Generic module wall damage prediction equations for habitable spacecraft crew survivability evaluations

The process used to calculate and reduce the consequences of meteoroid and orbital debris penetrations and their link to catastrophic failure has evolved over time. As the threat of the orbital debris population increased in the 1980s and early 1990s, NASA developed a tool to determine what percentage of space station penetrations might be survivable (referred to as the probability of no catastrophic failure, or PNCF) and how to improve that survivability percentage. The quantity PNCF is directly related to the PNP, or probability of no penetration, as calculated by Bumper, the code used by NASA to perform MOD risk assessments. Part of the process in determining PNCF involves calculating the size of the holes and cracks caused by any penetrations. A review of the original techniques used to calculate hole size and crack length as well as current equations revealed some serious concerns that needed to be addressed. As a result, a study was undertaken to develop revised models that would address these concerns. In this paper, the features of new generic hole- and crack-size prediction equations, as well as the phenomenology involved in the formation of holes and cracks in habitable space station modules are presented and discussed. By comparing the predictions of the new equations against the predictions of current hole and crack size models as well as against empirical data, we found that (1) the predictions of the new equations fit the empirical data just as well as, if not better than, the current models and that (2) the new equations displayed the appropriate phenomenological response characteristics as the diameters of impacting projectiles increased beyond the ballistic limit diameters. Based on the results, we believe that when the new hole and crack size equations are used in survivability assessments the fidelity of the PNCF calculations and predictions will also increase dramatically.

► NASA uses MSCSurv to calculate the probability of no catastrophic failure (PNCF) of the ISS due to orbital debris impacts.
► MSCSurv calculates hole and crack size following a penetration for the many different shield types on board the ISS.
► We present a new phenomenology-based model for calculating hole and crack size following an on-orbit module penetration.
► We compare the predictions of our new model against those of current hole and crack size models and empirical data.
► Based on results, we believe the new hole and crack size model will dramatically improve the fidelity of PNCF predictions.