Durability of ITO-MgF2 Films for Space-Inflatable Polymer Structures

This paper presents results from ITO-MgF 2 film durability evaluations that included tape peel, fold, thermal cycle and AO exposure testing. Polymer coupon preparation is described as well as ITO-MgF 2 film deposition equipment, procedures and film characterization. Durability testing methods are also described. The pre- and post-test condition of the films is assessed visually, microscopically and electrically. Results show that at ~500A ITO - 9 vol% MgF 2 film is suitable to protect polymer surfaces, such as those used in space-inflatable structures of the PowerSphere microsatellite concept, during a 1-year Earth orbiting mission. Future plans for ground-based and orbital testing of this film are also discussed. Introduction An increasing number of NASA missions will benefit from constellations of microsatellites (or microsats) to obtain broad-area, contemporaneous measurements. These multi-kilogram class microsats tend to be power poor due to limited spacecraft surface area to body-mount photovoltaic cells. At the same time, tracking planar solar array systems are mass prohibitive for this class of microsat. An elegant solution to this power pinch challenge is the PowerSphere (Lin, et al., 2003 and Simburger, et al., 2002) concept shown in Figure 1. The PowerSphere space-inflatable, geodetic solar array provides attitude-independent microsat power with very low mass and efficient launch packaging to enable microsat constellation deployment from a single carrier spacecraft. Once inflated, an ultraviolet (UV) activated resin impregnated in PowerSphere central columns and cylindrical solar cell connecting hinges is rigidized by exposure to sunlight and Earth albedo. These inflatable/rigidizable columns and hinges as well as thin-film solar cell substrates and encapsulants are all constructed of polymer materials. During operation in Earth orbit, virgin polymer surfaces could charge to high voltage leading to damaging electrostatic discharge (ESD). In addition, the presence of atomic oxygen (AO) in low Earth orbits leads to aggressive attack of unprotected polymers. Figure 1. PowerSphere Concept