The observatory's main instrument was theArecibo Telescope, a 305 m (1,000 ft)spherical reflectordish built into a naturalsinkhole, with a cable-mount steerable receiver and severalradar transmitters for emitting signals mounted 150 m (492 ft) above the dish. Completed in 1963, it was the world's largest single-aperture telescope for 53 years, surpassed in July 2016 by theFive-hundred-meter Aperture Spherical Telescope (FAST) in China. On August 10 and November 6, 2020, two of the receiver's support cables broke and the NSF announced that it would decommission the telescope. The telescope collapsed on December 1, 2020.[3] In 2022, the NSF announced the telescope will not be rebuilt, with an educational facility to be established on the site.
The observatory also includes a smallerradio telescope, aLIDAR facility, and a visitor center, which remained operational after the telescope's collapse.[4][5] The asteroid4337 Arecibo was named after the observatory bySteven J. Ostro, in recognition of the observatory's contributions to the characterization of Solar System bodies.[6]
In the 1950s, theUnited States Department of Defense (DoD)Advanced Research Projects Agency (ARPA) was seeking a means to detect missiles in Earth'sionosphere. On November 6, 1959,Cornell University entered into a contract with ARPA to carry out development studies for a large-scale ionospheric radar probe.[7] The Arecibo Telescope was consequently built to study the ionosphere as well as to serve as a general-purposeradio telescope. Construction of the telescope was started in September 1960. The telescope and supporting observatory were formally opened as the Arecibo Ionospheric Observatory on November 1, 1963.[8]
DoD transferred the observatory to theNational Science Foundation on October 1, 1969. NSF appointed Cornell University to manage the observatory. By September 1971, NSF had renamed the observatory the National Astronomy and Ionosphere Center (NAIC) and had made it afederally funded research and development center (FFRDC).[8]NASA began contributing funds to the observatory alongside NSF for its planetary radar mission.[9]
In the early 2000s, NASA eliminated funding for the Arecibo Observatory.[10] In 2006, NSF indicated that it would reduce funding for the observatory, and decommission it if other funding could not be found.[11] Academics and politicians lobbied to stave off its closure, and NASA recommitted funding in 2011 for study ofnear-earth objects.[12] In 2011, NSF delisted Arecibo as an FFRDC, which allowed the observatory to seek funding from a wider variety of sources; the agency also replaced Cornell as the site operator with a team led bySRI International.[13]
Damage to the telescope by 2017'sHurricane Maria led NSF again to suggest closing the observatory.[14] A consortium led by theUniversity of Central Florida (UCF) proposed to manage the observatory and cover much of the operations and maintenance costs, and in 2018, NSF made UCF's consortium the new site operators,[15][16] though no specific actions or funding were announced.
On August 6, 2020, an auxiliary cable broke on the telescope, followed by a main cable on November 7. The NSF announced that they would decommission the telescope through controlled demolition, but that the other facilities on the observatory would remain operational. Before demolition could occur, remaining support cables from one tower rapidly failed in the morning of December 1, 2020, causing the instrument platform to crash through the dish, shearing off the tops of the support towers, and partially damaging some of the other buildings, though with no injuries.[17][3] NSF officials said in 2020 that they aimed to have the other observatory facilities operational as soon as possible and were considering rebuilding a new telescope instrument in its place.[18] However, in 2022, the NSF announced the telescope will not be rebuilt but an educational facility would be established on the site.[19] The following year, NSF picked a consortium of universities—Cold Spring Harbor Laboratory in New York; theUniversity of Maryland, Baltimore County; theUniversity of Puerto Rico, Río Piedras Campus, in San Juan; and theUniversity of the Sacred Heart, also in San Juan—to set up and run an education center called Arecibo C3 (Arecibo Center for Culturally Relevant and Inclusive Science Education, Computational Skills, and Community Engagement).[20][21]
The observatory's main feature was its largeradio telescope, the main collecting dish of which was an invertedspherical dome 1,000 feet (305 m) in diameter with an 869-foot (265 m)radius of curvature,[22] constructed inside akarstsinkhole.[23] The dish's surface was made of 38,778 perforated aluminum panels, each about 3 by 7 feet (1 by 2 m), supported by a mesh of steel cables.[22] The ground beneath supported shade-tolerant vegetation.[24]
Since its completion in November 1963, the Telescope had been used forradar astronomy andradio astronomy, and had been part of theSearch for extraterrestrial intelligence (SETI) program. It was also used by NASA forNear-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, includingHurricane 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 a.m. local time on December 1, 2020, causing the receiver platform to fall into the dish and collapsing the telescope.[17][25]
NASA led an extensive failure investigation and reported the findings,[26] along with a technical bulletin with industry recommendations.[27] The investigation concluded that "a combination of low socketdesign margin and a high percentage of sustained loading revealed an unexpected vulnerability tozinc creep and environments, resulting in long-term cumulative damage and progressive zinc/wire failure".
