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The Arecibo Telescope was a spherical reflector
radio telescope A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency ...
built into a natural
sinkhole A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...
at the
Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science ...
located near
Arecibo, Puerto Rico Arecibo (; ) is a city and municipality on the northern coast of Puerto Rico, on the shores of the Atlantic Ocean, located north of Utuado and Ciales; east of Hatillo; and west of Barceloneta and Florida. It is about west of San Juan, the ca ...
. A cable-mount steerable receiver and several
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
transmitters for emitting signals were mounted above the dish. Completed in November 1963, the Arecibo Telescope was the world's largest single-aperture telescope for 53 years, until it was surpassed in July 2016 by the
Five-hundred-meter Aperture Spherical Telescope The Five-hundred-meter Aperture Spherical radio Telescope (FAST; ), nicknamed Tianyan (, lit. "Sky's/Heaven's Eye"), is a radio telescope located in the Dawodang depression (), a natural basin in Pingtang County, Guizhou, southwest China. FAST ...
(FAST) in
Guizhou Guizhou (; Postal romanization, formerly Kweichow) is a landlocked Provinces of China, province in the Southwest China, southwest region of the China, People's Republic of China. Its capital and largest city is Guiyang, in the center of the pr ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
. The Arecibo Telescope was primarily used for research in
radio astronomy Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object was in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation comin ...
,
atmospheric science Atmospheric science is the study of the Earth's atmosphere and its various inner-working physical processes. Meteorology includes atmospheric chemistry and atmospheric physics with a major focus on weather forecasting. Climatology is the study ...
, and
radar astronomy Radar astronomy is a technique of observing nearby astronomical objects by reflecting radio waves or microwaves off target objects and analyzing their reflections. Radar astronomy differs from '' radio astronomy'' in that the latter is a passive o ...
, as well as for programs that
search for extraterrestrial intelligence The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other ...
(SETI). Scientists wanting to use the observatory submitted proposals that were evaluated by independent scientific referees.
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
also used the telescope for near-Earth object detection programs. The observatory, funded primarily by the
National Science Foundation The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National ...
(NSF) with partial support from NASA, was managed by
Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to tea ...
from its completion in 1963 until 2011, after which it was transferred to a partnership led by
SRI International SRI International (SRI) is an American nonprofit scientific research institute and organization headquartered in Menlo Park, California. The trustees of Stanford University established SRI in 1946 as a center of innovation to support economic ...
. In 2018, a consortium led by the
University of Central Florida The University of Central Florida (UCF) is a public research university whose main campus is in unincorporated Orange County, Florida. UCF also has nine smaller regional campuses throughout central Florida. It is part of the State Universi ...
assumed operation of the facility. The telescope's unique and futuristic design led to several appearances in film, gaming and television productions, such as for the climactic fight scene in the
James Bond The ''James Bond'' series focuses on a fictional British Secret Service agent created in 1953 by writer Ian Fleming, who featured him in twelve novels and two short-story collections. Since Fleming's death in 1964, eight other authors hav ...
film ''
GoldenEye ''GoldenEye'' is a 1995 spy film, the seventeenth in the ''James Bond'' series produced by Eon Productions, and the first to star Pierce Brosnan as the fictional MI6 agent James Bond. Directed by Martin Campbell, it was the first in the se ...
'' (1995). It is one of the 116 pictures included in the
Voyager Golden Record The Voyager Golden Records are two phonograph records that were included aboard both Voyager spacecraft launched in 1977. The records contain sounds and images selected to portray the diversity of life and culture on Earth, and are intended for ...
. It has been listed on the US
National Register of Historic Places The National Register of Historic Places (NRHP) is the United States federal government's official list of districts, sites, buildings, structures and objects deemed worthy of preservation for their historical significance or "great artistic ...
since 2008. (72 pages, with many historic b&w photos and 18 color photos) The center was named an IEEE Milestone in 2001. Since 2006, the NSF has reduced its funding commitment to the observatory, leading academics to push for additional funding support to continue its programs. The telescope was damaged by
Hurricane Maria Hurricane Maria was a deadly Category 5 hurricane that devastated the northeastern Caribbean in September 2017, particularly Dominica, Saint Croix, and Puerto Rico. It is regarded as the worst natural disaster in recorded history to affect ...
in 2017 and was affected by earthquakes in 2019 and 2020. 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. Due to uncertainty over the remaining strength of the other cables supporting the suspended structure, and the risk of collapse owing to further failures making repairs dangerous, the NSF announced on November 19, 2020, that the telescope would be decommissioned and dismantled, with the radio telescope and
LIDAR Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...
facility remaining operational. Before it could be decommissioned, several of the remaining support cables suffered a critical failure and the support structure, antenna, and dome assembly all fell into the dish at 7:55 a.m. local time on December 1, 2020, destroying the telescope. The NSF determined that it would not rebuild the telescope or similar Observatory at the site in October 2022.


