Radiation from rocket-exhaust plumes

Abstract

An attempt is made here to present a unified review and evaluation of the current status concerning the emission of optical radiation from rocket-exhaust plumes. This topic has been under intensive investigation for various applications since the 1940's and of recent date centered upon the base-heating problem. Thus, this subject is of serious concern to the engine as well as the vehicle designer. The emission characteristics of rocket-exhaust plumes are strongly dependent upon the aerothermochemistry of the plume. The latter, of course, is related to rocket-engine parameters and the specific propellant system employed. Conditions created within the exhaust are different for liquid and solid propellants. Notably, the copious amount of large particles in the efflux of metal-based solid-propellant motors alter the fluid mechanics and radiative transfer of their exhaust plumes and therefore must be taken into account. Thus, to proceed with the problem the following steps are necessary: (1) determine the mole fraction of the constituents at the nozzle exit plane; (2) for the specific nozzle conditions, determine flow field and local conditions; (3) calculate band models; and (4) attempt to calculate the spectral radiance of the exhaust plume including the effect of particulate matter. In the above procedure one must recognize that as the altitude increases, two significant factors are altered: (1) the gases within the nozzle are highly underexpanded; and (2) the booster is accelerating or the relative flow conditions for the exhaust become hypersonic. The material presented in this paper considers each of the facets enumerated above in context of the current research programs. Finally, the possible gaps in our knowledge of the subject are discussed.