventually, they can replace the telescope with an instrument as futuristic and forward-looking as the Arecibo telescope was when first conceived. It was an ambitious and inspiring structure, and we sure will miss it.
https://youtu.be/3oBCtTv6yOw
Post by: harrystranger on 11/02/2021 01:40 pm
https://twitter.com/Harry__Stranger/status/1455544187395485700?s
Post by: Blackstar on 11/02/2021 04:28 pm
Post by: eeergo on 02/17/2022 08:55 am
https://twitter.com/genejm29/status/1494026288822210561 (https://twitter.com/genejm29/status/1494026288822210561)
In particular, forensic analysis appears to point towards the culprit being, other than slim design margins which were always in place (or at least since the Gregorian dome and latest hardware was added), inspections failing to account for and act upon visible zinc creep in the cable socket since at least 2019, aggravated by weather and earthquake/hurricane loads prompting unchecked corrosion - whose root cause could be traced back to a socket fabrication issue that caused some of the cable wires to fail inside said socket.
https://twitter.com/genejm29/status/1494054366147493898 (https://twitter.com/genejm29/status/1494054366147493898)
Post by: edzieba on 02/17/2022 02:17 pm
Immensely illustrative presentation:Original report is here: https://ntrs.nasa.gov/citations/20210017934
https://twitter.com/genejm29/status/1494026288822210561 (https://twitter.com/genejm29/status/1494026288822210561)
In particular, forensic analysis appears to point towards the culprit being, other than slim design margins which were always in place (or at least since the Gregorian dome and latest hardware was added), inspections failing to account for and act upon visible zinc creep in the cable socket since at least 2019, aggravated by weather and earthquake/hurricane loads prompting unchecked corrosion - whose root cause could be traced back to a socket fabrication issue that caused some of the cable wires to fail inside said socket.
https://twitter.com/genejm29/status/1494054366147493898 (https://twitter.com/genejm29/status/1494054366147493898)
Going by that last slide ("Summary of Contribution Factors") and the summary section of the full report[1]; the pre-2019 inspections[2] of Zinc extrusion were less of a contribution to failure than the fundamental design errors. i.e. even if the extrusion had been flagged (or was flagged but not ignored/overruled) prior to 2019 then it would still have necessitated replacement of and redesign of (given tower load limits) the suspended structure of the observatory.
[1]
Quote
The NASA/Aerospace team concludes that the most probable cause of the Aux M4N cable
failure was a socket joint design with insufficient design criteria that did not explicitly consider
socket constituent stress margins or time-dependent damage mechanisms. The socket attachment
design was found to have an initially low structural margin, notably in the outer socket wires,
which degraded primarily due to zinc creep effects that were activated by long-term sustained
loading and exacerbated by cyclic loading. Additionally, a few wires showed evidence of
hydrogen-assisted cracking (HAC) and wire surface defects that may have contributed to initial
outer wire failures.
In-service inspections showed evidence of progressive zinc extrusion on several Arecibo sockets,
which in hindsight indicated significant cumulative damage. However, the design did not contain
set service-life inspection intervals with pass/fail inspection criteria, nor did it specify an end-of-
life capability requirement associated with service life degradation.
[2] My reading was that 2019 was the most recent photo available to show the full extent of the extrusion, but that extrusion had been ongoing for the life of the telescope. e.g. the report p.17 notes observation of extrusion as far back as 2003. The problem was there was no defined criteria for the extrusion inspection, i.e. there was no "Xmm of extrusion is within tolerance, Ymm is a sign of imminent failure" listed in the maintenance schedule or calculated beforehand as part of the design.
Post by: Yiosie on 03/22/2022 05:47 am
Quote
The famous Arecibo Observatory in Puerto Rico, once home to the world's most powerful radio telescope, has reopened to visitors more than a year after the giant facility collapsed.
The visitor center and observation deck are now open to visitors who make reservations in advance. From the outdoor deck, visitors can see the valley and remaining reflective dish -- 1,000 feet in diameter.
<snip>
In addition to the visitor center, Arecibo is home to other active astronomical instruments, such as a 12-meter telescope and a LIDAR facility, which can study the atmosphere by bouncing laser beams off particles about 20 to 100 miles above the Earth.
Arecibo scientists also are using artificial intelligence computers to sift through decades of observational data from the telescope that dates back to the 1960s "to see if there is something we may have missed," Correa said.
<snip>
A new outdoor exhibit has also been added with artifacts recovered from the telescope and its platform.
To remove larger pieces of debris, crews had to build temporary roads into the large valley. Ongoing work includes planting native vegetation to prevent erosion, according to Arecibo's latest update on the work.
