The Orbiting Astronomical Observatory (OAO)-C was successfully launched into 400-nautical mile circular orbit on August 21, 1972. For this spacecraft, a unique sensitivity approach to the thermal design was developed which resulted in a predictal design—the merits of which should be considered for application on future spacecra. The OAO-C is also serving as a test bed for the evaluation of thermal control hardware. To provide flight data for space program applications, experiments for a new coating and four different heat pipe designs are on this spacecraft. The data derived from OAO-C will be extremely valuable for such future programs as the Large Space Telescope (LST) and the Earth Observation Satellite (EOS). This paper will describe the detailed of the sensitivity design approach and thermal control hardware. For all aspects discussed, a comparison of pertinent analysis, ground test data, and flight data [1] will be given.