Tuesday, March 15, 2005
New imaging process shows hidden defects in foam insulation.
KNIGHT RIDDER NEWSPAPERS
MIAMI -- Two University of Florida researchers were working on ways to use their X-ray system to find cracks and corrosion in airplanes and find abandoned land mines when a NASA contractor asked them if the device might help make space shuttles safer.
They tinkered with the machine and decided it could.
Ed Dugan, a nuclear engineering professor, and Alan Jacobs, who retired from the same job 18 months ago, patented an X-ray imaging process that can show tiny hidden defects in the foam insulation that covers the giant, orange external shuttle fuel tank.
A suitcase-sized chunk of that foam broke off of the tank attached to the shuttle Columbia on Jan. 16, 2003, gouging a hole in the leading edge of the orbiter's wing as it climbed into space.
Sixteen days later, as Columbia streaked through the skies 40 miles above Texas on its way home, super-hot gases poured into the hole, destroying the wing and causing the ship to break up. All seven astronauts aboard were killed.
Dugan and Jacobs hope their work will help prevent future disasters.
"That's a very satisfying accomplishment," said Dugan, 58, a father of two. "Any time you can develop something that can save lives, it is exciting."
"Anybody in my generation . . . would want to be a part of the safe exploration of space," added Jacobs, 72, a father of four and grandfather of two.
'Backspatter' X-rays
Finding flaws in something as light and porous as foam is impossible for regular X-rays, which shoot radiation called photons through targets onto film that's placed on the other side.
Dugan and Jacobs work with "backscatter" X-rays, developed for use when it's impossible to place film behind an object -- as with the shuttle tanks.
In backscatter, photons are scattered or reflected from the target and recorded on sensors. Dugan and Jacobs developed a computer-driven process that captures more photons than conventional backscatter X-ray systems and creates very detailed pictures. The system can locate even the smallest of voids and tiny cracks in composite material and metal on airplanes.
The researchers had trained their technology on abandoned land mines worldwide. In tests sponsored by the Army, the process was able to clearly distinguish land mines from other buried objects by revealing small empty spaces unique to buried mines.
Lockheed Martin Corp. learned of Dugan and Jacobs' work on land mines and wondered if it might apply to shuttle foam, explained Warren Ussery, a team leader at Lockheed Martin's Michoud Assembly Facility in New Orleans, where the external tanks are manufactured.
Two processes
Most of the foam on the tanks is about an inch thick and is applied by robots. Dugan and Jacobs' system is used on smaller areas of the tank with thicker foam that's applied manually.
Lockheed Martin also examines those areas with a similar process called tetrahertz imaging, using very high-frequency radio waves that reflect off the aluminum tank. Examination with both machines showed no defects in the foam for the shuttle Discovery, which is tentatively scheduled for launch between May 15 and June 3. It will be the first shuttle to return to flight since Columbia.
Lockheed Martin has bought four of the X-ray machines, and NASA has bought one. For now, the X-ray device is not used to certify that tanks are ready for flight.
"We're having great success with it," said NASA spokeswoman June Malone of the Marshall Space Flight Center in Huntsville, Ala.
The foam that broke off and damaged Columbia's wing came from the "bipod," one of the points at which the orbiter is attached to the external fuel tank. Since the accident, the foam has been replaced with a heater system to keep potentially dangerous ice from forming.