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UPDATE (December 1, 2020): The platform above the antenna fell this morning in an uncontrolled collapse. From the photos, it looks like the cables of a tower were broken and the 900-ton platform suspended 150 meters above the giant antenna toppled over and crashed into a rocky cliff. The tops of the three suspension towers were torn off. Pieces fell and damaged the satellite dish and several buildings. No injuries were reported.
The damage is extensive and I don’t know if it can be recovered. I’m waiting for more news and will update this post as it arrives.
The venerable Arecibo radio telescope, a gigantic 305-meter antenna nestled in the wooded hills of Puerto Rico, is to be decommissioned after a pair of cables break off that support a huge platform above the antenna.
The huge telescope has been in use since it was completed in 1963, operated by several organizations in cooperation with the National Science Foundation (NSF) of the United States. It has been used to study Earth’s upper atmosphere, map asteroids near Earth and the Moon, observe distant galaxies, and even send signals to a distant star cluster in an attempt to communicate with all potential civilizations. . The telescope has been featured in many movies and TV shows, including the James Bond film Golden eye, the brilliant science fiction film Contact, and the Doctor Who episode “The ambassadors of death”.
The telescope consists of two main structures. The 305-meter parabola is made up of nearly 40,000 panels, each approximately 1 meter by 3 meters. It is supported by steel cables that cross a natural concavity in the topography of the island (a chasm that left a great Depression). It reflects radio waves from space back to a platform suspended above it which contains various radio receivers for doing different types of science. The triangular platform weighs 900 tons and is suspended 150 meters above the parabola using huge cables suspended from three enormous towers (one about 110 meters high, the other two from about 80 meters).
In 1997, the facility was updated with a new structure on the platform called the Gregorian Dome, which allowed for the installation of several new receivers. A dozen auxiliary cables were installed to support the additional weight, attached to the three towers with the main cables.
On August 10, 2020, one of the auxiliary cables slipped off its pole and fell to the ground. The auxiliary cables are made of steel and are over 8 centimeters thick and are very heavy. When he fell, he damaged the dish, tore a 30-meter gash and damaged several of the panels making up the Gregorian dome. No one was hurt, but this incident prompted NSF to inspect the telescope to see what could be done to fix it.
By September, plans were in place to replace the broken auxiliary cable, but on November 6, one of the main the cables supporting the platform snapped, catching everyone off guard.
It is a much more serious problem. Each tower has four main cables attached to support the platform, so there are 12 in all. The main cable that broke was attached to the same tower where the auxiliary cable failed. In this case, however, the cable himself snapped.
The main cables are also about 8 cm thick, weigh 7 tonnes and are made of 160 steel wires braided together. A pre-break inspection of the main cable showed that 12 of these wires had broken there, but this was not considered an immediate threat; the other wires were intact enough that engineers concluded that there was enough redundancy in the wires that it did not pose an immediate emergency.
Also, after the incident engineers determined that the weight he was carrying was only 60% of his minimum breaking strength, and it was a calm day (no wind). Apparently, the cable issues ran deeper than previously thought. It also raises concerns that the remaining 11 cables may be worn more than previously thought. No one knows if the other cables are damaged or not, or if they can withstand the intended load longer.
After review and investigation by an engineering team, the NSF has concluded that there is no way to resolve these issues while maintaining the safety of the crew that would perform the work. Stabilizing or replacing the cable can also accelerate sag. The NSF therefore decided to decommission the telescope.
It is not known what may have damaged the cables. They were very old and the moisture that seeped in over the years may have contributed to the problem. Additionally, Puerto Rico was hit by hurricanes that put stress on the structure, and a series of earthquakes near the observatory also hit in late 2019. Some or all of these may have been part of the problem.
It is also unclear how the downgrade will be carried out at this time. The platform is really huge and heavy, and great care will have to be taken to disassemble it correctly and safely. However, the alternative is to do nothing, and it will almost certainly lead to an uncontrolled collapse of the platform, which would be catastrophic. There are historic buildings under a tower that need to be preserved, for example. In addition, there are wild animals (including endangered species) that thrive under the dish, and these should be considered as well.
At a press conference, NSF officials were careful to say that they intended to work with the Puerto Rican scientific community and Congress to maintain the observatory itself even as the 305 meters is closed. In other words, it is hoped that a new telescope will be built to replace it. Arecibo provides significant economic support to the citizens of the island, as well as STEM support to teachers and students. Making the observatory work with a new perimeter is an important mission.
But this is no small feat. Until China built its 500-meter dish in 2016, Arecibo was the largest single flat-filled radio telescope on the planet. Replacing it will be a big project.
I will note that in 1988 the 100 meter radio telescope at Green Bank in West Virginia collapsed. The tension on a metal plate caused it to warp, sending a cascade of blackouts through the structure of the then decades-old rifle scope. It’s been replaced by a huge, state-of-the-art 100-meter fully steerable telescope, so maybe the same can be done here.
In personal terms, well, I’m disappointed. This is obviously a blow to radio astronomy and to areas as important as the study of potentially dangerous asteroids. But also, Arecibo has been in my whole life, and was such a versatile and appreciated instrument. I am not a radio astronomer but many of my friends are and have used Arecibo in the past. Losing this installation is just horrible.
The desire to study the planet we live on and the universe around us is one of the noblest aspects of humanity. We have so many ways of doing it, so many different and critical senses that we use to understand our surroundings, both local and far, far away. It would be a shame to let this one slip away forever. I sincerely hope that a new facility, improved and with modern considerations, will rise in its place.
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