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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 379 records · Page 21

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NASA NTRS1978

Planet formation - Mechanism of early growth

Experiments in vacuum (approx. 0.5 to 1 mbar) and in air quantify mechanics of collisions, rebound, and fragmentation at low velocities (1-50 m/sec), under the conditions usually postulated for the preplanetary environment in the primitive solar nebula. Such collisions have been little studied experimentally. Contrary to widespread assumptions, accretionary growth of the largest meteoroid- and asteroid-sized bodies in a given swarm results spontaneously from the simple mechanics of these collisions, without other ad hoc sticking mechanisms. The smaller bodies in the swarm are less likely to grow. Granular surfaces form, either by gravitational collapse of dust swarms or by rapid formation of regolith surfaces on solid planetesimals; these surfaces strongly promote further growth by retarding rebound. Growth of large bodies increases modal collision velocities, causing fragmentation of smaller bodies and eventual production of interstellar dust as a by-product of planetesimal interactions.

Hartmann, W. K.↗

NASA NTRS1978

Measurement of dielectronic recombination rates for the iron ions Fe IX-XI

Iron is injected into a well-diagnosed theta-pinch plasma. The intensities of lines from various ionization stages are measured as functions of time and interpreted by means of a time-dependent corona ionization-recombination model. Effective coefficients for dielectronic recombination at electron densities of approximately 3 by 10 to the 16th power per cu cm are equal to or smaller than presently accepted theoretical values for low-density plasmas. Rate coefficients for ionization tend to be smaller than theoretical values.

Brooks, R. L.↗

NASA NTRS1978

Soft X-ray structure of the Perseus cluster of galaxies

A 0.5-1.5-keV X-ray image of the Perseus cluster of galaxies was obtained with a focusing telescope system aboard a sounding rocket. The source consists of a region of diffuse emission plus a superposed central source in the vicinity of NGC 1275 smaller than 4 arcmin in diameter that accounts for one-quarter of the total intensity within a radius of 25 arcmin. The results for the diffuse source are consistent with the isothermal-hydrostatic picture in which the hot gas has a core radius of 17 arcmin and is approximately symmetric about NGC 1275. Several isothermal-hydrostatic models are considered which relate the size and temperature of the diffuse X-ray source with the core radius of the galaxies and their velocity dispersion. Fixing the velocity dispersion at values measured by Chincarini and Rood (1971) requires the core radius of the galaxies to be 28 + or - 9 arcmin, which is larger than present measurements. Conversely, fixing the core radius of the galaxies at 8 arcmin requires a smaller velocity dispersion or a condition in which the velocity distribution is anisotropic. Upper limits on the intrinsic X-ray absorption of the central source place the bulk of its X-ray emission beyond the nuclear region of NGC 1275.

Gorenstein, P.↗

NASA NTRS1978

Satellites: A systems comparison

The advantages of using geostationary platforms as a means of accommodating future missions and payloads in lieu of individual, smaller satellites are reviewed. The cost effectiveness of large capacity communications platforms with separate smaller satellites on a systems basis considering total costs to the end user is assessed. For two specific systems: a system to provide communications for U.S. domestic applications and a system to serve the Atlantic INTELSAT requirements. These simple platform applications were selected because they minimize associated institutional problems. Although they do not exploit the full advantages that can ultimately be obtained from large platforms with multidiscipline missions, to the extent that these simple platforms demonstrate cost benefits, such benefits can be further enhanced by the addition of other payloads to the platforms.

Source record↗

NASA NTRS1979

Operator performance and localized muscle fatigue in a simulated space vehicle control task

Fourier transforms in a special purpose computer were utilized to obtain power spectral density functions from electromyograms of the biceps brachii, triceps brachii, brachioradialis, flexor carpi ulnaris, brachialis, and pronator teres in eight subjects performing isometric tracking tasks in two directions utilizing a prototype spacecraft rotational hand controller. Analysis of these spectra in general purpose computers aided in defining muscles involved in performing the task, and yielded a derived measure potentially useful in predicting task termination. The triceps was the only muscle to show significant differences in all possible tests for simple effects in both tasks and, overall, was the most consistently involved of the six muscles. The total power monitored for triceps, biceps, and brachialis dropped to minimal levels across all subjects earlier than for other muscles. However, smaller variances existed for the biceps, brachioradialis, brachialis, and flexor carpi ulnaris muscles and could provide longer predictive times due to smaller standard deviations for a greater population range.

