Issues and Advancements in Space Durable Multi-Functional Thermal Control Coatings

Abstract

Passive spacecraft thermal control coatings are required to possess properties of low solar absorptance, high thermal emittance, and stability to survive the space environment for the mission duration. The white paint coatings Z‐93, YB‐71 and S13G/LO, originally developed in the 1960s, have been successfully used for satellite thermal control and have served as standards for spacecraft white thermal control paints. Since their original development, these coatings have gone through re‐formulations as original raw materials became unavailable; however, their replacement products continue to serve as standards for spaceflight thermal control. Unique conditions of space exploration and space science missions have required that additional functionalities be incorporated into spacecraft thermal control coatings. Coating development efforts have addressed needs for long‐life stability, surface conductivity, and the ability to clean coating surfaces. Advancements in development of lightweight composite structures for spacecraft have led to the need for thermal control coatings that are adherent and compatible with these composite substrates, whereas the original formulations of white paints were developed for application to aluminum substrates. The pursuit of nuclear reactor powered spacecraft for future missions requires coating/substrate systems which are not only compatible with harsh space radiation environmental exposures, but must also perform at higher temperatures than have been previously required. Future missions to the lunar and Martian surfaces will additionally require thermal control coatings for which dust accumulation can be mitigated. Although advancements continue in the area of thermal control materials technologies, thermal control coatings are not currently commercially available to meet all of these advanced requirements. This paper presents some of the unique challenges for thermal control material systems for future space missions and some current approaches to meeting these challenges.