The second X-38 test series addressed the following question: if the X-38 TPS were struck by a projectile not large enough to cause target failure by itself, could subsequent heating during atmospheric entry cause failure at the damaged spot? In this test series, after impact, the targets were subjected to heating at the JSC Arc Jet Laboratory. Once a sufficient number of subpenetrating impacts were achieved for the heating studies, additional impact tests attempting full penetration were conducted.

Subpenetrating projectile sizes used were 3.57 mm (9/64") to 5.56 mm (7/32") against TUFI tile targets, and 2.8 mm to 3.57 mm (9/64") against AFRSI blanket targets.