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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Can cometary bombardment disrupt synchronous rotation of planetary satellites?

The distribution of craters on Jupiter's Galilean satellites Ganymede and Callisto and on Saturn's midsized airless moons is much more symmetric and uniform than theoretical analysis predicts. A number of explanations for this situation have been considered, taking into account also the possibility that impacts due to cometary bombardment might disrupt the synchronous rotation of the moons. The feasibility of such a disruption is explored in the present study. The results of this study are presented in a table. It is found that a disruption of the synchronous rotation of the considered moons by impacts is very unlikely.

Lissauer, J. J.↗
NASA NTRS1986

Binary collision model for neon Auger spectra from neon ion bombardment of the aluminum surface

A model is developed to account for the angle-resolved Auger spectra from neon ion bombardment of the aluminum surface recently obtained by Pepper and Aron. The neon is assumed to be excited in a single asymmetric neon-aluminum-collision and scattered back into the vacuum where it emits an Auger electron. The velocity of the Auger electron acquires a Doppler shift by virtue of the emission from a moving source. The dependence of the Auger peak shape and energy on the incident ion energy, angle of incidence and on the angle of Auger electron emission with respect to the surface is presented. Satisfactory agreement with the angle resolved experimental observations is obtained. The dependence of the angle-integrated Auger yield on the incident ion energy and angle of incidence is also obtained and shown to be in satisfactory agreement with available experimental evidence.

Pepper, S. V.↗
NASA NTRS1986

Carbon monoxide production in low energy oxygen ion bombardment of pyrolytic graphite and Kapton surfaces

The results of an investigtion of the interaction of low energy oxygen ions with pyrolytic graphite and Kapton surface are reported. CO molecules emitted from the surface as a result of the ion bombardment were detected by a mass spectrometer. Because the ion-induced signals were small compared to that arising from the CO background pressure in the vacuum system, the ion beam was modulated and the modulated component of the CO signal measured with a lock-in amplifier. The quantum yield (CO molecules emitted per incident oxygen ion) for graphite rose from 1.9 at 4.5 eV ion energy to 6.6 at 465 eV. Comparable yields were obtained for Kapton. The large size of the yields suggests contributions to the reaction process from the background O2 molecules in the vacuum system.

Horton, C. C.↗
NASA NTRS1987

Plasma properties in electron-bombardment ion thrusters

The paper describes a technique for computing volume-averaged plasma properties within electron-bombardment ion thrusters, using spatially varying Langmuir-probe measurements. Average values of the electron densities are defined by integrating the spatially varying Maxwellian and primary electron densities over the ionization volume, and then dividing by the volume. Plasma properties obtained in the 30-cm-diameter J-series and ring-cusp thrusters are analyzed by the volume-averaging technique. The superior performance exhibited by the ring-cusp thruster is correlated with a higher average Maxwellian electron temperature. The ring-cusp thruster maintains the same fraction of primary electrons as does the J-series thruster, but at a much lower ion production cost. The volume-averaged predictions for both thrusters are compared with those of a detailed thruster performance model.

Matossian, J. N.↗
NASA NTRS1988

Bombardment history of the Saturn system

Crater distributions on Voyager images of Saturn's satellites are analyzed and models of relative cratering rates on these bodies are developed on the basis of orbital dynamics. A history of satellite bombardment, disruption, and resurfacing in the Saturn system is constructed, concentrating on Rhea. It is suggested that the surface of Rhea has approached saturation equilibrium for craters with diameters up to 32 km. Also, the disruption probabilities of Saturn's inner moons are estimated.

Lissauer, Jack J.↗
NASA NTRS1988

Formation of particulates by ion bombardment of cryogenic ice mixtures

An analysis of the particulates which form upon the bombardment of a gaseous mixture reflecting cosmic molecular abundances with H2(+) ions accelerated at 350 keV. The model of Black and Dalgarno (1977) for the Zeta Oph cloud and an observational determination of the interstellar Ar abundances (Simpson et al., 1986) are used to determine the abundances of the gas mixture. The characteristics of the resulting residue are examined, including photographs and absorbance spectra. The possible astrophysical implications of the experiment are discussed.

Wdowiak, T. J.↗
NASA NTRS1990

Bombardment of planetary rings by meteoroids - General formulation and effects of Oort Cloud projectiles

A general solution is obtained for the angular distribution of the intensity and velocity of interplanetary projectiles impinging on a planetary ring system. Three significant results emerge from the solution: (1) a variation with orbital longitude is demonstrated in the impact velocity-weighted impact rate of the planetary rings' cometary meteoroids; (2) the angular distribution of ejecta intensity due to the bombardment of a planetary ring by interplanetary meteoroids is determined; and (3) the radial drift velocity due to both simple mass-loading and aberration-induced asymmetry in the impact rate is calculated for a planetary ring of arbitrary optical depth. Attention is given to results for projectiles with Oort Cloud-type orbits.

