Modeling of UV radiation from high altitude plumes and comparison with data from the Mir space station

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 MirEx experiment. The studies were performed with the direct simulation Monte Carlo method. The results presented include the sensitivity study of the simulations to different parameters of the numerical technique 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 reactions of atomic 0 with hydrazine fragments. The simulations are found to overpredict the data by approximately by a factor of 5 to 70, depending on the parameters of chemistry model chosen for water dissociation. However, the simulations are in close agreement with the variations observed in the near-field plume intensities as a function of mission elapsed time.