Sample of the foam used on the external tank of the space shuttle Columbia released by the Columbia Accident Investigation Board. CAIB Photo by Rick Stiles 2003

Using a technique pioneered by researchers at Rensselaer, terahertz (THz) radiation has been used to uncover small defects in a sample of space shuttle foam. This nondestructive method could help National Aeronautics and Space Administration (NASA) officials examine the insulating foam that is applied to each shuttle’s fuel tank prior to launch.

Fuel tank manufacturer Lockheed Martin Space Systems approached Xi-Cheng Zhang, the J. Erik Jonsson ’22 Distinguished Professor of Science at Rensselaer, and requested a study of a sample of the foam material. Zhang and his research team have employed terahertz radiation (T-rays) to spot defects, including air bubbles and separations, purposely embedded in a specially prepared sample. Such defects have proved difficult to locate using X-rays or ultrasound. Zhang’s team (including doctoral students Hua Zhong, Xie Xu, Tao Yuan, and Shaohong Wang) has been working closely with Lockheed Martin to study the sample.

A total of eight man-made defects of various sizes were scattered throughout the sample. The embedded imperfections mimic defects that could potentially occur in a normally produced foam application on the fuel tank. Two types of defects were hidden in the sample: voids (or air bubbles), ranging from one-quarter inch to one inch in size, and debonds (separations between layers of foam or between a foam layer and the aluminum base).

NASA investigators believe that the Columbia space shuttle crash may have been caused by foam insulation breaking away and striking the left wing of the craft.


Originally published in Rensselaer Magazine, Fall 2003

Published September 1, 2003