OH(A --> 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 similar to390 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 --> 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 O + H2O chemiluminescent 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. Evidence for process (iv) is observed in the night ram but not the night perpendicular exhaust atmospheric interaction, consistent with the threshold energy. Through the use of a nonequilibrium spectral emission model for OH, the integrated intensity, spectral distribution, and OH(A) internal state characterization for each of the above processes was deduced. Additional confirmation of the analysis is provided through the use of a model simulation of the space experiment to predict the total integrated intensities for processes (i) and (ii), for which the underlying spectroscopy, absorption cross sections, and solar excitation intensities are well established. Analysis of process (iii) has established, for the first time, a value for the far-UV conversion efficiency of absorbed photons to OH(A) photons of 0.26, which is twice the established value for Lyman-alpha. Under the assumption that O + H2O collisions are the source of process (iv), the analysis has established a chemiluminescence cross section at ram conditions of 1.7 x 10(-2) Angstrom(2). Evidence of OH(A) emission bands from predissociated vibrational levels suggests that the total reaction cross section for process (iv) may be significantly higher. While this cross section assumes a single-step reaction of O with H2O, the possibility of a two-step process of 0 with other plume species has yet to be explored.