Engineers help prepare space shuttle for return to flight

When the space shuttle Discovery rockets back into orbit, Argonne engineers will have done their part to ensure a safe return to flight. A team led by Bill Ellingson and including Dick Koehl, Chris Deemer, Zack Metzger, Michael Wyrick and George Forster used a locally designed and built high-resolution CAT scanner to characterize the damage caused when chunks of insulating foam impact space shuttle wing surfaces in test situations.

The insulating foam is similar to what fell off the space shuttle Columbia's liquid oxygen tank and punched a hole in the left wing during the 2003 launch. This damage proved fatal during Columbia's reentry into Earth's atmosphere.

The leading edge of each shuttle wing is covered by 22 uniquely shaped panels, each made of reinforced carbon-carbon composite. As part of NASA's effort to fully study the effects of foam impacts, a special cannon at the Southwest Research Institute in San Antonio shoots foam blocks at the wing surface. NASA engineers need reliable data on the depth and shape, or morphology, of any cracks in the impacted wing panels. These data are largely provided by the high-resolution CAT scanner at Argonne.

A CAT scanner uses X-rays to view inside an object; the digital data collected by the X-ray detector must be processed by computer into an image that humans can use. Depending on the kind of information needed and the type of detector used in a scan, Ellingson and coworkers are able to produce two- or three-dimensional images of internal features as small as 80 and 150 micrometers, respectively. Eighty micrometers is roughly the width of a single sheet of copy paper.

“ If you think in terms of a basketball, if you wanted to know what is inside the ball and where it is in relationship to everything else, you would want a 3-D image,” Ellingson said. “If you don't have an X-ray image, the only way to get internal information is to cut the panel apart.”

As Discovery lifts away from the launch pad, NASA will be looking for pieces of foam dislodging from the orange-colored liquid oxygen tank. Although there is no way to completely eliminate falling foam during the launch, NASA has worked since the Columbia tragedy to minimize the possibility that any foam pieces of significant size will break away from the tank.

However, should a large piece of foam break free during the launch, NASA engineers and astronauts will need to understand the extent of any possible damage so they can make repairs while in orbit. “In that situation you would like to go to a data set such as we're helping to form,” Ellingson said. NASA is developing various on-orbit damage assessment and repair methods for the wing segments.