Vibroacoustic Modeling for Space Shuttle Orbiter Thermal Protection System

Abstract

A ceramic tile has been developed as part of the thermal protection system of the Space Shuttle orbiter. These tiles are individually attached to the panels of the orbiter through a flexible pad. Closed-form and numerical linear random vibration models were formulated to predict tile dynamic stresses due to the broadband acoustic field on the outer surface and the base excitation on the bonded surface. Analytical results were compared to a full-scale random test. The analytical models were then used to predict dynamic stresses on selected tiles. Conditions were established as to the accuracy of the closed-form techniques. Nomenclature As = strain isolation pad (SIP) surface area A ( = tile exposed surface area c = linear viscous damping coefficient of SIP dB = decibels dco = frequency differential, rad/s fj = /th frequency, Hz fn = natural frequency of tile, Hz F (t) = acoustic force acting on tile g = acceleration of gravity H(fi) = transfer function between tile acceleration and panal acceleration for the /th one-third octave band //;(/,) = transfer function between tile velocity and acoustic pressure for the /th one-third octave band H2 (ff) = transfer function between tile displacement and