11.02.2022

Arecibo Observatory's cable-suspended science platform, as seen before damage accrued in 2020. (Image credit: UCF)

It's been more than a year since scientists lost one of the most iconic telescopes ever built — and yet the collapse of the famed Arecibo Observatory remains something of a mystery. 

Nestled into the jungle of Puerto Rico, the Arecibo Observatory's jewel was its vast radio dish, spanning 1,000 feet (305 meters) across and famous for its appearances in movies such as "Contact" and James Bond's "GoldenEye." But six decades after the telescope came online, on Dec. 1, 2020, the 900-ton science platform crashed through the delicate dish, abruptly ending the career of a workhorse telescope. 

The collapse put an end to a months-long sequence of damage, but even a month before the collapse, the National Science Foundation (NSF), which owned the observatory but did not directly manage it, believed that engineers could still save the telescope. Now, a team of engineers is on the case to understand what went wrong at Arecibo that made its troubles fatal. This analysis comes at the request of the NSF, in hopes of ensuring such a collapse never happens elsewhere.

"They don't want the same things to happen again to any other of the tremendous, one-of-a-kind, scientific assets in their charge," Roger McCarthy, a mechanical engineer and the chair of the committee gathered by the National Academies of Sciences, Engineering, and Medicine to execute the analysis, told Space.com.

Whatever the committee finds will be cold comfort to the scientists who worked at Arecibo or used its data — and that's three separate communities, since the instrument did key work in radio astronomy, planetary radar observations and atmospheric science. 

"Finding out what went wrong at Arecibo doesn't really help them with Arecibo, because Arecibo fell down," Mike Nolan, a planetary scientist now at the University of Arizona who was director of Arecibo Observatory from 2008 to 2011, told Space.com. 

And no other facility, NSF or otherwise, sports a design anything like Arecibo's massive dish and hanging platform. But if all goes well, the investigation will identify the factors that let the telescope become so delicate without anyone realizing how dire the situation was — factors that may well be present at other facilities the NSF supports. 

In astronomy alone, NSF's facilities include key observatories like the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the equator-crossing Gemini Observatory and the twin Laser Interferometer Gravitational Wave Observatory (LIGO) outposts in Washington and Louisiana. More are coming, like the Vera C. Rubin Observatory in Chile that is scheduled to begin observations next year. 

"Every one of these, by nature of being cutting-edge scientific instruments, puts a brand new design to its test over an extended period of time," McCarthy said. "So the NSF wants to know, how should we monitor these? Because every structure in the course of degrading sends you messages."

Reviewing a calamity 

In the past decade, Arecibo Observatory has faced challenges including a sequence of earthquakes and hurricanes, most notably Hurricane Maria that battered Puerto Rico in September 2017. By that time, the NSF was already evaluating proposals for what would be the second change in operating institutions in a decade and a management structure that would reduce the agency's financial commitment to the observatory. The University of Central Florida took over managing Arecibo, including the radio telescope and the rest of the site, in April 2018. 

Just over two years later, one of the massive cables supporting the heavy science platform above the vast dish unexpectedly slipped out of its socket and crashed through the telescope in August 2020. At the time, it was obviously concerning, but it wasn't considered an emergency. But just as engineers were preparing to stabilize the structure, another cable snapped in November, leaving NSF skeptical that the telescope could be saved.

A third cable snapped on Dec. 1, 2020, bringing the entire platform crashing down and leaving the three different scientific communities that had relied on the telescope for decades bereft. More than a year later, no one is particularly satisfied by the story pieced together so far, full of unsolved mysteries and unseen warnings — hence the new analysis. 

The first public meeting of the committee, held on Jan. 24 and Jan. 25, included presentations that described NSF's general practices in supporting and overseeing research facilities, as well as recounting the specific events that unfolded at Arecibo Observatory both before and during the failures. 

McCarthy said he expects the committee will meet a total of about five times. The next meeting, scheduled for next week, will include presentations from engineers who have been analyzing the collapse. In March, the committee is due to visit Arecibo Observatory in person to see what remains of the fallen telescope; the committee has eight months to pull its findings together into a report.

Missed signals 

In the story of Arecibo's collapse, engineers have a host of clues they can use to piece together the full picture. 

Among the evidence, there's a 600-some page NASA document inspecting the socket that failed in August 2020. That report determined that the socket failed because of a phenomenon called zinc creep, which the facility's consistent heavy load likely made more serious. 

Engineers wouldn't have pegged that socket as a weak spot; it had only been at work for about 25 years, where others were at 60 years and the sockets weren't considered a risk anyway. "This failure mode had never been identified before," Nolan said. "The conventional wisdom is, the joint is stronger than the cable. And clearly, that's not always the case."

In addition to this investigative report, the engineers who took the lead during the collapse are working on a similar report, due to NSF next month, that includes forensic work on other components of the observatory. 

Likewise, personnel at NSF and Arecibo Observatory, as well as engineers associated with the site have spent much of the intervening months revisiting old paperwork, making new models and forensically analyzing components of the observatory, all in hopes of figuring out what went wrong. 

Even as the full story is still coming together, the clues paint a picture of a situation far less stable than anyone realized at the time, even before the first cable failure. Engineers knew there was lingering damage from Hurricane Maria and the swarm of earthquakes that hit Puerto Rico beginning in late December 2019, but none of it was believed to need urgent attention. 

"Many items were being watched, so it wasn't like it was just one or two things — there were a lot of concerns," Ashley VanderLey, now senior advisor for facilities at NSF's astronomy division who was the program officer for Arecibo during the collapse, said of the months before the August failure during the committee meeting. "And we all knew that the weight of the platform was actually close to the limit because no new instruments were being allowed to be added to the platform, so that had been a concern for some time."

Budget tug of war 

But tracing the failures of concrete and steel can only tell one side of Arecibo's story. Also of concern to the committee are the processes that govern the NSF and its relationships with the institutions that manage their facilities, a task NSF is legally not permitted to do directly.

Foremost among those process is the never-ending challenge of budget management. In particular, as NSF officials noted during the introductory committee meeting, their facilities often face tension over money allocated to what is dubbed operations and maintenance, or O&M. 

But while operations and maintenance are lumped together, they tackle different priorities in the short term. Operations money directly feeds observation and analysis — the heart of the science that NSF wants to fund, but maintenance money never really leads to something to write up in a journal this year, even if the work is critical to the facility's long-term future. 

Unlike construction costs, O&M costs continue for decades, weighing down the NSF's budget far into the future. If the agency's overall budget doesn't increase NSF must also face down funding prioritization between new facilities and existing ones. 

"This is not a new problem, this is as old as NSF," Linnea Avallone, NSF's chief officer for research facilities, noted during the meeting. "We always have to keep in mind as we're building the next greatest thing," she added, "we are mortgaging our budget future."

That conflict between new and old facilities is why the NSF sought to step back from Arecibo as it forged ahead designing and building future observatories. But none of those projects will sport the same capabilities and versatility as Arecibo did, which continues to disappoint scientists watching the process.

"Most of these other facilities that they're talking about — telescopes and LIGO and accelerators and stuff — you decommission a facility because you've built the new one," Nolan said. 

"Well, they're not building a new bigger, better Arecibo," he said. "We're not closing it because we built the next greatest one, we're just deciding not to do that anymore."

Quelle: Space.com