Arecibo Telescope#Research and discoveries

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The telescope's main collecting dish had the shape of a spherical cap {{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, and was constructed inside a karst sinkhole. The dish 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. The ground beneath supported shade-tolerant vegetation.{{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.}}

The telescope had three radar transmitters, with effective isotropic radiated powers (EIRPs) of 22 TW (continuous) at 2380 MHz,{{cite journal |title=A Search for Technosignatures from 14 Planetary Systems in the Kepler Field with the Green Bank Telescope at 1.15–1.73 GHz |first1=Jean-Luc |last1=Margot |first2=Adam H.|last2= Greenberg|first3= Pavlo|last3= Pinchuk|first4= Akshay|last4= Shinde|first5= Yashaswi|last5= Alladi|first6= Srinivas|last6= Prasad|first7= M. Oliver|last7= Bowman|first8= Callum|last8= Fisher|first9= Szilard|last9= Gyalay|first10= Willow|last10= McKibbin|first11= Brittany |last11=Miles|first12= Donald|last12= Nguyen|first13= Conor|last13= Power|first14= Namrata|last14= Ramani|first15= Rashmi |last15=Raviprasad|first16= Jesse|last16= Santana|first17= Ryan S.|last17= Lynch |display-authors=1 |journal=Astronomical Journal |year=2018 |volume=155 |issue=5 |page=209 |doi=10.3847/1538-3881/aabb03 |arxiv=1802.01081 |bibcode=2018AJ....155..209M |s2cid=13710050 |doi-access=free}} 3.2 TW (pulse peak) at 430 MHz, and 200 MW at 47 MHz,{{cite web |url=https://www.naic.edu/~phil/hardware/xmiter430/430tx_manual_hagen.pdf |title=Areciebo 430 MHz Radar Operation and Maintenance Manual |pages=6–7 |last=Hagen |first=Jon |date=2005 |website=NAIC |access-date=November 21, 2020}} as well as an ionospheric modification facility operating at 5.1 and 8.175 MHz.{{cite web |url=https://www.naic.edu/~enossa/HF-docs/HF-Call2018-official.pdf |title=Arecibo Call for Ionospheric Modification (HF facility) Proposals – 2018 |date=December 8, 2017 |first=Eliana |last=Nossa |website=Arecibo Observatory}}

The dish remained stationary, while receivers and transmitters were moved to the proper focal point of the telescope to aim at the desired target.{{cite journal |last1=Cohen |first1=Marshall H. |year=2009 |title=Genesis of the 1000-foot Arecibo Dish |journal=Journal of Astronomical History and Heritage |volume=12 |issue=2 |pages=141–152 |doi=10.3724/SP.J.1440-2807.2009.02.06 |doi-access=free |bibcode=2009JAHH...12..141C |s2cid=18990068 |url=https://resolver.caltech.edu/CaltechAUTHORS:20091231-110730776}} [https://authors.library.caltech.edu/17042/1/Arecibo_Genesis_JAH2_2009.pdf PDF] As a spherical mirror, the reflector's focus was along a line rather than at one point. As a result, complex line feeds were implemented to carry out observations, with each line feed covering a narrow frequency band measuring 10–45 MHz. A limited number of line feeds could be used at any one time, limiting the telescope's flexibility.{{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 |year=1995 |volume=75 |bibcode=1995ASPC...75...90G |pages=90–98}}

The receiver was on an {{convert|900|ST|t|adj=on|order=flip}} platform suspended {{convert|150|m|ft|abbr=on|sigfig=3}} above the dish by 18 main cables running from three reinforced concrete towers (six cables per tower), one {{convert|365|ft|m|abbr=on|order=flip}} high and the other two {{convert|265|ft|abbr=on|order=flip}} high, placing their tops at the same elevation. Each main cable was a {{convert|8|cm|in|adj=on|abbr=on}} diameter bundle containing 160 wires, with the bundle painted over and dry air continuously blown through to prevent corrosion due to the humid tropic climate.{{cite news |url=https://www.science.org/content/article/how-famed-arecibo-telescope-fell-and-how-it-might-rise-again |title=How the famed Arecibo telescope fell—and how it might rise again |first=Daniel |last=Clery |date=January 14, 2021 |access-date=January 14, 2021 |magazine=Science}} The platform had a rotating, bow-shaped track {{convert|93|m|ft|abbr=on|sigfig=3}} long, called the azimuth arm, carrying the receiving antennas and secondary and tertiary reflectors. This allowed the telescope to observe any region of the sky in a forty-degree cone of visibility about the local zenith (between −1 and 38 degrees of declination). Puerto Rico's location near the Northern Tropic allowed the Arecibo telescope to view the planets in the Solar System over the northern half of their orbit. The round trip light time to objects beyond Saturn is longer than the 2.6-hour time that the telescope could track a celestial position, preventing radar observations of more distant objects.{{cite web |url=https://www.naic.edu/ao/telescope-description |title=Telescope Description |website=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}}{{cite journal |last1=Nicholson|first1= Philip D.|first2= Richard G.|last2= French|first3= Donald B.|last3= Campbell|first4= Jean-Luc|last4= Margot|first5= Michael C.|last5= Nolan|first6= Gregory J. |last6=Black|first7=Heikki J. |last7=Salo |title=Radar imaging of Saturn's rings |journal=Icarus |volume=177 |issue=1 |year=2005 |pages=32–62 |doi=10.1016/j.icarus.2005.03.023 |bibcode=2005Icar..177...32N |citeseerx=10.1.1.527.7256 }}

{{Wide image|Panorama arecibo telescope from observation deck.jpg|800px|The Arecibo Radio Telescope as viewed from the observation deck, October 2013}}

File:Arecibo_radio_telescope_SJU_06_2019_6144.jpg

File:Arecibo Radiotelescopio SJU 06 2019 7428.jpg arm rotated beneath it. To the right was the Gregorian sub-reflector, and to the left was the remains of the {{convert|96|ft|m|adj=mid|-long}} line feed tuned to 430 MHz (destroyed by Hurricane Maria). Also to the right was the catwalk and part of the rectangular waveguide that brought the 2.5 MW 430 MHz radar transmitter's signal up to the focal region.]]

The origins of the observatory trace to late 1950s efforts to develop anti-ballistic missile (ABM) defenses as part of the newly formed United States Department of Defense (DoD) Advanced Research Projects Agency (ARPA) ABM umbrella-effort, Project Defender. Even at this early stage it was clear that the use of radar decoys would be a serious problem at the long ranges needed to successfully attack a warhead, ranges on the order of {{convert|1000|mile|km|abbr=on|order=flip}}.{{Cite web |first=Barry |last=Rosenberg |url=http://www.darpa.mil/Docs/Missile_Defense_200807180930582.pdf |title=DARPA Paves the Way for U.S. Efforts in Ballistic Missile Defense |archive-url=https://web.archive.org/web/20160305010418/http://www.darpa.mil/Docs/Missile_Defense_200807180930582.pdf |archive-date=March 5, 2016 |work=50 Years of Bridging the Gap, DARPA}}{{Cite web |url=http://www.alternatewars.com/WW3/WW3_Documents/DARPA/DARPA_II_PRESS.htm |title=Defender Anti-Ballistic Missile |archive-url=https://web.archive.org/web/20140531234413/http://www.alternatewars.com/WW3/WW3_Documents/DARPA/DARPA_II_PRESS.htm |archive-date=May 31, 2014 |work=DARPA Technical Accomplishments Volume II: A Historical Review Of Selected DARPA Projects, April 1991, Section I: PRESS}}

Among the many Defender projects were several studies based on the concept that a re-entering nuclear warhead would cause unique physical signatures while still in the upper atmosphere. It was known that hot, high-speed objects caused ionization of the atmosphere that reflects radar waves, and it appeared that a warhead's signature would be different enough from decoys that a detector could pick out the warhead directly, or alternately, provide added information that would allow operators to focus a conventional tracking radar on the single return from the warhead.

Although the concept appeared to offer a solution to the tracking problem, there was almost no information on either the physics of re-entry or a strong understanding of the normal composition of the upper layers of the ionosphere. ARPA began to address both simultaneously. To better understand the radar returns from a warhead, several radars were built on Kwajalein Atoll, while Arecibo started with the dual purpose of understanding the ionosphere's F-layer while also producing a general-purpose scientific radio observatory.

