Space Shuttle Main Propulsion Test System Resonance Survey by Single Point Excitation Method

The single point excitation procedure employed to experimentally determine the natural modes of the Space Shuttle Main Propulsion Test Article (MPTA) installed in the static firing test stand at the National Space Technology Laboratory is described. Test techniques, equipment, and associated software are described and a comparison to math model results is included.

Three single point hydraulic exciters were individually used to apply random excitation forces to the MPTA thrust structure supporting the main engines. Resulting accelerations and force signals were processed with mini-computer test equipment to determine resonant frequencies, mode shapes, and damping values below 50 Hz. Two configurations, one involving empty H₂ and LOX tanks and the other involving 40% full LOX tank and feed lines, were tested. Results were obtained with minimum Main Propulsion Test schedule impact and at minimum cost.