General information

The telescope's main collecting dish had the shape of a
spherical cap In geometry, a spherical cap or spherical dome is a portion of a sphere or of a ball cut off by a plane. It is also a spherical segment of one base, i.e., bounded by a single plane. If the plane passes through the center of the sphere (formin ...
in diameter with an
radius of curvature In differential geometry, the radius of curvature, , is the reciprocal of the curvature. For a curve, it equals the radius of the circular arc which best approximates the curve at that point. For surfaces, the radius of curvature is the radius o ...
, and was constructed inside a
karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, Dolomite (rock), dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathe ...
sinkhole A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...
. The dish surface was made of 38,778 perforated aluminum panels, each about , supported by a mesh of steel cables. The ground beneath supported shade-tolerant vegetation. The telescope had three
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
transmitters, with
effective isotropic radiated power Effective radiated power (ERP), synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency (RF) power, such as that emitted by a radio transmitter. It is the total power in watts that would hav ...
s (EIRPs) of 22  TW (continuous) at 2380 MHz, 3.2  TW (pulse peak) at 430 MHz, and 200  MW at 47 MHz, as well as an ionospheric modification facility operating at 5.1 and 8.175 MHz. The dish remained stationary, while receivers and transmitters were moved to the proper focal point of the telescope to aim at the desired target. As a spherical mirror, the reflector's focus is 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. The receiver was on an platform suspended above the dish by 18 main cables running from three
reinforced concrete Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low ultimate tensile strength, tensile strength and ductility are compensated for by the inclusion ...
towers (six cables per tower), one high and the other two high, placing their tops at the same elevation. Each main cable was a bundle of 160 diameter wires, with the bundle painted over and dry air continuously blown through to prevent corrosion due to the humid tropic climate. The platform had a rotating, bow-shaped track long, called the
azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematical ...
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 The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction ( plumb line) opposite to the gravity direction at that location ( nadir). The zenith is the "high ...
(between −1 and 38 degrees of
declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of th ...
).
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...
's location near the Northern
Tropic The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
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 Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
is longer than the 2.6-hour time that the telescope could track a celestial position, preventing
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
observations of more distant objects.


History


Design and construction

The origins of the observatory trace to late 1950s efforts to develop
anti-ballistic missile An anti-ballistic missile (ABM) is a surface-to-air missile designed to counter ballistic missiles (missile defense). Ballistic missiles are used to deliver nuclear, chemical, biological, or conventional warheads in a ballistic flight trajec ...
(ABM) defenses as part of the newly formed
United States Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national sec ...
(DoD)
Advanced Research Projects Agency The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Adv ...
(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 .Barry Rosenberg
"DARPA Paves the Way for U.S. Efforts in Ballistic Missile Defense"
, 50 Years of Bridging the Gap, DARPA

