Ultraviolet radiation modeling from high-altitude plumes and comparison with Mir data

Modeling and calculations are presented with the goal of elucidating possible mechanisms of ultraviolet radiation from a Soyuz-TM spacecraft plume interacting with the ambient gas at altitudes of about 380 km, observed during the Mir experiment. The studies were performed with the direct simulation Monte Carlo method. The results presented include sensitivity studies of the simulations to various numerical parameters and an investigation of different radiation mechanisms. Among the mechanisms considered was the formation of OH(A) due to water dissociation by atomic O, collisional excitation of OH(X), and the formation of NH(A) by the reaction of atomic O with hydrazine fragments. The simulations are found to overpredict the data by approximately a factor of 5-70, depending on the parameters of the chemistry model chosen for water dissociation. However, the simulations are in close agreement with the near-field plume intensity profile.