Spacecraft glow

Spacecrft glow may be defined as optical emissions originating immediately above those surfaces of an orbiting spacecraft which face into the ram direction. In the case of the Space Shuttle at its lower orbital altitudes, the glow is bright enough to be seen by the unaided eye. The glow observed at the Dynamics Explorer was caused primarily by OH molecules which formed on the spacecraft surface from ionospheric atomic oxygen and hydrogen. The two theories which are currently considered to obtain an explanation for the glow phenomenon include the plasma interaction mechanism and the chemical mechanism. A number of difficulties appear to exclude the applicability of the plasma interaction mechanism. Thus, the chemical mechanism remains as the only viable theory. According to this mechanism, simple impact of incoming atmosphere atoms and molecules causes both formation and excitation of molecules at the surface of a spacecraft.