High-tech Testing Of The Space Shuttle's Foam

The spray-on foam that insulates and protects the space shuttle's super-cold external fuel tank is applied in thin layers. The top of each layer dries to a bumpy crust, marking each layer in the foam like rings mark a tree trunk.

Gray, the leader of the X-ray research group at Iowa State University's Center for Nondestructive Evaluation, is studying how X-ray backscatter imaging and computer simulation modeling can help the National Aeronautics and Space Administration look through those layers to find any defects in the foam. Unlike traditional X-rays that make images by transmitting radiation through an object to a detector, backscatter technology makes images based on the electromagnetic radiation deflected by objects back to a detector.

Pieces of the foam fell from the shuttle Columbia during its January 2003 launch, damaging the spacecraft's left wing and causing the shuttle to break apart when it re-entered the earth's atmosphere. The accident killed all seven astronauts aboard and grounded the shuttle while NASA engineers worked to solve the foam problem.

When the first shuttle flight since the Columbia accident blasted off in July, more foam chunks fell from Discovery's external fuel tank and sent engineers looking for more answers.

NASA is asking Gray and his research team -- Terry Jensen, a center physicist; Feyzi Inanc, a center scientist; and Scott Wendt, a center associate scientist -- to do an $88,000, three-month study to answer two questions about NASA's foam testing. Gray said NASA engineers want to know more about the ability of X-ray technology to detect bubbles when layers of shuttle foam curve around corners. And he said they want to know more about the technology's ability to see any bubbles near the foam's layer lines.

The Iowa State researchers are taking X-ray images of foam samples and loading that information into a computer simulation program. And they're running computer simulations that model the X-ray technology's ability to find defects in the foam. Gray said he expects to send NASA a final report of the research results in March.

"Our job has long been to do research, find new inspection technologies and develop a better understanding of those technologies," said R. Bruce Thompson, the director of the Center for Nondestructive Evaluation and an Iowa State Anson Marston Distinguished Professor of Materials Science and Engineering. "Now we're seeing those technologies put into practice on a real and national problem. It's very exciting for the center to participate in this research."

For the past four years center researchers have been working on 17 NASA research projects supported by a $7 million appropriation from Congress. The work is focused on finding new technologies to monitor and inspect spacecraft. One result of the work is that NASA officials know about the center and its capabilities.

"I feel good about this project because NASA asked us to help with this," Gray said. "They're taking advantage of some of the tools here that they have helped develop and support."

The shuttle's next flight is scheduled for May but a NASA official recently said engineers continue to study the foam problems and that launch could be delayed.