From: National Science Foundation
Posted: Thursday, December 3, 2020
This video, that starts with a view of the top of Tower 4, was taken from the vantage point of an Arecibo Observatory drone, utilized for monitoring the condition of Tower 4 support cables.
Four cables are seen in the center of this video. The top cable does not support the telescope platform, but instead supports the catwalk described in the narrative for the previous video. The three lower cables are, from left to right, M4-1, M4-2, and M4-3. Note that a number of individual wire strands of the M4-1 and M4-2 cables are noticeably broken at the beginning of this video. The M4-3 cable does not appear to have any broken wires at the beginning of this video. The first indication of the coming failure is the breaking of another M4-2 wire, accompanied by a puff of "smoke" and chips of paint flying away from the surface of the cable.
Four seconds later the entire M4-2 cable appears to disintegrate. The failure of M4-2 is followed a fraction of a second later by the demise of M4-1, followed a fraction of a second later by the failure of M4-3. The drone operator then swings the drone around to view the reflector dish and fallen platform, azimuth arm, Gregorian dome and the falling cables and catwalk.
The top section of Towe 12, near the Visitor Center, can be seen tumbling down the hill to the left of the operations building. The Tower 12 backstay cables that connect the top of Tower 12 to the ground cause damage behind Tower 12, well away from the edge of the telescope dish.
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