An investigation of space shuttle main engine shutdown chugging instability

The Space Shuttle Main Engines experience a low frequency pressure pulsation in both the fuel and oxidizer preburners during shutdown. The pressure pulsations (chugging) occur during the helium purge of oxidizer from the preburner manifolds. Possible causes and triggering mechanisms are considered as details of the chugging process are presented and discussed. A simple chugging model capable of predicting pressure excursion amplitudes and frequencies is proposed and preliminary results presented.