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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Neutral stellar winds that drive bipolar outflows in low-mass protostars

The Arecibo radio telescope at the 21-cm line of atomic hydrogen has been used to detect a neutral atomic wind in the bipolar flow source HH 7-11. An atomic mass of about 0.015 solar associated with the rapidly flowing gas is deduced. The stellar mass-loss rate is roughly 3 x 10 to the -6th solar mass/yr if the crossing time of the decelerating wind is 5000 yr. The excess emission in the H I line core gives a total duration of the outflow of about 70,000 yr. A detailed analysis of the H I line shape yields a reasonable deceleration rate for the atomic wind if the stellar wind continuously entrains ambient molecular gas as it propagates from the protostar. A stellar wind with the described characteristics and a terminal velocity of 170 km/s would be more than sufficient to drive the known extended CO bipolar outflow in HH 7-11.

Lizano, Susana↗
NASA NTRS1988

The megamaser galaxy Markarian 273. II - VLA observations of the neutral hydrogen absorption

The high-resolution A-array of the VLA was used to observe the wide neutral hydrogen absorption in the OH megamaser galaxy Mrk 273. The nuclear continuum of this galaxy is extended at 21 cm; Ulvestadt and Wilson (1984) find a double structure at 6 cm where the stronger component is resolved into a triple at 2 cm. The H I absorption is marginally resolved both spatially and spectrally and different features can be identified. These features are distinguishable as basically Gaussian components of the absorption but are probably not independent; several of these may form a rotating disk with a velocity gradient of 1.89 km/s per parsec. Assuming a typical rotational velocity of about 200 km/s, the radius of this disk would be R = 106 pc and the total internal mass can be estimated at M = 10 to the 9th solar masses. These parameters, when compared with the same values of other extragalactic H I absorption disks, are not highly unusual and are, possibly, quite believable.

Schmelz, J. T.↗
NASA NTRS1988

Constraints on the neutral hydrogen corona at Uranus from its interaction with magnetospheric plasma

Models of collisional reactions between the hot (several keV) protons and neutral atomic hydrogen corona observed at Uranus by Voyager 2 are compared with observations in order to deduce constraints on the coronal density. An upper limit is found for n sub H (5R sub U) of several tens of H/cu cm on the sunward side of Uranus and several H/cu cm on the dark side. The possibility that the hot plasma population might arise from photoionization and electron impact ionization of coronal and interstellar medium hydrogen in the magnetotail, followed by pickup and energization while convecting toward Uranus, is examined and rejected.

Herbert, Floyd↗
NASA NTRS1989

Turbulent small-scale neutral and ion density fluctuations as measured during MAC/Epsilon

During the MAC/Epsilon campaign (Fall 1987, from Andoya, Northern Norway, 69 N, 16 E) a total of four altitude profiles of neutral gas number densities and six profiles of ion number densities were measured with high spatial resolution in the height range from 60 to 120 km. First results of these rocket-borne experiments are presented with emphasis on small scale turbulent density variations and related turbulent parameter as structure function constants and energy dissipation rates.

Luebken, F.-J.↗
NASA NTRS1988

The terrestrial ring current - From in situ measurements to global images using energetic neutral atoms

Electrical currents flowing in the equatorial magnetosphere, first inferred from ground-based magnetic disturbances, are carried by trapped energetic ions. Spacecraft measurements have determined the spectrum and composition of those currents, and the newly developed technique of energetic-neutral-atom imaging allows the global dynamics of that entire ion population to be viewed from a single spacecraft.

Roelof, Edmond C.↗
NASA NTRS1988

Neutral atomic carbon in dense molecular clouds

The 370 micron 3P2-3P1 fine-structure line of neutral carbon was detected in seven sources: OMC 1, NGC 2024, S140, W3, DR 21, M17, and W51. Simultaneous analysis of J = 2-1 data and available observations of the J = 1-0 line make it possible to deduce optical depths and excitation temperatures for these lines. These data indicate that both C I lines are likely to be optically thin, and that the ratio of C I to CO column densities in these clouds is typically about 0.1.

Zmuidzinas, J.↗
NASA NTRS1989

Heavy ion beam-ionosphere interactions - Charging and neutralizing the payload

Three different electrical charging and neutralization processes were experienced during gun operation in the Argon Release Controlled Studies rocket flights, which carried ion generators to 400-500 km in the nighttime auroral ionosphere: DC charging of the vehicle, brief charging at gun turn-on, and extended oscillatory sequences. The present analysis of these phenomena has determined that, during oscillatory events, the entire environment of a payload could alternate between hot electron and cold electron configurations at rates which may have been in excess of 10 kHz.

