BMEWS - 510 Full Days - Detection Radar

In each of the three transmitter buildings lay the heart of the AN/FPS-50 Detection Radar (which we newly-arrived Tracker technicians soon irreverently labelled "Directional Radar"): the transmitters, receivers, and control systems for transmitter and receiver switching. The transmitters were on the first floor of the building. The cabinets which housed the transmitters, receivers, control units, and consoles were painted a light green, similar to the 1950's Ford color, "Seafoam green". The inside of the cabinets was an off-white. On a mezzanine which surrounded the open building center were the administrative and engineering offices, and receiver and control cabinets. Also on the mezzanine in each building was a small radar control room, the Detection Radar Automatic Monitoring (DRAM) room. The DRAM was responsible for the monitoring of the transmitters and receivers in that building. The lights in the DRAM rooms were dimmed so that the indicator lights on the control consoles could be easily seen. Green lights indicated a "nominal" component; yellow, a marginal component; and red, a failure. There were two consoles in each room: one for the DRAM systems, and the other to control the radar systems themselves. Because the relative humidity was so low, many times less than 5 percent, static electricity was an annoyance, but never seemed to affect the electronic systems. A few minutes of walking around was sufficient to build up a very large static charge. "Hush Puppies" shoes, with their foam soles were especially effective. It was fun to walk into the control room, move around enough to build up a charge, and touch someone's ear. The resulting spark would sometimes crack like a .22 rifle and flash in the dim light like a flashbulb! The victim rarely thought it was so funny, however.

Lined up on the ground floor were the transmitters, six pairs of 18 inch diameter klystron tubes, manufactured by Litton Corp., mounted in oil-filled transformers and extending up through the main floor some 10 feet. Each klystron tube would provide an average 2.5 megawatts of radar energy on the same frequency band as 2-meter amateur radio. Each pair of these klystron tubes was joined by waveguide nearly a yard wide and 18 inches deep, big enough for a small adult to crawl through. These pairs of transmitter tubes were routed to waveguide switches which routed the radar energy out of the building to the scanners.

The waveguide switches allowed any of the transmitter pairs to be switched into either of the adjacent scanners and allowed transmitters to be switched in or out as maintenance requirements or equipment failures dictated. Massive water-cooled dummy loads balanced the transmitter energy between the switches.

Each pair of klystron tubes was fed from an electrical charge built up on immense capacitors which lined the walls of a capacitor vault, an enclosed room about 18 by 30 feet in dimension. The capacitor vaults lay next to the transmitters against the walls of the main floor, several vaults on each side. The individual capacitors were cylindrical, about three feet tall and a foot in diameter. The capacitor vault held dozens of these capacitors which were connected together to make up the pulse forming network of the transmitter. Occasionally, a capacitor would fail, exploding in the vault, blowing the insulating tar-like substance all over the inside of the vault, sounding just like dynamite and occasionally causing a small fire.

The first explosion I heard was frightening, but after hearing several and not having responsibility for the transmitters, these explosions soon became just part of the sounds of the site. Never having had to clean up one of the capacitor vaults, I can nonetheless imagine it to be a terrible job that is time-consuming, stinking, and perhaps dangerous.

The middle transmitter building, Building Two, held the main control room for the radar system and the MIPS computer room. Special clearance was required to enter both these rooms. From the central control room, signals travelled to the other buildings commanding switching transmitters to scanners, bringing repaired receivers online, and executing other control tasks. Technicians had to receive permission from the controllers here in order to take a component offline for service.

The MIPS received signals from the three transmitter buildings, absorbing information about targets seen penetrating the detection radar energy beams. The MIPS consisted of a pair of IBM 7094 mainframe computers. Data from radar targets was analyzed and calculations made resulting in a prediction of whether a radar target could be a threat to North America. The MIPS output was sent to NORAD Headquarters at Cheyenne Mountain, near Boulder, Colorado. There, on a display panel representing a map of North America, would be displayed an ellipse which represented the probable impact area of a missile launched in the Soviet Union. Happily, with one exception, the only targets displayed on the display board were those of countless simulations run to test the effectiveness of the system.

The single exception occurred shortly after the BMEWS at Thule went into operation. In October, 1960, the moon rose over the horizon directly in line with one of J Site's detection radar beams. The engineers who designed the BMEWS system had apparently not considered that the ultra-high powered radar beams would reach the moon and in about 2 seconds, return to the super-sensitive BMEWS receivers. The resulting returns swamped the MIPS with return information, sending thousands of threat warnings to Cheyenne Mountain. While the angles, speeds, and doppler information did not fit the model algorithms of a real threat, the sheer vastness of the return information overwhelmed the system. The U.S. did not react to the point that we were brought to the brink of war, but the doors to Cheyenne Mountain were closed and locked for several hours while analysts tried to determine the cause of the fiasco. Once it was understood what caused the problem, a solution was quick to come. A modification to the radar receivers, called a "Moon Gater" for its ability to block, or gate, moon returns by shifting receiver frequency every one-and-a-half seconds, was designed by RCA engineers and installed on all the BMEWS receivers. When moonrise was forecast in one of the BMEWS sectors, the Gater was turned on. Every second and a half, the receiver frequency shifted, and the returns from the moon were ignored. The frequency shift caused the receivers to run somewhat detuned, and lights in the DRAM room routinely turned yellow.

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© Copyright 1996, Gene P. McManus, Baltimore, OH