Arecibo Observatory

General information

The main collecting dish is 305 m (1,000 ft) in diameter, constructed inside the depression left by a karst sinkhole. The dish surface is made of 38,778 perforated aluminum panels, each about 3 by 6 feet (1 by 2 m), supported by a mesh of steel cables. The ground beneath is accessible and supports shade-tolerant vegetation.

The observatory has four radar transmitters, with effective isotropic radiated powers of 20 TW (continuous) at 2380 MHz, 2.5 TW (pulse peak) at 430 MHz, 300 MW at 47 MHz, and 6 MW at 8 MHz.

The reflector is a spherical reflector, not a parabolic reflector. To aim the device, the receiver is moved to intercept signals reflected from different directions by the spherical dish surface of 270 m (870 ft) radius. A parabolic mirror would have varying astigmatism when the receiver is off the focal point, but the error of a spherical mirror is uniform in every direction.

The receiver is on a 900-ton platform suspended 150 m (492 ft) above the dish by 18 cables running from three reinforced concrete towers, one 111 m (365 ft) high and the other two 81 m (265 ft) high, placing their tops at the same elevation. The platform has a rotating, bow-shaped track 93 m (305 ft) long, called the azimuth arm, carrying the receiving antennas and secondary and tertiary reflectors. This allows the telescope to observe any region of the sky in a forty-degree cone of visibility about the local zenith (between −1 and 38 degrees of declination). Puerto Rico's location near the Northern Tropic allows Arecibo to view the planets in the Solar System over the Northern half of their orbit. The round trip light time to objects beyond Saturn is longer than the 2.6 hour time that the telescope can track a celestial position, preventing radar observations of more distant objects.

Design and architecture

The origins of the observatory trace to late 1950s efforts to develop anti-ballistic missile (ABM) defences as part of the newly formed ARPA's 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 1,000 miles (1,600 km).

Among the many Defender projects were several studies based on the concept that a re-entering nuclear warhead would cause unique physical signatures while still in the upper atmosphere. It was known that hot, high-speed objects caused ionization of the atmosphere that reflects radar waves, and it appeared that a warhead's signature would be different enough from decoys that a detector could pick out the warhead directly, or alternately, provide added information that would allow operators to focus a conventional tracking radar on the single return from the warhead.

Although the concept appeared to offer a solution to the tracking problem, there was almost no information on either the physics of re-entry or a strong understanding of the normal composition of the upper layers of the ionosphere. ARPA began to address both simultaneously. To better understand the radar returns from a warhead, several radars were built on Kwajalein Atoll, while Arecibo started with the dual purpose of understanding the ionosphere's F-layer while also producing a general-purpose scientific radio observatory.

The observatory was built between mid-1960 and November 1963 and designed by William E. Gordon of Cornell University, who intended to use it to study Earth's ionosphere. He was attracted to the sinkholes in the karst regions of Puerto Rico that offered perfect cavities for a very large dish. Originally, a fixed parabolic reflector was envisioned, pointing in a fixed direction with a 150 m (492 ft) tower to hold equipment at the focus. This design would have limited its use in other research areas, such as radar astronomy, radio astronomy and atmospheric science, which require the ability to point at different positions in the sky and track those positions for an extended time as Earth rotates. Ward Low of the Advanced Research Projects Agency (ARPA) pointed out this flaw and put Gordon in touch with the Air Force Cambridge Research Laboratory (AFCRL) in Boston, Massachusetts, where one group headed by Phil Blacksmith was working on spherical reflectors and another group was studying the propagation of radio waves in and through the upper atmosphere. Cornell University proposed the project to ARPA in mid-1958 and a contract was signed between the AFCRL and the University in November 1959. Cornell University and Zachary Sears published a request for proposals (RFP) asking for a design to support a feed moving along a spherical surface 435 feet (133 m) above the stationary reflector. The RFP suggested a tripod or a tower in the center to support the feed. On the day the project for the design and construction of the antenna was announced at Cornell University, Gordon had also envisioned a 435 ft (133 m) tower centered in the 1,000 ft (305 m) reflector to support the feed.

