Gas phase collisional excitation of infrared emissions in the vicinity of the space shuttle

Abstract

Recent models of the gas concentrations around orbiting vehicles have predicted concentration enhancements of up to 50 times ambient near ram surfaces for the shuttle at altitudes of 200 km. For some models, the mean free path decreases by a factor of ∼100 below that of the undisturbed ambient gas. The predicted scale length for the induced enhancement is relatively large, 5 m, which results in large column concentrations. In this paper we explore the possible implications of such a gas buildup in terms of induced photon emissions. When a large variety of interactions involving the enhanced local shuttle atmosphere are considered, it is predicted that significant effects arise from gas phase collisions between the relatively energetic ambient atoms and molecules and the atoms and molecules in the shuttle environment, particularly in front of ram surfaces. It is shown that such collisions have the potential to transfer considerable energy to the gases in the shuttle environment. Using reasonable estimates for cross sections we find that the most likely emission outcome will be vibrational and rotational radiation losses in the infrared due to direct collisional excitation. Estimates are made of the anticipated intensities of this radiation as a function of vehicle altitude or neutral atmosphere concentration.