Scattering properties of black pigments: Implications for detecting faint sources near the moon using ground-based telescopes

The search for artificial and natural objects in both cis-lunar and trans-lunar space has grown increasingly important. To accurately detect and track small objects, stray light mitigation is a necessity. Observations conducted in 2022 from a ground-based telescope intended to track such objects have been hampered by excess lunar stray light. In this paper, we present work done to resolve this problem by applying black pigments to the optical tube and thus suppressing its surface scattering. A non-sequential ray tracing model was created to analyze the telescope’s final focal plane irradiance. This model was used to identify critical and illuminated surfaces to determine the stray light paths that have affected observations. We conducted experimental tests to measure the Bidirectional Reflectance Distribution Function (BRDF) of various practical, readily available, and robust black coatings, including paints such as Black 3.0 and Musou. After application on the actual telescope tube, the new surface coating reduced the photon count on the detector from a variable-angle off-axis point source by 76% over all angles measured.