page_title: Ballistic Missile Early Warning System
section_title: Equipment
hierarchical_section_title: Ballistic Missile Early Warning System / Equipment
context_page_description: The RCA 474L Ballistic Missile Early Warning System was a United States Air Force Cold War early warning radar, computer, and communications system, for ballistic missile detection. The network of twelve radars, which was constructed beginning in 1958 and became operational in 1961, was built to detect a "mass ballistic missile attack launched on northern approaches [for] 15 to 25 minutes' warning time" also provided Project Space Track satellite data.
context_section_description: BMEWS consisted of two types of radars and various computer and reporting systems to support them. The first type of radar consisted of very large, fixed rectangular partial-parabolic reflectors with two primary feed points. They produced two fan-shaped microwave beams that allowed them to detect targets across a very wide horizontal front at two narrow vertical angles. These were used to provide wide-front coverage of missiles rising into their radar horizon, and by tracking them at two points as they climbed, enough information to determine their rough trajectory. 
  The second type of radar was used for fine tracking of selected targets, and consisted of a very large steerable parabolic reflector under a large radome. These radars provided high-resolution angular and ranging information that was fed to a computer for rapid calculation of the probable impact points of the missile warheads. The systems were upgraded several times over their lifetime, replacing the mechanically scanned systems with phased-array radar that could perform both roles at the same time.
  BMEWS equipment included:
  General Electric AN/FPS-50 Radar Set, a UHF (440 MHz) detector with transmitter having an organ-pipe scanner feed, fixed 1,500 ton parabolic-torus reflector, and receiver with Doppler filter bank to scan with 2 horizontally-sweeping fans for as many as ~12,000 observations per day for surveillance (determining range, position, and range rate) of space objects
  RCA AN/FPS-49 Radar Set, a five-horn monopulse tracker (e.g., 3 at Site III) and FPS-49A variant (different radome) at Thule ("vacuum tubes 10 feet tall [in] transmitter buildings  [are] used to warm" the site.)
  RCA AN/FPS-92 Radar Set, an upgraded FPS-49 "featuring more elaborate receiver circuits and hydrostatic bearings" at Clear
  Sylvania AN/FSQ-53 Radar Monitoring Set, with console and Signal Data Converter Group ("data take-off unit")
  Sylvania AN/FSQ-28 Missile Impact Predictor Set, with duplex IBM-7090 TX solid-state computers e.g., in Building 2 at Thule  and part of the AN/FPA-21 Radar Central Computer at Site III—Satellite Information Processor (SIP) software was later added at Site III for use on the backup IBM 7090.
  RCA Communications Data Processor (CDP), as used in the Western Electric Air Force Communications Network (AF DATACOM) of AUTODIN
  Western Electric BMEWS Rearward Communications System, a "network to link the separate elements" and 1 of 6 ADC comm systems: "BMEWS Rearward Long-Lines System" at CFS Resolution Island & CFS Saglek, (cf. Pole Vault system on the Pine Tree Line, White Alice in Alaska, and to RAF Fylingdales, NARS)
  BMEWS Central Computer and Display Facility (CC&DF) at Ent AFB (ZI portion of BMEWS), with RCA Display Information Processor (DIP)—DIPS displays were also at the Offutt AFB war room floor and balcony, as well as at the Pentagon
  To predict when parts "might break down", the contractor also installed RCA 501 computers with 32k "high speed memory", 5-76KC 556 bpi 3/4" tape drives, & 200 track random access LFE drums.  The initially-replaced portions of BMEWS included the Ent CC&DF by the Burroughs 425L Missile Warning System at the Cheyenne Mountain Complex (FOC July 1, 1966.) The original Missile Impact Predictors were replaced (IOC on August 31, 1984), and BMEWS systems were entirely replaced by 2001 (e.g., radars were replaced with AN/FPS-120 SSPARS) after Satellite Early Warning Systems had been deployed (e.g., 1961 MIDAS, 1968 Project 949, and 1970 DSP satellites).
caption: Three of the huge AN/FPS-50 radars, BMEWS Site 2, near Anderson, Alaska, in 1962.
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