Toward a Model for Biological Contaminant Dispersal by Spacecraft Operating and Landing in Near-Vacuum

When spacecraft operate and land in near-vacuum, as for Earth’s Moon or icy moons like Enceladus, they introduce contaminant into their environments that may impact mission science at local and global scales. The rarefied gas dynamic plume flows generated by chemical propulsion systems may remove and dis-perse terrestrial particles borne on such spacecraft, including microbes and spores. These high-speed flows provide a unique vector for transport of biological contaminant far from a spacecraft in near-vacuum, i.e. in the absence of atmospheric drag. This paper describes the initial development of gas dynamic and orbital mechanics models for spacecraft-generated plume flows and induced particle transport, and an investigation of necessary boundary conditions to address two key questions: how can plume flows remove and disperse microorganism-laden particles or independent microorganisms borne on a spacecraft? And how can biological contaminants redeposit both locally (to the spacecraft, its instruments, and landing site) and globally (i.e. to regions of scientific interest)?