Variable‐emittance infrared electrochromic skins combining unique conducting polymers, ionic liquid electrolytes, microporous polymer membranes, and semiconductor/polymer coatings, for spacecraft thermal control

Variable emittance (ε) is a property vital for the increasing needs in thermal control of future microspacecraft. This article describes fabrication, function, and performance of thin‐film, flexible, variable‐emittance (V‐E) electrochromic skins that use a conducting polymer/‐Au/‐microporous membrane (CP/Au/µP) base, and a new, unique ionic liquid electrolyte (IonEl). Poly(aniline‐co‐diphenyl amine) with a long‐chain polymeric dopant is used as the CP. A unique, patented device design yields no barrier between the active, electrochromic CP surface and the external environment, except for a thin, infrared‐transparent semiconductor/polymer film that lowers solar absorptance [α(s)] and protects from atomic‐O/far‐UV. Use of the IonEl requires special activation methods. Data presented show tailorable ε variations from 0.19 to 0.90, Δε values of >0.50 (which is the highest reported thus far for any functional V‐E material, to our knowledge), α(s) < 0.35, and nearly indefinite cyclability. Extended space durability testing, including calorimetric thermal vacuum and continuous light/dark cycling over >7 months under space conditions (<10−5Pa vacuum, far‐UV), show excellent durability. Other data show resistance to solar wind, atomic‐O, electrostatic discharge, and micrometeoroids. These lightweight, inexpensive, advanced polymeric materials represent the only technology that can work with micro‐ (<20 kg) and nano‐ (<2 kg) spacecraft, thus eventually allowing for much greater flexibility in their design and potentially “democratizing” the entire space industry, for example, allowing small firms to launch their own, dedicated satellites.