Why Did We Stop Using the Arecibo Telescope, and What Did We Lose?

By O.C. Wanderer ·

arecibo, radio astronomy, planetary radar, cable failure, arecibo message, seti@home, FAST telescope, project phoenix, ngRADAR

Why Did We Stop Using the Arecibo Telescope, and What Did We Lose?

Written by OC Wanderer, author of Destiny Among the Stars, a LitRPG sci-fi series set in the real stellar neighborhood. Published October 26, 2026.

A reply from the Perseus Arm would take more than 12,000 years. That is the round trip for a question and its answer at the speed of light. At that distance, listening offers a chance to hear someone without waiting millennia for a reply. The 305-meter telescope at Arecibo, in Puerto Rico, did that listening for decades until it fell in 2020.

I have been to Puerto Rico many times, and visiting Arecibo still fills me with sadness and dread for what was lost. What stays with me is the feeling that we lost something critical there. It seems possible to me that a golden age of space exploration crumbled with that dish. I am also disappointed, personally, that the infrastructure was never rebuilt, and that disappointment is what sent me to find out what happened to the telescope. I wonder what we gave up when it came down, and whether anything has taken its place.

The collapse ended Arecibo’s work, but it did more than take away a telescope. Other dishes have picked up the listening. What I want to understand is the gap left by an instrument that could send a powerful beam into space and catch its echo.

The dish fell because its cables failed

Imagine suspending 913 tons of receivers and transmitters above a bowl 305 meters across. That was Arecibo: a fixed dish below, a platform hanging from cables strung to towers around it. Each cable ended in a socket filled with zinc, and the zinc gripped the cable’s wires. Over the years the zinc slowly deformed under the load, which engineers call creep, and the wires began to slide out.1

Inspections in late 2018 and early 2019 found cables that had already slipped more than an inch out of their sockets. The National Academies committee that investigated the collapse wrote that those slips should have raised a concern that cables might fail.2 In August 2020 one cable pulled free and fell onto the dish. The alarming part is how little weight it took: less than half the cable’s design load. That left a frightening question hanging over the platform. Could the other cables still be trusted? A second cable failed in November.

Later that month the National Science Foundation (NSF), the U.S. agency responsible for the observatory, announced that repairs could not be done safely and that the telescope would be taken down. The platform fell on December 1, before that work could start.3 Engineers had used zinc-filled sockets for more than a century, yet the investigating committee could find no other documented failure of this kind. A familiar piece of engineering had failed in an unfamiliar way.4

In Book 4 of Destiny Among the Stars, Luca’s crew meets a team that is rebuilding the dish. Camila, who has fabricated most of the replacement panels herself, walks them along a catwalk around it and tells them, “When the original dish collapsed and the cables snapped, the receiver platform crashed down. The whole thing was declared unsalvageable.” She shrugs. “We disagreed.”

It listened for decades and sent a famous message

The message came first. On November 16, 1974, at a ceremony for an upgrade to the telescope, Arecibo transmitted 1,679 bits, each a one or a zero, toward M13, a cluster of stars about 25,000 light-years away.5

There is a lovely decoding puzzle inside those 1,679 bits. The number is 23 times 73, both prime numbers; arrange the bits 23 across and 73 down, and a picture emerges. Frank Drake and his colleagues put into it the chemicals of life, the formula for DNA, a diagram of our solar system, and simple figures of a human being and of the telescope.6

The message was sent once and lasted about three minutes. It has covered roughly one five-hundredth of the way so far, so it will reach M13’s distance around 25,000 years from now, and an answer would need as long again to come back.7

An astronomer who was on the observatory’s staff that day later called the transmission “strictly a symbolic event, to show that we could do it.” What a way to announce a new transmitter: send a picture of humanity toward a distant star cluster. The message demonstrated what the newly installed radar and that enormous dish could do together.8

The listening went on for far longer. The dish was in heavy demand from other astronomers, so a group at the University of California, Berkeley, attached its own equipment and recorded whatever part of the sky the telescope happened to be pointed at.9 The group’s SETI@home project sent recordings made that way to volunteers’ home computers for analysis. Those recordings covered the quarter of the sky the dish could reach, most of it several times over, and the computers logged about 12 billion detections, each one a brief rise in radio power at one frequency from one point in the sky.10

