Large 8 inch (barrel) gun (Credit: NASA).

NASA’s Glenn Research Center has over a decade of experience in ballistic impact testing. Because of their expertise in this area, the Structural Mechanics and Dynamics Branch at Glenn was called on after the Columbia accident to help test the effects of debris (such as foam or ice) colliding with the space shuttle.

Foam and ice impact testing on RCC panels (Credit: NASA).

For the Return to Flight phase of their work, the ballistic impact team tested numerous debris materials and analyzed the threat to the orbiter’s Reinforced Carbon-Carbon (RCC) leading edges, which are located in the hottest areas of the vehicle during re-entry. From these tests, computational models were developed to predict impact damage to the shuttle from each type of debris.

Glenn’s Structural Mechanics and Dynamics Branch worked with Langley Research Center, Johnson Space Center, and Boeing to complete hundreds of ballistic impact tests. Materials tested included gap filler, tile repair putty, external tank insulating foam, and ice.

Gap filler shims are used to fill unacceptable gaps between the thermal protection tiles on the orbiter while tile repair putty is used to fill holes in damaged orbiter tiles. Insulating foam on the shuttle’s external tank keeps cryogenic propellants cold. Ice can form at various locations on the external tank before launch. Any of these materials may shed during launch and impact the shuttle.

During testing, RCC was impacted by each type of debris material. In addition, Glenn tested aged RCC since new material does not accurately represent the true properties of the actual orbiter’s leading edge panels that have been exposed to harsh entry conditions over multiple missions.

Analysis material models for RCC, foams, and ice (Credit: NASA).

Ballistic impact research at Glenn involved two kinds of testing: characterization and validation tests. Characterization tests were conducted to gather data to characterize and build computer models for materials of interest to accurately simulate real impact events. Validation tests involved impacting RCC with gap filler, putty, foam or ice and comparing observed results to ensure that the computer models predicted the event correctly. High speed cameras filmed each instance while the data was collected and recorded.

Flight safety is the most important benefit of ballistic impact testing. Glenn’s extensive work in ballistics, which spanned nearly five years, has led to a significant technology gain in understanding impact dynamics. Additionally, results from the testing can be applied to benefit Orion, NASA’s crew exploration vehicle.