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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 145 records · Page 8

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NASA NTRS1978

A review of electron bombardment thruster systems/spacecraft field and particle interfaces

Information on the field and particle interfaces of electron bombardment ion thruster systems was summarized. Major areas discussed were the nonpropellant particles, neutral propellant, ion beam, low energy plasma, and fields. Spacecraft functions and subsystems reviewed were solar arrays, thermal control systems, optical sensors, communications, science, structures and materials, and potential control.

Byers, D. C.↗

NASA NTRS1978

Effect of anode-cathode geometry on performance of the HIP-1 hot ion plasma

Hot-ion hydrogen plasma experiments were conducted in the NASA Lewis HIP-1 magnetic mirror facility to determine how the ion temperature was influenced by the axial position of the cathode tips relative to the anodes. A steady-state EXB plasma was formed by applying a strong radially inward dc electric field near the throats of the magnetic mirrors. The dc electric field was created between hollow cathode rods inside hollow anode cylinders, both concentric with the magnetic axis. The highest ion temperatures, 900 eV, were attained when the tip of each cathode was in the same plane as the end of its anode. These temperatures were reached with 22 kV applied to the electrodes in a field of 1.1 tesla. Scaling relations were empirically determined for ion temperature and the product of ion density and neutral particle density as a function of cathode voltage, discharge current, and electrode positions. Plasma discharge current vs voltage (I-V) characteristics were determined.

Lauver, M. R.↗

NASA NTRS1978

A review of electron bombardment thruster systems/spacecraft field and particle interfaces

This paper collates and summarizes information on the field and particle interfaces of electron bombardment ion thruster systems. Major areas discussed are the nonpropellant particles, neutral propellant, ion beam, low energy plasma, and fields. Spacecraft functions and subsystems reviewed are solar arrays, thermal control systems, optical sensors, communications, science, structures and materials, and potential control. An appendix is included to facilitate identification of specific interaction areas.

Byers, D. C.↗

NASA NTRS1978

Molecular hydrogen emission from T Tauri stars

Results are presented for a search for molecular hydrogen emission in the v = 1-0 S(1) line at 2.2 microns in five T Tauri stars, including T Tau itself, RY Tau, SU Aur, DK Tau, and HL Tau. Molecular hydrogen emission was detected only in T Tau; the results suggest that the emitting region is probably larger than 5 arcsec (2.5-sigma confidence level) and that the emission is probably centered on the star. Upper limits on the line strengths are given for the other four stars. Various excitation mechanisms for the H2 in T Tau are considered, and the mass-loss rate and neutral-particle density in the shocked region are estimated for the case of shock excitation.

Beckwith, S.↗

NASA NTRS1979

The effect of energetically produced O2/+/ on the ion temperatures of the Martian thermosphere

The heating rates and ion temperatures of the Martian thermosphere resulting from the thermalization of the energetic O2(+) ions produced by the reactions of the solar ionization products CO2(+) and O(+) with neutral particles are calculated and the effects of small magnetic fields on the ion thermal balance are investigated. The energy transfer and transport of energetic ions is modelled by solving the continuity equation for the ions over a series of finite energy cells yielding the equilibrium densities as a function of energy and altitude. Particles which are able to proceed upwards without collisions are dealt with separately from the continuity equation. It is shown that the thermalization of the energetic O2(+) ions can greatly increase ion temperatures above 200 km compared to those calculated for only ambient electron heating. Current solar wind interaction models predict that small horizontal magnetic fields act to restrict the ion thermal conductivity and to increase upper altitude ion temperatures. The combined effects of these processes provide a partial agreement with measurements made by Viking 1.

Rohrbaugh, R. P.↗

NASA NTRS1980

On the secular decrease in the semimajor axis of Lageos orbit

The semimajor axis of the Lageos orbit is decreasing secularly at the rate of -1.1 mm/day due to an unknown force. Nine possible mechanisms are investigated. Five of the mechanisms, resonance with the Earth's gravitational field, gravitational radiation, the Poynting-Robertson effect, transfer of spin angular momentum to the orbital angular momentum, and drag from near Earth dust are ruled out because they are too small to require unacceptable assumptions to account for the observed rate. Three other mechanisms, the Yarkovsky effect, the Schach effect, and terrestrial radiation pressure could possibly give the proper order of magnitude for the decay rate, but the characteristic signatures of these perturbations do not agree with the observed secular decrease. Atmospheric drag from a combination of charged and neutral particles is the most likely cause for the orbital decay. This mechanism explains at least 71 percent of the observed rate of decrease of the semimajor axis.

