Vibration Analysis of the Space Shuttle External Tank Cable Tray Flight Data with and without PAL Ramp

External Tank Cable Tray vibration data for three successive Space Shuttle flights were analyzed to assess response to buffet and the effect of removal of the Protuberance Air Loads (PAL) ramp. Waveform integration, spectral analysis, cross-correlation analysis and wavelet analysis were employed to estimate vibration modes and temporal development of vibration motion from a sparse array of accelerometers and an on-board system that acquired 16 channels of data for approximately the first 2 min of each flight. The flight data indicated that PAL ramp removal had minimal effect on the fluctuating loads on the cable tray. The measured vibration frequencies and modes agreed well with predicted structural response. Nomenclature a instantaneous (time dependent) value of measured accelerometer signal v instantaneous (time dependent) value of time-integrated accelerometer signal (velocity) x instantaneous (time dependent) value of double time-integrated accelerometer signal (displacement)