The utility of microwave and millimeter wave nondestructive testing and evaluation (NDT&E) methods, for testing the Space Shuttle external fuel tank spray on foam insulation (SOFI) and the acreage heat tiles has been investigated during the past two years. Millimeter wave NDE techniques are capable of producing internal images of SOFI. This paper presents the results of testing several diverse panels with embedded voids and debonds at millimeter wave frequencies. It has clearly shown the potential utility of using millimeter wave continuous wave (CW) imaging for testing different SOFI panels containing a diverse array of inserts simulating voids and debonds. Microwave and millimeter wave nondestructive testing techniques are quite mature. Using these systems and employing low incident power (less than 10 mW) and focused lenses or small horn antennas it was shown that it is readily possible to inspect SOFI that is 10 inch thick (and more). It is important to note that SOFI is primarily a low loss and low permittivity polymer material. Therefore, the dielectric loss factor associated with the SOFI polymer is not a cause of great signal attenuation. However, the microstructure of the SOFI (i.e., the tiny air bubbles that makes it to be a foam) can cause considerable scattering at frequencies higher than ~250 GHz. Therefore, at much higher than millimeter wave range frequencies the extinction coefficient (which accounts for both attenuation and scattering) may be high and therefore signal penetration into SOFI may be limited. Through these investigations it was also found that the sensitivity to surface rind (where SOFI acreage areas) is minimal and therefore this surface feature is not a limiting factor is using these methods.
Microwave and millimeter wave testing for the inspection of the space shuttle spray on foam insulation (SOFI) and the acreage heat tiles
Mikrowellen- und Millimeter-Wellenprüfung zur Untersuchung der aufgesprühten Schaumisolierung der Raumfähren und der Hitzekachelnfläche
2006
8 Seiten, 9 Bilder, 9 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch