Long-term zinc creep in the cable spelter sockets was the root cause of the 2020 collapse of the National Science Foundation’s 57-year-old telescope at the Arecibo Observatory in Puerto Rico, according to a report from the National Academies of Sciences, Engineering, and Medicine, which also draws lessons learned for other unique, critical science facilities.

The failure sequence began with Hurricane Maria, over three years before the collapse, the report says.

The telescope’s main platform hung over the 305-metre reflector dish on a set of cables. Each cable ended in a socket filled with zinc, and the zinc held the cable in place. The report says the zinc gradually lost its hold on the cables and allowed several of them to pull out. The platform then fell into the reflector.

A failure mode with no documented precedent

Zinc-filled sockets of this kind have been in use for more than a century, the report notes. It calls the Arecibo failure “the first documented case of long-term zinc-induced creep failure despite a long history of usage over a century”. Before the hurricane, indications of cable pullout were minimal.

After the hurricane, visual inspections showed large and progressive cable pullouts, which the report says should have prompted remedial action. Safety factor calculations made after the first cable failure did not recognise the accelerated time-dependent materials failure process that governed the eventual zinc pullout.

The electroplasticity hypothesis

The report offers one possible explanation for why the creep accelerated.

Long-term low-current electroplasticity, induced by the electromagnetic waves from the Arecibo telescope itself, may have sped up the zinc creep, it says. The report recommends that NSF offer the remaining socket and cable sections for study by the research community.

More broadly, the report says building and operating cutting-edge, custom-designed research facilities presents unique challenges, where prior designs and experience may not be a reliable guide and unprecedented modes of failure can never be fully anticipated.

Careful monitoring should be increased as facilities age, to detect deterioration and potential novel failure modes, to the extent that is reasonable, it says.

The report also says NSF should make explicit funding provisions for detailed, ongoing condition maintenance and monitoring. NSF maintained research operations at Arecibo for its National Astronomy and Ionosphere Center.

The committee that wrote the report reviewed forensic investigations commissioned by the University of Central Florida and NSF, gathered information from Arecibo Observatory employees, studied relevant research, consulted other experts, and examined structural analyses, engineering plans, inspection reports, photographs and repair proposals.

The full report, a consensus study report published in 2024, is titled Failure Analysis of the Arecibo Observatory 305-Meter Telescope Collapse. The National Academies announced its release in a media advisory last updated on October 25, 2024.

It also contains recommendations on operations and maintenance manuals, inspection regimes and independent audits.

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