The second-largest radio telescope in the world collapsed on Tuesday morning.
The Arecibo Observatory’s 900-ton platform, which sent and received radio waves and was suspended 450 feet in the air, crashed into the 1,000-foot-wide disk below. When it fell, it pulled down with the tops of three surrounding support towers.
Videos of the crash show that it began when cables that connected the hanging platform to one of the towers snapped. Previously, an auxiliary cable on that same tower broke in August, then one of its main cables broke in November. Since then, the National Science Foundation, which owns Arecibo, had been rushing to disassemble the telescope, since it was clear a complete collapse was possible.
But the platform fell before engineers made much headway in the deconstruction process.
Jonathan Friedman, who has been part of the Arecibo Observatory’s scientific staff since 1993, told local news outlet NotiCentro the collapse sounded like the rumble of an earthquake, a train, or an avalanche.
The video below, captured from a nearby control tower, shows the platform falling at 7:54 a.m. local time. A cable takes out the catwalk that allowed engineers to access the platform. The top of the tower where the cables broke, visible in the background, then falls. Then the top of another broken tower comes rolling down the hillside on the left.
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“As you can see, this was a very violent and kind of unpredictable failure,” Ashley Zauderer, NSF program manager for the Arecibo Observatory, said in a briefing on Thursday.
In a separate video, drone footage shows the cables snapping and the resulting crash from above. The drone happened to be doing reconnaissance over the telescope’s platform at that moment, since drone surveillance was a key source of information for engineers trying to figure out how to deconstruct the telescope. Due to the known risk of collapse, nobody had been allowed to approach the unstable structure since the fateful cable break in mid-November.
The vicinity around the dish and the three towers had been cordoned off, so nobody was injured in the collapse, the NSF said.
A inevitable collapse
Arecibo’s downward spiral began in August, when a 3-inch-thick auxiliary cable popped out of its socket on one of the telescope’s three towers and crashed into the dish. It tore a 100-foot gash in the panels.
Then the second failure, a snapped main cable, surprised the telescope’s managers in November. An engineering assessment afterward found that the remaining cables were liable to break at any time and send the platform tumbling.
Since the structure was too unstable to save without risk of it collapsing on technicians while they worked on the repairs, the NSF decided to say goodbye to Arecibo, decommissioning the world’s most iconic radio telescope.