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Ultraviolet radiation from hydrazine spacecraft thruster plumes interacting with ambient atomic oxygen is modeled for low-Earth-orbit conditions. Two numerical techniques that employ the direct simulation Monte Carlo method are applied for the rst time to the modeling of space plume radiation transient and three-dimensional ows. These ef cient procedures allow one to analyze the effect of atomic oxygen penetration of the thruster plume, which is a key factor in modeling rare ed space plume radiation. The overlay technique is used to model the transient ow evolution during the rst several seconds after motor ignition. Good agreement between modeling and experiment are obtained before 1-s motor burn time. The sensitivity of the plume radiation to the molecular total collision model is analyzed using the overlay technique, and the radiation spatial distribution was found to be strongly dependent on the temperature exponent of the coef cient of viscosity. Three-dimensional computations are conducted for different angles between the plume axis and the freestream directions, and the radiation maps for OH(A) and NH(A) are presented. Signi cant difference between OH(A) and NH(A) radiation elds as a function of the angle of attack is shown.

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