On November 6, 1959, Cornell University entered into a contract with ARPA to carry out development studies for a large-scale ionospheric radar probe, exploring how this instrument could also be utilized in radio astronomy and other scientific areas.{{Cite web |title=Arecibo Observatory |url=https://www.darpa.mil/about-us/timeline/arecibo-observatory |access-date=September 28, 2024 |website=darpa.mil}} The observatory was built between mid-1960 and November 1963. William E. Gordon and George Peter of Cornell University oversaw its design for study of the Earth's ionosphere.{{Citation |last=Gold |first=Thomas| author-link =Thomas Gold |date=May 23, 2012 |title=Taking the Back off the Watch: A Personal Memoir |volume=381 |chapter=7| chapter-url =https://books.google.com/books?id=vlaFA0zgmSoC&q=gordon |edition=1 |publisher=Springer Heidelberg |location=New York |language=en |page=119 |isbn=978-3-642-27587-6 |url=https://books.google.com/books?id=vlaFA0zgmSoC&q=Gordon+ |doi=10.1007/978-3-642-27588-3 |series=Astrophysics and Space Science Library |access-date =October 14, 2020 |archive-date =November 20, 2020 |archive-url=https://web.archive.org/web/20201120204556/https://books.google.com/books?id=vlaFA0zgmSoC&q=Gordon+ |url-status=live}}{{Citation |last=Frè |first=Pietro |date=2013 |title=Gravity, a geometrical course |chapter=7| chapter-url =https://books.google.com/books?id=1klJvLbHEQYC&q=radio+telescope+suspension+system&pg=PA276 |edition=1 |volume=1:Development of the theory and basic physical applications |publisher=Springer |location=New York |language=en |page=276 |isbn=978-94-007-5360-0 |doi=10.1007/978-94-007-5361-7 |bibcode=2013ggc1.book.....F |access-date=October 14, 2020 |archive-date=November 20, 2020 |archive-url=https://web.archive.org/web/20201120204542/https://books.google.com/books?id=1klJvLbHEQYC&q=radio+telescope+suspension+system&pg=PA276 |url-status=live}}{{cite journal |last1=Mathews |first1=J. D. |title=A short history of geophysical radar at Arecibo Observatory |journal=History of Geo- and Space Sciences |date=13 March 2013 |volume=4 |issue=1 |pages=19–33 |doi=10.5194/hgss-4-19-2013 |bibcode=2013HGSS....4...19M |doi-access=free}} He was attracted to the sinkholes in the karst regions of Puerto Rico that offered perfect cavities for a very large dish.{{cite web |url=http://www.ieee.org/web/aboutus/history_center/arecibo.html |title=IEEE History Center: NAIC/Arecibo Radiotelescope, 1963 |publisher=Institute of Electrical and Electronics Engineers |access-date=September 2, 2008 |archive-date=July 6, 2008 |archive-url=https://web.archive.org/web/20080706035625/http://www.ieee.org/web/aboutus/history_center/arecibo.html |url-status=dead}}{{cite web |publisher=National Astronomy and Ionosphere Center |url=http://www.naic.edu/history_gal/historicgal.html |title=Pictures of the construction of Arecibo Observatory (start to finish) |access-date=May 5, 2009 |archive-url=https://web.archive.org/web/20090505205805/http://www.naic.edu/history_gal/historicgal.html |archive-date=May 5, 2009 |url-status=live}}{{cite web |work=Acevedo, Tony (June 2004) |url=http://www.naic.edu/public/descrip_eng.htm |title=Description of Engineering of Arecibo Observatory |access-date=May 5, 2009 |archive-url=https://web.archive.org/web/20090504055743/http://www.naic.edu/public/descrip_eng.htm |archive-date=May 4, 2009 |url-status=dead |df=mdy-all}} Originally, a fixed parabolic reflector was envisioned, pointing in a fixed direction with a {{convert|150|m|ft|abbr=on|sigfig=3}} tower to hold equipment at the focus. This design would have limited its use in other research areas, such as radar astronomy, radio astronomy and atmospheric science, which require the ability to point at different positions in the sky and track those positions for an extended time as the Earth rotates.

Ward Low of the ARPA pointed out this flaw and put Gordon in touch with the Air Force Cambridge Research Laboratory (AFCRL) in Boston, Massachusetts, where one group headed by Phil Blacksmith was working on spherical reflectors and another group was studying the propagation of radio waves in and through the upper atmosphere. Cornell University proposed the project to ARPA in mid-1958 and a contract was signed between the AFCRL and the University in November 1959. Cornell University and Zachary Sears published a request for proposals (RFP) asking for a design to support a feed moving along a spherical surface {{convert|435|ft|m|0|order=flip}} above the stationary reflector. The RFP suggested a tripod or a tower in the center to support the feed. On the day the project for the design and construction of the antenna was announced at Cornell University, Gordon had also envisioned a {{convert|435|ft|m|abbr=on|order=flip}} tower centered in the {{convert|1000|ft|m|abbr=on|sigfig=3|order=flip}} reflector to support the feed.{{Citation |last=Gordon |first=William| author-link = William E. Gordon |title=Cornell will build a radar to observe the ionosphere |newspaper=New York Herald Tribune |location=New York City |type=Engineer's News Supplement |date=October 25, 1959 |page=1}}{{cite book |first1=William E. |last1=Gordon |author-link =William E. Gordon |first2=Henry |last2=Booker |author2-link =Henry G. Booker |first3=Ben |last3=Nichols |chapter=Design Study of a Radar to Explore the Earth's Ionosphere and Surrounding Space | title=Research Report EE 395 |year=1958 |page=23 |place=Ithaca, New York |publisher=Cornell University, School of Electrical Engineering}}

George Doundoulakis, who directed research at the General Bronze Corporation in Garden City, New York, along with Zachary Sears, who directed Internal Design at Digital B & E Corporation, New York, received the RFP from Cornell University for the antenna design and studied the idea of suspending the feed with his brother, Helias Doundoulakis, a civil engineer. George Doundoulakis identified the problem that a tower or tripod would have presented around the center, (the most important area of the reflector), and devised a better design by suspending the feed. He presented his proposal to Cornell University for a doughnut or torus-type truss suspended by four cables from four towers above the reflector, having along its edge a rail track for the azimuthal truss positioning. This second truss, in the form of an arc, or arch, was to be suspended below, which would rotate on the rails through 360 degrees. The arc also had rails on which the unit supporting the feed would move for the feed's elevational positioning. A counterweight would move symmetrically opposite to the feed for stability and, if a hurricane struck, the whole feed could be raised and lowered. Helias Doundoulakis designed the cable suspension system which was finally adopted. The final configuration was substantially the same as in the original drawings by George and Helias Doundoulakis, although with three towers, instead of the four drawn in the patent, which was granted to Helias Doundoulakis by the U.S. Patent office.{{cite journal |first=W. |last=Cooke |title=Arecibo radio antenna |journal=IEEE Antennas and Propagation Society Newsletter |volume=18 |issue=5 |pages=6–8 |date=October 1976 |doi=10.1109/MAP.1976.27265 |s2cid=31708779}}

The suspended structure was designed by Dr. Thomas C. Kavanagh, Fred Severud, and Dr. Hans Bandel, who were selected after the 1959 RFP issued by Cornell University. A proposal by the General Bronze Corporation was not selected as it did not meet specifications, according to an editorial response by Donald Cooke (Cornell's spokesperson) to Helias Doundoulakis in a newsletter of the Institute of Electrical and Electronics Engineers (IEEE). Cooke stated that Doundoulakis used an incorrect feed/paraxial surface measurement. However, the measurement Cooke used was from Doundoulakis’ patent issued in 1966, and not from the 1959 RFP meetings which predated the patent by seven years.{{US patent reference |number=3273156 |y=1966 |m=09 |d=13 |inventor=Helias Doundoulakis |title=Radio Telescope having a scanning feed supported by a cable suspension over a stationary reflector}} Furthermore, proposal measurements presented by George Doundoulakis and Helias Doundoulakis at the RFP meeting on December 10, 1959, were not referenced in Cooke's editorial response. The originators of this proposal subsequently filed a dispute, originally for $1.2 million but was settled for $10,000 because "the defense in a court trial would cost far more than the $10,000 for which the case was settled," and accordingly, on April 11, 1975, Doundoulakis v. U.S. (Case 412-72) had been ruled in plaintiff's favor by the United States Court of Federal Claims, that “(a) a judgment has been entered in favor of the plaintiffs (Helias Doundoulakis, William J. Casey, and Constantine Michalos) against the United States and (b) in consideration of the sum of $10,000 to be paid by the United States Government to the plaintiff, the plaintiffs grants to the United States Government an irrevocable, fully-paid, non-exclusive license under the aforesaid U.S. Patent No. 3, 273, 156 to Cornell University.”

