During the Spacelab 1 shuttle mission, the first spectral images of the N2+ first negative system in the dayglow were made with the Imaging Spectrometric Observatory, an array of imaging spectrometers that covered a wavelength range extending from the extreme ultraviolet to the near infrared. These data have been the subject of a comprehensive study involving additional ground-based observations, modeling of the causative mechanisms, and assessments of the predicted N2+ first negative system airglow on a semiglobal basis. Two surprising findings from these spectral images are that the bands of the N2+ first negative system exhibit very unusual vibrational distributions and that the intensities are significantly higher than anticipated. The spectra show unexpected populations up to &ngr;'=4, a result that was not anticipated on the basis of prior theories. It is found that an apparent rotational temperature of ~3000 K is needed to explain the data, while the closest apparent vibrational temperature is ~6000 to 8000 K. Conventional thermospheric theory is not able to account for these vibrational distributions which appear to be present throughout the 10-day shuttle mission and in quite different vehicle orientations.

In this paper we show examples of these spectra and then concentrate on comparing the measured absolute intensities of the 0-0 band at 3914 ¿ with the results from our inter-hemispheric thermospheric airglow model. After appropriate corrections are included for radiation backscattered from the atmosphere and the ground, the intensities are found to be larger than current theory predicts for midday conditions by factors greater than 3. At large solar zenith angles, these intensity data are consistent with the Atmosphere Explorer results. The question arises as to whether the enhanced midday intensities are due to unexplained processes in the natural dayglow or whether sources of N2+ exist in the shuttle environment which can lead to large intensity and vibrational population enhancements. Like the enhanced vibrational populations, the enhanced intensities are present over the course of the 10-day mission and do not appear to be associated with any particular vehicle attitude or viewing geometry. The intensity variation with solar zenith angle and viewing elevation appears to support the existence of a significant induced N2+ component near the shuttle, which fluoresces when the shuttle is sunlit. ¿American Geophysical Union 1992