Spectroscopic imaging of the thermosphere from the Space Shuttle

An important need for studies of the thermospheric chemistry and dynamics is multispectral information on the emissions over a broad wavelength range. An instrument that has been developed to meet this need is the Imaging Spectrometric Observatory which is currently undergoing integration for flight on the Shuttle Spacelab 1 mission (mid-1983). The instrument represents the coincidence of three major factors: the payload capacity of the Shuttle which permits the placing into orbit of a sufficiently large and comprehensive spectrometric system; the recent advances in solid state imaging detector components which have permitted use of very fast multiplexing detectors; and the maturing of knowledge of the thermosphere permitting clear identification of the desired measurements. The instrument consists of an array of five imaging spectrometers, each covering a portion of the 300-12000-A total wavelength range. The five spectrometers operate simultaneously with the spectrum being dispersed in one dimension on the focal plane detectors and spatial information along the slit length being resolved in the other. The detector system in each spectrometer is an intensified-charge coupled device, optimized for the wavelength region in question. The instrument has been designed in a modular fashion to permit variation in instrument parameters on subsequent flights. For the first flight the typical spectral resolution is 3 A (6 A below 1200 A). The sensitivity has been selected to permit coverage of a large dynamic range extending from weak nocturnal signals (approximately 1 R) to the bright earth (approximately10(7) R/A). The instrument has a minicomputer system which is located in the Spacelab module itself allowing payload crew interaction with the observation sequences. In addition, during the actual 7 days in orbit, the telemetry data stream from the instrument will be recorded directly on an instrument ground support minicomputer, permitting real-time and near-real-time evaluation of the data. The objectives on the initial flight are to obtain a survey atlas of the dayglow, nightglow, and twilightglow over the full wavelength range together with obtaining data necessary for the solution of several specific problems.