A study of the neutral, plasma, and radiation environment induced around spacecraft in low Earth orbit is presented. The three-dimensional evolution of an artificial plasma cloud created by spacecraft which release neutrals and/or plasma into the ambient ionosphere is examined. Simulations of spacecraft operations which release neutral water and create a water plasma cloud, such as thruster firings or effluent dumps, are performed. It is shown that for time scales of interest in contamination studies the flow of the released neutrals is in the free-molecular regime. The effects of the altitude of the release, the orientation of the thrust vector with respect to the magnetic field, and the magnitude of the release velocity on the induced environment are considered. It is shown that a large water ion cloud is formed with densities of the order of the ambient oxygen ions. The role of the plasma expansion along the magnetic field lines is discussed. It is predicted that the ambient oxygen forms depletion and enhancement regions. The ultraviolet radiation intensity is estimated. The electrostatic ''snowplow'' effect and the mapping of the electric field to other regions of the ionosphere are demonstrated. The ambient plasma density is perturbed and forms ''image'' clouds. The model predictions are discussed and compared with measurements and previous results. ¿ American Geophysical Union 1992