.webp)
The Arecibo Telescope was a 305 m spherical reflector radio telescope built into a natural sinkhole at the Arecibo Observatory located near Arecibo, Puerto Rico.
A cable-mount steerable receiver and several radar transmitters for emitting signals were mounted 150 m above the dish. Completed in November 1963, the Arecibo Telescope was the world's largest single-aperture telescope for 53 years, until it was surpassed in July 2016 by the Five-hundred-meter Aperture Spherical Telescope (FAST) in Guizhou, China.
The Arecibo Telescope was primarily used for research in radio astronomy, atmospheric science, and radar astronomy, as well as for programs that search for extraterrestrial intelligence (SETI).
Scientists wanting to use the observatory submitted proposals that were evaluated by independent scientific referees.
NASA also used the telescope for near-Earth object detection programs. The observatory, funded primarily by the National Science Foundation (NSF) with partial support from NASA, was managed by Cornell University from its completion in 1963 until 2011, after which it was transferred to a partnership led by SRI International.
More information: National Science Foundation
In 2018, a consortium led by the University of Central Florida assumed operation of the facility.
The telescope's unique and futuristic design led to several appearances in film, gaming and television productions, such as for the climactic fight scene in the James Bond film GoldenEye (1995). It is one of the 116 pictures included in the Voyager Golden Record.
It has been listed on the US National Register of Historic Places since 2008. The telescope was named an IEEE Milestone in 2001.
The NSF reduced its funding commitment to the observatory from 2006, leading academics to push for additional funding support to continue its programs. The telescope was damaged by Hurricane Maria in 2017 and was affected by earthquakes in 2019 and 2020.
Two cable breaks, one in August 2020 and a second in November 2020, threatened the structural integrity of the support structure for the suspended platform and damaged the dish. Due to uncertainty over the remaining strength of the other cables supporting the suspended structure, and the risk of collapse owing to further failures making repairs dangerous, the NSF announced on November 19, 2020, that the telescope would be decommissioned and dismantled, with the LIDAR facility remaining operational.
Before it could be decommissioned, several of the remaining support cables suffered a
critical failure and the support structure, antenna, and dome assembly
all fell into the dish at 7:55 a.m. local time on December 1, 2020,
destroying the telescope. The NSF decided in October 2022 that it would not rebuild the telescope, or build a similar observatory at the site.
.jpg)
The origins of the observatory trace to late 1950s efforts to develop anti-ballistic missile (ABM) defenses as part of the newly formed United States Department of Defense (DoD) Advanced Research Projects Agency (ARPA) ABM umbrella-effort, Project Defender.
Even at this early stage it was clear that the use of radar decoys would be a serious problem at the long ranges needed to successfully attack a warhead, ranges on the order of 1,600 km.
The Astronomical Sciences and Atmospheric Sciences divisions of the NSF had financially supported Arecibo since its completion in the 1970s, with incremental support by NASA, for operating the planetary radar. Between 2001 and 2006, NASA decreased, then eliminated, its support of the planetary radar.
Several hurricanes and storms over the 2010s had raised the concerns of structural engineers over the stability of the observatory.
On September 21, 2017, high winds associated with Hurricane Maria caused the 430 MHz line feed to break and fall onto the primary dish, damaging roughly 30 of the 38,000 aluminum panels. Most Arecibo observations did not use the line feed but instead relied on the feeds and receivers located in the dome. Overall, the damage inflicted by Maria was minimal, but it further clouded the observatory's future. Restoring all the previous capabilities required more than the observatory's already-threatened operating budget, and users feared the decision would be made to decommission it instead.
On August 10, 2020, an auxiliary platform support cable separated from Tower 4, causing damage to the telescope, including a 30 m gash in the reflector dish. Damage included six to eight panels in the Gregorian dome, and to the platform used to access the dome. No one was reported to have been hurt by the partial collapse. The facility was closed as damage assessments were made.
Before repairs could be started, on November 7, 2020, one of the two main support cables from Tower 4 snapped, shattering part of the dish itself as it fell.
The UCF engineering staff, which had been monitoring the cables with support from the U.S. Army Corps of Engineers, and the engineering firms they had hired previously evaluated the remaining cables from Tower 4.
One engineering firm proposed stabilization efforts, while another suggested that they try to sever parts of the instrument platform such as the Gregorian dome to reduce the load. The third firm made the determination that there was no way to safely repair the damage at this point, as the remaining cables could be suspect, and furthermore that a controlled decommissioning of the telescope was the only effective means to avoid catastrophic failure which would threaten the other buildings on campus.
More information: BBC
The NSF took this advice and made the announcement on November 19, 2020 that they would decommission Arecibo over the following few weeks after determining the safest route to do so with a safety exclusion zone immediately put in place.
NSF's Sean Jones stated, This decision is not an easy one for NSF to make, but safety of people is our number one priority. The lidar facility will remain operational.
While waiting for NSF to make the decommissioning plans, steps had been taken to try to reduce the load that each of the towers were carrying, including reducing the strain on the backstay support cables for the individual towers. Other plans, such as having helicopters hoisting part of the load while hovering above the telescope, were proposed but deemed too risky.
Engineers from UCF had been monitoring the telescope and observed that wires in the backstay cables for the support towers had been breaking at a rate of one or two a day, and estimated that the telescope would soon collapse.
In the weekend prior to December 1, 2020, wire strands in the receiver's supporting cables had also been snapping apart at a rapid rate, according to Ángel Vázquez, the director of operations. This culminated in the collapse of the receiver platform at around 6:55 a.m. AST (10:55 UTC) on December 1, 2020, as the second main cable from Tower 4 failed with the other two remaining support cables failing moments later. The collapse of the receiver structure and cables onto the dish caused extensive additional damage.
In the weeks following Arecibo's collapse, the administration of the Five-hundred-metre Aperture Spherical Telescope (FAST) in China, which had drawn some design principles from Arecibo, stated that they would start taking applications for international researchers to use the telescope starting in 2021.
NSF decided in October 2022 that the Arecibo site would not be used for a new telescope, instead converting the site to be a STEM educational center.
The Arecibo Salvage Survey committee preserved some parts of the telescope, including parts of the zenith and azimuth tracks, a corner of the platform, the rotary joint, and the cable car.
More information: The New Yorker
together with increased knowledge of things,
brought men to see that the earth is not
what man had once thought it to be.
No comments:
Post a Comment