Brendan Hermalyn - Academia.edu (original) (raw)
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Papers by Brendan Hermalyn
Icarus, 2011
The depth and duration of energy and momentum coupling in an impact shapes the formation of the c... more The depth and duration of energy and momentum coupling in an impact shapes the formation of the crater. The earliest stages of crater growth (when the projectile transfers its energy and momentum to the target) are unrecoverable when the event is described by late stage parameters, which collapse the initial conditions of the impact into a singular point in time and space. During the coupling phase, the details of the impact are mapped into the ejecta flow field. In this experimental study, we present new experimental and computational measurements of the ejecta distribution and crater growth extending from early times into main-stage ballistic flow for hypervelocity impacts over a range of projectile densities. Specifically, we assess the effect of projectile density on coupling depth and location in porous particulate (sand) targets. A non-invasive high-speed imaging technique is employed to capture the velocity of individual ejecta particles very early in the cratering event as a function of both time and launch position. These data reveal that the effects of early-stage coupling, such as non-constant ejection angles, manifest not only in early-time behavior but also extend to main-stage crater growth. Time-resolved comparisons with hydrocode calculations provide both benchmarking and insight into the parameters controlling the ejection process. Measurements of the launch position and metrics for the transient diameter to depth ratio as a function of time demonstrate non-proportional crater growth throughout much of excavation. Low-density projectiles couple closer to the surface, thereby leading to lower ejection angles and larger effective diameter to depth ratios. These results have implications for the ballistic emplacement of ejecta on planetary surfaces, and are essential to interpreting temporally resolved data from impact missions.
We observed the Lunar Crater Observation and Sensing Satellite (LCROSS) lunar impact on 9 October... more We observed the Lunar Crater Observation and Sensing Satellite (LCROSS) lunar impact on 9 October 2009 using the Agile camera with a V filter on the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory. We employed a principal component analysis (PCA) to filter out large-scale seeing effects and imperfections in image registration from a series of 0.5-second images spanning eight minutes centered on the Centaur upper stage impact time. After applying the PCA filter, we detected an evolving plume from approximately 5-35 seconds after impact. We validated our detection method by comparing the time-varying plume brightness profiles from the LCROSS plume to those extracted from a synthetic image sequence that included a simulated plume. We performed 3-D ballistic simulations of trial plumes, extracted images with the correct viewing geometry from these simulations at 0.5-second intervals, superimposed these onto a computer-generated lunar landscape, and added ac...
Icarus, 2011
The depth and duration of energy and momentum coupling in an impact shapes the formation of the c... more The depth and duration of energy and momentum coupling in an impact shapes the formation of the crater. The earliest stages of crater growth (when the projectile transfers its energy and momentum to the target) are unrecoverable when the event is described by late stage parameters, which collapse the initial conditions of the impact into a singular point in time and space. During the coupling phase, the details of the impact are mapped into the ejecta flow field. In this experimental study, we present new experimental and computational measurements of the ejecta distribution and crater growth extending from early times into main-stage ballistic flow for hypervelocity impacts over a range of projectile densities. Specifically, we assess the effect of projectile density on coupling depth and location in porous particulate (sand) targets. A non-invasive high-speed imaging technique is employed to capture the velocity of individual ejecta particles very early in the cratering event as a function of both time and launch position. These data reveal that the effects of early-stage coupling, such as non-constant ejection angles, manifest not only in early-time behavior but also extend to main-stage crater growth. Time-resolved comparisons with hydrocode calculations provide both benchmarking and insight into the parameters controlling the ejection process. Measurements of the launch position and metrics for the transient diameter to depth ratio as a function of time demonstrate non-proportional crater growth throughout much of excavation. Low-density projectiles couple closer to the surface, thereby leading to lower ejection angles and larger effective diameter to depth ratios. These results have implications for the ballistic emplacement of ejecta on planetary surfaces, and are essential to interpreting temporally resolved data from impact missions.
We observed the Lunar Crater Observation and Sensing Satellite (LCROSS) lunar impact on 9 October... more We observed the Lunar Crater Observation and Sensing Satellite (LCROSS) lunar impact on 9 October 2009 using the Agile camera with a V filter on the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory. We employed a principal component analysis (PCA) to filter out large-scale seeing effects and imperfections in image registration from a series of 0.5-second images spanning eight minutes centered on the Centaur upper stage impact time. After applying the PCA filter, we detected an evolving plume from approximately 5-35 seconds after impact. We validated our detection method by comparing the time-varying plume brightness profiles from the LCROSS plume to those extracted from a synthetic image sequence that included a simulated plume. We performed 3-D ballistic simulations of trial plumes, extracted images with the correct viewing geometry from these simulations at 0.5-second intervals, superimposed these onto a computer-generated lunar landscape, and added ac...