ATOMIC-OXYGEN-DURABLE AND ELECTRICALLY-CONDUCTIVE CARBON NANOUBE-BASED NANOCOMPOSITES FOR SPACE APPLICATIONS

Polyimide (PI) is extensively used in various space applications, e.g., as an exterior layer of thermal control blankets that are aimed to maintain a spacecraft’s instrumentation at working temperature. However, PI is degraded by electrostatic discharge (ESD) and atomic oxygen (AO), which are the dominant space environment hazards in geo-synchronous Earth orbit (GEO) and low Earth orbit (LEO), respectively. A common solution to this challenge is to coat the outer PI layer with indium tin oxide (ITO) which is AO resistant and electrically conductive and can therefore prevent local voltage build-up. However, ITO coatings are extremely brittle and cannot tolerate folding or bending when applied to flexible spacecraft surfaces. In this research, electrically-conductive PI-based composites for ESD protection were prepared by infiltration of PI-based blends into chemical vapor deposition (CVD)-grown carbon nanotube (CNT) sheets. AO durability was attained by the addition of polyhedral oligomeric silsesquioxane (POSS) to the PI precursor. This method prevents CNT agglomeration and degradation of the CNT properties. CNT-POSS-PI films with varying POSS content (0, 5, and 15 wt%) were prepared and exhibited homogeneous CNT distribution within the PI-based matrix. The composite films demonstrated sheet resistivities as low as 200 Ω/□, essentially preserving the original CNT sheet resistivity and well satisfying the ESD criterion. These resistivities remained essentially unchanged after mechanical manipulation, thermal cycling, and exposure to ionizing radiation. CNT-15%POSS-PI films exhibited an erosion yield of roughly one order of magnitude lower than that of pure PI films, and hence a 20 µm thick film could be functional for more than 10 years in the AO environment at LEO altitudes. CNT-PI and CNT-15%POSS-PI films are suggested for space applications such as the outer layers of spacecraft thermal blankets.