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Now available online: Whitney, Lonsdale, and Fish, "Insights into the Universe: Astronomy with Haystack's Radio Telescope," originally published in Lincoln Laboratory Journal 21(1), 2014.

Construction of the Haystack facility by MIT Lincoln Laboratory began in 1960 as a technological step in the evolution of high-performance microwave systems. Operations began in 1964, and for the first ten years the primary role of Haystack was as a planetary astronomy radar, observing the reflection characteristics and orbital parameters of the Moon, Venus, Mars, and Mercury. Topographical characteristics of the lunar surface were examined with emphasis on the proposed landing sites for the Apollo lander, and similar observations were made in support of the Viking lander on Mars. The "fourth test" of Einstein's general theory of relativity was also carried out at Haystack by making precise measurements of the round trip travel time of the radar echo from Mercury, which, passing near the sun, was delayed due to the intense solar gravitational field.

In 1970, the Haystack facility was transferred from the Air Force to MIT to be operated under agreement with NEROC to foster and encourage radio astronomy. Haystack is renowned for many astronomical discoveries such as the initial detections of various molecular species in interstellar space. Under grants from the NSF for the radio astronomy program, the Observatory is available for observations by qualified scientists and students from all universities and research institutions. As many as 100 investigators, including about 20 graduate students, utilize the facility annually in their research projects.

The Haystack radio telescope is a fully steerable parabolic antenna 37 meters in diameter, enclosed in the world's largest space-frame radome. The telescope configuration is Cassegrain, where the energy focused by the large primary reflector is redirected by a small subreflector to electronic receivers near the center of the primary "dish." The Haystack radome is 46 meters in diameter, and its 932 triangular membranes are made of 0.6-mm thick Tedlar-coated dacron cloth manufactured by ESSCO of Concord, Massachusetts. This material has been designed to minimize signal loss across the frequency bands of astronomical interest.

The Haystack antenna was initially designed for operation at a frequency of 8 GHz (one GigaHertz is 1 billion cycles per second). Frontier radio astronomical observations have driven observations towards higher frequencies, which require a more accurate reflector surface, and the main Haystack surface has thus been continually improved since its initial construction. In 1991-1993, the surface was adjusted to a root-mean-square deviation of 0.25 mm from a perfect parabola, the thermal environment in the radome and on the antenna was accurately controlled, and a deformable subreflector was installed, to allow use of the telescope up to a frequency of 115 GHz during cold and dry winter nights. At that frequency lies an important emission line of the carbon monoxide molecule, which traces high-density interstellar gas in the stellar nurseries where new stars form. Astronomers using Haystack can now observe this line, along with other molecular transitions in the 85-115 GHz range, with high resolution - the telescope's beam size at 100 GHz is 20 arcseconds, or about the size of a basketball at a distance of 2 miles. Recent feasibility studies indicate that it is possible to further improve the telescope's performance by adding an actuated set of light-weight panels and a laser measurement system that could allow operations up to 150 GHz in all seasons and times of day.

The pointing capabilities of the telescope have also been improved to allow its narrow beam to be steered accurately. Good pointing is simplified by the enclosure of the telescope in a radome, which provides protection from snow, ice, wind loading, and direct radiation from the sun. The antenna can be moved at rates of 2 ° per second about both elevation and azimuth axes. Because of the antenna's usage at a number of frequencies for astronomy, and also as a high-power radar for satellite imaging, it has been designed to use interchangeable electronics modules ("boxes") at the antenna focus, which can be exchanged in a few hours. One module contains the three primary astronomy receivers for use at 20-26 GHz, 35-50 GHz, and 85-115 GHz, and a second contains a radar transmitter and receiver operating at 10 GHz. The astronomical receivers consist of amplifiers or mixers and other components cryogenically cooled to as low as 4 ° above absolute zero (4 Kelvins). Such low temperatures are required to reduce electronic noise and allow sensitive observations of the extremely weak astronomical signals originating from sources as diverse as planets in our own solar system and quasars at the edge of the universe. A variety of computers control and direct the radio telescope subsystems, and versatile digital processors are available to reduce the data. The first digital correlation spectrometer for radio astronomy was built at Haystack in the early sixties. It was used for the discovery at Millstone Hill in 1963 of the OH (hydroxyl) radical, which was the first molecule to be detected in interstellar space.

cut-away view of Haystack antenna

A cutaway view of the Haystack antenna showing the Cassegrain subreflector and the hoisting system for the interchangeable equipment boxes.

The Haystack 37-m diameter antenna surface is made of 96 honeycomb aluminum panels which are set to a root-mean-square tolerance of 0.25 mm.

The Haystack antenna subreflector is made of fiber-reinforced plastic with a set of nineteen actuators that precisely control its surface to compensate for residual errors in the primary surface, and that can focus, translate, and tilt the ubreflector.



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