Semi-Automatic Ground Environment - Description

Description

The AN/FSQ-7 is, physically, the largest computer ever built, and will likely hold that record for the future. Each machine used 55,000 vacuum tubes, about ½ acre (2,000 m²) of floor space, weighed 275 tons and used up to three megawatts of power. Although the machines used a large number of vacuum tubes, the failure rate of an individual tube was low due to efforts in quality control and a novel quality assurance system called marginal checking that discovered tubes that were growing weak, before they failed. Each SAGE site included two computers for redundancy, with one processor on "hot standby" at all times. In spite of the poor reliability of the tubes, this dual-processor design made for remarkably high overall system uptime. 99% availability was not unusual.

SAGE sites were connected to multiple radar stations which transmitted tracking data (range and azimuth) in digitized format by modem over ordinary telephone lines. These digitized inputs were automatically prepared from analog radar inputs by the AN/FST-2B (or successor, AN/FYQ-47) at the radar stations. The SAGE computers then collected the tracking data for display on a CRT as icons. Situation Display (SD) console operators at the center could select any of the "targets" on the display with a light gun, and then display additional information about the tracking data reported by the radar stations. Up to 150 operators could be supported from each center. Each SD operator console was equipped with an integral cigarette lighter and ashtray.

SAGE site operators could also request height data when needed from their CRT. These height requests were digitized and sent to a radar station that was tracking the "targets". At the radar station, the height requests were displayed to an operator on an analog Range Height Indicator (RHI) CRT display by moving the height cursor. The operator then centered the height cursor on the "target" and depressed a button to send the updated height information back to the SAGE site in much the same way as the tracking data.

When a target was of interest, SAGE also helped the operator to select a proper response. Reports similar to those from the radar stations kept the SAGE system up to date with information on the availability and status of various weapons and aircraft, including all airfields, BOMARC and Nike Hercules anti-aircraft missile sites. When the operator chose one of these to intercept the target, orders would automatically be sent via teletype to local controllers who would take control. Additional messages would also be sent to higher headquarters, as well as other SAGE centers.

In normal operation, communications between the SAGE centers and the interceptor aircraft was relayed via radio equipment at the radar sites, which were more widely spread out than the SAGE centers themselves. A properly equipped aircraft, like the F-106 Delta Dart, could feed the SAGE directions into the autopilot and fly "hands off" to the interception. Older aircraft, which were common when SAGE was first being deployed, could be directed by voice.

On occasion, SAGE weapons directors would get "fam flights" (familiarization flights) on board two-seat interceptors like the F-94 Starfire, F-89 Scorpion, F-101B Voodoo, and various versions of the F-4 Phantom. This was done, in order for the weapons director to gain working knowledge of the ever improving radar systems, and for timing & systems calibration. Various versions of the EC-121 Warning Star were also utilized under the SAGE system.