[en] Recent laboratory studies of ion-molecule reactions relevant to the analysis of ion densities in the vicinity of space vehicles in low-Earth orbit are discussed. The studies include new cross-section measurements of the important O⁺ + H₂O charge transfer collisions and the H₃O⁺ - producing charge transfer reaction rate is found to be less collision energy dependent than previously assumed, whereas the H₃O⁺-producing reaction rate is highest at thermal energies and decreases rapidly with increasing collision energy. Implications of the new results on previous interpretations and recent space observations are discussed