SOLAR-STELLAR IRRADIANCE COMPARISON EXPERIMENT-1 .1. INSTRUMENT DESIGN AND OPERATION

The main objective for the Solar-Stellar Irradiance Comparison Experim ent (SOLSTICE) is to accurately measure the full disk solar spectral i rradiance in the ultraviolet (UV) spectral region over a long time per iod. To meet this objective, SOLSTICE has the unique capability of mak ing routine observations of the UV radiation from a set of early-type stars, using the identical optical elements and detectors employed for the solar observations. The stars selected for this calibration are a ssumed, on the basis of stellar evolution theory, to be extremely stab le in the UV spectral region. Moreover, it is the average flux from a number of stars, perhaps from as many as 25, that is assumed to be sta ble. The SOLSTICE 1 is on the Upper Atmosphere Research Satellite (UAR S), and the overall design and operation of the instrument are discuss ed. The quality of the solar and stellar data is extremely high and pr eliminary results indicate that the technique is working well.