Provided are a spacecraft liquid propulsion system failure diagnosis system that can reliably diagnose a failure of a spacecraft, and a spacecraft liquid propulsion system failure diagnosis method. The spacecraft liquid propulsion system includes a plurality of thrusters and supply pipes that are connected to the thrusters. The system comprising: a pressure sensor that detects the pressure inside the supply pipe as time series data; a frequency spectrum conversion unit that converts time series data into frequency spectrum data; a storage unit that stores, as a data set, frequency spectrum data generated on the basis of an analysis model based on computer simulation or test results of a test device; a comparison unit that compares the data set with the frequency spectrum data generated by the frequency spectrum conversion unit; and a determination unit that determines a failure in any of the plurality of thrusters on the basis of the comparison result of the comparison unit.
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