\ Abstract This paper presents the theoretical foundation and application of two univariate failure detection algorithms to Space Shuttle Main Engine (SSME) test firing data. Both algorithms were applied to data collected during steady-state operation of the engine. One algorithm, the time series algorithm, is based on time series techniques and involves the computation of autoregressive models. Time series techniques have been previously applied to SSME data. The second algorithm is based on

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... andard signal processing techniques. It consists of tracking the variations in the average signal power with time. The average signal power algorithm is a newly proposed SSME failure detection algorithm. Seven nominal test firings were used to develop failure indication thresholds for each algorithm. These thresholds were tested using four anomalous firings aud one additional nominal firing. Both algorithms provided significantly earlier failure indication times than did the current redline limit system. Neither algorithm gave false failure indications for the nominal firing. The strengths and weaknesses of, the two algorithms are discussed and compared. The average signal power algorithm was found to have several advantages over the time series algorithm. AR ARMA CADS e(i)