The end of the Arecibo telescope in Puerto Rico

The iconic radio telescope is no more:

On Monday night, the enormous instrument platform that hung over the Arecibo radio telescope's big dish collapsed due to the failure of the remaining cables supporting it. The risk of this sort of failure was the key motivation behind the National Science Foundation's recent decision to shut down the observatory, as the potential for collapse made any attempt to repair the battered scope too dangerous for the people who would do the repairs.

The Arecibo Radio Observatory was built in the jungles of Puerto Rico in 1963. It consisted of an aluminum dish 1,000 feet in diameter that reflected incoming radio signals to receivers hanging from a massive, 900-ton instrument package that was suspended almost 500 feet above it. The steel cable suspension system was supported by three reinforced concrete towers. When these cables failed and snapped, the instrument platform crashed into the dish below it, destroying the apparatus. The concrete support towers themselves were damaged, as well.

The NSF has released rather dramatic stationary and drone camera footage of last week's collapse:

Fortunately, nobody was injured by the collapse.

Just two weeks earlier, the NSF determined that the aging telescope was too dangerous to repair and would be decommissioned:

Since its commissioning in the 1960s, the observatory has played a role in many discoveries, primarily in the field of pulsars, a class of radio-emitting neutron stars. It has also been involved with SETI searches, and it transmitted an image to a star cluster under the assumption that any intelligent life there might be partaking in its own SETI program. But over the last 15 years or so the NSF, Arecibo's primary means of support, has cut its funding for the observatory, which has struggled to maintain full operations over this period.

But it wasn't money that eventually doomed Arecibo; instead, it was the instrument platform. In August of this year, one of the auxiliary cables that help support the platform snapped, creating a gash in the radio-reflective dish below. While plans were being made to replace that cable and repair the dish—replacement cables were already on order—one of the 7.5cm main cables on the same tower snapped on November 6.

An engineering analysis subsequently determined that this cable failure happened despite the fact that the strain on it was only about 60 percent of what should be its minimum breaking strength. This raised serious questions about the stability of the remaining cables, and thus the ability of the structure to support its instrument platform. The analysis concluded that it was unsafe to find out; the platform could collapse without warning, and any snapped cables would present a danger to any workers on the towers, as the large cables would move at very high speeds following a break. Of the three additional engineering firms consulted by NSF and the University of Central Florida, two agreed with this assessment.

"Until these assessments came in, our question was not if the observatory should be repaired but how," said the NSF's Ralph Gaume. "But in the end, a preponderance of data showed that we simply could not do this safely. And that is a line we cannot cross."

I'm thankful that I got to visit the Arecibo telescope during a trip to the Eastern Caribbean five years ago. It was definitely an impressive sight:

Kirby's grown a bit since this picture was taken.

The Arecibo facility will remain open, as a 12-meter radio dish, a lidar for atmospheric observations and the visitor's center were all undamaged by the collapse. But the prospects for a replacing the massive telescope itself are unclear:  

With repair no longer an option, the debate now turns to whether the radio telescope should be rebuilt. At the briefing, NSF’s Gaume said it was too soon to evaluate if the telescope will be rebuilt.

“With regards to replacement, NSF has a very well-defined process for funding and constructing large-scale infrastructure, including telescopes,” he said. “It’s a multi-year process that involves congressional appropriations and the assessment and needs of the scientific community. So, it’s very early for us to comment on the replacement.”