TABLE OF CONTENTS Spacecraft thermal designs employ wavelength-dependent thermal-control coatings for various purposes. Solar reflectors, such as second-surface mirrors, white paints, and silver- or aluminum-backed Teflon, are used to minimize absorbed solar energy, yet they emit energy almost as a blackbody would. To minimize both the absorbed solar energy and infrared (IR) emission, polished metal such as aluminum foil or gold plating is used. Black paint is commonly utilized on the interior of the vehicle, to facilitate radiant heat transfer among internal components. Thus the existing state of the art includes a rather wide variety of wavelength-dependent coatings. The problems of in-space stability, outgassing, and mechanical adhesion to the substrate have all been resolved for most coatings. Many fully qualified coatings are available, so development and qualification of a new coating is normally unnecessary.
The external surfaces of a spacecraft radiatively couple the spacecraft to space. Because these surfaces are also exposed to external sources of energy, such as sunlight and Earth-emitted IR, their radiative properties must be selected to achieve an energy balance at the desired temperature between spacecraft internal dissipation, external sources of heat, and reradiation to space, as illustrated in Fig. 4.1.
The two primary surface properties of importance are the IR emittance and the solar absorptance. Figure 4.2 indicates the range of properties available for...
