Interaction of solid-rocket exhaust with the atmosphere

Photometrically calibrated, ground-based, wide-band images were recently obtained for the exhaust trail of an aluminized solid-rocket motor of 10,000-kgf thrust operating and smoldering near 110 km. These observations were made in the visible and near infrared using an intensified video camera mounted on the acquisition telescope of the 1.6-m telescope at the U.S. Air Force Maul Optical Site. The burn-associated luminous volume expands within a few frames to about 1 km transverse to the trajectory, with most of the emission occurring near its stationary edges. Its initial lifetime, determined from individual as well as sequential images, is 13 +/- 3 s. This spatial distribution and persistence show that the emission is not due to thermal radiation from or catalyzed by micrometer-scale Al2O3 exhaust particles. Assuming that the chemiluminescence is due to the reaction of ambient atomic oxygen with the combustion products of the exhaust, the data lead to a depletion-rate coefficient of about 10(-12) cm(3) molecule(-1) s(-1). We suggest that a key step in producing the emission is due to Al-containing complexes reacting exothermally with O atoms in the upper atmosphere. The visible-light-emitting species is likely to be an electronically excited state of AlO2 or AlO. Analysis of the hydrodynamic development of the radiating volumes leads to their scaling to other solid-rocket thrusts and altitudes.