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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

In vivo synthesis of phosphatidylcholine in rat brain via the phospholipid methylation pathway

The in vivo synthesis of brain phosphatidylcholine (PC) by the methylation of phosphatidylethanolamine (PE) was examined. (H-3)methyl)methionine was infused i.c.v., by indwelling cannula, and brain samples were taken 0.5-18 h thereafter and assayed for (H-3)PC, as well as for its biosynthetic intermediates (H-3)phosphatidyl monomethylethanolamine ((H-3)PMME) and (H-3)phosphatidyl dimethylethanolamine ((H-3)PDME), and for (H-3)lysophosphatidylcholine ((H-3)LPC) and S-(H-3)adenosylmethionine ((H-3)SAM). Most of the (H-3)PC (79-94 percent) was present ipsilateral to the infusion site; indicating that the radioactivity in the (H-3)PC was primarily of intracerebral origin, and not taken up from the blood. Moreover, only very low levels of (H-3)PC were attained in brains of animals receiving (H-3)methionine i.p. and these levels were symmetrically distributed. (H-3)PMME and (H-3)PDME turned over with apparent half-lives of 2.2 h and 2.4 h. In contrast, the accumulation of brain (H-3)PC was biphasic, suggesting the existence of two pools, the more labile of which turned over rapidly (t(sub 1/2) = 5 h) and was formed for as long as (H-3)PMME and (H-3)PDME are present in the brain, and another, which was distinguishable only at 18 h after the (H-3)methionine infusion. (The latter pool may have been synthesized from (H-3)choline that was released via the hydrolysis of some of the brain (H-3)PC previously formed by the methylation of PE.) Subcellular fractionation of brain tissue obtained after in vivo labelling with (H-3)methionine revealed that mitochondrial PC had the highest specific radioactivity (dpm per micromol total lipid phosphorus), and myelin the least. These observations affirm that rat brain does synthesize PC in vivo by methylating PE, and the technique provides an experimental system which may be useful for examining the physiological regulation of this process.

Lakher, Michael↗
NASA NTRS1994

The peak brightness of SN 1937C in IC 4182 and the Hubble constant

The light curve of the Type Ia supernova SN 1937C (in IC 4182) is important because Sandage et al. have measured a distance to the host galaxy by means of Cepheid variables and thus have derived the Hubble constant. However, the peak brightness of SN 1937C has only been derived with the relatively poor original comparison star brightnesses and without regard to a large body of data in the literature. In this paper, I will correct these and other procedural difficulties. I find that the late time photographic light curve appears to have a broken exponential decay with equivalent half-lives of 46 and 58 days with the break near 300 days after maximum. I also find that the peak B-magnitude was 8.71 +/- 0.14 on JD 2428770.0 +/- 1.0 at which time the B-V was -0.03 +/- 0.13. With these improved peak brightnesses, the distance modulus of Sandage et al., and peak absolute magnitudes in the center of the range of modern estimates, I derive the Hubble constant to be 50 km/s Mpc.

Schaefer, Bradley E.↗
NASA NTRS1995

The Origin of Life--Did It Occur at High Temperatures

A high-temperature origin of life has been proposed, largely for the reason that the hyperthermophiles are claimed to be the last common ancestor of modern organisms. Even if they are the oldest extant organisms, which is in dispute, their existence can say nothing about the temperatures of the origin of life, the RNA world, and organisms preceding the hyperthermophiles. There is no geological evidence for the physical setting of the origin of life because there are no unmetamorphosed rocks from that period. Prebiotic chemistry points to a low-temperature origin because most biochemicals decompose rather rapidly at temperatures of 100 C (e.g., half-lives are 73 min for ribose, 21 days for cytosine, and 204 days for adenine). Hyperthermophiles may appear at the base of some phylogenetic trees because they outcompeted the mesophiles when they adapted to lower temperatures, possibly due to enhanced production of heat-shock proteins.

