Shirley Y. Chung

Molecular microbial diversity of a spacecraft assembly facility.

In ongoing investigations to map and archive the microbial footprints in various components of the spacecraft and its accessories, we have examined the microbial populations of the Jet Propulsion Laboratorys Spacecraft Assembly Facility (JPL-SAF). Witness plates made up of spacecraft materials, some painted with spacecraft qualified paints, were exposed for approximately 7 to 9 months at JPL-SAF and examined the particulate materials collected for the incidence of total cultivable aerobic heterotrophs and heat-tolerant (80 degrees C for 15-min.) spore-formers. The results showed that the witness plates coated with spacecraft qualified paints attracted more dust particles than the non-coated stainless steel witness plates. Among the four paints tested, witness plates coated with NS43G accumulated the highest number of particles, and hence attracted more cultivable microbes. The conventional microbiological examination revealed that the JPL-SAF harbors mainly Gram-positive microbes and mostly spore-forming Bacillus species. Most of the isolated microbes were heat resistant to 80 degrees C and proliferate at 60 degrees C. The phylogenetic relationships among 23 cultivable heat-tolerant microbes were examined using a battery of morphological, physiological, molecular and chemotaxonomic characterizations. By 16S rDNA sequence analysis, the isolates fell into seven clades: Bacillus licheniformis, B. pumilus, B. cereus, B. circulans, Staphylococcus capitis, Planococcus sp. and Micrococcus lylae. In contrast to the cultivable approach, direct DNA isolation, cloning and 16S rDNA sequencing analysis revealed equal representation of both Gram-positive and Gram-negative microorganisms.

Mechanical Properties and Morphology of Poly(etheretherketone)

Mechanical properties and morphology of poly(etheretherketone) (PEEK) were studied for samples having different thermal histories. Isothermal and rate-dependent crystallization were studied to ascertain the relationship between crystallinity/morphology and processing condition. Degree of crystallinity and microstructure were controlled by cooling the melt at different rates, ranging from quenching to slowly cooling, and by annealing amorphous material above the glass transition temperature Tg. It is found that degree of crystallinity was not as important as processing history in determining the room temperature mechanical properties. Samples with the same degree of crystallinity had very different tensile properties, depending on rate of cooling from the melt. All samples yielded by shear band formation and necked down. Quenched films had the largest breaking strains, drawing to 270 percent. Slowly cooled films exhibited ductile failure at relatively low strains. Best combined mechanical properties were obtained from semicrystalline films cooled at intermediate rates from the melt.

Tensile behaviour of blends of poly(vinylidene fluoride) with poly(methyl methacrylate)

Blends of poly(vinylidene fluoride) (PVF2) and poly(methyl methacrylate) (PMMA) were prepared over a wide concentration range and tested in tension at the same relative temperature below the glass transition. Testing was performed at strain rates ranging from 10 to 0.01 min−1 at test temperatures fromTg-40 toTg-10. By normalizing the test temperature to fixed increments belowTg, blends and homopolymers can be compared on the basis of PVF2 and PMMA composition and crystallinity. In nearly all blends, under conditions favouring disentanglement, (decrease in strain rate, or increase in test temperature), the yield stress and drawing stress decreased while the breaking strain increased. For materials with about the same degree of crystallinity, those with a higher proportion of amorphous PVF2 exhibited brittle-like behaviour as a result of interlamellar tie molecules. In the semicrystalline blends, yield stress remains high as the test temperature approachesTg, whereas in the amorphous blends the yield stress falls to zero nearTg. Results of physical ageing support the role of interlamellar ties which cause semicrystalline blends to exhibit ageing at temperatures aboveTg.

Supercritical CO 2 Cleaning for planetary protection and contamination control

We have designed and built a new Supercritical CO2 Cleaning (SCC) system1,2 to conduct cleaning efficiency studies using Supercritical CO2 and liquid CO2 to remove trace amounts of microbial and organic contaminants from spacecraft material surfaces. The objective of this task is to develop an effective CO2 cleaning method and to demonstrate and validate its ability to achieve ultra-clean surfaces of sample handling devices, sample storage units, and science instruments. This new capability will meet planetary protection and contamination control requirements for future Astrobiology science missions. The initial cleaning test results using this new cleaning device showed that both supercritical CO2 and liquid CO2 could achieve cleanliness levels of 0.01 µg/cm2 or less for hydrophobic contaminants. Experiments under supercritical condition using compressed Martian air mix, which consists of 95% CO2, produced similar cleaning effectiveness on the hydrophobic compounds. This opens up the possibility of further development potential for in situ CO2 cleaning and sterilization using Martian air for future Mars missions. We plan to further investigate the cleaning condition for hydrophilic compounds and bacterial spores, as well as introducing polar co-solvent to the cleaning apparatus.

