On the current limits of simulating gas giant entry flows in an expansion tube

Atmospheric entry to the Gas Giants involves entry velocities from 20 - 50 km/s, which is mostly beyond the capabilities of current ground testing facilities. This paper details an investigation exploring the operating limits of the X2 superorbital expansion tube at the University of Queensland (UQ) for the simulation of radiating gas giant entry flow condi- tions. Theoretical calculations show that the X2 expansion tube can simulate a proposed Uranus entry at 22.3 km/s but falls below the necessary 26.9 km/s velocity to simulate a proposed Saturn probe mission. An experimental analysis was able to confirm theoretical results for a 19 km/s gas giant entry flow condition, but not for two proposed conditions above 22.3 km/s at this time. Further theoretical analysis investigated the possibility of using an established blunt body test gas substitution to allow Uranus and Saturn entry shock layers to be simulated at achievable test flow velocities. This analysis showed that with an increased amount of helium diluent in the test gas (or a change to neon, a heavier diluent), Uranus and Saturn entry shock layers can be simulated in the X2 expansion tube. Due to the current interest in sending atmospheric entry probes to Uranus and Saturn, this is a useful conclusion, demonstrating that there are experimental facilities capable of producing aerodynamic test flows for simulating gas giant entry conditions.