TABLE OF CONTENTS Surfaces can either naturally or after treatment be made to absorb and emit radiant energy at specific rates corresponding to the spectrum of radiation. Some of these properties and their directional and spectral behavior are discussed in Chapter 3.
Thermal control coatings (TCCs) have been classified as follows:
Solar reflectors, which have a low solar absorptivity but high emissivity, are useful in a solar or albedo environment as they reflect much of the impinging energy while retaining the high IR emissivity needed for efficient rejection of spacecraft waste heat. They include white paints, with as-applied ratio of ? s/ ? as low as 0.2, and optical solar reflectors (OSRs) that work on the principle of the second-surface mirror, where solar radiation penetrates a thin transparent high-emissivity material (Teflon, glass, etc.) then reflects off a metallic substrate, effectively producing a low- ? s, high- ? surface. A schematic is given in Fig. 6.3a. A popular OSR is the flexible silvered Teflon ( ? 127 ?m thick with the Teflon facing outward toward the environment), which can be made with an adhesive backing for direct application on a surface. Some measurements on the 127- ?m silvered Teflon show as-applied values of ? s/ ? as low as 0.07/0.79. Quartz mirrors (with average measured as-applied ? s/ ? = 0.08/0.78) have also seen extensive use. They come in the shape of wafers (2 4 cm squares, ?150 200
