Semi-Automatic Ground Environment
'SAGE'

On this page: SAGE, the F-106 and the MA-1 System     SAGE System Facts     SAGE Direction Center (DC) and Control Center (CC) Locations

Semi-Automatic Ground Environment - SAGE

SAGE Weapons Directors Console with cathode ray tube display screen. SAGE Console. The light pen, which was shaped similar to a handheld power drill or gun, is resting on the console.  It could work directly on the scope or in holes just right of the scope (2nd photo). The SAGE was a real-time, computer based command and control system designed in the late 1950's and fully functional and deployed by 1963 and used up though 1983. This automated control system was used by NORAD for tracking and intercepting enemy bomber aircraft.  In the later versions the system could automatically direct aircraft to an interception by sending instructions directly to the aircraft's autopilot. The system consisted of 24 Directional Centers around the United States as well as 3 Combat Centers.  Data was collected at each of the directional centers from over 100 different sources such as radar, human volunteers and aircraft sightings.  This information was collated and forwarded via telephone communication lines to one of the three combat centers.  The information was interpreted by the computer and displayed on something totally revolutionary for that time period: a cathode ray tube display screen. The display, while similar to a radar screen, was extremely versatile. The operator of the terminal could pull up past positions of aircraft or missiles, as well as project future locations. In addition, the system used another feature far in advance of its time: a light gun. The gun was used by the operators to point at an aircraft on the screen, and the computer would respond by displaying related identification information about that aircraft. The system has the dubious distinction of holding the record for the world's largest (physical size) computer ever created.

THESE FILMS MADE MY US GOVERNMENT AND ARE PUBLIC DOMAIN SAGE - Semi Automatic Ground Environment - Part 1/2 SAGE - Semi Automatic Ground Environment - Part 2/2

SAGE consoles and operators	SAGE Sector Control Room. The 'big screen' depicts the North American eastern coast from the extreme west end of Nova Scotia (upper right) to Philadelphia (lower left). Cape Cod is approximately centered with Long Island to its left, and two "targets" are being tracked offshore	SAGE Light Gun. It could work directly on the scope or in the holes in the consoles [MITRE Corporation]
SAGE Combat Center, Syracuse Air Force Station. Command post staff communicate with other SAGE sectors, monitor the air battle, and direct weapons [1959].	Control room for the FSQ-7 computer equipped with separate consoles, standard IBM punched-card units and magnetic tape units for each of the duplicate computers	SAGE Light Gun prototype [MITRE Corporation]

By the time the SAGE system was fully deployed, it was obsolete, no match for the speed of new ICBMs.  SAGE was never designed to counter a space or missile threat.  It was designed to counter the air threat.  SAGE was operating long after the ICBM threat was recognized.  Maybe it would have been closed due to ICBMs had the Soviets gotten rid of its manned bomber force and maintained only the Strategic Rocket Forces.  SAGE was eventually closed because the bomber threat diminished, thus the mission became airspace sovereignty not defense.  Some SAGE centers continued to operate until 1983, more than 20 years after its technology was obsolete and its mission rendered militarily insignificant by the ICBM.  As a final irony, in the last years of its use, replacement vacuum tubes had to be purchased from Soviet-bloc countries where they were still being widely manufactured.

Nevertheless, SAGE was extremely important and its many technical advances in on-line systems, interactive and real-time computing including modems for communication between sites over telephone lines, networking, light guns, graphical displays, and reliable magnetic core memory.  The technology led to Sabre, the airline reservation system still in use today.

The SAGE system and its development is generally considered to be one of the most advanced and successful large computer systems ever developed.  According to Jim Ray, "SAGE was one of the engineering marvels of the century. In fact if it looked better, it might have been ranked with the Eiffel Tower, the Saturn Rocket or the Golden Gate Bridge for engineering accomplishment. It also pioneered some of the most of the important technology used to facilitate internet processing today: i.e., the modem, the mouse [light gun], multi-tasking, array processing, computer learning, fault detection, magnetic memory, and interactive computer graphics. Most important, it worked well enough for each center to coordinate about 100 operators , track 300 simultaneous flights, control numerous sorties against a maneuvering radar-jamming 'enemy', and coordinate 'friendly' NIKE and Bomarc defenses."

IBM built the SAGE hardware based on the Whirlwind computer design at MIT.  The software was written by The Rand Corporation and the System Development Corporation (SDC) and employed about 20% of the world's programmers at the peak of the project. When it was complete, the 250,000 lines of code was the most complex piece of software in existence.

Each of the 27 SAGE installations had two separate computers, the second serving as a "hot standby" in case the active computer failed.  With this backup, availability was an unprecedented 99.6%, when many other computers from that era would fail every few hours. The computer weighed 300 tons and typically occupied one floor of a huge windowless 4-story concrete blockhouse. On another floor, dozens of Air Force operators watched their display screens and waited for signs of enemy activity.

Some SAGE centers continued to operate until 1983, more than 20 years after its technology was obsolete and its mission rendered militarily insignificant by the ICBM.  As a final irony, in the last years of its use, replacement vacuum tubes had to be purchased from Soviet-bloc countries where they were still being widely manufactured.

