Modeling of infrared radiation in a space transportation system environment

An approach for modeling the infrared (IR) glow radiation about the space shuttle at low-Earth-orbit flight altitudes is examined. The study builds on the modeling and numerical techniques developed for understanding the visible glow of the Atmospheric Explorer. Because of the rarefied nature of the flow, a direct simulation Monte Carlo method is used. The study extends the earlier gas-phase reaction model to include NO vibrational-state-specific formation using cross sections derived from quasi-classical trajectory calculations. IR spectra are computed using the state-specific NO vibrational levels and an accurate line-by-line spectral model. The effect of internal and translational energy accommodation coefficients in the Maxwell gas-surface interaction model was studied. The translational energy accommodation coefficient affects the width of the NO overtone transition (Δν = 2) spectral peak, and a value less than unity is required to give good agreement between modeling and experiment. The vibrational energy accommodation coefficient significantly impacts the magnitude of the NO infrared spectra. The influence of surface reactions on the IR spectra was also examined and shown to be small. Finally, simulated spectra are compared with IR data obtained from shuttle space flight experiments. The comparison shows that the postulated gas and gas-surface phase models used in particle simulation enable one to predict quantitatively IR spectra at high altitudes.