, 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 A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...
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 Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
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 The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...
. ARPA began to address both simultaneously. To better understand the radar returns from a warhead, several radars were built on
Kwajalein Atoll Kwajalein Atoll (; Marshallese: ) is part of the Republic of the Marshall Islands (RMI). The southernmost and largest island in the atoll is named Kwajalein Island, which its majority English-speaking residents (about 1,000 mostly U.S. civilia ...
, while Arecibo started with the dual purpose of understanding the ionosphere's F-layer while also producing a general-purpose scientific radio observatory. The observatory was built between mid-1960 and November 1963. William E. Gordon and George Peter of
Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to tea ...
oversaw its design for study of the Earth's
ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...
. He was attracted to the
sinkholes A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...
in the
karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, Dolomite (rock), dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathe ...
regions of
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...
that offered perfect cavities for a very large dish. Originally, a fixed parabolic reflector was envisioned, pointing in a fixed direction with a tower to hold equipment at the focus. This design would have limited its use in other research areas, such as
radar astronomy Radar astronomy is a technique of observing nearby astronomical objects by reflecting radio waves or microwaves off target objects and analyzing their reflections. Radar astronomy differs from '' radio astronomy'' in that the latter is a passive o ...
,
radio astronomy Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object was in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation comin ...
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 The Air Force Research Laboratory (AFRL) is a scientific research organization operated by the United States Air Force Air Force Materiel Command, Materiel Command dedicated to leading the discovery, development, and integration of aerospace w ...
(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 wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (sho ...
s 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 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 tower centered in the reflector to support the feed. The suspended structure was designed by Dr. Thomas C. Kavanagh,
Fred Severud Fred Severud (June 8, 1899 - June 11, 1990) was a Norwegian born, American structural engineer. His projects included the St. Louis Gateway Arch, Seagram Building and Madison Square Garden. Background Fred N. Severud was born Fridtjov Nikolai S� ...
, and Dr. Hans Bandel, who were selected after the 1959 RFP issued by Cornell University. A proposal by 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. 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 The United States Court of Federal Claims (in case citations, Fed. Cl. or C.F.C.) is a United States federal court that hears monetary claims against the U.S. government. It was established by statute in 1982 as the United States Claims Court, ...
, that “(a) a judgment has been entered in favor of the plaintiffs ( Helias Doundoulakis,
William J. Casey William Joseph Casey (March 13, 1913 – May 6, 1987) was the Director of Central Intelligence from 1981 to 1987. In this capacity he oversaw the entire United States Intelligence Community and personally directed the Central Intelligence Agency ...
, 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.” George Doundoulakis, who directed research at General Bronze Corporation in
Garden City, New York Garden City is a village located on Long Island in Nassau County New York. It is the Greater Garden City area's anchor community. The population was 23,272 at the 2020 census. The Incorporated Village of Garden City is primarily located within ...
, along with Zachary Sears, who directed Internal Design at Digital B & E Corporation, New York, received the RFP from
Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to tea ...
for the antenna design and studied the idea of suspending the feed with his brother, Helias Doundoulakis, a
civil engineer A civil engineer is a person who practices civil engineering – the application of planning, designing, constructing, maintaining, and operating infrastructure while protecting the public and environmental health, as well as improving existing ...
. 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 Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to tea ...
for a doughnut or
torus In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle. If the axis of revolution does n ...
-type
truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...
suspended by four cables from four towers above the reflector, having along its edge a rail track for the
azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematical ...
al truss positioning. This second truss, in the form of an arc, or
arch An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it. Arches may be synonymous with vau ...
, 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 A counterweight is a weight that, by applying an opposite force, provides balance and stability of a mechanical system. The purpose of a counterweight is to make lifting the load faster and more efficient, which saves energy and causes less we ...
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 Cable may refer to: Mechanical * Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof * Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
suspension system which was finally adopted. The present configuration is 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 The United States Patent and Trademark Office (USPTO) is an agency in the U.S. Department of Commerce that serves as the national patent office and trademark registration authority for the United States. The USPTO's headquarters are in Alexa ...
. The idea of a spherical reflecting mirror with a steerable secondary has since been used in optical telescopes, in particular, the
Hobby–Eberly Telescope The Hobby–Eberly Telescope (HET) is a 10-meter (30-foot) aperture telescope located at the McDonald Observatory in Davis Mountains, Texas. The Hobby–Eberly Telescope is one of the largest optical telescopes in the world. It combines a numb ...
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.


