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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The sidereal semi-diurnal variation observed at high zenith angles at Mawson, 1968-1984, and the polarity of the solar main field

High zenith-angle North/South telescopes viewing equatorially and at midlatitudes through 40 MWE of atmosphere have been operating at Mawson since early 1968. It is evident that a sidereal semi-diurnal component of galactic origin has been observed, over and above a possible spurious component proposed by Nagashima, arising from a bi-directional component of the solar anisotropy. Although a very pronounced reduction in the semi-diurnal galactic response followed the reversal of polarity of the solar main field during 1969 to 1971, so far the observations indicate that there has been no recurrence of a larger galactic response following the reversal of polarity around 1981. The possible role of the latitudional extent lambda omicron of the wavy neutral sheet is discussed.

Jacklyn, R. M.↗
NASA NTRS2004

Elemental Abundance Variations Observed in Solar Energetic Particle Events During Solar Cycle 23

We report on observations of the abundances of elements from Helium to Nickel in over 50 different solar energetic particle events using the Solar Isotope Spectrometer (SIS) on-board the Advanced Composition Explorer (ACE) spacecraft. It had originally been expected that the energy spectra of different elements would show spectral roll-overs at energies related to the Q/M ratio of each element. Due to the partial stripping of Fe and essentially complete stripping of O, it was expected that the Fe/O ratio would be observed to decrease with increasing energy. While many events show this pattern, others have Fe/O which is constant with energy, while for yet others Fe/O actually increases with energy. Events having constant Fe/O could simply have their spectral breaks outside of the observed energy range. However, events which show increasing Fe/O cannot be explained within the framework of spectral breaks. Possible explanations include injection of remnant heavy ions from earlier impulsive events, hybrid Events consisting of a combination of flare-accelerated and shock-accelerated particles from a single solar event, and some new physical process in shock acceleration. We will report on efforts to distinguish these possible explanations.

vonRosenvinge, T. T.↗
NASA NTRS2014

Martian Cryogenic Carbonate Formation: Stable Isotope Variations Observed in Laboratory Studies

The history of water on Mars is tied to the formation of carbonates through atmospheric CO2 and its control of the climate history of the planet. Carbonate mineral formation under modern martian atmospheric conditions could be a critical factor in controlling the martian climate in a means similar to the rock weathering cycle on Earth. The combination of evidence for liquid water on the martian surface and cold surface conditions suggest fluid freezing could be very common on the surface of Mars. Cryogenic calcite forms easily from freezing solutions when carbon dioxide degasses quickly from Ca-bicarbonate-rich water, a process that has been observed in some terrestrial settings such as arctic permafrost cave deposits, lake beds of the Dry Valleys of Antarctica, and in aufeis (river icings) from rivers of N.E. Alaska. A series of laboratory experiments were conducted that simulated cryogenic carbonate formation on Mars in order to understand their isotopic systematics. The results indicate that carbonates grown under martian conditions show variable enrichments from starting bicarbonate fluids in both carbon and oxygen isotopes beyond equilibrium values.

Socki, Richard A.↗
NASA NTRS1995

An Analysis of the TOPEX/Poseidon Operational Orbit: Observed Variations and Why

Launched in August 1992, TOPEX/Poseidon began and continues a very successful global study of the earth's ocean circulation using a combination of dual-frequency radar altimetry and precision orbit determination (POD). POD results are utilized here to reconstruct the operational orbit history in terms of precise classical mean elements. Elaborations of various facets related to mean elements is discussed.

TOPEX↗
NASA NTRS1978

Meteorological control of lower stratospheric minor species variations - An observational example

Lower stratospheric air trajectories entering the region over Alaska at the approximately 125 mb level during late May, 1975 indicate a substantial shift in the geographical source regions for the air masses present during that time. This shift coincides with an approximately 25% decrease in the observed halocarbon mixing ratios at the 125 mb level as determined from a daily sequence of halocarbon profiles. Since the halocarbon species measured are essentially chemically inactive at this level, the observed variation is linked to the changing meteorological pattern.

Alyea, F. N.↗
NASA NTRS1991

Variability of solar ultraviolet irradiance

A model of solar Lyman alpha irradiance developed by multiple linear regression analysis, including the daily values and 81-day running means of the full disk equivalent width of the Helium line at 1083 nm, predicts reasonably well both the short- and long-term variations observed in Lyman alpha. In contrast, Lyman alpha models calculated from the 10.7-cm radio flux overestimate the observed variations in the rising portion and maximum period of solar cycle, and underestimates them during solar minimum. Models are shown of Lyman alpha based on the He-line equivalent width and 10.7-cm radio flux for those time intervals when no satellite observations exist, namely back to 1974 and after April 1989, when the measurements of the Solar Mesosphere Satellite were terminated.