George Doundoulakis, who directed research at General Bronze Corporation in Garden City, New York, along with Zachary Sears, who directed Internal Design at Digital B & E Corporation, New York, received the RFP from Cornell University for the antenna design and studied the idea of suspending the feed with his brother, Helias Doundoulakis, a civil engineer. George Doundoulakis identified the problem that a tower or tripod would have presented around the center, (the most important area of the reflector), and devised a better design by suspending the feed. He presented his proposal to Cornell for a doughnut truss suspended by four cables from four towers above the reflector, having along its edge a rail track for the azimuth truss positioning. This second truss, in the form of an arc, or arch, was to be suspended below, which would rotate on the rails through 360 degrees. The arc also had rails on which the unit supporting the feed would move for the feed's elevational positioning. A counterweight would move symmetrically opposite to the feed for stability and, if a hurricane struck, the whole feed could be raised and lowered. Helias Doundoulakis designed the cable suspension system which was finally adopted. Although the present configuration is substantially the same as the original drawings by George and Helias, (though with three towers instead of the original four), the U.S. Patent office granted Helias a patent, for the brothers' innovative idea. Another assignee on the patent, William J. Casey, later became director of the Central Intelligence Agency under President Ronald Reagan.

The idea of a spherical reflecting mirror with a steerable secondary has since been used in optical telescopes, in particular the Hobby–Eberly Telescope and the Southern African Large Telescope.

Construction began in mid-1960, with the official opening on November 1, 1963. As the primary dish is spherical, its focus is along a line rather than at one point, as would be the case for a parabolic reflector. As a result, complex line feeds were implemented to carry out observations. Each line feed covered a narrow frequency band: 2–5% of the center frequency of the band. A limited number of line feeds could be used at any one time, limiting the telescope's flexibility.

Since then, the telescope has been upgraded several times. Initially, when the maximum expected operating frequency was about 500 MHz, the surface consisted of half-inch galvanized wire mesh laid directly on the support cables. In 1974, a high-precision surface consisting of 40,000 individually adjustable aluminum panels replaced the old wire mesh, and the highest usable frequency rose to about 5000 MHz. A Gregorian reflector system was installed in 1997, incorporating secondary and tertiary reflectors to focus radio waves at one point. This allowed installing a suite of receivers, covering the full 1–10 GHz range, that could be easily moved to the focal point, giving Arecibo more flexibility. A metal mesh screen was also installed around the perimeter to block the ground's thermal radiation from reaching the feed antennas. Finally, a more powerful 2400 MHz transmitter was added.

Research and discoveries

Many scientific discoveries have been made with the observatory. On April 7, 1964, soon after it began operating, Gordon Pettengill's team used it to determine that the rotation period of Mercury was not 88 days, as formerly thought, but only 59 days. In 1968, the discovery of the periodicity of the Crab Pulsar (33 milliseconds) by Lovelace and others provided the first solid evidence that neutron stars exist. In 1974, Hulse and Taylor discovered the first binary pulsar PSR B1913+16, an accomplishment for which they later received the Nobel Prize in Physics. In 1982, the first millisecond pulsar, PSR B1937+21, was discovered by Donald C. Backer, Shrinivas Kulkarni, Carl Heiles, Michael Davis, and Miller Goss. This object spins 642 times per second and, until the discovery of PSR J1748-2446ad in 2005, was identified as the fastest-spinning pulsar.

In August 1989, the observatory directly imaged an asteroid for the first time in history: 4769 Castalia. The following year, Polish astronomer Aleksander Wolszczan made the discovery of pulsar PSR B1257+12, which later led him to discover its three orbiting planets. These were the first extrasolar planets discovered. In 1994, John Harmon used the Arecibo Radio Telescope to map the distribution of ice in the polar regions of Mercury.

In January 2008, detection of prebiotic molecules methanimine and hydrogen cyanide were reported from the observatory's radio spectroscopy measurements of the distant starburst galaxy Arp 220.

From January 2010 to February 2011, American astronomers Matthew Route and Aleksander Wolszczan detected bursts of radio emission from the T6.5 brown dwarf 2MASS J10475385+2124234. This was the first time that radio emission had been detected from a T dwarf, which has methane absorption lines in its atmosphere. It is also the coolest brown dwarf (at a temperature of ~900K) from which radio emission has been observed. The highly polarized and highly energetic radio bursts indicated that the object has a >1.7 kG-strength magnetic field and magnetic activity similar to both the planet Jupiter and the Sun.

The Arecibo Message

In 1974, the Arecibo Message, an attempt to communicate with potential extraterrestrial life, was transmitted from the radio telescope toward the globular cluster Messier 13, about 25,000 light-years away. The 1,679 bit pattern of 1s and 0s defined a 23 by 73 pixel bitmap image that included numbers, stick figures, chemical formulas and a crude image of the telescope.

