The large dish of the Arecibo observatory has reached the end of the line

Today, the National Science Foundation announced the closure of its famous Arecibo radio observatory. Built on top of a hill in Puerto Rico, the main course of the observatory measures over 300 meters in diameter and its massive size has made it a feature of popular culture ranging from James Bond films to video games. But despite a long history of scientific contributions, the observatory has struggled for funding for more than a decade, and two cables that support it have failed this year, leaving it in a precarious state.

After engineering studies determined that there was no way to fix the equipment without putting workers at risk, the NSF made the decision to close the observatory.

More than a big dish

While the sheer scale of Arecibo’s main course attracted the most attention, the dish was purely a reflector. The actual commercial end of the telescope, where radio waves were detected, was an instrument platform suspended above it by cables suspended from three towers. The instrument’s platform contained a receiver that could be moved to different locations above the disc, allowing it to resolve signals coming from more directions than its fixed dish might suggest.

Since its commissioning in the 1960s, the observatory has played a role in many discoveries, mainly in the field of pulsars, a class of radio-emitting neutron stars. He was also involved in SETI research and transmitted an image to a star cluster assuming that all intelligent life could participate in its own SETI program. But over the past 15 years or so, the NSF, Arecibo’s primary support, has cut funding for the observatory, which has struggled to maintain full operations during this time.

But it wasn’t the money that ultimately doomed Arecibo; it was rather the platform of instruments. In August of this year, one of the auxiliary cables that help support the platform broke, creating a gash in the radio-reflective antenna below. While plans were underway to replace that cable and repair the antenna – replacement cables were already on order – one of the 3-inch main cables from the same tower broke on November 6.

Engineering analysis subsequently determined that this cable break occurred despite the fact that the stress on the cable was only about 60% of what should be its minimum breaking strength. This raised serious questions about the stability of the remaining cables, and therefore the ability of the structure to support its instrument platform. The analysis concluded that it was not safe to find out; the platform could collapse without warning and any broken cable would present a hazard to tower workers as large cables would move at very high speeds after a break. Of the three other engineering firms consulted by NSF and the University of Central Florida, two agreed with this assessment.

“Until those assessments came, our question was not whether the observatory should be repaired but how,” said Ralph Gaume of the NSF. “But at the end of the day, a preponderance of data showed that we just couldn’t do this safely. And that’s a line we can’t cross.”

The end is near

Right now, the NSF is just announcing that it will start planning the decommissioning process. Work was already underway to move the data archive from the instrument to a cloud service, and plans for the safe removal of the platform will obviously involve a lot of additional technical analysis. The NSF said several other science programs associated with the site will remain open. The observatory also serves as a major axis of communication between the scientific community and Puerto Rican society – understanding how to maintain this momentum in the absence of an active instrument will also require further study.

It’s hard to argue with risk analysis. And it’s not hard to imagine that more modern and flexible instruments can accomplish the science we’ve come to expect from Arecibo at a lower cost, which is why Arecibo has been fighting for funding for over a decade. Considering these two factors, it’s clear that Arecibo’s time has come.

But it’s still hard to accept the loss of an icon like this.