Precision Eddy Current Sensor for Nondestructive Evaluation of Spacecraft Structures

In order to mitigate risk to equipment and crew, NASA needs nondestructive evaluation (NDE) techniques and sensors that are capable of detecting holes, pits, cracks, and corrosion of structures that are not visually accessible. The Independent Assessment of Instrument for ISS On-Orbit NDE highlights the challenges and importance of performing NDE of the international space station (ISS) pressure walls. These walls are subject to impacts from space debris and micrometeroids, causing punctures in the walls, which are then patched with pressure wall repair kits (PWRKs). Commercially available NDE tools are unable to meet all the requirements of scanning through PWRK patches to assess the nature of the covered defects.EHT has developed an innovative NDE tool that is able to circumvent the usual limitations of eddy-current based NDE. The EHT NDE tool generates eddy currents by physically moving a permanent magnet over a sample made of a conductive material. The magnetic perturbation caused by passing over non-uniform regions of the sample under test is picked up by an inductive coil. EHT's High Gain Integrator technology is capable of measuring the small signals produced. Using this tool, EHT has demonstrated increased scanning depth compared to other NDE tools, up to 1/4" depth, already thicker than ISS walls. A through hole defect under a PWRK patch has been successfully imaged.Throughout the Phase II, the sensitivity and spatial resolution of the NDE tool will continue to be improved and a standalone system developed. EHT's NDE tool will be specifically engineered to meet NASA's on-orbit NDE needs, including for the ISS application and for other applications of interest such as Composite Overwrapped Pressure Vessels (COPVs).