Cuzzi, Jeffrey N.↗
NASA NTRS1989

Evaluation of large format electron bombarded virtual phase CCDs as ultraviolet imaging detectors

In conjunction with an external UV-sensitive cathode, an electron-bombarded CCD may be used as a high quantum efficiency/wide dynamic range photon-counting UV detector. Results are presented for the case of a 1024 x 1024, 18-micron square pixel virtual phase CCD used with an electromagnetically focused f/2 Schmidt camera, which yields excellent simgle-photoevent discrimination and counting efficiency. Attention is given to the vacuum-chamber arrangement used to conduct system tests and the CCD electronics and data-acquisition systems employed.

Opal, Chet B.↗
NASA NTRS1991

Optical glow spectra arising from low-energy N2, N2(+) and electron bombardment of MgF2 surfaces

Photon emission spectra resulting from the impact of N2, N2(+), and electron beams on magnesium fluoride in an ultrahigh vacuum environment were measured and compared for beam energies in the range 200-2000 eV. Unexpectedly, only the ion- and electron-induced spectra exhibited broad fluorescence. The observed data suggest that the broad fluorescence arising from low-energy ion bombardment is due primarily to the transfer of electronic energy to the surface by resonance or Auger neutralization. Since molecular nitrogen is a major constituent of the atmosphere at orbital altitudes, these measurements bear directly on radiation-induced glow and erosion processes on surfaces of spacecraft in low-earth orbit.

Qi, J.↗
NASA NTRS1992

Sputtering of ions from Cu and Al by low energy oxygen ion bombardment

The sputtering of Cu(+) and Al(+) ions from copper and aluminum while the target surface is bombarded with low energy oxygen ions (20 to 500 eV), is investigated. Both the ion yield, as a function of oxygen ion energy, and the kinetic energy distribution of the sputtered ions at a given oxygen ion energy are determined.

Eck, T. G.↗
NASA NTRS1992

Asteroids and Archaean crustal evolution: Tests of possible genetic links between major mantle/crust melting events and clustered extraterrestrial bombardments

Since the oldest intact terrestrial rocks of ca. 4.0 Ga and oldest zircon xenocrysts of ca. 4.3 Ga measured to date overlap with the lunar late heavy bombardment, the early Precambrian record requires close reexamination vis a vis the effects of megaimpacts. The identification of microtektite-bearing horizons containing spinals of chondritic chemistry and Ir anomalies in 3.5-3.4-Ga greenstone belts provides the first direct evidence for large-scale Archaean impacts. The Archaean crustal record contains evidence for several major greenstone-granite-forming episodes where deep upwelling and adiabatic fusion of the mantle was accompanied by contemporaneous crustal anatexis. Isotopic age studies suggest evidence for principal age clusters about 3.5, 3.0, and 2.7 (+/- 0.8) Ga, relics of a ca. 3.8-Ga event, and several less well defined episodes. These peak events were accompanied and followed by protracted thermal fluctuations in intracrustal high-grade metamorphic zones. Interpretations of these events in terms of internal dynamics of the Earth are difficult to reconcile with the thermal behavior of silicate rheologies in a continuously convecting mantle regime. A triggering of these episodes by mantle rebound response to intermittent extraterrestrial asteroid impacts is supported by (1) identification of major Archaean impacts from microtektite and distal ejecta horizons marked by Ir anomalies; (2) geochemical and experimental evidence for mantle upwelling, possibly from levels as deep as the transition zone; and (3) catastrophic adiabatic melting required to generate peridotitic komatites. Episodic differentiation/accretion growth of sial consequent on these events is capable of resolving the volume problem that arises from comparisons between modern continental crust and the estimated sial produced by continuous two-stage mantle melting processes. The volume problem is exacerbated by projected high accretion rates under Archaean geotherms. It is suggested that impact shock effects have been largely obscured by (1) outpouring of voluminous basic/ultrabasic lavas, inundating shock-deformed crust and extending beyond the perimeters of impact excavated basins; (2) gravity subsidence and downfaulting of terrestrial maria, accounting for the burial and anatexis of subgreenstone basement; and (3) extensive shearing and recrystallization at elevated temperatures of impact structure, breccias, and mineral deformation features beneath impact-excavated basins, relics of which may be retained in structural windows in high-grade metamorphic terranes.

Glikson, A. Y.↗
NASA NTRS1993

A Unique Photon Bombardment System for Space Applications

The innovative Electromagnetic Radiation Collection and Concentration System (EMRCCS) described is the foundation for the development of a multiplicity of space and terrestrial system formats. The system capability allows its use in the visual, infrared, and ultraviolet ranges of the spectrum for EM collection, concentration, source/receptor tracking, and targeting. The nonimaging modular optical system uses a physically static position aperture for EM radiation collection. Folded optics provide the concentration of the radiation and source autotracking. The collected and concentrated electromagnetic radiation is utilized in many applications, e.g., solar spectrum in thermal and associative photon bombardment applications for hazardous waste management, water purification, metal hardening, hydrogen generation, photovoltaics, etc., in both space and terrestrial segment utilization. Additionally, at the high end of the concentration capability range, i.e., 60,000+, a solar-pulsed laser system is possible.

