Numerical study of projectile shape effect on the bumper performance under hypervelocity impact

Impacts in orbit from small micrometeoroids and small non-trackable orbital debris are generally unavoidable and pose a threat to spacecraft due to the high collision speeds exceeding 7 km/s. The design of spacecraft protection against micrometeoroids and orbital debris (MMOD) is generally based on experiments and models involving spherical projectiles. However, observations of collision fragments from ground-based satellite impact experiments have shown that orbital debris are non-spherical in shape. To adjust spacecraft protection to accommodate non-spherical projectiles, a relationship between spherical projectiles and their threat-equivalent non-spherical projectiles was established. The threat-equivalent relationship was found through a numerical methodology developed to quantitatively compare the ability of spheres and cylinders with varying length-to-diameter ratios to cause failure in a rear wall behind the bumper, referred to as the projectile threat. The study employed the smoothed-particle hydrodynamics method and explicit finite element method in commercial software ANSYS Autodyn to simulate the hypervelocity impact at 7km/s of differently shaped projectiles on to an all-aluminum bumper and rear-wall configuration. The craters produced by the debris cloud of spheres and cylinders of various geometries were compared and used to establish relationships between the threat posed by each projectile. The study found that the threat posed by cylindrical projectiles was significantly influenced by the projectile geometry, with an increase in threat observed as the cylinder length-to-diameter (L/D) ratio was reduced below or increased beyond L/D=1. Furthermore, the threat of the projectile was found to significantly depend on the thickness of the bumper and the standoff distance between the shielding and the protected surface. The established projectile threat relationship can be applied to assess the ability of the existing MMOD bumpers to withstand cylindrical projectiles by representing them with an equivalent sphere. This approach can help reduce uncertainty and improve the safety of spacecraft when dealing with non-spherical projectiles. Furthermore, the methodology developed in this study can be utilized to establish threat relationships between projectiles under different conditions, such as irregular shapes or different impact angles.

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