Kaufmann, R. L.↗
NASA NTRS1989

Linear, collisionless, bi-Maxwellian neutral-sheet tearing instability

The problem of linear bi-Maxwellian neutral-sheet tearing instability has been solved, using neither an approximation of the orbits nor the constant-psi approximation. The present method has a larger range of validity than the best previous approximation, the three-region approximation. It is found that as the temperature anisotropy is increased, the growth rate increases and the wavelength associated with the peak growth decreases. It is suggested that if small-island formation is experimentally observed, then temperature anisotropy may be present.

Burkhart, G. R.↗
NASA NTRS1989

Collisionless tearing instability of a bi-Maxwellian neutral sheet - An integrodifferential treatment with exact particle orbits

The integrodifferential equation describing the linear tearing instability in the bi-Maxwellian neutral sheet is solved without approximating the particle orbits or the eigenfunction psi. Results of this calculation are presented. Comparison between the exact solution and the three-region approximation motivates the piecewise-straight-line approximation, a simplification that allows faster solution of the integrodifferential equation, yet retains the important features of the exact solution.

Burkhart, G. R.↗
NASA NTRS1989

Si II mapping of the neutral gas ring in the Galactic center - Evidence for dust destruction

The distribution of Si II emission in the Galactic center has been measured and found to extend beyond 4 pc from the center. The observed forbidden Si II 34.8 micron line, which is thermally excited by H I and H2 collisions, originates from the photodissociation region formed in the neutral gas ring surrounding the ionized core. Two peaks in the Si II emission are found, one lying 20 arcsec northeast of Sgr A-asterisk along the Galactic plane and the other located about 80 arcsec north of Sgr A-asterisk. The latter peak is located beyond the northern arm seen in the ionized gas. The ratio of Si II to dust mass density varies in the ring, indicating changes in the gas-to-dust ratio. The mass density of Si II and dust are anticorrelated, indicating that Si II tracks the destruction of dust.

Herter, T.↗
NASA NTRS1989

Ultra-sensitive inertial sensors via neutral-atom interferometry

Upon looking at the various colossal interferometers, etc., discussed at this conference to test gravitational theory, one cannot avoid feeling that easier approaches exist. The use of low velocity, neutral atom matter waves in place of electromagnetic waves in sensitive inertial interferometer configurations is proposed. For applications, spacecraft experiments to sense a drag-free condition, to measure the Lense-Thirring precession, to measure the gravitomagnetic effect and/or the earth's geopotential (depending on altitude), and to detect long period gravitational waves are considered. Also, a terrestrial precision test of the equivalence principle on spin polarized atoms, capable of detecting effects of the 5th force is considered. While the ideas described herein are preliminary, the orders of magnitude are sufficiently tantalizing to warrant further study. Although existing proposed designs may be adequate for some of these experiments, the use of matter-wave interferometry offers reduced complexity and cost, and an absence of cryogenics.

Clauser, John F.↗
NASA NTRS1989

Remote sensing of the ring current using energetic neutral atoms

Energetic neutral atom images of the storm-time ring current obtained from the ISEE-1 spacecraft provide information for a 'zero-order' global model of the energetic ion distribution. With the assumption of isotropic pressure and magnetostatic, nonconvective pressure balance, the global system of electrical currents driven by the ion pressure can be calculated using Euler potentials for the divergenceless current density. Radial pressure gradients drive azimuthal currents, and azimuthal pressure gradients drive radial currents. The radial currents cause current lines in the inner magnetosphere to close in the ionosphere, forming a partial ring current. The intensities and locations of these field-aligned currents driven into and out of the ionosphere resemble those of the observed Region 2 current system, but not all observed properties of the Region 2 system are reproduced by the zero-order model.

Roelof, Edmond C.↗
NASA NTRS1990

Northern dwarf and low surface brightness galaxies. I - The Arecibo neutral hydrogen survey

Neutral hydrogen observations of a large sample of dwarf and other low surface brightness galaxies are presented. Nearly all galaxies classified in the Uppsala General Catalogue as dwarf, irregular, Sd-m, or later and in the declination range of the Arecibo telescope have now been observed; here observations for 762 galaxies are reported. About 40 percent of these galaxies have no previously published detections. In total, counting previous detections, over 90 percent of these late-type systems are detected at Arecibo. The galaxies are examined for potential confusion with nearby galaxies, and substantially better SNR are derived for many previously detected galaxies.

