Major Warning Signs of Arecibo Telescope Collapse Were Missed, Report Finds

A National Academies report exploring the cause of the 2020 collapse of the National Science Foundation’s Arecibo Observatory in Puerto Rico says major warning signs were missed by engineers prior to the telescope’s collapse.

The report, published on Oct. 25 by a committee appointed to investigate the collapse, explains that the cables holding up the central platform of the telescope most likely failed because of a process called zinc creep. Over time, deformation of the zinc used to anchor the steel cables holding up the telescope’s 900-ton receiver caused the cables to slip out of their sockets. This slippage, which took place over several years, should have raised alarm among structural engineers but was not identified as a major issue in maintenance checks, the report says.

The report notes that zinc creep is not a problem that has been documented at other facilities, which could be why engineers overlooked the issue at Arecibo. The committee says the uniquely powerful electromagnetic radiation environment at the telescope likely accelerated the deformation of the zinc but was unable to prove this definitively. Nonetheless, the movement of the cables from their sockets should have prompted further investigation and concern, the committee argues.

The committee recommends that NSF prioritize maintenance funding for aging facilities and increase the number of maintenance checks they perform as facilities age. Over time, as management of the Arecibo facility changed hands, less, rather than more, monitoring of the facility took place, and funding became more restrained, the report says.

“For aged structures such as the Arecibo Telescope, additional facility maintenance and monitoring (and their associated costs) may be warranted,” the report says. “The committee does not know how much of this monitoring and inspection reduction was caused directly or indirectly by NSF’s reduction in Arecibo funding over its final decade of service. The committee concluded that the safety consequences of a structural failure of the Arecibo Telescope were not considered in decision-making during its design and operation or in decisions about extending its life.”

The telescope’s collapse in December 2020 was not entirely unexpected, as two cables holding up the 900-ton central platform had failed in the months prior. Days before the receiver platform crashed into the dish below, NSF announced that the facility could not safely be repaired and would be decommissioned. NSF now plans to use the site as an educational center, but its opening was recently delayed to 2025.

Hurricane Maria, which hit the telescope on Sept. 20, 2017, may have exacerbated the decline of the facility’s structural integrity, the report suggests. While the telescope had survived many natural disasters before, Hurricane Maria was the most significant, with cables subjected to the “highest structural stress they had ever endured since it opened in 1963,” the report says. Records indicate the telescope faced wind speeds well over 100mph, but the report authors were unable to determine what maximum wind speed the telescope was designed to withstand.

The report says photographs of cable sockets from 2019 provide a “clear indication of major socket deterioration” post-Maria. This should have raised “serious concern,” the report says, but it finds there was “no mention of such anomalies anywhere in the inspection reports.” It concludes that the telescope operators “would have benefited from more detailed engineering or structural risk guidance concerning inspection protocol, documentation, and/or other indicators of structural deterioration and unexpected performance.”

At the time of Hurricane Maria, NSF was considering proposals for the management and operations of the telescope. The University of Central Florida was awarded the contract, which started in April 2018. A transition period from SRI International to UCF took place from February through June of that year. 

Ray Lugo, former director of UCF’s Florida Space Institute and principal investigator for the Arecibo Observatory operations grant, told the report committee he inspected the facility post-Maria as part of the handover to UCF. Lugo noticed cables had begun to pull out of their sockets but was told they had been reviewed by an external engineer and there was “not any real concern about cable failure.” NSF told the committee it does not have a record of this exchange and that “at no time during the review of damage post-Maria was increasing socket slippage ever brought to NSF’s attention as one of the issues to be considered for further inspection, analysis or in need of a repair.”

In 2018, Lugo applied to NSF for funding for structural repairs, but these remained incomplete by the time the telescope collapsed. The report notes that none of the proposed repairs would have saved the Arecibo Observatory from collapse.

“Only after the first socket failure did the consultants focus technical attention on the cable sockets, but even then, failed to consider the degradation mechanisms of the sockets. By the time a socket failed, there remained only a few months to respond,” the report states. It recommends that NSF offer the remaining socket and cable sections “to the research community for continued fundamental research on large-diameter wire connections, the long-term creep behavior of zinc spelter connections, and materials science.” 

Asked for comment on the report, an NSF spokesperson thanked the committee for their “thorough review of the circumstances” resulting in the collapse, adding, “We welcome the opportunity to consider their findings and how we can incorporate their recommendations in the future.”