Dynamic and static modeling of the Shuttle Orbiter's Thermal Protection System

Abstract

Seventy percent of the surface of the Shuttle Orbiter is covered by a Thermal Protection System, consisting of ceramic tiles bonded to the Orbiter's aluminum skin through a felt pad. The structural evaluation of the tile/pad system is complicated by the nonlinear elastic properties of the pad. This paper describes the dynamic and static analysis methods utilized to model this nonlinear behavior. Comparisons between test and analysis are shown. Vibration tests of individual tiles identified tile response which results from the nonlinearity of the pad. These phenomena include a highly distorted response waveform when the tile/pad system is base-driven dinusoidally and resonant frequencies which are dependent on both steady pre-load and amplitude of the base drive input. The dynamic analysis accounts for the nonlinear stiffening, hysteresis and viscous behavior of the pad material. Material characterization tests of the pad revealed a load displacement nonlinearity which is agravated with repeated load cycles. A nonlinear stress analysis procedure was developed and programmed to permit the calculation of stresses at the tile/pad bondline for an arbitrary pad contiguration.