Bad fate for the telecope, good fate for the technicians. If they had tried to enforce the structure, it would have collapsed with the workers on it, costing their lives. So we can be happy the telescope broke before the catastrophe.
https://www.youtube.com/watch?v=59WQIRvezzI[*quote*]
Analyzing Video Footage Of Collapse of Massive Arecibo Telescope
•Dec 4, 2020
Scott Manley
1.15M subscribers
The collapse was on Tuesday morning, but yesterday the NSF made video of the catastrophic collapse available, and so many viewers asked I continue my long tradition of 'coping by analyzing failure' and document what I see in this footage. It's hard to watch because this magnificent structure has always been part of the world of astronomy for me.
For those that feel moved into action a starting point may well be this petition ask the White House to consider rebuilding the facility.
https://petitions.whitehouse.gov/peti...
Juan R Costa's images of the structure after collapse are available on the NotiCel site, they're the best images of this:
https://www.noticel.com/galeria/20201201/imagenes-aereas-exclusivas-del-colapso-del-observatorio-de-arecibo/Buy Scott Manley merchandise
[*/quote*]
https://www.noticel.com/galeria/20201201/imagenes-aereas-exclusivas-del-colapso-del-observatorio-de-arecibo/[*quote*]
Galeria
Imágenes aéreas exclusivas del colapso del Observatorio de AreciboPor: Juan R. Costa
Publicado: Dec 01, 2020 11:46 AM
Actualizado: Dec 01, 2020 11:16 AM
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
Foto: Juan R. Costa / NotiCel
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
La estructura del radiotelescopio colapsó hoy.
El colapso ocurrió luego de que durante semanas se advirtiera del riesgo.
La estructura estaba comprometida tras la falla de dos de sus cables, que anteriormente ya habían colapsado.
La Fundación Nacional de Ciencias (NFC, por sus siglas en inglés) había anunciado su desmantelamiento y cierre.
Luego de que varias firmas de ingenieros verificaran la estructura.
No obstante, la comunidad científica buscaba salvar el radiotelescopio.
Bajo el hashtag #SalvemoselRadiotelescopio, decenas de personas contaron su experiencia.
Además, solicitaban fondos al Congreso.
Hasta la gobernadora, Wanda Vázquez Garced, emitió una carta la pasada semana, con miras a abogar por la estructura.
No obstante, hoy la estructura no resistió.
Así quedó. Mira las fotos a continuación.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
1 de diciembre de 2020 - Colapso total del Observatorio de Arecibo.
Juan R. Costa
'Chief Staff Photographer' de NotiCel y periodista multimedios con casi una década de experiencia profesional en los medios digitales. Graduado con doble grado en Periodismo y Ciencia Política de la Universidad de Puerto Rico en Río Piedras y reconocido por el Overseas Press Club y la Asociación de Fotoperiodistas de Puerto Rico. Amante de las ciencias, posee un sable de luz y sueña con viajar al espacio.
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They already knew it was doomed.Putting too many sacks of coal on a donkey is its end...
https://www.youtube.com/watch?v=IEe4Wlc5Vp0[*quote*]
Worlds Largest Radar Astronomy Dish To Be Demolished!381,153 views
•Nov 21, 2020
Scott Manley
1.15M subscribers
The iconic Arecibo observatory has suffered a second cable break and now the engineers who were trying to reinforce the structure think that it's no longer safe to try and save the structure. The National Science Foundation which has been funding the installation for decades have decided to authorize demolition of the historic structure to avoid damage to other parts of the facility.
http://www.naic.edu/~phil/hardware/telescope/auxmain200810/NSF-arecibo-engineering_report.pdfBuy Scott Manley merchandise
[*/quote*]
A must to see, with technical drawings and tables:
http://www.naic.edu/~phil/hardware/telescope/auxmain200810/NSF-arecibo-engineering_report.pdf[*quote*]
EMBARGOED UNTIL 11:30 A.M. U.S. Eastern Time, 11/19/2020
National Science Foundation Arecibo Observatory Damage Press CallAdvance materials contents:
•
•
•
•
•
Page 2: NSF press release
Page 5: NSF fact sheet
Page 7: Thornton Tomasetti recommendation for course of action at Arecibo Observatory
Page 50: WSP recommendation for future efforts at Arecibo Observatory
Page 52: WJE memorandum on Arecibo Observatory stabilization efforts
1
EMBARGOEDEMBARGOED UNTIL 11:30 A.M. U.S. Eastern Time, 11/19/2020
NSF begins planning for decommissioning of Arecibo Observatory’s 305-meter
telescope due to safety concerns
Following a review of engineering assessments that found damage to the Arecibo Observatory cannot
be stabilized without risk to construction workers and staff at the facility, the U.S. National Science
Foundation will begin plans to decommission the 305-meter telescope, which for 57 years has served as
a world-class resource for radio astronomy, planetary, solar system and geospace research.
The decision comes after NSF evaluated multiple assessments by independent engineering companies
that found the telescope structure is in danger of a catastrophic failure and its cables may no longer be
capable of carrying the loads they were designed to support. Furthermore, several assessments stated
that any attempts at repairs could put workers in potentially life-threatening danger. Even in the event
of repairs going forward, engineers found that the structure would likely present long-term stability
issues.
"NSF prioritizes the safety of workers, Arecibo Observatory’s staff and visitors, which makes this decision
necessary, although unfortunate," said NSF Director Sethuraman Panchanathan. "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."
Engineers have been examining the Arecibo Observatory 305-meter telescope since August, when one
of its support cables detached. NSF authorized the University of Central Florida, which manages Arecibo,
to take all reasonable steps and use available funds to address the situation while ensuring safety
remained the highest priority. UCF acted quickly, and the evaluation process was following its expected
timeline, considering the age of the facility, the complexity of the design and the potential risk to
workers.
The engineering teams had designed and were ready to implement emergency structural stabilization of
the auxiliary cable system. While the observatory was arranging for delivery of two replacement
auxiliary cables, as well as two temporary cables, a main cable broke on the same tower Nov. 6. Based
on the stresses on the second broken cable -- which should have been well within its ability to function
without breaking -- engineers concluded that the remaining cables are likely weaker than originally
projected.
