A pogo suppression system
prevents the transmission of low-frequency flow oscillations into
the high-pressure turbopump and, ultimately, prevents main combustion
chamber pressure (engine thrust) oscillation. Flow oscillations
transmitted from the space shuttle vehicle are suppressed by a partially
filled gas accumulator, which is attached by flanges to the high-pressure
oxidizer turbopump's inlet duct.
The system consists of a 0.6-cubic-foot accumulator with an internal
standpipe, helium precharge valve package, gaseous oxygen supply
valve package and two recirculation isolation valves (one located
on the orbiter).
During engine start, the accumulator is charged with helium 2.4
seconds after the start command to provide pogo protection until
the engine heat exchanger is operational and gaseous oxygen is
The accumulator is partially chilled by liquid oxygen during
the engine chill-down operation. It fills to the overflow standpipe
line inlet level, which is sufficient to preclude gas ingestion
at engine start.
During engine operation, the accumulator is charged with a continuous
gaseous oxygen flow maintained at a rate governed by the engine
The liquid level in the accumulator is controlled by the overflow
standpipe line in the accumulator, which is orificed to regulate
the gaseous oxygen overflow over the engine's operating power
level. The system is sized to provide sufficient replenishment
of gaseous oxygen at the minimum flow rate and to permit sufficient
gaseous oxygen overflow at the maximum decreasing pressure transient
in the low-pressure oxidizer turbopump discharge duct. At all
other conditions, excess gaseous and liquid oxygen are recirculated
to the the low-pressure oxidizer turbopump inlet through the engine
oxidizer bleed duct. The pogo accumulator is charged (pressurized)
at engine shutdown to provide a positive pressure at the HPOT
inlet, which prevents HPOT overspeed in the zero-gravity environment.