Project Phoenix took the more deliberate approach: pick a nearby star and listen, then move to the next. The SETI Institute’s search covered about 800 stars and spent its final years at Arecibo. It could have caught a transmitter with power similar to a military airport radar, but found no signal from another civilization. That is a striking silence for the signals it could detect; it leaves me wondering what quieter neighbors might be doing.11

The size of the dish is what made searches like these sensitive. A radio dish collects the energy that lands on it, so a wider dish gathers more of a weak signal, and the opening of Arecibo’s bowl covered roughly ten soccer fields.12 The collapse left an unfinished listening puzzle. The SETI@home team narrowed the recordings down to about a hundred candidates worth another look, then faced the problem of hearing them again without Arecibo. By their assessment, only China’s 500-meter FAST dish had the sensitivity they needed, and they have been revisiting those spots with it. I would love to know what survives that second look.13

Other telescopes do the listening; the radar went down with the dish

FAST is larger than Arecibo was, it has searched for signals from other civilizations since 2019, and it is at least twice as sensitive to the kinds of signal SETI@home looked for.14 That makes it a powerful successor for listening, but sending is a different engineering problem: FAST cannot carry the weight of a radar transmitter and its cooling equipment.15

Arecibo could ask an asteroid a question and hear the answer. Its main transmitter sent one megawatt of continuous radio power through the dish in a narrow beam; aim it at an asteroid or a planet, then listen for the echo. The time the echo took to return gave the distance, and the shift in its frequency gave the speed at which the object was approaching or receding. For objects millions of kilometers away, that echo could pin down the distance to within 50 meters. Imagine measuring something across that gulf with an uncertainty smaller than a soccer field.16

The 1974 message went out through that radar transmitter, installed the same year, and the radar’s everyday signals left the solar system as well. The staff astronomer who called the message symbolic said in 1999 that anyone who detected those signals would see they were made by intelligent beings, and the post on the Fermi paradox asks whether we want to be noticed that way.17

Between 1997 and 2020 the radar observed 889 near-Earth asteroids and comets. Survey telescopes found the objects, and the radar then measured their orbits, sizes and shapes.

NASA counted Arecibo as one of its two major planetary radars. The other is a 70-meter antenna at Goldstone in California, which was about one tenth as sensitive. Goldstone is offline for repairs. Losing Arecibo therefore cost us a way to get much sharper measurements after an asteroid was discovered. The 2026 review of its radar work concludes that no existing or planned facility can match it.18

Illustration of two Destiny Among the Stars characters beside a ruined Arecibo dish

Designs for a replacement exist; construction funding remains unannounced

The people who knew Arecibo best began imagining its successor within three weeks of the collapse. Their Next Generation Arecibo Telescope concept, public since March 2021, puts many small dishes on a platform that can tilt. Together they would collect as much as a single 300-meter dish and transmit with five times the old radar’s power. I can see why that possibility would make simply walking away from the site so hard.19

In October 2022 the NSF asked for proposals for an education center at the site, and its announcement said the plan “does not include rebuilding the 305-meter telescope.”20

In 2023 the designers published a smaller version: many dishes working together, but with under a fifth of the old dish’s collecting area.21 The designs keep the possibility alive, but they remain studies on paper. The NSF updates cited here announce no construction funding, and the 2026 radar review judges a rebuild unlikely.22

Part of the radar work may come back at another site. A project called ngRADAR is designing a transmitter for the 100-meter Green Bank Telescope in West Virginia. Its tests so far have used a 700-watt prototype, less than a thousandth of the power of Arecibo’s transmitter, and the full-power system is in the design stage.23

In Book 4, Camila’s team has spent three years rebuilding the dish on its own. She tells Luca that every time they petition for “funding for the telescope, we get the same answer,” and her teammate Miguel supplies it: “They want to keep the area wild. The telescope is inconvenient to that plan.” In the next chapter Luca asks what it would take to finish. With proper funding, “Maybe six months.” Without it, “Maybe never.”

