Air Force Rome Air Development Center [RADC] developed the Back-Up Intercept Control (BUIC) system, which would later be improved in order to replace the Semi-Automatic Ground Environment (SAGE) air defense system. BUIC was 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 provided the AN/GSA-51 Radar Course Directing Group which functioned as the central control for Air Surveillance and Weapons Control for the BUIC system. The AN/GSA-51 included the following general capabilities:
The AN/GSA-51 consisted of a Burroughs D825 modular data processing system in which the operational program was stored and executed. For the BUIC application, two computer modules, six memory modules and three input/output modules were utilized. Data exchange occured simultaneously between any memory and any computer or input/output module. The modular nature of the equipment not only permited operation of the system when some modules are inoperative, but also permited convenient expansion to increase capability. The data processor could 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 accepted radar information from long range radar sites via the message processors. The data was 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, performed all the computations necessary for generating appropriately formatted display data. The display data, stored in core memory, was transferred via a controller-comparator to the display fields of a drum, which in turn automatically presented this data to each display console 30 times each second. To accomplish all of this, the computer executed a succession of program segments called up from the drums.
Display data available at each display console, which included up to 12,288 symbols or vector segments, was selected by an operator by means of 15 category selectors. Radar data displayed included current data together with up to seven history points to permit track initiation. Once the operator initiated 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 were automatically generated and transmitted based on track priority, or may be operator initiated.
When it established that defensive action was to be taken, the operator could call up weapons status information, which was continually updated via card reader inputs. He could then call upon the computer for solutions to possible intercepts, the solutions being made to appear at the requesting display console. Once a weapon was assigned, the computer generated the necessary launch and guidance commands, and the track on the weapon was initiated automatically. The launch and guidance commands, stored momentarily in core memory, were accepted by the message processor, formatted, and transmitted over the appropriate communication lines. All the while, messages were exchanged as required with adjacent air defense sectors.
Peripheral equipment performed support functions. Magnetic tape units are used for simulation inputs and recording for training, and backup storage for programs. A typewriter was a backup input for the card reader and is also used in system maintenance. A status display console presented indications of which units are "on-line," or "in test," or in a failed state. It also housed the central power control to assure orderly system shutdown without loss of stored data in the event of a power failure. A line printer provided high-speed printout to permit rapid program evaluation and change, and evaluation of test missions. Simulator message composers were training aids for weapons director, for both initial training and maintenance proficiency.
Since the D825 was a functionally modular data processing system, it was possible to achieve increased availability without full duplexing. This was accomplished by providing additional modules of the computer, memory, input/output module and an additional display. While the operational program was functioning, an error recovery program cycled in one computer, one memory, and one controller-comparator.
Computers were continually exchanged between the "backup" and operational group and other modules were continually checked. The operational program continually stored "safe data" to permit recovery from a temporary computation interruption. If an error was indicated, the operational computation was temporarily suspended and the system is turned over to the error recovery diagnostics program, which identified the faulty module and notified the operator via the status console and typewriter printout. The system returned automatically to the operational function with information on what modules were available for use, and the operational program reconfigured, utilizing the safe data previously stored. This recovery period varied from about 15 to 30 seconds. The failed module was then further analyzed, repaired and returned to the operational system.