Upgrades

Since its construction, the telescope was upgraded several times, following the facility's oversight from the DoD to the
National Science Foundation The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National ...
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 Focal point may refer to: * Focus (optics) * Focus (geometry) * Conjugate points, also called focal points * Focal point (game theory) * Unicom Focal Point UNICOM Focal Point is a portfolio management and decision analysis tool used by the p ...
, giving Arecibo more flexibility. The additional instrumentation added 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. In 1997, a more powerful 2400 MHz transmitter was added. Finally, in 2013 with a grant of , 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.


Funding reductions

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. Between 2001 and 2006, NASA decreased, then eliminated, its support of the planetary radar. A November 2006 report by the Astronomical Sciences division recommended substantially decreased astronomy funding for the Arecibo Observatory, from in 2007 to in 2011. The report further stated that if other sources of funding could not be found, closure of the Observatory was recommended. 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. An additional in bonds were secured from the government of Puerto Rico. Academics, media and influential politicians pressured the
United States Congress The United States Congress is the legislature of the federal government of the United States. It is Bicameralism, bicameral, composed of a lower body, the United States House of Representatives, House of Representatives, and an upper body, ...
on the importance of the work of the observatory. led to additional in funding to support Arecibo in the
American Recovery and Reinvestment Act of 2009 The American Recovery and Reinvestment Act of 2009 (ARRA) (), nicknamed the Recovery Act, was a stimulus package enacted by the 111th U.S. Congress and signed into law by President Barack Obama in February 2009. Developed in response to the Gr ...
. This was used for basic maintenance and for a second, much smaller, antenna to be used for
very long baseline interferometry Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth or in space. T ...
, new
Klystron A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian,Pond, Norman H. "The Tube Guys". Russ Cochran, 2008 p.31-40 which is used as an amplifier for high radio frequen ...
amplifiers for the planetary radar system and student training. Arecibo's budget from NSF continued to wane in the following years."Major multi-user research facilities"
p. 35–38. Retrieved February 10, 2010
Starting in FY2010, NASA restored its historical support by contributing $2.0 million per year for
planetary science Planetary science (or more rarely, planetology) is the scientific study of planets (including Earth), celestial bodies (such as moons, asteroids, comets) and planetary systems (in particular those of the Solar System) and the processes of their ...
, particularly the study of
near-Earth object A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (Apsis, perihelion) is less than 1.3 astronomical unit ...
s, at Arecibo. NASA implemented this funding through its Near Earth Object Observations program. NASA increased its support to $3.5 million per year in 2012. In 2011, NSF removed
Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to tea ...
, which had managed the National Astronomy and Ionosphere Center (NAIC) since the 1970s, as the operator and transferred these responsibilities to
SRI International SRI International (SRI) is an American nonprofit scientific research institute and organization headquartered in Menlo Park, California. The trustees of Stanford University established SRI in 1946 as a center of innovation to support economic ...
, along with two other managing partners,
Universities Space Research Association The Universities Space Research Association (USRA) was incorporated on March 12, 1969, in Washington, D.C. as a private, nonprofit corporation under the auspices of the National Academy of Sciences (NAS). Institutional membership in the asso ...
and Universidad Metropolitana de Puerto Rico, with a number of other collaborators. 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. 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 deconstructing the unit. The NSF continued to indicate it would like to reduce funding to the Observatory in the near future. As in 2008, academics expressed their concern over the loss of scientific discoveries that could occur should the Observatory be shut down.