So why did we stop using Arecibo, and what did we lose?

Arecibo’s cables slid out of their sockets, and the platform fell before it could be taken down safely. Other dishes continue the search for company, but the combination of listening and powerful planetary radar remains a real loss. There are designs for a successor; the sources above offer no announced funding to build it. I still wonder what a rebuilt Arecibo could discover. Meanwhile, the listening continues elsewhere. What have those telescopes heard? Has SETI actually found anything, or is it just a long silence?

If you want to meet the crew that finds a team rebuilding the Arecibo dish with their own hands, start Destiny Among the Stars.

Endnotes

  1. National Academies of Sciences, Engineering, and Medicine, Failure Analysis of the Arecibo Observatory 305-Meter Telescope Collapse (National Academies Press, 2024), Summary, doi:10.17226/26982: “the root cause of the Arecibo Telescope’s collapse was unprecedented and accelerated long-term zinc creep induced failure of the telescope’s cable spelter sockets”; “The 913-ton platform collapsed, swung across the dish, and smashed through the reflector.” The National Academies’ news release (October 25, 2024) describes the sockets: the zinc “lost its hold on the cables and allowed several of them to pull out.” The telescope entered service in 1963 and was 57 years old when it fell. ↩

  2. National Academies, Failure Analysis, Summary: inspections in late 2018 and early 2019 “observed cable slippage greater than 1.5 inches on auxiliary sockets at the ground end of backstay B12W and 1.125 inches at the tower end of M4N”; the report quotes the forensic engineers that the slips “should have raised a concern that cables may fail.” The committee dates the failure sequence from Hurricane Maria on September 20, 2017, and also reports that the storm’s wind loads should not have damaged the cables; it names zinc creep in the sockets as the root cause. ↩

  3. National Academies, Failure Analysis, Summary: on August 10, 2020, auxiliary cable M4N-T, “at less than half its design load, pulled out of its zinc-filled spelter socket and failed,” struck the dome under the platform and “crashed onto the dish below”; on November 6, main cable M4-4 failed at its socket; “On November 19, NSF announced that safe repairs would not be possible and that Arecibo Telescope would be closed in a controlled decommissioning”; on December 1 a third socket failed and the platform collapsed. ↩

  4. National Academies, Failure Analysis, Summary: the failure “has never been documented elsewhere despite a century of zinc-filled cable spelter sockets use.” ↩

  5. Bill Steele, “It’s the 25th anniversary of Earth’s first attempt to phone E.T.,” Cornell Chronicle, November 12, 1999. Cornell University managed the observatory for the NSF at the time. The article gives the date, the dedication ceremony, 1,679 bits at 2,380 MHz, and the target: “about 300,000 stars called the Great Cluster in Hercules, Messier 13. The globular cluster is 25,000 light-years away.” NASA’s Messier 13 page gives the same distance. The article calls it humanity’s “first and only deliberate radio message” as of 1999 and says no other formal messages had been sent from Arecibo. One later transmission is on record: in November 2009 the artist Joe Davis sent a coded gene sequence from the dish toward three nearby stars to mark the message’s 35th anniversary (MIT News). ↩

  6. Steele, Cornell Chronicle (1999): the message “forms a symbolic picture 23 characters wide by 73 long” and “included representations of the fundamental chemicals of life, the formula for DNA, a crude diagram of our solar system and simple pictures of a human being and the Arecibo telescope.” Its content was developed by Frank Drake with Richard Isaacman, Linda May and James C. G. Walker, with contributions from Carl Sagan. Author calculation: 23 × 73 = 1,679, and 23 and 73 are both prime, so 1,679 has no other pair of whole-number factors except 1 × 1,679. ↩

  7. Steele, Cornell Chronicle (1999): “It was sent only once, over a period of about three minutes.” Author calculation: 2026 − 1974 = 52 years of travel at the speed of light, so 52 light-years; 52 ÷ 25,000 = 0.0021, or about 1 part in 480; 1974 + 25,000 puts the arrival near the year 26,974, and a reply sent at once would return 25,000 years after that. The same article notes that the cluster will have moved along its orbit in the Galaxy by then. ↩

