Editing Arecibo Observatory (section)

===Arecibo Telescope===
{{Main|Arecibo Telescope}}
The observatory's main feature was its large [[Arecibo Telescope|radio telescope]], whose main collecting dish was an inverted [[spherical dome]] {{convert|305|m|ft|sigfig=3|order=flip}} in diameter with an {{convert|265|m|ft|sigfig=3|adj=on|order=flip}} [[radius of curvature]],<ref name="arecibo-multifeed">{{cite journal |last1=Goldsmith |first1=P. F. |last2=Baker |first2=L. A. |last3=Davis |first3=M. M. |last4=Giovanelli |first4=R. |title=Multi-feed Systems for the Arecibo Gregorian |journal=Astronomical Society of the Pacific Conference Series |date=1995 |volume=75 |bibcode=1995ASPC...75...90G |pages=90–98}}</ref> constructed inside a [[karst]] [[sinkhole]].<ref>{{cite web |url=https://www.naic.edu/ao/telescope-description |title=Telescope Description |publisher=[[National Astronomy and Ionosphere Center]] |access-date=November 20, 2020 |archive-date=November 20, 2020 |archive-url=https://web.archive.org/web/20201120035144/https://www.naic.edu/ao/telescope-description |url-status=live}}</ref> The dish's surface was made of 38,778 perforated aluminum panels, each about {{convert|1|by|2|m|ft|0|order=flip}}, supported by a mesh of steel cables.<ref name="arecibo-multifeed"/> The ground beneath supported shade-tolerant vegetation.<ref>{{cite web |url=https://www.nsf.gov/mps/ast/env_impact_reviews/arecibo/eis/DEIS.pdf |website=nsf.gov |publisher=NSF |page=66 |title=Environmental Impact Statement for the Arecibo Observatory Arecibo, Puerto Rico (Draft) |quote=At the Arecibo Observatory, a mix of shade-tolerant species have colonized the area beneath the 305-meter radio telescope dish. |access-date=November 23, 2020 |archive-date=December 16, 2020 |archive-url=https://web.archive.org/web/20201216232114/https://www.nsf.gov/mps/ast/env_impact_reviews/arecibo/eis/DEIS.pdf |url-status=live }}</ref>

Since its completion in November 1963, the Telescope had been used for [[radar astronomy]] and [[radio astronomy]], and had been part of the [[Search for extraterrestrial intelligence]] (SETI) program. It was also used by NASA for [[Near-Earth object]] detection. Since around 2006, NSF funding support for the telescope had waned as the Foundation directed funds to newer instruments, though academics petitioned to the NSF and Congress to continue support for the telescope. Numerous hurricanes, including [[Hurricane Maria]], had damaged parts of the telescope, straining the reduced budget.

Two cable breaks, one in August 2020 and a second in November 2020, threatened the structural integrity of the support structure for the suspended platform and damaged the dish. The NSF determined in November 2020 that it was safer to decommission the telescope rather than to try to repair it, but the telescope collapsed before a controlled demolition could be carried out. The remaining support cables from one tower failed around 7:56&nbsp;a.m. local time on December 1, 2020, causing the receiver platform to fall into the dish and collapsing the telescope.<ref name="guardian collapsed">{{cite news |date=1 December 2020 |title=Giant Arecibo radio telescope collapses in Puerto Rico |work=[[The Guardian]] |agency=[[Associated Press]] |url=https://www.theguardian.com/world/2020/dec/01/arecibo-radio-telescope-collapses-puerto-rico |access-date=1 December 2020 |archive-date=December 25, 2020 |archive-url=https://web.archive.org/web/20201225005405/https://www.theguardian.com/world/2020/dec/01/arecibo-radio-telescope-collapses-puerto-rico |url-status=live }}</ref><ref name="APNews1Dec2020">{{cite news |last1=Coto |first1=Danica |title=Huge Puerto Rico radio telescope, already damaged, collapses |url=https://apnews.com/article/technology-arecibo-observatory-puerto-rico-science--0da6abb251f455977bf0c752348e712e |access-date=5 December 2020 |work=AP NEWS |date=1 December 2020 |archive-date=April 22, 2021 |archive-url=https://web.archive.org/web/20210422013836/https://apnews.com/article/technology-arecibo-observatory-puerto-rico-science--0da6abb251f455977bf0c752348e712e |url-status=live }}</ref>

NASA led an extensive failure investigation and reported the findings,<ref name="collapsed">{{cite news |date=30 June 2021 |title=Arecibo Observatory Auxiliary M4N Socket Termination Failure Investigation |url=https://ntrs.nasa.gov/citations/20210017934 |website=[[NASA]] |access-date=July 1, 2021 |archive-date=July 3, 2021 |archive-url=https://web.archive.org/web/20210703000546/https://ntrs.nasa.gov/citations/20210017934 |url-status=live }}</ref> along with a technical bulletin with industry recommendations.<ref>{{Cite web |date=2 August 2021 |title=NASA Engineering and Safety Center Technical Bulletin No. 21-05, Industry Recommendations from Arecibo Observatory Zinc Spelter Socket Joint Failure Analysis |url=https://www.nasa.gov/sites/default/files/atoms/files/tb_21-05_arecibo_failure_analysis_080221_final.pdf |url-status=live |website=[[NASA]] |archive-url=https://web.archive.org/web/20220103160714/https://www.nasa.gov/sites/default/files/atoms/files/tb_21-05_arecibo_failure_analysis_080221_final.pdf |archive-date=2022-01-03}}</ref> The investigation concluded that "a combination of low socket [[design margin]] and a high percentage of sustained loading revealed an unexpected vulnerability to [[Creep (deformation)|zinc creep]] and environments, resulting in long-term cumulative damage and progressive zinc/wire failure".