"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," said Ralph Gaume,
director of NSF's Division of Astronomical Sciences. "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."
The scope of NSF's decommissioning plan would focus only on the 305-meter telescope and is intended
to safely preserve other parts of the observatory that could be damaged or destroyed in the event of an
unplanned, catastrophic collapse. The plan aims to retain as much as possible of the remaining
2
EMBARGOEDinfrastructure of Arecibo Observatory, so that it remains available for future research and educational
missions.
The decommissioning process involves developing a technical execution plan and ensuring compliance
with a series of legal, environmental, safety and cultural requirements over the coming weeks. NSF has
authorized a high-resolution photographic survey using drones, and is considering options for forensic
evaluation of the broken cable -- if such action could be done safely -- to see if any new evidence could
inform the ongoing plans. This work has already begun and will continue throughout the
decommissioning planning. Equipment and other materials will be temporarily moved to buildings
outside the danger zone. When all necessary preparations have been made, the telescope would be
subject to a controlled disassembly.
After the telescope decommissioning, NSF would intend to restore operations at assets such as the
Arecibo Observatory LIDAR facility -- a valuable geospace research tool -- as well as at the visitor center
and offsite Culebra facility, which analyzes cloud cover and precipitation data. NSF would also seek to
explore possibilities for expanding the educational capacities of the learning center. Safety precautions
due to the COVID-19 pandemic will remain in place as appropriate.
Some Arecibo operations involving the analysis and cataloging of archived data collected by the
telescope would continue. UCF secured enhanced cloud storage and analytics capabilities in 2019
through an agreement with Microsoft, and the observatory is working to migrate on-site data to servers
outside of the affected area.
Areas of the observatory that could be affected by an uncontrolled collapse have been evacuated since
the November cable break and will remain closed to unauthorized personnel during the
decommissioning. NSF and UCF will work to minimize risk in the area in the event of an unexpected
collapse. NSF has prioritized a swift, thorough process with the intent of avoiding such an event.
NSF recognizes the cultural and economic significance of Arecibo Observatory to Puerto Rico, and how
the telescope serves as an inspiration for Puerto Ricans considering education and employment in STEM.
NSF's goal is to work with the Puerto Rican government and other stakeholders and partners to explore
the possibility of applying resources from Arecibo Observatory for educational purposes.
"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," said Michael Wiltberger, head of NSF's Geospace Section. "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."
Engineering summary
Arecibo Observatory’s telescope consists of a radio dish 1,000 feet (305 meters) wide in diameter with a
900-ton instrument platform hanging 450 feet above. The platform is suspended by cables connected to
three towers.
On Aug. 10, 2020, an auxiliary cable failed, slipping from its socket in one of the towers and leaving a
100-foot gash in the dish below. NSF authorized Arecibo Observatory to take all reasonable steps and
3
EMBARGOEDuse available funds, which amounted to millions of dollars, to secure the analysis and equipment needed
to address the situation. Engineers were working to determine how to repair the damage and determine
the integrity of the structure when a main cable connected to the same tower broke Nov. 6.
The second broken cable was unexpected -- engineering assessments following the auxiliary cable
failure indicated the structure was stable and the planning process to restore the telescope to operation
was underway. Engineers subsequently found this 3-inch main cable snapped at about 60% of what
should have been its minimum breaking strength during a period of calm weather, raising the possibility
of other cables being weaker than expected.
Inspections of the other cables revealed new wire breaks on some of the main cables, which were
original to the structure, and evidence of significant slippage at several sockets holding the remaining
auxiliary cables, which were added during a refit in the 1990s that added weight to the instrument
platform.
Thornton Tomasetti, the engineering firm of record hired by UCF to assess the structure, found that
given the likelihood of another cable failing, repair work on the telescope -- including mitigation
measures to stabilize it for additional work -- would be unsafe. Stress tests to capture a more accurate
measure of the remaining cables' strength could collapse the structure, Thornton Tomasetti found. The
firm recommended a controlled demolition to eliminate the danger of an unexpected collapse.
"Although it saddens us to make this recommendation, we believe the structure should be demolished
in a controlled way as soon as pragmatically possible, " said the recommendation for action letter
submitted by Thornton Tomasetti. "It is therefore our recommendation to expeditiously plan for
decommissioning of the observatory and execute a controlled demolition of the telescope."
UCF also hired two other engineering firms to provide assessments of the situation. One recommended
immediate stabilization action. The other, after reviewing Thornton Tomasetti's model, concurred that
there is no course of action that could safely verify the structure's stability and advised against allowing
personnel on the telescope's platforms or towers.
“Critical work remains to be done in the area of atmospheric sciences, planetary sciences, radio
astronomy and radar astronomy,” UCF President Alexander N. Cartwright said. “UCF stands ready to
utilize its experience with the observatory to join other stakeholders in pursuing the kind of
commitment and funding needed to continue and build on Arecibo’s contributions to science.”
After receiving the contracted assessments, NSF brought in an independent engineering firm and the
Army Corps of Engineers to review the findings. The firm NSF hired concurred with the
recommendations of Thornton Tomasetti and expressed concern about significant danger from
uncontrolled collapse. The Army Corps of Engineers recommended gathering additional photographic
evidence of the facility and a complete forensic evaluation of the broken cable.
Given the fact that any stabilization or repair scenario would require workers to be on or near the
telescope structure, the degree of uncertainty about the cables' strength and the extreme forces at
work, NSF accepted the recommendation to prepare for controlled decommissioning of the 305-meter
telescope.
4
EMBARGOEDNational Science Foundation | FACT SHEET
ARECIBO: FACTS AND FIGURES
Completed in 1963 and stewarded by the U.S. National Science Foundation since the 1970s, Arecibo Observatory has
contributed to many important scientific discoveries, including the first discovery of a binary pulsar, the first discovery of an
extrasolar planet, the composition of the ionosphere, and the characterization of the properties and orbits of a number of
potentially hazardous asteroids.
Location: Arecibo Observatory’s principal observing facilities are located 19 kilometers south of the city of Arecibo, Puerto Rico.
