Experimental and Flight Determination of the Solar Absorptance for an OSR Radiator as a Function of Incidence Angle

An INTELSAT-funded experiment to determine the solar absorptance of optical solar reflectors (OSRs) as a function of incidence angle has confirmed the initial findings from flight data reduction on the COMSAT COMSTAR Beacon experiments. The OSR solar absorptance is shown to increase with increasing sun incidence angle. The magnitude of the increase for a body-stabilized spacecraft in geosynchronous orbit during peak solar illumination and a 66.5° incidence angle is 20 percent larger than the value normally derived from spectrophotometer measurements. These results help to explain the increases in spacecraft temperature and OSR degradation observed on many spacecraft immediately after launch which heretofore have been attributed to outgassing effects.