2020 damage, decommissioning plans, and collapse

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 Hurricane Maria was a deadly Category 5 hurricane that devastated the northeastern Caribbean in September 2017, particularly Dominica, Saint Croix, and Puerto Rico. It is regarded as the worst natural disaster in recorded history to affect ...
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, 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 the decision would be made to decommission it instead. A consortium consisting of the
University of Central Florida The University of Central Florida (UCF) is a public research university whose main campus is in unincorporated Orange County, Florida. UCF also has nine smaller regional campuses throughout central Florida. It is part of the State Universi ...
(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. With this, the UCF consortium were named the new operators of the observatory in 2018. On August 10, 2020, an auxiliary platform support cable separated from Tower 4, causing damage to the telescope, including a gash in the reflector dish. 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. 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 . 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. The UCF engineering staff, which had been monitoring the cables with support from the
U.S. Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...
, and the engineering firms they had hired previously evaluated the remaining cables from Tower 4. One engineering firm proposed stabilization efforts, 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 this 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 Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...
facility will remain operational. While waiting for NSF to make the decommissioning plans, steps had been taken to try to reduce the load that each of the towers were 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. 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. 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. 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.


Post-collapse

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. 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. As required by the
Consolidated Appropriations Act, 2021 The Consolidated Appropriations Act, 2021 () is a $2.3trillion spending bill that combines $900 billion in stimulus relief for the COVID-19 pandemic in the United States with a $1.4trillion omnibus spending bill for the 2021 federal fiscal yea ...
, 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 recibo Observatoryfacilities and surrounding areas, and the process for determining whether to establish comparable technology at the site, along with any associated cost estimates". 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." A team from the
University of Texas at Austin The University of Texas at Austin (UT Austin, UT, or Texas) is a public research university in Austin, Texas. It was founded in 1883 and is the oldest institution in the University of Texas System. With 40,916 undergraduate students, 11,075 ...
was able to completely recover and back up the 3
petabyte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
s 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 The Texas Advanced Computing Center (TACC) at the University of Texas at Austin, United States, is an advanced computing research center that provides comprehensive advanced computing resources and support services to researchers in Texas and acr ...
to be made available for continued research. An early plan developed by NSF scientists suggest one possible replacement called the Next Generation Arecibo Telescope, using 1000 closely-packed telescopes mounted on one or more flat plate(s) that would cover the 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 compared to the original Arecibo Telescope, and be twice as sensitive with four times the radar power. It is expected this would cost roughly to build. This would enable better study of the supermassive black hole at the center of the Milky Way as a prime target. NSF determined in October 2022 that the Arecibo site will not be used for a new telescope, instead converting the site to be a STEM educational center. 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.


Research and discoveries

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 Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
period of Mercury was not 88 days, as formerly thought, but only 59 days. In 1968, the discovery of the periodicity of the
Crab Pulsar The Crab Pulsar (PSR B0531+21) is a relatively young neutron star. The star is the central star in the Crab Nebula, a remnant of the supernova SN 1054, which was widely observed on Earth in the year 1054.Richard V. E. Lovelace Richard Van Evera Lovelace is an American astrophysicist and plasma physicist. He is best known for the discovery of the period of the pulsar in the Crab Nebula (Crab pulsar), which helped to prove that pulsars are rotating neutron stars, for d ...
and others provided the first solid evidence that
neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...
s exist. In 1974, Hulse and Taylor discovered the first binary pulsar
PSR B1913+16 PSR may refer to: Organizations * Pacific School of Religion, Berkeley, California, US * Palestinian Center for Policy and Survey Research * Physicians for Social Responsibility, US ;Political parties: * Revolutionary Socialist Party (Portugal) ( ...
, an accomplishment for which they later received the Nobel Prize in Physics. In 1982, the first
millisecond pulsar A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The leading theory for the origin of ...
, PSR B1937+21, was discovered by Donald C. Backer, Shrinivas Kulkarni, Carl Heiles, Michael Davis, and Miller Goss. This object spins 642 times per second and, until the discovery of
PSR J1748-2446ad PSR may refer to: Organizations * Pacific School of Religion, Berkeley, California, US * Palestinian Center for Policy and Survey Research * Physicians for Social Responsibility, US ;Political parties: * Revolutionary Socialist Party (Portugal) ( ...
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 Comet Encke , or Encke's Comet (official designation: 2P/Encke), is a periodic comet that completes an orbit of the Sun once every 3.3 years. (This is the shortest period of a reasonably bright comet; the faint main-belt comet 311P/PanSTARRS ha ...
. In August 1989, the observatory directly imaged an
asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
for the first time in history:
4769 Castalia 4769 Castalia (; '' prov. designation:'' ) is a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately in diameter and was the first asteroid to be modeled by radar imaging. It was discovered on 9 August 1989, ...
. The following year, Polish astronomer
Aleksander Wolszczan Aleksander Wolszczan (born 29 April 1946) is a Polish astronomer. He is the co-discoverer of the first confirmed extrasolar planets and pulsar planets. Early life and education Wolszczan was born on 29 April 1946 in Szczecinek located in pre ...
made the discovery of pulsar PSR B1257+12, which later led him to discover its three orbiting planets. 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. In January 2008, detection of prebiotic molecules methylene imine, methanimine and hydrogen cyanide were reported from the observatory's radio spectroscopy measurements of the distant starburst galaxy Arp 220. From January 2010 to February 2011, astronomers Matthew Route and
Aleksander Wolszczan Aleksander Wolszczan (born 29 April 1946) is a Polish astronomer. He is the co-discoverer of the first confirmed extrasolar planets and pulsar planets. Early life and education Wolszczan was born on 29 April 1946 in Szczecinek located in pre ...
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 Gauss (unit), kG-strength magnetic field and magnetic activity similar to both the planet Jupiter and the Sun.