Miller, Stanley L.↗
NASA NTRS2002

Potential Operating Orbits for Fission Electric Propulsion Systems Driven by the SAFE-400

Safety must be ensured during all phases of space fission system design, development, fabrication, launch, operation, and shutdown. One potential space fission system application is fission electric propulsion (FEP), in which fission energy is converted into electricity and used to power high efficiency (Isp greater than 3000s) electric thrusters. For these types of systems it is important to determine which operational scenarios ensure safety while allowing maximum mission performance and flexibility. Space fission systems are essentially nonradioactive at launch, prior to extended operation at high power. Once high power operation begins, system radiological inventory steadily increases as fission products build up. For a given fission product isotope, the maximum radiological inventory is typically achieved once the system has operated for a length of time equivalent to several half-lives. After that time, the isotope decays at the same rate it is produced, and no further inventory builds in. For an FEP mission beginning in Earth orbit, altitude and orbital lifetime increase as the propulsion system operates. Two simultaneous effects of fission propulsion system operation are thus (1) increasing fission product inventory and (2) increasing orbital lifetime. Phrased differently, as fission products build up, more time is required for the fission products to naturally convert back into non-radioactive isotopes. Simultaneously, as fission products build up, orbital lifetime increases, providing more time for the fission products to naturally convert back into non-radioactive isotopes. Operational constraints required to ensure safety can thus be quantified.

Houts, Mike↗
NASA NTRS2002

Potential Operating Orbits for the SAFE-400

Safety must be ensured during all phases of space fission system design, development, fabrication, launch, operation, and shutdown. One potential space fission system application is fission electric propulsion (FEP), in which fission energy is converted into electricity and used to power high efficiency (Isp is greater than 3000s) electric thrusters. For these types of systems it is important to determine which operational scenarios ensure safety while allowing maximum mission performance and flexibility. Space fission systems are essentially non-radioactive at launch, prior to extended operation at high power. Once high power operation begins, system radiological inventory steadily increases as fission products build up. For a given fission product isotope, the maximum radiological inventory is typically achieved once the system has operated for a length of time equivalent to several half-lives. After that time, the isotope decays at the same rate it is produced, and no further inventory builds in. For an FEP mission beginning in Earth orbit, altitude and orbital lifetime increase as the propulsion system operates. Two simultaneous effects of fission propulsion system operation are thus (1) increasing fission product inventory and (2) increasing orbital lifetime. Phrased differently, as fission products build up, more time is required for the fission products to naturally convert back into non-radioactive isotopes. Simultaneously, as fission products build up, orbital lifetime increases, providing more time for the fission products to naturally convert back into non-radioactive isotopes. Operational constraints required to ensure safety can thus be quantified.

Houts, Mike↗
NASA NTRS2004

The Mean Life Squared Relationship for Abundances of Extinct Radioactivities

We discovered that the abundances of now extinct radioactivities (relative to stable reference isotopes) in meteorites vary as a function of their mean lifetimes squared. This relationship applies to chondrites, achondrites, and irons but to calcium-aluminum inclusions (CAIs). Certain meteorites contain excesses in isotopic abundances from the decay of radioactive isotopes with half-lives much less than the age of the solar system. These short-lived radioactivities are now extinct, but they were alive when meteorites assembled in the early solar system. The origin of these radioactivities and the processes which control their abundances in the solar nebula are still not well understood. Some clues may come from our finding that the meteoritic abundances of now extinct radioactivities (relative to stable reference isotopes) vary as a function of their mean lifetimes squared. This relationship applies to chondrites, achondrites, and irons, but not to CAIs. This points to at least two different processes establishing the abundances of short-lived isotopes found in the meteoritic record.

Lodders, K.↗
NASA NTRS2004

More on Ru Endemic Isotope Anomalies in Meteorites

We reported last year on endemic isotope anomalies for Ru in iron meteorites, pallasites, ordinary chondrites, and on a whole-rock sample of Allende. We have extended the Ru measurements to more meteorites, to refractory Ca-Al-rich inclusions (CAI) from Allende, and to a whole rock sample of Murchison (CM2). In a companion abstract we report on new measurements for the Mo isotopes, in some of the same samples. There has been a renewed interest in searching for isotope anomalies in this nuclide region, as Ru and Mo include many isotopes from r-, s-, and p-process nucleosynhesis. Furthermore, the Ru and Mo p-process isotopes show atypically high abundances, which have been hard to explain through the standard nucleosynthetic processes. Effects are possible in Ru-98 and Ru-99 from Tc-98 (with a poorly known t(sub 1/2)=4.2 to 10Ma) and from Tc-99 (t(sub 1/2)=0.21Ma). Natural Tc is now extinct on Earth due to the short half-lives, but may have been present in the early solar system. Both radiogenic and general isotope anomalies are important in understanding the processes for the formation of the early solar system. The current emphasis on Ru and Mo is also the result of the development of Negative-ion Thermal Ionization Mass Spectrometry and of Multiple-Collector, Inductively-Coupled-Mass-Spectrometry. We have also developed specific chemical siparation techniques for Ru, which eliminated mass interference effects.