Operation and management: Arecibo Observatory is operated and managed for NSF by the Arecibo Observatory
Management Team, which is led by the University of Central Florida in partnership with the Universidad Ana G. Méndez
and Yang Enterprises Inc.
NSF has invested over $200 million in Arecibo operations, management and maintenance over the past two decades. The
observatory has undergone two major upgrades in its lifetime (during the 1970s and 1990s), which NSF funded (along
with partial NASA support), totaling $25 million. Since Fiscal Year 2018, NSF has contributed around $7.5 million-per-year
to Arecibo operations and management.
Technical specifications and observational capabilities: Arecibo Observatory’s principal astronomical research instrument is a
1,000 foot (305 meter) fixed spherical radio/radar telescope. Its frequency capabilities range from 50 megahertz to 11
gigahertz. Transmitters include an S-band (2,380 megahertz) radar system for planetary studies and a 430 megahertz
radar system for atmospheric science studies and a heating facility for ionospheric research.
THE HISTORY
Funding for initial radar design studies came from military sources, including the Office of Naval Research and the U.S. Air
Force. The Advanced Research Projects Agency, or ARPA, agreed to finance the engineering and construction of the dish,
signing a contract with Cornell University, which the Air Force monitored.
Arecibo Observatory was originally intended for ionospheric research and radio astronomy, but the former was of more
interest to ARPA, which wanted to study and monitor the Earth’s ionosphere as part of its Defender Program to develop
ballistic missile defenses.
The Arecibo Ionospheric Observatory, as it was originally named, was the world’s largest radio telescope at the time of its
dedication in 1963.
By the late 1960s, however, Arecibo’s fate was uncertain due to ARPA’s shrinking research budget.
In 1967, NSF agreed to replace the Air Force as the government agency monitoring the Arecibo contract, beginning the
transformation of Arecibo into a civilian facility.
5
EMBARGOEDIn 1971, Arecibo received a new name: the National Astronomy and Ionospheric Center. That same year, NSF and NASA
signed a memo of understanding to share the costs of major upgrades to Arecibo. NSF funded the resurfacing of the dish
reflector and NASA funded the addition of S-band radar equipment.
In 1997, a second major upgrade, which included the Gregorian dome and a second line feed for the ionospheric radar,
was completed.
As a result of the upgrades, Arecibo became a powerful tool for scientific research focused on ionospheric physics, radar
and radio astronomy, and aeronomy.
EXAMPLES OF DISCOVERIES MADE BY ARECIBO
1967
Arecibo discovered that the rotation rate of Mercury is 59 days, not the previously estimated 88 days.
1972
Arecibo was used to simultaneously heat and observe the D- and E- regions of the ionosphere.
1974
Arecibo discovered the first ever binary pulsar. The 1993 Nobel Prize in physics was awarded to Russell A. Hulse and
Joseph H. Taylor for this discovery.
1975
Arecibo made S-band radar observations of Mars to support NASA’s Viking mission.
1981
Arecibo produced the first radar maps of the surface of Venus.
1992
Arecibo discovered the first ever exoplanet: In subsequent observations, an entire planetary system was found around
the pulsar PSR 1257+12.
1994
Arecibo mapped the distribution of polar ice on Mercury.
1996
Detection of ionized helium layer in the ionosphere made by Arecibo.
2006
Arecibo used to make observations of ionospheric perturbations driven by a tropical storm.
2008
Astronomers use Arecibo to detect for the first time, methanimine and hydrogen cyanide molecules -- two organic molecules
that are key ingredients in forming amino acids -- in a galaxy 250 million light-years away.
2016
Arecibo discovered the first-ever repeating fast radio burst. Repeating fast radio bursts are millisecond-duration radio
pulses that appear to be extragalactic. The repeater demonstrates that its source survives the bursts and rules out a
class of models requiring catastrophic explosions.
2017
Arecibo discovered two pulsars that seem to vanish and reappear intermittently, upending the widely held view that all
pulsars are the orderly ticking clocks of the universe.
Image credit: University of Central Florida
2415 Eisenhower Avenue | Alexandria, VA 22314
6
EMBARGOED
www.nsf.govVia email:Ramon.lugo@ucf.edu
November 12, 2020
Ramon Lugo III
Director, Florida Space Institute
University of Central Florida
12354 Research Parkway
Partnership 1 Building, Suite 214
Orlando, Florida 32826
RE: RECOMMENDATION FOR COURSE OF ACTION AT ARECIBO OBSERVATORY
TT Project No. U20209
Dear Ray:
This letter is to inform you of our opinion as engineer of record for the stabilization and
remediation of the damaged telescope, which is to decommission the telescope and perform a
controlled demolition of the structure as soon as pragmatically possible. As you know, on the
morning of August 10 a 31⁄4-inch-diameter cable, spanning from Tower 4 to the platform, failed
as the tower end of the cable pulled from its socket and fell to the ground. This cable was one of
the auxiliary system of twelve cables installed twenty-seven years ago. The auxiliary cables
supplemented the cables from the telescope’s original construction in the 1960s to
accommodate the weight added to the receiver platform by the installation of the Gregorian
dome.
Thornton Tomasetti, Inc. was retained to produce the design of any components necessary
to stabilize the structure and then to design the remediation to engage permanent repairs. The
assignment required TT to develop a digital model of the structure to determine the state of load
effects in the platform components, towers and cables in their current and possible future
configurations. We calibrated the model using survey data, data from instrumentation installed
on the telescope after the failure and data obtained by the observatory upon the cable’s failure.
The model was checked internally and peer reviewed by an external party, Wiss, Janney,
Elstner Associates, Inc. [WJE]. The model is a tool that predicts load effects, or forces and
deformations of the structure, hence the demands on its elements. The model does not predict
capacity of the elements. The true capacity of these original cables and auxiliary sockets as
they exist today is unknown, because the specific cause and extent of the deterioration in each
7
EMBARGOEDRamon Lugo
RE: RECOMMENDATION FOR COURSE OF ACTION AT ARECIBO OBSERVATORY
TT Project No. U20209
November 12, 2020
Page 2 of 4
of these elements is not currently known. Each has failed at forces significantly less than the
specified minimum breaking strength.
