Honeycomb vs. foam: Evaluating potential upgrades to ISS module shielding

A series of 19 hypervelocity impact tests have been performed on ISS-representative structure walls to evaluate the effect on micrometeoroid and orbital debris (MMOD) protective capability caused by replacing honeycomb sandwich panel cores with metallic open-cell foam. In the experiments, secondary impacts on individual foam ligaments were found to raise the thermal state of projectile and bumper fragments, inducing break-up and melt at lower impact velocities than the baseline honeycomb configuration. A ballistic limit equation is derived for the foam-modified configuration, and in comparison with the honeycomb baseline a performance increase of 3–15% at normal incidence was predicted. With increasing impact obliquity, the enhancement in protective capability provided by modification is predicted to further increase. Reduction in penetration and failure risk posed by MMOD impacts is achieved by the foam-modified configuration without a significant decrease in mechanical or thermal performance, and with no additional weight. As such, it is considered a promising upgrade to MMOD shielding on ISS modules, which incorporate honeycomb sandwich panels and are yet to fly.