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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Solution of Boltzmann equation for highly nonequilibrium diatomic gases rotational translational energy relaxation

The direct simulation Monte Carlo method is applied to solve the Boltzmann equation for collisions between internally excited diatomic gases in highly nonequilibrium states. The semiclassical transition probability is incorporated in the simulation for energy exchange between rotational and translational energy. The results provide details on the fundamental mechanisms of gas kinetics where analytical methods are impractical. The validity of the local Maxwellian assumption and relaxation time, rotational-translational energy transition, and a velocity analysis of the inelastic collision are discussed in detail.

Yoshikawa, K. K.↗
NASA NTRS1997

Centric rings, acentric rings and excess acentric fragments based on a random-walk interphase chromosome model

Excess acentric fragments, consisting of acentric rings and acentric linear fragments, are among the most frequent kinds of chromosome-type aberrations produced by radiation. The frequency of acentric rings cannot be obtained directly by experiment but is estimated here from the ratio of acentric to centric rings, evaluated using a random-walk model for the organization of chromatin during interphase and an assumption that the probability of an exchange formation is proportional to the rate of collision between two DSB. This ratio is calculated to be 2.5 in low-LET irradiated human fibroblasts, significantly greater than the ratio if proximity effects are not considered. The calculated frequency of acentric rings is insufficient to account for all the observed excess acentric fragments. Assuming that the rest of the excess acentric fragments are due to incomplete exchanges, all possible recombinations between two DSB that result in acentric rings and acentric linear fragments have been identified. From the chromosome aberration data, the incompleteness parameter has been estimated. Intra-arm chromosome exchanges, either complete or incomplete, were estimated to account for more than 50% of the excess acentric fragments in human fibroblasts.

NASA Center JSC↗
NASA NTRS1995

Magnetic merging in colliding flux tubes

We develop an analytical theory of reconnection between colliding, twisted magnetic flux tubes. Our analysis is restricted to direct collisions between parallel tubes and is based on the collision dynamics worked out by Bogdan (1984). We show that there is a range of collision velocities for which neutral point reconnection of the Parker-Sweet type can occur, and a smaller range for which reconnection leads to coalescence. Mean velocities within the solar convection zone are probably significantly greater than the upper limit for coalescence. This suggests that the majority of flux tube collisions do not result in merging, unless the frictional coupling of the tubes to the background flow is extremely strong.

Zweibel, Ellen G.↗
NASA NTRS1974

Semiclassical S-matrix theory of vibrationally inelastic collisions between two diatomic molecules

We derive a semiclassical S matrix for vibrationally inelastic collisions between two diatomic molecules, assuming a collinear geometry. Our theory incorporates a quantum mechanical superposition principle with classical dynamics and, as such, is an extension of the atom-diatomic molecule theory of Miller. The several approximations to the S matrix differ in the complexity with which the interference between various classical trajectories is treated. We report numerical calculations for H2-D2 and D2-D2 collisions based on two different interaction potentials. The cruder approximations yield transition probabilities which agree with exact quantum mechanical results to within a factor of 2. More sophisticated approximations to the S matrix yield excellent quantitative agreement with the quantum calculations.

Cohen, S. C.↗
NASA NTRS1980

AMTV headway sensor and safety design

A headway sensing system for an automated mixed traffic vehicle (AMTV) employing an array of optical proximity sensor elements is described, and its performance is presented in terms of object detection profiles. The problem of sensing in turns is explored experimentally and requirements for future turn sensors are discussed. A recommended headway sensor configuration, employing multiple source elements in the focal plane of one lens operating together with a similar detector unit, is described. Alternative concepts including laser radar, ultrasonic sensing, imaging techniques, and radar are compared to the present proximity sensor approach. Design concepts for an AMTV body which will minimize the probability of injury to pedestrians or passengers in the event of a collision are presented.

Johnston, A. R.↗
NASA NTRS1979

F + H2 collisions on two electronic potential energy surfaces - Quantum-mechanical study of the collinear reaction

Collinear quantum calculations are carried out for reactive F + H2 collisions on two electronic potential energy surfaces. The resulting transmission and reflection probabilities exhibit much greater variation with energy than single-surface studies would lead us to anticipate. Transmission to low-lying product channels is increased by orders of magnitude by the presence of the second surface; however, branching ratios among product states are found to be independent of the initial electronic state of the reactants. These apparently contradictory aspects of the calculation are discussed and a tentative explanation put forward to resolve them.

