Pogo Suppression System

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 available.

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 operation point.

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.