Health and Maintenance Status Determination and Predictive Fault Diagnosis System, Phase I (HMSD/PFDS) develops intelligent health and maintenance status determination and predictive fault-diagnosis techniques for NASA rocket engines using model-based residual generation, neural-fuzzy evaluation, data fusion, and simulated or sensed engine data. The completed Stennis Space Center project focused on design and simulation of a functional prototype intended to improve safety, cost, graceful degradation, and re-optimization after failures.