Zimmerman, I. H.↗
NASA NTRS1982

Drop processes in natural clouds

A model of the diffusive mixing of dry and cloudy air, a process considered to be fundamental to the development of natural clouds, is presented. Water drops are formed at the cloud base by condensation upon nuclei and as they rise they grow by vapor diffusion in the slightly supersaturated environment of the clouds. Turbulent mixing between cloudy air and undersaturated air entrained from outside produces fluctuations in supersaturation, not linked to changes in vertical velocity, which cause broadening of the condensate spectrum and the rapid production of droplets large enough to engage in growth by coalescence. The probabilities of permanent union or the production of satellite droplets following the collision of a pair of raindrops is a sensitive function of several parameters. In some circumstances electrohydrodynamic bursting may influence the properties of clouds.

Latham, J.↗
NASA NTRS1990

Hot and cold gas toward young stellar objects

High-resolution M band spectra are presented for the seven embedded IR sources W3 IRS 5, S140 IRS1, NGC 7538 IRS 1, NGC 7538 IRS 9, GL 2136, LkH-alpha 101, and MWC 349A, and the data are combined with previously published work for W33A and GL 2591. Cold CO is seen toward all nine sources, with temperatures from 11 K to 66 K. Column densities of cold CO are presented. Hot gas is seen toward eight of the nine objects with temperatures from 120 K to 1010 K. New lower limits to the hot gas density are obtained. The hot gas toward GL 2591, GL 2136, W3 IRS 5, and S140 IRS 1 is probably very near the central source and heated via gas-grain collisions. The optical depth in the silicate feature is strongly correlated with the (C-13)O column density, confirming that silicate optical depth is a useful measure of gas column density. The ratio of solid-to-gaseous CO is obtained for seven sources.

Mitchell, George F.↗
NASA NTRS2010

The Impact of a Large Object on Jupiter in 2009 July

On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55 S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory in the opposite direction and with a Tower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4800 km east west and 2500 km north south, with those produced by the SL9 fragments and dynamical calculations of pre-impact orbit indicates that the impactor was most probably an icy body with a size of 0.5-1 km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890 nm and K (2.03--2.36 micrometer) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary clouds.

Sanchez-Lavega, A.↗
NASA NTRS2011

Design of Spacecraft Missions to Test Kinetic Impact for Asteroid Deflection

There are currently over 8,000 known near-Earth asteroids (NEAs), and more are being discovered on a continual basis. More than 1,200 of these are classified as Potentially Hazardous Asteroids (PHAs) because their Minimum Orbit Intersection Distance (MOID) with Earth's orbit is <= 0.05 AU and their estimated diameters are >= 150 m. To date, 178 Earth impact structures have been discovered, indicating that our planet has previously been struck with devastating force by NEAs and will be struck again. Such collisions are aperiodic events and can occur at any time. A variety of techniques have been proposed to defend our planet from NEA impacts by deflecting the incoming asteroid. However, none of these techniques have been tested. Unless rigorous testing is conducted to produce reliable asteroid deflection systems, we will be forced to deploy completely untested -- and therefore unreliable -- deflection missions when a sizable asteroid on a collision course with Earth is discovered. Such missions will have a high probability of failure. We propose to address this problem with a campaign of deflection technology test missions deployed to harmless NEAs. The objective of these missions is to safely evaluate and refine the mission concepts and asteroid deflection system designs. Our current research focuses on the kinetic impactor, one of the simplest proposed asteroid deflection techniques in which a spacecraft is sent to collide with an asteroid at high relative velocity. By deploying test missions in the near future, we can characterize the performance of this deflection technique and resolve any problems inherent to its execution before needing to rely upon it during a true emergency. In this paper we present the methodology and results of our survey, including lists of NEAs for which safe and effective kinetic impactor test missions may be conducted within the next decade. Full mission designs are also presented for the NEAs which offer the best mission opportunities.

Hernandez, Sonia↗
NASA NTRS2006

New Accurate Oscillator Strengths and Electron Excitation Collision Strengths for N1

The nonorthogonal orbitals technique in a multiconfiguration Hartree-Fock approach is used to calculate oscillator strengths and transition probabilities of N(I) lines. The relativistic effects are allowed by means of Breit-Pauli operators. The length and velocity forms of oscillator strengths show good agreement for most transitions. The B-spline R-matrix with pseudostates approach has been used to calculate electron excitation collision strengths and rates. The nonorthogonal orbitals are used for an accurate description of both target wave functions and the R-matrix basis functions. The 24 spectroscopic bound and autoionizing states together with 15 pseudostates are included in the close-coupling expansion. The collision strengths for transitions between fine-structure levels are calculated by transforming the LS-coupled K-matrices to K-matrices in an intermediate coupling scheme. Thermally averaged collision strengths have been determined by integrating collision strength over a Maxwellian distribution of electron energies over a temperature range suitable for the modeling of astrophysical plasmas. The oscillator strengths and thermally averaged collision strengths are presented for transitions between the fine-structure levels of the 2s(sup 2)p(sup 3) (sup 4)S(sup 0), (sup 2)D(sup 0), (sup 2)P(sup 0), 2s2p(sup 4) (sup 4)P, 2s(sup 2)2p(sup 2)3s (sup 4)P, and (sup 2)P terms and from these levels to the levels of the 2s(sup 2)2p(sup 2)3p (sup 2)S(sup 0), (sup 4)D(sup 0), (sup 4)P(sup 0), (sup 4)S(sup 0), (sup 2)D(sup 0), (sup 2)P(sup 0),2s(sup 2)2p(sup 2)3s(sup 2)D, 2s(sup 2)2p(sup 2)4s(sup 4)P, (sup 2)P, 2s(sup 2)2p(sup 2)3d(sup 2)P, (sup 4)F,(sup 2)F,(sup 4)P, (sup 4)D, and (sup 2)D terms. Thermally averaged collision strengths are tabulated over a temperature range from 500 to 50,000 K.