The structural design is highly redundant (meaning it has the ability to survive collapse after the
loss of a critical element). Each of the three towers has four 3-inch-diameter original cables
spanning to the near apex of the triangular platform and two 31⁄4-inch auxiliary cables connecting
farther back on the platform. When the auxiliary cable that spans to Tower 4 failed in August,
load was shed to the four original cables and the remaining auxiliary cable still connecting the
platform to the tower. After the failure, observatory staff, TT, WJE and WSP inspected/reviewed
the remaining structure for signs of distress and deterioration. Given the generally good
appearance of the remaining elements; suitable factor-of-safety remaining in the platform
elements, as shown through analysis; and adequate redundancy of the cable system, we
believed the platform to be stable then and for some time forward. Our analysis had shown that
the loss of another cable would not cause catastrophic collapse of the platform. Therefore, we
believed work to stabilize the structure could begin, with continuous monitoring and safe
operational procedures. The observatory procured materials and supplies and planned for
installation.
As you know, TT proposed the stabilization scheme and until recently was developing remedial
works to return the telescope to operating condition, with enhanced capability and performance
such that the 60-year-old original cables would have less tension force in the them than in the
past during normal operating conditions. Reduction of the load in these cables seemed prudent
due to their age and a few documented wire breaks on the original cables over the years. We
recommended that all remaining cables be inspected to determine their condition, to be certain
that the wire breaks that were documented in the past were the full extent of the breaks and that
the internal core of each cable was in good condition. Furthermore, TT recommended the
replacement of all of the auxiliary cables, since the one 31⁄4-inch auxiliary cable completely
pulled from its socket and numerous other auxiliary cables exhibited unusual slip at their
sockets.
Another cable failed on November 6. This cable was one of the four 3-inch-diameter original
cables also supporting the platform from Tower 4. These original cables had been operating at a
factor of safety of 1.67, based upon specified minimum breaking strength for the cable just prior
to failure. This corresponded to a load or tension force of 647 kips (1 kip = one thousand
pounds) in the original cables. The tension in the remaining three original cables has increased
from the 647 kips to 790 kips. This places them at a factor of safety of 1.32 (force in
cable/specified minimum breaking strength = 790/1044). This is nearly 75% of the specified
8
EMBARGOEDRamon Lugo
RE: RECOMMENDATION FOR COURSE OF ACTION AT ARECIBO OBSERVATORY
TT Project No. U20209
November 12, 2020
Page 3 of 4
minimum breaking strength. The original cable failed near the anchor socket at the tower but did
not pull from the socket. The design of the original structure and the upgrade in the 1990s
intended a factor of safety of 2.1 or more for the cables.
With the loss of two cables, there are now three original cables (of four) and one auxiliary cable
(of two) connecting the platform to Tower 4. Should another of these three original cables fail,
the two remaining original cables will undergo static force demands at or above the specified
minimum breaking strength. A catastrophic failure would be very likely. These cables are not
capable of handling the required dynamic demands of a sudden failure of an adjacent cable.
The structural redundancy is no longer available and cannot be factored into determining safety.
We have noted wire breaks on the three remaining 3-inch-diameter original cables from Tower
4, which occurred during the November event. We continue to monitor the structure and
continue to note wire breaks since the failure last week. Furthermore, there is no evidence that
the existing original cables can achieve the specified minimum breaking strength and certainly
evidence to the contrary, since one failed at 62% of this strength. The failure event may have
occurred over a period of eight minutes as evidenced by the increase in stress, measured from
instrumentation installed on the south auxiliary cable to Tower 4, just prior to failure. Weather at
the time of failure was calm, with no unusual winds or ambient temperatures and no ground
shaking. Failure was unexpected.
Given the likelihood of additional cable failure, unless redundancy can be added to the structure
at Tower 4 (by connecting more cables to the platform from Tower 4), it is unsafe to work on the
platform or around the towers unless hazards are mitigated. However, mitigation cannot be
practically achieved without working for long periods in these locations. There are no means
within engineering certainty to provide an estimate of the factor of safety other than significantly
reducing tension in these 3-inch-diameter original cables. We have modeled and studied
several options, and it is unlikely any of these methods will yield sufficient reductions without
placing crews in jeopardy.
It has been suggested that proof-loading the structure for a period of time – to demonstrate that
the critical structural elements can sustain forces approximately 10% more than the predicted
forces in these elements during the implementation of any remedial work – will provide a
calculable margin of safety over some duration, and that repeated proof-loading could provide
the means to ensure safety throughout the duration of work. However, we believe that even if
proof loading does not cause collapse or further failure of an element, it will cause damage and
reduce reserve capacity, making the structure less safe. If we accept collapse to be an
9
EMBARGOEDRamon Lugo
RE: RECOMMENDATION FOR COURSE OF ACTION AT ARECIBO OBSERVATORY
TT Project No. U20209
November 12, 2020
Page 4 of 4
acceptable outcome, we need to understand the collapse mechanism to reduce risk. Collapse
from a proof-testing event will not be predictable and hence creates undue risk.
Now that we have witnessed two cables fail, one from the original set of cables and one from
the auxiliary cables, both at tension forces significantly below their design strengths, it would
appear that remediation will require replacement of all of the cables. This factor needs to be
considered, as does the timing of the replacement program.
We believe the structure will collapse in the near future if left untouched. Controlled demolition,
designed with a specific collapse sequence determined and implemented with the use of
explosives, will reduce the uncertainty and danger associated with collapse. 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.
Very truly yours,
THORNTON TOMASETTI, INC.
