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At least 559 records · Page 31

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NASA NTRS1973

Description of the docking module ECS for the Apollo-Soyuz Test Project.

The role of the Docking Module ECS (Environmental Control System) to be used on the Apollo-Soyuz Test mission is to provide a means for crewmen to transfer safely between the Apollo and Soyuz vehicles in a shirtsleeve environment. This paper describes the Docking Module ECS and includes the philosophy and rationale used in evaluating and selecting the capabilities that are required to satisfy the Docking Module's airlock function: (1) adjusting the pressure and composition of the atmosphere to effect crew transfer and (2) providing a shirtsleeve environment during transfer operations. An analytical evaluation is given of the environmental parameters (including CO2 level, humidity, and temperature) during a normal transfer timeline.

Guy, W. W.↗

NASA NTRS1973

Preliminary results from the noctilucent sampling from Kiruna in 1970.

On Aug. 8, 1970 at 0148 and 0354 local time, two Pandora sounding rocket payloads were launched from the ESRO range in Kiruna, Sweden, during a noctilucent cloud display. Large numbers of particles were collected, many of which appear to be micrometeorites coated with a low density material. Typical electron micrographs are shown, and numerical densities as a function of altitude are given. Particle composition information has been obtained by use of dispersive X-ray analysis equipment attached to our Philips EM 300 electron microscope.

Hallgren, D. S.↗

NASA NTRS1974

Solar cosmic ray composition above 10 MeV/nucleon and its energy dependence in the 4 August 1972 event

Observations of the proton, helium (C,N,O) and Fe-group nuclei fluxes made during the large 4 August 1972 solar particle event are presented. The results show a small, but significant variation of the composition of multicharged nuclei as a function of energy in the energy region above 10 MeV/nucleon. In particular, the He/(C,N,O) abundance ratio varies by a factor approximately 2 between 10 and 50 MeV/nucleon, and the Fe-group/(C,N,O) ratio suggests a similar variation. Abundance ratios from the 4 August 1972 event are compared as a function of energy with ratios measured in other solar events. At energies approximately greater than 50 MeV/nucleon, the He/(C,N,O) abundance ratio for August 1972 is consistent with all earlier measurements made above that energy.

Bertsch, D. L.↗

NASA NTRS1974

Propagation of cosmic rays in the galaxy

The characteristics of a model for analyzing the propagation of cosmic rays are discussed. The requirements for analyzing the relevant observational data on cosmic rays are defines as: (1) the chemical and isotopic composition of cosmic rays as a function of energy, (2) the flux and energy spectrum of the individual nucleonic components, (3) the flux and energy spectrum of the electronic component, (4) the cosmic ray prehistory, and (5) the degree of isotropy in their arrival directions as a function of energy. It is stated that the model which has been able to bring to pass the greatest measure of success is the galactic confinement model.

Daniel, R. R.↗

NASA NTRS1976

Water vapor diffusion membranes, 2

Transport mechanisms were investigated for the three different types of water vapor diffusion membranes. Membranes representing porous wetting and porous nonwetting structures as well as dense diffusive membrane structures were investigated for water permeation rate as a function of: (1) temperature, (2) solids composition in solution, and (3) such hydrodynamic parameters as sweep gas flow rate, solution flow rate and cell geometry. These properties were measured using nitrogen sweep gas to collect the effluent. In addition, the chemical stability to chromic acid-stabilized urine was measured for several of each type of membrane. A technology based on the mechanism of vapor transport was developed, whereby the vapor diffusion rates and relative susceptibility of membranes to fouling and failure could be projected for long-term vapor recovery trials using natural chromic acid-stabilized urine.

Holland, F. F.↗

NASA NTRS1976

Flame stability in combusting turbulent jets

The paper develops a model for the stability of turbulent methane/air flames on the assumption that reaction kinetics is much more important than the fluid dynamics near blowout. Flame stability is predicted as a function of ambient atmospheric temperature and composition, initial preheat temperature, and the percentage of external product gas recirculation. A one-step reaction and a well-stirred reactor are used to equate the rate at which the mass is supplied to the flame to the rate at which the mass chemically reacts in the flame.

