Detection of Space Shuttle tile defects using millimeter-wave radiometry

This paper describes the potential of millimeter-wave radiometry in the detection of subsurface anomalies in layered dielectric structures. Remote sensing techniques combined with automated vehicle health monitoring may be used to reduce the considerable expense of maintaining the thermal protection system (TPS) that makes possible the safe re-entry of NASA's reusable launch vehicle (RLV or Space Shuttle) into the Earth's atmosphere. Extensive surface damage to the TPS is readily detectable by optical techniques, so our applications will be on the thermal breeches, which occur underneath the reusable surface insulation (RSI), thereby making them difficult to find by visual means. This proof of concept was performed by first designing and building a 94-GHz Dicke radiometer. The system was calibrated, tested for sensitivity, stability, and accuracy, and then used to measure a sample of ideal and defective tiles provided by NASA/Ames Research Center.