Hydrazine gas generator performance on Space Shuttle

The design, functions, performance, and applications of the hydrazine gas generators (GG) on the STS are detailed. The GGs provide gas horse power for the APUs that drive the hydraulic pumps on the SRBs, which have two cross-linked systems. The Orbiter has three-cross-linked APU systems, used for gimballing the main engine and booster nozzles, actuating the main engine fuel valves and the ET umbilical disconnect, actuation of the control surfaces, and powering the landing gear, brakes, and nose wheel steering. The major design components of the Orbiter GGs are an injector, a catalyst bed, a decomposition chamber, an exhaust nozzle, and an interface structure, with the main structural material being Hasteloy B. Hydrazine injected and dispersed into the catalyst bed decomposes into gas and exits for expansion in an APU turbine. Twenty-six GGs have flown on missions STS-1 through STS-6 with over three tons of hydrazine having been expended over 44 hr of operations, as no refurbishment to that point was necessary.