Papanastassiou, D. A.↗
NASA NTRS1995

Amino acid racemization on Mars: implications for the preservation of biomolecules from an extinct martian biota

Using kinetic data, we have estimated the racemization half-lives and times for total racemization of amino acids under conditions relevant to the surface of Mars. Amino acids from an extinct martian biota maintained in a dry, cold (<250 K) environment would not have racemized significantly over the lifetime of the planet. Racemization would have taken place in environments where liquid water was present even for time periods of only a few million years following biotic extinction. The best preservation of both amino acid homochirality and nucleic acid genetic information associated with extinct martian life would be in the polar regions.

NASA Discipline Exobiology↗
NASA NTRS2003

Lunar and Planetary Surface Dynamics and Early History

This document, submitted as part of this proposal renewal represents the Final Report required by NASA for Grant NAGS-9442. It should be emphasized that, while this work statement in the original proposal outlined anticipated directions of our research, the specific activities we carried out during this period differed slightly from those proposed, capitalizing on new unexpected results and new advances in analytical capability. The thrust of all the work we completed were completely within the stated research goals of the proposal and significantly advanced our knowledge of planetary processes and our understanding of the early solar system. The following summary outlines our achievements in the different areas of research. These include: A) Early solar system processes and time scales using I-Xe chronometry; B) The Active Capture of Volatiles: A new mechanism for the capture of heavy noble gases, possible implications for phase Q and planetary heavy noble gases; C) Separation of Xe-L from Xe-H: Physically selective experiments; D) Abundances of Presolar grains; E) Studies of Neon and Helium from single interstellar SiC and graphite grains; F) Pre-compaction exposure of meteoritic grains and chondrules; G) Geochemically Measured Half-Lives: Double beta-decay of Te and Ba isotopes; H) Noble gases in stratospheric interplanetary dust particles; I) New Analytical Instrument.

Source record↗
NASA NTRS2005

Stability of chromosome aberrations in the blood lymphocytes of astronauts measured after space flight by FISH chromosome painting

Follow-up measurements of chromosome aberrations in the blood lymphocytes of astronauts were performed by FISH chromosome painting at various intervals from 5 months to more than 5 years after space flight and compared to preflight baseline measurements. For five of the six astronauts studied, the analysis of individual time courses for translocations revealed a temporal decline of yields with half-lives ranging from 10 to 58 months. The yield of exchanges remained unchanged for the sixth astronaut during an observation period of 5 months after flight. These results may indicate complications with the use of stable aberrations for retrospective dose reconstruction, and the differences in the decay time may reflect individual variability in risk from space radiation exposure.

Astronauts↗
NASA NTRS2006

Stability of Radiation Induced Chromosome Damage in Human Peripheral Blood Lymphocytes

Chromosome damage in an individual's peripheral blood lymphocytes can be an indicator of radiation exposure and this data can be used to evaluate dose after accidental or occupational exposure. Evidence suggests that the yield of chromosome damage in lymphocytes is also a relevant biomarker of cancer risk in humans that reflects individual cancer susceptibility. It follows that biomonitoring studies can be used to uncover subjects who are particularly susceptible to radiation damage and therefore at higher risk of cancer. Translocations and other stable aberrations are commonly believed to persist in peripheral blood cells for many years after exposure, and it has been suggested that translocations can be used for assessing retrospective radiation doses or chronic exposures. However, recent investigations suggest that translocations might not always persist indefinitely. We measured chromosome aberrations in the blood lymphocytes of six astronauts before their respective missions of approximately 3 to 6 months onboard the international space station, and again at various intervals up to 5 years after flight. In samples collected a few days after return to earth, the yield of chromosome translocations had significantly increased compared with preflight values, and results indicate that biodosimetry estimates lie within the range expected from physical dosimetry. However, for five of the astronauts, follow up analysis revealed a temporal decline in translocations with half-lives ranging from 10 to 58 months. The yield of exchanges remained unchanged for the sixth astronaut during an observation period of 5 months post-flight. These results may indicate complications with the use of stable aberrations for retrospective dose reconstruction and could affect cancer risk predictions that are estimated from yields of chromosome damage obtained shortly after exposure.