John Abruzzo, PE, SE
Managing Principal
Attachments:
Model Calibrations
Results of model for various scenarios
Copy:
Francisco Cordova
Director, Arecibo Observatory
10
EMBARGOEDDigital Model Scope and Nomenclature
Frame elements
Cable elements
Main cables
Auxiliary main
cable
Waveguide
cable
Waveguide
tiedown
Model boundaries
Platform + Azimuth
Tiedown
Backstays
Tower
Platform
Auxiliary backstay
Azimuth
11
DRAFT – Confidential
1Digital Model Cable Nomenclature
N
M12W_AUX
B12E_AUX
B12W_AUX
M = Main cable
B = Backstay cable
T = Tiedown cable
AUX = Auxiliary cable (added 1992)
Wave Guide cables not shown
M12E_AUX
T12
T12W T12E
T8
T8N
T8S
T4N
T4S
T4
12
DRAFT – Confidential
2Platform Nomenclature
To Tower 12
N
Trusses and Outriggers
O1
Platform
X1
AT1
Track
BT1
MT3
ST6
MT1
ST1
Original structure:
• MT = Main Trusses
• BT = Bracing Trusses
• ST = Secondary Bracing Trusses
• Track
ST5
ST2
BT3 ST4
AT3
O3
ST3
X3
BT2
AT2
1992 upgrade structure:
• AT = Auxiliary trusses
• X = X-Bracing
• O = Outriggers
X2
MT2
O2
To Tower 8
To Tower 4
13
DRAFT – Confidential
32020 Sag Survey Processing
First point
considered
For each cable:
Missing
data near
cable end
Sag
Last point
considered
1) Select first and last points along top of cable, staying
away from cable ends where data is missing or noisy.
2) Determine equation of straight line between first and
last points.
3) For 10 points on top cable and approximately evenly-
spaced between first and last points, calculate
elevation difference between point and straight line.
The maximum difference is the measured sag.
4) Using catenary equations, calculate cable force such
that maximum sag matches measured sag. For this
step, the cable is assumed to span between the first
and last points considered above, and not the start
and end points of the actual cable.
5) Using catenary equations, calculate vertical
component of cable force at connection with
suspended platform. The sum of these results is the
suspended platform weight (+ tiedown forces).
Laser scan
points
Actual cable
centerline
Noisy data
near cable end
14
DRAFT – Confidential
4Sag Survey (Before Second Cable Failure)
Cables(s)
M4
M4S
M8
M8N
M8S
M12
M12E
M12W
Number of
Cables
4
1
4
1
1
4
1
1
Average Vertical Force
Horizontal
Axial Force at Platform
Force [kip]
[kip]
End [kip]
629
599
483
522
724
501
390
683
645
609
495
531
736
514
396
694
137
98
104
84
120
108
61
113
Cables(s) Number of
Cables
B4
B4N
B4S
B8
B8N
B8S
B12
B12E
B12W 5
1
1
5
1
1
5
1
1
Horizontal Average Axial
Force [kip] Force [kip]
465
535
535
485
535
540
455
575
490
572
657
657
540
598
603
560
706
601
Total vertical force on platform = 1,871 kip
Total tiedown force = 45 kip
→ Weight of suspended structure = 1,871 – 45 = 1,826 kip
15
DRAFT – Confidential
5Validation: Platform Corner Elevation Change During Failure
Monitoring
FE Model
Looking West.
Deformation x 20.
Corner 4
+0.30’
Corner 8
Corner 12
-2.5’
Corner 12
-2.4’
Looking North.
Deformation x 20.
Corner 4 Corner 8 Corner 12
Monitoring 0.30’ (3.6") 0’ (0") -2.4’ (-28.8")
FE Model 0.14’ (1.6") -0.32’ (-3.9")
Corner 8
-0.32’
Corner 4
+0.14’
-2.5’ (30.1")
16
DRAFT – Confidential
6Validation: Platform Rotation During
Monitoring
SAP Model
Deformation x 20
West axis
0.73 deg
West
0.80 deg
Vertical
0.50deg
North axis
-0.12 deg
Deformation x 20
North
-0.10 deg
West axis North axis Vertical axis
Monitoring 0.800 -0.100 0.500
FE Model 0.730 -0.120 0.530
17
DRAFT – Confidential
Deformation x 20
Vertical axis
0.53deg
7Validation: Natural Frequency After Failure
FE Model
Monitoring
Tiedown forces during failure
Modal analysis with total structure mass of 1,826 kip and tiedown 12
removed
Tiedown 12 is slack
→ f = 0.233 Hz
→ T = 4.30 s
24.5 cycles in 100 sec
→ f = 0.245 Hz
→ T = 4.08 s
18
DRAFT – Confidential
8Cable Force Change
Due to Second Cable Failure
Before [kip]
After [kip]
19Cable Force Change
If De-Jacking all
Backstays by 18"
Before [kip]
After [kip]
(starting from current condition)
20Cable Force Change
If Moving Gregorian Out
(starting from current condition)
Before [kip]
After [kip]
21Cable Force Change
If Moving Line Feed In
(starting from current condition)
Before [kip]
After [kip]
22Cable Force Change
If Dropping 38kip
Counterweight
Before [kip]
After [kip]
(starting from current condition)
23Cable Force Change
If Cutting M4-4
(starting from current condition)
Before [kip]
After [kip]
24Cable Force Change
If Dropping Gregorian
(starting from current condition)
Before [kip]
After [kip]
25Cable Force Change
If Dropping 100kip
Uniformly from Platform
Before [kip]
After [kip]
(starting from current condition)
26Cable Force Change
If Reconnecting M4N_AUX
and Re-tensioning by 300kip
Before [kip]
After [kip]
(starting from current condition)
27Cable Force Change
If Lifting Platform from
Waveguide System
Before [kip]
After [kip]
(starting from current condition)
28Cable Force Change
If Dropping Tiedowns
(starting from current condition)
Before [kip]
After [kip]
29Cable Force Change
If Dropping Line Feed
