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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 73 records · Page 4
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NASA NTRS2017

Collision Avoidance Short Course Part I: Theory

Satellite conjunction assessment is perhaps the fastest-growing area in space situational awareness and protection, with military, civil, and commercial satellite owner operators embracing more and more sophisticated processes to avoid the avoidable namely collisions between high-value space assets and orbital debris. NASA and CNES have collaborated to offer an introductory short course on all the major aspects of the conjunction assessment problem. This half-day course will cover satellite conjunction dynamics and theory, JSpOC conjunction data products, major risk assessment parameters and plots, conjunction remediation decision support, and present and future challenges. This briefing represents the NASA portion of the course.

conjunction assessment↗
NASA NTRS2017

Consideration of Collision "Consequence" in Satellite Conjunction Assessment and Risk Analysis

Classic risk management theory requires the assessment of both likelihood and consequence of deleterious events. Satellite conjunction risk assessment has produced a highly-developed theory for assessing collision likelihood but holds a completely static solution for collision consequence, treating all potential collisions as essentially equally worrisome. This may be true for the survival of the protected asset, but the amount of debris produced by the potential collision, and therefore the degree to which the orbital corridor may be compromised, can vary greatly among satellite conjunctions. This study leverages present work on satellite collision modeling to develop a method by which it can be estimated, to a particular confidence level, whether a particular collision is likely to produce a relatively large or relatively small amount of resultant debris and how this datum might alter conjunction remediation decisions. The more general question of orbital corridor protection is also addressed, and a preliminary framework presented by which both collision likelihood and consequence can be jointly considered in the risk assessment process.

Hejduk, M.↗
NASA NTRS1980

Collisions between hydrogen atoms and helium ions

By the use of a new theory developed for collisions between atomic hydrogen and arbitrary ions or atoms, the cross section for the direct excitation process He(+)(1s) + H(1s) yields He(+)(2s) + H(Sigma) in which the H atom is left in any discrete or continuum final state is calculated. The results are compared with other theories and with recent measurements for He-3(+) energies between 22 and 346 keV. The theory predicts a maximum near 84 keV, in excellent agreement with the data. Above 200 keV all theories yield cross sections which do not decrease rapidly enough with increasing energy when compared with the data.

Franco, V.↗
NASA NTRS1967

Collisions in the asteroid belt.

Generalization of Oepik theory of planetary bodies collision to include case where orbits of both colliding bodies are ellipses

LIFETIME↗
NASA NTRS1984

Kinetic theory of current and density drift instabilities with weak charged-neutral collisions

This paper describes the linear kinetic theory of electrostatic instabilities driven by a density gradient drift and a magnetic-field-aligned current in a plasma with weak charged neutral collisions. The configuration is that of a uniform magnetic field B, a weak, uniform density gradient in the x direction and a weak, uniform electric field in the z direction. Collisions are represented by the BGK model. The transition from the (kinetic) universal density drift instability to the (fluidlike) current convective instability is studied in detail, and the short wavelength properties of the latter mode are investigated.

Gary, S. P.↗
NASA NTRS1993

Collision-induced absorption in mixtures of symmetrical linear and tetrahedral molecules - Methane-nitrogen

The far infrared absorption of a CH4-N2 mixture was measured at 297, 195, and 162 K from 30 to 650/cm. The spectral invariants gamma1 and alpha1, proportional, respectively, to the zeroth and first spectral moments, due to bimolecular collisions between CH4 and N2 were obtained from these data and compared with theoretical values. The theory for collision-induced dipoles between a tetrahedral and a diatomic or symmetrical linear molecule includes contributions not previously considered. Whereas the theoretical values of gamma1 are only somewhat greater than experiment at all temperatures, the theoretical values of alpha1 are significantly lower than the experimental values. From the theoretical spectral moments for the various induced dipole components, the parameters of the BC shape were computed, and theoretical spectra were constructed. Good agreement was obtained at the lower frequencies, but with increasing frequencies the theoretical spectra were increasingly less intense than the experimental spectra. Although the accuracy of the theoretical results may suffer from the lack of a reliable potential function, it does not appear that this high frequency discrepancy can be removed by any conceivable modification in the potential.

Birnbaum, G.↗
NASA NTRS1992

A far wing line shape theory and its application to the water vibrational bands (II)

Attention is given to a far wing line shape theory based on binary collision and quasi-static approximations. The theory is applicable for both the LF and HF wings of vibrational-rotational bands. It is used to calculate the frequency and temperature dependence of the continuous absorption coefficient for frequencies up to 10,000/cm for pure water vapor. The results are compared with existing laboratory data in the 2400-2700/cm window and in the 3000-4300/cm band center region, with field measurements in the 2000-2225/cm region and with a recent experimental measurement near 9466/cm. It is concluded that both the magnitude and temperature dependence of the water vapor continuum can be accounted for by the present theory without the introduction of any adjustable parameters. Refinements of the theory and extension to foreign-broadened absorption are also discussed.

