Excitation of N2 Lyman‐Birge‐Hopfield Bands Emission by Low Earth Orbiting Spacecraft

The spectral distributions in the artefactual Lyman‐Birge‐Hopfield bands observed from the S3‐4 satellite and Spacelab 1 are shown to be consistent with excitative recombination of ground‐state N atoms catalyzed by spacecraft and instrument surfaces exposed to the atmosphere. This heterogeneous (and most probably Langmuir‐Hinshelwood) reaction is analogous to the homogeneous reactions that produce the well‐known VUV afterglow of active nitrogen. Promoting/interfering surface processes (perhaps involving conditioning) and undocumented systematic changes in vehicle orientation are among the possible causes of the strong dependence of the measured nadir system intensities on the ambient density of N(4S).