Using Aerothermodynamic Similarity to Experimentally Study Nonequilibrium Giant Planet Entry

Abstract

Peak heating points for the entry into Uranus, Neptune, and Saturn exhibit highly nonequilibrium shock layers, and are not well understood. This paper describes an experimental study in the X2 expansion tube at the University of Queensland, using a condition with a higher concentration of helium than exists on Saturn, with a shock speed of , to simulate radiation during blunt body Saturn entry at . High speed imaging and emission spectrometry were employed to measure shock layer radiation. Axial and radial spectroscopic measurements were performed through planes along and perpendicular to stagnation streamline, and an Abel inversion was used to quantify the radial radiation profile. Regions at different nonequilibrium stages were identified by radiation measurements. Nonequilibrium shock layers with a slow ionization rate, which were observed in other Saturn entry radiation tests, were successfully recreated. This paper shows increasing the amount of helium enables expansion tubes or other facilities to simulate nonequilibrium giant planet entry, thus providing more ground testing data for future study.