The effects of evolving surface contamination on spacecraft charging have been investigated through (i) ground-based measurements of the change in electron emission properties of a conducting surface undergoing contamination and (ii) modeling of the charging of such surfaces using the NASCAP code. Specifically, we studied a Au surface as adsorbed species were removed and a very thin disordered carbon film was deposited as a result of exposure to an intense, normal incidence electron beam. As a result of this contamination, we found an ~50% decrease in secondary electron yield and an ~20% reduction in backscattered yield. The type and rates of contamination observed are similar to those encountered by operational spacecraft. Charging potentials of an isolated panel of the material were determined under both sunlit and eclipse conditions in geosynchronous orbits for typical and extreme environments. In all environments studied, just monolayers of contamination lead to predictions of an abrupt threshold effect for spacecraft charging; panels that charged to small positive values when uncontaminated developed kilovolt negative potentials. The relative effect of NASCAP parameters for modeling secondary and backscattered electron emission and plasma electron distributions were also investigated. We conclude that surface contamination must be considered to avoid the serious detrimental effects associated with severe spacecraft charging.

The 2D dielectric phases and phase transitions of adsorbed dipolar molecules are modeled using a dilute spin-one Ising model. This model is studied in the Blume-Emery-Griffiths formalism, using a mean-field approximation, where the interaction parameters are related to system interaction energies using a unique averaging procedure. The model is applied to four halogenated methane species physisorbed on MgO(100) and NaCl(100) surfaces using previous experimental and theoretical studies to estimate the interaction energy parameters. We find that temperature-and coverage-dependent antiferroelectric to ferroelectric, coverage-dependant ferroelectric up to ferroelectric down, reentrant ferroelectric to ferroelectric, and order-disorder dipole phase transitions can occur. Phase diagrams based on this model are presented.