Sky & Telescope - March 2021 - 8

W The 900-ton
platform suspended above the
Arecibo telescope
fell 140 meters
(450 feet), damaging the dish
and surrounding
structures.

OBSERVATORIES

Damaged Arecibo
Telescope Collapses
AT 7:55 A.M. ON DECEMBER 1ST, a

rumble echoed through the hilly terrain surrounding Arecibo, the iconic
305-meter (1,000-foot) radio telescope
nestled in a natural sinkhole in Puerto
Rico. The 900-ton receiver platform
that had been suspended above the dish
had come crashing down.
While no injuries occurred, the
collapse ended hopes for a controlled
dismantling of the telescope, which
National Science Foundation (NSF)
ofﬁcials had announced less than two
weeks earlier after two unexpected and
devastating events that compromised
the safety of the telescope.
First, an auxiliary cable, which
helped suspend the receiver platform,
tore out of its socket on August 10th,
gashing the dish below. A redundant
design transferred the load of that
auxiliary cable to the four original
cables and the remaining support cable.
Engineers were called in to assess the
damage and, after determining the
structure was stable, to begin repairs.
Replacement cables were on order,
but before they could arrive, one of
the main cables from the same tower
snapped on November 6th. This unexpected second break caused engineers to
doubt the entire structure's integrity.
" Any engineering approach to better
understanding the strength left in the
8

MARCH 2 021 * SK Y & TELESCOPE

main cables
involves considerable risk
for human life
and could in
fact accelerate
the uncontrolled collapse of the structure, " said
Ralph Gaume, director of NSF's Division of Astronomical Sciences.
Engineers warned that another
cable break would cause " catastrophic
failure. " A representative from the engineering ﬁrm Thornton Tomasetti wrote
in support of dismantling the telescope:
" We believe the structure will collapse
in the near future if left untouched. "
Drone footage in the days following
the announcement showed additional
breakages in the remaining cables.
Ultimately, the uncontrolled collapse
happened before engineers could devise
a plan for controlled decommmissioning. A preliminary assessment indicated
that the top sections of all three support
towers broke off. Then, as the platform
fell, the cables also dropped, causing
signiﬁcant damage to the observatory's
learning center.
The loss of the 57-year-old observatory came as a shock to the astronomy
community (see page 12). Arecibo's
huge collecting area, incredible sensitivity, and powerful radar capabilities

enabled it to study everything from
near-Earth asteroids to distant galaxies; scientists had also used the dish to
investigate Earth's atmosphere.
" I'm devastated, " says Alessondra
Springmann (University of Arizona),
who had used the facility to characterize comets and asteroids. " There's nothing else like this in the world. "
" Arecibo is so much more than a
scientiﬁc instrument, " says Edgard
Rivera-Valentín (Lunar and Planetary
Institute). " It has been an icon in
Puerto Rico that has served to inspire
generations of scientists. "
" Pretty much every schoolchild on the
island has been to Arecibo, " Springmann
says. " Everyone has had family who
worked there, who helped build it. You
can't have an observatory without the
people, and the people also derive great
beneﬁt from the observatory being there. "
Arecibo is also irreplaceable for scientists. " The Arecibo Observatory is the
world's most powerful and most sensitive planetary radar, " Rivera-Valentín
explains. " This makes Arecibo invaluable for planetary defense. "
Technically, Arecibo is the secondlargest radio dish in the world -
China's Five-hundred-meter Aperture
Spherical Telescope, or FAST, recently
broke the record that Arecibo had held
for decades (S&T: Feb. 2017, p. 26). But
FAST's suspended platform cannot hold
the weight of radar instrumentation.
Other radar-capable radio dishes, such
as NASA's Goldstone, lack Arecibo's
sensitivity and availability.
Over almost six decades, Arecibo
survived multiple earthquakes, hurricanes, and funding struggles. Even
upon the telescope's collapse, NSF ofﬁcials have emphasized that they are not
closing the Arecibo Observatory. The
NSF continues to authorize repairs for
the facility's 12-meter radio telescope
and the roof of the LIDAR facility, used
for geospace research. Both were damaged in 2017 during Hurricane Maria.
The observatory's visitor center has
managed to survive unscathed.
MONICA YOUNG

S A ground view shows the suspended receiver
platform in better days.

* See drone footage of the collapse at
https://is.gd/Arecibocollapse.

A RECIBO: RICA RDO A RDUENGO / A FP / G E T T Y IM AG ES;
RECEIV ER PL ATFOR M: A L A N DY ER

NEWS NOTES

https://www.is.gd/Arecibocollapse

Sky & Telescope - March 2021

Table of Contents for the Digital Edition of Sky & Telescope - March 2021