The Space Shuttle Columbia catastrophic structural failure was caused by a dislodged piece of spray-on foam insulation (SOFI) from the external fuel tank. Separation of SOFI pieces may be caused by the presence within the foam of anomalies such as voids, delaminations and disbonds. These unwanted discontinuities may occur during the spraying of the foam onto the external tank or may be due to post-spray damage. High spatial resolution millimeter wave nondestructive testing and imaging techniques have shown great potential and overall system utility for evaluating internal SOFI structures. This paper presents the basic design of a 150 GHz imaging reflectometer system and discusses the results of a critical investigation of the capabilities of this system that examined a SOFI panel with subtle embedded delaminations and voids without sharp boundaries, and another special panel possessing unknown natural discontinuities (the result of intentional manufacturing processes). Finally, the information obtained from the millimeter wave images was correlated with information obtained from post-imaging dissection of the panel. It was shown that 91 % of the discontinuities (such as extended and localized voids and delaminations) were successfully identified using this millimeter wave imaging system.


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    Title :

    High resolution millimeter wave imaging of space shuttle external fuel tank spray-on foam insulation


    Additional title:

    Hoch auflösende Millimeterwellen-Abbildung von externen aufgeschäumten Tankisolationen


    Contributors:
    Kharkovsky, S. (author) / Zoughi, R. (author) / Hepburn, F.L. (author)

    Published in:

    Materials Evaluation ; 65 , 12 ; 1220-1229


    Publication date :

    2007


    Size :

    10 Seiten, 10 Bilder, 2 Tabellen, 24 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English