Laboratory Characterization of Homogeneous Spacecraft Materials

Abstract

This paper presents laboratory measurements and analysis of optical spectral bidirectional reflectance distribution functions of materials commonly found on the surfaces of spacecraft. A goniospectrometer sensitive to light with wavelengths between 350 and 1100 nm was constructed, and four classes of materials were studied in a variety of illumination and observational geometries: triple-junction photovoltaic cells, aluminum, white-coated metallic surface, and aluminized polyimide films. The measurements were analyzed to study how specific materials could be characterized based on their spectral bidirectional reflectance distribution function and how it varies with changing illumination and observational geometry. In the end, the experiment yielded two significant outcomes. First, the results provide a better understanding of how the spectral energy distribution of light reflected from these materials behaves as the illumination and observational geometry is varied. This result will be particularly useful in the interpretation of spectra and color photometric measurements of artificial objects in Earth orbit. Second, and more important, this experiment convincingly demonstrates that any spectral library of materials commonly found on spacecraft must include measurements taken throughout the widest range of observational geometries. With this in mind, the measurements collected during this experiment now serve as the first entries in an open-access spectral library of spacecraft material.