Internal Government Report Shows Why Arecibo Couldn’t Be Saved

Officials warned of a “catastrophic failure” just days before the iconic observatory collapsed in December 2020.
Officials warned of a “catastrophic failure” just days before the iconic observatory collapsed in December 2020.
Damage to Arecibo after its 2020 collapse. Image: RICARDO ARDUENGO/AFP via Getty Images
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Puerto Rico’s Arecibo Observatory, which reigned as the largest single-dish telescope on Earth for more than half a century, is a site of consequential scientific discovery, a popular landmark for tourists, and a beloved setting in movies and books. That’s why the 1,000-foot-wide observatory was so widely mourned when it dramatically collapsed on December 1, 2020, following cable malfunctions that destabilized the structure during the prior months.


New documents released by the National Science Foundation (NSF), the U.S. federal agency that owned Arecibo, shed light on the difficult decisions faced by government officials after an auxiliary cable snapped and smashed through the reflector dish on August 10 of the same year. 

The documents, which were published by Government Attic in response to a Freedom of Information Act (FOIA) request, reveal the initial plan to respond and repair the damage, which was sent to the University of Central Florida (UCF), the institution that manages Arecibo for NSF, in the weeks following the summer cable break. 

The documents also include a letter, sent only eight days before the December collapse, that confirms NSF’s agonizing choice to conduct a controlled demolition of the telescope after a second cable malfunction made the structure too dangerous for restoration. 

That letter, dated November 23, is addressed to Elizabeth A. Klonoff, UCF’s vice president for research and dean of the college of graduate studies, and is signed by Jeff S. Leithead, NSF’s grants and agreements officer. The document confirms NSF’s later public statements that the famed observatory was shut down over safety concerns and is eerily prescient in its warning of a “catastrophic failure,” an outcome that materialized just over a week later.


“This decision is predicated on the paramount priority of human safety,” Leithead said. “NSF has evaluated multiple engineering assessments that found the telescope structure is in danger of a catastrophic failure. Its cables may no longer be capable of carrying the loads they were rated to support and attempts at repairs could put workers in harm’s way. Furthermore, the assessments found that even in the event of some stabilization actions, questions would remain as to the long-term stability of the structure.”

“Given that key stabilization and repair efforts would require workers to be on or near the telescope structure, the degree of uncertainty about the cables’ strength, and the extreme forces at work, NSF accepted the recommendation to cease recovery efforts and plan for a controlled demolition,” he continued. “We regret that this action is necessary but could not approve any scenario that might put repair crews at risk or leave Arecibo staff and visitors vulnerable, including to any hidden structural issues.”

In a note attached to the documents, a FOIA officer also clarifies that “NSF pursued a controlled decommissioning based on engineering assessments listed above,” but that “unfortunately, the telescope platform collapsed before the controlled demo could be planned and executed.”

In August, following the first cable malfunction, UCF was considering a “response plan” prepared by the Illinois-based firm Wiss, Janney, Elstner Associates, Inc. (WJE). The company proposed a detailed list of measures to investigate and stabilize the structure, and emphasized that its approach to eventual repairs and rehabilitation would be informed by those initial actions.


“Using the findings of the laboratory and analytical studies, a determination as to the root cause of the failure will be prepared,” WJE principals Jonathan C. McGormley and Brian J. Santosuosso told Ramon Lugo, principal investigator of UCF’s Florida Space Institute, in their attached letter. 

“With the root cause determined, a plan to assess the remaining cables can then be developed and executed,” the pair continued. “If an accurate assessment is not possible, then a plan to provide supplemental connections at the socketed ends will be needed.” 

The decision to decommission the telescope took a few months to materialize, but it was verbally communicated to UCF on November 18, in the wake of the second cable break on November 7, according to the documents. NASA also released a detailed investigation of the cable malfunctions and ultimate collapse of the telescope on June 1, 2021.

 NSF issued an update on the site in November 2021, noting that it has consulted with the Advisory Council on Historic Preservation, the Puerto Rico State Historic Preservation Office, and other interested parties, to prepare for a post-Arecibo world that still pays homage to the many contributions of the iconic observatory.  

“NSF held an Arecibo Observatory Options Workshop in the summer to assemble a diverse, multidisciplinary group of researchers, engineers, and educators with the common goal of developing and expanding the breadth of radio science in Puerto Rico, as well as facilitating the generation of innovative ideas for the future of Arecibo Observatory,” NSF said in its statement. 

At this point, the future of Arecibo remains a matter of speculation. Many proposals have been put forward to honor its legacy, including a concept for a next-generation replacement telescope. But while it's unclear what will become of this legendary site in the coming years and decades, its unique history and impact on our understanding of the universe live on, even as its wreckage is cleared away and salvaged.