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View of the liquid propellant gas generator (LPGG) and turbine.

Picture 2 of 2.

The LPGG is essentially a small, inefficient rocket engine; it burns RP-1 and LOX to produce hot gas, which is routed to the turbine, spinning the turbine's two wheels, to spin a shaft and drive the turbopumps through a gearbox.

The grey disk on the LPGG is a non-OEM closure to cover the opening where the solid propellant gas generator (SPGG) would attach.