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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
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↗
DOE OSTI2024

Systematic Local Simulations of Fast Neutrino Flavor Conversions with Scattering Effects

We investigate the dynamics of fast neutrino flavor conversions (FFCs) in the one-dimensional (1D) and zero-dimensional (0D) models, in which spatial advection is considered and ignored, respectively. In this study, we employ snapshots obtained by our self-consistent, realistic Boltzmann-neutrino-radiation-hydrodynamics simulations. We show that the FFC growth rate is considerably larger in the 1D model than in the 0D model, as expected from the previous linear analysis results. We find that the momentum space dimension does not significantly influence the neutrino transition probability in 1D models. On the other hand, in the 0D model without collisions, the FFC depends on the momentum space, and the azimuthal angle dependence breaks the periodicity of the FFC. Our study demonstrates that collisional instability can lead to further flavor conversions on a long timescale in 1D models after the asymptotic state of FFC has been reached. Such an effect should be taken into consideration when the fast and collisional flavor instabilities coexist.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Intrinsic charm and the 𝐷 + − 𝐷 − asymmetry produced in proton-proton collisions

We investigate the contribution of the charm-anticharm (𝑐⁢$\overline{𝑐}$) asymmetry of the proton eigenstate obtained from QCD lattice gauge to the asymmetry of 𝐷 + , 𝐷 − and 𝐷 0 , $\overline{𝐷}$ 0 mesons produced in 𝑝⁢𝑝 collisions at large Feynman variables 𝑥. It is shown that an important tool for establishing the intrinsic charm (IC) content of the proton is the charm hadron-antihadron asymmetry formed in 𝑝⁢𝑝 collisions. Predictions for the asymmetry as a function of 𝑥 for different IC probabilities are presented. We show that the interference of the intrinsic |𝑢⁢𝑢⁢𝑑⁢𝑐⁢$\overline{𝑐}$⟩ Fock state with the standard contribution from the perturbative QCD evolution leads to a large 𝐷 + ⁢𝐷 − asymmetry at large Feynman 𝑥.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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.↗
NASA NTRS1975

Close encounters of small bodies and planets

A small body in an orbit which crosses that of a planet may be eliminated by collision or ejected from the solar system. A method is developed for computing the probabilities of these fates. With some simplifying assumptions, the probabilities can be expressed as functions of the relative velocity only, rather than the orbital elements. The ejection probability does not vary greatly with velocity. The results are in agreement with those of Bandermann and Wolstencroft, but not with those of Opik; a reason for this disagreement is suggested. This method can be adapted to compute probabilities of generalized orbital changes. Some applications are discussed.

Weidenschilling, S. J.↗
DOE OSTI2025

Analytic Sensitivity Coefficients for Bethe's Solution of the Neutron Slowing Down Equation

Neutron slowing down theory is used to derive expressions for the sensitivity coefficients of the neutron collision density in a hydrogenous infinite medium with respect to the fixed source, scattering probability, and macroscopic nuclear cross sections. Analytic expressions for Bethe’s solution of the neutron slowing down equation are derived for the constant cross section approximation with a point, uniform, and gamma lethargy spectrum. Analytic expressions for the corresponding sensitivity coefficients are derived and used to verify Monte Carlo neutron transport calculations.

Analytic Benchmark↗
NASA NTRS2006

Cross Sections for Electron Impact Excitation of Astrophysically Abundant Atoms and Ions

Electron collisional excitation rates and transition probabilities are important for computing electron temperatures and densities, ionization equilibria, and for deriving elemental abundances from emission lines formed in the collisional and photoionized astrophysical plasmas. Accurate representation of target wave functions that properly account for the important correlation and relaxation effects and inclusion of coupling effects including coupling to the continuum are essential components of a reliable collision calculation. Non-orthogonal orbitals technique in multiconfiguration Hartree-Fock approach is used to calculate oscillator strengths and transition probabilities. The effect of coupling to the continuum spectrum is included through the use of pseudostates which are chosen to account for most of the dipole polarizabilities of target states. The B-spline basis is used in the R-matrix approach to calculate electron excitation collision strengths and rates. Results for oscillator strengths and electron excitation collision strengths for transitions in N I, O I, O II, O IV, S X and Fe XIV have been produced

Tayal, S. S.↗
NASA NTRS1975

Clumping of interstellar grains during formation of the primitive solar nebula

The author has previously shown that a considerable amount of clumping of interstellar grains is likely to take place during the free-fall collapse phase of an interstellar cloud which is forming the primitive solar nebula, with the assumption of sonic turbulence in the gas. The original estimate involved the crude assumption of hierarchal amalgamation of the grains upon collision. A Monte Carlo simulation of this process confirmed the general features of the results, but it was further found that the introduction of a low sticking probability reduced the size of the lumps quite significantly. A more realistic calculation was therefore carried out in which it was assumed that clumps of grains would tend to stick together if their collisions were approximately head-on, but that they would tend to fragment into smaller pieces if the collisions were more tangential. For typical values of the amalgamation parameter, this tends to spread the mass of the interstellar grains over a wide range of clump sizes, ranging from individual grains to objects in the millimeter or centimeter size.

Cameron, A. G. W.↗
NASA NTRS1983

H2O heating in molecular clouds - Line transfer and thermal balance in a warm dusty medium

An investigation is undertaken into the possibility of the heating of molecular gas through collisions with radiatively pumped H2O, in the context of the overall thermal balance of optically thick molecular clouds with embedded sources. In order to solve the line transfer equation, which includes warm dust grains, an extended method of escape probability approximation is developed in which the equilibrium gas temperature arises from the balance of heating by cosmic ray ionization of H2, and by collisions with warm dust grains and radiatively pumped H2O molecules against cooling by collisions with CO and C I. The equilibrium gas temperature for a given dust temperature strongly depends on the efficiency of the cooling species, and is therefore most sensitive to the cloud optical depth. It is less dependent, in decreasing order, on H2O abundance, gas density, and velocity dispersion.

Takahashi, T.↗
NASA NTRS1993

The Probable Ages of Asteroid Families

There has been considerable debate recently over the ages of the Hirayama families, and in particular if some of the families are very oung(u) It is a straightforward task to estimate the characteristic time of a collision between a body of a given diameter, d_o, by another body of diameter greater of equal to d_1. What is less straightforward is to estimate the critical diameter ratio, d_1/d_o, above which catastrophic disruption occurs, from which one could infer probable ages of the Hirayama families, by knowing the diameter of the parent body, d_o. One can gain some insight into the probable value of d_1/d_o, and of the likely ages of existing families, from the plot below. I have computed the characteristic time between collisions in the asteroid belt of a size ratio greater of equal to d_1/d_o, for 4 sizes of target asteroids, d_o. The solid curves to the lower right are the characteristic times for a single object...

Harris, A. W.↗