The RuBisCo Stars

On November 7, 2009, as part of the 35th anniversary of the Drake/Sagan transmission to M13, the RuBisCO gene sequence was transmitted to three nearby stars: GJ 83.1, Teagarden's star SO 025300.5+165258 and Kappa Ceti (G5B). The project was by artist Joe Davis with support from Paul Gilster, the Arecibo Observatory, Cornell University and others.

SETI and METI projects

Search for Extra-Terrestrial Intelligence (SETI) is a program to search for extraterrestrial life or advanced technologies. SETI aims to answer the question "Are we alone in the Universe?" by scanning the skies for transmissions from intelligent civilizations elsewhere in our galaxy. In comparison, METI (Messaging to Extra-Terrestrial Intelligence) refers to the active search by transmitting messages.

Arecibo is the source of data for the SETI@home and Astropulse distributed computing projects put forward by the Space Sciences Laboratory at the University of California, Berkeley and was used for the SETI Institute's Project Phoenix observations. The Einstein@Home distributed computing project has found more than 20 pulsars in Arecibo data.

Other uses

Terrestrial aeronomy experiments at Arecibo have included the Coqui 2 experiment, supported by NASA. The telescope also has military intelligence uses, some of which include locating Soviet radar installations by detecting their signals bouncing off the Moon.

Limited amateur radio operations have occurred, using moon bounce or Earth–Moon–Earth communication, in which radio signals aimed at the Moon are reflected back to Earth. The first of these operations was on June 13–14, 1964, using the call KP4BPZ. A dozen or so two-way contacts were made on 144 and 432 MHz. On July 3 and July 24, 1965, KP4BPZ was again activated on 432 MHz, making approximately 30 contacts on 432 MHz during the limited time slots available. For these tests, a very wide-band instrumentation recorder captured a large segment of the receiving bandwidth, enabling later verification of other amateur station callsigns. These were not two-way contacts. From April 16–18, 2010, again, the Arecibo Amateur Radio Club KP4AO conducted moon-bounce activity using the antenna. On November 10, 2013, the KP4AO Arecibo Amateur Radio Club conducted a Fifty-Year Commemoration Activation, lasting 7 hours on 14.250 MHz SSB, without using the main dish antenna.

Funding concerns

Since the early 1970s, the Arecibo Observatory has been supported by the NSF (National Science Foundation divisions of Astronomical Sciences and of Atmospheric Sciences) with incremental support by NASA, for operating the planetary radar. Between 2001 and 2006, NASA decreased, then eliminated, its support of the planetary radar, but restored and increased the funding in FY-2010.

A report by the NSF division of Astronomical Sciences, made public on November 3, 2006, recommended substantially decreased astronomy funding for the Arecibo Observatory, from $10.5 million in 2007 to $4.0 million in 2011. If other sources of money could not be obtained, the observatory would be forced to close. The report also advised that 80 percent of observing time be allocated to the surveys already in progress, reducing available time for smaller programs.

Academics and researchers responded by organizing to protect and advocate for the observatory. They established the Arecibo Science Advocacy Partnership (ASAP), to advance the scientific excellence of Arecibo Observatory research and to publicize its accomplishments in astronomy, aeronomy and planetary radar. ASAP's goals included mobilizing the existing broad base of support for Arecibo science within the fields it serves directly, the broad scientific community; provide a forum for the Arecibo research community and enhance communication within it; promote the potential of Arecibo for groundbreaking science; suggest paths that will maximize it into the foreseeable future, and showcase the broad impact and far-reaching implications of the science currently carried out with this unique instrument.

Contributions by the government of Puerto Rico may be one way to help fill the funding gap, but remain controversial and uncertain. At town hall meetings about the potential closure, Puerto Rican Senate President Kenneth McClintock announced an initial local appropriation of $3.0 million during fiscal year 2008 to fund a major maintenance project to restore the three pillars that support the antenna platform to their original condition, pending inclusion in the next bond issue. The bond authorization, with a $3.0 million appropriation, was approved by the Senate of Puerto Rico on November 14, 2007, on the first day of a special session called by Aníbal Acevedo Vilá. The Puerto Rico House of Representatives repeated this action on June 30, 2008. Puerto Rico's governor signed the measure into law in August 2008. These funds were made available during the second half of 2009.

In a letter published on September 19, 2007, José Enrique Serrano, a member of the U.S. House of Representatives Appropriations Committee, asked the National Science Foundation to keep Arecibo operating.

