Robert A. Beaudet

Microwave Spectrum, Barrier to Internal Rotation, and Dipole Moment of Cis‐Crotononitrile

The microwave spectrum of cis‐CH3CH=CHCN has been measured and assigned in the region 8–34 kMc/sec. The transitions were split by tunneling of the methyl group through the potential barrier to internal rotation. From these separations the barrier was determined as 1400 cal/mole. The total dipole moment is 4.08 D.

Microwave Spectrum, Isomeric Form, and Dipole Moment of 1,1‐Difluorobutadiene

The microwave spectrum of 1,1‐difluorobutadiene has been studied. The small inertial defect indicates that the molecule is planar. From the allowed transition selection rules and the magnitudes of the moments of inertia, the molecule is shown to exist predominantly as the trans isomer. Attempts to find the spectrum of the cis form were unsuccessful.

Determination of Lethality Rate Constants and D-Values for Bacillus atrophaeus (ATCC 9372) Spores Exposed to Dry Heat from 115°C to 170°C

Dry heat microbial reduction is the NASA-approved sterilization method to reduce the microbial bioburden on spaceflight hardware for missions with planetary protection requirements. The method involves heating the spaceflight hardware to temperatures between 104 degrees C and 125 degrees C for up to 50 hours, while controlling the humidity to very low values. Collection of lethality data at temperatures above 125 degrees C and with ambient (uncontrolled) humidity conditions would establish whether any microbial reduction credit can be offered to the flight project for processes that occur at temperatures greater than 125 degrees C. The goal of this research is to determine the survival rates of Bacillus atrophaeus (ATCC 9372) spores subjected to temperatures higher than 125 degrees C under both dry (controlled) and room ambient humidity (36-66% relative humidity) conditions. Spores were deposited inside thin, stainless steel thermal spore exposure vessels (TSEVs) and heated under ambient or controlled humidity conditions from 115 degrees C to 170 degrees C. After the exposures, the TSEVs were cooled rapidly, and the spores were recovered and plated. Survivor ratios, lethality rate constants, and D-values were calculated at each temperature. At 115 degrees C and 125 degrees C, the controlled humidity lethality rate constant was faster than the ambient humidity lethality rate constant. At 135 degrees C, the ambient and controlled humidity lethality rate constants were statistically identical. At 150 degrees C and 170 degrees C, the ambient humidity lethality rate constant was slightly faster than the controlled humidity lethality rate constant. These results provide evidence for possibly modifying the NASA dry heat microbial reduction specification.

Determination of Lethality Rate Constants and D-Values for Heat-Resistant Bacillus Spores ATCC 29669 Exposed to Dry Heat from 125°C to 200°C

Exposing flight hardware to dry heat is a NASA-approved sterilization method for reducing microbial bioburden on spacecraft. The existing NASA specification only allows heating the flight hardware between 104°C and 125°C to reduce the number of viable microbes and bacterial spores. Also, the NASA specifications only allow a four log reduction by dry heat microbial reduction because very heat-resistant spores are presumed to exist in a diverse population (0.1%). The goal of this research was to obtain data at higher temperatures than 125°C for one of the most heat-resistant microorganisms discovered in a spacecraft assembly area. These data support expanding the NASA specifications to temperatures higher than 125°C and relaxing the four log reduction specification. Small stainless steel vessels with spores of the Bacillus strain ATCC 29669 were exposed to constant temperatures between 125°C and 200°C under both dry and ambient room humidity for set time durations. After exposures, the thermal spore exposure vessels were cooled and the remaining spores recovered and plated out. Survivor ratios, lethality rate constants, and D-values were determined at each temperature. The D-values for the spores exposed under dry humidity conditions were always found to be shorter than those under ambient humidity. The temperature dependence of the lethality rate constants was obtained by assuming that they obeyed Arrhenius behavior. The results are compared to those of B. atrophaeus ATCC 9372. In all cases, the D-values of ATCC 29669 are between 20 and 50 times longer than those of B. atrophaeus ATCC 9372.

Simple Mathematical Models for Estimating the Bio-Contamination Transported from a Lander or a Rover to the Martian Soil

To enable reliable in situ, or sample return, life detection missions, it is critical that Mars Sample Return missions be free of any biological materials that originated from Earth.

Extended Temperature Range Studies for Dry Heat Microbial Reduction

This paper will present the lethality data that has been collected at this time and the planned future studies. The results show that rapid ramp-up heating times are critical to obtaining valid lethality data at high temperatures because an extensive number of spores are killed before reaching the target temperature. Exploratory experiments have also been performed using a laser to rapidly heat coupons.