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NASA SBIR Phase I/II: Precision Eddy Current Sensor for Nondestructive Evaluation of Spacecraft Structures

Left: Illustration of NDE tool. Right top: Photo of Al test piece with various defects in the surface. Right bottom: Output from EHT HGI NDE as the probe is swept from left to right past each defect.

NASA develops and manufactures complex high-performance structures for space applications. Structural damage to spacecraft during missions can often be difficult to detect especially in multilayered or deep subsurface levels, including spacecraft structures, multilayered walls, and pressure tanks. For example, corrosion can occur beneath layer stack-ups and near fasteners that can be under at least 0.2” of Al or 0.5” of composite material. Visual inspection to identify areas of corrosion or cracks requires removal of the surface layers and can be time consuming and expensive, if not impossible. In order to mitigate risk to equipment and crew, NASA needs nondestructive evaluation (NDE) techniques and sensors that are capable of detecting cracks and corrosion of structures when these defects reside below conducting and non-conducting surfaces.

Eagle Harbor Technologies, Inc. (EHT) is developing an eddy current NDE tool based their high gain integrator developed for fusion science applications. The high gain integrator sensitivity is comparable with superconducting quantum interference devices (SQUIDS), without the need for low temperature components. The pre-Phase I mock-up has demonstrated improvements in depth detection of both cracks and small defects under Al stack-ups and continued work on this technique is expected to further increase sensitivity. EHT proposes further evaluation and optimization to produce a NDE for NASA applications.

NDE tool could detect 0.001′ crack under 0.8065″ of aluminum plates.

NASA is the primary customer for the high gain integrator based NDE tool. A handheld version of the NDE tool could be used by ground personnel, spacecraft crew, or automated robots to evaluate structures for subsurface defects. Additionally, this system could be built into materials for in situ evaluation. The eddy current NDE tool based on the EHT high gain integrator will have applications beyond spacecraft evaluation. EHT anticipates that this type of tool could be used for other aerospace applications including evaluation of aging commercial and military aircraft. With EHT’s ability to print small, flexible coils, these probes could be inserted into hard to access locations like piping or tubing.