Arecibo Telescope
2020 damage, decommissioning plans, and collapse

While waiting for NSF to make the decommissioning plans, steps had been taken to try to reduce the load that each of the towers were carrying, including reducing the strain on the backstay support cables for the individual towers. Other plans, such as having helicopters hoisting part of the load while hovering above the telescope, were proposed but deemed too risky. Engineers from UCF had been monitoring the telescope and observed that wires in the backstay cables for the support towers had been breaking at a rate of one or two a day, and estimated that the telescope would soon collapse. In the weekend prior to December 1, 2020, wire strands in the receiver's supporting cables had also been snapping apart at a rapid rate, according to Ángel Vázquez, the director of operations. This culminated in the collapse of the receiver platform at around 6:55 a.m. AST (10:55 UTC) on December 1, 2020, as the second main cable from Tower 4 failed with the other two remaining support cables failing moments later. The collapse of the receiver structure and cables onto the dish caused extensive additional damage. As the receiver fell, it also sheared the tips of the towers which the support cables ran through. Once the main cables from Tower 4 released, the backstay cables, which normally balanced the horizontal component of force from the main cables, pulled the tower outwards and broke off the top. The other two towers, once the force of supporting the platform was released, also had their tips sheared off due to the backstay cable tension. The top of Tower 12 caused some structural damage to other buildings on the observatory as it fell. No injuries from the collapse were reported.
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