From Columbia to Discovery: Understanding the impact threat to the space shuttle

The loss of the space shuttle Columbia in 2003 was caused by the impact of foam insulation on the leading edge of the wing. The foam strike created a hole in reinforced carbon–carbon panel 8 that led to excessive heating during re-entry, loss of the integrity of the left wing, and subsequent loss of the vehicle and crew. In the 2.5 years following the accident, there was a concerted effort to understand the impact threat to the space shuttle system. The effort was a large one, and was comprised of five integrated parts: (1) identifying the debris that can be shed by the External Tank and Solid Rocket Boosters; (2) determining the impact speeds and angles that debris can strike the Orbiter; (3) quantifying the amount of damage to the thermal protection system caused by those strikes; (4) estimating the temperature rise in the damaged regions during re-entry; and (5) deciding whether the temperature rise is sufficient to affect structural integrity. Each of these parts was addressed through experimentation and the development of what are called within the space shuttle program Critical Math Models. These models are extensively verified and validated to give high confidence in their results and are baselined by the shuttle program. This paper overviews the extensive experimental and modeling efforts of the return-to-flight program, emphasizing the impact testing and modeling.