Unsteady DSMC simulations of the aerodynamics of sounding rockets

Over the past several decades, atomic oxygen concentration measurements taken from sounding rocket sensor payloads in the altitude range of 80-140 kilometers have shown marked variability. Many sounding rocket payloads including the Nasa sponsored, Coupling of Dynamics and Aurora experiment (CODA II), contain atomic oxygen sensors that are located in close proximity to the payload surface and are thus significantly influenced by flow field disturbances. Previous research has utilized numerical simulations; including the Direct Simulation Monte Carlo (DSMC) method to analyze the effect of flow field disturbances on atomic oxygen concentrations. These previous studies however, were performed under steady-state assumptions and did not account for changes due to translations and angle of attack. The degree to which these unsteady effects contribute to the overall accuracy of the solution was the objective of this research. The present study is a comparative analysis between the steady and unsteady approaches for the three-dimensional, rarefied gas flow particular to the CODA II mission. The study was conducted at an altitudes of 110 km using the unsteady DSMC method. The numerical simulations show conclusively that the unsteady effects contribute substantially to the overall accuracy of the solution.