Lewis, J. L., Jr.↗

NASA NTRS1978

Spin-related magnetism of interstellar grains

The magnetic dipole moments and internal magnetic fields due to the spin of electrically charged elongated nonmagnetic interstellar grains in kinetic equilibrium with their surroundings are computed for the grain-size range from 0.01 to 1.0 micron. It is shown that the induced magnetic moments and internal magnetic fields of charged spinning nonmagnetic grains of arbitrary composition and prolate spheroidal shape can be appreciable, possibly even exceeding 0.01 emu/cu cm for 0.01-micron grains. The results indicate that virtually all grains smaller than 0.1 micron in mean diameter, and all elongated grains smaller than about 1 micron in length, are immersed in local magnetic fields due to spin that are much larger than the ambient galactic field. Some implications of this effect are discussed in relation to the polarization of starlight by aligned dust grains and the primordial remanent magnetization found in primitive carbonaceous chondrites.

Srnka, L. J.↗

NASA NTRS1978

Morphology and elemental composition analysis by size of rocket particulate effluent

Particulate samples collected on six stages of a quartz crystal microbalance cascade impactor mounted in an aircraft traversing the plume of a large solid-fueled rocket are analyzed, postflight, by scanning electron microscopy (SEM) and energy dispersed X-ray (EDXRA). The results indicate the morphology and elemental composition of the particles fall into several distinct groups. Those larger than about 0.5 micron in diameter and nearly spherical in shape contain, among elements with atomic numbers of 11 and higher, only aluminum, suggesting they are aluminum oxide formed in the solid rocket fuel combustion. Still larger but less symmetrical particles contain only sodium and chlorine. Particles much smaller than 0.5 micron seem to end up as agglomerates after impaction (or during the impaction process), and show a complex elemental make-up of Na, Al, S, Cl, K, Ca, Fe and Zn. The unagglomerated single particles smaller than 0.2 micron, on the other hand, show no evidence of elements above atomic number 11 at all, suggesting they may be carbon or hydrocarbon particles.

Chuan, R. L.↗

NASA NTRS1979

Refinement of the aeronomically determined rate coefficient for the reaction of N2/+/ with O

An earlier aeronomic determination of the rate coefficient for the reaction N2(+) + O yields NO(+) + N using Atmosphere Explorer data indicated a small increase in the rate coefficient with ion temperature, contrary to laboratory observations. This was incorrectly attributed to neglect of an increase in the N2(+) recombination rate with vibrational excitation. Recent aeronomical results have shown that the rate coefficient for charge exchange of O(+)(2D) with N2 is about an order of magnitude smaller at thermal temperatures than at energies greater than 0.5 eV (i.e., energies at which laboratory measurements have been made). It is shown that the use of the smaller charge exchange rate coefficient coupled with recent results on N2 quenching of O(+)(2D) yields a temperature dependence in excellent agreement with the laboratory results for the rate coefficient.

Torr, D. G.↗

NASA NTRS1981

Spraying suspensions uniformly

With head on each of its ends, bolt can be disengaged from its blind side. Bolt has conventional hexagonal head on one end and smaller hexagonal head on its threaded end. Since reduced head is smaller than bolt diameter, it does not interfere with insertion of bolt shank in bolthole. However, it can be turned by wrench to release bolt from its blind (threaded) end. Bolt should be tethered on its large-head end so that it does not drop away from assembly.

