CHARGING OF CERAMIC MATERIALS DUE TO SPACE-BASED RADIATION ENVIRONMENT

Radiation-induced charging of spacecraft coatings depends on material properties such as resistivity, dielectric constant, and photoelectron and secondary electron emission. Surface charging of a spacecraft is a complex phenomenon that depends on these material properties, as well as spacecraft geometry, orientation, sunlight intensity and distribution, temperature, and radiation environment. Ceramics can be problematic as spacecraft coatings due to their potential to store charge and develop differential voltage potentials. This paper examines the relative charging between a bare carbon-carbon heat shield and one coated with Al(2)O(3) in near solar (0.3 AU), Jovian, and deep space (2.5 AU, 5 AU) radiation environments, corresponding to points along a notional Solar Probe trajectory. Findings indicate that when modeled as a simple conical heat shield, the carbon structure alone does not develop a differential potential, whereas the Al(2)O(3) does, primarily in the cold Jovian environment. However, differential charging appears to be mitigated by photoelectron and secondary electron emission from the Al(2)O(3). The electrical conductivity of the ceramic increases near the sun due to increasing temperature, thus enabling equilibration of charge. The results of this study reject the initial hypothesis that electrically insulating coatings will create insurmountable charging issues for solar missions. Trajectory-dependent spacecraft illumination and temperature can be used to exploit desirable characteristics of the ceramic such as emission and conductivity, thus mitigating the problem. Integrated spacecraft charging simulations are planned.