Experimental and simulated terminal ballistics effects on lunar material analogs
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Date
2022-06
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University of New Brunswick
Abstract
This thesis applies a combination of physical experiments and analytical and numerical modeling to better understand impact mechanisms associated with the penetration of lunar materials. The first part of the thesis reports the results of eleven hypervelocity impact experiments involving the launch of stainless steel projectiles into anorthosite rock, under near vacuum conditions using a two-stage light gas gun. Three stages of impact were identified: initial contact; crater excavation, where the ejecta velocity is supersonic and proportional to impact energy; and spallation, where the ejecta velocity is subsonic and unrelated to impact energy. Three-Dimensional scans of the resulting craters were generated, and curve fitting was performed on crater cross-sections, with comparisons made between parabolic, hyperbolic, and power law fits. A hyperbolic description was found to be the best fit, in contrast to the long held understanding that initial impact crater shapes are parabolic. All three equations were then used to reconstruct the volumes of the excavated craters prior to the loss of material to spallation.
The second part of the thesis concerns the optimization of the design of a lunar penetrator for impact into ice-nearing lunar regolith. Emphasis is placed on the nose cone of the penetrator and its performance in terms of ground penetration, frictional heating, and regolith sampling. An existing analytical method for modeling penetration, known as spherical cavity modeling, is adapted to the surface of a dart-nosed penetrator. From this, the effects of several design parameters were identified, and a parametric sweep to find the optimal nose dimensions was performed. Mechanical properties of the target were based on existing ballistic test results for frozen terrestrial soil, while thermal properties were adapted from measurements performed on lunar samples collected during the Apollo missions. The predicted penetration and deceleration results were compared to a series of finite element models as a form of validation, which were found to be in good agreement. These results contribute to the design of an efficient lunar penetrator, currently being considered for instrument delivery and sample collection in a permanently shaded polar crater, with the possibility of adaptation to other lunar terrains. An optimal nose design was found within a set of externally applied constraints.