Sky & Telescope - March 2025 - 8

ARECIBO: UNIVERSITY OF CENTRAL FLORIDA; ARECIBO DAMAGE:
MICHELLE NEGRON / NATIONAL SCIENCE FOUNDATION
NEWS NOTES
TELESCOPE
Arecibo's Powerful Radar May Have Contributed
to the Telescope's Demise
stress that ultimately led to the telescope's
demise.
Initially, the collapse made little
sense. " As far as we know, there is no
recorded case of a cable that has stood
the initial loading, and then over time
pulls out at loads that are lower than
the initial level, " says Habib Tabatabai
(University of Wisconsin-Milwaukee),
a civil engineer who served on the committee.
The pattern of cable pullouts
were also puzzling, he notes. The cables
pulled out more at the tower level
than at the platform, and some newer
cables failed before older ones did. That
pattern didn't match weakening from
hurricane winds alone.
After some digging, the team found a
Aerial view of
Arecibo Observatory
in 2019
THE RADAR SYSTEM at the Arecibo
Observatory in Puerto Rico was once
the most powerful source of electromagnetic
radiation on this planet,
enabling the mapping of Venus, the
Moon, and near-Earth asteroids. Then,
in 2020, support cables for the giant
dish's observing platform failed, resulting
in the collapse and permanent
closing of the storied telescope (S&T:
Mar. 2021, p. 8). Now, an inquiry has
found those very radar transmissions
may have helped trigger the collapse.
Arecibo consisted of a 1,000-footwide
dish mounted over a natural sinkhole;
three concrete towers suspended
a 900-ton receiver and transmitter
platform above the dish. To hold the
radar platform's support cables in place,
molten zinc was poured into tapered
steel sockets - a standard method used
for well over 100 years in a wide variety
of industrial settings. Yet a committee
formed by the National Academy of
Sciences and sponsored by the National
Science Foundation concludes that
those zinc sockets might have weakened
unexpectedly in a phenomenon called
zinc creep. The raging winds of Hurricane
Maria in 2017 provided additional
In a photo taken on December 8, 2020, the
damage is visible a week after the telescope's
collapse. The remains of the instrument platform
are visible on the telescope's dish.
1963 study that documented zinc creep
when high currents were applied over
a short period of time, such as during
manufacturing processes. But the
panel realized that if currents had been
induced that were orders of magnitude
lower but sustained over longer periods,
the same effect could occur.
The likely source of those currents:
the telescope's powerful S-band
planetary radar system, added to the
facility in 1997. Its emissions could have
induced surface currents in the steel
cables that would have flowed through
the sockets, weakening the zinc there.
While this scenario isn't proven, Tabatabai
cautions, it would explain why the
cables on the towers, within the beam
of the radar emissions, were the ones
most affected.
While the phenomenon was unanticipated,
the report nevertheless notes
that clear danger signs were missed.
After Hurricane Maria, inspections
showed that cables were pulling out
of their sockets by more than an inch.
Major steps should have been taken
to improve the supports at that time,
and a much more rigorous program of
inspections and maintenance should
have been in place for such an important
facility.
" We hope that our report can at least
shed some light on what happened, "
Tabatabai says, " and guide the way for
the future. "
¢DAVID L. CHANDLER
8 MARCH 2025 * SKY & TELESCOPE
Sky & Telescope - March 2025

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