Measurements of ionic species made in the space shuttle bay area during low-earth orbit are interpreted within the framework of a kinetic analysis that incorporates shuttle cloud/ambient interactions, flow, and electromagnetic phenomena. This analysis indicates that a pressure of water vapor near the shuttle surface of 10-6 torr is consistent with [H2O+>/[O+> and [H3O+>/[H2O+> ratios of 0.1 and 0.2, respectively, and the latter ratio is within the range of measurements. For CO2 the analysis shows that a [CO2+>/[O+> ratio of 0.01 is consistent with a CO2 pressure near the shuttle of 8¿10-8 torr. For these conditions the dominant formation of ions is by charge exchange from ambient O+ ions, and the dominant loss of ions is by parallel flow along the magnetic field lines. In addition, Monte Carlo calculations of the slowing of the incident O+ ions indicate that charge exchange with H2 molecules occurs before the ions have lost a significant amount of energy when the H2O pressure near the shuttle surface is less than 10-6 to 10-5 torr.