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#40
by
Nomadd
on 15 Nov, 2020 23:15
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Would this facility ever be replaced is the worst comes to pass, or are array type setups a lot more practical now days?
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.
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#41
by
russianhalo117
on 16 Nov, 2020 00:04
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Would this facility ever be replaced is the worst comes to pass, or are array type setups a lot more practical now days?
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.
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.
It boils down to cost and timeframe and funding.
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#42
by
Blackstar
on 16 Nov, 2020 11:33
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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.
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#43
by
trm14
on 16 Nov, 2020 12:24
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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.
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#44
by
edzieba
on 16 Nov, 2020 12:38
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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?
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#45
by
Swedish chef
on 16 Nov, 2020 18:28
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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.htmlTo 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.
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.
Edit: Spelling
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#46
by
Zed_Noir
on 17 Nov, 2020 02:53
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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.
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#47
by
Star One
on 17 Nov, 2020 07:14
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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.
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#48
by
edzieba
on 17 Nov, 2020 11:11
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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
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.
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
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#49
by
DaveS
on 19 Nov, 2020 15:46
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Bad news:
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/1329463766308753414William 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
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#50
by
Orbiter
on 19 Nov, 2020 16:00
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#51
by
Nomadd
on 19 Nov, 2020 16:41
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The cable autopsies should be interesting.
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.
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#52
by
Blackstar
on 19 Nov, 2020 16:54
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#53
by
eeergo
on 19 Nov, 2020 16:58
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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.
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
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#54
by
libra
on 19 Nov, 2020 17:08
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Another casualty in a deeply shitty year - 2020, how we hate you. Clarke and Sagan will spin in their graves.
Then again, if it can't be repaired...
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#55
by
Nomadd
on 19 Nov, 2020 17:23
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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.
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#56
by
whitelancer64
on 19 Nov, 2020 17:41
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#57
by
Frogstar_Robot
on 19 Nov, 2020 17:46
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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."]
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#58
by
Bananas_on_Mars
on 19 Nov, 2020 18:05
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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.
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.
https://en.wikipedia.org/wiki/Square_Kilometre_Array
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#59
by
racevedo88
on 19 Nov, 2020 18:10
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