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

Radiation-Induced Conductivity (RIC) is an important dielectric property for evaluating the likelihood of electrostatic discharge (ESD) due to radiation in the space environment. Since RIC can greatly increase the bleed-off of charge during irradiation, spacecraft charging assessments that fail to account for its effects may be overly conservative. This study examines the impact of common fillers on RIC properties in a few spacecraft polymers and is a follow-on to our previous work on the impact of inorganic fillers on dark conductivity. As described in our earlier work, the charge storage method was used to measure the conductivity of up to 34 samples at a time in a vacuum chamber equipped with an electron flood gun and a robotic system to automatically measure surface potential using a Kelvin-type probe. The system was modified for these tests by the addition of penetrating electrons to stimulate RIC. The impacts on RIC of glass fiber fill are examined in three engineering plastics (PEI, PI, and PEEK). The inclusion of glass beads-typically used for bond line control-is discussed for typical epoxy and silicone adhesives. Finally, we discuss the effects of ceramic and fumed silica fillers in urethane adhesives. The impact of inorganic fillers on RIC varies greatly from case to case.