Evaluation of holographic subsurface radar for NDE of space shuttle thermal protection tiles

Experiments have been carried out to evaluate holographic subsurface radar (RASCAN) for non-destructive evaluation (NDE) of subnominal bond conditions between the Space Shuttle Thermal Protection System tiles and the aluminum substrate. Initial results have shown detection of small voids and spots of moisture between Space Shuttle thermal protection tiles and underlying aluminum substrate. The characteristic feature of this device is the ability to obtain one-sided radar soundings/images with high sensitivity (detecting of wire of 20 micron and less in diameter), and high resolution (2 cm lateral resolution) in the frequency band of 3.6-4.0 GHz. JPL's advanced high-speed image processing and pattern recognition algorithms can be used to process the data generated by the holographic radar and automatically detect and measure the defects. Combining JPL's technologies with the briefcase size, portable RASCAN system will produce a simple and fully automated scanner capable of inspecting dielectric heat shielding materials or other spacecraft structures for cracks, voids, inclusions, delamination, debonding, etc.. We believe this technology holds promise to significantly enhance the safety of the Space Shuttle and the future CEV and other space exploration missions.