Biocidal Conditions in Low-Mars-Orbit Can Inactivate Bioburden on External Mars Spacecraft Surfaces and Dust...

Area of Science:

• Astrobiology
• Planetary Protection
• Spacecraft Sterilization

Background:

• Mars Sample Return Program requires spacecraft sterilization in low-Mars-orbit (LMO).
• External spacecraft surfaces may encounter Mars dust and potential microbial contamination during sample transfer.
• Understanding microbial survival under LMO conditions is crucial for mission success.

Purpose of the Study:

• To assess the impact of LMO conditions (UV, vacuum, solar heating) on microbial survival.
• To quantify the synergistic effects of these conditions on UV-resistant and heat-tolerant microorganisms.
• To determine the efficacy of LMO sterilization in achieving mandated Sterility Assurance Levels (SALs).

Main Methods:

• Exposure of bacterial spores (Bacillus pumilus, Geobacillus stearothermophilus), yeast (Naganishia onofrii), and fungal spores (Aspergillus fumigatus) to simulated LMO conditions.
• Testing microbial survival with and without a Mars simulant dust layer.
• Analysis of UV transmittance through microbial spore aggregates.

Main Results:

• Direct UV exposure in LMO achieved SALs rapidly for Aspergillus fumigatus (2.0 h) and Bacillus pumilus (76.6 min).
• The presence of Mars simulant dust significantly increased time to SAL: 22 h for A. fumigatus and 1.72 h for B. pumilus.
• UV transmittance through 12 µm spore aggregates was low (~4-5%), indicating shielding effects.

Conclusions:

• The LMO environment is a viable method for reducing spacecraft bioburden.
• Mars dust and microbial aggregation act as shields, attenuating UV radiation and extending required sterilization times.
• Mission planning must account for dust and aggregation effects to ensure adequate bioburden reduction.