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Detail of the liquid propellant gas generator.

On a normal H-1, this is where the solid propellant gas generator would attach. The SPGG, sometimes called a "spinner", would provide the initial gasses to spin the turbine, allowing the turbopumps to provide enough pressure to supply propellants to the LPGG.

However, this is not an SPGG. With the threaded fitting, I wonder if the Cold Calibration test stand facility provided a substitute to provide the initial turbopump spin.