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Design Of A Laboratory Study Of Contaminant Film Darkening In Space

One of the most deleterious effects of spacecraft contaminant films is that they increase the solar absorptance of optics, such as silvered fused silica thermal control mirrors or solar cell cover slips. However, this effect cannot currently be predicted with precision. Here we discuss the design of a laboratory program to enhance the quantitative understanding of this effect, as determined by the composition of the contaminant film and subsequent simulated environmental radiation-induced darkening. This effort includes four major elements: the quantitative identification of the classes of organic materials likely to be precursors of photochemically deposited contaminant films; prediction of these materials' sensitivities to energetic irradiation in the space environment; measurement of rates of deposition and optical absorption spectra of photochemically deposited films on fused silica; and measurements of further film darkening by irradiation with electrons, vacuum ultraviolet light, and ions. Each of these elements is discussed. A set of organic materials that have been chosen as analogs for major classes of spacecraft contaminants is presented, including the rationale for their selection and a prioritization of their potential importance. Apparatus design and performance and early experimental results are also described.