The iconic Arecibo telescope, damaged by two cable failures within three months, is beyond repair.

An image of Arecibo in better days shows the Gregorian dome suspended from the receiver platform above the dish, which is built in a natural sinkhole.

Arecibo Observatory, the iconic 305-meter (1,000-foot) radio dish nestled in the forested hills in Puerto Rico, is to be decommissioned for safety reasons, say officials with the National Science Foundation (NSF).

The announcement follows two unexpected and devastating events. In August, a cable that helped support the receiver platform suspended over the dish wrenched out of its socket, crashing down on the dish below. Engineers assessed the damage, but before orders for replacements had a chance to come through, another cable snapped on November 6th, causing additional damage and leaving the structural integrity of the telescope unclear. Attempts to repair the telescope could put lives at risk.

“Any engineering approach to better understanding the strength left in the main cables involves considerable risk for human life and could in fact accelerate the uncontrolled collapse of the structure,” says Ralph Gaume, director of NSF’s Division of Astronomical Sciences.

Arecibo in the jungle
Arecibo in 2011
© 2011 Alan Dyer

The loss of the 57-year-old observatory comes as a shock to the astronomy community. Arecibo’s huge collecting area, incredible sensitivity, and radar capabilities enables it to study everything from near-Earth asteroids to distant galaxies; scientists also use the dish for investigations of Earth’s atmosphere.

“I’m devastated,” says Alessondra Springmann (University of Arizona). “There’s nothing else like this in the world, there’s nothing that can do what Arecibo does.”

What Went Wrong

Multiple cables suspend a 900-ton platform 450 feet above Arecibo’s dish. Twelve 3.25-inch-thick cables were added in the 1990s to support additional weight added to this platform as part of a major upgrade to the observatory. On August 10th, one of those 12 auxiliary cables tore out of its socket and fell to the ground.

Arecibo dish damage
The August 10th cable failure caused damage to Arecibo's dish.

Arecibo’s structure is designed to be redundant, so when the auxiliary cable failed, load transferred to the four original cables and the remaining support cable. Engineers were called in immediately to assess the damage and, on determining the structure was stable, to begin repairs. Supplies were on order for temporary cables to help carry the load, as well as two replacement cables for both the cable that had failed and the other auxiliary cable for that tower.

But before those replacements could arrive, one of the main cables to the same tower snapped on November 10th. This unexpected break caused engineers to doubt the entire structure’s integrity. The engineering companies reported individual wires breaking on other main cables, as well as additional slippage of other auxiliary cables in their sockets. If another cable breaks, “a catastrophic failure would be likely,” writes John Abruzzo, from the engineering consulting firm Thornton Tomasetti. “We believe the structure will collapse in the near future if left untouched.”

Arecibo antennas in 2009
This view of the cluster of receivers suspended high above Arecibo Observatory's reflecting 305-m-wide dish was captured several years ago.
Sky & Telescope / J. Kelly Beatty

Despite inspections following the August event, nobody had any inkling that the main cable would break — it should have been able to bear much more weight than it did. It could be that the older design of the main cable, which could have let moisture in even with regular maintenance, led it to snap, says Arecibo program director Ashley Zauderer.

The support cable failure is a different story: “The auxiliary cable, installed in the 1990s, was much younger and should not have failed the way it did,” Zauderer says. “It slipped right out of the socket. The team is looking very closely at why that happened. It should not have happened.”

What Happens Now

The engineering firms are recommending that Arecibo be decommissioned in a controlled way, but what that looks like remains to be seen. The engineering firms will take 5 or 6 weeks to develop a plan, Gaume says, but until then both the cost and the timeline of the decommissioning are up in the air.

“Our engineers are not able to tell us when the structure would collapse on its own,” Gaume adds. “So we’re working against the clock to develop plans for a controlled decommissioning with the priorities being safety, and the safety and preservation of the rest of the assets of the observatory.”

Front Row Seat
This radar image by the Arecibo telescope clearly shows peanut-shape asteroid 2014 JO25. You can even see a small mountain poking from the one end of the asteroid. Click image to see the animation. Arecibo offered 18 times the sensitivity of other existing facilities, such as NASA's Goldstone receiver.
Planetary Radar Science Group / NSF

Gaume and Zauderer both emphasize that the decommissioning does not mean the end of the observatory. Even as they take down the main dish and suspended dome, they will preserve important buildings under Tower 12. The observatory’s LIDAR facilities, which use lasers to investigate Earth’s atmosphere, will also continue.

“We’re talking about a structure made of steel and cables, but it truly is the people who had the ideas,” Zauderer says. Dedicated staff has helped the observatory survive earthquakes and hurricanes, and the observatory functioned as a staging area for aid following Hurricane Maria.

"Arecibo is so much more than a scientific instrument," says Edgard Rivera-Valentín (Lunar and Planetary Institute). "It has been an icon in Puerto Rico that has served to inspire generations of scientists, I for one being one of them."

