A major system program, the ASG-18 tracker for the F-108 died early in this period when the Air Force canceled the aircraft. SBRC had developed this unique tracking concept based on an idea of project engineer John Reed, who had radar experience on the SCR584 in World War II. This radar system employed an offset spinning dipole at the focal point of a parabolic dish to achieve tracking error signals. He applied this concept to passive infrared systems to achieve better rejection of spurious targets caused by variations in the infrared background radiation by using a line array of detectors at the focal plane. The conventional system imaged the entire scene on a rotating reticle, which caused signals to be generated from all variations in the infrared scene. In order to generate tracking information he made the detector array in a cross form and nutated the field of view. The servoed gimbals drove the center of the field so that the target was equispaced on the arms of the cross. Searching was accomplished by a raster scan until the target was detected. SBRC developed the tracker, called the ‘beer can tracker’ because of its size, and Hughes Culver City developed the remainder of the system. A PbSe detector array, available only at SBRC, operated at liquid nitrogen temperature, using a liquid nitrogen transfer system. Although the original application was terminated, Hughes continued work using company funds and later received government support and developed search-track sets, called 90-C, 100-C, and S71N, which were used on the F101, F106 and foreign aircraft. SBRC supplied the PbSE and later InSb arrays in glass dewars which were cooled originally by liquid nitrogen transfer and later by Joule-Thomsen cryostats.
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