Pap, J. M.↗
DOE OSTI2022

Development towards stable chlorine isotope measurements of astromaterials using the modified Middleton source of an accelerator mass spectrometer

The volatile element Cl can be lost during the formation and evolution of planetary bodies, leading to fractionation of its two stable isotopes 35 Cl and 37 Cl. Chlorine isotope variations (reported as δ 37 Cl in parts per thousand (‰) relative to Standard Mean Ocean Chloride, SMOC) are documented to exceed 80‰ between different lunar rock samples and have been variably interpreted as the fingerprint of degassing during accretion, magma ocean, or volcanic portions of lunar history. The large intersample and intrasample variations observed by both bulk isotope ratio mass spectrometry (IRMS) and in-situ secondary ion mass spectrometry (SIMS) methods are difficult to interpret in part because of a paucity of bulk Cl isotope measurements. This lack of high-precision bulk data is due to the relative rarity of IRMS laboratories capable of making these high precision measurements on small samples of precious planetary materials such as those returned by human or robotic exploration. Here we present a new method for performing high precision δ 37 Cl measurements using the modified Middleton ion source of an existing accelerator mass spectrometer. For samples with as little as 1 μg Cl–the equivalent of 2–4 mm 3 of a typical lunar rock sample–the average cathode accuracy is ~1‰. Finally, cathode reproducibility is typically ~1‰ (2σ) for samples with at least 10 μg of Cl, increasing to ~3–6‰ for aliquots with ~1–2 μg Cl, similar to published SIMS results and sufficient to study astromaterials from the Moon, Mars, or 4 Vesta, which have tens of ‰ observed variations.

07 ISOTOPE AND RADIATION SOURCES↗
NASA NTRS2022

Development Towards Stable Chlorine Isotope Measurements of Astromaterials Using the Modified Middleton Source of an Accelerator Mass Spectrometer

The volatile element Cl can be lost during the formation and evolution of planetary bodies, leading to fractionation of its two stable isotopes 35Cl and 37Cl. Chlorine isotope variations (reported as δ37Cl in parts per thousand (‰) relative to Standard Mean Ocean Chloride, SMOC) are documented to exceed 80‰ between different lunar rock samples and have been variably interpreted as the fingerprint of degassing during accretion, magma ocean, or volcanic portions of lunar history. The large intersample and intrasample variations observed by both bulk isotope ratio mass spectrometry (IRMS) and in-situ secondary ion mass spectrometry (SIMS) methods are difficult to interpret in part because of a paucity of bulk Cl isotope measurements. This lack of high-precision bulk data is due to the relative rarity of IRMS laboratories capable of making these high precision measurements on small samples of precious planetary materials such as those returned by human or robotic exploration. Here we present a new method for performing high precision δ37Cl measurements using the modified Middleton ion source of an existing accelerator mass spectrometer. For samples with as little as 1 μg Cl–the equivalent of 2–4 mm3 of a typical lunar rock sample–the average cathode accuracy is ∼1‰. Cathode reproducibility is typically ∼1‰ (2σ) for samples with at least 10 μg of Cl, increasing to ∼3–6‰ for aliquots with ∼1–2 μg Cl, similar to published SIMS results and sufficient to study astromaterials from the Moon, Mars, or 4 Vesta, which have tens of ‰ observed variations.

Tyler S. Anderson↗
NASA NTRS1984

Copernicus observations of Iota Herculis velocity variations

Observations of Iota Her at 109.61-109.67 nm obtained with the U1 channel of the Copernicus spectrophotometer at resolution 5 pm during 3.6 days in May, 1979, are reported. Radial-velocity variations are detected and analyzed as the sum of two sinusoids with frequencies 0.660 and 0.618 cycles/day and amplitudes 9.18 and 8.11 km/s, respectively. Weak evidence supporting the 13.9-h periodicity seen in line-profile variations by Smith (1978) is found.

Rogerson, J. B., Jr.↗
NASA NTRS1979

A comparison of Pioneer Venus and Venera bow shock observations - Evidence for a solar cycle variation

Observations by the Venera 9 and 10 orbiters in 1975-76 have been used in previous studies to determine the mean location and shape of the Cytherean bow shock. In addition it has also been reported that the shock is found to be more distant from the planet above regions of the ionosheath where draped IMF field lines are oriented perpendicular to the flow as opposed to parallel. An examination of the dependence of shock altitude in the terminator plane on upstream IMF direction using 86 Pioneer Venus orbiter bow shock crossings in 1978-79 sets an upper limit on this asymmetry of 12% or approximately half that derived earlier from the Venera data. More significantly, the mean distance to the bow shock observed by Pioneer Venus Orbiter is 35% greater than was the case in 1975-76 near solar minimum. As the growth in effective obstacle radius is an order of magnitude larger than can be accounted for in terms of varying ionopause altitude due to all causes, these results strongly suggest that Venus can absorb significantly more of the incident solar wind plasma during solar minimum when EUV flux is low than during the current epoch in which maximum is approaching.

Slavin, J. A.↗