Thermal Control Coatings on Mg-Li Alloys

Integral black anodizing and gold plating on Mg-Li alloys were developed for spacecraft thermal control applications. The influence of various process conditions have been investigated to optimise the process. The deposits were characterized by morphological studies, adhesion test, thickness measurement, microhardness evaluation and porosity inspection. The space worthiness of the coatings has been evaluated by humidity, thermal cycling, and thermovacuum tests and measurement of optical properties. The high solar absorptance and infrared emittance (α_s = 0.95, ε_IR = 0.93) value of black anodic film showed that these can be effectively utilized to improve heat radiation characteristics. The gold coating on the other hand provides the infrared emittance as low as 0.03, is extremely suitable in minimising the radiative coupling with other components within the spacecraft. Such gold metallised surfaces with extremely low infrared emittance values are useful as radiation shields for achieving temperatures as low as 80°K in space application such as very high resolution radiometers.