forensic examination of Arecibo collapse

After almost three years of hasty and unplanned dismantling of the Arecibo radio telescope, we finally found out the cause of the breakdown: a faulty plug.

In case you missed it, in 2020 we started receiving unwanted reports that the tethers supporting the 900 ton instrument platform above the 300 meter main reflector of what was once the world’s largest radio telescope are slowly unraveling. From the first signs of failure in August, when the cable broke through a reflector, to the second cable failure in November, it seemed that Arecibo’s days were numbered and he would fall prey to all other problems. In that fateful year, failure seemed to come quickly. The inevitable finally happened on December 1, when the overstressed cables of the fourth support tower finally collapsed, causing the platform to swing gracefully next to a natural depression covering the reflector, damaging the telescope beyond repair.

The long period of time leading up to final telescope operation gives engineers and scientists the ability to closely monitor faults in real time. So there is no mystery about what happened, at least in terms of the big picture. But we always want to know all the details of a fiasco, and that task lies with the criminal investigations firm Thornton Tomasetti. They enlisted the help of Columbia University’s Materials Strength Laboratory, which sent pieces of damaged cable to a high-flux isotope reactor at Oak Ridge National Laboratory for surgery. Neutron imaging. It’s similar to X-rays, but uses a stream of neutrons that interact with the core of matter rather than electrons.

Full Report (PDF) It identified five immediate causes of the collapse, the most important of which is “(T) Inconsistent manual laying of cables during cable splicing”, by which we mean that each strand of the cable was improperly secured. distributed before molten zinc. Separator nests are formed around them. The resulting shear stress causes the zinc to slowly flow through the strands of the cable, allowing them to slip out of the surrounding steel sleeves – well, you can see the rest for yourself below.

As is often the case with these crashes, there were multiple causes, all of which were covered in the 300+ page report. But being able to blame most failures on one weakness that is easy to understand and easy to fix is ​​a welcome relief. Perhaps this is a consolation for astronomers and Arecibo staff, but at least it is a lesson that can prevent future failures of cable-supported structures.

(via New Atlas)

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