The idea of a spherical reflecting mirror with a steerable secondary has since been used in optical telescopes, in particular, the Hobby–Eberly Telescope{{cite book |doi=10.1117/12.458223 |chapter=The Hobby-Eberly Telescope Completion Project |title=Large Ground-based Telescopes |year=2003 |editor1-last=Oschmann |editor1-first=Jacobus M |last1=Booth |first1=John A. |last2=Wolf |first2=Marsha J. |last3=Fowler |first3=James R. |last4=Adams |first4=Mark T. |last5=Good |first5=John M. |last6=Kelton |first6=Philip W. |last7=Barker |first7=Edwin S. |last8=Palunas |first8=Povilas |last9=Bash |first9=Frank N. |last10=Ramsey |first10=Lawrence W. |last11=Hill |first11=Gary J. |last12=MacQueen |first12=Phillip J. |last13=Cornell |first13=Mark E. |last14=Robinson |first14=Edward L. |volume=4837 |page=919 |s2cid=121019413 |editor2-first=Larry M |editor2-last=Stepp}}

Construction began in mid-1960, with the telescope operational about three years later. The telescope's and the supporting observatory's official opening as the Arecibo Ionospheric Observatory (AIO) was held on November 1, 1963.{{cite web |url=http://www.history.com/encyclopedia.do?vendorId=FWNE.fw..ar136000.a |title=Arecibo Observatory |website=History.com |access-date=September 2, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20090314225635/http://www.history.com/encyclopedia.do?vendorId=FWNE.fw..ar136000.a |archive-date=March 14, 2009}}{{cite magazine |url=https://www.govinfo.gov/content/pkg/CREC-2003-10-31/pdf/CREC-2003-10-31.pdf |title=The 40th Anniversary of the Arecibo Observatory |page=E2181 |first=Aníbal |last=Acevedo-Vila |date=October 30, 2003 |access-date=January 14, 2021 |magazine=Congressional Record |volume=149 |issue=156}}

Since its construction, the telescope was upgraded several times, following the facility's oversight from the DoD to the National Science Foundation on October 1, 1969, and subsequent renaming of the AIO to the National Astronomy and Ionosphere Center (NAIC) in September 1971. Initially, when the maximum expected operating frequency was about 500 MHz, the surface consisted of half-inch galvanized wire mesh laid directly on the support cables. In 1973, a high-precision surface consisting of 38,000 individually adjustable aluminum panels replaced the old wire mesh, and the highest usable frequency rose to about 5000 MHz. A Gregorian reflector system was installed in 1997, incorporating secondary and tertiary reflectors to focus radio waves at one point. This allowed installing a suite of receivers, covering the full 1–10 GHz range, that could be easily moved to the focal point, giving Arecibo more flexibility. The additional instrumentation added {{convert|300|ST|t|adj=on|order=flip}} to the platform, so six additional support cables were added, two for each tower. A metal mesh screen was also installed around the perimeter to block the ground's thermal radiation from reaching the feed antennas. As part of this upgrade the power of the 2380 MHz transmitter was doubled to 1 MW by adding a second Klystron tube and improving the design.{{cite web |url=https://news.cornell.edu/stories/1997/06/inauguration-upgrade-arecibo-observatory-june-14 |title=World's largest radio telescope is even more powerful, sensitive |first=Larry |last=Bernard |date=June 12, 1997 |access-date=November 20, 2020 |work=Cornell Chronicle |archive-date=November 20, 2020 |archive-url=https://web.archive.org/web/20201120204542/https://news.cornell.edu/stories/1997/06/inauguration-upgrade-arecibo-observatory-june-14 |url-status=live}} Finally, in 2013 with a grant of {{USD|2.5 million}}, work for adding the ionospheric modification HF facility began which was completed in 2015. The HF facility consisted on the sender side of six foldable 100 kW crossed dipoles inside the main dish and a hanging 100m wide subreflector mesh between the dish and platform.{{cite web |url=https://grantome.com/grant/NSF/AGS-0742925 |title=The Arecibo High Frequency (HF) Facility: An Instrument to Study Ionospheric Physics |date=2007 |access-date=December 17, 2020 |last1=Sulzer |first1=Michael |last2=Gonzalez |first2=Sixto }}{{WP:Image citation/template | file=The Arecibo Observatory's main reflector and platform.jpg |title=The radio telescope as seen from the cableway |repository=Wikimedia Commons |medium=digital|url=https://commons.wikimedia.org/wiki/File:The_Arecibo_Observatory%27s_main_reflector_and_platform.jpg|id=online |date=Dec 18, 2018}}photo showing 6 cross dipoles and hanging 100m wire mesh reflector

{{wide image|Arecibo Radiotelescopio Panamorama SJU 06 2019 7446.jpg|1200px|Panoramic view of the Arecibo radio telescope primary dish in June 2019. The HF transmitting antennas can be seen at the base of the dish.}}

The Astronomical Sciences and Atmospheric Sciences divisions of the NSF had financially supported Arecibo since its completion in the 1970s, with incremental support by NASA, for operating the planetary radar.{{cite journal |last1=Butrica |first1=Andrew J. |title=To See the Unseen: A History of Planetary Radar Astronomy |journal=NASA Special Publication |year=1996 |volume=4218 |publisher=National Aeronautics and Space Administration |isbn=978-0-16-048578-7 |bibcode=1996NASSP4218.....B |url=https://ntrs.nasa.gov/citations/19960045321 |page=103}} In 2001 NASA announced a rampdown and elimination of its support of the planetary radar by 2005.{{cite web |url=http://www.space.com/scienceastronomy/astronomy/arecibo_cuts_011220.html |title=NASA Trims Arecibo Budget, Says Other Organizations Should Support Asteroid Watch |access-date=July 8, 2008 |first=Robert Roy |last=Britt |date=December 20, 2001 |work=Space.com |publisher=Imaginova |url-status=dead |archive-url=https://web.archive.org/web/20081205190409/http://www.space.com/scienceastronomy/astronomy/arecibo_cuts_011220.html |archive-date=December 5, 2008}}

In 2002, after several years of discussion, the US Congress passed a bill to double the NSF budget, and instructed the NSF to begin new projects.{{cite web |title=Congress Passes Bill Authorizing Doubling of NSF Budget |date=November 1, 2002 |url=https://ww2.aip.org/fyi/2002/congress-passes-bill-authorizing-doubling-nsf-budget |access-date=May 21, 2024 }} As a result, the NSF began committing to major projects. However, the funding increase never arrived and the NSF was left with the new commitments. In 2005 the Astronomical Sciences division commissioned a "Senior Review" of its facilities to deal with its increasingly constrained budget. The Senior Review report released in November 2006 "regretfully" recommended substantially decreased astronomy funding for the Arecibo Observatory, beginning with a cut to {{USD|10.5 million}} in 2007 and continuing to decrease to {{USD|4.0 million}} in 2011. The report further stated that if other sources of funding could not be found, closure of the Observatory was recommended.{{cite web |last=Blandford |first=Roger |title=From the Ground Up: Balancing the NSF Astronomy Program |website=National Science Foundation |date=October 22, 2006 |url=https://www.nsf.gov/mps/ast/seniorreview/sr_report_mpsac_updated_12-1-06.pdf |access-date=July 7, 2008 |archive-url=https://web.archive.org/web/20080626170308/https://www.nsf.gov/mps/ast/seniorreview/sr_report_mpsac_updated_12-1-06.pdf| archive-date=June 26, 2008| url-status=live}}{{cite news |last=Weiss |first=Rick Weiss |title=Radio Telescope And Its Budget Hang in the Balance |url=https://www.washingtonpost.com/wp-dyn/content/article/2007/09/08/AR2007090801654.html?hpid=moreheadlines |newspaper=The Washington Post |location=Arecibo, Puerto Rico |page=A01 |date=September 9, 2007 |access-date=July 8, 2008 |quote=The cash crunch stems from an NSF senior review completed last November. Its $200 million astronomy division, increasingly committed to ambitious new projects, but long hobbled by flat Congressional budgets, was facing a deficit of at least $30 million by 2010. |archive-date=November 6, 2012 |archive-url=https://web.archive.org/web/20121106141623/http://www.washingtonpost.com/wp-dyn/content/article/2007/09/08/AR2007090801654.html?hpid=moreheadlines |url-status=live}}

Academics and researchers responded by organizing to protect and advocate for the observatory. They established the Arecibo Science Advocacy Partnership (ASAP) in 2008, to advance the scientific excellence of Arecibo Observatory research and to publicize its accomplishments in astronomy, aeronomy and planetary radar as to seek additional funding support for the observatory.{{cite web |url=http://areciboscience.org/index.html |title=Arecibo Science Advocacy Partnership |website=Areciboscience |access-date=May 11, 2012 |archive-date=May 14, 2011 |archive-url=https://web.archive.org/web/20110514213802/http://areciboscience.org/index.html |url-status=live}} An additional {{USD|3 million}} in bonds were issued by the government of Puerto Rico to fund the Observatory, which were used to modernize power generation and improve other aging infrastructure.{{cite news |url=http://www.primerahora.com/XStatic/primerahora/template/nota.aspx?n=128502 |title=Senado aprueba emisión de bonos de $450 millones |trans-title=Senate approves $450 million bond issue |newspaper=Primera Hora |location=Guaynabo, Puerto Rico |language=es |date=November 14, 2007 |agency=Associated Press |access-date=September 4, 2008 |archive-url=https://web.archive.org/web/20081208135546/http://www.primerahora.com/XStatic/primerahora/template/nota.aspx?n=128502 |archive-date=December 8, 2008 |url-status=dead}}{{cite news |last1=Gerardo |first1=E. |last2=Alvarado |first2=León |title=Gobernador firma emisión de bonos |newspaper=El Nuevo Día |location=Guaynabo, Puerto Rico |date=August 10, 2008}} Academics, media and influential politicians pressured the United States Congress on the importance of the work of the observatory.{{Cite web |last=Chang |first=Kenneth |date=November 20, 2007 |url=https://www.nytimes.com/2007/11/20/science/space/20scop.html?scp=2 |title=A Hazy Future for a 'Jewel' of Space Instruments |archive-url=https://web.archive.org/web/20151016214548/http://www.nytimes.com/2007/11/20/science/space/20scop.html?scp=2 |archive-date=October 16, 2015 |work=The New York Times}}{{Cite web |first=Jacqui |last=Goddard |date=July 12, 2008 |url=https://www.telegraph.co.uk/news/worldnews/northamerica/usa/2291068/Threat-to-world%27s-most-powerful-radio-telescope-means-we-may-not-hear-ET.html |title=Threat to world's most powerful radio telescope means we may not hear ET |archive-url=https://web.archive.org/web/20081205104758/http://www.telegraph.co.uk/news/worldnews/northamerica/usa/2291068/Threat-to-world%27s-most-powerful-radio-telescope-means-we-may-not-hear-ET.html |archive-date=December 5, 2008 |work=The Daily Telegraph}} led to additional {{USD|3.1 million}} in funding to support Arecibo in the American Recovery and Reinvestment Act of 2009. This was used for basic maintenance and for a second, much smaller, antenna to be used for very long baseline interferometry, new Klystron amplifiers for the planetary radar system and student training.{{cite web |url=http://www.naic.edu/science/new12m_antenna_arecibo.html |title=12-m Phase Reference Antenna |website=NAIC |date=June 28, 2010 |access-date=May 11, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120315121910/http://www.naic.edu/science/new12m_antenna_arecibo.html |archive-date=March 15, 2012}}

