A highly reflective, white conductive coating system was developed using a layered approach with a combination of commercially available white conductive pigments within a conductive binder system. The top coating is a space-stable, radiation-resistant, highly reflective coating that has been tailored to provide optimum reflectance properties and meet vacuum thermal surface resistivities. The combined layer is a mixture of a highly reflective, electrically dissipative coating and a moderately reflective but highly conductive pigment in a conductive binder. A second, underlying layer of conductive white coating offers optimum adhesion to metal substrates and the topcoat. The system vacuum resistivity at room temperature is approximately 1 × 109 ohms/sq, and has a solar absorptance of less than 0.13 as measured on a Cary 5000 spectrophotometer.
A layered thermal coating approach has been formulated and tested. The combination of these two components allows for a top layer that reflects, or scatters, the majority of incident solar flux (solar absorptance of 0.13), while allowing the longer-wavelength radiation to scatter within the coating to the second layer. The second underlying layer consists of a coating that is highly reflective and electrically conductive, and binds well to the underlying metal substrate and to the top coating. The ranges in dry film thickness of the top and underlying coatings top are between 0.002 to 0.003 in. (≈51 to 76 μm), and between 0.001 and 0.002 in. (≈25 to 51 μm), respectively.
The thickness of the top coat prevents the very large populations of low-energy electrons from damaging the underlying coating. Application of the two systems is similar to standard silicate coating application procedures. The combined, layered system results in a coating that has a beginning-of-life solar absorptance that is 0.01 lower than the most reflective available coating, Z93C55; meets the ESD 1 × 109 ohms/sq surface resistivity requirements; will not have adhesion or corrosion issues with aluminum; will be stable in the geosynchronous environment;, and will have the lowest end-of-life solar absorptance of those products that meet ESD surface resistivity requirements.
This work was done by Mark Hasegawa, Kenneth O’Connor, Gilbert Castillo, and John Petro of Goddard Space Flight Center. GSC-16155-1