Semi-Automatic Ground Environment (SAGE) Back Up Interceptor Control System (BUIC) Fact Sheet

The following fact sheet is from a memo in the Burroughs Corporation Collection (CBI 90), Product Literature (Box37) at the Charles Babbage Institute for Computer History, Minneapolis, MN.

Detroit, Michigan 48232
Phone: 875-2260, Ext. 2234
or contact:
Richard J. Brady
Defense, Space and Special Systems Group
Paoli, Pennsylvania
Phone: NIagara 4-6962



AN/GSA-51 Radar Course Directing Group for the Back Up Interceptor Control System (BUIC)

FUNCTIONAL DESCRIPTION: BUIC is a semi-automatic backup to SAGE which provides for conduct of the air battle in the event that portions of SAGE become inoperative. Burroughs Corporation is providing the AN/GSA-51 Radar Course Directing Group which functions as the central control for Air Surveillance and Weapons Control for the BUIC system and includes the following general capabilities:

  • Air Surveillance
    • Acceptance of radar data from long range radars.
    • Formation of tracks based on radar input presentation of this data for evaluation by operators.
    • Provision of capability for manual track information and automatic maintenance of tracks.
  • Weapon Control
    • Display of available weapons to permit pairing with tracks and manual commitment.
    • Automatic analysis of commitment to assure intercept ability.
    • Automatic transmission of pre-launch and fire command based on operator input.
    • Automatic generation and transmission of guidance commands.

The AN/GSA-51 consists of a Burroughs D825 modular data processing system. It is in the modular data processor that the operational program is stored and executed. For the BUIC application, two computer modules, six memory modules and three input/output modules are utilized. Data exchange occurs simultaneously between any memory and any computer or input/output module. The modular nature of the equipment not only permits operation of the system when some modules are inoperative, but also permits convenient expansion to increase capability. The data processor can be readily expanded to up to four computers, 16 memories and 20 input/output modules with no obsolescence of hardware or software. Input/output modules for the BUIC system consist of message processors and controller-comparators.

BUIC accepts radar information from long range radar sites via the message processors. The data is temporarily stored, formatted into computer words, and transferred to core memory via a controller-comparator. Controller-comparators handle data transfers between core memory and all devices except computers.

A computer, operating on the data stored in core memory, performs all the computations necessary for generating appropriately formatted display data. The display data, stored in core memory, is transferred via a controller-comparator to the display fields of a drum, which in turn automatically presents this data to each display console 30 times each second. To accomplish all of this, the computer executes a succession of program segments called up from the drums.

Display data available at each display console, which includes up to 12,288 symbols or vector segments, is selected by an operator by means of 15 category selectors. Radar data displayed includes current data together with up to seven history points to permit track initiation. Once the operator initiates a tracking action by means of a light pen on the display, the computing system automatically maintains the track by prediction and examination of incoming data for correlation. Height requests are automatically generated and transmitted based on track priority, or may be operator initiated.

When it is established that defensive action is to be taken, the operator can call up weapons status information, which is being continually updated via card reader inputs. He can then call upon the computer for solutions to possible intercepts, the solutions being made to appear at the requesting display console. Once a weapon is assigned, the computer generates the necessary launch and guidance commands, and the track on the weapon is initiated automatically. The launch and guidance commands, stored momentarily in core memory, are accepted by the message processor, formatted, and transmitted over the appropriate communication lines. All the while, messages are being exchanged as required with adjacent air defense sectors.

Peripheral equipment performs support functions. Magnetic tape units are used for simulation inputs and recording for training, and backup storage for programs. A typewriter is a backup input for the card reader and is also used in system maintenance. A status display console presents indications of which units are “on-line,” or “in test,” or in a failed state. It also houses the central power control to assure orderly system shutdown without loss of stored data in the event of a power failure. A line printer provides high-speed printout to permit rapid program evaluation and change, and evaluation of test missions. Simulator message composers are training aids for weapons director, for both initial training and maintenance proficiency.

Since the D825 is a functionally modular data processing system, it is possible to achieve increased availability without full duplexing. This is accomplished by providing additional modules of the computer, memory, input/output module and an additional display. While the operational program is functioning, an error recovery program is being cycled in one computer, one memory, and one controller-comparator.

Computers are continually exchanged between the “backup” and operational group and other modules are continually checked. The operational program continually stores “safe data” to permit recovery from a temporary computation interruption. If an error is indicated, the operational computation is temporarily suspended and the system is turned over to the error recovery diagnostics program, which identifies the faulty module and notifies the operator via the status console and typewriter printout. The system is returned automatically to the operational function with information on what modules are available for use, and the operational program reconfigures, utilizing the safe data previously stored. This recovery period will vary from about 15 to 30 seconds. The failed module is then further analyzed, repaired and returned to the operational system.