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A satellite image of Arecibo taken on November 17, showing damage to the giant antenna caused by two broken cables supporting the platform suspended above it. (credit: Satellite Image © 2020 Maxar Technologies) |
by Jeff Foust
Monday 23 November 2020
Some astronomical observatories are iconic in the sense that they are distinctive enough to be recognized in the wider culture. The Arecibo Observatory certainly qualifies, with its main parabola of 305 meters embedded in the ground of Puerto Rico and a platform that houses receivers suspended above it, connected by cables to three towers. Few people may know much about astronomy done at Arecibo (other than, perhaps, its supporting role in the pursuit of extraterrestrial intelligence), but it has become famous in films such as Contact is Golden eye.
| “NSF has concluded that this recent damage to the 305-meter telescope cannot be addressed without endangering the life and safety of the work crews and personnel,” Jones said. |
But icons don’t last forever. In August, an auxiliary cable connecting the platform to a tower, installed in the 1990s, detached from its socket and crashed into the dish below, creating a gash about 30 meters long. Earlier this month, a main cable, connected to the same tower but dating from the observatory construction in the early 1960s, broke, causing further damage.
The National Science Foundation, which funds Arecibo, threw in the towel last Thursday. “NSF has concluded that this recent damage to the 305-meter telescope cannot be addressed without risking the life and safety of the work crews and personnel,” said Sean Jones, deputy director of the NSF Directorate of Mathematical and Physical Sciences. in a hastily arranged call with reporters, “and NSF has decided to begin the planning process for a controlled dismantling of the 305-meter telescope.”
A “controlled deactivation” is something like a “controlled reentry” of a spacecraft. “We will bring our engineering team together, and they are working on it right now, to develop a plan to tear down the platform in a controlled manner so that we can protect and prevent cables from entering the buildings,” said Ralph Gaume, Division Director. of Astronomical Sciences of the NSF. The idea is to prevent damage to buildings around the telescope, including at the base of one of the towers, as well as a separate lidar structure used for atmospheric studies.
“The 305-meter telescope itself will be a loss,” he said. The platform itself will also likely be destroyed, but the towers and other structures will be saved. “The rest of the observatory will be preserved.”
NSF made this decision after engineering companies hired by the observatory warned it was at risk of uncontrolled collapse and was too dangerous for crews to work on. “After the recent failure, WSP does not recommend allowing personnel on the platform or towers, or anywhere in the immediate physical vicinity in the event of a potential sudden structural failure,” said WSP, an engineering company involved in that analysis, in a letter to the University of Central Florida (UCF), which leads a consortium that manages Arecibo on behalf of the NSF. An uncontrolled collapse could tear down the towers and damage other buildings and structures the NSF wants to preserve.
The fact that both broken cables were connected to the same tower was of particular concern. “The engineers warned us that another cable is breaking [at that tower] it will cause an uncontrolled collapse of the facility, “Gaume said.
Additionally, the cable that broke only did so at around 62% of its rated resistance, suggesting that it, and potentially other cables, had weakened since their installation decades ago. Ashley Zauderer, program director for Arecibo at NSF, said that according to the agency’s records, the observatory has followed adequate maintenance plans for the cables. But, he added, those cables, produced in the 1950s and 1960s, “were designed in such a way that it was difficult, even with regular maintenance like painting, to prevent moisture and other things from getting in.”
Exactly how controlled dismantling will be carried out is still under study, a process that Gaume says will take at least several weeks. Actual dismantling could be done “very quickly,” he said, perhaps through the use of explosives, an approach recommended by an engineering company. “Controlled demolition, designed with a specific collapse sequence determined and implemented with the use of explosives, will reduce the uncertainty and danger associated with the collapse,” Thornton Tomasetti advised in a report to UCF.
| “By hastily dismantling the facility, we would compromise existing capabilities and eliminate a remarkable piece of American technology that has promoted a number of scientific breakthroughs,” González-Colón wrote. |
Equally uncertain is the cost of doing it and who will pay it. NSF officials said during the call that they would work with the Office of Management and Budget and Congress on how to pay for the decommissioning. Environmental assessments performed in 2016, when NSF was evaluating options for Arecibo’s future, estimated the cost of “deconstructing” the telescope to be between $ 10.6 million and $ 18.7 million, depending on which facilities, if any. they are, they are left behind. Gaume, however, warned that those estimates needed to be revised.
