On this day thirteen years ago, the U.S. Space Program experienced one of its darkest days. During reentry to the Earth’s atmosphere, the Space Shuttle Columbia broke apart, killing all seven crewmembers on board. An investigation launched immediately to determine what had occurred, as well what steps could be taken to prevent further accidents. As part of the investigation, NASA brought in experts from around the world to examine the exact cause of the accident, and how to reduce the chance for reoccurrence. Bill Ellingson (B.S. ’62, M.S. ’70, Ph.D. ’74), an Iowa State Aerospace Engineering alum who was working as a senior scientist at Argonne National Laboratory was one of those experts who got the call from NASA.
Less than two minutes into the launch of Columbia’s 27th mission, STS-107, a piece of foam from the large external fuel tank broke off, striking one of the panels of the space shuttle’s left leading edge wing, causing a briefcase-sized hole. The leading edge of each of those wings were constructed from 22 individual reinforced carbon-carbon (RCC) panels that protected the wing during reentry, due to their ability to withstand extremely high temperatures. Because of the hole in the light gray RCC panel, hot gasses, with temperatures that reached up to 3,000 degrees Fahrenheit, penetrated the wing during reentry and ate away at the shuttle causing it to disintegrate.
When they were built, the reinforced carbon-carbon panels were designed to be strong enough that they could be used on the shuttle for years and years, as long as they stayed at the right temperature. If the RCC panels exceeded 3,000 degrees Fahrenheit for an extended period of time, they would start to weaken and need to be replaced sooner than planned. After each mission, technicians would see how long the RCC panels stayed at an extreme temperature to determine how much strength had been reduced. In addition, a technician would push along the bottom edge of the pieces with his or her hand, looking for soft spots. After the Columbia accident, it was clear that NASA needed a way to nondestructively assess the condition of the RCC panels in a quantitative way.
NASA needed someone who had years of experience working with different types of ceramic composites at extremely high temperatures. In addition, they needed someone who had developed noncontact and nondestructive methods to examine different types of ceramics, preferably one of the leaders in his or her field. That’s when Ellingson came in. “When NASA had this issue with Columbia, what was interesting is that they did not have people doing what I was doing, which was developing nondestructive test methods for ceramic composites,” Ellingson recalls. “So when they looked around the United States, they saw who was working with these materials, and that’s when I showed up.”
Ellingson and about 100 other scientists were split into groups to evaluate and modify different methods of nondestructive testing. The teams looked at ultrasound, Eddy current technology, shearography, and flash infrared thermal imaging. In the end, it was determined that infrared thermal imaging was the best solution. NASA called back five specialists, including Ellingson, to determine the best inspection procedure following each flight. “The five of us were tasked to come up with a procedure so that after every return from flight, NASA could do the large area flash thermal imaging, and look at the data and to assess the remaining residual strength of the wing leading edge part,” Ellingson said.
The final protocol ended up requiring a combination of three of the testing methods then comparing the results to see if a piece needed to be replaced. “We can’t afford to have false positives,” Ellingson told Argonne in 2005. “These components can cost $100,000 per part.”
In 2004, Ellingson, along with other team members, were presented with the NASA Turning Goals Into Reality Award, which celebrates the year’s most significant accomplishment that adds to the NASA legacy.
The protocol that Ellingson and his team developed was used for the final 22 missions of the space shuttle program. In July of 2011, NASA invited Ellingson along with other involved scientists to Cape Canaveral to witness the final launch of the space shuttle program.