As cleanup operations are underway at Arecibo Observatory in Puerto Rico, some scientists are proposing a replacement for the esteemed radio dish.
The National Science Foundation (NSF) made a report to Congress last week that details the damage to the 1,000-foot radio telescope following the collapse of the 900-ton instrument platform that was suspended above the aluminum dish. The report revealed details about the events leading up to the collapse, as well as a look forward to what’s next for the Arecibo Observatory.
Even as some of Arecibo’s operations continue, the NSF is considering its options for repairing other capabilities. Meanwhile, a group of scientists and engineers is proposing not just repairs but a full-on replacement that promises a dramatic increase in power and sensitivity.
The NSF report outlines a detailed timeline of events:
- August 10, 2020, 3 a.m. ET
An auxiliary cable from Tower 4 pulls loose from its socket. The cable falls onto the dish below, damaging some 250 of 40,000 aluminum tiles that make up the reflective dish.
- August and September
Engineers model support structures and determine a safety plan in order to access the failed socket on Tower 4. They also develop a stabilization plan for repairs.
- End of September
NSF authorizes an order for replacement cables, due to arrive in December. Stabilization efforts prior to replacement are set to begin November 9th.
- Early October
Engineers remove the failed socket and send it to the NASA Kennedy Space Center for analysis.
- November 6, 2020, 8:15 p.m.
A main cable from the same tower, Tower 4, breaks.
- November 19, 2020
NSF announces that the 305-meter radio telescope will have to be dismantled, as repairs cannot be made without jeopardizing safety.
- November 24, 2020
NSF confirms that additional wires within the thick cables are continuing to snap.
- December 1, 2020, 7:00 a.m.
The remaining cables from Tower 4 snap and the suspended platform crashes down on the dish below, causing extensive damage.
The collapse also ripped off the top 18 meters (60 feet) of Towers 4 and 12, and the top 37 meters of the taller Tower 8. Outside of the dish, towers, and other support structures, damage was surprisingly limited, mostly to building roofs. A number of the observatory’s facilities, including LIDAR and optics to observe the atmosphere as well a 12-meter radio telescope, are still operational.
NSF states that investigation into the collapse is ongoing. Engineers continue to investigate the failed socket involved in the auxiliary cable’s loss as well as the main cables, which NSF says were “weaker than expected.” The main and auxiliary cables date to the 1960s and the 1990s, respectively. NSF expects to have final reports on these investigations by December 2021.
Cleanup has begun, but it’s a long process that will continue into 2022, costing some $30–50 million. Engineers have mapped the debris from the collapse and workers have made good progress, as can be seen in the overhead image below. Cleanup isn’t only about removing machinery; there are environmental effects, too. For example, workers are also excavating soil contaminated with hydraulic oil released during the collapse.
Anything that’s still scientifically usable is staying put, though, as NSF is still deciding how to proceed with repairs. The organization is convening a meeting of scientists and engineers in the April timeframe to consider next steps.
One option on the table is to rebuild the 305-meter reflecting dish and continue studies of Earth’s atmosphere using instruments like the High Frequency ionospheric heaters and incoherent scatter radar.
But to conduct astronomy or planetary studies, the dish would have to be replaced. Some, led by Arecibo senior scientist Anish Roshi, are proposing a replacement that would be vastly different — and more powerful — than what’s there now.
Here’s the idea as outlined in a white paper circulated by Roshi and his colleagues: The Next Generation Arecibo Telescope would pack hundreds, maybe even more than 1,000 smaller radio dishes into the same space now occupied by the single 305-meter dish. Those smaller antennas would combine forces to act like a single larger telescope (no suspended instrument platform required).
Ideally, those dishes would be on a single, tiltable platform to access more of the sky from the Arecibo site; it’s possible multiple platforms could do the same.
The revamped telescope would have twice the sky coverage of the legacy dish, 500 times the field of view in individual images, at least double the sensitivity, and five times the radar power.
Those new capabilities open up a lot of new science. For example, the increased sky coverage would put the galactic center in view, allowing astronomers to search for pulsars orbiting the supermassive black hole lurking there and enabling unprecedented tests of general relativity.
A rough estimate puts the cost of such a facility at $454 million, less than the cost of producing and marketing Avengers: Endgame. A truer estimate will come once the telescope’s design is hammered out.
“The Next Generation Arecibo Telescope will not start from scratch,” the team states on their website. “It will take advantage of the existing infrastructure, decades of experience, and the support of the local people and government.”
To Be Decided
The plan is exciting to be sure, but the final decision is likely a long way off.
“NSF has a very well-defined process for funding and constructing large scale infrastructure, including telescopes,” said Ralph Gaume, director of NSF’s astronomy division. “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.” While Gaume issued that statement at a December press conference, it’s no less true now.
And it’s worth keeping in mind that in addition to any Arecibo repairs, NSF also needs to fund the under-construction Vera C. Rubin Observatory, the just-commissioned Daniel K. Inouye Solar Telescope, the ALMA radio array in Chile, the LIGO gravitational-wave detectors, and several other facilities. All those big, expensive instruments compete for the same available funds.
A separate Congressional appropriation is theoretically possible — that’s what helped rebuild the 100-meter Green Bank Telescope following its unexpected collapse in 1988. The political realities are a bit different in Puerto Rico than in West Virginia, but a number of representatives have expressed support for rebuilding Arecibo.
The astronomy community’s decadal survey, which outlines funding priorities for the next 10 years (or more) and is due out in the next couple months, may also play a role in deciding Arecibo's fate.
In the meantime, NSF is considering all proposals — the floor is open.