(starting from current condition)
Before [kip]
After [kip]
30Cable Force Change
If Adding Two 55mm Cables
where M4-4 was, Tensioned
to 50% Breaking Strength
Before [kip]
After [kip]
(starting from current condition)
31Cable Force Change
If Adding a 1in Wire Rope
where M4-4 was, Tensioned
to Breaking Strength
Before [kip]
After [kip]
(starting from current condition)
32Cable Force Change
Starting From Current Condition
If adding 2 x
55mm
If
If Dropping
If Lifting
cables
Reconnectin
100kip
Platform
where M4-4
If Dropping
g M4N_AUX
If dropping If dropping
Uniformly
From
was,
Gregorian
and Re-
Tiedowns Line Feed
from
Waveguide
tensionned
Tensionning
Platform
Cables
to 50%
to 300kip
breaking
strength
-7.7%
-4.7%
-10.4%
-4.0%
-0.7%
-2.1%
-18.1%
If adding a
1in wire
rope where
M4-4 was,
tensionned
to breaking
strength
Cable(s) Effect of
Second
Cable
Failure M4 22.2% -3.8% -4.4% -0.4% -3.1% -0.7% M4N_AUX n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a
M4S_AUX
M8 20.5%
-1.8% -8.8%
-2.2% 10.9%
7.3% 1.1%
0.7% 2.4%
0.4% 0.3%
-0.2% -13.9%
-15.8% -3.2%
-5.3% -1.0%
0.7% -0.7%
-1.1% -0.4%
-0.8% 0.4%
-0.8% -11.7%
1.4% -1.1%
0.1%
M8N_AUX -3.7% -9.5% -9.5% -0.9% -4.0% -0.3% -0.9% -2.9% 6.5% -2.2% -0.4% -2.1% 2.2% 0.2%
M8S_AUX
M12 -1.9%
-0.5% -9.7%
-2.1% -12.4%
-2.0% -1.2%
-0.2% -4.8%
-2.4% -1.0%
-0.2% 0.9%
-9.5% -2.7%
-4.9% -5.1%
-2.9% -4.5%
-1.7% -0.4%
-0.8% -2.4%
-1.8% -3.0%
0.3% -0.3%
0.0%
M12E_AUX -20.4% -12.6% -15.1% -1.4% -6.0% -2.7% 0.0% -3.9% 44.2% -20.5% -0.5% -3.1% 7.5% 0.7%
M12W_AUX 0.3% -9.9% 10.5% 1.1% 2.3% -0.1% -13.3% -3.0% -3.7% -0.2% -0.4% 0.4% -0.1% 0.0%
B4
B4N_AUX
B4S_AUX
B8
B8N_AUX
B8S_AUX
B12 -2.5%
-0.5%
-4.5%
-1.8%
-1.9%
-1.7%
-2.4% -11.0%
-11.7%
-12.7%
-9.3%
-11.6%
-12.1%
-11.1% -0.7%
-1.1%
-0.2%
0.2%
0.4%
-0.1%
-0.5% 0.0%
-0.1%
0.0%
0.0%
0.1%
0.0%
0.0% -1.5%
-1.6%
-1.3%
-1.2%
-1.2%
-1.3%
-1.4% -0.4%
-0.4%
-0.4%
-0.3%
-0.3%
-0.4%
-0.4% -7.4%
-7.0%
-7.8%
-8.2%
-8.2%
-8.0%
-7.8% -3.5%
-3.5%
-3.6%
-3.6%
-3.6%
-3.6%
-3.7% 0.9%
2.2%
-0.4%
0.2%
0.8%
-0.3%
1.5% 0.8%
-1.0%
2.7%
1.5%
1.4%
1.5%
1.3% -0.5%
-0.5%
-0.5%
-0.5%
-0.5%
-0.5%
-0.5% -1.2%
-1.2%
-1.2%
-1.1%
-1.1%
-1.2%
-1.2% 0.7%
-1.0%
2.7%
0.4%
0.7%
0.2%
0.8% 0.1%
-0.1%
0.2%
0.0%
0.1%
0.0%
0.1%
B12E_AUX -2.4% -11.3% -0.9% -0.1% -1.4% -0.4% -6.6% -3.2% 2.0% 1.7% -0.5% -1.1% 0.8% 0.1%
B12W_AUX -2.1% -13.2% 0.1% 0.0% -1.3% -0.3% 33
-8.6% -3.8% 0.7% 0.6% -0.6% -1.2% 0.8% 0.1%
If Dejacking If Moving
If Dropping
If Moving
all Backstays Gregorian
Counterwei
Line Feed In
by 18"
Out
ght
If Cutting
M4-4
-1.7%Cable Safety Factors
Before Second Cable Failure
SF
34Cable Safety Factors
Current Condition
SF
35Cable Safety Factors
If De-Jacking all
Backstays by 18"
(starting from current condition)
SF
36Cable Safety Factors
If Moving Gregorian Out
(starting from current condition)
SF
37Cable Safety Factors
If Moving Line Feed In
(starting from current condition)
SF
38Cable Safety Factors
If Dropping 38kip
Counterweight
(starting from current condition)
Drop Counterweight (kip)
SF
39Cable Safety Factors
If Cutting M4-4
(starting from current condition)
SF
40Cable Safety Factors
If Dropping Gregorian
(starting from current condition)
SF
41Cable Safety Factors
If Dropping 100kip
Uniformly from Platform
(starting from current condition)
SF
42Cable Safety Factors
If Reconnecting M4N_AUX
and Re-tensioning by 300kip
(starting from current condition)
SF
43Cable Safety Factors
If Lifting Platform from
Waveguide System
(starting from current condition)
Lift from Waveguide (kip)
SF
44Cable Safety Factors
If Dropping Tiedowns
(starting from current condition)
Drop Tiedowns (kip)
SF
45Cable Safety Factors
If Dropping Line Feed
(starting from current condition)
Drop Line Feed (kip)
SF
46Cable Safety Factors
If Adding Two 55mm Cables
where M4-4 was, Tensioned
to 50% Breaking Strength
Add Two 55mm Cables (kip)
SF
(starting from current condition)
47Cable Safety Factors
If Adding a 1in Wire Rope
where M4-4 was, Tensioned
to Breaking Strength
Add a 1in Wire Rope (kip)
SF
(starting from current condition)
48Cable Safety Factors
Starting From Current Condition
If adding 2
If
x 55mm If adding a
If
If Dropping Reconnecti If Lifting
cables
1in wire
Dejacking If Moving If Moving If Dropping
100kip
on
Platform
where M4- rope where
Current
If Cutting If Dropping
If dropping If dropping
all
Gregorian Line Feed Counterwe
Uniformly M4N_AUX
From
4 was, M4-4 was,
Condition
M4-4
Gregorian
Tiedowns Line Feed
Backstays
Out
In
ight
from
and Re- Waveguide
tensionned tensionned
by 18"
Platform Tensionnin Cables
to 50% to breaking
g to 300kip
breaking strength
strength
1.32
1.37
1.38
1.33
1.33
1.43
1.39
1.47
1.38
1.36
1.33
1.35
1.61
1.34
Cable(s) Before
Second
Cable
Failure M4 1.61 M4N_AUX n/a n/a n/a n/a n/a n/a n/a n/a n/a 4.40 n/a n/a n/a n/a n/a
M4S_AUX
M8 2.15
2.10 1.79
2.14 1.96
2.19 1.61
1.99 1.77
2.12 1.74
2.13 1.78
2.14 2.07
2.54 1.84
2.26 1.80
2.13 1.80
2.16 1.79
2.16 1.78
2.16 2.02
2.11 1.80
2.14
M8N_AUX 2.47 2.57 2.84 2.84 2.59 2.67 2.57 2.59 2.64 2.41 2.63 2.58 2.62 2.51 2.56