Tayal, S. S.↗
NASA NTRS1987

Collisional excitation of interstellar sulfur dioxide

State-to-state rotational excitation rates for the asymmetric top molecule SO2 in collisions with low-energy He atoms have been computed. The intermolecular forces were obtained from an electron gas model, and collision dynamics were treated with the finite-order sudden approximation. The total excitation rate is probably accurate to better than 50 percent; however, individual state-to-state rates may be in error by factors of 2 or 3, and some smaller rates may be accurate only to an order of magnitude. Present results are expected to reflect within the same level of accuracy rates for excitation by collisions with H2 molecules.

Palma, Amedeo↗
NASA NTRS2011

Polymeric Materials With Additives for Durability and Radiation Shielding in Space

Polymeric materials are attractive for use in space structures because of their light weight and high strength In addition, polymers are made of elements with low atomic numbers (Z), primarily carbon (C), hydrogen (H), oxygen (0), and nitrogen (N) which provide the best shielding from galactic cosmic rays (GCR) (ref. 1). Galactic cosmic rays are composed primarily of nuclei (i.e., fully ionized atoms) plus a contribution of about 2% from electrons and positrons. There is a small but significant component of GCR particles with high charge (Z > 10) and high energy (E >100 GeV) (ref. 2). These so-called HZE particles comprise only 1 to 2% of the cosmic ray fluence but they interact with very high specific ionization and contribute 50% of the long- term dose to humans. The best shield for this radiation would be liquid hydrogen, which is not feasible. For this reason, hydrogen-containing polymers make the most effective practical shields. Moreover, neutrons are formed in the interactions of GCR particles with materials. Neutrons can only lose energy by collisions or reactions with a nucleus since they are uncharged. This is a process that is much less probable than the Coulombic interactions of charged particles. Thus, neutrons migrate far from the site of the reaction in which they were formed. This increases the probability of neutrons reaching humans or electronic equipment. Fast neutrons (> 1 MeV) can interact with silicon chips in electronic equipment resulting in the production of recoil ions which can cause single event upsets (SEU) in sensitive components (ref. 3). Neutrons lose energy most effectively by elastic collisions with light atoms, particularly hydrogen atoms. Therefore, hydrogen-containing polymers are not only effective in interacting with GCR particles; they are also effective in reducing the energy of the neutrons formed in the interactions.

Kiefer, Richard↗
NASA NTRS1995

Determining large-scale heliospheric structure using ultraviolet resonance line observations

Currently the Pioneer 10 and Voyager 1 and 2 spacecraft are beyond the orbit of Pluto, traveling outward from the Sun. Each is capable of detecting ultraviolet radiation resonantly scattered from hydrogen and helium atoms in the heliosphere and local interstellar medium. These observations are particularly well suited for the investigation of the large-scale heliospheric H and He distributions because the Voyager spacecraft are heading upstream, into the direction of local interstellar flow, whereas Pioneer 10 is heading downstream. Observations of the brightest resonance line, H Lyman-alpha, reveals that beyond about 20 AU from the Sun, upstream intensities decrease less quickly as a function of solar distance than downstream intensities. This implies that the heliospheric H distributions in the upstream and downstream directions are significantly different. Heliospheric H atoms originate in the local interstellar flow, and must penetrate through the heliospheric interface, where they are subject to charge exchange collisions with solar wind and interstellar protons. Models indicate that this process is probably responsible for the upstream/downstream difference in H Lyman-alpha. In addition, a recent spectroscopic determination of the H atom velocity distribution in the inner heliosphere implies a significant deceleration in the bulk flow speed of the heliospheric hydrogen gas relative to the helium flow, an effect that is also likely due to H-p charge exchange occurring in the upstream heliospheric interface region. In this presentation, recent heliospheric resonance line observations and their interpretations will be reviewed, focusing on their sensitivity to large-scale heliospheric structure.

