Roger W. Dahl

Miniature microwave powered steam sterilization chamber

A small device for the rapid ultrahigh temperature sterilization of surfaces is described. Microwave power generated by a 2.45 GHz magnetron is delivered via coaxial cable to a silicon carbide block housed within the chamber. Small quantities of water or aqueous hydrogen peroxide are introduced into the chamber. Upon application of power, the liquid flashes to vapor and superheats producing temperatures to 300 °C. The hot vapor permeates the enclosed space and contacts all exposed surfaces. Complete microbial kill of >10 6 colony forming units of the spore forming thermophile, Bacillus stearothermophilus, has been demonstrated using a variety of temperatures and exposure times in both steady state and thermal pulse modes of operation.

A Microwave-Powered Sterilizable Interface for Aseptic Access to Bioreactors That Are Vulnerable to Microbial Contamination

Novel methods and apparatus that employ the rapid heating characteristics of microwave irradiation to facilitate the aseptic transfer of nutrients, products, and other materials between microbially sensitive systems and the external environment are described. The microwave‐sterilizable access port (MSAP) consists of a 600‐W magnetron emitting at a frequency of 2.45 GHz, a sterilization chamber with inlet and outlet flow lines, and a specimen transfer interface. Energy is routed to the sterilization chamber via a coaxial transmission line where small quantities of water couple strongly with the incident radiation to produce a superheated vapor phase. The efficiency of energy transfer is enhanced through the use of microwave susceptors within the sterilization chamber. Mating surfaces are thermally sterilized through direct contact with the hot gas. Efficacy has been demonstrated using the thermophile Bacillus stearothermophilus.

NONHAZARDOUS URINE PRETREATMENT METHOD FOR FUTURE EXPLORATION SYSTEMS

acceptance of sodium benzoate as an antifungal agent in food, and the use of organic acids as food preservatives. Urine pretreatment in use aboard the International Space Station (ISS) is based upon the strong oxidant, hexavalent chromium, and operates at a pH < 1.8, which necessitates triple containment. This carcinogenic oxidant generates harmful oxidation products in urine and is rapidly rendered inactive by oxidation-reduction reactions. In comparison, the nonhazardous urine pretreatment chemicals are stable and safe to handle with benign storage and use requirements. These characteristics will lower urine pretreatment Equivalent System Mass (ESM) by decreasing containment volume and mass, expendable chemical mass, system complexity, and crew time needed to handle pretreatment chemicals.

Advanced Plasma Pyrolysis Assembly (PPA) Reactor and Process Development

Design and development of a second generation Plasma Pyrolysis Assembly (PPA) reactor is currently underway as part of NASAs Atmosphere Revitalization Resource Recovery effort. By recovering up to 75% of the hydrogen currently lost as methane in the Sabatier reactor effluent, the PPA helps to minimize life support resupply costs for extended duration missions. To date, second generation PPA development has demonstrated significant technology advancements over the first generation device by doubling the methane processing rate while, at the same time, more than halving the required power. One development area of particular interest to NASA system engineers is fouling of the PPA reactor with carbonaceous products. As a mitigation plan, NASA MSFC has explored the feasibility of using an oxidative plasma based upon metabolic CO2 to regenerate the reactor window and gas inlet ports. The results and implications of this testing are addressed along with the advanced PPA reactor development.