M8S_AUX
M12 1.78
2.02 1.81
2.03 2.01
2.07 2.07
2.07 1.83
2.03 1.90
2.08 1.83
2.03 1.80
2.24 1.86
2.13 1.91
2.09 1.90
2.06 1.82
2.04 1.86
2.07 1.87
2.02 1.82
2.03
M12E_AUX 3.31 4.16 4.76 4.89 4.22 4.42 4.27 4.16 4.33 2.88 5.23 4.18 4.29 3.87 4.13
1.88 1.87 2.08 1.70 1.85 1.83 1.88 2.16 1.93 1.95 1.88 1.88 1.87 1.88 1.87
2.13
2.46
2.46
2.27
2.73
2.70
2.18 2.18
2.48
2.58
2.31
2.78
2.75
2.23 2.45
2.81
2.95
2.55
3.15
3.13
2.51 2.19
2.51
2.58
2.31
2.77
2.76
2.24 2.18
2.48
2.58
2.31
2.78
2.75
2.23 2.21
2.52
2.61
2.34
2.81
2.79
2.27 2.19
2.49
2.59
2.32
2.79
2.76
2.24 2.35
2.66
2.80
2.52
3.03
2.99
2.42 2.26
2.57
2.67
2.40
2.89
2.85
2.32 2.16
2.43
2.59
2.30
2.76
2.76
2.20 2.16
2.50
2.51
2.28
2.74
2.71
2.21 2.19
2.49
2.59
2.32
2.80
2.77
2.25 2.21
2.51
2.61
2.34
2.81
2.78
2.26 2.16
2.50
2.51
2.30
2.76
2.75
2.22 2.18
2.48
2.57
2.31
2.78
2.75
2.23
2.30 2.36 2.66 2.38 2.36 2.39 2.37 2.53 2.44 2.31 2.32 2.37 2.39 2.34 2.36
3.03 2.88 2.75 2.75 2.78 2.80 2.75 2.76
M12W_AU
X
B4
B4N_AUX
B4S_AUX
B8
B8N_AUX
B8S_AUX
B12
B12E_AUX
B12W_AUX
2.71
2.77
3.19
2.76
2.77
2.80
2.78
49November 11, 2020
Ramon Lugo
Director, Florida Space Institute
SUBJECT: Recommendation for Future Efforts at Arecibo Observatory
Dear Mr. Lugo:
There are currently two main cables that have failed at the Arecibo Observatory, both located from
Tower 4 to the platform. It is known that the M4N Aux main cable failed from the socket on August
10, which is undergoing forensic analysis to confirm the hypothesis that fabrication or installation was
at fault. When the M4-4 cable failed on November 6, the cable was at approximately 60% of its
minimum breaking strength per available documentation. M4-4 failed in tension, the cause of which
is believed to be degradation of the cable itself, potentially due to corrosion.
From Thornton Tomasetti’s (TT) model, we can conclude with a high level of confidence, that if an
additional main cable fails, a catastrophic collapse of the entire structure will soon follow.
All options initially considered to reduce the weight on the platform or to install cables to stabilize the
structure would require having personnel on the platform and the towers. After the recent failure, WSP
does not recommend allowing personnel on the platform or the towers, or anywhere in their immediate
physical vicinity in case of potential sudden structural failure.
The current stability of the structure is unknown, and we cannot quantify the structure’s factor of
safety. Wiss, Janney, Elstner (WJE) has proposed using a proof load test to quantify the current factor
of safety. WSP does not recommend performing a proof load test on the system for the following
reasons:
1. Due to the compromised state and additional damage being observed in the remining cables from
Tower 4, the maximum capacity of the remaining cables is unknown, and the additional load
could cause additional cable failures.
2. It is not recommended to put the structure through additional load cycles due to the additional
degradation that can occur by adding load to the system through proof loading.
3. The proof load proves capacity at that moment in time and it is unknown if the cables can support
that load again in the future.
Conclusions and Recommendations
Since we are observing additional wire breaks, this leads us to believe that there is additional
degradation of the cables and therefore less capacity than expected. At this time, WSP believes that
there is no course of action that can be taken to confidently verify the structural integrity of the existing
cables/structure. WSP strongly advises against allowing personnel on the platform or towers, or
anywhere in their immediate physical vicinity in case of potential sudden structural failure.
WSP USA Solutions, Inc.
One Penn Plaza
New York, NY 10119
+1 212-462-8500
wsp.com
50
EMBARGOEDTherefore, based on an engineering alternatives assessment, WSP recommends the following course
of action as the recommended alternative: controlled de-commissioning of the structure, with
appropriate site access restriction and other safety precautions as determined by safety lead WJE in-
place until decommissioning is complete.
Regards,
Vincent M. Antes, SE, PE
Program Manager
51
EMBARGOED
Page 2Wiss, Janney, Elstner Associates, Inc.
330 Pfingsten Road
Northbrook, Illinois 60062
847.272.7400 tel
www.wje.comMEMORANDUM November 12, 2020
Arecibo Observatory
Stabilization Efforts
WJE PROJECT NO. 2020.5191
TO
FROM
Ramon Lugo
Principal Investigator
University of Central Florida
Florida Space Institute
12354 Research Parkway
Partnership 1 Building, Suite 214
Orlando, FL 32826-0650
Jonathan C. McGormley, Brian J. Santosuosso
Engineering efforts have been underway to reevaluate the structure and reexamine options going forward
after the November 6, 2020 failure of the M4-4 cable. Despite the many uncertainties regarding critical
structural elements, WJE believes there is a possibility to save the structure without undue risk to workers.