Nelson, H. F.↗

NASA NTRS1976

Diffusion analysis for two-phase metal-matrix composite

Diffusion controlled filament matrix interaction in a metal matrix composite, where the filaments and matrix comprise a two phase binary alloy system, was mathematically modeled. The problem of a diffusion controlled, two phase moving interface by means of a one dimensional, variable grid, finite difference technique was analyzed. Concentration dependent diffusion coefficients and equilibrium solubility limits were used, and the change in filament diameter and compositional changes in the matrix were calculated as a function of exposure time at elevated temperatures. With the tungsten nickel (W-Ni) system as a model composite system, unidirectional composites containing from 0.06 to 0.44 initial filament volume fraction were modeled. Compositional changes in the matrix were calculated by superposition of the contributions from neighboring filaments. Alternate methods for determining compositional changes between first and second nearest neighbor filaments were also considered. The results show the relative importance of filament volume fraction, filament diameter, exposure temperature, and exposure time as they affect the rate and extent of filament matrix interaction.

Tenney, D. R.↗

NASA NTRS1978

On the propagation of cosmic rays in the Galaxy

Cosmic ray propagation in the Galaxy is examined within the framework of the leaky-box model, whereby phenomenological aspects of diffusion and propagation are related to the physical properties of the interstellar medium. The model is parameterized by data on composition, spectra, spectral change as a function of energy, and cosmic ray particle lifetime. It is assumed that electrons and nucleons have a common source within the Galaxy (probably associated with supernova remnants). Lifetime data and leakage length are compared with radio synchrotron and gamma-ray data to establish a place of origin for cosmic rays observed at earth, i.e., at a radius of 0.5-1.0 kpc from earth. It is noted that if the escape length becomes energy independent, all nuclear spectra will flatten, while the electron spectrum remains unchanged.

Ormes, J.↗

NASA NTRS1975

Rare gases and Ca, Sr, and Ba in Apollo 17 drill-core fines

Trapped gas isotopic compositions and spallation gas concentrations as functions of depth in the Apollo 17 drill core were determined from mass spectrometer studies by means of correlation techniques. The distribution of He, Ne, Ar, Kr, and Xe as well as Ca, Sr, and Ba was investigated, and rare-gas spallation and neutron capture profiles are compared with attention to proposed depositional models for the Taurus-Littrow regolith. The data exclude a sedimentation pattern similar to that found at the Apollo 15 site but are possibly compatible with long-term continuous accretion models or models of very recent rapid accumulation of regolith.

Pepin, R. O.↗

NASA NTRS1979

On matching the spectrum of Io - Variations in the photometric properties of sulfur-containing mixtures

The problem of comparing laboratory spectra of sulfur-containing binary mixtures with the spectrum of Io is discussed. For the satellite, the observable is the geometric albedo as a function of wavelength, whereas in the laboratory one often measures some other type of albedo. A previous paper demonstrated that for pure sulfur the multiplicative factor which converts the laboratory albedos to geometric albedos can be strongly wavelength dependent. The present paper demonstrates that this is also true for binary sulfur-containing mixtures. Furthermore, there is no universal conversion factor applicable to all binary mixtures, nor can the factor be interpolated for a particular mixture from the conversion factors of the two end members. The conversion factor is a function not only of the specific composition of a binary mixture but also of the relative particle size distributions of the two components, and must be measured specifically for each individual sample if a quantitative comparison between a laboratory sample and Io's surface is desired.