Rubincam, D. P.↗

NASA NTRS1980

Radiative cooling efficiencies and predicted spectra of species of the Io plasma torus

Calculations of the physical condition of the Io plasma torus have been made based on the recent Voyager EUV observations. The calculations represent an assumed thin plasma collisional ionization equilibrium among the states within each species. The observations of the torus are all consistent with this condition. The major energy loss mechanism is radiative cooling in discrete transitions. Calculations of radiative cooling efficiencies of the identified species leads to an estimated energy loss rate of at least 1.5 x 10 to the 12th watts. The mean electron temperature and density of the plasma are estimated to be 100,000 K and 2100/cu cm. The estimated number densities of S III, S IV, and O III are roughly 95, 80, and 190-740/cu cm. Upper limits have been placed on a number of other species based on the first published Voyager EUV spectrum of the torus. The assumption that energy is supplied to the torus through injection of neutral particles from Io leads to the conclusion that ion loss rates are controlled by diffusion, and relative species abundances consequently are not controlled by collisional ionization equilibrium.

Shemansky, D. E.↗

NASA NTRS1981

Cosmic ray drift, shock wave acceleration and the anomalous component of cosmic rays

A model of the anomalous component of the quiet-time cosmic ray flux is presented in which ex-interstellar neutral particles are accelerated continuously in the polar regions of the solar-wind termination shock, and then drift into the equatorial regions of the inner heliosphere. The observed solar-cycle variations, radial gradient, and apparent latitude gradient of the anomalous component are a natural consequence of this model.

Pesses, M. E.↗

NASA NTRS1981

EUV flux variations during solar cycle 21 from AE-E He/+/ abundances

The ionization rate of helium in the thermosphere is inferred from AE-E ion and neutral particle composition measurements, made on several days during solar cycle 21, in the context of a steady state photochemical model for helium ions. The inferred ionization rate varies by a factor of 4 between July 1976 and January 1979, a value consistent with the variation in the flux measured during the same period by the EUV spectrometer on board the AE-E satellite.

Oppenheimer, M.↗

NASA NTRS1981

Cosmic ray drift, shock wave acceleration, and the anomalous component of cosmic rays

A model of the anomalous component of the quiet-time cosmic ray flux is presented in which ex-interstellar neutral particles are accelerated continuously in the polar regions of the solar-wind termination shock and then drift into the equatorial regions of the inner heliosphere. The observed solar-cycle variations, radial gradient, and apparent latitude gradient of the anomalous component are a natural consequence of this model.

Pesses, M. E.↗

NASA NTRS1981

The Dynamics Explorer Wind and Temperature Spectrometer

The Wind and Temperature Spectrometer, designed to measure the concentration, kinetic temperature, and motion (three mutually perpendicular components of the wind) of the neutral particles, is described, noting that measurements of the concentration and velocity of the ambient thermal ions are also possible. Two of the three wind components, the temperature and the concentration of the dominant constituent, can be measured to an altitude of approximately 650 km; the third component can be measured to about 375 km (estimated). Ion measurements can be taken throughout the orbit. The quadrupole mass spectrometer is the principal sensor for the instrument. Measurements of the zonal and vertical components of the wind are made by interpreting the modulation of the particle stream entering the mass spectrometer, induced by baffles that scan slowly (one vertically and one horizontally) in front of the entrance port of the mass spectrometer.

N W Spencer↗

NASA NTRS1982

Short-term EUV flux variations from AE-E He/+/ abundances

The ionization rate of helium in the thermosphere is inferred from AE-E ion and neutral particle composition measurements made on 20 days from January 1979 to June 1980. The variations in the inferred rate are consistent with variations in the UV flux measured during the same period by the AE-E UV spectrometer. The approximately 27-day modulation of the calculated ionization rate is the result of cyclical variations in the UV flux, which are in turn coupled to the rotation period of the sun. Results indicate that the ionization structure of helium in the thermosphere is closely coupled to both the long and short term EUV flux variations.

