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Dramatic video released Thursday shows the catastrophic failure of a support cable and the subsequent 450-foot drop of a 900-ton lattice-like instrument platform onto the massive satellite dish of the iconic Arecibo radio telescope.
Already scheduled for demolition following two previous cable failures, the sudden collapse on December 1 it marked the end of the road for an observatory that was once the largest facility of its kind in the world.
“I want to express how deeply saddened we are here,” said Ralph Gaume, director of astronomy for the National Science Foundation. “And NSF is very grateful that no one was injured. As you know, safety has always been and continues to be our top priority.”
The National Science Foundation, which operates the Arecibo Observatory through the University of Central Florida, released video of the collapse Thursday during a Zoom update with reporters.
A view, from a camera on the roof of the observatory’s control center, showed that the instrument platform crashed into Earth, along with the upper 60 feet of two reinforced concrete cable support towers being ripped away. Another view came from a drone parked just above Support Tower 4 where two cables failed on August 10 and November 6.
As the drone camera watched, another support cable uncoiled and suddenly snapped. An instant later, the support platform began to fall toward the plate 45 stories below. The drone operator managed to rotate the camera in time to capture the moment of impact and the failures of the other two support towers.
“You can see the suspended platform in the center of the screen, you can see in the distance, just to the left of the center, is Tower 4,” said John Abruzzo, manager of Thornton Tomasetti, an engineering company called before the collapse to evaluate the structure.
“You can see, I hope, the cables that go from the top of Tower 4 to the platform … And then it’s those cables that fail near the top of the tower first. And once they fail, the platform loses stability and starts to go down. “
The Arecibo Observatory was comprised of a 1,000-foot fixed parabolic antenna built in a natural depression that reflected radio waves or radar beams to the receiver array suspended 450 feet above cables extending from three support towers.
While the dish itself only moved with Earth’s rotation, the instrument platform featured a steerable receiving platform that allowed astronomers to observe targets up to 40 degrees from the vertical axis of the telescope.
Operating for more than half a century, the The observatory played an important role observing deep space targets, bodies in the solar system and, in an adjacent facility using powerful lasers, the composition and behavior of Earth’s upper atmosphere.
National Science Foundation / University of Central Florida
But on August 10, an auxiliary cable broke free from its socket on support tower 4 and crashed into the dish below, opening a 100-foot-long cutout. Engineers were developing repair plans when one of the main 3-inch-wide support cables connected to the same tower unexpectedly broke on November 6.
Due to stress on the remaining cables, engineers concluded that the system could not be safely repaired, and the NSF announced on November 19 that the observatory would be dismantled.
“We knew it was only a matter of time,” Abruzzo said. “And it was a very dangerous and precarious situation, because (the remaining cables) could have really gone at any time.”
Engineers were evaluating how to carry out a controlled demolition when the third cable broke, bringing down the instrument platform.
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