UV Reflectance of Spacecraft Materials and Analog Soils: Implications for Bioburden Reductions on the Undersides of Mars Rovers

Abstract
The Mars Sample Return mission architecture will utilize three spacecraft to collect, cache, recover, launch, and return to Earth a diversity of regolith and rock samples. However, no comprehensive Mars Microbial Survival (MMS) model currently exists.  As an initial effort in building a MMS model, we examined the UV reflectance of 15 spacecraft materials and seven Mars analog soils within the context of the Perseverance mission. Data were used to predict the times required to achieve one lethal dose (syn., Sterility Assurance Level [SAL]; def. as a bioburden reduction of ‒12 logs).  Results suggest that a single SAL dosage of UVC was achieved on exposed surfaces on the upper deck of Perseverance within a few hours to a few sols post-landing at Jezero Crater. The overall average for UVC reflectance from spacecraft materials was approx. 10%.  The overall UVC reflectance from Mars analog soils was measured at 1.3%.  The Adaptive Caching Assembly (ACA) on Perseverance is located on the forward edge of the underbelly of the spacecraft.  Modeling of the accumulated UVC dosage for the ACA yielded a prediction of reaching one SAL for downward facing surfaces at 93 sols that receive 'single bounce' UVC photons from the local terrain.  The SAL increases to 930 sols, if an additional 'bounce' of the solar UV irradiation is required to reach a partially protected site in the ACA hardware.  The current study is the first to report on the UVC reflectance from a diversity of spacecraft materials.