This paper describes International Space Station (ISS) micro-meteoroid orbital debris (MMOD) impact shielding including requirements for protection as well as technical approaches to meeting requirements. Current activities in providing MMOD protection for ISS are described, including efforts to augment MMOD protection by adding shields on-orbit. Another activity is to observe MMOD impact damage on ISS elements and returned hardware, and to compare the observed damage with predicted damage using Bumper code risk assessment software. A conclusion of this paper is that ISS will be protected adequately from MMOD impact after completing augmentation of ISS shielding for Service Module, and after improving MMOD protection for Soyuz and Progress vehicles. Another conclusion is that impact damage observed to the ISS mini-pressurized logistics module matches the distribution of impacts predicted by Bumper code.

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Abstract. The novel structure of metallic foams is of interest in the design of next-generation debris shields as it introduces physical mechanisms that are advantageous to hypervelocity impact shielding (e.g. increased fragmentation/melt/vaporization, energy dissipation, etc.). Preliminary investigations have shown improved shielding capability over traditional spacecraft primary structures. In this paper, the results of a current hypervelocity impact test program on metallic open-cell foam core sandwich panels are reported. A preliminary ballistic limit equation has been derived from the experimental results, and is presented in a form suitable for implementation in risk assessment software codes.

Toughened thermal blankets have been developed that greatly improve protection from hypervelocity micrometeoroid and orbital debris (MMOD) impacts. Three types of materials were added to the thermal blanket to enhance its MMOD performance: (1) disrupter layers, near the outside of the blanket to improve breakup of the projectile, (2) standoff layers, in the middle of the blanket to provide an area or gap that the broken-up projectile can expand, and (3) stopper layers, near the back of the blanket where the projectile debris is captured and stopped. Hypervelocity impact tests were performed on candidate toughened thermal blanket configurations at the NASA White Sands Test Facility and at the University of Dayton Research Institute. From these tests the best disrupter materials were found to be betacloth and fiberglass fabric. Polyimide open-cell foams provide a light-weight means to increase the blanket thickness and improve MMOD protection. The best stopper material is Spectra™ 1000-952 or Kevlar™ KM2-705. These blankets can be outfitted if so desired with a reliable means to determine the location, depth and extent of MMOD impact damage by incorporating an impact sensitive piezoelectric film. Nomenclature d projectile diameter (cm) d n projectile diameter on failure threshold of shield, nth step (cm) d n+1 projectile diameter on failure threshold of shield, n+1 step (cm) d change in calculated projectile diameter; d = dn+1 -dn f MLI MLI effectiveness factor (non-dimensional) m b areal density of bumpers (g/cm 2 ) m back-cover areal density of the blanket's back-cover (g/cm 2 ) m disrupter areal density of all beta-cloth or fiberglass disrupter layers (g/cm 2 ) m foam areal density of foam spacer (g/cm 2 ) m front-cover areal density of the blanket's front-or outer-cover (g/cm 2 ) m MLI areal density of MLI (g/cm 2 ) m MLI-foam_eff Effective areal density of MLI (g/cm 2 ) m Sh areal density of shield (g/cm 2 ) m Sh_eff areal density of shield including effective contribution of MLI (g/cm 2 ) m w areal density of rear wall (g/cm 2 ) 74 Eric L. Christiansen and Dana M. Lear / Procedia Engineering 103 ( 2015 ) 73 -80 M p projectile mass (g) p projectile density (g/cm 3 ) impact angle (deg) measured from surface normal (0 deg impact angle is normal to the surface) cos cosine of impact angle S Total thickness of the MLI and/or the total shield thickness and standoff distance (cm) V impact velocity (km/s) Vn normal component of impact velocity (km/s) = V cos

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