Cucinotta, F. A.↗
NASA NTRS2008

The Miniaturized Moessbauer Spectrometers MIMOS II on MER: Four Years of Operation - A Summary

The two Miniaturized Moessbauer Spectrometers (MIMOS II) on board the two Mars Exploration Rovers Spirit and Opportunity have now been collecting important scientific data for more than four years. The spectrometers provide information about Fe-bearing mineral phases and determine Fe oxidation states. The total amount of targets analized exceeds 600, the total integration time exceeds 260 days for both rovers. Since landing, more than five half-lives of the Co-57 MB sources have past (intensity at the time of landing approx. 150 mCi). Current integration times are about 50 hours in order to achieve reasonable statistics as opposed to 8 hours at the beginning of the mission. In total, 13 different mineral phases were detected: Olivine, pyroxene, hematite, magnetite and nanophase ferric oxide were detected at both landing sites. At Gusev, ilmenite, goethite, a ferric sulfate phase and a yet unassigned phase (in the rock Fuzzy Smith) were detected. At Meridiani, jarosite, metallic iron in meteoritic samples (kamacite), troilite, and an unassigned ferric phase were detected. Jarosite and goethite are of special interest, as these minerals are indicators for water activity. In this abstract, an overview of Moessbauer results will be given, with a focus on data obtained since the last martian winter. The MER mission has proven that Moessbauer spectroscopy is a valuable tool for the in situ exploration of extraterrestrial bodies and for the study of Febearing samples. The experience gained through the MER mission makes MIMOS II a obvious choice for future missions to Mars and other targets. Currently, MIMOS II is on the scientific payload of two approved future missions: Phobos Grunt (Russian Space Agency; 2009) and ExoMars (European Space Agency; 2013).

Fleischer, I.↗
NASA NTRS2008

Persistence of Space Radiation Induced Cytogenetic Damage in the Blood Lymphocytes of Astronauts

Cytogenetic damage in astronaut's peripheral blood lymphocytes is a useful in vivo marker of space radiation induced damage. Moreover, if radiation induced chromosome translocations persist in peripheral blood lymphocytes for many years, as has been assumed, they could potentially be used to measure retrospective doses or prolonged low dose rate exposures. However, as more data becomes available, evidence suggests that the yield of translocations may decline with time after exposure, at least in the case of space radiation exposures. We present our latest follow-up measurements of chromosome aberrations in astronauts blood lymphocytes assessed by FISH painting and collected a various times beginning directly after return from space to several years after flight. For most individuals the analysis of individual time-courses for translocations revealed a temporal decline of yields with different half-lives. Since the level of stable aberrations depends on the interplay between natural loss of circulating T-lymphocytes and replenishment from the stem or progenitor cells, the differences in the rates of decay could be explained by inter-individual variation in lymphocyte turn over. Biodosimetry estimates derived from cytogenetic analysis of samples collected a few days after return to earth lie within the range expected from physical dosimetry. However, a temporal decline in yields may indicate complications with the use of stable aberrations for retrospective dose reconstruction, and the differences in the decay time may reflect individual variability in risk from space radiation exposure. In addition, limited data on multiple flights show a lack of correlation between time in space and translocation yields. Data from one crewmember who has participated in two separate long-duration space missions and has been followed up for over 10 years provides limited information on the effect of repeat flights and show a possible adaptive response to space radiation exposure.

George, Kerry↗
NASA NTRS2009

Persistence of Space Radiation-Induced Cytogenetic Damage in the Blood Lymphocytes of Astronauts and the Effects of Repeat Long Duration Space Missions

The yield of chromosome damage in astronauts blood lymphocytes has been shown to increase after long duration space missions of a few months or more. This provides a useful in vivo measurement of space radiation induced damage that takes into account individual radiosensitivity and considers the influence of microgravity and other stress conditions. We present our latest follow-up analyses of chromosome damage in astronauts blood lymphocytes assessed by fluorescence in situ hybridization (FISH) chromosome painting and collected at various times, from directly after return from space to several years after flight. For most individuals the analysis of individual time-courses for translocations revealed a temporal decline of yields with different half-lives. Dose was derived from frequencies of chromosome exchanges using preflight calibration curves, and estimates derived from samples collected a few days after return to earth lie within the range expected from physical dosimetry. However, a temporal decline in yields may indicate complications with the use of stable aberrations for retrospective dose reconstruction, and the differences in the decay time may reflect individual variability in risk from space radiation exposure. Limited data on three individuals who have participated in repeat long duration space flights indicates a lack of correlation between time in space and translocation yields, and show a possible adaptive response to space radiation exposure.

