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NASA NTRS1985

CCD observations of comet Tuttle 1980 XIII - The H2O(+) ionosphere

A CCD spectrum of comet Tuttle 1980h has been analyzed with emphasis on the emission of H2O(+) ions. The fine angular resolution (1.5 arcsec) and the capability of absolute brightness calibration of the CCD instrument made it possible to determine the spatial concentration of the H2O(+) ions of this faint comet and the total number of these ions confined within a spherical region. Solar photoionization of the H2O atmosphere can account for the production of the H2O(+) ions observed in the confined region. The dimension of the H2O(+) ionosphere at the time of observation was found to be comparatively small, implying the possible existence of an ionopause sharply delineating the extension of the cometary ionosphere.

Ip, W.-H.↗

NASA NTRS1985

Thrust changes induced by ground and ceiling planes on a rotor in hover

The thrust produced by a helicopter motor in hover has been studied by measuring the thrust on a model rotor 0.234 meters in diameter operating between ground and ceiling planes. The distance between the two planes and the rotor disk was in the range 0.08-6.0 rotor diameters. It was found that the confining surfaces changed the rotor thrust almost linearly with the logarithm of the distance from the confining surface. When both planes were near the rotor the variation was no longer linear. The measured thrust of the rotor was compared to predictions based on the theoretical calculations of Rossow (1985), and the results are given in a table.

Rossow, V. J.↗

NASA NTRS1985

Evidence for collisionless conduction fronts in impulsive solar flares

The present paper is concerned with an analysis of new observations of impulsive hard X-ray and microwave bursts. The results are compared with predictions of a thermal flare model. A description is presented of the thermal model with conduction-front confinement, taking into account the development and previous applications of the model, the high-energy limit of confinement and its implications for microwave emission, the formation of a test based on the revised predictions of the model, and derived parameters. The observations and the test of the model are discussed, giving attention to instrumentation, event selection, selection of a homogeneous sample of impulsive rises,. observed and derived parameters for each rise, a correlation analysis of observed and predicted rise times, uncertainties in the measurements, consistency checks, and a comparison with results of Crannell et al. (1978).

Batchelor, D. A.↗

NASA NTRS1985

Dilution jet mixing program, phase 3

The main objectives for the NASA Jet Mixing Phase 3 program were: extension of the data base on the mixing of single sided rows of jets in a confined cross flow to discrete slots, including streamlined, bluff, and angled injections; quantification of the effects of geometrical and flow parameters on penetration and mixing of multiple rows of jets into a confined flow; investigation of in-line, staggered, and dissimilar hole configurations; and development of empirical correlations for predicting temperature distributions for discrete slots and multiple rows of dilution holes.

Srinivasan, R.↗

NASA NTRS1986

Crystal growth of device quality GaAs in space

It was established that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail. It was further established that in compound semiconductors with a volatile constituent, control of stoichiometry is far more critical than any other crystal growth parameter. It was also shown that, due to suppression of nonstoichiometric fluctuations, the advantages of space for growth of semiconductor compounds extend far beyond those observed in elemental semiconductors. A novel configuration was discovered for partial confinement of GaAs melt in space which overcomes the two major problems associated with growth of semiconductors in total confinement. They are volume expansion during solidification and control of pressure of the volatile constituent. These problems are discussed in detail.

Gatos, H. C.↗

NASA NTRS1985

Implications of privacy needs and interpersonal distancing mechanisms for space station design

Privacy needs, or the need of people to regulate their degree of contact with one another, and interpersonal distancing mechanisms, which serve to satisfy these needs, are common in all cultures. Isolation, confinement, and other conditions accociated with space flight may at once accentuate privacy needs and limit the availability of certain common interpersonal contact. Loneliness occurs when people have less contact with one another than they desire. Crowding occurs when people have more contact with one another than they desire. Crowding, which is considered the greater threat to members of isolated and confined groups, can contribute to stress, a low quality of life, and poor performance. Drawing on the general literature on privacy, personal space, and interpersonal distancing, and on specialized literature on life aboard spacecraft and in spacecraft-analogous environments, a quantitative model for understanding privacy, interpersonal distancing, loneliness, and crowding was developed and the practical implications of this model for space station design were traced.

Harrison, A. A.↗

NASA NTRS1986

Interface stability in a slowly rotating low-gravity tank Theory

The equilibrium configuration of a bubble in a rotating liquid confined by flat axial boundaries (baffles) is found. The maximum baffle spacing assuring bubble confinement is bounded from above by the natural length of a bubble in an infinite medium under the same conditions. Effects of nonzero contact angle are minimal. The problem of dynamic stability is posed. It can be solved in the limit of rapid rotation, for which the bubble is a long cylinder. Instability is to axisymmetric perturbations; nonaxisymmetric perturbations are stable. The stability criterion agrees with earlier results.