Post by: aj834 on 10/12/2022 11:16 pm
There are still some instruments on-site (12 meter antenna, project PRISMA, and LIDAR research), but what will happen to these has apparently not been discussed.
Source (in Spanish) : https://teleonce.com/noticias/locales/fundacion-nacional-de-las-ciencias-decide-cerrar-el-observatorio-de-arecibo-para-septiembre-del-2023/
Post by: su27k on 10/13/2022 03:44 am
Post by: catdlr on 10/13/2022 06:16 am
Quote
Local media in Puerto Rico are reporting today that NSF had a last-minute virtual meeting with staff at the observatory and announced that facilities will be closed by September 30, 2023 after a “transformation” to become a science education center. They were also told there would be a meeting with details on Friday and that NSF staff would be visiting the island this month.
There are still some instruments on-site (12 meter antenna, project PRISMA, and LIDAR research), but what will happen to these has apparently not been discussed.
Source (in Spanish) : https://teleonce.com/noticias/locales/fundacion-nacional-de-las-ciencias-decide-cerrar-el-observatorio-de-arecibo-para-septiembre-del-2023/
Post by: eeergo on 10/13/2022 01:17 pm
Still waiting for the final report on exactly how unavoidable the damage was that led to its difficult situation (and later, demise), and how undebatable the impossibility for a fix was, taking into account the structure's performance during the failure.
Post by: edzieba on 10/13/2022 01:53 pm
Still waiting for the final report on exactly how unavoidable the damage was that led to its difficult situation (and later, demise), and how undebatable the impossibility for a fix was, taking into account the structure's performance during the failure.They were released years ago (https://forum.nasaspaceflight.com/index.php?topic=43786.msg2202156#msg2202156), you just did not like their conclusions.
Post by: eeergo on 10/13/2022 02:02 pm
Still waiting for the final report on exactly how unavoidable the damage was that led to its difficult situation (and later, demise), and how undebatable the impossibility for a fix was, taking into account the structure's performance during the failure.They were released years ago (https://forum.nasaspaceflight.com/index.php?topic=43786.msg2202156#msg2202156), you just did not like their conclusions.
Those are the engineering reports, not the full failure investigation, whose recommendations were based on pre-failure assessments, and whose overconservatism has been challenged, not least by the simple observations I showed in the main thread. There are more recent failure investigation documents, most notably the Auxiliary Termination Socket Failure Investigation (whose conclusions are pretty damning for the "it could not be foreseen" camp), as you yourself linked in that thread, but they always defer responsibility and full chain of events to future reports, concentrating on single issues instead.
Post by: edzieba on 10/13/2022 03:31 pm
Post by: jstrotha0975 on 10/13/2022 03:38 pm
Post by: eeergo on 10/13/2022 03:50 pm
Re-attached the most recent report, conclusions are still the same. It, and the ones linked previously, were not based on "pre-failure assessments" as you claim, but post-failure examination of the cables and sockets and experimental testing of the zinc-slip mechanism in the spelter sockets.
That's not an independent board's report. Of course Thompson-Tomasetti is going to agree with its own prior conclusions. Still, no time to go through it in detail now, so I'll hold my judgement about its contents and the relationship with prior analyses.
Post by: edzieba on 10/13/2022 04:07 pm
I thought they had a plan to build a new radio telescope using a bunch of smaller ones?There were a few different ideas proposed, but no funding.
Post by: aj834 on 10/13/2022 05:22 pm
Exactly as predicted in the thread by some of us, while some were very much against even entertaining the idea. So much for the science-fiction studies to "rebuild it better".
Still waiting for the final report on exactly how unavoidable the damage was that led to its difficult situation (and later, demise), and how undebatable the impossibility for a fix was, taking into account the structure's performance during the failure.
It is the feeling on the island (I’m from Puerto Rico for context) that a not insignificant part of the reason why it wont be rebuilt is because of the federal governments unwillingness to invest in Puerto Rico. I do not know of how real that is, but that is the feeling on the island.
I don’t know how much you guys know of this, but shortly after the collapse one of the local meteorologists & biggest science communicators on the island had a Facebook live conversation with people who work at the observatory, and the head of the Puerto Rico NASA Space Grant, and the Space Grant head said NASA was interested in operating it. A few days later is when the UCF & NASA agreement was talked about publicly. Im very sad that didn’t go through.
Post by: eeergo on 10/13/2022 05:27 pm
Exactly as predicted in the thread by some of us, while some were very much against even entertaining the idea. So much for the science-fiction studies to "rebuild it better".
