Investigation of the Scratched Tape Scattered Light Artifact at Rubin Observatory

Abstract

The “scratched tape” stray light feature is the most prominent and prevalent stray light artifact identified during the commissioning of the Vera C. Rubin Observatory. This feature originates when light from large off-axis angles (∼20 deg) passes between the mid-level and center-section light baffles of the Simonyi Survey Telescope, reflects off of the primary mirror, and illuminates the LSST Camera. This scenario represented an unobstructed light path to the sky during Rubin commissioning that arose due to delays in the integration of the dome slit light–wind screen. Once identified and characterized, the scratched tape light path was successfully mitigated by extending the mid-level light baffle outward by ∼22 cm. This document describes the identification, modeling, characterization, and mitigation of the scratched tape stray light artifact.