The results suggest that most individuals with well-controlled medical conditions can withstand acceleration forces involved in launch/landing profiles of commercial spaceflight vehicles. Further investigation will help refine which conditions present significant risk during suborbital flight and beyond.

We present the performance characteristics of a time-of-flight secondary ion mass spectrometer designed for 157 nm laser postionization of sputtered neutrals for high sensitivity elemental and isotopic analyses. The instrument was built with the aim of analyzing rare element abundances in micron to submicron samples such as interstellar grains and cometary dust. Relative sensitivity factors have been determined for secondary ion mass spectrometry which show an exponential dependency against the first ionization potential. This allows elemental abundances to be measured with errors below 25% for most major elements. The accuracy for isotope ratios, where isotopes can be resolved from isobaric interferences, is usually limited only by counting statistics. In laser secondary neutral mass spectrometry, the spatial and temporal overlaps between the laser and sputtered neutral atoms are modeled and predictions of total detection efficiency and isotopic and elemental fractionation are compared with experimental data. Relative sensitivity factors for laser-ionized secondary neutrals from a stainless steel standard are found to vary less than 3% above saturation laser pulse energy enabling more accurate quantification.

Abstract-We report the first measurements of lithium and boron isotope ratios and abundances measured in "gently separated" presolar SiC grains. Almost all analyses of presolar SiC grains since their first isolation in 1987 have been obtained from grains that were separated from their host meteorite by harsh acid dissolution. We recently reported a new method of "gently" separating the grains from meteorites by using freeze-thaw disaggregation, size, and density separation to retain any nonrefractory coatings or alteration to the surfaces of the grains that have been acquired in interstellar space. Nonrefractory coats or amorphized surfaces will almost certainly be removed or altered by the traditional acid separation procedure. High Li/Si and B/Si ratios of up to ~10 -2 were found implanted in the outer 0.5 μm of the grains dropping to ~10 -5 in the core of the grains. 7 Li/ 6 Li and 11 B/ 10 B ratios indistinguishable from solar system average values were found. Analyses obtained from SiC grains from the acid dissolution technique showed isotope ratios that were the same as those of gently separated grains, but depth profiles that were different. These results are interpreted as evidence of implantation of high velocity (1200-1800 km s -1 ) Li and B ions into the grains by shock waves as the grains traveled through star-forming regions some time after their condensation in the outflow of an AGB star that was their progenitor. The results are in line with spectroscopic measurements of Li and B isotope ratios in star-forming regions and may be used to infer abundances and isotopic sources in these regions.

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Abstract-This paper describes the development of a new, effective, and non-destructive method of SiC isolation from meteorites by freeze-thaw disaggregation, size, and density separation. This new method is important because there is evidence that current methods, which use strong acids and chemical treatments to dissolve silicates and separate out the interstellar grains, may alter the surfaces of the grains chemically and isotopically. Furthermore, any non-refractory coating present on the grains would be destroyed. Using our new separation method, SiC grains were enriched from ∼6 ppm abundance in Murchison whole rock to 0.67% abundance in the 0.4-1.4 µm size range and 0.27% abundance in the 1.4-17 µm size range. Individual SiC grains were easily identified using electron probe microanalysis (EPMA) mapping of grains distributed thinly on gold foil; a small aliquot from these fractions has so far yielded >150 SiC grains for isotopic analysis. The method separates out SiC grains efficiently, is applicable to very small or rare samples, and avoids the harsh acid treatments that may alter possible amorphous or non-refractory coats on the grains. The procedure also preserves the remainder of the original sample and it is hoped that it may be extended to other micron-sized presolar grains found in meteorites such as corundum, graphite, and silicon nitride.

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