The 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. 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.


SETI and METI projects

Search for extraterrestrial intelligence (SETI) 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 SETI, active search by transmitting messages. Arecibo is 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 (SETI), Project Phoenix observations. The Einstein@Home distributed computing project has found more than 20 pulsars in Arecibo data.


Other uses

Terrestrial aeronomy experiments at Arecibo have included the NASA Coqui, Coqui 2 experiment, supported by
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
. The telescope also originally had military intelligence uses, including locating Soviet Union, Soviet
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
installations by detecting their signals EME (communications), bouncing off the Moon. Limited amateur radio operations have occurred, 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 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 callsigns. These were not two-way contacts. From April 16–18, 2010, again, the Arecibo Amateur Radio Club KP4AO conducted moon-bounce activity using the antenna. 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.


Cultural significance

Due to its unique shape and concept, the telescope had been featured in many contemporary works. It was used as a filming location in the films ''
GoldenEye ''GoldenEye'' is a 1995 spy film, the seventeenth in the ''James Bond'' series produced by Eon Productions, and the first to star Pierce Brosnan as the fictional MI6 agent James Bond. Directed by Martin Campbell, it was the first in the se ...
'' (1995), ''Species (film), Species'' (1995), and ''Contact (1997 American film), Contact'' (1997) (based on Carl Sagan's Contact (novel), novel of the same name, which also featured the observatory), ''The Losers (2010 film), The Losers'' (2010), and in ''The X-Files'' television episode "Little Green Men (The X-Files), Little Green Men". One map in the 2013 video game ''Battlefield 4'', while set in China, is based on the distinctive layout of the Arecibo Telescope. In 2014, a video art installation piece titled ''The Great Silence'' by artists Allora & Calzadilla, 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 juxtaposed text was later published as a short story with the same title in a special issue of the art journal ''E-flux publications, e-flux'' in 2015 and was included in the author's short story collection ''Exhalation: Stories'' in 2019. 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.


See also

* List of radio telescopes * Orgov Radio-Optical Telescope


References


Further reading

* * * * * *
Entry into the National Register of Historic Places
* *


External links

*
Youtube video of collapse 12.56 mins

The wondrous life—and dramatic death—of Puerto Rico's Arecibo Observatory
{{Authority control 1963 establishments in Puerto Rico 2020 disestablishments in Puerto Rico Arecibo, Puerto Rico Buildings and structures completed in 1963 Building collapses in 2020 Historic districts on the National Register of Historic Places in Puerto Rico Historic Mechanical Engineering Landmarks Museums in Arecibo, Puerto Rico National Science Foundation Radio telescopes Science museums in Puerto Rico Search for extraterrestrial intelligence 2020 in science