This program is designed as a real-time aid to analyze system health.

The Propulsion Advisory Tool (PAT) is a knowledge-based computer program that monitors real-time data from more than 300 sensors in the space shuttle Main Propulsion System (MPS). The thermal conditions within the launch pad storage/transfer facility, MPS, and External Tank (ET) must be monitored during the propellant-loading process in order to maintain subcooled cryogenic-liquid conditions and prevent an LO2 geyser. The PAT knowledge base can provide a quick and accurate assessment of an anomaly by identifying both actual and potential system failures in addition to pertinent data for anomaly resolution.

In the terminology of artificial intelligence, this software is characterized as a knowledge-based reasoning tool. The knowledge base is coded using a natural language interface (plain English) and is developed based on existing requirements documents and knowledge captured from experts working in the propulsion arena. In this way, the expert system works within a framework similar to the way humans would; a system based on human logic and reasoning on quantitative real-time data.

The knowledge base was developed using a hybrid methodology of commercial off-the-shelf (COTS) tools and custom computer code. The COTS tools currently used in the PAT system are Gensym's G2 expert system shell and Oracle. Relational data bases containing real-time, full-rate shuttle data are used to assess the health of the data coming from the vehicle. The PAT uses rule and model-based approaches for the analysis of system health. Rules are used primarily for limit checking, formulating diagnostics, determining state conditions, and user interface tasks. The model base evaluates system configuration and component connectivity.

Pressure, temperature, and flowrates within the propellant loading system can be calculated, and the information can then be extrapolated in order to infer fluid conditions in other locations. Objects representing pressure and temperature sensors contain both the true system redline conditions and engineering estimates of what their values should be for each phase of the propellant load process. For a visual reference, the current value of key pressure/temperature sensors are plotted against the theoretical saturation curve.

Component electrical circuits have been modeled within the G2 knowledge base to reflect the active current path. The electrical circuit shows "live" wires along with active objects that represent the various talkbacks within the circuit. The power of this feature is that the systems engineer can directly relate the data provided by the orbiter with the paper-based drawings that describe the circuit design.

PAT displays include a page that informs the user of the current step in the propellant-loading procedure. Another display shows the loading system schematic. The components within the system are represented as live objects with user-defined attributes. Selecting these objects displays detailed information about that object. In addition, the fluid lines are colorized based upon the phase conditions of the propellant.

The PAT knowledge base will be part the expert-system tools for the next generation of shuttle-launch-processing software, referred to as the Checkout & Launch Control System (CLCS). In addition, the PAT software is used on the day of launch in the Launch Control Center at KSC for each shuttle mission. The PAT knowledge base architecture has been used as a prototype to design and as a basis for building several expert systems, one of which includes command and control for the ground checkout of flight-test hardware.

This work was done by Laurence H. Fineberg, James M. Engle, Anton C. Melichar, James R. Lane, John A. Marinuzzi, Jose Gallardo, Jim Howarth, Janice L. Lessman, and Manuel Beltran of Boeing North American Corp. for Kennedy Space Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to

the Patent Counsel
Kennedy Space Center; (407) 867-6225

Refer to KSC-11902.

NASA Tech Briefs Magazine

This article first appeared in the December, 1998 issue of NASA Tech Briefs Magazine.

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