The interaction of the atmosphere with the space shuttle thruster plume: The NH(A‐X) 336‐nm emission

Abstract

Observations of the optical emissions from the space shuttle's thrusters have been examined. Particular attention has been paid to the interaction of the thruster plume with the atmosphere. Emissions from CN, CH, C2, HNO, and NO 2 have been observed near the nozzle of the thruster in the vacuum core region of the plume, but these emissions are the direct result of the combustion process. Other emissions including OI and NH have been observed in the downstream region of the plume, where the plume effluents interact with the atmosphere. The NH emission is one of the most dominant UV/ visible wavelength emissions observed in the plumes. This emission was observed to extend several thousand meters from the shuttle, and detailed analysis shows that the total intensity of the emission depends on the ram angle (angle in the shuttle reference frame between the plume effluents and the ramming atmosphere) and altitude, indicating an interaction process with the atmosphere. Data from two observational experiments are presented. The Air Force Maui Optical Site (AMOS) experiment includes ground-based spectral and spatial measurements of the shuttle plumes as the thrusters were fired over the AMOS site on top of Haliakala Volcano on the island of Maui in the mid-Pacific. The GLO experiment was flown in the payload bay of the space shuttle and also includes spectral and spatial measurements of the shuttle plumes. During both of these experiments, the primary reaction control system (PRCS) engines (870 lb (394 kgf) thrust) and Vernier reaction control system (VRCS) engines (25 lb (11 kgf) thrust) were fired at various angles relative to the ram, thus providing a range of collision velocities (4.5-11 km/s) between the thruster plume and the atmosphere. In this report the dependence of the NH emission on ram angle, thruster size, and distance from the shuttle is presented and analyzed using a three-dimensional Monte Carlo simulation of the plume-atmosphere interactions called spacecraft/orbiter contamination representation accounting for transiently emitted species (SOCRATES). The chemical reactions deemed most likely involve collisions of the plume products HNC, HNCO, and CH2NH with atmospheric O, and all of these processes are examined. The ram-angle dependence is used to determine a threshold energy required for the reaction that leads to the NH emission and to conclude that the most likely reaction involves CH2NH collisions with O. orbit (-200-500 km) undergo complex interactions with the atmosphere because of the rarefied and reactive nature of the atmosphere at these altitudes. These interactions lead to the generation of local atmospheres that are quite different from the ambient atmosphere. The rarefied atmosphere and the relatively high orbit velocity also produce a unique opportunity to study high-velocity one-step and twostep chemical processes. The large scale lengths provide an environment where it is possible to study extremely long lived metastable species. The state of the local spacecraft environ-Paper number 95JA...

Studying of Atomic and Molecular Interaction Processes in Rarified Hypervelocity Expanding Flows by Methods of Emissive Spectroscopy

“…The OH(A→X) 310-320 nm and NH(A→X) 336-337 nm molecular band emissions were found to be most intensive glow emissions in the UV region of spectrum. In particular, this idea was supported by spectral measurements of the glow radiation 1,7,36 . Corresponding single step collisional processes were suggested to explain these emissions 1,2 :…”

“…Some evidence that reaction (8.1) might take a place was found in Ref. 1 , where the OH(A→X) emission is visible in some spectra. In more recent paper 147 calculations of the potential energy surfaces related to collision of atomic oxygen with water molecules were presented.…”

“…Measurements of absolute intensity and spatial distribution of this radiation provide valuable data for studying of the collision characteristics. It should be noted that such kind of glow was observed yet earlier both from the US Shuttles 1 and Russian "Mir" space station 2 . Essential difference between the glow observations from the Shuttles and "Mir" was that Shuttle instruments looked at the plumes of the LP motors installed on the Shuttle itself, whereas "Mir" instruments observed the plumes of Russian space vehicles "Soyuz" and "Progress" located at a distance of 10 to 60 kilometers away from the station.…”

“…Task_C activity was particularly addressed to testing of commonly used collisional models at abovementioned energies of colliding partners. These tests seem to be well-timed, because all earlier simulations of the plume glow had one or another cross-section model involved 1,4,20,21,22,23 . Spatial distribution of the glow radiation was demonstrated to be sensitive to elastic collision cross-section choice.…”

“…Analysis of the plume images obtained on board of the "Mir" station since 1993 resulted in an idea that OH(A→X) emissions must be one of the main contributor to the UV-glow radiation intensity measured by the imager 2,3,4,5 . Strong NH(A→X) radiation observed in the Shuttle plume 1 was supposed to be filtered off by the imager. However, some degree of uncertainty remained about the final conclusion on how big were shares of the OH(A→X) and NH(A→X) radiation in the broadband filtered imager's signal.…”