Arecibo's budget from NSF continued to wane in the following years.{{Cite web |url=https://www.nsf.gov/about/budget/fy2010/toc.jsp |title=FY2010 Budget Request to Congress |archive-url=https://web.archive.org/web/20180303050446/https://www.nsf.gov/about/budget/fy2010/toc.jsp |archive-date=March 3, 2018 |work=National Science Foundation |access-date=May 26, 2009}}{{Cite web |url=https://www.nsf.gov/about/budget/fy2011/pdf/22-Facilities_fy2011.pdf |title=Major multi-user research facilities |archive-url=https://web.archive.org/web/20170718123127/https://www.nsf.gov/about/budget/fy2011/pdf/22-Facilities_fy2011.pdf |archive-date=July 18, 2017

|work=National Science Foundation |pages=35–38 |access-date=February 10, 2010}} Starting in FY2010, NASA restored its historical support by contributing $2.0 million per year for planetary science, particularly the study of near-Earth objects, at Arecibo. NASA implemented this funding through its Near Earth Object Observations program.{{Cite web |url=http://science.nasa.gov/media/medialibrary/2010/04/27/NASAsupport_to_Planetary_Radar.pdf |title=NASA Support to Planetary Radar |archive-url=https://web.archive.org/web/20121006232826/http://science.nasa.gov/media/medialibrary/2010/04/27/NASAsupport_to_Planetary_Radar.pdf |access-date=July 7, 2011|archive-date=2012-10-06 }} NASA increased its support to $3.5 million per year in 2012.

In 2011, NSF removed Cornell University, which had managed the National Astronomy and Ionosphere Center (NAIC) since the 1970s, as the operator and transferred these responsibilities to SRI International, along with two other managing partners, Universities Space Research Association and Universidad Metropolitana de Puerto Rico, with a number of other collaborators.{{cite press release |url=http://www.sri.com/newsroom/press-releases/sri-international-selected-national-science-foundation-manage-arecibo-observ |title=SRI International to Manage Arecibo Observatory |publisher=SRI International |date=July 10, 2013 |access-date=July 10, 2013|archive-date=July 3, 2013|archive-url=https://web.archive.org/web/20130703073001/http://www.sri.com/newsroom/press-releases/sri-international-selected-national-science-foundation-manage-arecibo-observ|url-status=live}}{{cite news |url=http://www.news.cornell.edu/stories/June11/AreciboStmt.html |title=SRI International to manage Arecibo Observatory |work=Cornell Chronicle |date=June 3, 2011 |access-date=January 11, 2012 |archive-date=January 3, 2012 |archive-url=https://web.archive.org/web/20120103082345/http://www.news.cornell.edu/stories/June11/AreciboStmt.html |url-status=live}} NSF also decertified NAIC as a Federally Funded Research and Development Center (FFRDC), which the NSF said would give NAIC greater freedom to establish broader scientific partnerships and pursue funding opportunities for activities beyond the scope of those supported by NSF,{{Cite web |url=https://www.nsf.gov/funding/pgm_summ.jsp?pims_id=5652 |title=Management and Operation of the NAIC |date=30 September 2002 |archive-url=https://web.archive.org/web/20180303050341/https://www.nsf.gov/funding/pgm_summ.jsp?pims_id=5652 |archive-date=March 3, 2018 |access-date=April 6, 2013}} but which would also remove the FFRDC's promise of stability intended to retain the very best technical staff.

While the Observatory continued to operate under the reduced NSF budget and NASA funds, NSF signaled in 2015 and 2016 that it was looking towards potential decommissioning of the Observatory by initiating environmental impact statements on the effect of disassembling the unit.{{cite web |url=https://www.nationalgeographic.com/science/phenomena/2016/06/10/with-earths-largest-telescope-threatened-its-homeland-rallies/ |title=With Earth's Largest Telescope Threatened, Its Homeland Rallies |first=Nadia |last=Drake |author-link=Nadia Drake |date=June 10, 2016 |access-date=November 20, 2020 |work=National Geographic | archive-date = November 17, 2020 | archive-url = https://web.archive.org/web/20201117193113/https://www.nationalgeographic.com/science/phenomena/2016/06/10/with-earths-largest-telescope-threatened-its-homeland-rallies/ | url-status = dead}} The NSF continued to indicate it would like to reduce funding to the Observatory in the short term.{{cite web |url=https://www.nsf.gov/pubs/2016/nsf16005/nsf16005.jsp |title=Dear Colleague Letter: Concepts for Future Operation of the Arecibo Observatory |date=October 26, 2015 |access-date=November 11, 2015 |archive-date=October 29, 2015 |archive-url=https://web.archive.org/web/20151029235529/http://www.nsf.gov/pubs/2016/nsf16005/nsf16005.jsp |url-status=live}}{{cite web |url=https://www.nsf.gov/pubs/2016/nsf16144/nsf16144.jsp |title=Dear Colleague Letter: Intent to Release a Solicitation Regarding Future Continued Operations of the Arecibo Observatory |date=September 30, 2016 |access-date=October 2, 2016 |archive-date=October 5, 2016 |archive-url=https://web.archive.org/web/20161005081900/https://www.nsf.gov/pubs/2016/nsf16144/nsf16144.jsp |url-status=live}} As in 2008, academics expressed their concern over the loss of scientific discoveries that could occur should the Observatory be shut down.

File:Arecibo_observatory_damage_map.svg

Several hurricanes and storms over the 2010s had raised the concerns of structural engineers over the stability of the observatory. On September 21, 2017, high winds associated with Hurricane Maria caused the 430 MHz line feed to break and fall onto the primary dish, damaging roughly 30 of the 38,000 aluminum panels. Most Arecibo observations did not use the line feed but instead relied on the feeds and receivers located in the dome. Overall, the damage inflicted by Maria was minimal,{{cite news |url=https://www.washingtonpost.com/news/speaking-of-science/wp/2017/09/20/arecibo-observatory-puerto-ricos-famous-radio-telescope-is-battered-by-hurricane-maria/ |title=Arecibo Observatory, Puerto Rico's famous telescope, is battered by Hurricane Maria |last=Kaplan |first=Sarah |newspaper=The Washington Post |date=September 22, 2017|access-date=September 24, 2017|archive-date=September 21, 2017|archive-url=https://web.archive.org/web/20170921090157/https://www.washingtonpost.com/news/speaking-of-science/wp/2017/09/20/arecibo-observatory-puerto-ricos-famous-radio-telescope-is-battered-by-hurricane-maria/|url-status=live}}{{cite web |url=http://news.nationalgeographic.com/2017/09/arecibo-radio-telescope-damaged-puerto-rico-hurricane-maria-science/ |title=Hurricane Damages Giant Radio Telescope—Why It Matters |last=Drake |first=Nadia |work=National Geographic |date=September 22, 2017|access-date=September 23, 2017|archive-date=September 24, 2017|archive-url=https://web.archive.org/web/20170924010319/http://news.nationalgeographic.com/2017/09/arecibo-radio-telescope-damaged-puerto-rico-hurricane-maria-science/|url-status=dead}}{{cite news |title=Damage to Arecibo less than feared |url=http://spacenews.com/damage-to-arecibo-less-than-feared/ |work=SpaceNews |first=Jeff |last=Foust |date=September 27, 2017 |access-date=February 5, 2018 }}{{Dead link|date=December 2021 |bot=InternetArchiveBot |fix-attempted=yes }}{{cite news |title=Good news, earthlings! Puerto Rico telescope still guarding the galaxy despite Maria |url=http://www.miamiherald.com/news/nation-world/world/americas/article180486971.html |work=Miami Herald |date=October 23, 2017 |language=en|access-date=October 24, 2017|archive-date=October 24, 2017|archive-url=https://web.archive.org/web/20171024011837/http://www.miamiherald.com/news/nation-world/world/americas/article180486971.html|url-status=live}} but it further clouded the observatory's future. Restoring all the previous capabilities required more than the observatory's already-threatened operating budget, and users feared that the decision would be made to decommission it instead.{{cite journal |title=Hurricane damage threatens Arecibo Observatory's future |first=Daniel |last=Clery |date=September 26, 2017 |journal=Science |doi=10.1126/science.aaq0598 |doi-access=}}

