<title>Effect of the space environment on thermal control coatings</title>

Abstract

3322 Memorial Parkway, SW, Huntsville, AL 35801ABSTRACTThe optical characteristics of spacecraft surfaces are fundamental parametersin controlling its temperature. Passive thermal control coatings with designedsolar absorptance and infrared emittance properties have been developed for variousspace conditions and environments. In this total environment, the coatings must bestable and maintain their desired optical and mechanical properties for the courseof a particular mission ranging up to a lifetime of thirty years.This paper reviews stable polymeric and inorganic materials which we havedeveloped for different orbital missions, both near earth and geosynchronous.Physical characteristics of these coatings such as hardness, flexibility, and out—gassing behavior are presented. The response of optical properties as a function ofconditions such as ultraviolet—vacuum and atomic oxygen and also the function oftime are discussed.1. INTRODUCTIONIn the early days of spacecraft materials' development, ultraviolet (Uv) irrad—iation in vacuum testing was the principal means for evaluating optical stability.Additionally, the contributions of high energy electron and proton radiation,micrometeoroids and space debris, system—generated contamination and atomic oxygen(Ao), were also recognized and addressed. The particularly degrading effects of AOhave been observed from experiments on the Space Shuttle1 and most recently from theLong Duration Exposure Facility (LDEF).Our studies to develop spacecraft thermal control coatings for different mis—sions have been directed primarily toward optical stability in this severe environ—ment. In addition, our focus has been on coating systems which can be applied onrelatively large surfaces under ambient conditions and also cured at roomtemperature. Maintaining the simplicity of the processing procedure was consideredan important factor in obtaining desired materials reproducibility in optical andmechanical properties.2. RESULTS AND DISCUSSION2.1 Pigment screeningThe early studies consisted of ultraviolet—vacuum screening tests for a largenumber of white powders as potential solar reflector pigments.2 These tests wereperformed so that the less stable materials could be eliminated rapidly from any