Applied Approach for Assessing Bioburden of the Mars 2020 Parachute Assembly

The Mars 2020 mission delivered the Perseverance rover to the surface of Mars using a supersonic parachute manufactured at Airborne Systems, California. The Mars 2020 spacecraft, including the flight parachute, was subject to Planetary Protection spore bioburden compliance. Many previous missions with similar parachutes applied manufacturing specifications for calculating bioburden. Although the Mars 2020 parachute was manufactured in an uncontrolled environment, preliminary sampling of a flight-like parachute manufactured in the same facility suggested that the actual spore bioburden levels were potentially orders of magnitude lower than specification values for uncontrolled manufacturing (100,000 spores/m²). Several experiments were designed and carried out throughout the project timeline in an effort to estimate a representative bioburden for the flight parachute. Tests were performed on various parachute materials, including direct sampling and destructive assays of proxy materials. Different bioburden densities were applied to large continuous areas of the canopy, which experienced minimal handling, and seamed areas of the parachute that were likely to experience more handling during the stitching process. In addition, an approach to account for various thermal zones was developed and applied toward calculating log reduction for the parachute assembly. These various methods that were used toward different areas and materials of the Mars 2020 flight parachute provided a nuanced and data-backed estimate of spore bioburden density that can be adopted by future missions.