A consortium consisting of the University of Central Florida (UCF), Yang Enterprises and UMET came forward to supply funding in February 2018 to allow the NSF to reduce its contribution towards Arecibo's operating costs from $8 million to $2 million from the fiscal year 2022–2023, thus securing the observatory's future.{{cite journal |last=Clery |first=Daniel |title=Arecibo telescope saved by university consortium |journal=Science |date=March 2, 2018 |volume=359 |issue=6379 |pages=965–966 |bibcode=2018Sci...359..965C |doi=10.1126/science.359.6379.965 |pmid=29496850}} With this, the UCF consortium were named the new operators of the observatory in 2018.{{cite news |url=https://www.science.org/content/article/iconic-arecibo-radio-telescope-saved-university-consortium |title=Iconic Arecibo radio telescope saved by university consortium |work=Science |date=February 22, 2018 |url-status=live |access-date=March 3, 2018 |archive-url=https://web.archive.org/web/20180304172439/http://www.sciencemag.org/news/2018/02/iconic-arecibo-radio-telescope-saved-university-consortium |archive-date=March 4, 2018}}{{cite press release |url=https://today.ucf.edu/ucf-led-consortium-manage-arecibo-observatory-puerto-rico/ |title=UCF-led Consortium to Manage Arecibo Observatory in Puerto Rico |publisher=UCF Today |date=February 22, 2018|access-date=April 18, 2018|archive-date=April 19, 2018|archive-url=https://web.archive.org/web/20180419120618/https://today.ucf.edu/ucf-led-consortium-manage-arecibo-observatory-puerto-rico/|url-status=live}}

On August 10, 2020, an auxiliary platform support cable separated from Tower 4, causing damage to the telescope, including a {{cvt|100|ft}} gash in the reflector dish.{{Cite web |last=Gonzalez Kotala |first=Zenaida |title=Broken Cable Damages Arecibo Observatory |url=https://www.ucf.edu/news/broken-cable-damages-arecibo-observatory/ |work=UCF Today |publisher=University of Central Florida |date=August 11, 2020 |language=en |access-date=August 12, 2020 |archive-date=August 11, 2020 |archive-url=https://web.archive.org/web/20200811230030/https://www.ucf.edu/news/broken-cable-damages-arecibo-observatory/ |url-status=live}}{{Cite web |title=Cable roto causa daños al Observatorio de Arecibo |url=https://www.notiuno.com/noticias/cable-roto-causa-da-os-al-observatorio-de-arecibo/article_3287f3bc-dc04-11ea-b705-63a6ba353c61.html |date=August 11, 2020|access-date=August 11, 2020 |work=WUNO |publisher=UNO Radio Group |location=San Juan, Puerto Rico |language=es|archive-date=September 16, 2020|archive-url=https://web.archive.org/web/20200916021326/https://www.notiuno.com/noticias/cable-roto-causa-da-os-al-observatorio-de-arecibo/article_3287f3bc-dc04-11ea-b705-63a6ba353c61.html|url-status=live}} Damage included six to eight panels in the Gregorian dome, and to the platform used to access the dome. No one was reported to have been hurt by the partial collapse. The facility was closed as damage assessments were made.{{cite web |url=https://www.businessinsider.com/broken-cable-tears-100-foot-hole-in-arecibo-observatory-2020-8 |title=A broken cable smashed a hole 100 feet wide in the Arecibo Observatory, which searches for aliens and tracks dangerous asteroids |publisher=Insider Inc. |work=Business Insider |date=August 11, 2020 |access-date=August 24, 2020 |last=McFall-Johnsen |first=Morgan |quote=One of the world's most prominent astronomical observatories has a hole. On Monday, a 3-inch-thick cable at the Arecibo Observatory broke, tearing a gash 100 feet long in the reflector dish of the 20-acre radio telescope in Puerto Rico. | archive-date=August 14, 2020 | archive-url=https://web.archive.org/web/20200814234421/https://www.businessinsider.com/broken-cable-tears-100-foot-hole-in-arecibo-observatory-2020-8 | url-status=live}}

The facility had recently reopened following the passing of Tropical Storm Isaias. It was unclear if the cable failure was caused by Isaias. Former Arecibo Observatory director Robert Kerr stated that prior to the 1997 installation of the Gregorian dome, the main support cables and support towers had been engineered with a safety factor of two, as to be able to sustain twice the weight of the platform. When the dome was added in 1997, the auxiliary cables were intended to retain the safety factor of two once all design factors were considered, but Kerr believed that that was never the case, as evenly distributing the loads following that install would be difficult to do. Kerr also stated that there had been periods of neglect at the Observatory, during which the fans that were used to blow dry air along the wire bundles were not operating. The earlier storms would have brought seawater to the cables, which could accelerate the rate of corrosion as well, according to Kerr. Engineering firms hired by UCF inspected the socket area where the cable had failed, and found a similar problem that had been observed in the 1980s during a routine cable replacement, in which the use of molten zinc to affix the cable to the socket mount at the tower was not complete, allowing moisture to get into the wire bundle and cause corrosion, and leading to the cable slipping from its socket. The firms had developed models of the telescope that showed that the safety factor for Tower 4 had dropped to 1.67, believing that the structure was still safe while repairs could be effected, even if another cable collapsed. Plans were made to replace all six auxiliary cables since their socket welds were all considered suspect, at a cost of {{US$|10.5 million}}.

Before repairs could be started, on November 7, 2020, one of the two main support cables from Tower 4 snapped, shattering part of the dish itself as it fell.{{cite web |url=https://spaceref.com/news/viewpr.html?pid=56545 |title=A Second Cable Fails at NSF's Arecibo Observatory in Puerto Rico |publisher=University of Central Florida |website=spaceref.com |date=November 8, 2020 |access-date=November 8, 2020}}{{dead link|date=June 2021|bot=medic}}{{cbignore|bot=medic}} The UCF engineering staff, which had been monitoring the cables with support from the U.S. Army Corps of Engineers, and the engineering firms they had hired previously evaluated the remaining cables from Tower 4. One engineering firm proposed stabilization efforts,{{Cite web|date=2020-11-12|title=Letter WJE|url=https://www.nsf.gov/news/stabilizationefforts.pdf|url-status=live|archive-url=https://web.archive.org/web/20201120231440/https://www.nsf.gov/news/stabilizationefforts.pdf|archive-date=2020-11-20}} while another suggested that they try to sever parts of the instrument platform such as the Gregorian dome to reduce the load. The third firm made the determination that there was no way to safely repair the damage at that point, as the remaining cables could be suspect, and furthermore that a controlled decommissioning of the telescope was the only effective means to avoid catastrophic failure which would threaten the other buildings on campus. The NSF took this advice and made the announcement on November 19, 2020, that they would decommission Arecibo over the following few weeks after determining the safest route to do so, with a safety exclusion zone immediately put in place. NSF's Sean Jones stated, "This decision is not an easy one for NSF to make, but safety of people is our number one priority." The lidar facility was to remain operational.{{cite web |url=https://www.theverge.com/2020/11/19/21575025/arecibo-observatory-puerto-rico-decommission-structural-collapse-cable-break |title=Facing collapse, the famed Arecibo Observatory will be demolished |first=Loren |last=Grush |date=November 19, 2020 |access-date=November 19, 2020 |work=The Verge | archive-date = November 19, 2020 | archive-url = https://web.archive.org/web/20201119165655/https://www.theverge.com/2020/11/19/21575025/arecibo-observatory-puerto-rico-decommission-structural-collapse-cable-break | url-status = live}}