Sternberg, A.↗

NASA NTRS1982

Observations and photochemistry of O/++/ in the daytime thermosphere

An analysis is conducted for the Atmosphere Explorer C observations of O(++) in the daytime thermosphere which supercedes that of Breig et al (1977) and restricts attention to five orbits of data from the high-grain mode of the magnetic ion-mass spectrometer. The present investigation adopts a model for O(++) ionospheric chemistry which has been revised in light of recent laboratory measurements of a fast loss rate for O(++) through reaction with N2. An improved procedure is also introduced which analyzes the basic ion currents recorded by the magnetic ion-mass spectrometer and has special application for the very low concentrations near and below 200 km. It is found that large scale features in the low altitude data are best represented with an additive term which is proportional to the N2 or O2 density, with the preferred interpretation as a contaminant signal induced by neutral particles impinging on instrument or spacecraft surfaces.

Breig, E. L.↗

NASA NTRS1982

Neutral and charged clusters in the atmosphere - Their importance and potential role in heterogeneous catalysis

An assessment is presented of current knowledge concerning the role and importance of neutral and charged clusters in atmospheric heterogeneous catalysis, with a view to the recommendation of future studies needed for progress in the quantification of aerosol formation and catalytic reactivity. It is established that nucleation from the gaseous to the aerosol state commences via the formation of clusters among molecules participating in the phase-transformation process. Nucleation may proceed in some cases by way of the formation of prenucleation embryos, which then evolve through the energy barrier and undergo phase transformation. In other cases, cluster-cluster interaction among neutral particles or stagewise building of alternate-sign ion clusters may be important in the gas-to-particle conversion process.

Castleman, A. W., Jr.↗

NASA NTRS1984

Magnetron Sputtered Gold Contacts on N-gaas

Direct current planar magnetron sputtering was used to deposit gold Schottky barrier electrical contacts on n-type GaAs of varying doping densities. The electrical character of the contact was determined from current voltage and electron beam induced voltage data. Without reducing the surface concentration of carbon and oxide, the contacts were found to be rectifying. There is evidence that energetic neutral particles reflected from the magnetron target strike the GaAs and cause interfacial damage similar to that observed for ion sputtering. Particle irradiation of the surface during contact deposition is discussed.

Buonaquisti, A. D.↗

NASA NTRS1984

Interstellar-gas experiment (A0038)

The objectives of this experiment are to collect and isotopically analyze interstellar gas atoms around the orbit of the Earth for the purpose of obtaining new data relevant to understanding nucleosynthesis, and to study the dynamics of the interstellar wind inside the heliosphere and the isotopic composition of the interstellar medium outside the heliosphere. The experiment hardware will act as a set of simple cameras with high-purity copper-beryllium collecting foils serving as the film. The experiment housing will mount and thermally control the foils, establish the viewing angles and viewing direction, provide baffling to reject ambient neutral particles, provide a voltage grid to reject ionospheric charged particles, sequence collecting foils, control exposure times, and protect the foils from contamination during the deployment and retrieval of the LDEF. After being returned to Earth, the entrapped atoms can be analyzed by mass spectroscopy to determine the relative abundance of the different isotopes of helium and neon. An attempt will also be made to detect argon.

Lind, D. L.↗

NASA NTRS1983

Implications of Voyager data for energetic ion erosion of the icy satellites of Saturn

The possible production of a neutral-particle torus by magnetosphere-particle sputtering of the icy satellites (Enceladus, Tethys, Dione, Rhea) of Saturn is discussed. Particle spectra from the Voyager low-energy-charged-particle experiment are used together with laboratory-derived erosion rates and velocity distributions for the ejected species. An extended torus region in the inner magnetosphere of Saturn is expected, with H2O escape fluxes in the vicinities of the satellites varying from about 2 to 7 x 10 to the 7th mol/sq cm sec for incident protons and from about 6 to 14 x 10 to the 9th mol/sq cm sec if the incident ions are all oxygen.

Lanzerotti, L. J.↗

NASA NTRS1986

Mass spectrometric studies of the electrical breakdown of thin polymer films

The composition of the neutral particles released during the electrical breakdown of 50-micron and 75-micron insulating films of the type used on spacecraft exteriors investigated experimentally using a time-of-flight mass spectrometer triggered by the breakdown event. The experimental apparatus is described in detail, and the results are presented in photographs. It is found that the particle flux from Teflon FEP and PFA films comprise mainly fluorocarbon fragments, some with mass 350 amu or greater, but the flux from Kapton oxygen-ion-beam treated Kapton, Tefzel, and Mylar comprises mainly molecules of mass 44 amu or less.

Kendall, B. R. F.↗