An outgassing jet model is presented in support of spacecraft navigation for future missions to comets. The outgassing jet is modeled as an emission cone while the comet is modeled as a uniform density triaxial ellipsoid. The comet's motion about the sun is included in the model. The model is used to explore the effects on a spacecraft passing through an outgassing jet field. The outgassing jet model is also used for simulation and estimation of the physical outgassing properties of jets at and near the surface of a comet. Methods for estimating the locations and sizes of multiple outgassing jets are presented.