While waiting for NSF to make the decommissioning plans, steps had been taken to try to reduce the load that each of the towers was carrying, including reducing the strain on the backstay support cables for the individual towers. Other plans, such as having helicopters hoisting part of the load while hovering above the telescope, were proposed but deemed too risky.{{cite web | url = https://www.engadget.com/arecibo-observatory-collapse-video-details-nsf-172859619.html | title = NSF offers a closer look at how the Arecibo Observatory collapsed | first = Chris | last = Velazco | date = December 3, 2020 | access-date = December 3, 2020 | work = Engadget }} Engineers from UCF had been monitoring the telescope and observed that wires in the backstay cables for the support towers had been breaking at a rate of one or two a day, and estimated that the telescope would soon collapse.{{cite web | url =https://www.science.org/content/article/arecibo-telescope-collapses-ending-57-year-run | title = Arecibo telescope collapses, ending 57-year run | first= Eric | last = Hand | date = December 1, 2020 | access-date = December 1, 2020 | work = Science Magazine }} In the weekend prior to December 1, 2020, wire strands in the receiver's supporting cables had also been snapping apart at a rapid rate, according to Ángel Vázquez, the director of operations. This culminated in the collapse of the receiver platform at around 6:55 a.m. AST (10:55 UTC) on December 1, 2020, as the second main cable from Tower 4 failed, with the other two remaining support cables failing moments later. The collapse of the receiver structure and cables onto the dish caused extensive additional damage.{{cite web | url = https://www.upi.com/Science_News/2020/12/01/Iconic-dome-at-Arecibo-Observatory-collapses/3861606831206/ | title = Iconic dome at Arecibo Observatory collapses | first = Paul | last = Brinkman | date = December 1, 2020 | access-date = December 1, 2020 | publisher = UPI }} As the receiver fell, it also sheared the tips of the towers which the support cables ran through. Once the main cables from Tower 4 released, the backstay cables, which normally balanced the horizontal component of force from the main cables, pulled the tower outwards and broke off the top. The other two towers, once the force of supporting the platform was released, also had their tips sheared off due to the backstay cable tension. The top of Tower 12 caused some structural damage to other buildings on the observatory as it fell. No injuries from the collapse were reported.{{cite web | url = https://www.nationalgeographic.com/science/2020/12/arecibo-radio-telescope-in-puerto-rico-collapses/ | archive-url = https://web.archive.org/web/20201201145250/https://www.nationalgeographic.com/science/2020/12/arecibo-radio-telescope-in-puerto-rico-collapses/ | url-status = dead | archive-date = December 1, 2020 | title = Iconic radio telescope in Puerto Rico collapses | first = Nadia | last =Drake | date = December 1, 2020 | access-date = December 1, 2020 | work = National Geographic }}{{cite news|date=30 June 2021|title=Arecibo Observatory Auxiliary M4N Socket Termination Failure Investigation|url=https://ntrs.nasa.gov/citations/20210017934}}

{{multiple image

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| image1=Collapse of Arecibo Radio Telescope 01.webm

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| caption1 = Collapse of Arecibo radio telescope captured from the control tower (Tower 12) camera. Tower 4 can be seen in the background, while the top of Tower 12 appears rolling in front of the camera later in the video.

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| caption2 = Collapse of the Arecibo telescope from the vantage point of a drone initially monitoring the cables at the top of Tower 4.

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| caption3 = Synchronized views of the Arecibo Telescope collapse.

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File:Arecibo Telescope, December 2021.jpg

In the weeks following Arecibo's collapse, the administration of the Five-hundred-metre Aperture Spherical Telescope (FAST) in China, which had drawn some design principles from Arecibo, stated that they would start taking applications for international researchers to use the telescope starting in 2021.{{cite web | url = https://www.space.com/china-fast-radio-telescope-open-international-scientists | title = China is opening the world's largest radio telescope up to international scientists | first = Chelsea | last= Gohd | date = December 18, 2020 | access-date = December 19, 2020 | work = Space.com }}

In late December 2020, Wanda Vázquez Garced, then governor of Puerto Rico signed an executive order for $8 million for the removal of debris and for the design of a new observatory to be built in its place. The governor stated reconstruction of the observatory is a "matter of public policy". The executive order also designated the area as a history site.{{cite web | last=Kuilan | first=Gloria Ruiz | title=8 million approved to rebuild the Arecibo Observatory Telescope | website=El Nuevo Día | date=2020-12-29 | url=https://www.elnuevodia.com/english/news/story/8-million-approved-to-rebuild-the-arecibo-observatory-telescope/ | access-date=2020-12-31}}

As required by the Consolidated Appropriations Act, 2021, the NSF sent a report to Congress in March 2022 "on the causes and extent of the damage, the plan to remove debris in a safe and environmentally sound way, the preservation of the associated [Arecibo Observatory] facilities and surrounding areas, and the process for determining whether to establish comparable technology at the site, along with any associated cost estimates".{{cite web | url = https://www.space.com/arecibo-observatory-congress-report-puerto-rico-funding.html | title= Congress asks for report on Arecibo radio telescope collapse |first = Doris Elin | last = Urrutia | date = January 5, 2021 | access-date = January 5, 2021| work = Space.com }}{{cite web |title=Report to Congress on the Arecibo Observatory (March 2022) |url=https://www.nsf.gov/news/reports/AreciboReportFINAL-Protected_508.pdf |website=nsf.gov |publisher=National Science Foundation |access-date=13 June 2022}} On March 25, 2022, a survey salvage committee formed by UCF and the NSF issued a final report, identifying materials from the site that may be salvaged for their "historic importance or scientific utility."{{cite web |title=AOSSC Report and Recommendations (March 25, 2022) |url=https://www.naic.edu/documents/AOSSC_REPORT_FINAL20220325.pdf |publisher=Arecibo Observatory Survey Salvage Committee |access-date=13 June 2022}}

A team from the University of Texas at Austin was able to completely recover and back up the 3 petabytes of data that the telescope had captured since opening in the 1960s by May 2021 before further harm could come to the storage equipment. The data was relocated to the school's servers at the Texas Advanced Computing Center to be made available for continued research.{{cite web | url = https://news.utexas.edu/2021/05/10/priceless-astronomy-data-saved-after-collapse-of-arecibo-telescope/ | title = Priceless Astronomy Data Saved After Collapse of Arecibo Telescope | date = May 10, 2021 | access-date = June 20, 2021 | publisher = The University of Texas at Austin }}

An early plan developed by NSF scientists suggest one possible replacement called the Next Generation Arecibo Telescope, using 1000 closely-packed {{convert|9|m|ft|adj=on|sp=us}} telescopes mounted on one or more flat plate(s) that would cover the {{convert|300|m|ft|adj=on|sp=us}} width of the Arecibo sinkhole. While the telescopes themselves would be fixed, the plate(s) would be able to be rotated more than 45° off the horizontal in any direction. This would allow the new instrument to have 500 times the field of view of the original Arecibo Telescope, and be twice as sensitive with four times the radar power. It was expected this would cost roughly {{USD|450 million}} to build.{{cite web |title=The Future of the Arecibo Observatory: The Next Generation Arecibo Telescope |url=http://www.naic.edu/NGAT/NGAT_WhitePaper_v2_01022021.pdf |website=The Arecibo Observatory |publisher=NAIC |archive-url=https://web.archive.org/web/20230701074046/http://www.naic.edu/NGAT/NGAT_WhitePaper_v2_01022021.pdf |archive-date=1 July 2023 |id=White Paper, ver 2.0, 02-01-2021 |access-date=26 February 2021 |url-status=live }} This would enable better study of the supermassive black hole at the center of the Milky Way as a prime target.

NSF decided in October 2022 that the Arecibo site would not be used for a new telescope, instead converting the site to be a STEM educational center.{{cite journal |last1=Witze |first1=Alexandra |title=Renowned Arecibo telescope won't be rebuilt — and astronomers are heartbroken |journal=Nature |date=14 October 2022 |volume=610 |issue=7933 |pages=618–619 |doi=10.1038/d41586-022-03293-4 |pmid=36241884 |bibcode=2022Natur.610..618W |s2cid=252903742 |doi-access= }}

The Arecibo Salvage Survey committee preserved some parts of the telescope, including parts of the zenith and azimuth tracks, a corner of the platform, the rotary joint, and the cable car.{{cite web |title=Arecibo Salvage Survey Committee Update for History of Astronomy {{!}} The Arecibo Observatory |url=https://www.naic.edu/ao/blog/arecibo-update-history-astronomy |website=www.naic.edu}}

In 2024 the National Academies of Sciences, Engineering and Medicine issued a report on the collapse.National Academies of Sciences, Engineering, and Medicine. 2024. Failure Analysis of the Arecibo Observatory 305-Meter Telescope Collapse. Washington, DC: The National Academies Press. https://doi.org/10.17226/26982.

File:Arecibo message.svg with added color to highlight the separate parts. The actual binary transmission carried no color information.]]

Many scientific discoveries were made with the observatory. On April 7, 1964, soon after it began operating, Gordon Pettengill's team used it to determine that the rotation period of Mercury was not 88 days, as formerly thought, but only 59 days.{{cite journal |last1=Dyce |first1=R. B. |first2=G. H. |last2=Pettengill |author-link2=Gordon Pettengill |first3=I. I. |last3=Shapiro |author-link3=Irwin I. Shapiro |title=Radar determination of the rotations of Venus and Mercury |journal=Astron. J. |volume=72 |issue=3 |pages=351–359 |doi=10.1086/110231 |date=April 1967 |bibcode=1967AJ.....72..351D}} In 1968, the discovery of the periodicity of the Crab Pulsar (33 milliseconds) by Richard V. E. Lovelace and others provided the first solid evidence that neutron stars exist.{{cite web |url=http://www.aep.cornell.edu/pdf/CrabPeriodDiscovery.pdf |title=Discovery of the Period of the Crab Nebula Pulsar |author=Richard V.E. Lovelace |publisher=Cornell University |access-date=September 2, 2008 |archive-url=https://web.archive.org/web/20080912173347/http://www.aep.cornell.edu/pdf/CrabPeriodDiscovery.pdf |archive-date=September 12, 2008|url-status=dead}} In 1974, Hulse and Taylor discovered the first binary pulsar PSR B1913+16,{{cite journal |last1=Hulse |first1=R. A. |last2=Taylor |first2=J. H. |title=Discovery of a pulsar in a binary system |journal=The Astrophysical Journal |date=January 1975 |volume=195 |pages=L51 |doi=10.1086/181708 |bibcode=1975ApJ...195L..51H |doi-access=free }} an accomplishment for which they later received the Nobel Prize in Physics. In 1982, the first millisecond pulsar, PSR B1937+21, was discovered by Donald C. Backer, Shrinivas Kulkarni, Carl Heiles, Michael Davis, and Miller Goss.{{cite journal |last1=Backer |first1=D. C. |last2=Kulkarni |first2=Shrinivas R. |last3=Heiles |first3=Carl |last4=Davis |first4=M. M. |last5=Goss |first5=W. M. |title=A millisecond pulsar |journal=Nature |date=December 1982 |volume=300 |issue=5893 |pages=615–618 |doi=10.1038/300615a0 |bibcode=1982Natur.300..615B |s2cid=4247734 }} This object spins 642 times per second and, until the discovery of PSR J1748-2446ad in 2005, was identified as the fastest-spinning pulsar.