Prasthofer, W. P.↗

NASA NTRS1980

Simulation study of a geometric shape factor technique for estimating earth-emitted radiant flux densities from wide-field-of-view radiation measurements

Geometric shape factors were computed and applied to satellite simulated irradiance measurements to estimate Earth emitted flux densities for global and zonal scales and for areas smaller than the detector field of view (FOV). Wide field of view flat plate detectors were emphasized, but spherical detectors were also studied. The radiation field was modeled after data from the Nimbus 2 and 3 satellites. At a satellite altitude of 600 km, zonal estimates were in error 1.0 to 1.2 percent and global estimates were in error less than 0.2 percent. Estimates with unrestricted field of view (UFOV) detectors were about the same for Lambertian and limb darkening radiation models. The opposite was found for restricted field of view detectors. The UFOV detectors are found to be poor estimators of flux density from the total FOV and are shown to be much better as estimators of flux density from a circle centered at the FOV with an area significantly smaller than that for the total FOV.

Weaver, W. L.↗

NASA NTRS1980

Recent theoretical work on Cepheids and other types of variables

Some important problems in the theory of Cepheids and of other types of variables are pointed out. Three of these are: (1) large-amplitude mode behavior; (2) convection; and (3) Cepheid masses, which must essentially always be inferred indirectly. Of the several types of indirect mass which can be defined, the inferred masses of the 'beat (or double-mode) Cepheids,' seem to be smaller than one expects for this period range by factors of 2-3. For the nonbeat Cepheids, the indirect masses also appear to be low as compared with conventional stellar evolution theory, but by a smaller amount, say some 20-40 percent. Some conceivable ways of explaining these mass discrepancies are discussed. The question of whether the apparently predominantly radial pulsations of the beat Cepheids could be contaminated with a small admixture of nonradial pulsations, so that the use of purely radial pulsation theory may not be applicable to the beat Cepheids is addressed. Some other conjectures which may bear on ordinary or beat Cepheids are offered.

Cox, J. P.↗

NASA NTRS1979

Scaling characteristics of MPD propulsion

Experiments in which a high-power, quasi-steady MPD thruster is scaled down by a factor of two indicate that the key features of MPD thruster operation are replicated in the smaller version. Voltage-current data over a 24:1 mass flow range show that the ablation onset parameter is constant for each thruster, although the constant is not the same. Time-integrated photographs of the discharge radiance reveal strikingly similar features at scaled values of current and mass flow. The measured terminal properties of the half-scale thruster are similar to the full-scale thruster, but the regime of operation is smaller and generally less efficient, except within a restricted range of arc current and mass flow.

Mead, F. B., Jr.↗

NASA NTRS1980

Collapsing cloud models for Bok globules

The dynamic collapse of rotating gas clouds is calculated for a wide range of initial conditions. Properties of cloud models are compared with observed radio and optical properties of Bok globules, to test the hypothesis that globules undergo collapse and to determine parameters which are not easily observed. Five of the six globules studied are consistent with collapse models. It is inferred that these objects have masses of about 100 solar masses and ages smaller than their free-fall times. Inferred initial densities are much larger than minimum densities for gravitational collapse, suggesting that collapse is initiated by strong external compression or that globules are fragments of larger condensed clouds. Values inferred for the (C-13)O/H2 ratio are smaller than previous estimates and depend strongly on cloud density.

Villere, K. R.↗

NASA NTRS1980

Seasonal variations in high-latitude ozone and metastable molecular oxygen emissions - A theoretical interpretation

Comparison of photochemical calculations of atmospheric ozone between 40 and 55 km with measurements from a satellite-borne remote sensor shows agreement in the high-latitude summer hemisphere. However, in the sunlit high-latitude winter, the available data imply either a smaller water vapor mixing ratio than generally accepted or a temperature 15 - 20 K colder than contained in published model atmospheres. As with the ozone data the infrared emission in winter implies an odd oxygen loss rate smaller than predicted on the basis of standard water vapor and temperature models. The magnitude of the 1.27 micron signals and their consistency with upper stratospheric ozone data cast doubt on the large mesospheric ozone abundances deduced in independent experiments.

