Photometric and Spectral Characterization of Spacecraft Materials With Application to Lunar Trailblazer

Abstract If a spacecraft loses contact with Earth, ground‐based observatories can collect observations to assist the recovery effort by providing information on spacecraft location and state. Optical observations converted to a light curve of spacecraft magnitude over time show the spin period and/or orientation of the spacecraft. For definitive interpretation, knowledge of the spacecraft's shape and reflectance properties are required. We conducted laboratory measurements of the visible/near‐infrared reflectance of common spacecraft materials (multilayer insulation (MLI), bare aluminum, solar cell, coated composite solar panel backing) at different orientations under controlled lighting conditions using a spectrogoniometer to obtain wavelength‐dependent characterization of material photometric properties for comparison with ground based optical observations. The materials are representative of the Lunar Trailblazer (LTB) spacecraft, which experienced an anomaly after launch and had several optical observations of the spacecraft collected during the recovery effort. All four materials are dark with reflectances 100x specular peak) with a small diffuse component, and the solar cell stands out with sharp specular peaks at the illumination angle together with a strong reflectance near 850–900 nm and a quasi‐periodic oscillation. This data set is available to constrain observations of future spacecraft.