In 1980, Arecibo made the first radar observation of a comet when it successfully detected Comet Encke.{{cite journal |last1=Harmon |first1=J.K |last2=Campbell |first2=D.B |last3=Ostro |first3=S.J|last4=Nolan |first4=M.C |date=1999 |title=Radar observations of comets |url=https://echo.jpl.nasa.gov/asteroids/harmon+comets_1999_pss.pdf |journal=Planetary and Space Science |volume=47 |issue=12 |pages=1409–1422 |doi=10.1016/S0032-0633(99)00068-9 |bibcode=1999P&SS...47.1409H |access-date=22 November 2020}} In August 1989, the observatory directly imaged an asteroid for the first time in history: 4769 Castalia.{{cite web |url=http://echo.jpl.nasa.gov/asteroids/4769_Castalia/cast01.html |title=Asteroid 4769 Castalia (1989 PB) |publisher=NASA |access-date=September 2, 2008 |archive-url=https://web.archive.org/web/20080916092150/http://echo.jpl.nasa.gov/asteroids/4769_Castalia/cast01.html |archive-date=September 16, 2008|url-status=live}} The following year, Polish astronomer Aleksander Wolszczan made the discovery of pulsar PSR B1257+12 (Lich), which later led him to discover its three orbiting planets.{{cite journal |last1=Wolszczan |first1=A. |title=Confirmation of Earth-Mass Planets Orbiting the Millisecond Pulsar PSR B1257 + 12 |journal=Science |date=22 April 1994 |volume=264 |issue=5158 |pages=538–542 |doi=10.1126/science.264.5158.538 |pmid=17732735 |bibcode=1994Sci...264..538W |s2cid=19621191 }} These were the first extrasolar planets discovered. In 1994, John Harmon used the Arecibo Radio Telescope to map the distribution of ice in the polar regions of Mercury.{{cite journal |last1=Harmon |first1=J. K. |last2=Slade |first2=M. A. |last3=Vélez |first3=R. A. |last4=Crespo |first4=A. |last5=Dryer |first5=M. J. |last6=Johnson |first6=J. M. |title=Radar mapping of Mercury's polar anomalies |journal=Nature |date=May 1994 |volume=369 |issue=6477 |pages=213–215 |doi=10.1038/369213a0 |bibcode=1994Natur.369..213H |s2cid=4320356 }}

In January 2008, detection of prebiotic molecules methanimine and hydrogen cyanide were reported from the observatory's radio spectroscopy measurements of the distant starburst galaxy Arp 220.{{cite news|title=Life's Ingredients Detected in Far Off Galaxy |url=https://www.sciencedaily.com/releases/2008/01/080114110715.htm |via=ScienceDaily|date=January 15, 2008|publisher=Cornell University|archive-url=https://web.archive.org/web/20080421095946/https://www.sciencedaily.com/releases/2008/01/080114110715.htm |archive-date=April 21, 2008|url-status= live}}

From January 2010 to February 2011, astronomers Matthew Route and Aleksander Wolszczan detected bursts of radio emission from the T6.5 brown dwarf 2MASS J10475385+2124234. This was the first time that radio emission had been detected from a T dwarf, which has methane absorption lines in its atmosphere. It is also the coolest brown dwarf (at a temperature of ~900K) from which radio emission has been observed. The highly polarized and highly energetic radio bursts indicated that the object has a >1.7 kG-strength magnetic field and magnetic activity similar to both the planet Jupiter and the Sun.{{cite journal |last1=Route |first1=M. |last2=Wolszczan |first2=A. |title=The Arecibo Detection of the Coolest Radio-flaring Brown Dwarf |journal=The Astrophysical Journal |date=10 March 2012 |volume=747 |issue=2 |pages=L22 |doi=10.1088/2041-8205/747/2/L22 |arxiv=1202.1287 |bibcode=2012ApJ...747L..22R |s2cid=119290950 }}

{{main|Arecibo message}}

In 1974, the Arecibo message, an attempt to communicate with potential extraterrestrial life, was transmitted from the radio telescope toward the globular cluster Messier 13, about 25,000 light-years away.{{cite web |url=http://www.zwire.com/site/news.cfm?newsid=15663534&BRD=1395&PAG=461&dept_id=216620&rfi=6 |title=Making Contact |author=Larry Klaes |work=Ithaca Times |date=November 30, 2005 |access-date=September 2, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20081205064953/http://www.zwire.com/site/news.cfm?newsid=15663534&BRD=1395&PAG=461&dept_id=216620&rfi=6 |archive-date=December 5, 2008}} The 1,679 bit pattern of 1s and 0s defined a 23 by 73 pixel bitmap image that included numbers, stick figures, chemical formulas and a crude image of the telescope.{{cite web |url=http://www.physics.utah.edu/~cassiday/p1080/lec06.html |title=The Arecibo Message |author=Geaorge Cassiday |publisher=The University of Utah: Department of Physics |access-date=July 27, 2007 |archive-url=https://archive.today/20070717133904/http://www.physics.utah.edu/~cassiday/p1080/lec06.html |archive-date=July 17, 2007 |url-status=live}}

{{main|SETI|Active SETI}}

Search for extraterrestrial intelligence (SETI){{cite journal |last1=Tarter |first1=Jill |title=The Search for Extraterrestrial Intelligence (SETI) |journal=Annual Review of Astronomy and Astrophysics |date=September 2001 |volume=39 |issue=1 |pages=511–548 |doi=10.1146/annurev.astro.39.1.511 |bibcode=2001ARA&A..39..511T |s2cid=53122223 }} is the search for extraterrestrial life or advanced technologies. SETI aims to answer the question "Are we alone in the Universe?" by scanning the skies for transmissions from intelligent civilizations elsewhere in our galaxy.

In comparison, METI (messaging to extraterrestrial intelligence) refers to the active search by transmitting messages.

Arecibo was the source of data for the SETI@home and Astropulse distributed computing projects put forward by the Space Sciences Laboratory at the University of California, Berkeley, and was used for the SETI Institute's Project Phoenix observations.{{cite news |url=https://www.space.com/searchforlife/seti_arecibo_prep_030414.html |title=Project Phoenix: SETI Prepares to Observe at Arecibo |author=Peter Backus |work=Space.com |date=April 14, 2003 |access-date=September 2, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20081204130953/http://www.space.com/searchforlife/seti_arecibo_prep_030414.html |archive-date=December 4, 2008}} The Einstein@Home distributed computing project has found more than 20 pulsars in Arecibo data.{{cite web |url=http://einstein.phys.uwm.edu/radiopulsar/html/BRP4_discoveries/ |title=Einstein@Home new discoveries and detections of known pulsars in the BRP4 search |date=August 27, 2012 |access-date=August 28, 2012|archive-date=June 18, 2016|archive-url=https://web.archive.org/web/20160618054737/https://einstein.phys.uwm.edu/radiopulsar/html/BRP4_discoveries/|url-status=live}}

Terrestrial aeronomy experiments at Arecibo included the Coqui 2 experiment, supported by NASA. The telescope also originally had military intelligence uses, including locating Soviet radar installations by detecting their signals bouncing off the Moon.Steve Blank "Secret history of Silicon Valley" talk

