Origin of the shuttle glow

Abstract

A GLOW around exposed surfaces of the space shuttle facing the direction of orbital motion was first seen in 19831,2. This 'shuttle glow' extends about 10cm from the surfaces, is peaked in wavelength at 680 nm, and within a resolution of about 3.5 nm forms a continuum3-6. Similar anomalies were reported in rocket experiments as long ago as 19587 and in more recent space-based studies8. Apart from its interest as an unusual physical phenomenon, shuttle glow may be a source of interference in space-based spectroscopy; anomalous airglow observations made by the Atmospheric Explorer spacecraft9,10 have been attributed to it. The most likely explanation seems to be the recombination of fast oxygen atoms in the upper atmosphere with NO absorbed on the shuttle's surface. This forms excited NO2, which radiates light as it desorbs6,7. On a recent shuttle mission (STS-39) four gases, NO, CO2, Xe and Ne were released for a plasma experiment. Unintentionally, enough gas was scattered onto the surfaces of the shuttle tail that when NO was released a much more intense version of shuttle glow was observed. The other gases did not affect the normal shuttle glow. Under normal conditions the adsorbed NO that causes the glow probably comes either from the ambient atmosphere6 or from reactions in exhaust gases from the shuttle thrusters14,15. © 1991 Nature Publishing Group.