Sample tube seal testing for Mars Sample Return

Four sealing methods for encapsulating samples in 1 cm diameter thin-walled sample tubes were designed, along with a set of tests for characterization and evaluation of sample preservation capability for the proposed Mars Sample Return (MSR) campaign. The sealing methods include a finned shape memory alloy (SMA) plug, expanding torque plug, contracting SMA ring cap, and expanding SMA ring plug. Mechanical strength and hermeticity of the seal were measured. Robustness of the seal to Mars simulant dust, surface abrasion, and pressure differentials were tested. Survivability tests were run to simulate thermal cycles on Mars, vibration from a Mars Ascent Vehicle (MAV), and shock from Earth Entry Vehicle (EEV) landing. Material compatibility with potential sample minerals and organic molecules were studied to select proper tube and seal materials that would not lead to adverse reactions nor contaminate the sample. Cleaning and sterilization techniques were executed on coupons made from the seal materials to assess compliance with planetary protection and contamination control. Finally, a method to cut a sealed tube for sample removal was designed and tested.

Conductive Sphere in a Radio Frequency Field: Theory and Applications to Positioners, Heating, and Noncontact Measurements

An electrically conductive spherical sample located in an electromagnetic field excited by rf (radio frequency) current in a system of coaxial coils is treated theoretically. Maxwell’s equations are solved exactly and all integrals in the formulas for the fields are evaluated analytically for the case where the sphere is on the axis and the coil system is modeled by a stack of filamentary circular loops. Formulas are also derived for electromagnetic force exerted on the sphere, excess impedance in the coil system due to the presence of the sphere, and power absorbed by the sphere. All integrals in those formulas have been evaluated analytically. Force measurements are presented and they are in excellent agreement with the new theory. A low‐power electromagnetic levitator that is accurately described by the theory has been demonstrated and is discussed. Experimental measurements of excess impedance are presented and compared with theory, and those results are used to demonstrate an accurate noncontact meth...

Particulate removal using a CO2 composite spray cleaning system

The Planetary Protection surface cleanliness requirements for potential Mars Sample Return hardware that would come in contact with Martian samples may be stricter than previous missions. The Jet Propulsion Laboratory has developed a new technology that will enable the removal of sub-micron size particles from critical hardware surfaces. A hand-held CO2 composite cleaning system was tested to verify its cleaning capabilities. This convenient, portable device can be used in cleanrooms for cleaning after rework or during spacecraft integration and assembly. It is environmentally safe and easy to use. This cleaning concept has the potential to be further developed into a robotic cleaning device on a Mars Lander to be used to clean sample acquisition or sample handling devices in situ. Contaminants of known sizes and concentrations, such as fluorescent microspheres and spores were deposited on common spacecraft material surfaces. The cleaning efficiency results will be presented and discussed.

Amine Analysis Using AlexaFluor 488 Succinimidyl Ester and Capillary Electrophoresis with Laser-Induced Fluorescence

Fluorescent probes enable detection of otherwise nonfluorescent species via highly sensitive laser-induced fluorescence. Organic amines are predominantly nonfluorescent and are of analytical interest in agricultural and food science, biomedical applications, and biowarfare detection. Alexa Fluor 488 N-hydroxysuccinimidyl ester (AF488 NHS-ester) is an amine-specific fluorescent probe. Here, we demonstrate low limit of detection of long-chain (C9 to C18) primary amines and optimize AF488 derivatization of long-chain primary amines. The reaction was found to be equally efficient in all solvents studied (dimethylsulfoxide, ethanol, and N,N-dimethylformamide). While an organic base (N,N-diisopropylethylamine) is required to achieve efficient reaction between AF488 NHS-ester and organic amines with longer hydrophobic chains, high concentrations (>5 mM) result in increased levels of ethylamine and propylamine in the blank. Optimal incubation times were found to be >12 hrs at room temperature. We present an initial capillary electrophoresis separation for analysis using a simple micellar electrokinetic chromatography (MEKC) buffer consisting of 12 mM sodium dodecylsulfate (SDS) and 5 mM carbonate, pH 10. Limits of detection using the optimized labeling conditions and these separation conditions were 5–17 nM. The method presented here represents a novel addition to the arsenal of fluorescent probes available for highly sensitive analysis of small organic molecules.

Phylogenetic Characterization and Description of Novel Heat-tolerant Bacillus Species Isolated form Spacecraft Assembly Facility

Microbial biofilms representing both Gram-positive and Gram-negative bacteria were artificially coated onto aluminum metal surfaces that are chiefly used in building spacecraft.

Molecular deformation and stress‐strain behavior of poly(bisphenol‐A‐diphenyl sulfone)

Stress‐optical studies have been carried out to determine the modes of molecular deformation in poly(bisphenol‐A‐diphenyl sulfone) and its relationship to stress‐strain behavior. Stress and birefringence were measured simultaneously as a function of strain at a strain rate of 0.0133 min−1 in the temperature range −179 to 150 °C. In the temperature range from 150 to −100 °C, measurements were performed using four strain rates, 0.0133 min−1, 0.133, 1.33, and 13.3 min−1 at each testing temperature. The results indicate that the processes involved in the molecular deformation appear to be invariant at temperatures below −100 °C. At higher temperatures, the statistical chain segments participate in the deformation process and the degree of participation increases with increasing temperature. The mechanism controlling the stress‐strain response is attributed to chain orientation. The stress‐strain response at temperatures below −100 °C is attributed to the temperature dependence of an internal energy contributi...