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A satellite image of Arecibo taken November 17, showing the damage to the giant dish caused by two broken cables that support the platform suspended over it. (credit: Satellite image ©2020 Maxar Technologies)

An iconic observatory faces its demise

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A few astronomical observatories are iconic, in the sense they are distinctive enough to be recognized in the broader culture. The Arecibo Observatory certainly qualifies, with its 305-meter main dish nestled in the terrain of Puerto Rico and a platform hosting receivers suspended above it, connected by cables to three towers. Few people might know much about the astronomy done at Arecibo (beyond, perhaps, its supporting role in the search for extraterrestrial intelligence), but it became famous in movies like Contact and GoldenEye.

“NSF has concluded that this recent damage to the 305-meter telescope cannot be addressed without risking the lives and safety of work crews and staff,” said Jones.

But icons do not last forever. In August, one auxiliary cable connecting the platform to a tower, installed in the 1990s, pulled out of its socket and crashed to the dish below, creating a gash about 30 meters long. Earlier this month, a main cable, connected to the same tower but dating back to the observatory’s construction in the early 1960s, broke, causing additional damage.

Last Thursday, the National Science Foundation, which funds Arecibo, threw in the towel. “NSF has concluded that this recent damage to the 305-meter telescope cannot be addressed without risking the lives and safety of work crews and staff,” said Sean Jones, assistant director of the NSF’s Mathematical and Physical Sciences Directorate, in a hastily arranged call with reporters, “and NSF has decided to begin the process of planning for a controlled decommissioning of the 305-meter telescope.”

A “controlled decommissioning” is something like a “controlled reentry” of a spacecraft. “We will put our engineering team together—and they’re working on this right now—to develop a plan to bring down the platform in a controlled way such that we can protect and prevent any of the cables from whipping into the buildings,” said Ralph Gaume, director of the NSF’s Division of Astronomical Sciences. 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 facility 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 saved. “The rest of the observatory will be preserved.”

NSF made that decision after engineering firms hired by the observatory warned it was at risk of an 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 the towers, or anywhere in their immediate physical vicinity in case of potential sudden structural failure,” stated WSP, one engineering firm involved in that analysis, in a letter to the University of Central Florida (UCF), which leads a consortium that operates Arecibo for the NSF. An uncontrolled collapse could tear down the towers and damage the other buildings and facilities that the NSF wants to preserve.

The fact that both broken cables were linked to the same tower was particularly worrisome. “The engineers have advised us that the break of one more cable [at that tower] will result in an uncontrolled collapse of the structure,” Gaume said.

Moreover, the cable that broke did so at only about 62% of its rated strength, suggesting that it, and potentially other cables, have weakened since their installation decades ago. Ashley Zauderer, program director for Arecibo at NSF, said that, according to the agency’s records, the observatory followed proper maintenance plans for the cables. But, she added, those cables, manufactured in the 1950s and 1960s, “were designed in such a way that it was hard, even with regular maintenance such as painting, to keep moisture and other things from seeping in.”

Exactly how that controlled decommissioning will be done is still being studied, a process Gaume said will take at least several weeks. The actual decommissioning could be done “very rapidly” he said, perhaps through the use of explosives, an approach recommended by one engineering firm. “Controlled demolition, designed with a specific collapse sequence determined and implemented with the use of explosives, will reduce the uncertainty and danger associated with collapse,” advised Thornton Tomasetti in a report to UCF.

“By hastily dismantling the structure, we would be compromising existing capabilities and eliminating a remarkable piece of American technology that has promoted a variety of scientific discoveries,” wrote González-Colón.

Also uncertain is the cost for doing so, and who will pay for it. NSF officials said on the call they would work with the Office of Management and Budget, and with Congress, on how to pay for the decommissioning. Environmental assessments performed in 2016, when NSF was considering options for Arecibo’s future, put the cost of “deconstruction” of the telescope at between $10.6 million and $18.7 million, depending on what structures, if any, are left behind. Gaume, though, cautioned that those estimates would need to be revisited.

Some are not giving up hope to try and find a way, despite the conclusions of the engineering analyses, to somehow repair Arecibo. Congresswoman Jenniffer González-Colón, who represents Puerto Rico in Congress, wrote a letter Friday to the leaders of House and Senate appropriations committees, asking them to “allocate the funds necessary to enable NSF to continue exploring options to safely stabilize the structure and maintain the telescope and surrounding areas.”

“By hastily dismantling the structure, we would be compromising existing capabilities and eliminating a remarkable piece of American technology that has promoted a variety of scientific discoveries,” she wrote in the letter, which was also signed by Reps. Stephanie Murphy and Darren Soto of Florida.

It’s not clear there’s appetite in Congress to do so, given both the uncertain cost and the risk involved. “While we are saddened by the loss of the facility, we commend [NSF director] Dr. Sethuraman Panchanathan and his team for prioritizing the lives and safety of observatory staff and repair crews throughout this process,” said Reps. Eddie Bernice Johnson and Frank Lucas, the chair and ranking member, respectively, of the House Science Committee in a statement. They didn’t call for repairing the telescope but instead asked the NSF to “explore opportunities to use the site for exciting new science in the future.”

The NSF’s decision, though, make more sense in a larger context. Arecibo had a run of bad luck in recent years, including both earthquakes and hurricanes, like Maria in 2017, that caused damage to the telescope. Some of the repairs from Maria were still in progress when the auxiliary cable broke free in August. A repair plan for that was in place, including placing monitoring equipment that might have been able to detect problems with the other cables, when the second main cable broke.

“If we have been able to get that fixed, potentially inspections and future modern methods would have been able to catch the main cables and we could start replacing those,” Zauderer said. “It is truly unfortunate that this main cable failed before we had a chance to get things stabilized.”

Arecibo’s future was in question earlier in 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 that included the cost estimates for deconstructing Arecibo came from that process, since one option for divestment was to close the facility. Ultimately, NSF awarded a contract to a group led by UCF to take over operations of Arecibo, with the goal of reducing costs.

“Their passion to continue to explore, to learn,” said Zauderer of those who used and operated the telescope, “is the true heart and soul of Arecibo.”

Arecibo was, by this time, not at the cutting edge of radio astronomy. It had been 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 upgrades to the Very Large Array in New Mexico or the new Square Kilometer Array under development in South Africa and Australia.

NSF, though, continued to support development of improved instruments for Arecibo. NASA has also been a major user of Arecibo, taking advantage of its ability to serve as a planetary radar, transmitting signals that reflect off objects, like passing asteroids, that are reflected back to the dish. Arecibo has played a major role in efforts to characterize near Earth asteroids, a role NASA says will now be handed by 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 the form of both its scientific research and broader societal impact. “We’re discussing the decommissioning of a structure made of steel and cables,” Zauderer said, but emphasized the roles played by the people who came up with the design of the telescope, and who have used it and continue to operate it, often in trying conditions. “Their passion to continue to explore, to learn, is the true heart and soul of Arecibo.”

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