Modelling, simulation, and applied fuzzy logic for inlet pressure control for a Space Shuttle main engine at technology test bed

An oxidizer propellant system is currently exhibiting bottom tank pressure oscillation before and during Space Shuttle Main Engine (SSME) testing at NASA's Marshall Space Flight Center in Huntsville, Alabama. Excessive oscillation may cause inlet SSME Low Pressure Oxidizer Turbopump (LPOTP) pressure tolerances to be exceeded. To understand and remedy this problem, models of the system and its PID controller are developed. The performance characteristics are analyzed to locate any system design flaws. The models are verified by comparing simulation plots to actual plots of controller and system response. A fuzzy logic based proportional-derivative controller is investigated as an alternative to the classical PID controller. Fuzzy set membership functions and inference rules are established from an analysis of various command responses of the currently operative controller. Responses of the system controlled by the fuzzy controller and the system controlled by the PID controller are simulated and compared to actual system behavior. Both controllers are found to control the system adequately at the operating point chosen for their design. The PID controller also performed satisfactorily over the full operating range but the fuzzy controller failed to stabilize the system in some operating regions.