Abstract Responsible space exploration is a cornerstone of planetary protection, particularly at sites in the Solar System with a high potential for the existence of extant life. To limit bioburden, spacecraft assembly occurs in cleanroom facilities. Cleanroom levels are established through air particulate counters that can assess particle size distribution and concentration but cannot detect bioaerosols. Additionally, these devices do not detect in real-time, which poses a risk to critical flight hardware assemblies or even mission timelines. A first-of-its-kind study was conducted to simultaneously detect bioaerosols, inert particles, and their size distribution in real-time in operational spacecraft assembly cleanrooms at NASA's Jet Propulsion Laboratory in Pasadena, CA, USA, using the BioVigilant IMD-A® 350 (Azbil Corporation, Tucson, AZ, USA). The IMD-350A continuously sampled during operations and no-operation 6 h intervals in two facilities per cleanroom class: ISO 6, ISO 7, and ISO 8. A positive correlation was established between human presence in the cleanroom and elevated bioaerosol counts. Smaller particles of sizes 0.5 and 1 μm constituted an average ∼91% of the total bioaerosols detected in At Work intervals across all ISO classes observed. The results of this study were used to establish bioburden particulate thresholds for the most stringent JPL cleanrooms used in the assembly of the Sample Caching System for the Mars 2020 Perseverance rover.
Keywords: Bioaerosols; Bioburden; Cleanrooms; Particle size distribution; Planetary protection.