Veverka, J.↗

NASA NTRS1979

Silt-clay aggregates on Mars

Viking observations suggest abundant silt and clay particles on Mars. It is proposed that some of these particles agglomerate to form sand size aggregates that are redeposited as sandlike features such as drifts and dunes. Although the binding for the aggregates could include salt cementation or other mechanisms, electrostatic bonding is considered to be a primary force holding the aggregates together. Various laboratory experiments conducted since the 19th century, and as reported here for simulated Martian conditions, show that both the magnitude and sign of electrical charges on windblown particles are functions of particle velocity, shape and composition, atmospheric pressure, atmospheric composition and other factors. Electrical charges have been measured for saltating particles in the wind tunnel and in the field, on the surfaces of sand dunes, and within dust clouds on earth. Similar, and perhaps even greater, charges are proposed to occur on Mars, which could form aggregates of silt and clay size particles

Greeley, R.↗

NASA NTRS1980

ISEE-3 measurements of solar energetic particle composition

Preliminary observations of energetic particles from solar flares beginning on September 23 and November 10, 1978 are reported. The measurements were made from the ISEE-3 spacecraft using very thin, large area solid-state detectors. Charge composition was measured for all elements from Z = 2 to Z = 26 above approximately 2 MeV/nucleon. More than 100,000 nuclei with Z greater than 2 were pulse-height analyzed during the course of the first event, while the second was substantially smaller. These good statistics enable the observation of variations in composition at low energies as a function of time. For example, the Fe/O ratio (2.0-3.1 MeV/n) was observed in the September event to decrease by a factor of approximately 5. By contrast, this same ratio increased by a factor of approximately 1.5 during the November 10 event. Similar variations have been reported earlier by Scholer et al. (1978). These authors, however were unable to observe the He/O ratio which has now been observed also to show significant variation.

Von Rosenvinge, T. T.↗

NASA NTRS1980

Axial rotation, tangled magnetic fields, and theoretical models of very massive stars

A simple method of computing theoretical models of very massive stars endowed with fast axial rotation and tangled magnetic fields is described and used in the present paper. Both of the two perturbing (nongravitational) forces induce changes in the luminosity and radius that are studied as functions of zero-age chemical composition, opacity, and evolutionary state of the interior. The central condensation of the star is found to have a significant influence on shifts of the upper main-sequence band in the H-R diagram if the perturbing force is concentrated in the stellar envelope (but not if the perturbing force is distributed so as to be approximately proportional to gravity everywhere); the layers of the envelope that contribute most heavily to the central condensation lie approximately at a radius fraction of r/R = 0.5. It is shown that fast uniform rotation and intense envelope magnetic fields lead to probably the largest possible shifts of the main-sequence band in the H-R diagram that rotation and magnetic fields can induce. These displacements are, however, too small to account for the total width of the observed main-sequence band at luminosities brighter than log (L/solar luminosity) = 4.5.

Stothers, R.↗

NASA NTRS1983

Pushbroom radiometry and its potential using large space antennas

Electromagnetic radiation is emitted by matter which was heated to a temperature above absolute zero. The amount of blackbody radiation in the microwave frequency region of interest (10 to the 8th power f 10 to the 10th power Hz) emitted by matter can be determined from the Rayleigh-Jeans approximation to Planck's Radiation Law. The amount of electromagnetic radiation from matter which is not a blackbody is a function of the emissivity of the material. The emissivity is a factor less than unity and is a function of several parameters including chemical composition, temperature, frequency, surface characteristics, and viewing angle. A radiometer is an instrument which detects and provides a measure of the electromagnetic radiation being emitted by a material or surface area within the radiometer's antenna beamwidth. Microwave radiometers provide the capability for remote measurements from Earth orbits of geophysical parameters. These measurements will require the use of a microwave imaging radiometer using a large aperture deployable antenna with multiple beams in a pushbroom mode to achieve high spatial resolution and large swath width.

Harrington, R. F.↗

NASA NTRS1984

Spectrophotometry of 17 comets. I - The emission features

The present 112 sets of image dissector scanner data were obtained at Lick Observatory from 17 comets during a 2.5-yr period, 1980-1982. Results obtained include column densities for CN, C3, CH, C2, and forbidden line O I, new Haser parent scale lengths for CN, C3, and C2, and a large body of data on the composition of cometary comae as a function of heliocentric distance. Particularly notable is the well-defined C2-to-CN ratio, which decreases roughly as r to the -1.4 power out to r of about 1.8 AU, and then falls precipitously. Although there is considerable chemical uniformity in most comets studied, two (P/Borrelly and P/Swift-Gehrels) appear significantly deficient in both C2 and C3. The apparent systematics within the crude Haser paradigm offer suggestions for more realistic chemical modelling studies.