 

A SAGE diagram showing the "Elements of the Air Defense Semi-Automatic Ground Environment System": Interceptor fighter (F-106 shown); Long range radar; Texas Tower; Gap Filler Radar; Picket Ship; Airborne Early Warning Radar; and Guided Missiles. [June 27, 1958 Bendix Aviation Corporation]	Typical SAGE site "cube" with four floors, air conditioning and wiring on the ground, the computers on the second floor, offices on the third and the combat center on top.  A "big screen" in the control room extends from the third to fourth floor.	Magnetic Cores were the basic technology for computer main memory from the 1950s into the early 1970s. The tiny iron oxide cores could be magnetized clockwise or counterclockwise to represent bits of information. Data could be retrieved in millionths of a second. This array is from an IBM-built SAGE computer from the 1950s.
Air Defense diagram showing relationship of SAGE to national air defense system [1955]	Typical 4-story SAGE Direction Center. 1st floor: Air cooling and ducting equipment plus telephone frames, cables, and equipment to maintain communication and radar data flow. Power house attaches to operations part of building by a common wall. 2nd floor: The SAGE FSQ-7 duplex computers. 3rd floor: Service area for the operation room above plus office and storage space, the subsector command post, and the Kelvin-Hughes projector and air-situation display screen. 4th floor: Operational areas where Air Force staff supervised each major air defense function (weapons direction, identification, air surveillance, etc.) from separate areas.

SAGE, the F-106 and the MA-1 System [see History of the F-106 page]

The F-106A Delta Dart operated in conjunction with the SAGE (Semi-Automatic Ground Environment) network linked via the Hughes MA-1 fire-control system to the F-106.  It operated by plotting the course needed to intercept an enemy aircraft, automatically sighted the target, fired the air-to-air missiles, and then automatically placed the F-106 on the correct course to disengage.  The F-106 could actually be computer-flown during most of its mission, the pilot being needed only for takeoff, landing, or in case something went wrong with the automation.

The primary means of communication between SAGE and the F-106 was accomplished using Time Division Data Link (TDDL), intent being to provide non-verbal commands for vectoring the aircraft towards a successful intercept.  Signals from the SAGE AN/GKA-5 transmitter were received by the F-106 data link receiver; either an AN/ARR-60 or AN/ARR-61.  SAGE provided two modes of control for interceptor command and navigation: Close Control (CC) and Modified Close Control (MCC).  The SAGE transmission would dictate which of the two modes would be dominant in a given scenario i.e. SAGE would dictate if the intercept would be conducted under CC or MCC.

Close Control (CC) - The primary mode of the data link was Close Control.  In this mode the SAGE transmitter would send an encoded message to the aircraft Data Link receiver which would check it for validity and proper aircraft address before sending the information on to the F-106 Delta Dart's MA-1 computer.  The MA-1 computer would in turn use this information to send commands for mach, altitude and heading to the Automatic Flight Control System (AFSC) and cockpit displays for vectoring the interceptor towards the target.  While the AFSC could automatically accomplish the altitude and heading commands, the pilot needed to manually adjust the throttle to achieve the command speed.

Modified Close Control (MCC) - When an F-106 was paired up with a target, in addition to the altitude, speed and heading CC commands for the interceptor, SAGE would also send MCC messages that contained extensive target information.  The Data Link receiver would validate the messages and pass them on to the MA-1 computer.  The MA-1 computer would use this information to calculate the tactics required and send the corresponding speed, altitude and heading commands to the cockpit displays and AFSC.  Two types of MCC messages were transmitted by SAGE: MCC-Region Origin (MCC TACAN) and MCC-Interceptor (MCC-NO TACAN).

• In MCC Region Origin, target X and Y coordinates were referenced with respect to the SAGE origin

• In MCC-Interceptor, target position was referenced with respect to the interceptor.

The default mode was MCC-Region Origin.  MCC-Interceptor usually had to be requested by the pilot except when MCC messages where sent as backup messages during the CC dominant mode.

In the Cockpit - TDDL interaction between SAGE and the F-106 was controlled in the cockpit using the Data Link Converter Receiver Control Panel located on the right console.  The pilot could select a SAGE frequency using one of 26 preset channels, or manually insert a four digit channel.  Using the Address Select switch, the pilot could select one of 32 aircraft addresses that would be compared to the aircraft address embedded in the SAGE signal as one of the means for validating the transmission.  The receiver also accommodated back-up data link voice communication.

The Display/Automatic Mode Selector Switch on the main instrument panel determined what data link information was displayed and how intercept tactics would be executed.  There were two positions for the switch: MAX RANGE and DL MIN TIME.  Each had different meanings depending on which data link mode was dominant (CC or MCC).  For example if by SAGE command the dominant mode was CC, then there was no difference between the MAX RANGE and DL MIN TIME settings because SAGE was performing and issuing the interceptor guidance calculations.  However, if the dominant mode was MCC, the position of the switch governed the profile and tactics commanded by the MA-1 computer to approach and attack the target.  Typical tactics included:

• Cutoff

• Pursuit

• Stern Before Offset

• Stern After Offset

• Non-commit

The pilot could determine the selected tactic by setting his Homing Point Selector Switch to “U” and monitoring the target altitude marker on the AVVI.  The marker would position at an altitude corresponding to one of the above tactics for a period of time, and then revert back to its normal function.

Additional TDDL displays in the cockpit included:

• the positioning of target and interceptor “bugs” on the Tactical Situation Display (TSD)

• command airspeed and mach on the Airspeed Mach Indicator (AMI)

• command altitude and target altitude on the Altitude Vertical Velocity Indicator (AVVI)

• command bank and steering on the Attitude Direction Indicator (ADI)

• command heading and target course and bearing on the Horizontal Situation Indicator (HSI)

• time to offset and target range and azimuth relative to interceptor on the radar scope

The proper functioning of the data link was indicated by the Computer Mode Annunciator on the main instrument panel, which could display either “DL” for current data link, “DR” for dead reckoning or a barber pole if target information is over one minute old or no MCC data link was received during attack. Once the pilot locked the radar onto the target, all data link information was suspended while the MA-1 computer conducted the attack and firing sequence. Upon completion of the attack and selection of AUTO NAV by the pilot, data link information would resume for return to base vectoring.

SAGE System Facts