This past summer, the Arecibo Observatory suffered major damage when an auxiliary cable that supports the platform above the telescope broke and struck the reflector dish. Immediately thereafter, technicians with the observatory and the University of Central Florida (UCF) began working to stabilize the structure and assess the damage. Unfortunately, about two weeks ago (on Nov. 6th), a second cable broke causing even more damage.
Following a thorough review, the U.S. National Science Foundation (NSF) announced that the observatory cannot be stabilized without risking the lives of construction workers and staff at the facility. As such, after 57 years of faithful service and countless contributions to multiple fields of astronomy, the NSF has decided to commence plans for decommissioning the Arecibo Observatory.
This decision came shortly after the NSF evaluated assessments from a number of independent experts and companies to determine the cause of the structural failures and recommend steps for effecting repairs. These assessments indicated that the support cables are no longer capable of carrying the loads required of them and that the telescope structure is in danger of a catastrophic failure.
Damage at the Arecibo Observatory in August, 2020. Credit: NSF/NAIC
In addition, several assessments stated that any attempt to make repairs could put the lives of workers in danger. They also found that even if the repairs were successful, the structure would still be suffering from long-term stability issues. As Director Sethuraman Panchanathan said in an NSF statement:
“NSF prioritizes the safety of workers, Arecibo Observatory’s staff and visitors, which makes this decision necessary, although unfortunate. For nearly six decades, the Arecibo Observatory has served as a beacon for breakthrough science and what a partnership with a community can look like. While this is a profound change, we will be looking for ways to assist the scientific community and maintain that strong relationship with the people of Puerto Rico.”
After the first incident, engineering teams wasted no time coming up with an emergency stabilization plan of the auxiliary cable system. Despite the damage the broken auxiliary cable caused to the Gregorian Dome, the supporting structure, and the 30-meter (100 foot) gash it left in the reflector dish, the engineers were prepared to commence repairs by Nov. 9th (three days after the second cable broke).
The observatory was even arranging for the delivery of two replacement auxiliary cables (and two temporary ones) when the second failure occurred. This time, it was a main cable that broke, indicating that the structural problems extended to all the cable networks that connect the main dish to the instrument platform above it.
Aerial view of the NSF”s Arecibo Observatory in Puerto Rico. Credit: NAIC
According to Ralph Gaume, director of NSF’s Division of Astronomical Sciences, this was the decisive factor in the decision to decommission:
“Leadership at Arecibo Observatory and UCF did a commendable job addressing this situation, acting quickly and pursuing every possible option to save this incredible instrument. Until these assessments came in, our question was not if the observatory should be repaired but how. 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.”
Engineering assessments quickly followed that indicated that this 7.62 cm (3-inch) main cable was stressed to about 60% of its minimum tolerance (during calm weather) when it broke. Inspections of the other cables revealed new wire breaks on some of the other main cables and evidence of significant slippage at several sockets holding the remaining auxiliary cables.
These findings confirmed that both the main and auxiliary support cables were weakened more than originally projected. This led the engineering teams to conclude that decommission and demolition were the only option. John Abruzzo was the manager of the assessment made by Thornton Thomasetti, one of the structural engineering companies evaluating the observatory. As he summarized in their recommendation for action letter:
“Although it saddens us to make this recommendation, we believe the structure should be demolished in a controlled way as soon as pragmatically possible. It is therefore our recommendation to expeditiously plan for decommissioning of the observatory and execute a controlled demolition of the telescope.”
The Arecibo Observatory, The Arecibo Legacy Fast ALFA Survey. Credit: egg.astro.cornell.edu
The NSF’s plan for decommissioning the observatory would involve shutting down the 305 m (100 ft) telescope while safely preserving the other parts of the observatory that could be damaged or destroyed in the event of a catastrophic failure. In short, they hope to retain as much of the remaining infrastructure as possible so that it can still be of use for future research and educational purposes.
The decommissioning process is complex and requires that the NSF, UCF, and all participatory institutions comply with a series of legal, environmental, safety, and cultural requirements. In the meantime, the NSF has commenced a high-resolution photographic survey using aerial drones and is considering conducting a forensic evaluation of the broken cable (assuming it can be done safely).
When all necessary preparations are finished, the telescope would be subject to a controlled disassembly. Once that is done, the NSF intends to restore operations to Arecibo’s LIDAR facility, its visitor center, and the offsite Culebra meteorological facility. The analysis and cataloguing of archival data collected by the telescope will also continue.
While the decommissioning of Arecibo is certainly a sad development, it’s clearly necessary at this juncture. Said Michael Wiltberger, head of NSF’s Geospace Section:
“Over its lifetime, Arecibo Observatory has helped transform our understanding of the ionosphere, showing us how density, composition and other factors interact to shape this critical region where Earth’s atmosphere meets space.
“While I am disappointed by the loss of investigative capabilities, I believe this process is a necessary step to preserve the research community’s ability to use Arecibo Observatory’s other assets and hopefully ensure that important work can continue at the facility.”
Artist’s impression of the Arecibo Message, the coded message intended for extraterrestrials sent in 1974 from the Arecibo Observatory. Credit and Copyright: Danielle Futselaar
Throughout its 57 years of service, the Arecibo Observatory was the world’s premier radio telescope and one of the most iconic astronomical facilities in the world. Until the completion of the Five hundred meter Aperture Spherical Telescope (FAST) in China, it was also the largest radio observatory in the world. It’s accomplishment are unparalleled and include a number of firsts.
These include the confirmation of neutron stars, detecting the first binary pulsar, the first-millisecond pulsar, and the first exoplanets. The facility is also home to the Planetary Radar Project which (with support provided by NASA’s Near-Earth Object Observations Program) tracks and characterizes near-Earth objects (NEOs). In addition, the facility has also played an important role in the Search for Extraterrestrial Intelligence (SETI).
Aside from providing the source data for [email protected] and the SETI Institute’s Project Pheonix, the observatory is also one of the few installations in the world to actively send an encoded message to space intended for extraterrestrials. – aka. the Arecibo Message. She’s done so much in her lifetime, and she will continue to contribute in retirement.
So long, Arecibo! You will be missed!
Further Reading: NSF