Today, the National Science Foundation announced that its famed Arecibo radio observatory would be shut down. Built into a hilltop in Puerto Rico, the main dish of the observatory is over 300 meters across, and its massive size has made it a feature in popular culture ranging from James Bond movies to video games. But despite a long history of scientific contributions, the observatory has been struggling for funding for over a decade, and two cables that support it have failed this year, leaving it in a precarious state.
After engineering studies determined there was no way to repair the hardware without putting workers at risk, the NSF made the decision to shut the observatory down.
More than a big dish
While the sheer scale of the main dish at Arecibo grabbed the most attention, the dish was purely a reflector. The actual business end of the telescope, where radio waves were sensed, was an instrument platform suspended high above it by cables strung from three towers. The instrument platform held a receiver that could be moved to different locations above the disk, giving it the ability to resolve signals from more directions than its fixed dish might suggest.
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.”
The end is near
Right now, the NSF is simply announcing that it will start planning for the decommissioning process. Work was already underway to move the data archives from the instrument onto a cloud service, and the plans for safely removing the platform will obviously involve a lot of additional engineering analyses. The NSF said that several other scientific programs associated with the site will remain open. The observatory also serves as a major focus of outreach between the scientific community and Puerto Rican society—understanding how to maintain that dynamic in the absence of an active instrument will also require further study.
It’s difficult to argue with the risk analysis. And it’s not difficult to imagine that more modern and flexible instruments can accomplish the science we’d expect from Arecibo at a lower cost, which explains why Arecibo has been struggling for funding for over a decade. Given both of these factors, it’s clear that Arecibo’s time has come.
But it’s still difficult to accept the loss of an icon like this.