Still waiting for the final report on exactly how unavoidable the damage was that led to its difficult situation (and later, demise), and how undebatable the impossibility for a fix was, taking into account the structure's performance during the failure.
It is the feeling on the island (I’m from Puerto Rico for context) that a not insignificant part of the reason why it wont be rebuilt is because of the federal governments unwillingness to invest in Puerto Rico. I do not know of how real that is, but that is the feeling on the island.
I don’t know how much you guys know of this, but shortly after the collapse one of the local meteorologists & biggest science communicators on the island had a Facebook live conversation with people who work at the observatory, and the head of the Puerto Rico NASA Space Grant, and the Space Grant head said NASA was interested in operating it. A few days later is when the UCF & NASA agreement was talked about publicly. Im very sad that didn’t go through.
That's one of the reasons I believe can be seen through the inconsistencies in all the technicalities regarding the Observatory's neglect/lack of repairs/lack of action towards design flaws leading to its collapse. Obviously not something you're going to find printed in big letters, or in forensic analyses of the steel's crystalline structure.
Post by: deadman1204 on 10/13/2022 06:05 pm
I thought they had a plan to build a new radio telescope using a bunch of smaller ones?Any new thing would need to be competed with all other NSF projects through the regular way.
There is also the thing that if NSF was gonna replace Aricebo, it wouldn't do it in Puerto Rico as the southern hemisphere would give much better science returns.
Post by: russianhalo117 on 10/13/2022 08:31 pm
I thought they had a plan to build a new radio telescope using a bunch of smaller ones?AFAIU: That was solely an informal feasibility exercise which concluded with dismal intergovernmental interest by the time of its conclusion. The alternative locations to which to build its replacement were viewed more favourably because a high dessert or steppe is a better place to build it.
Post by: Robotbeat on 10/13/2022 09:24 pm
Exactly as predicted in the thread by some of us, while some were very much against even entertaining the idea. So much for the science-fiction studies to "rebuild it better".There is a difference between being stridently against the *suggestion* not to rebuild it and being against the *prediction* that it won’t be.
Still waiting for the final report on exactly how unavoidable the damage was that led to its difficult situation (and later, demise), and how undebatable the impossibility for a fix was, taking into account the structure's performance during the failure.
Although it becomes somewhat complicated by the fact that such things become self-fulfilling prophecies. If enough people predict it won’t happen, decisionmakers may just decide it *shouldn’t* be rebuilt.
Post by: zubenelgenubi on 10/14/2022 07:54 am
Post by: AmigaClone on 10/14/2022 08:27 am
Post by: Hobbes-22 on 10/15/2022 07:58 am
https://apnews.com/article/astronomy-technology-science-caribbean-puerto-rico-f4dff01350154a2eb5460e5834564fbd (https://apnews.com/article/astronomy-technology-science-caribbean-puerto-rico-f4dff01350154a2eb5460e5834564fbd)
Quote
The National Science Foundation announced Thursday that it will not rebuild a renowned radio telescope in Puerto Rico, which was one of the world’s largest until it collapsed nearly two years ago.
Instead, the agency issued a solicitation for the creation of a $5 million education center at the site that would promote programs and partnerships related to science, technology, engineering and math. It also seeks the implementation of a research and workforce development program, with the center slated to open next year in the northern mountain town of Arecibo where the telescope was once located.
The solicitation does not include operational support for current infrastructure at the site that is still in use, including a 12-meter radio telescope or the Lidar facility, which is used to study the upper atmosphere and ionosphere to analyze cloud cover and precipitation data.
Post by: edzieba on 10/19/2022 10:13 am
The collapse of the Arecibo Radio Telescope made the decision to decommission the entire observatory a lot easier. Granted, for many years while the US Budget as a whole has grown, the budget to maintain and improve that telescope didn't keep pace with inflation, much less the needs after being hit by earthquakes and hurricanes.The post-collapse studies found that the hurricanes and earthquakes over the years likely did not make a meaningful contribution to the collapse, with the primary cause being the cable spelter sockets on the anchors failing over time (zinc shear + incorrect cable splay) and the lack of load margin in the cable structure. Apart from a wholesale replacement of all affected cables (i.e. all cables) at Arecibo, receiving the proper maintenance would only have extended the time until that complete replacement was required.
Even among the pre-collapse studies, all 3 advised that collapse was imminent and recommended demolition before uncontrolled collapse occurred, with only one mentioning an alternative scheme of dangling people from a helicopter to place weights onto the spans to potentially qualify them for works underneath via testing at an increased load to prove presence of additional margin. Which we now know from post-collapse studies, that would have likely triggered a collapse (and very likely a fatal accident too), since such a theorised margin did not exist in reality.