“Pretty much every schoolchild on the island has been to Arecibo. Everyone has had family who worked there, who helped build it,” Springmann explains. “You can’t have an observatory without the people, and the people also derive great benefit from the observatory being there.”

Arecibo is also irreplaceable for scientists. "The Arecibo Observatory is the world’s most powerful and most sensitive planetary radar," Rivera-Valentín explains. "There is currently no other facility, nor one under construction that can fully replace it. This makes Arecibo invaluable for planetary defense."

Technically, Arecibo is the second-largest radio dish in the world — China’s Five-hundred-meter Aperture Spherical Telescope, or FAST, recently broke the record that Arecibo held for decades. But FAST's platform cannot hold the weight of a radar instrumentation. “FAST cannot do radar, it’s specifically incapable of doing active observation,” Springmann explains. Other radio dishes that are capable of radar, such as NASA's Goldstone, can't take Arecibo's place either, due to the lack of both sensitivity and availability, as Goldstone is part of the Deep Space Network that spends most of its time communicating to our fleet of interplanetary spacecraft. 

Over the past decade, Arecibo has survived earthquakes, hurricanes, and funding struggles. “They try to kill it every few years, and someone pulls a rabbit out of a hat,” Springmann says. But what the observatory’s future holds isn’t clear. “I’m not sure what’s going to happen to it now.”

Read the reaction from Puerto Ricans and from the international scientific community on Twitter by following #WhatAreciboMeansToMe.




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November 19, 2020 at 2:25 pm

This is horrible news... almost as if the HST had been taken out by a piece of space junk.

It was a marvel of engineering when it was built. Hopefully they can take it down safely so (keep fingers crossed) it can be re-built some day.

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November 19, 2020 at 6:56 pm

I lived in Puerto Rico from November 1968 - April 1970. I visited the Arecibo Radio Telescope several times in that period.

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Chuck Hards

November 20, 2020 at 12:46 am

Sad news. Arecibo was the giant of radio and related long-wave astronomy for much of my life. I wonder if NSF has considered selling small, certified pieces of the old structure to help defray decomissioning/dismantling costs. I'm sure many people would love to own a piece of science history.

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Alan MacRobert

November 20, 2020 at 10:23 am

Somehow, this tragedy reminds me this season of that sad, scraggly giant Christmas tree that was just erected at Rockefeller Center.

A joke going around: The positive integers have gathered for the annual numbers convention. At the opening dinner, the number 13 stands up and says, "I'm the baddest number there is. Everyone's afraid of me."

To that 666 gets up and says, "That's nothing. I'm in the Bible itself as the sign of the Apocalypse."

The number 2020 slowly pushes back its chair, stands up, and says to its buddies, 'Hold my beer.' "

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November 20, 2020 at 4:29 pm

While my company owned 7 TV stations on the island I got to know the staff there. These folks were dedicated and top notch. This is a loss, a shame they cannot get funding to make repairs.

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RC Silk

November 20, 2020 at 5:25 pm

This sounds suspiciously akin to sabotage in my considerably objective and detached opinion. To declare it unsalvageable only reflects the limited thinking of someone (or even a group of someones) called in to look at it. After all, with God, ALL things are possible. In this case, however, all one needs is enough MONEY to begin the refit. Sure, it may need to be totally dismantled first in order to be rebuilt better, but still, the amount of SALVAGEABLE parts on this makes the process *WAY* less expensive than it would be to rebuild it all from scratch. "Can't be done" is the attitude of those who CAN'T THINK outside the box.

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November 20, 2020 at 5:44 pm

So that leaves the Chinese dish as the remaining monster radio telescope? Not going to comment any further at this point...

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November 20, 2020 at 7:56 pm

It would be nice if the tech billionaires would under write a rebuild instead of using their billions to spy on the public and create political mischief. I would help out..

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Howard Ritter

November 21, 2020 at 9:41 am

The unique geographic features of Arecibo that made it feasible to build a radio telescope are still there. Would it not be feasible to do so again? Even if the feed structure can't be safely disassembled and must be let down onto the dish, destroying both, the support towers are still in place, as are all the electronics and the support infrastructure. Why not build back and build better?

We can't expect a major Federal commitment of money in these inflated and contrained times – but Bill Gates, Elon Musk, Jeff Bezos, Warren Buffett? One percent of your combined net worth should do it. We're waiting for your call.

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November 27, 2020 at 6:33 pm

Sorry to be late to the party, but was occupied...
...As the old Abo once said, "Maybe you will wait long."
If the 1% isn't going to 'step forward' when it comes to homelessness, hunger, and other similar issues here in the US, (overseas is fine if your last name is Gates) what makes you think the 1% is going to do it for (in their eyes) something that doesn't affect the next quarter?

Maybe the new Admin, which believes in Science, can cut a few mil worth loose...But don't look to the current one!

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