Electron Density Measurement in Reentry Shocks for Lunar Return

Results of electron density measurements in the Electric Arc Shock Tube at NASA Ames Research Center are reported here. Measurements are made at conditions relevant for lunar return of the Orion Command Module. Normal shocks are produced in the Electric Arc Shock Tubewith freestreampressures of 0.1–1.0 Torr and velocities from 8–12 km=s. Nonintrusive electron densitymeasurements aremade by observing optical emission from various lines at high resolution and employing analysis of Stark broadening effects. Themeasurements show electron density in the shock to be up to several times larger than equilibrium density up to a few centimeters behind the shock front. The disagreement with equilibrium improves at higher velocities.