Simulation of aerodynamic influences on rocket-mounted oxygen sensors

Over the past several decades, atomic oxygen measurements taken from sounding rocket sensor payloads in the altitude range of 80-140 kilometers have shown marked variability. Many sounding rocket payloads contain atomic oxygen sensors that are located In close proximity to the payload surface, and are thus significantly influenced by flow field disturbances. Although several additional factors including Doppler shift and sensor contamination may also play a significant role in the accurate measurement of atomic oxygen concentrations, this work focuses solely on the effects due to the flow field. The present study utilizes the three-dimensional, steady-state, direct simulation Monte Carlo technique. In addition, the lower altitudes corresponding to near-continuum flow are solved via the Navier-Stokes equations with slip wall boundary conditions. The flow is simulated at 13 different altitudes, each with three separate rocket orientations, along both the rocket's upleg and downleg trajectory for a total of 75 simulations. The numerical simulations show conclusively that the relative magnitudes of undisturbed versus disturbed atomic oxygen concentrations are highly dependent upon rocket orientation, and provide a quantitative means by which existing atomic oxygen concentration data sets may be corrected for aerodynamic influences.