Arecibo Observatory, located in Puerto Rico, was the world’s second-largest single-dish radio telescope until its sudden collapse on Dec. 1, 2020. Despite strong support from the astronomy community to build a replacement facility, the National Science Foundation determined in 2022 it would not rebuild the iconic telescope.
The striking Arecibo was iconic both for its science and for its appearance, as it included a platform suspended high above a gigantic radio dish, rising out of a tropical forest.
Arecibo contributed an astounding catalog of astronomy work, including contributions that led to two Nobel prizes, during its half-century in operation. But it is perhaps most famous for being the site of the huge Search for Extraterrestrial Intelligence (SETI) message directed at the globular cluster M13 in 1974.
In February 2018, the National Science Foundation (NSF) — which provided most of the observatory’s funding since the 1970s — announced that it would cut its annual contribution from $8 million to $2 million in the following five years. In April 2018, the University of Central Florida in Orlando took over the management and operations of the observatory.
Arecibo never made it that long. On Dec. 1, 2020, the radio telescope’s science platform collapsed after the National Science Foundation had decided the facility was too precarious to repair. Scientists around the world, but especially Puerto Rican astronomers, mourned its loss, but experts say the loss of the observatory was inevitable given the recent lack of funding for scientific infrastructure.
The first function of Arecibo was supposed to be studying the ionosphere, a region of the upper atmosphere that is important to understand to properly transmit radio signals, according to an NSF fact sheet(opens in new tab). The Advanced Research Projects Agency (today’s DARPA) was interested in this region to advance ballistic missile defense projects, which meant the observatory attracted military funding from the Office of Naval Research and the U.S. Air Force (as Space Force had not been created back then.)
The Air Force-managed telescope was dedicated in 1963 and hailed as the world’s largest radio telescope, but in a few short years, it was already facing funding issues as ARPA’s research budget diminished. The NSF agreed to become Arecibo’s caretaker in 1967 and the research transferred to the civilian sector and astronomy.
NASA came on board in 1971 through a cost-sharing agreement with NSF, allowing for the dish reflector to be resurfaced and for more radar equipment to be added. The partners brought in a new dome and a second line for ionospheric radar in 1997. In these decades, NSF wrote, “Arecibo became a powerful tool for scientific research focused on ionospheric physics, radar and radio astronomy, and aeronomy.”
When the telescope concluded its work, Arecibo was part of the National Astronomy and Ionosphere Center. The National Science Foundation had a cooperative agreement with the three entities that operated Arecibo: SRI International, the Universities Space Research Association, and Puerto Rico’s Metropolitan University (UMET).
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The reflective dish was 1,000 feet (305 meters) in diameter, 167 feet (51 m) deep, and covers an area of about 20 acres (81,000 square meters). A triangular platform was suspended 450 feet (137 m) above the dish by three concrete towers. The platform held the azimuth arm, a dome containing two sub-reflector, and a set of antennae that could be tuned to a narrow band of frequencies.
Arecibo was the largest radio telescope until July 2016, when China finished the Five-hundred-meter Aperture Spherical Telescope’s (FAST) giant dish. That dish — the size of 30 football fields — is 1,650 feet (503 m) wide.