Post by: eeergo on 08/15/2023 12:17 pm
https://twitter.com/Dr_ThomasZ/status/1691201378423631872
Yesterday was the last day the Observatory was such, even if in a degraded quiescent state. Now it's only an understaffed "educational-center-to-be", i.e. moldy breadcrumbs, since "The Arecibo Observatory was disconnected from the web today Monday, August 14, 2023, at 6:03 PM AST."
https://twitter.com/ProfAbelMendez/status/1691075133098594304
Of note, willful neglect of its heritage is ongoing, with only last-ditch individual efforts allowing to save some of the increasingly scattered remains. In particular, software and documentation to interpret the archived data (in Texas) is reported to be unsupported, as well as hardware to keep it in.
Post by: deadman1204 on 08/15/2023 04:26 pm
They'd want to see the milky way directly.
Post by: matthewkantar on 08/15/2023 04:35 pm
Post by: jstrotha0975 on 08/15/2023 06:59 pm
Post by: matthewkantar on 08/15/2023 07:10 pm
Hawaii won't let them build the 30 meter telescope, never mind a large radio telescope.
I mean Hawaii would welcome removal of the current installation.
Post by: Star One on 08/15/2023 08:58 pm
I don’t think the Hawaiians who work there would think that. Or did you think no local people were scientists.Hawaii won't let them build the 30 meter telescope, never mind a large radio telescope.
I mean Hawaii would welcome removal of the current installation.
Post by: matthewkantar on 08/15/2023 09:24 pm
I don’t think the Hawaiians who work there would think that. Or did you think no local people were scientists.Hawaii won't let them build the 30 meter telescope, never mind a large radio telescope.
I mean Hawaii would welcome removal of the current installation.
Exactly.
Post by: Eric Hedman on 08/15/2023 09:49 pm
Hawaii won't let them build the 30 meter telescope, never mind a large radio telescope.Supposedly construction starts before the end of the year:
https://scitechdaily.com/construction-begin-thirty-meter-telescope/ (https://scitechdaily.com/construction-begin-thirty-meter-telescope/)
After all these years, we'll find out soon if it gets started.
Post by: Blackstar on 08/15/2023 10:12 pm
The location is rather remote and not easy to get to. Without the dish, the only science that could be done there might be a nature facility. There are buildings, and some living quarters. It would not surprise me if the plans for a "science facility" are to use it for nature and biology studies out in the forest. Nobody is going to go there for anything astronomy-related now.
Post by: deadman1204 on 08/16/2023 02:54 pm
That article has a 2014 date at the top unfortunatelyHawaii won't let them build the 30 meter telescope, never mind a large radio telescope.Supposedly construction starts before the end of the year:
https://scitechdaily.com/construction-begin-thirty-meter-telescope/ (https://scitechdaily.com/construction-begin-thirty-meter-telescope/)
After all these years, we'll find out soon if it gets started.
Post by: Paul451 on 08/16/2023 06:02 pm
Clean up the site and turn it over to the locals, science there is a thing of the past, money spent will be wasted.
Unfortunately, they're facing the problems that a lot of end-of-life projects face, there's no funding for basic historical preservation. Not preserving the data, not documenting the code, not preserving historical buildings and artefacts, nor doing basic cleanup on the site. It's just being left to rot. 60 years of history.
[Aside: The site also has other co-located research facilities that are still operational.]
Post by: matthewkantar on 08/16/2023 08:18 pm
Clean up the site and turn it over to the locals, science there is a thing of the past, money spent will be wasted.
Unfortunately, they're facing the problems that a lot of end-of-life projects face, there's no funding for basic historical preservation. Not preserving the data, not documenting the code, not preserving historical buildings and artefacts, nor doing basic cleanup on the site. It's just being left to rot. 60 years of history.
[Aside: The site also has other co-located research facilities that are still operational.]
If historians are interested, let history money pay for it. NSF funds are for science, not sentimentality.
Post by: laszlo on 08/16/2023 08:35 pm
Clean up the site and turn it over to the locals, science there is a thing of the past, money spent will be wasted.
Unfortunately, they're facing the problems that a lot of end-of-life projects face, there's no funding for basic historical preservation. Not preserving the data, not documenting the code, not preserving historical buildings and artefacts, nor doing basic cleanup on the site. It's just being left to rot. 60 years of history.
[Aside: The site also has other co-located research facilities that are still operational.]
If historians are interested, let history money pay for it. NSF funds are for science, not sentimentality.
