Feasibility of Ablation Measurements in Small Particle Hypervelocity Impact Range Facility

The use of free-flight hypervelocity projectiles for ablation measurements is considered in this work. The California Institute of Technology’s Small Particle Hypervelocity Impact Range (SPHIR) features a two-stage light gas gun that launches a 1.8mm projectile with masses between 5-10mg at velocities up to 10 km/s. With the application of modern high-speed high-sensitivity optical detectors, measurements of the exterior ballistics phenomena considered herein can be done with the very high temporal and spatial resolution. The state-of-the-art cameras, spectrometers and trigger/timing circuitry with 1 to 10 ns response time and up to GHz framing rates allows to collect data on crucial thermo-physical parameters including the ablative species concentration, velocities, and temperature which can be extracted to validate and improve existing high-enthalpy flow and ablation models. Direct Simulation Monte Carlo flow and heat transfer calculations are presented for spherical projectiles at conditions typical for the SPHIR facility, e.g., 1 Torr ambient pressure and 5 km/s velocity. The analysis is used to assess the feasibility of reaching significant rates of ablation within the thin outer layer of the projectiles. The threshold levels of ablation products in the shock cap and wake of projectiles are estimated that can be determined from the radiation intensity map in a spectral range away from atomic and molecular peaks