Language similar to that of the letter of September 19 was included in the FY-2008 omnibus spending bill. In October 2007, Puerto Rico's then-Resident Commissioner, Luis Fortuño, along with Dana Rohrabacher, filed legislation to assure the continued operation of the famed observatory. A similar bill was filed in the U.S. Senate in April 2008 by the Junior Senator from New York, Hillary Clinton.

Since the Arecibo observatory is owned by the Government of the United States, donations by private or corporate donors cannot be made. However, as non-profit (501(c)(3)) "public charities" under US law, the operators, SRI International and Universidad Metropolitana, can accept contributions on behalf of the Arecibo Observatory.

In September 2007, in an open letter to researchers, the NSF clarified the status of the budget for NAIC, stating the present plan could hit the targeted budgetary revision. No mention of private funding was made. However, in the event that its budget target is not reached, it must be noted that the NSF is undertaking studies to mothball or demolish the observatory to return it to its natural setting.

In November 2007, The Planetary Society urged the U.S. Congress to prevent the Arecibo Observatory from closing because of insufficient funding, since its radar contributes greatly to the accuracy of predictions of asteroid impacts on the Earth. The Planetary Society believes that continued operation of the observatory will reduce the cost of mitigation (that is, deflection of a near-Earth asteroid on collision to Earth), should that be necessary.

Also in November of that year The New York Times described the consequences of the budget cuts at the site. In July 2008, the British newspaper The Daily Telegraph reported that the funding crisis, due to federal budget cuts, was still very much alive.

The SETI@home program is using the telescope as a primary source for ET research. The program urges people to send a letter to their political representatives in support of full federal funding of the observatory.

The NAIC received $3.1 million from the American Recovery and Reinvestment Act of 2009. This was used for basic maintenance and for a second, much smaller, antenna to be used for very long baseline interferometry, new Klystron amplifiers for the planetary radar system and student training. This allotment was an increase of about 30 percent over the FY-2009 budget. However, the FY-2010 funding request by NSF was cut by $1.2 million (−12.5%) over the FY-2009 budget, in light of their continued plans to reduce funding.

The 2011 NSF budget was reduced by a further $1.6 million, −15% compared to 2010, with a further $1.0 million reduction projected by FY-2014. Starting in FY-2010, NASA restored its historical support by contributing $2.0 million per year for planetary science, particularly the study of near-Earth objects, at Arecibo. NASA implemented this funding through its Near Earth Object Observations program. NASA increased its support to $3.5 million per year in 2012.

Furthermore, in 2010 the NSF issued a call for new proposals for the management of NAIC starting in FY-2012. On May 12, 2011, the agency informed Cornell University that, as of October 1, 2011, it would no longer be the operator of the NAIC and the Arecibo Observatory. At that time, Cornell transferred its operations to SRI International, along with two other managing partners, Universities Space Research Association and Universidad Metropolitana de Puerto Rico, with a number of other collaborators. Upon the award of the new cooperative agreement for NAIC management and operation, NSF also decertified NAIC as a Federally Funded Research and Development Center (FFRDC), with the stated goal of providing the NAIC with greater freedom to establish broader scientific partnerships and pursue funding opportunities for activities beyond the scope of those supported by NSF.

In October 2015, the NSF released a "Dear Colleague Letter" reiterating its desire for a "substantially reduced funding commitment from NSF".

On 2016 September 30, the NSF released a followup to the October 2015 "Dear Colleague Letter" announcing a solicitation for future operation of the Observatory stating "The subject Solicitation will request the submission of formal proposals involving the continued operation of Arecibo Observatory under conditions of a substantially reduced funding commitment from NSF."

Ángel Ramos Foundation Visitor Center

Opened in 1997, the Ángel Ramos Foundation Visitor Center features interactive exhibits and displays about the operations of the radio telescope, astronomy and atmospheric sciences. The center is named after the financial foundation that honors Ángel Ramos, owner of the El Mundo newspaper and founder of Telemundo. The Foundation provided half of the funds to build the Visitor Center, with the remainder received from private donations and Cornell University.

The center, in collaboration with the Caribbean Astronomical Society, host a series of Astronomical Nights throughout the year, which feature diverse discussions regarding exoplanets, and astronomical phenomena and discoveries (such as Comet ISON). The main purpose of the center is to increase public interest in astronomy, the observatory's research successes, and space endeavors.

List of directors

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