Analysis of pogo on the space shuttle: Accumulator design guidelines and planar multiengine model development

The design guidelines were generated to support the selection of the baseline accumulator configuration for the space shuttle. They were based upon the elimination of the instabilities that had been predicted for the shuttle system (in the absence of accumulators) using the single-engine model. The multiengine pitch plane stability model was subsequently developed to enable a more refined analysis of the pogo problem. The results obtained with this refined model, in the absence of accumulators, indicated a generally stable system. However, it was found that reasonable adjustment of the axial motion of the feedline aft support on the external tank could induce instability of the system. This instability was eliminated by the addition of high-pressure oxidizer turbopump inlet accumulators to the system. The results obtained with the refined model did not suggest a need to alter the design guidelines that had been obtained previously. The analyses with the multiengine model also treated the question of the use of a phase margin in the system stability requirements