The Exploration Extravehicular Mobility Unit's (xEMU) helmet is a complex assembly designed to accomplish several critical tasks. In addition to maintaining a suitable environment for the wearer, it must also allow for appropriate mobility and provide a wide and undistorted view of the surroundings. A critical component of the helmet's optical system is the anti-fog coating. While previous versions of the anti-fog coating have provided suitable anti-fog performance, they have been difficult to apply, lacked mechanical/chemical durability, and/or resulted in unanticipated failures (e.g., outgassing of eye-irritating materials during use). This work will describe the use of a new coating technology, aerosol impact driven assembly (AIDA), to develop the next generation permanent anti-fog coating for the xEMU helmet. We will use AIDA's unique ability to tune both the refractive index and surface roughness of the film to deposit a thin (85% transmittance of visible light), and hydrophilic (contact angle <10°) anti-fog coating. We will characterize the anti-fog, optical, and durability (abrasion and chemical resistance) performance on polycarbonate substrates up to 15" x 20" -- the size required to manufacture operational helmets. We will conclude with an analysis on the path towards commercial production of the coating and discuss other potential use-cases within and beyond the xEMU helmet.
Firth et al. (Sun,) studied this question.