Some do not give up hope of trying to find a way, despite the conclusions of the engineering analysis, to somehow fix Arecibo. Congresswoman Jenniffer González-Colón, who represents Puerto Rico in Congress, wrote a letter to the leaders of the House and Senate appropriations committees on Friday, asking them to “allocate the necessary funds to allow the NSF to continue exploring options. to safely stabilize the structure and maintain the telescope and surrounding areas. ”
“By hastily dismantling the facility, we would compromise existing capabilities and eliminate a remarkable piece of American technology that has promoted a number of scientific breakthroughs,” he wrote in the letter, also signed by Florida representatives Stephanie Murphy and Darren Soto.
It is not clear that Congress is interested in doing so given both the uncertain cost and the risk. “While we are saddened by the loss of the facility, we commend ourselves [NSF director] Dr Sethuraman Panchanathan and his team for prioritizing the lives and safety of observatory personnel and repair teams during this process, “said reps Eddie Bernice Johnson and Frank Lucas, respectively president and ranking member of the House Scientific Committee … They did not ask for the telescope to be repaired, but instead asked the NSF to “explore opportunities to use the site for exciting new scientific discoveries in the future.”
The NSF decision, however, makes more sense in a broader context. Arecibo has had a number of misfortunes in recent years, including earthquakes and hurricanes, such as Maria in 2017, which caused damage to the telescope. Some of Maria’s repairs were still in progress when the auxiliary cable broke in August. A repair plan was in place, including placing monitoring equipment that could have detected problems with the other cables, when the second main cable broke.
“If we had been able to get it repaired, potential inspections and future modern methods would have been able to capture the main cables and we could start replacing them,” Zauderer said. “It’s really a shame this main cable failed before we had a chance to stabilize things.”
Arecibo’s future was under discussion at the beginning of the decade. NSF included it on a list of astronomical facilities it was considering for “divestment,” as the agency sought to reduce the cost of older facilities as newer ones came into service. The environmental assessment which included the cost estimates for the deconstruction of Arecibo came from that process, as one option for divestment was the closure of the plant. Finally, NSF awarded a contract to a UCF-led group to take over Arecibo’s operations, with the aim of reducing costs.
| “Their passion to keep exploring, to learn,” Zauderer said of those who have used and operated the telescope, “is the very heart and soul of Arecibo.” |
At this point Arecibo was not at the forefront of radio astronomy. It was dethroned as the largest single-dish radio telescope in 2016 by China’s Five Hundred Meter Aperture Spherical Telescope (FAST), which, as the name suggests, is 500 meters in diameter. Others were working on upgrading the Very Large Array in New Mexico or the new Square Kilometer Array under development in South Africa and Australia.
NSF, however, continued to support the development of improved tools for Arecibo. NASA was also a major user of Arecibo, taking advantage of its ability to act as a planetary radar, transmitting signals that reflect on objects, such as passing asteroids, which are reflected on the dish. Arecibo has played a major role in efforts to characterize near-Earth asteroids, a role that NASA says will now be entrusted to a smaller antenna at the Goldstone Observatory in California.
Arecibo may be at the end of its scientific life, but it will live on in both the form of scientific research and a wider social impact. “We are discussing the dismantling of a steel and cable structure,” Zauderer said, but he stressed the role played by the people who conceived the telescope design and who have used and continue to operate it, often in difficult conditions. “Their passion to keep exploring, to learn, is the true heart and soul of Arecibo.”
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