Effect of an Altitude-Dependent Background Atmosphere on Shuttle Plumes

THE shuttle ionospheric modification with pulsed localized exhaust (SIMPLEX) experiments conducted by the Naval Research Laboratory (NRL) were designed to 1) assess the effects of rocket exhaust interactions in the ionosphere and 2) mimic large ionospheric disturbances that occur naturally [1-5]. These experiments use space shuttle orbital maneuver subsystem (OMS) engines to inject exhaust over ground radar sites. The shuttle exhaust provides a high-speed neutral gas that streams through the ambient plasma of the ionosphere. The neutral exhaust molecules exchange charge with ambient O(+) ions in the ionosphere. This interaction between the plasma and neutrals results in the formation of ion-ring and beam velocity distributions of plasma particles in the ionosphere. During the SIMPLEX experiments, these distributions are studied with ground radars using incoherent scatter of radio waves from electrons in the ionosphere.