Large intensities of hot positive ions are observed out to distances of several hundred meters from the space shuttle Challenger (Spacelab 2) with a plasma analyzer on board a small free-flying satellite, the Plasma Diagnostics Package. This ion plasma is inferred to be generated by the charge exchange of ionosphere O+ ions with a large cloud of water molecules from the space shuttle. The measured ion density ranges from ~30 to 104 H2O+ ions cm-3. The hot ion plasma forms an ion trail in the wake of the space shuttle. A model for the water vapor cloud provides the basis for density estimates as high 109 H2O molecules cm-3 at a distance of 50 m from the space shuttle. Thus the space shuttle possesses a substantial coorbiting atmosphere. ¿ American Geophysical Union 1989