Hall, Doyle T.↗
NASA NTRS2017

The Effect of the Spin-Forbidden Co((sup 1) Sigma plus) plus O((sup 3) P) Yields CO2 (1 Sigma (sub G) plus) Recombination Reaction on Afterbody Heating of Mars Entry Vehicles

Vibrationally excited CO2, formed by two-body recombination from CO((sup 1) sigma plus) and O((sup 3) P) in the wake behind spacecraft entering the Martian atmosphere reaction, is potentially responsible for the higher than anticipated radiative heating of the backshell, compared to pre-flight predictions. This process involves a spin-forbidden transition of the transient triplet CO2 molecule to the longer-lived singlet. To accurately predict the singlet-triplet transition probability and estimate the thermal rate coefficient of the recombination reaction, ab initio methods were used to compute the first singlet and three lowest triplet CO2 potential energy surfaces and the spin-orbit coupling matrix elements between these states. Analytical fits to these four potential energy surfaces were generated for surface hopping trajectory calculations, using Tully's fewest switches surface hopping algorithm. Preliminary results for the trajectory calculations are presented. The calculated probability of a CO((sup 1) sigma plus) and O((sup 3) P) collision leading to singlet CO2 formation is on the order of 10 (sup -4). The predicted flowfield conditions for various Mars entry scenarios predict temperatures in the range of 1000 degrees Kelvin - 4000 degrees Kelvin and pressures in the range of 300-2500 pascals at the shoulder and in the wake, which is consistent with a heavy-particle collision frequency of 10 (sup 6) to 10 (sup 7) per second. Owing to this low collision frequency, it is likely that CO((sup 1) sigma plus) molecules formed by this mechanism will mostly be frozen in a highly nonequilibrium rovibrational energy state until they relax by photoemission.

CO2 recombination↗
NASA NTRS1995

Collisional Time Scales in the Kuiper Disk and Their Implications

We explore the rate of collisions among bodies in the present-day Kuiper Disk as a function of the total mass and population size structure of the disk. We find that collisional evolution is an important evolutionary process in the disk as a whole, and indeed, that it is likely the dominant evolutionary process beyond approx. 42 AU, where dynamical instability time scales exceed the age of the solar system. Two key findings we report from this modeling work are: that unless the disk's population structure is sharply truncated for radii smaller than approx. 1-2 km, collisions between comets and smaller debris are occurring so frequently in the disk, and with high enough velocities, that the small body (i.e., KM-class object) population in the disk has probably developed into a collisional cascade, thereby implying that the Kuiper Disk comets may not all be primordial, and that the rate of collisions of smaller bodies with larger 100 less R less 400 km objects (like 1992QB(sub 1) and its cohorts) is so low that there appears to be a dilemma in explaining how QB(sub 1)s could have grown by binary accretion in the disk as we know it. Given these findings, it appears that either the present-day paradigm for the formation of Kuiper Disk is failed in some fundamental respect, or that the present-day disk is no longer representative of the ancient structure from which it evolved. This in turn suggests the intriguing possibility that the present-day Kuiper Disk evolved through a more erosional stage reminiscent of the disks around the stars Beta Pictorus, alpha PsA, and alpha Lyr.

Stern, S. Alan↗
NASA NTRS1975

Early scattering by Jupiter and its collision effects in the terrestrial zone

When Jupiter was on the order of three to ten earth masses in size, there undoubtedly was a considerably larger mass of condensed matter in its zone, since Jupiter would have perturbed most of it to other parts of the solar system. Monte Carlo studies indicate a significant portion would have crossed the earth's orbit. If the earth and moon had not yet fully formed, the probability of earth-zone planetesimals being hit by this Jupiter-scattered material was high. Further Monte Carlo models of these collisions and their products indicate a significant portion of matter was heated to melting, even if less than 5% of the relative kinetic energy went into heat. The models include capture probabilities by an embryo earth and a protolunar swarm. Because heat energy is correlated with comminution energy, and because the capture probability of the swarm is mass-dependent while embryo's is not, the protolunar material suffered much higher heating on the average than did the proto-earth material.

Kaula, W. M.↗
NASA NTRS1973

Background of the completed research; relevances to solar physics

Research activities reported consider the atomic structures of highly stripped heavy ions and their modes of formation and destruction in collisions. The lifetime of the metastable 2 3p1 state of the two electron ion F-7(+) was determined by measuring the radiative decay of an excited helium-like fluorine beam, Metastable state quenching measurements were performed on a helium-like ion to obtain the 1 1S0 to 2 3p2 transition probability. Exponential exchange state dependence of X-ray production cross sections was studied in heavy target atoms during collisions with light charged particles.

Sellin, I. A.↗