Ma, Q.↗
NASA NTRS1974

Electron detachment in low-energy collisions of H/-/ and D/-/ with He

The applicability of the complex-potential theory to H(-)-He collisions is investigated. Measurements are conducted of the elastic differential cross section for H(-)-He collisions, taking into account energies in the range from 5 to 120 eV. A preliminary determination is made of the energy spectrum of detached electrons. The results are interpreted in terms of the complex-potential theory. The crossing point is determined together with the general shape of the HeH(-) potential curve.

Lam, S. K.↗
NASA NTRS1987

Collisional excitation of interstellar cyclopropenylidene

Theoretical rotational excitation rates were computed for C3H2 in collisions with He atoms at temperatures from 30 to 120 K. The intermolecular forces were obtained from accurate self-consistent field and perturbation theory calculations, and collision dynamics were treated within the infinite-order sudden approximation. The accuracy of the latter was examined by comparing with the more exact coupled states approximation.

Green, Sheldon↗
NASA NTRS1972

Use of the Glauber approximation in atomic collisions - A progress report.

Recent progress in the use of the Glauber (1970) theory for estimating atomic collision cross sections is reviewed. It appears that the Glauber approximation is reliable for electron-hydrogen elastic scattering and excitation at incident energies exceeding 30 eV. For more complicated atomic collisions, the usefulness of the Glauber approximation has not yet been significantly tested.

Gerjuoy, E.↗
NASA NTRS1977

Quantum mechanical theory of a structured atom-diatom collision system - A + BC/1-Sigma/

The problem of a 2-p state atom colliding with a singlet sigma state diatom, which involves multiple potential surfaces, is investigated. Within a diabatic representation for the electronic degrees of freedom (plus spin-orbit interaction), coupled scattering equations are derived in both space-fixed and body-fixed coordinate systems. Coefficients, analogous to Percival-Seaton coefficients, are obtained. Approximations to the exact equations, including angular momenta decoupling approximations, are discussed for both the space-fixed and body-fixed formalisms.

Devries, P. L.↗
NASA NTRS1985

New theory of transport due to like-particle collisions

Cross-magnetic-field transport due to like-particle collisions is discussed for the parameter regime lambda sub D much greater than r sub L, where lambda sub D is the Debye length and r sub L is the characteristic Larmor radius of the colliding particles. A new theory based on collisionally produced E x B drifts predicts a particle flux which exceeds the flux predicted previously, by the factor (lambda sub D/r sub L)-squared much greater than 1.

Oneil, T. M.↗
NASA NTRS1969

Dielectronic recombination

Dielectronic recombination rate coefficient determined by quantum theory of resonance- collision processes, considering coupling, degeneracy and overlapping resonances

Shore, B. W.↗
NASA NTRS1970

Correlation effects in semi-infinite plasmas

Pair correlations effect in equilibrium and nonequilibrium theory, taking Coulomb collisions into account for ionized plasmas confined to half space by reflecting boundary

Guernsey, R. L.↗
NASA NTRS1975

On ionospheric aerodynamics

This paper presents theoretical methods to determine the gas dynamic and the electrostatic effects due to the interaction caused by a rapidly moving body in the ionosphere. The principles of the methods are derived from the kinetic theory of collision-free plasma. It is shown that the collective behavior of the collision-free plasma makes it possible to use the fluid approach to treat the problems of ionospheric aerodynamics. Various solutions to the system of fluid and field equations that have direct bearing on the ionospheric aerodynamics are presented and discussed. Physical significances of the mathematical results are stressed. Some outstanding unsolved problems in ionospheric aerodynamics are elaborated and discussed.

Liu, V. C.↗
NASA NTRS1977

Comment on the relation between the nonadiabatic coupling and the complex intersection of potential energy curves

Simple relations are discussed that provide a correspondence between the complex intersection of two potential surfaces and the nonadiabatic coupling matrix element between those surfaces. These are key quantities in semiclassical and quantum-mechanical theories of collision-induced electronic transitions. Within the two-state approximation, the complex intersection is shown to be directly related to the location and magnitude of the peak in the nonadiabatic coupling. Two cases have been considered: (1) the avoided crossing between two potential surfaces, and (2) the spin-orbit interaction due to a 2P halogen atom. Comparisons are made between the results of the two-state model and the results of ab initio quantum chemical calculations.

Jaffe, R. L.↗