Electron beam irradiation for microbial reduction on spacecraft components

The highest degree of Planetary Protection (PP) applies to landed planetary missions and sample return missions. To date, Dry Heat Microbial Reduction (DHMR) treatment is the only NASA approved PP technique for meeting the stringent sterility requirements for life detection missions and to prevent forward contamination. However, spacecraft (s/c) and payloads are made up of a diverse set of man-made materials and components, some of which are incompatible with DHMR. NASA has therefore begun investigating several complementary sterilization techniques to DHMR. Here, we report on our progress in the investigation of the effectiveness of electron beam (e-beam) irradiation technique funded by a NASA Mars Exploration Program (MEP'03) award. E-beam irradiation using deep penetrating (several centimeters) high-energy (10 MeV) electrons is a well-developed method used for sterilization of food products in bulk quantities using linear accelerators. In contrast, low-energy (100 keV) electrons deposit their energy into about 50 micrometers, comparable to the scale of bacterial spores (typically several micrometers). The match between the depth of the penetration and spore size makes the "low-energy" electron irradiation extremely efficient for surface sterilization. E-beam irradiation is non-contact, leaves no residues, and as our preliminary results indicate is compatible with many s/c materials. Secondary contamination is often unavoidable since pre-sterilized s/c parts are used again for functional testing and re-assembly, necessitating reapplication of sterilization treatment. The 100 keV electron source is sufficiently small so that it could be made portable, which would make it suited for treatment localized, previously sterilized parts and subsystems.