NASA ground terminal communication equipment: Automated fault isolation expert systems

This paper describes the prototype expert systems that diagnose the Distribution and Switching System I and II (DSS1 and DSS2), Statistical Multiplexers (SM), and Multiplexer and Demultiplexer systems (MDM) at the NASA Ground Terminal (NGT) located at White Sands, New Mexico. A system-level fault isolation expert system monitors the activities of a selected data stream, verifies that the fault exists in the NGT and identifies the faulty equipment. Equipment-level fault isolation expert systems will be invoked to isolate the fault to a Line Replaceable Unit (LRU) level. Input and sometimes output data stream activities for the equipment are available. The system-level fault isolation expert system will compare the equipment input and output status for a data stream and perform loopback tests (if necessary) to isolate the faulty equipment. The equipment-level fault isolation system utilizes the process of elimination and/or the maintenance personnel's fault isolation experience stored in its knowledge base. The DSS1, DSS2, and SM fault isolation systems, using the knowledge of the current equipment configuration and the equipment circuitry, will issue a set of test connections according to the predefined rules. The faulty component or board can be identified by the expert system by analyzing the test results. The MDM fault isolation system correlates the failure symptoms with the faulty component based on maintenance personnel experience. The faulty component can be determined by knowing the failure symptoms.

The NGT fault isolation prototype is implemented in Prolog, C, and VP-Expert, on an IBM AT compatible workstation. The DSS1, DSS2, SM, and MDM equipment simulators are implemented in PASCAL. The equipment simulator receives connection commands and responds with status for the expert system according to the assigned faulty component in the equipment. The DSS1 fault isolation expert system was converted to C language from VP-Expert and integrated into the NGT automation software for offline switch diagnoses.

Potentially, the NGT fault isolation algorithms can be used for the DSS1, SM, and MDM located at Goddard Space Flight Center (GSFC). The prototype could be a training tool for the NGT and NASA Communications (Nascom) Network maintenance personnel.