The MMOD Hypervelocity Impact Modeling Approach for Dragonfly

This paper outlines the micrometeoroid orbital debris (MMOD) hypervelocity impact modeling approach used to ensure an acceptable risk tolerance to the Dragonfly mission. We evaluate the shielding performance of three Whipple shield designs comprised of multi-layer insulation (MLI) Kapton layers, with varying areal densities. A two-pronged strategy is leveraged to address the challenges of predicting the protective capability of non-standard MLI Whipple shields in the hyper-velocity (V ≥ 7 km/s) regime. We outline how the two-wall design and performance ballistic limit equations (BLEs) can be simultaneously used to predict shielding capacity. We also address the implications of the hypervelocity regime ballistic limit scaling with kinetic energy and lack of dependence on shield thickness. In addition, the numerical methodology previously developed and implemented for the Parker Solar Probe mission is used to derive BLEs. The impacts are modeled with the Sandia CTH hydrodynamics code because of its ability to handle shockwaves, multi-phase materials, high states of deformation, fracture, and failure, tabular equations of state (EOS) accounting for physical and chemical phenomena, and versatility in assigning material strength properties. CTH is used to predict the material response upon impact in a regime that is largely inaccessible experimentally. The CTH results in conjunction with modified BLEs are used to safely determine the threshold of tolerable impacts for each shielding configuration. We discuss the sources of differences, as well as present examples of the rear wall failure progression.