Today the National Science Foundation released a pair of videos that document the collapse of the Arecibo Observatory with incredible detail. A wide shot, apparently taken from the Visitors Center, shows the 900 ton instrument platform breaking free and swinging on the remaining support cables until it smashes into the edge of the dish. The second clip, recorded by an airborne drone, is focused directly on the cables as they failed. Both can be seen in the video embedded below.
Together, they produce an invaluable visual record of what finally brought the iconic radio telescope down. As was predicted by engineers earlier in the month, the failure of another support cable on tower 4 triggered a chain reaction that brought the entire platform crashing down onto the 305 meter reflector. Footage from a drone observing the top of tower 4 shows that the entire sequence, from the first visual wire break to the remaining cables being torn from their mounts, only took five seconds. While some initially doubted the NSF’s determination that it was too dangerous to repair Arecibo, this footage seems to prove just how tenuous the structural integrity of the Observatory really was.
These videos will hopefully help investigators who still need to determine why the cables failed in the first place. The cable in August didn’t snap, it simply pulled lose from its mount. It was suspected that the cable may have been incorrectly installed, but as it was only a backup, the situation was not seen as critical. But when the second cable failed in November it was found to have snapped at just 60% of its minimum breaking strength.
This immediately called into question the condition of the remaining cables, and ultimately lead to the decision by the NSF to proceed with a controlled demolition of the Observatory that would preserve as much of the scientific equipment as possible. Unfortunately, the remaining cables didn’t last long enough to put that plan into action.