Gans, R. F.↗

NASA NTRS1986

Thermal equilibrium of a cryogenic magnetized pure electron plasma

The thermal equilibrium correlation properties of a magnetically confined pure electron plasma (McPEP) are related to those of a one-component plasma (OCP). The N-particle spatial distribution rho sub s and the Helmholtz free energy F are evaluated for the McPEP to O(lambda sub d-squared/a-squared), where lambda sub d is the thermal de Broglie wavelength and is an interparticle spacing. The electron gyromotion is allowed to be fully quantized while the guiding center motion is quasi-classical. The distribution rho sub s is shown to be identical to that of a classical OCP with a slightly modified potential. To O(lambda sub d-squared/a-squared) this modification does not affect that part of F that is caused by correlations, as long as certain requirements concerning the size of the plasma are met. This theory is motivated by a current series of experiments that involve the cooling of a magnetically confined pure electron plasma to the cryogenic temperature range.

Dubin, D. H. E.↗

NASA NTRS1986

Impact ionization across the conduction-band-edge discontinuity of quantum-well heterostructures

Impact ionization across the band-edge discontinuity of quantum-well heterostructures is studied theoretically. A heterolayer structure of alternating Al(x)Ga(1-x)As and GaAs layers is considered where the GaAs layers are heavily doped with donors. Thus a large number of electrons is confined to the quantum-well region. Incident electrons are heated up by applied electric fields and collide with the electrons confined in the well regions. Both the ionization rate as a function of the incident energy, and average ionization rates are computed. Device applications of such multiple quantum-well structures and the possibility of a complete analog to the conventional photomultiplier are discussed.

Chuang, S. L.↗

NASA NTRS1986

Concentration distributions in a model combustor

A hot-wire concentration probe with a spatial resolution of 0.13 mm is used to measure concentration in a model cylindrical combustor. The flow inside the combustor is simulated by injecting a helium jet into a cylindrical confinement with or without swirling air flow present. Mean concentrations are essentially zero outside of the jet region, indicating complete confinement of the scalar field by the swirling flow. Consequently, concentration fluctuations are found to be relatively weak compared to velocity fluctuations, and are maximum off-axis at a point which corresponds to the interface between helium and air flows. However, in the absence of a swirling air flow, the helium diffuses quickly to fill the combustor. The resulting helium concentrations are constant and do not resemble the jet-like behavior of the velocity field.

Ahmed, S. A.↗

NASA NTRS1986

Antimatter propulsion, status and prospects

The use of advanced propulsion techniques must be considered if the currently envisioned launch date of the manned Mars mission were delayed until 2020 or later. Within the next thirty years, technological advances may allow such methods as beaming power to the ship, inertial-confinement fusion, or mass-conversion of antiprotons to become feasible. A propulsion system with an ISP of around 5000 s would allow the currently envisioned mission module to fly to Mars in 3 months and would require about one million pounds to be assembled in Earth orbit. Of the possible methods to achieve this, the antiproton mass-conversion reaction offers the highest potential, the greatest problems, and the most fascination. Increasing the production rates of antiprotons is a high priority task at facilities around the world. The application of antiprotons to propulsion requires the coupling of the energy released in the mass-conversion reaction to thrust-producing mechanisms. Recent proposals entail using the antiprotons to produce inertial confinement fusion or to produce negative muons which can catalyze fusion. By increasing the energy released per antiproton, the effective cost, (dollars/joule) can be reduced. These proposals and other areas of research can be investigated now. These short term results will be important in assessing the long range feasibility of an antiproton powered engine.

Howe, Steven D.↗

NASA NTRS1986

Physics through the 1990s: Plasmas and fluids

The volume contains recommendations for programs in, and government support of, plasma and fluid physics. Four broad areas are covered: the physics of fluids, general plasma physics, fusion, and space and astrophysical plasmas. In the first section, the accomplishments of fluid physics and a detailed review of its sub-fields, such as combustion, non-Newtonian fluids, turbulence, aerodynamics, and geophysical fluid dynamics, are described. The general plasma physics section deals with the wide scope of the theoretical concepts involved in plasma research, and with the machines; intense beam systems, collective and laser-driven accelerators, and the associated diagnostics. The section on the fusion plasma research program examines confinement and heating systems, such as Tokamaks, magnetic mirrors, and inertial-confinement systems, and several others. Finally, theory and experiment in space and astrophysical plasma research is detailed, ranging from the laboratory to the solar system and beyond. A glossary is included.

