Most commercial paints are unsuitable for use in space. Painted materials or structures present a large surface area to environmental conditions. Only
with careful selection, application and control of processes can paints fulfil the specified function.
The most critical use of paints is in the thermal-control subsystem. They can also be employed for corrosion protection. Inks are used for marking and for identification purposes.
Common organic binders are epoxies, acrylics, silicones, and polyurethanes. Inorganic bases are mainly silicates. Pigments are chosen to produce the specified optical properties:
for low solar absorptance and high emittance (zinc oxide (ZnO), titanium dioxide (TiO2 ), zinc orthotitanate (Zn2 TiO4 ) and zirconium dioxide (ZrO2 ) are the most common);
-aluminium flakes for medium absorptance and emittance;
-carbon black for high absorptance and emittance.
Electrically conductive thermal-control paints were developed to avoid charging and discharging in geostationary orbit. Some, which are based on metal or carbon pigments, can be used when a α /ratio
close to one is acceptable. Electrically conductive white paints are based on semi-conductive pigments; their stability in the space environment has now been assessed in some cases. Paints normally contain several proprietary components intended to give them good application properties. They come in the form of one-part or two-part, rather viscous liquids. They are brought to the right viscosity by mixtures of solvents. Solvent-free paints also exist.