Ballistic Missile Early Warning System
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Image:PAVE PAWS Radar Clear AFS Alaska.jpg
The Ballistic Missile Early Warning System (BMEWS) was the first operational ballistic missile detection radar. Built in 1959, BMEWS could provide long-range warning of a missile attack over the polar region of the northern hemisphere. They also provided satellite tracking data. There are three installations:
- A United States Air Force facility at Thule Air Base, Greenland
- A second USAF facility at Clear Air Force Station, Alaska
- A Royal Air Force facility of Fylingdales, in the United Kingdom
Information received from the BMEWS radars is forwarded to Cheyenne Mountain Air Station, Colorado. BMEWS can only spot missiles when they appeared over the horizon, which led the Soviet Union to develop FOBS. Defense Support Program (DSP) early warning satellites were developed in part to counter this threat.
The original sites used two types of radars, the L-band AN/FPS-50, with three fence antennas for initial detection, each 165 feet tall and 400 feet wide, and an AN/FPS-92 fully steerable tracking dish, 85 feet in diameter, installed in a large radome. One fence antenna covered a 40 degree sector of the horizon, for a total site coverage of 120 degrees. A prototype of BMEWS, located in Trinidad, began providing surveillance and tracking of ballistic missiles by 1958, and went operational on February 4, 1959, to gather data on missiles fired at the Atlantic Missile Range, as well as satellites and meteors. The full BMEWS radar network became operational in the early 1960s. Each site had dual IBM 7094 computers for signal processing and impact prediction.
Moon alarm
In October, 1960, the moonrise occurred directly in the path of one of the radars, producing a strong signal return. While the computer system never generated an impact prediction, the large amount of data caused enough concern that Cheyenne Mountain closed its blast doors for several hours. The equipment was subsequently modified to reject moon returns based on their long (2 second) delay.
Upgrades
The Thule and Fylingdales sites were upgraded with phased array radars in the 1990s. BMEWS 3, located in Fylingdales, was upgraded by Raytheon/Cossor AeroSpace and Control Data Corporation at a cost of US $100M. The new antenna was a 3 faced phased array antenna providing 360 degrees of coverage. The embedded computer was a CDC-Cyber running JOVIAL. The Clear, Alaska site was upgraded with PAVE PAWS radars in 2001. The phased array radars operate in the 420-450 MHz (UHF) frequency range.