The key element in pursuing this path is reducing structural uncertainty to acceptable levels by
demonstrating that key elements have the capacities needed to support the work that must be done.
It is apparent from the failure of M4N in August 2020 and M4-4 more recently that cable or socket
capacity degradation has taken place over time. Thus, the ultimate capacities of the cables supporting the
structure are currently unknown. We recognize that because of the unknown capacity of critical elements
of the structure and the difficulty associated with executing their repair, demolition of the facility is an
option if attempts to repair it cannot be pursued. However, we believe repairs are possible if stabilization
efforts commence immediately. Therefore, we have developed a plan that starts with immediate reduction
of load in all cables with the goal of obtaining a 10 percent demonstrated margin of capacity for each
cable. We anticipate, however, that the load reduction process may not achieve this margin. Select cables
will therefore require load testing to prove an appropriate margin. However, this does not necessarily
mean that the load must be increased in the cables by 10 percent. For example, a cable carrying 100 kips
whose load is reduced to 94 kips as part of the load reduction efforts would have shown a 6 percent
reduction in load. In order to prove a 10 percent margin on 94 kips, the proof load would be 103 kips,
which represents an increase of 3 percent over the current load.
Demonstrating adequate capacity for a given task may increase the risk of structural collapse (e.g., by
temporarily increasing the load on critical elements). Of course, any such demonstration would be done
without personnel in threatened positions. In short, risks during occupied times can be kept reasonably
low by performing higher risk demonstrations while the structure is not occupied. Since the alternative to
repair is demolition of the facility, the risk of possibly collapsing the unoccupied structure during an
attempt to save it may be acceptable. Of course, if the requisite capacity cannot be successfully
demonstrated at any time, risks to occupants would be excessive and repair efforts would cease, leaving
demolition as the only option. In our opinion, areas threatened by a collapse of the structure should only
be occupied if the Tower 4 cable group has a demonstrated capacity that is at least 10 percent greater
than the demands that exist during occupancy.
52
EMBARGOEDArecibo Observatory
Stabilization Efforts
As time passes, the capacities of the cables will decrease as evidenced by the two recent failures. In order
to maintain a demonstrable 10 percent reserve capacity, the initial load reduction efforts may have to be
supplemented by load testing. For example, if load reduction cannot keep up with a conservative estimate
of strength loss, it may be necessary to demonstrate that adequate capacity remains by temporarily
applying loads. When done properly, such proof testing can be used to demonstrate capacities, which is
why load testing is a staple of the engineering profession. Such testing is done because there is
uncertainty regarding the system’s strength; hence there is a possibility that the structure will collapse
during a test. As noted previously, this risk is taken on (while the structure is not occupied) so as to reduce
the risk of collapse while it is occupied. And, since the alternative is destroying the structure, the risk of
failure during a load test may be acceptable.
The following outlines activities designed to establish a 10 percent reserve capacity in the Tower 4 main
cables so that work within the backstay anchorage perimeter including on the feed platform can be done.
Immediate Priority Tasks
Task 1 – Tower 4 Backstay relaxation. At the tower anchorages, all seven backstays will be relaxed in a
sequenced approach to relieve load in the main cables. The tower top will move inward about 18 inches
during this process, which will lower the main cable forces by about 2 percent. This work can be
completed without subjecting personnel to hazards associated with an additional cable failure.
Task 2 – Towers 12 and 8 Backstay relaxation. Similar to the work carried out at Tower 4, the backstays
at Towers 12 and 8 can be relaxed. This will further reduce the loads in the Tower 4 main cables by an
additional approximate 2 percent.
Task 3 – Installation of 7/8-inch Wire Rope. Based on the possible availability of equipment currently at
the facility, a 7/8-inch diameter wire rope will be connected to the pin at the platform connection of the
M4 cables using a properly rated fabric sling. The cable will run to the top of Tower 4 and be redirected to
a winch anchored near the tower base. The work to install the cable and hardware will utilize a helicopter.
No personnel will be on the platform or top of tower. Installation of the wire rope will reduce the tension
in the Tower 4 cables by about 2 percent
Task 4 – Cutting of Hanging M4-4 Cable. Using a helicopter, the failed M4-4 cable will be cut from its
connection to the platform. This will reduce the load in the M4 cables by about 0.8 percent.
Task 5 – Removal of Azimuth Counterweight. There is currently about 45,000 pounds of lead
counterweight positioned on the top of the azimuth structure. Most of the lead is in slabs weighing
approximately 200-lbs each. An attempt will be made to throw the lead from the azimuth using workers
positioned from a helicopter. If this is not successful, then some other method to remove the
counterweight is needed that does not place personnel on the platform. Removal of the lead
counterweight is estimated to reduce the M4 forces by 4 percent.
MEMORANDUM | WJE No. 2020.5191 | November 12, 2020
53
Page 2
EMBARGOEDArecibo Observatory
Stabilization Efforts
Additional Tasks. If Tasks 1 through 5 are successful and the load in the M4 cables is reduced by
approximately 10 percent, limited and controlled access onto the platform and space below the reflector
dish will be permitted. Additional tasks to be completed during this period would include the following:
1.
2.
3.
4.
5.
Removal of the Gregorian dome hurricane stow pin
Movement of the Gregorian dome to a position on the current azimuth that further reduces the
M4 main cable tensions
Repair of the tie-down anchors to improve load testing capabilities
Install two 55-mm temporary cables between Tower 4 and the platform that will replace the
capacity lost by the failed main cable
Periodic load testing of the system to confirm the margin of safety has not been diminished by
continued degradation of various cables/sockets
If the immediate priority tasks listed above cannot all be completed, hold-down cables will be used to
load the system to the extent necessary to provide at least a 10 percent reserve capacity upon removal of
the hold down load.
With the additional tasks completed, we are confident the stability of the structure will no longer be
compromised by the failure of an additional M4 main cable. Restoration and investigative work can then
safely proceed with the original plan.
MEMORANDUM | WJE No. 2020.5191 | November 12, 2020
54
Page 3
EMBARGOED
[*/quote*]