Schneider, Stephen E.↗
NASA NTRS1990

Electron collection enhancement arising from neutral gas jets on a charged vehicle in the ionosphere

Observations of current collection enhancements due to cold nitrogen gas control jet emissions from a highly charged, isolated rocket payload in the ionosphere have been made during the cooperative high altitude rocket gun experiment (CHARGE) 2 using an electrically tethered mother/daughter payload system. The current collection enhancement was observed on a platform (daughter payload) located 100 to 400 m away from the main payload firing an energetic electron beam (mother payload). These results are interpreted in terms of an electrical discharge forming in close proximity to the daughter vehicle during the short periods of gas emission. The results indicate that it is possible to enhance the electron current collection capability of positively charged vehicles by means of deliberate neutral gas releases into an otherwise undisturbed space plasma. The results are also compared with recent laboratory observations of hollow cathode plasma contactors operating in the 'ignited' mode.

Gilchrist, Brian E.↗
NASA NTRS1989

Neutral buoyancy methodology for studying satellite servicing EVA crewmember interfaces

Current economic constraints indicate the need for incorporating the satellite servicing philosophy of commonality within the design of spacecraft subsytems. This philosophy is essential for conserving resources including hardware/software development and implementation costs, on-orbit and ground-based manpower, crew training/testing time, and documentation. In addition, spacecraft subsystem commonality may be coupled with standardization of operation procedures, and test and verification techniques for spacecraft design. Several spacecraft have adopted this practice, including Hubble Space Telescope, Space Station Freedom, and the Explorer Platform. As these and other programs continue and if effective crew interfaces and procedures are clearly and consistently defined, crew retraining for similar spacecraft subsystems will lessen, and procurement efforts will diminish. A relatively high fidelity zero-gravity simulation using water immersion is available to establish crew interfaces economically. The flexibility and utility of this space simulation medium for planning and assisting on-orbit operations was exemplified by astronaut evaluations of potential EVA electrical connectors. The testing was conducted at a NASA underwater neutral buoyancy training facility.

Barnby, Mary E.↗
NASA NTRS1990

Wind velocity measurements in the neutral boundary layer above hilly prairie

The Flint Hills region in eastern Kansas is characterized by a strongly dissected rolling to hilly terrain with an average about 25 m of relief between steep ridges and valleys, and with ridges typically separated by distances of the order of 600 m. Intensive radiosonde observations during summer and fall of 1987 allowed the determination of some aspects of the wind regime in the region. For an assumed ground-surface reference of 330 m above sea level (asl), analysis of neutral profiles yielded a value z(0) of about 1.05 m, approximately. Good agreement was obtained between the values of friction velocity derived from wind profiles and values determined independently from the corresponding humidity profiles.

Sugita, Michiaki↗
NASA NTRS1990

IMP-8 observations of traveling compression regions - New evidence for near-earth plasmoids and neutral lines

An examination of IMP-8 tail lobe magnetic field measurements has been conducted to determine whether the traveling compression region (TCR) phenomena detected by ISEE-3 in the distant geotail, and believed to be caused by tailward moving plasmoids, are present closer to the earth. The study produced 16 examples of TCRs at distances of X = -31 to -37 R(E). For two events considered in detail, TCRs were observed in close association with substorm growth phase signatures in the lobes. The lengths of these TCRs are estimated to be 8-12 R(E). The conclusion is that the IMP-8 TCR observations provide new evidence that small plasmoids and, hence, multiple reconnection neutral lines can sometimes exist earthward of X = -35 R(E).

Slavin, J. A.↗
NASA NTRS1990

Plasma sources for spacecraft neutralization

The principles of the operation of plasma sources for the neutralization of the surface of a spacecraft traveling in the presence of hot plasma are discussed with special attention given to the hollow-cathode-based plasma contactors. Techiques are developed that allow the calculation of the potentials and particle densities in the near environment of a hollow cathode plasma contactor in both the test tank and the LEO environment. The techniques and codes were validated by comparison of calculated and measured results.

Davis, V. A.↗