Evaluation of thermal control coatings exposed to ambient weather conditions at Haleakala High Altitude Observatory

The derived heat loads from thermal models are used to size the equipment that controls exterior enclosure seeing for the Advanced Technology Solar Telescope. These loads are highly dependent on the radiative properties assumed for the surface coatings of the enclosure. The properties of traditional white coatings and paints are known to degrade with time as they are exposed to the elements, but not by how much or how quickly. The solar reflectance and thermal emissivity of coatings considered for use on the enclosure, in a weathered condition, are not readily available from coatings manufacturers or in the scientific literature. The results from a one-year test of nine different coatings that were weathered at the summit of Haleakala on the island of Maui, Hawaii are reported and discussed.