Pulsed Electrophoretic Deposition of Carbon Nanotube Based Low-Reflective Coatings for Space Applications

Abstract

Space observatory missions requires the development of low-reflectivity surfaces/coatings for space-borne instruments, such as seeker telescopes, optical sensors, etc., to minimize stray and reflected light across the visible and infrared wavebands for facilitating the direct exoplanet detection and characterization. All space application materials require lightweight, good thermo-structural properties, and durability when exposed to harsh environments, such as UV, atomic oxygen, vacuum, etc. The excellent mechanical, thermal, optical, and electrical properties of carbon nanotubes (CNTs) make them as ideal coating materials for obtaining low reflectivity surfaces for space applications.In this presentation, Faraday Technology Inc. will discuss an innovative electrophoretic deposition (EPD) manufacturing process, based on the use of pulsed electric fields, for controlled, reproducible, scalable application of low reflective CNT based coatings. The low-reflectivity CNT coatings have been successfully deposited on a variety of geometries: flat coupons, curved surfaces, sharp edges, and internal and external surface of square tubes using the FARADAYIC® EPD process with different anode-cathode configurations (Figure 1 A). The CNT coatings show the total hemispherical reflection of ~ 1% across visible to near infrared (NIR) wavebands, which is 5 times better than the reflectance of the typically used Z306 black paint (Figure 1 B). Most importantly, the CNT coating shows no measurably discernible spectral reflectance changes after 2500 equivalent solar hours (ESH) UV/VUV illumination (Figure 1B). As a comparison, Z306 black paint shows more than 2% reflectance increases with same ESH UV/VUV illumination. These CNT coatings also withstood simulated launch conditions vibrational tests, and demonstrated no weight loss or optical degradation. Furthermore, the CNT coatings were evaluated for atomic oxygen erosion resistance in a simulated low earth orbit (LEO) environment, and showed enhanced resilience when compared to Kapton and HOPG.In summary, a scalable manufacturing process for fabricating CNT based coatings with low reflectivity across visible to near infrared wavebands has been demonstrated and shown great potential in facilitating space observatory missions by minimizing stray and reflected light on targeted telescope and baffle materials and construction. The CNT based coatings will also be beneficial for optoelectronic fields for minimizing unwanted surface reflections for solar thermal power generation and storage, solar-driven steam generation for sanitization and water purification, and so on. Acknowledgements: The financial support of NASA SBIR program through contracts No. 80NNSC18P2062 & 80NSSC19C0177 is acknowledged. The authors acknowledge Alan Hopkins, Peter Fuqua, Amber Hennessy, Aura C Labatete-Goeppinger, Martin Ciofalo, and Lee Wizda from the Aerospace Corporation for simulated launch conditions vibration tests, optical characterization, and UV radiation effect tests. David Oakes and Alan Hoskinson from Physical Sciences Inc. are acknowledged for the atomic oxygen erosion tests on the CNT based coatings. Figure 1