Source record↗

NASA NTRS1986

A preliminary theory of the origin of the 40-50 day oscillation

A theory of the 40 to 50 day oscillation in the tropical atmosphere which encompasses predominantly eastward propagation along the equator, spatial scales of wavenumber 1 and 2, slow time scales (20 to 70 days), and strong amplitude modulation in associated large-scale convective activity as a function of geographical location, i.e., pronounced convection is confined to the Indian Ocean and western Pacific, is presented. An initial disturbance generated near the equator disperses away from the source region, eastward by Kelvin waves and westward by Rossby waves. When the eastward disturbance passes over warm water it is expected to amplify by CISK due to enhanced supply of moisture from the ocean surface. Over cold water, its amplitude is expected to reduce due to decreased moisture supply. The climatological sea surface temperature contrast between the Indian Ocean/western Pacific and the eastern Pacific sets the spatial scale of the wave and its modulation to low wavenumbers and confines pronounced convection to the warm sector. If the eastward propagating wave can maintain itself over dissipation one circuit around the globe, it has a good chance to continue the process indefinitely, provided it is rejunvenated over the warm water with enough energy to go around for the next cycle.

Lau, K. M.↗

NASA NTRS1987

X-rays from the radio halo of M87

The Einstein Observatory and the VLA were used to scan the radio halo of the galaxy M87 to detect the presence, if any, of inverse Compton X-ray (ICX) emissions. The scans revealed a coincidence of an asymmetrical X-ray structure with a luminosity near 4 x 10 to the 41st ergs/sec and dominant symmetrical emission from the hot interstellar gas. The emission can be attributed to ICX if the magnetic field of the proposed halo varies between 3-8 times below equipartition levels of 2-5 micro-gauss, which would imply that the confinement is produced by an outside medium. The necessary characteristics of the confining mechanism are discussed.

Feigelson, E. D.↗

NASA NTRS1985

Dilution jet mixing program, phase 3

The objectives of the program were: (1) to extend the data base on mixing of a single-sided row of jets with a confined crossflow, (2) to collect a data base on mixing of multiple rows of jets with confined crossflow, (3) to develop empirical jet mixing correlations, and (4) to perform limited three-dimensional calculations for some of these test configurations. The tests were performed with uniform mainstream conditions for several orifice plate configurations. Schematics of the test section and the orifice configurations are given. Temperature and pressure measurements were made in the test section at 4 axial and 11 transverse stations, using a 60-element rake probe. The measured temperature distributions for these tests are reported.

Srinivasan, R.↗

NASA NTRS1988

Crew productivity issues in long-duration space flight

Considerable evidence suggests the importance of teamwork, coordination, and conflict resolution to the performance and survival of isolated, confined groups in high-technology environments. With the advent of long-duration space flight, group-related issues of crew functioning will take on added significance. This paper discusses the influence of crew roles, status, leadership, and norms on the performance of small, confined groups, and offers guidelines and suggestions regarding organizational design, crew selection, training, and team building for crew productivity and social well-being in long-duration spaceflight.

Nicholas, John M.↗

NASA NTRS1988

Cosmic-ray lifetime in the Galaxy - Experimental results and models

The separation of the cosmic-ray Be isotopes achieved by two satellite experiments is discussed. From the measured isotopic ratio between the radioactive Be-10 (half-life = 1,500,000 years) and the stable Be-9, it is deduced that the cosmic rays propagate through matter with an average density of 0.24 = or - 0.07 atoms/ cu cm. The implications of this result for the cosmic-ray age is reviewed in the context of two models of confinement and propagation: the homogeneous model, normally identified with confinement ot the galactic gaseous disk, and a diffusion model in which the cosmic rays extend into a galactic halo. A newly deduced cosmic-ray pathlength distribution, a self-consistent model of solar modulation, and a set of fragmentation cross sections are calculated. It is concluded that in a homogeneous model, the cosmic-ray age is 15 (+7, -4) million years, about a factor longer than early estimates based on the abundances of the light nuclei Li, Be, and B and a nominal interstellar density of 1 atom/ cu cm.

Simpson, J. A.↗

NASA NTRS1989

New ion trap for atomic frequency standard applications

A novel linear ion trap that permits storage of a large number of ions with reduced susceptibility to the second-order Doppler effect caused by the radio frequency (RF) confining fields has been designed and built. This new trap should store about 20 times the number of ions a conventional RF trap stores with no corresponding increase in second-order Doppler shift from the confining field. In addition, the sensitivity of this shift to trapping parameters, i.e., RF voltage, RF frequency, and trap size, is greatly reduced.

Prestage, J. D.↗