Klein, E. J.↗
NASA NTRS1992

Comet impacts and chemical evolution on the bombarded earth

Amino acids yields for previously published shock tube experiments are used with minimum Cretaceous-Tertiary (K/T) impactor mass and comet composition to predict AIB amino acid K/T boundary sediment column density. The inferred initial concentration of all amino acids in the K/T sea and in similar primordial seas just after 10 km comet impacts would have been at least 10 exp -7 M. However, sinks for amino acids must also be considered in calculating amino acid concentrations after comet impacts and in assessing the contribution of comets to the origin of life. The changing concentration of cometary amino acids due to ultraviolet light is compared with the equilibrium concentration of amino acids produced in the sea from corona discharge in the atmosphere, deposition in water, and degradation by ultraviolet light. Comets could have been more important than endogenous agents for initial evolution of amino acids. Sites favorable for chemical evolution of amino acids are examined, and it is concluded that chemical evolution could have occurred at or above the surface even during periods of intense bombardment of earth before 3.8 billion years ago.

Oberbeck, Verne R.↗
NASA NTRS2002

A New Dynamical Model for the Lunar Late Heavy Bombardment

We describe a new dynamical model for the late heavy bombardment in which a 5th terrestrial planet existed on an orbit that became unstable after 600 Myr, began crossing the asteroid belt, and enhanced the flux of impactors into the inner Solar System. Additional information is contained in the original extended abstract.

Chambers, J. E.↗
NASA NTRS1995

Cereal transformation through particle bombardment

The review focuses on experiments that lead to stable transformation in cereals using microprojectile bombardment. The discussion of biological factors that affect transformation examines target tissues and vector systems for gene transfer. The vector systems include reporter genes, selectable markers, genes of agronomic interest, and vector constructions. Other topics include physical parameters that affect DNA delivery, selection of stably transformed cells and plant regeneration, and analysis of gene expression and transmission to the progeny.

NASA Discipline Plant Biology↗
NASA NTRS1990

Crater taphonomy and bombardment rates in the Phanerozoic

Impact structures can be catalogued according to the age of the rocks in which they are now found ("country rocks"). The observed frequency distribution of craters by age of country rock is shown to be statistically indistinguishable from the predictions of a simple model in which it is assumed that the survival time for craters is the same as that for their target rocks. Other models are considered, but do not match the data. A lower limit of the rate of bombardment through the Phanerozoic, based only on documented craters, is 0.13 +/- 0.09 events/ma/10(8) km2 for craters with diameters > or = 10 km and 0.09 +/- 0.08 events/ma/10(8) km2 for craters with diameters > or = 20 km. The data allow, but do not demand, an increase in meteorite flux over the Phanerozoic but do not allow any significant decrease. We estimate that only about 6% of the existing terrestrial impact structures of diameter greater than 10 km have been discovered to date, and only 16% of those with diameter greater than 20 km.

NASA Program Exobiology↗
NASA NTRS2011

Spitzer Evidence for a Late Heavy Bombardment and the Formation of Urelites in {eta}Corvi at Approximately 1 Gyr

We have analyzed Spitzer and NASA/IRTF 2 - 35 micrometer spectra of the warm, ~350 K circumstellar dust around the nearby MS star eta Corvi (F2V, 1.4 plus or minus 0.3 Gyr). The spectra show clear evidence for warm, water- and carbon-rich dust at ~3 AU from the central star, in the system's Terrestrial Habitability Zone. Spectral features due to ultra-primitive cometary material were found, in addition to features due to impact produced silica and high temperature carbonaceous phases. At least 9 x 10(exp 18) kg of 0.1 - 100 micrometer warm dust is present in a collisional equilibrium distribution with dn/da ~ a(exp -3.5), the equivalent of a 130 km radius KBO of 1.0 grams per cubic centimeter density and similar to recent estimates of the mass delivered to the Earth at 0.6 - 0.8 Gyr during the Late Heavy Bombardment. We conclude that the parent body was a Kuiper-Belt body or bodies which captured a large amount of early primitive material in the first Myrs of the system's lifetime and preserved it in deep freeze at approximately 150 AU. At approximately 1.4 Gyr they were prompted by dynamical stirring of their parent Kuiper Belt into spiraling into the inner system, eventually colliding at 5-10 kilometers per second with a rocky planetary body of mass less than or equal to M(sub Earth at approximately 3 AU, delivering large amounts of water (greater than 0.1 % of M(sub Earth's Oceans)) and carbon-rich material. The Spitzer spectrum also closely matches spectra reported for the Ureilite meteorites of the Sudan Almahata Sitta fall in 2008, suggesting that one of the Ureilite parent bodies was a KBO.

Lisse, C. M.↗