Frederick, J. E.↗

NASA NTRS1980

Zero-length, slotted-lip inlet for subsonic military aircraft

Zero-length, slotted-lip inlet performance and associated fan blade stresses were determined during model tests using a 20-inch diameter fan simulator in the NASA-LeRC 9- by 15-foot low-speed wind tunnel. The model configuration variables consisted of inlet contraction ratio, slot width, circumferential extent of slot fillers, and length of a constant area section between the inlet throat and fan face. Inlet configurations having contraction ratios of 1.2 and 1.3 satisfied all critical low-speed inlet operating requirements for a fixed horizontal nacelle and tilt-nacelle-type subsonic V/STOL aircraft, respectively. Relative to a conventional axisymmetric tilt-nacelle inlet, the zero-length, slotted-lip inlet has a 27-percent smaller inlet lip contraction ratio, an 83-percent shorter total length, and a 5-percent smaller maximum cowl diameter.

Glasgow, E. R.↗

NASA NTRS1980

Vertical and off-diagonal eddy diffusivities in the Northern Hemispheric stratosphere and lower mesosphere

Meteorological rocket soundings, launched between 1968-74 at six locations representative of low, middle and high latitudes in the Northern Hemisphere, are employed to determine the vertical, meridional, and off-diagonal components of the eddy diffusivity in the Northern Hemispheric stratosphere and lower mesosphere. It is shown that the distribution of the vertical and meridional components of the eddy diffusivity are similar in the Northern Hemisphere, although the magnitude of the former is ten million times smaller than that of the latter; the magnitude of the off-diagonal eddy diffusivity is about one thousand times smaller than that of the meridional eddy diffusivity. In the troposphere, a maximum eddy diffusivity occurs in the mid-latitude at about 7 km above the mean sea level for both the summer and winter seasons.

Kao, S. K.↗

NASA NTRS1981

Solar power satellite system sizing tradeoffs

Technical and economic tradeoffs of smaller solar power satellite systems configured with larger antennas, reduced output power, and smaller rectennas, are considered. The differential costs in electricity for seven antenna/rectenna configurations operating at 2.45 GHz and five satellite systems operating at 5.8 GHz are calculated. Two 2.45 GHz configurations dependent upon the ionospheric power density limit are chosen as examples. If the ionospheric limit could be increased to 54 mW sq/cm from the present 23 mW sq/cm level, a 1.53 km antenna satellite operating at 2.45 GHz would provide 5.05 GW of output power from a 6.8 km diameter rectenna. This system gives a 54 percent reduction in rectenna area relative to the reference solar power satellite system at a modest 17 percent increase in electricity costs. At 5.8 GHz, an 0.75 km antenna providing 2.72 GW of power from a 5.8 km diameter rectenna is selected for analysis. This configuration would have a 67 percent reduction in rectenna area at a 36 percent increase in electricity costs. Ionospheric, atmospheric, and thermal limitations are discussed. Antenna patterns for three configurations to show the relative main beam and sidelobe characteristics are included.

Arndt, G. D.↗

NASA NTRS1980

Preliminary results of polarimetry and photometry of Titan at large phase angles from Pioneer 11

The imaging photopolarimeter (IPP) aboard the Pioneer 11 spacecraft measured the linear polarization of the integrated disk of Titan in red and blue light at a variety of phase angles from 15 to 97 deg. The large polarization (54%) measured in blue light at 90 deg phase constrains the size of the aerosols near the top of Titan's atmosphere to have radii smaller than about 0.09 microns if they have a refractive index of 2.0. The polarization at 90 deg phase in red light is smaller (41%) and implies that the optical thickness of the layer of small aerosols is about 0.6 above an effectively depolarizing surface. The shape of the polarization versus phase curve in blue light suggests increasing particle size with increasing depth into the atmosphere. The limb darkening of Titan was measured at 28 deg phase by using the imaging mode of the IPP. The limb darkening observed in both colors is reasonably consistent with that given by the scattering models derived from the polarization observations.

Tomasko, M. G.↗