Role of Water Vapor in Solar Array Arc Initiation: Dissociative Recombination Processes

Abstract

Strong supporting evidence that adsorbed water vapor residing at the triple junction sites on a solar array is a leading contributing factor to arcing onset in conventional silicon photovoltaic arrays immersed in low Earth orbital plasmas is presented. It is suggested that an adsorbed water vapor layer becomes ionized by energetic electrons and that the discharge develops in the area of a triple junction. The fastest process to extinguish the discharge is the dissociative recombination of water molecular ions. Arc plasma spectroscopic data throughout the wavelength range 260-680 nm is obtained. The two most intensive silver lines in the UV spectrum (Ag 1, 328 and 338 nm), an atomic silver line (Ag I, 358.6 nm), and two lines of singly ionized silver atoms (Ag II, 318.7 and 368.2 nm) are identified. Additionally, atomic line spectra Fe I (415.87 nm) and Ni I (480.7 nm) are found. More importantly, identification of several species that appear to validate a dissociative recombination process involving water vapor is also found. The observations involved are the OH molecular band (302-309 nm) and two intensive atomic lines (H-α, 656.3 nm, and H-β, 486 nm). The following species with molecular bands, CH (432 nm), SiH (387 nm), and SiN (472 nm) are also identified.