  8. Steele, Cornell Chronicle (1999), quoting Donald Campbell, a research associate at the observatory in 1974 and later a Cornell professor of astronomy: “It was strictly a symbolic event, to show that we could do it.” The article adds that the real purpose was “to call attention to the tremendous power of the radar transmitter newly installed at Arecibo and the ability of the telescope’s 1,000-foot diameter dish antenna to project a powerful signal into space.” ↩

  9. Steele, Cornell Chronicle (1999), describes SERENDIP at Arecibo as collecting data “during all the telescope’s other operations.” Robert Sanders, “Stuart Bowyer, pioneer of EUV astronomy and SETI, dies at 86,” Berkeley News, October 2, 2020: “Astronomers point the radio telescope wherever they want, and we connect our detectors and listen; we go along for the ride.” The search was called SERENDIP, and astronomers call this method commensal observing. ↩

  10. David P. Anderson, Eric J. Korpela, Dan Werthimer, Jeff Cobb, and Bruce Allen, “SETI@home: Data Analysis and Findings,” arXiv:2506.14737 (2025): observations “began in 1998” and continued with a more sensitive seven-beam receiver from 2006 through 2020, which is the data the paper analyzes; the dish could see “about 25% of the sky”; the first stage of analysis produced about 12 billion detections; SETI@home “observed most of the Arecibo sky several times.” The companion paper, Korpela et al., “SETI@home: Data Acquisition and Front-End Processing,” arXiv:2506.14718 (2025), covers the recordings from 1998 to 2020. The 1999 public launch is from Berkeley News, “For 21 years, enthusiasts used their home computers to search for ET” (January 12, 2026), which puts the visible sky at a third. ↩

  11. SETI Institute, “Project Phoenix”: at Arecibo “the search used 2,400 hours of telescope time in 11 twice-yearly sessions from October 1998 to March 2004”; the second telescope for the 1,200–1,750 MHz observations was at Jodrell Bank Observatory; “Phoenix would have been sensitive to transmitters with power similar to our military airport radars”; across its campaigns in Australia, West Virginia and Puerto Rico it “observed more than 800 stars to a distance of about 240 light years. No ET signals were detected.” The project began at the Parkes telescope in Australia in February 1995. ↩

  12. Author calculation: a circle 305 meters across has an area of π × 152.5² ≈ 73,060 square meters; a 105 × 68 meter soccer field is 7,140 square meters, and 73,060 ÷ 7,140 ≈ 10.2. The telescope used only part of the bowl at any one moment. Nolan, Carter and Rivera-Valentín (note 15) list the radar’s effective receiving area as 27,610 square meters. ↩

  13. Anderson et al. (2025): “The 300 meter Arecibo telescope collapsed in December 2020. Only the Five-hundred-meter Aperture Spherical Telescope (FAST) in China has sufficient sensitivity to check SETI@home candidates.” The team was granted 23 hours on FAST, enough to observe 92 candidates again. Berkeley News (January 12, 2026) gives the round figure of 100 and says the team had been pointing FAST at them “since July,” with the analysis of those observations still to come. ↩

  14. Zhi-Song Zhang et al., “First SETI Observations with China’s Five-hundred-meter Aperture Spherical radio Telescope (FAST),” The Astrophysical Journal 891 (2020): 174, arXiv:2002.02130; Tong-Jie Zhang et al., “SETI at FAST in China,” Journal of Physics: Conference Series 2877 (2024): 012053, arXiv:2312.16847 (observations from 2019; the Far Neighbour Project from 2023). Anderson et al. (2025), section XI.1: at FAST the sensitivity to SETI@home’s signal types is about 2.0 to 2.5 times that of the Arecibo observations. ↩

  15. Michael C. Nolan, Lynn M. Carter, and Edgard G. Rivera-Valentín, “Planetary Radar at the Arecibo Observatory,” Reviews of Modern Physics 98 (2026): 011003, arXiv:2604.00332: “The larger FAST radio telescope in China became operational in 2020, right at the end of Arecibo’s life, but cannot carry the weight of a radar transmitter and its associated cooling.” ↩

