The recent failure of two support cables at the Arecibo Observatory in Puerto Rico has destabilised the structure such that it cannot be repaired without placing construction workers at significant risk, according to officials with the National Science Foundation. As feared, the beloved 305 metre telescope will have to be decommissioned.
As if 2020 couldn’t get any worse, we received news this morning that the giant dish at Arecibo will have to be demolished. The National Science Foundation came to this hard decision following a review of engineering assessments, which concluded that the observatory is in seriously bad shape and that it cannot be stabilised without placing workers in danger. The NSF is now planning for the controlled decommission of the dish, ending a historic 57-year run.
“I want to say this as forcefully as possible,” said Ralph Gaume, the director of NSF’s Division of Astronomical Sciences, at a call for reporters earlier today. “We’re not closing the Arecibo Observatory.”
Indeed, while the 305 metre dish will have to be demolished, it will need to be done in such a way to protect the facility’s other assets, including many important buildings under Tower 12. Once the observatory is deemed safe, scientific activities will resume at the site, including work with LIDAR to study Earth’s atmosphere. The University of Central Florida manages Arecibo for the NSF, in a cooperative agreement that involves Universidad Ana G. Méndez and Yang Enterprises.
The problem started on August 10, when an auxiliary cable slipped from its socket, falling onto the dish below and causing considerable damage. Then on November 6, a main cable snapped, and it too fell onto the structure. With those two support cables gone, concerns emerged about the overall stability of the structure.
Independent engineering assessments grimly concluded that the observatory is at imminent risk of catastrophic failure, as the remaining cables are no longer capable of carrying the loads they were initially designed for. These cables are currently holding a 816 T platform that’s dangling 450 feet (137 meters) above the dish. Three towers hold these cables in place, and they too are at risk of collapsing and falling into the dish, Gaume explained. What’s more, repairs to these cables would put work construction workers in serious danger.
“Although it saddens us to make this recommendation, we believe the structure should be demolished in a controlled way as soon as pragmatically possible,” read the recommendation letter from Thornton Tomasetti, an engineering firm hired to evaluate the situation at Arecibo. “It is therefore our recommendation to expeditiously plan for decommissioning of the observatory and execute a controlled demolition of the telescope.”
Back in August, when the auxiliary cable failed, the facility still seemed salvageable. Officials forged ahead with plans to temporarily stabilise the structure, and four new cables (two auxiliary cables and two temporary cables) were ordered, while a forensic analysis was commissioned to determine the reason for the unexpected slippage. But the break in the 3-inch main cable in November dramatically altered the situation, showing that the cables were weaker than presumed.
“All cables are now considered suspect, including the main cables,” explained Ashley Zauderer, program director for Arecibo Observatory at NSF, during the presser today, adding that the cables, which weigh upwards of 6,804 kg, were subject to storms, earthquakes, and excessive moisture.
Visual inspections of the remaining cables validated these concerns, as some cables exhibited new wire breaks, and some auxiliary cables appeared to be slipping out from their sockets. This prompted a re-evaluation of the situation, resulting in the decision to decommission the dish.
“This was not an easy decision for the NSF to make,” Sean Jones, NSF assistant director for the Mathematical and Physical Sciences Directorate, told reporters. “But safety is our number one priority.”
Gaume said it’s even too risky to study the remaining cables, as the structure is “currently at risk of an unexpected, uncontrolled collapse.” It’s a structure for which “we don’t understand the safety margins,” he added, but a controlled demolition “gives us the opportunity to preserve the remaining assets at this observatory,” which he described as a key component of Puerto Rico’s STEM educational capability.
Responding to a question from Gizmodo, Jones said the NSF is “laser focused” on preserving the remaining infrastructure at Arecibo and that the agency “remains dedicated to the people of Puerto Rico.” Jones is looking forward to the kind of science that will be done in the future, but “it’s going to take some time,” in a process that will involve the local community.
A formal plan to decommission the big dish is currently in development, and few details were given as to how this “controlled disassembly” will happen, aside from the team’s emphasis on doing it in such a way to protect the surrounding infrastructure. This plan will likely take weeks to develop, as it will need to meet legal, environmental, safety, and cultural requirements. Frighteningly, the structure could collapse before then.
“A break of one more cable on Tower 4 will likely result in an uncontrolled collapse, in which the platform will come crashing down into the main dish,” said Gaume. “It’s also possible the three main towers themselves — all 91.44 m tall — will potentially topple over,” he said.
The area around the dish is currently off limits, given the danger.
During the call with reporters, both Gaume and Zauderer were adamant that the facility was being managed properly.
Inspectors were brought in over the years to evaluate the structure, and they did “everything to the best of our knowledge to inspect the cables as necessary,” including the monitoring of the cables after hurricanes or earthquakes, said Gaume. These inspectors “didn’t provide any inkling that there was an issue.”
Echoing Gaume’s comments, Zauderer said regular inspections of the observatory were completed according to schedule. There are still many unknowns, she said, and forensic investigations are still underway. The slippage of the auxiliary cable in August “should not have happened,” said Zauderer, and the event precipitated the extra load on the main cable.
Work at Arecibo, should all go well with the decommissioning, will continue. The LIDAR facility in particular will continue to assist with research into the upper atmosphere and ionosphere, as will a sister facility on the island of Culebra. As for the main dish’s contributions in this area, that’s done, as is its ability to do radio astronomy.
It’s devastating news for the science community, but we should celebrate the various achievements made possible by the Arecibo Observatory, including the first detection of a binary pulsar, the first discovery of an extrasolar planet, and the many discoveries of nearby asteroids, including some potentially dangerous ones. For now, we’ll just have to wait to see what might be in store for Arecibo.