Green Bank Interferometer
Coordinates: 38°25′58.23″N 79°50′21.88″W / 38.4328417°N 79.8394111°W
The Green Bank Interferometer (GBI) is a former radio astronomy telescope located at Green Bank, West Virginia (USA) and operated by the National Radio Astronomy Observatory (NRAO). It included three on-site radio telescopes of 85-foot (26m) diameter, designated 85-1, 85-3, and 85-2 (85-1 is also known as the Tatel Telescope) and a portable telescope.
The first telescope (85-1, Tatel) was built in 1959 at a fixed location. It was used in Project Ozma in 1960 without Interferometer. In 1963, in anticipation of adding movable telescopes for interferometer, the second 85-foot (26 m) telescope kit identical to 85-1 was ordered. The construction of the second telescope (85-2) was completed in 1964 along with a 1.5-mile (2.4 km) track from 85-1. At that time, the 85-2 telescope was placed at the end of the track and cables were connected between the two telescopes. The GBI began operation that year as a two element interferometer in order to test large aperture synthesis arrays and study radio astrometry and interstellar scintillation.
In 1967 the array was upgraded with construction of the third element (85-3) to be located in the middle of the track. Both 85-2 and 85-3 had truck tires mounted on either side to allow them to be moved along the track to test different baselines. The limitation of the 3-element interferometer along a short track became apparent. A 42-foot (13 m) portable telescope was procured. The portable telescope was placed 8 miles (13 km) away from Green Bank site and then moved to 11 miles (18 km) forming a T shape with the length of the bottom arm of the T to be similar to the length of each arm of the Y configuration at Karl G. Jansky Very Large Array (VLA) which was still in a design phase. The portable telescope was later placed on a mountaintop in Huntersville, West Virginia, 26 miles (42 km) away from Green Bank, which is the same distance of the longest baseline of VLA. The portable telescope was replaced in 1973 with 45-foot (14 m) portable telescope which was in use until 1983.
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