History is not sentimentality. It's what keeps us from repeating mistakes, re-inventing the wheel and otherwise wasting science money.
Post by: DanClemmensen on 08/16/2023 09:19 pm
“Those who cannot remember the past are condemned to repeat it.”Clean up the site and turn it over to the locals, science there is a thing of the past, money spent will be wasted.
Unfortunately, they're facing the problems that a lot of end-of-life projects face, there's no funding for basic historical preservation. Not preserving the data, not documenting the code, not preserving historical buildings and artefacts, nor doing basic cleanup on the site. It's just being left to rot. 60 years of history.
[Aside: The site also has other co-located research facilities that are still operational.]
If historians are interested, let history money pay for it. NSF funds are for science, not sentimentality.
History is not sentimentality. It's what keeps us from repeating mistakes, re-inventing the wheel and otherwise wasting science money.
-- George Santayana
In particular, we are apparently at risk of losing the data. Why spend millions to gather data if you are not making provision to preserve it? It's a virtual certainty that there is information buried within the 50 years of Arecibo data that could be used to find the past history of something we will recognize only in the future, and often a longer timeline results in higher precision. The lesson to learn: spend a little time ans money now for archiving and curation of data from our current experiments like JWST and Mars rovers.
Post by: ccdengr on 08/16/2023 09:37 pm
In particular, we are apparently at risk of losing the data.According to https://news.utexas.edu/2021/05/10/priceless-astronomy-data-saved-after-collapse-of-arecibo-telescope/ all the data were supposed to be moved to TACC starting in 2021.
Post by: eeergo on 08/16/2023 09:57 pm
In particular, we are apparently at risk of losing the data.According to https://news.utexas.edu/2021/05/10/priceless-astronomy-data-saved-after-collapse-of-arecibo-telescope/ all the data were supposed to be moved to TACC starting in 2021.
Not the documentation or the interpreter software or even the specialized equipment needed to run some of it - as reported a few posts back. Without that, raw data will soon be as good as gibberish, if not immediately.
Post by: Paul451 on 08/16/2023 10:17 pm
Archiving scientific data takes money and effort, and is generally an ongoing project.
Post by: DanClemmensen on 08/16/2023 10:41 pm
This is why I included curation. Just storing the data is not enough. Curation includes all that stuff, but it also includes mundane stuff like making copies for redundant geographically-separated backup, copying from obsolete media to new media, etc.In particular, we are apparently at risk of losing the data.According to https://news.utexas.edu/2021/05/10/priceless-astronomy-data-saved-after-collapse-of-arecibo-telescope/ all the data were supposed to be moved to TACC starting in 2021.
Not the documentation or the interpreter software or even the specialized equipment needed to run some of it - as reported a few posts back. Without that, raw data will soon be as good as gibberish, if not immediately.
Post by: Star One on 08/16/2023 11:00 pm
And this is not the first important project where it's happened. (Hell, it might be more common than not.) We nearly lost a tonne of irreplaceable Apollo footage, except for a grassroots project by interested amateurs. NASA is kind of notorious for this kind of stuff.
Archiving scientific data takes money and effort, and is generally an ongoing project.
You paint a depressing picture here. I know that there have projects where stuff has nearly been lost due to the data being held on defunct methods of data storage. Like with the modern Domesday book in the UK where it was all stored on laserdisc and if not for CAMiLEON project the data could have been lost.
https://www.historyofinformation.com/detail.php?id=1661
Post by: deadman1204 on 08/17/2023 03:29 pm
However, restoring the buildings and preserving them? Thats a waste of NSF funds. We can have vague feel good quotes about history all day long, but constantly paying money for upkeep on some buildings in the jungle that no one will visit isn't "preventing us from making the mistakes of the past".
Its just a constant fiscal drain on buildings that serve literally no purpose.
No one is gonna go there except the people who live in the area. There is no point. Why spend millions on pointless buildings that can go to new science instead? Or simply go towards further processing of existing data.
Post by: ccdengr on 08/17/2023 03:39 pm
Not the documentation or the interpreter software or even the specialized equipment needed to run some of it ...It's not clear to me that some of that stuff existed in a usable form at Arecibo before the collapse either, except the last generation. Arecibo has been operating since the mid-60s and obviously computing and storage have evolved. I imagine that for each specific observing run, the investigators got the data and have it at their home institutions.
NASA, at least the planetary side, has tried to address these issues with the Planetary Data System. https://pds.nasa.gov/datasearch/keyword-search/search.jsp?q=arecibo shows quite a few data collections, though I doubt this is all of the NASA-funded stuff that was ever done there.
Post by: Blackstar on 08/20/2023 02:47 am