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The 85-3 and the 85-2 twin 85-foot telescopes working together with the 85-1 (not shown) in the Green Bank Interferometer, the NRAO’s first array. The GBI operated from 1967-2006. From 1978-1996, it was operated in support of USNO and NRL geodetic and astronomy programs; after 1996 in support of NASA High Energy Astrophysics programs.

All three 85-foot telescopes of the roughly east-west arm of the Green Bank Interferometer, the NRAO’s first array. A fourth member of the GBI would have been in operation about 13 miles away. The GBI operated from 1967-2006. From 1978-1996, it was operated in support of USNO and NRL geodetic and astronomy programs; after 1996 in support of NASA High Energy Astrophysics programs.

In the 1960s and 1970s, this was a state-of-the-art supercalculator known as an autocorrelator. Its job was to combine the data taken by the Green Bank Interferometer’s four antennas and produce a single data package from them. The output was a plot produced by a chart recorder. A common sight during these years was of astronomers studying long rolls of GBI data plots in the hallways.

Inside the correlator, an instrument that was used to combine the signals from the three 85-foot telescopes and a fourth outlier into the Green Bank Interferometer. The GBI was the NRAO’s first array and served as a testbed for the Very Large Array (VLA).

The outer members of the Green Bank Interferometer, called 85-3 and 85-2, are 85-foot dish radio telescopes used with a third, the Howard E. Tatel, to form a northeast-southwest aligned array. The GBI was active in the 1960s and 1970s as a testbed for the Very Large Array (VLA).