CALIBRATION FACILITY AND PREFLIGHT CHARACTERIZATION OF THE PHOTOMETERIN THE INFRARED SPACE-OBSERVATORY

A calibration facility simulating the optical and cryogenic environmen t of the Infrared Space Observatory (ISO) satellite has been built for characterizing the ISO photometer (ISOPHOT). This facility uses a com mercially calibrated 900-K blackbody radiation source and optics at ro om temperature to provide an f/15 beam to the instrument, which is con tained in a LHe cryostat. The low-level infrared flux levels of the IS O are obtained by using a light-sealed instrument chamber and cold att enuation filters. The infrared flux can be calculated using the known blackbody emission and the cold calibrated transmission spectra of the filters. The calibration facility further provides a scanning mechani sm, a light modulator, and filters for polarization measurements and w avelength calibrations of the ISOPHOT spectrometer channels. Electrica l support equipment for the instrument operation and software for data archiving and analysis have been customized for this project. The tes t program comprised a standardized acceptance test for the entire inst rument and special tests addressing individual instrument properties. The data obtained contain the photometric sensitivities of ISOPHOT, op timized instrument settings, reference data for the integrated system tests, and inputs for the ongoing mission planning.