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Flow Modeling of the Galaxy XII Dual Mode Bipropellant Propulsion Subsystem

The Galaxy XII dual mode bipropellant propulsion subsystem (monopropellant hydrazine/nitrogen tetroxide) i s used for orbit transfer to geosynchronous orbit, three -axis stabilization, and stationkeeping. Analytical flow modeling of the bipropellant portion of the propulsion subsystem is primarily necessary to determine the flow orifice pressure drops required t o meet engine inlet pressure requirements. In addition, subsystem modeling provides a determination of propellant consumption and distribution by simulating each of the bipropellant ascent maneuvers. This also allows it to be a tool for mission operations personnel to utilize as it provides predictions on pressurant and propellant tank blowdown pressure, latching isolation valve timing, pressure regulator performance, pressure transducer telemetry, and inlet conditions at the bipropellant engines. The devel opment and use of this model for a dynamic, pressure -regulated, multi -thruster system as well as the model’s successful on -orbit simulation of the propulsion subsystem after Galaxy XII’s April 2003 launch are documented.