Details surface on the collapse of the famous Arecibo Observatory telescope

The collapse of the iconic Arecibo Observatory telescope dismayed scientists across the globe. The telescope, whose majestic dish became famous from the movie GoldenEye, collapsed on December 1st 2020. An impressive video of the moment of the collapse is shown below.

credits: Science Magazine

The Arecibo Observatory was constructed in the early 1960s by the United States Pentagon’s Advanced Research Projects Agency to detect incoming Soviet missiles. The National Science Foundation took over the facility in 1969, and moved forward by making upgrades in order to use the telescope for a variety of science projects. Later, in 1997 an igloo-shaped structure, the so-called “Gregorian dome”, was added to the structure, an addition that may have contributed to its collapse.

The telescope’s cables were initially designed with a safety factor of just over two. The “Gregorian dome” and other new equipment added 300 tons to the platform. To accommodate the additional loads, six auxiliary cables were added to bring the safety factor back to two. Nonetheless, in August 2020, one of these auxiliary cables failed. Professor Lark of Cardiff University stated to Science Magazine: “One of the difficulties of adding or replacing cables is the accurate distribution of load.[ ] The new cable could have been bearing more than it should.”

After the aforementioned failure of the auxiliary cable, three engineering consulting firms were called to assess the facility’s structural integrity. The engineering firm Thornton Tomasetti built a full structural model of the telescope, and through their analysis, they showed that the four main cables from the strained Tower No 4 to the platform, were bearing a load corresponding to about 60% of their ultimate strength, i.e., a safety factor of 1.67. Once their assessment was concluded, all three consulting firms indicated that the structure was stable. Nonetheless, Thornton Tomasetti recommended replacing all the auxiliary cables and accordingly NSF approved the $10.5 million request.

Then, on 6 November 2020, a second cable completely snapped; this time it wasn’t an auxiliary cable, but a main, load-bearing cable. To save the telescope, the engineers had to urgently reduce the load on the remaining three main cables. To that end, they considered using helicopters to install extra cables or remove structural components to reduce the overall weight. Removal of the Gregorian dome was also considered. One of the consulting firm, Wiss, Janney, Elstner Associates, proposed the stabilization of the telescope by installing extra support cables, and removing weight from the platform. Contrary, the other two consultants, i.e., Thornton Tomasetti and WSP, proposed that the structure should be demolished in a controlled way. On November 19, 2020, NSF announced the initialization ofthe decommissioning of Arecibo Observatory’s 305-meter telescope due to safety concerns. "NSF prioritizes the safety of workers, Arecibo Observatory’s staff and visitors, which makes this decision necessary, although unfortunate," said NSF Director Sethuraman Panchanathan. "For nearly six decades, the Arecibo Observatory has served as a beacon for breakthrough science and what a partnership with a community can look like. While this is a profound change, we will be looking for ways to assist the scientific community and maintain that strong relationship with the people of Puerto Rico", Panchanathan added.

A few days later, on December 1st 2020, just after 8 a.m., the structure of the iconic Arecibo Observatory came crashing down. Puerto Rico’s pride, the giant telescope of the Arecibo Observatory, was now part of history.