The Effects of Inorganic Fillers on the Radiation-Induced Conductivity of Spacecraft Polymers

Radiation-Induced Conductivity (RIC) is an importantdielectric property for evaluating the likelihood of electrostaticdischarge (ESD) due to radiation in the space environment. SinceRIC can greatly increase the bleed-off of charge duringirradiation, spacecraft charging assessments that fail to accountfor its effects may be overly conservative. This study examines theimpact of common fillers on RIC properties in a few spacecraftpolymers and is a follow-on to our previous work on the impact ofinorganic fillers on dark conductivity. As described in our earlierwork, the charge storage method was used to measure theconductivity of up to 34 samples at a time in a vacuum chamberequipped with an electron flood gun and a robotic system toautomatically measure surface potential using a Kelvin-typeprobe. The system was modified for these tests by the addition ofpenetrating electrons to stimulate RIC. The impacts on RIC ofglass fiber fill are examined in three engineering plastics (PEI, PI,and PEEK). The inclusion of glass beads—typically used for bondline control—is discussed for typical epoxy and silicone adhesives.Finally, we discuss the effects of ceramic and fumed silica fillers inurethane adhesives. The impact of inorganic fillers on RIC variesgreatly from case to case.