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

The main objective for the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) is to accurately measure the full disk solar spectral irradiance in the ultraviolet (UV) spectral region over a long time period. To meet this objective, SOLSTICE has the unique capability of making 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 assumed, on the basis of stellar evolution theory, to be extremely stable 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 stable. The SOLSTICE 1 is on the Upper Atmosphere Research Satellite (UARS), and the overall design and operation of the instrument are discussed. The quality of the solar and stellar data is extremely high and preliminary results indicate that the technique is working well.