The Space Shuttle Columbia's catastrophic accident emphasizes the growing need for developing and applying effective, robust, and life-cycle-oriented nondestructive testing (NDT) methods for inspecting the shuttle external fuel tank spray on foam insulation (SOFI). Millimeter-wave NDT techniques were one of the methods chosen for evaluating their potential for inspecting these structures. Several panels with embedded anomalies (mainly voids) were produced and tested for this purpose. Near-field and far-field millimeter-wave NDT methods were used for producing images of the anomalies in these panels. This paper presents the results of an investigation for the purpose of detecting localized anomalies in several SOFI panels. To this end, continuous-wave reflectometers at single frequencies of 33.5, 70, or 100 GHz representing a relatively wide range of millimeter-wave spectrum [Ka-band (26.5-40 GHz) to W-band (75-110 GHz)] and utilizing different types of radiators were employed. The resulting raw images revealed a significant amount of information about the interior of these panels. However, using simple image processing techniques, the results were improved in particular as it relates to detecting the smaller anomalies. This paper presents the results of this investigation and a discussion of these results.


Electrical and Computer Engineering

Keywords and Phrases

100 GHz; 26.5 to 40 GHz; 33.5 GHz; 70 GHz; 75 to 110 GHz; Insulating Foam; SOFI; Space Shuttle; Continuous-Wave Reflectometers; Embedded Anomalies; Far-Field Millimeter-Wave NDT Methods; Foams; Fuel Systems; Image Processing; Image Processing Techniques; Insulating Foam; Insulating Materials; Millimeter Waves; Millimeter-Wave NDT Techniques; Millimeter-Wave Detection; Millimeter-Wave Spectrum; Millimetre Wave Measurement; Near-Field Millimeter-Wave NDT Methods; Nondestructive Testing; Nondestructive Testing (NDT); Nondestructive Testing Methods; Reflectometers; Space Shuttle External Fuel Tank; Space Vehicles; Spray on Foam Insulation; Spray on Foam Insulation (SOFI); Tanks (Containers); Voids (Solid); Composite Testing and Evaluation; Microwave and Millimeter Wave Imaging

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version

Final Version

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© 2006 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Jul 2006