  16. Nolan, Carter, and Rivera-Valentín (2026): “one Megawatt of continuous power, formed into a narrow beam”; “Radar directly measures line-of-sight distance, via the time required for a radio signal to travel to the target and back, and line-of-sight velocity, via Doppler shifting of the frequency of a transmitted signal”; “ranges can be measured to <50 m accuracy for objects millions of kilometers away." The transmitter worked at 2,380 MHz, and the focused beam was equivalent to 20 terawatts radiated in all directions. Its power was doubled from half a megawatt in the upgrade of the late 1990s. ↩

  17. Steele, Cornell Chronicle (1999): “Since the transmitter was installed in 1974, Arecibo radar has been used for extensive explorations of the solar system”; “many of the radar signals have continued on out of our solar system and if detected would clearly be seen as created by intelligent beings, Campbell says.” ↩

  18. Nolan, Carter, and Rivera-Valentín (2026): “radar observations of 889 near-Earth asteroids and comets from 1997 to 2020, compared to the 40 achieved in the previous 30 years”; from 2000 to 2020 the Arecibo radar “was more sensitive than the next-best individual system (the Goldstone 70-meter antenna) by an order of magnitude”; “No existing or planned facility can match its sensitivity, flexibility, or number of observable asteroids.” NASA, “Statement on NSF’s Planned Controlled Decommissioning of Arecibo Radio Telescope” (November 19, 2020): Arecibo “has served as one of two major planetary radar capabilities” and let NASA “fully characterize the precise orbits, sizes, and shapes” of near-Earth objects after survey telescopes discovered them. NASA, “NASA Concludes Antenna Mishap Investigation, Releases Report” (June 5, 2026): Goldstone’s 70-meter antenna, Deep Space Station 14, over-rotated on September 16, 2025, and “will remain offline” through a maintenance and upgrade period “expected to be completed by October 2028.” ↩

  19. D. Anish Roshi et al., “The Future of the Arecibo Observatory: The Next Generation Arecibo Telescope,” arXiv:2103.01367 (2021), written “in the three weeks following the collapse” and posted in March 2021: a compact array of fixed dishes on a tiltable structure with a collecting area equivalent to a 300-meter dish and 5 megawatts of continuous transmitter power at 2 to 6 GHz. Five megawatts is five times the old radar’s one megawatt. ↩

  20. National Science Foundation, “NSF Arecibo Observatory Historic District,” updated January 15, 2026, update of October 13, 2022: “The solicitation does not include rebuilding the 305-meter telescope or operational support for current scientific infrastructure, such as the 12-meter radio telescope or Lidar facility.” The same page records the award of September 25, 2023, of over $5 million over five years for the education center, called NSF Arecibo C3. ↩

  21. D. Anish Roshi et al., “The Next Generation Arecibo Telescope: A Preliminary Study,” arXiv:2305.07780 (2023): 102 dishes of 13 meters, a collecting area equivalent to a dish of about 130 meters, and an array that “would function both as a transmitter and as a receiver.” Author calculation: √102 × 13 ≈ 131 meters; (130 ÷ 305)² ≈ 0.18, so about 18 percent of the area of a 305-meter dish. ↩

  22. Nolan, Carter, and Rivera-Valentín (2026), closing remarks: “the Arecibo telescope collapsed on December 1, 2020, and is not likely to be rebuilt.” The body’s statement that no funding to build a successor has been announced rests on three things: the NSF’s 2022 solicitation, which excludes a rebuild (note 20); the absence of any construction award for the Next Generation Arecibo Telescope in the NSF’s public Arecibo updates through January 2026; and this review. No source states it as a finding. ↩

  23. National Radio Astronomy Observatory, “ngRADAR: Timeline”: the NSF approved a concept-design award on October 29, 2021; a 700-watt transmitter at 13.9 GHz was first deployed on the Green Bank Telescope in November 2020 and again through April 2026; work toward a preliminary design review began in March 2025; “System requirements review passed” on August 5, 2026. The timeline lists no later design review and no construction award, which is what “in the design stage” rests on. Author calculation: 1,000,000 ÷ 700 ≈ 1,430. ↩

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