Nondestructive Evaluation of Foam Insulation for the External Tank Return to Flight

Nondestructive evaluation methods have be en developed to identify defects in the foam thermal protection system (TPS) of the Space Shuttle External Tank (ET). Terahertz imaging and backscatter radiography have been brought from prototype lab systems to production hardened inspection tools in just a few years. These methods have b een demonstrated to be capable of detecting void type defects under many inches of foam which , if not repaired, could lead to detrimental foam loss. T he evolution of these methods from lab tools to implementation on the ET will be discussed.