In 2024, the National Academies of Science, Engineering, and Medicine published their definitive report, "Failure Analysis of the Arecibo Observatory 305-Meter Telescope Collapse". The report cited many of the previous reports and findings, including the role of the high-energy output interacting with the zinc wire rope "brooming". It also raised the issue of the original design standards available in the 1980s versus the later advances in wind load engineering.[28]
The Arecibo Observatory also has other facilities beyond the main telescope, including a 12-meter (39 ft) radio telescope intended forvery-long-baseline interferometry (VLBI) with the main telescope;[29] and a LIDAR facility[30] whose research has continued since the main telescope's collapse.
The Arecibo Radio Telescope as viewed from the observation deck, October 2013
Opened in 1997, the Ángel Ramos Foundation Visitor Center features interactive exhibits and displays about the operations of the radio telescope,astronomy andatmospheric sciences.[31] The center is named after the financial foundation that honorsÁngel Ramos, owner of theEl Mundo newspaper and founder ofTelemundo. The Foundation provided half of the funds to build the Visitor Center, with the remainder received from private donations andCornell University.
The center, in collaboration with the Caribbean Astronomical Society,[32] hosts a series of Astronomical Nights throughout the year, which feature diverse discussions regardingexoplanets, astronomical phenomena, and discoveries (such asComet ISON). The purposes of the center are to increase public interest in astronomy, the observatory's research successes, and space endeavors.
^National Park Service (October 3, 2008)."Weekly List Actions"(PDF).Archived from the original on March 29, 2013. RetrievedFebruary 6, 2018.
^abNational Academies of Sciences, Engineering, and Medicine (2024). Failure Analysis of the Arecibo Observatory 305-Meter Telescope Collapse (Report). The National Academies Press.doi:10.17226/26982.ISBN978-0-309-70222-5.{{cite report}}: CS1 maint: multiple names: authors list (link)
^Weiss, Rick Weiss (September 9, 2007)."Radio Telescope And Its Budget Hang in the Balance".The Washington Post. Arecibo, Puerto Rico. p. A01.Archived from the original on November 6, 2012. RetrievedJuly 8, 2008.The cash crunch stems from an NSFsenior 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.
^"Arecibo C3". U.S. National Science Foundation. RetrievedDecember 10, 2024.
^abGoldsmith, P. F.; Baker, L. A.; Davis, M. M.; Giovanelli, R. (1995). "Multi-feed Systems for the Arecibo Gregorian".Astronomical Society of the Pacific Conference Series.75:90–98.Bibcode:1995ASPC...75...90G.
^Roshi, D. Anish; Anderson, L. D.; Araya, E.; Balser, D.; Brisken, W.; Brum, C.; Campbell, D.; Chatterjee, S.; Churchwell, E.; Condon, J.; Cordes, J.; Cordova, F.; Fernandez, Y.; Gago, J.; Ghosh, T.; Goldsmith, P. F.; Heiles, C.; Hickson, D.; Jeffs, B.; Jones, K. M.; Lautenbach, J.; Lewis, B. M.; Lynch, R. S.; Manoharan, P. K.; Marshall, S.; Minchin, R.; Palliyaguru, N. T.; Perera, B. B. P.; Perillat, P.; Pinilla-Alonso, N.; Pisano, D. J.; Quintero, L.; Raizada, S.; Ransom, S. M.; Fernandez-Rodriguez, F. O.; Salter, C. J.; Santos, P.; Sulzer, M.; Taylor, P. A.; Venditti, F. C. F.; Venkataraman, A.; Virkki, A. K.; Wolszczan, A.; Womack, M.; Zambrano-Marin, L. F. (July 13, 2019). "Astro2020 Activities and Projects White Paper: Arecibo Observatory in the Next Decade".arXiv:1907.06052 [astro-ph.IM].
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