George, Kerry A.↗
NASA NTRS2009

The Formation and Stability of Carbonic Acid on Outer Solar System Bodies

The radiation chemistry, thermal stability, and vapor pressure of solid-phase carbonic acid (H2CO3) have been studied with mid-infrared spectroscopy. A new procedure for measuring this molecule's radiation stability has been used to obtain intrinsic IR band strengths and half-lives for radiolytic destruction. Results are compared to literature values. We report, for the first time, measurements of carbonic acid's vapor pressure and its heat of sublimation. We also report the first observation of a chemical reaction involving solid-phase carbonic acid. Possible applications of these findings are discussed, with an emphasis on the outer Solar System.

Peeters, Z.↗
NASA NTRS2012

In-Situ Measurements of the Radiation Stability of Amino Acids at 15-140 K

We present new kinetics data on the radiolytic destruction of amino acids measured in situ with infrared spectroscopy. Samples were irradiated at 15, 100, and 140 K with D.8-MeV protons, and amino-acid decay was followed at each temperature with and without H2O present. Observed radiation products included CO2 and amines, consistent with amino-acid decarboxylation. The half-lives of glycine, alanine, and phenylalanine were estimated for various extraterrestrial environments. Infrared spectral changes demonstrated the conversion from the non-zwitterion structure NH2-CH2(R)-COOH at 15 K to the zwitterion structure +NH3-CH2(R)-COO- at 140 K for each amino acid studied.

Gerakines, Perry A.↗
NASA NTRS2020

The Radiation Stability of Thymine in Solid H2O

Nucleobases are of significant importance to all known organisms, may be an important building block of life, and could be important biosignatures of current or past life. Given their potential significance to the field of astrobiology, it is important to understand the survival of these molecules when subjected to ionizing radiation as is present in a range of extraterrestrial environments. In this work we present data on the kinetics of the radiolytic destruction of pure thymine, and water + thymine ice mixtures at temperatures from 13 to 150 K. Rate constants were measured using in situ infrared spectroscopy and radiolytic half-lives for thymine were computed for different planetary and interstellar environments. Our results demonstrate that the survival of thymine decreases as the dilution of thymine in water increases. Additionally, we find that thymine survival increases with ice temperature and that this decrease may be related to structure of the ice matrix.

nucleobases, radiolysis, astrobiology↗
NASA NTRS2024

Constraining the Surface Exposure Age of Asteroid Bennu Using Cosmogenic Radionuclides in an OSIRIS-REx Aggregate Sample and Individual Particles

Observations by NASA’s OSIRIS-REx spacecraft of asteroid Bennu revealed evidence that this small rubble-pile asteroid experiences several active surface processes that likely control its recent surface exposure history. In October 2020, the spacecraft collected a surface sample from a relatively young ~20 m diameter crater (Hokioi) on asteroid Bennu, and the sample was successfully delivered to Earth on September 24, 2023. Based on the population of craters >50 m diameter, Bennu’s surface is 0.1–1 Ga old, but the old surface is affected by recent processes including smaller meteoroid impacts, mass movement, and particle ejections. The sampling location within Hokioi crater was selected based on its relatively flat surface devoid of large boulders, but the crater floor is also believed to be one of the youngest surfaces on asteroid Bennu, with an age of <100 kyr. As the crater is ~2 m deep, the samples that were collected by OSIRIS-REx may have been relatively shielded from cosmic rays during most of its recent history. This scenario is different from the samples that were collected by Hayabusa2 from asteroid Ryugu, where cosmogenic noble gas and radionuclides indicate cosmic-ray exposure (CRE) ages of ~5 Myr near the surface. Our goal is to understand the recent exposure history of surface samples of asteroid Bennu utilizing radionuclides ( 10 Be, 26 Al, 36 Cl, 41 Ca) produced by both galactic (GCR) and solar (SCR) cosmic rays. With half- lives ranging from 0.1 to 1.36 million years (Myr), the concentrations of these cosmogenic nuclides provide information on the duration and exposure conditions (irradiation depth) of these samples on a timescale of a few Myr. This work will test one of the OSIRIS-REx mission’s driving hypotheses about asteroid Bennu’s recent evolution: that Hokioi crater is part of a population of small (25 m) spectrally red craters on Bennu that are less than 0.1 Myr old.

K. C. Welten↗