Space Shuttle Columbia's catastrophic failure, the separation of a piece of spray-on-foam insulation (SOFI) from the external tank (ET) in the Space Shuttle Discovery's flight in 2005 and crack detected in its ET foam prior to its successful launch in 2006 emphasize the need for effective nondestructive methods for inspecting the shuttle ET SOFI. Millimeter wave nondestructive testing methods have been considered as potential and effective inspection tools for evaluating the integrity of the SOFI. This paper presents recent results of an investigation for the purpose of detecting vertical cracks in SOFI panels using a focused millimeter wave (150 GHz) reflectometer. The presented images of the SOFI panels show the capability of this reflectometer for detecting tight vertical cracks (also as a function of crack opening dimension) in exposed SOFI panels and while covered by a piece of SOFI ramp simulating a more realistic and challenging situation.

Meeting Name

Review of Progress in Quantitative Nondestructive Evaluation (2006: Jul. 30-Aug. 4, Portland, OR)


Electrical and Computer Engineering

Keywords and Phrases

Computer Simulation; External Tanks; Flaw Detection; High Resolution; Mathematical Models; Millimeter Waves; Nondestructive Testing; Reflectometers; Space Shuttles; Composite Testing and Evaluation; Microwave and Millimeter Wave Imaging

International Standard Book Number (ISBN)


International Standard Serial Number (ISSN)


Document Type

Article - Conference proceedings

Document Version

Final Version

File Type





© 2006 American Institute of Physics (AIP), All rights reserved.

Publication Date

01 Aug 2006