Limited amateur radio operations were carried out, using Moon bounce or Earth–Moon–Earth communication, in which radio signals aimed at the Moon are reflected back to Earth. The first of these operations was on June 13–14, 1964, using the call sign KP4BPZ. A dozen or so two-way contacts were made on 144 and 432 MHz. On July 3 and 24, 1965, KP4BPZ was again activated on 432 MHz, making approximately 30 contacts on 432 MHz during the limited time slots available. For these tests, a very wide-band instrumentation recorder captured a large segment of the receiving bandwidth, enabling later verification of other amateur station call signs. These were not two-way contacts. From April 16–18, 2010, the Arecibo Amateur Radio Club KP4AO again conducted Moon-bounce activity using the antenna.{{cite web |url=http://www.arrl.org/news/moonbounce-for-everyone-courtesy-of-the-arecibo-radio-telescope |title=ARRL; Moonbounce for everyone |access-date=January 10, 2013|archive-date=September 18, 2012|archive-url=https://web.archive.org/web/20120918045432/http://www.arrl.org/news/moonbounce-for-everyone-courtesy-of-the-arecibo-radio-telescope|url-status=live}} On November 10, 2013, the KP4AO Arecibo Amateur Radio Club conducted a Fifty-Year Commemoration Activation, lasting seven hours on 14.250 MHz SSB, without using the main dish antenna.{{Cite web |url=http://www.arrl.org/news/arecibo-observatory-50th-anniversary-special-event-set |title=Arecibo Observatory 50th Anniversary Special Event Set |access-date=November 20, 2020 |archive-date=May 31, 2020 |archive-url=https://web.archive.org/web/20200531221237/http://www.arrl.org/news/arecibo-observatory-50th-anniversary-special-event-set |url-status=live }}

Due to its unique shape and concept, the telescope had been featured in many contemporary works. It serves as one of the central locations in The Sparrow, a science fiction novel written by Mary Doria Russell. It was used as a filming location in the films GoldenEye (1995), Species (1995), and Contact (1997) (based on Carl Sagan's novel of the same name, which also featured the observatory), The Losers (2010),{{cite web |url=https://www.upi.com/Top_News/US/2019/11/29/Iconic-space-observatory-in-Puerto-Rico-recovers-after-Hurricane-Maria/4561573856192/ |title=Iconic space observatory in Puerto Rico recovers after Hurricane Maria |first=Paul |last=Brinkman |date=November 29, 2019 |access-date=November 19, 2020 |work=UPI | archive-date = November 18, 2020 | archive-url = https://web.archive.org/web/20201118150444/https://www.upi.com/Top_News/US/2019/11/29/Iconic-space-observatory-in-Puerto-Rico-recovers-after-Hurricane-Maria/4561573856192/ | url-status = live}}{{cite magazine |url=https://www.nationalgeographic.com/science/2020/11/arecibo-observatory-in-puerto-rico-at-risk-of-collapsing/ |title=Iconic radio telescope in Puerto Rico is at risk of collapsing |first=Nadia |last=Drake |date=November 12, 2020 |magazine=National Geographic | archive-date = November 19, 2020 | archive-url = https://web.archive.org/web/20201119030316/https://www.nationalgeographic.com/science/2020/11/arecibo-observatory-in-puerto-rico-at-risk-of-collapsing/ | url-status = dead}} and in The X-Files television episode "Little Green Men".{{cite web |url=https://www.nytimes.com/2020/11/19/science/arecibo-observatory.html |title=Arecibo Observatory, a Great Eye on the Cosmos, Is Going Dark |first=Dennis |last=Overbye |date=November 19, 2020 |access-date=November 19, 2020 |work=The New York Times | archive-date = November 19, 2020 | archive-url = https://web.archive.org/web/20201119170116/https://www.nytimes.com/2020/11/19/science/arecibo-observatory.html | url-status = live}} One map in the 2013 video game Battlefield 4, while set in China, is based on the distinctive layout of the Arecibo Telescope.{{cite web | url = https://www.pcgamer.com/how-goldeneyes-arecibo-observatory-became-a-scientific-and-cultural-icon/ | title = How GoldenEye's Arecibo Observatory became a scientific and cultural icon | first = Ian | last =Evenden | date = March 25, 2021 | access-date = March 25, 2021 | work =PC Gamer }} In 2014, a video art installation piece titled The Great Silence by artists Jennifer Allora and Guillermo Calzadilla in collaboration with science fiction writer Ted Chiang featured the radio telescope at Arecibo Observatory to represent the search for extraterrestrial life. The next year, Chiang published a novelette also called The Great Silence. The juxtaposed text was later published as a short story with the same title in a special issue of the art journal e-flux in 2015 and was included in the author's short story collection Exhalation: Stories in 2019.{{cite web |url=https://www.avclub.com/ted-chiang-the-mind-behind-arrival-returns-with-anoth-1834449060 |title=Ted Chiang, the mind behind Arrival, returns with another awe-inducing sci-fi collection |first=Adam |last=Morgan |date=May 6, 2019 |access-date=November 19, 2020 |work=The A.V. Club | archive-date = November 7, 2020 | archive-url = https://web.archive.org/web/20201107223523/https://aux.avclub.com/ted-chiang-the-mind-behind-arrival-returns-with-anoth-1834449060 | url-status = live}}

The asteroid 4337 Arecibo is named after the observatory by Steven J. Ostro, in recognition of the observatory's contributions to the characterization of Solar System bodies.{{cite web |title=(4337) Arecibo = 1933 HE = 1979 FR3 = 1979 HG2 = 1985 GB |url=https://minorplanetcenter.net/db_search/show_object?utf8=%E2%9C%93&object_id=4337 |url-status=live |archive-url=https://web.archive.org/web/20161004175246/http://www.minorplanetcenter.net/db_search/show_object?utf8=%E2%9C%93&object_id=4337 |archive-date=4 October 2016 |publisher=Minor Planet Center |accessdate=16 June 2022}}

• List of radio telescopes
• Lunar Crater Radio Telescope - a proposed project by NIAC to place a radio telescope on the far side of the Moon

• Orgov Radio-Optical Telescope

{{Reflist}}

• {{cite news |title=Research rockets, including an experiment from Cornell, are scheduled for launch into the ionosphere next year from Puerto Rico |date=November 14, 1997 |publisher=Cornell University |last=Friedlander |first=Blaine |url=https://news.cornell.edu/stories/1997/11/research-rockets-including-experiment-cornell-are-scheduled-launch-ionosphere-next |ref=none}}
• {{cite news |title=Activists protest US Navy radar project |date=March 3, 1998 |last=Ruiz |first=Carmelo |publisher=Global Network Against Weapons and Nuclear Power in Space |url=http://www.globenet.free-online.co.uk/actions/prico2.htm|archive-url=https://web.archive.org/web/20010501002404/http://www.globenet.free-online.co.uk/actions/prico2.htm|url-status=dead|archive-date=May 1, 2001 |ref=none}}
• {{cite web |url=http://www.planetary.org/programs/projects/advocacy_and_education/space_advocacy/20080703.html |title=Budget Cuts Threaten Arecibo Observatory |author=Amir Alexander |publisher=The Planetary Society |date=July 3, 2008|url-status=dead |archive-url=https://web.archive.org/web/20080721105122/http://www.planetary.org/programs/projects/advocacy_and_education/space_advocacy/20080703.html |archive-date=July 21, 2008 |ref=none}}
• {{cite web |url=http://www.eurekalert.org/pub_releases/2008-06/cuc-ajg061008.php |title=Arecibo joins global network to create {{convert|6000|mi|km |adj=on}} telescope

|author=Blaine Friedlander

|publisher=EurekAlert

|date=June 10, 2008|ref=none}}

• {{cite web |url=http://www.news.cornell.edu/stories/June08/arecibo.clintons.html |title=Clintons (minus Hillary) visit Arecibo; former president urges more federal funding for basic sciences |author=Lauren Gold |publisher=Cornell university |date=June 5, 2008 |ref=none}}
• {{cite news |url=https://www.nytimes.com/2007/12/25/science/25obtele.html |title=Arecibo Radio Telescope Is Back in Business After 6-Month Spruce-Up |author=Henry Fountain |work=New York Times |date=December 25, 2007 |ref=none}}
• [http://www.nps.gov/history/nr/feature/weekly_features/IonosphereCenter.pdf Entry into the National Register of Historic Places]
• {{cite journal |last1=Cohen |first1=Marshall H. |date=2009 |title=Genesis of the 1000-foot Arecibo Dish |journal=Journal of Astronomical History and Heritage |volume=12 |issue=2 |pages=141–152 |doi=10.3724/SP.J.1440-2807.2009.02.06|doi-access=free|bibcode=2009JAHH...12..141C |s2cid=18990068 |url=https://resolver.caltech.edu/CaltechAUTHORS:20091231-110730776}} [https://authors.library.caltech.edu/17042/1/Arecibo_Genesis_JAH2_2009.pdf PDF]
• {{cite journal |first1=Daniel R. |last1=Altschuler |first2=Christopher J. |last2=Salter |title=The Arecibo Observatory: Fifty astronomical years |journal=Physics Today |volume=66 |number=11 |page=43 |doi=10.1063/PT.3.2179 |date=2013 |bibcode=2013PhT....66k..43A |ref=none|author1-link=Daniel R. Altschuler }}

{{Commons category}}

• {{Official website|www.naic.edu}}
• [https://www.youtube.com/watch?v=59WQIRvezzI Youtube video of collapse 12.56 mins]
• [https://www.science.org/content/article/wondrous-life-and-death-puerto-rico-s-arecibo-observatory?et_rid=309215399&et_cid=3640016 The wondrous life—and dramatic death—of Puerto Rico's Arecibo Observatory]

{{Radio-astronomy|state=uncollapsed}}

{{Registered Historic Places}}

{{Extraterrestrial life}}

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