Molecular Beams in Space: Sources of OH(A yields X) Emission in the Space Shuttle Environment
Abstract
OH(A yields X) emission bands have been observed in the molecular beam jets produced by Space Shuttle engine exhaust using the GLO imager spectrograph located in the payload bay. Spectra were collected at a resolution of 4 Angstrom for both daytime and nighttime solar illumination conditions, all at an altitude of approximately 390 km. A spectral analysis is presented that identifies and quantifies four separate OH(A) excitation processes. These include (i) solar-induced fluorescence of the OH(X) in the exhaust flow, (ii) solar-induced photodissociation of H2O in the exhaust at the strong Lyman-alpha solar emission line (1216 Angstrom), (iii) solar-induced photodissociation of H2O in the far UV, at shorter wavelengths than Lyman-alpha, and (iv) luminescent collisions between atmospheric species and exhaust constituents, most probably the reaction O + H2O yields OH(A) + OH(X). Process (i) produces a very rotationally cold and spectrally narrow component due to the rapid cooling of the OH(X) in the supersonic expansion of the exhaust flow. Processes (ii) and (iii) produce extremely excited OH(A), not well characterized by thermal vibrational or rotational distributions. The 0 + H2O chemiluminescence reaction has a substantial activation energy, 4.79 eV, and is only slightly above threshold for the ram geometry, where the engine exhaust is directed into the atmospheric wind.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 2003
- Accession Number
- ADA423353
Entities
People
- A. L. Broadfoot
- J. A. Gardner
- L. S. Bernstein
- M. I. Lester
- Y. Chiu
Organizations
- Air Force Research Laboratory