Newburn, R. L., Jr.↗

NASA NTRS1986

Terrestrial Kr-81-Kr ages of Antarctic meteorites

The production rate of Ar-38 in meteorites P(38), has been determined, as a function of the sample's chemical composition, from Kr-81-Kr exposure ages of four eucrite falls. The cosmogenic Kr-78/Kr-83 ratio is used to estimate the shielding dependence of P(38). From the 'true' Ar-38 exposure ages and the apparent Kr-81-Kr exposure ages of nine Antarctic eucrite finds, terrestrial ages are calculated. They range from about 300,000 ages (Pecora Escarpment 82502) to very recent falls (Thiel Mountains 82502). Polymict eucrites from the Allan Hills (A78132, A79017, and A81009) have within the limits of error the same exposure age (15.2 x 10 to the 6th ages) and the same terrestrial age (110,000 ages). This is taken as strong evidence that these meteorites are fragments of the same fall. A similar case is the Elephant Moraine polymict eucrites A79005, A79006, and 82600 with an exposure age of 26 x 10 to the 6th ages and a terrestrial age of 180,000 ages. EETA 79004 may be different from this group because its exposure age and terrestrial age are 21 x 10 to the 6th ages and 250,000 ages, respectively. The distribution of terrestrial ages of Allan Hills meteorites is discussed. Meteorites from this blue ice field have two sources: directly deposited falls and meteorites transported to the Allen Hills inside the moving Antarctic ice sheet. During the surface residence time meteorites decompose due to weathering processes. The weathering 'half-life' is about 160,000 ages. From the different age distributions of Allan Hills and Yamato meteorites, it is concluded that meteorite concentrations of different Antarctic ice fields need different explanations.

Freundel, M.↗

NASA NTRS1987

Apollo 17 KREEPy basalts - Evidence for nonuniformity of KREEP

Breccia 72275 contains pristine KREEPy basalt clasts that are not found among other samples collected at Apollo 17. These basalts occur as discrete clasts and as clasts enclosed within basaltic microbreccias. Mineral and whole-rock chemical analyses reveal that the microbreccias are compositionally indistinguishable from the basalt clasts. Samples of the 72275 matrix also have the same compositions as the basalts and the basaltic microbreccias. 72275 was assembled in situ from a single flow or series of closely related flows of Apollo 17 KREEPy basalt before it was transported to the Apollo 17 site. As a rock type, Apollo 17 KREEPy basalts are distinct from Apollo 15 KREEP basalts. The Apollo 17 samples have lower REE concentrations, steeper negative slopes of the HREE, and are less magnesian than the Apollo 15 samples. The two basalt types cannot be related by fractional crystallization, partial melting, or assimilation. This is evidence for the compositional nonuniformity of KREEP as a function of geography.

Salpas, Peter A.↗

NASA NTRS1987

Interfacial strength development in thermoplastic resins and fiber-reinforced thermoplastic composites

An experimental program to develop test methods to be used to characterize interfacial (autohesive) strength development in polysulfone thermoplastic resin and graphite-polysulfone prepreg during processing is reported. Two test methods were used to examine interfacial strength development in neat resin samples. These included an interfacial tension test and a compact tension (CT) fracture toughness test. The interfacial tensile test proved to be very difficult to perform with a considerable amount of data scatter. Thus, the interfacial test was discarded in favor of the fracture toughness test. Interfacial strength development was observed by measuring the refracture toughness of precracked compact tension specimens that were rehealed at a given temperature and contact time. The measured refracture toughness was correlated with temperature and contact time. Interfacial strength development in graphite-polysulfone unidirectional composites was measured using a double cantilever beam (DCB) interlaminar fracture toughness test. The critical strain energy release rate of refractured composite specimens was measured as a function of healing temperature and contact time.

Howes, Jeremy C.↗