Ejecta Evolution and Dynamics from Hypervelocity Impacts: Time-Resolved Experimental Studies and Applications to Planetary Cratering

Hermalyn, Brendan

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Year:: 2011
Contributor:: Hermalyn, Brendan (creator); Schultz, Peter (Director); Forsyth, Donald (Reader); Mustard, John (Reader); Parmentier, Edgar (Reader); Crawford, David (Reader); Brown University. Geological Sciences (sponsor)
Genre:: theses
Subject:: impact cratering; ejecta velocity; oblique impacts; hypervelocity impacts; Particle tracking velocimetry
Extent:: xiv, 179 p.
DOI: https://doi.org/10.7301/Z0WM1BPT

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Abstract:: The ejection of mass during an impact event is a shock-driven process that shapes the distribution of materials on planetary surfaces. Ejection velocities dictate the ballistic emplacement and appearance of ejecta patterns. Prior studies of vertical impacts into granular targets provide canonical ejecta-velocity relationships; however, these do not hold during early stages of growth when velocities are highest. Virtually all planetary impacts occur at oblique angles, which cause significant deviations from vertical impacts. Additionally, temporal (rather than spatial) descriptions of velocity are required for interpretation of mission data. To date, no simple analytical ejection velocity model incorporating impactor obliquity has been proposed. This dissertation presents new temporally-resolved studies of the early- to main-stage ejecta velocity distribution from impact experiments performed at the NASA Ames Vertical Gun Range. First, the role of projectile density in vertical impacts was examined using a noninvasive high-speed imaging technique to measure ejecta velocity as a function of both time and launch position. The temporal resolution of this technique allows measurement of ejecta an order of magnitude faster (and earlier) than captured in previous studies, and reveals early-time, high-speed deviations that reflect initial conditions and material flow-field inside the transient crater. In chapter two, these results were applied to the LCROSS mission, which used an empty rocket booster as a kinetic impactor to excavate material from permanent shadow on the moon. The sunlight horizon of ~830 meters required ejection velocities corresponding to early stages of growth. The third chapter presents the first time-resolved experimental studies of ejecta velocities for oblique impacts, captured by a novel three-dimensional particle tracking velocimetry implementation developed for this application. These data permit an analytical description of ejecta velocities from oblique impacts. Lastly, chapter four employs this velocity distribution in an ejecta propagation model to reconstruct ejecta pattern emplacement. Measured obliquity effects include velocity, existence and closure of the uprange zone of avoidance, and flow-field center migration. These parameters represent a first step toward parametric investigation of the factors controlling uprange ejecta patterns and non-radial emplacement on planetary surfaces.
Notes:: Thesis (Ph.D. -- Brown University (2011)

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Rights: In Copyright
Restrictions on Use: Collection is open for research.

Citation

Hermalyn, Brendan, "Ejecta Evolution and Dynamics from Hypervelocity Impacts: Time-Resolved Experimental Studies and Applications to Planetary Cratering" (2011). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0WM1BPT

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Earth, Environmental and Planetary Sciences Theses and Dissertations

Theses and Dissertations for the Earth, Environmental and Planetary Sciences department.
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