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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Architecture Study for a Fuel Depot Supplied from Lunar Assets

This architecture study sought to determine the optimum architecture for a fuel depot supplied from lunar assets. Four factors - the location of propellant processing (on the Moon or on the depot), the depot location (on the Moon, L1, GEO, or LEO), the propellant transfer location (L1, GEO, or LEO), and the propellant transfer method (bulk fuel or canister exchange) were combined to identify 18 candidate architectures. Two design reference missions (DRMs) - a commercial satellite servicing mission and a Government cargo mission to Mars - created demand for propellants, while a propellant delivery DRM examined supply issues. The study concluded Earth-Moon L1 is the best location for an orbiting depot. For all architectures, propellant boiloff was less than anticipated, and was far overshadowed by delta-v requirements and resulting fuel consumption. Bulk transfer is the most flexible for both the supplier and customer. However, since canister exchange bypasses the transfer of bulk cryogens and necessary chilldown losses, canister exchange shows promise and merits further investigation. Overall, this work indicates propellant consumption and loss is an essential factor in assessing fuel depot architectures.

Perrin, Thomas M.↗
NASA NTRS1983

Alterations in calcium homeostasis and bone during actual and simulated space flight

Skeletal alteration in experimental animals induced by actual and simulated spaceflight are discussed, noting that the main factor contributing to bone loss in growing rats placed in orbit aboard Soviet Cosmos biosatellites appears to be diminished bone formation. Mechanical unloading is seen as the most obvious cause of bone loss in a state of weightlessness. Reference is made to a study by Roberts et al. (1981), which showed that osteoblast differentiation in the periodontal ligament of the maxilla was suppressed in rats flown in space. Since the maxilla lacks a weight-bearing function, this finding indicates that the skeletal alterations associated with orbital flight may be systemic rather than confined to weight-bearing bones. In addition, the skeletal response to simulated weightlessness may also be systemic (wronski and Morey, 1982). In suspended rats, the hindlimbs lost all weight-bearing functions, while the forelimbs maintained contact with the floor of the hypokinetic model. On this basis, it was to be expected that there would be different responses at the two skeletal sites if the observed abnormalities were due to mechanical unloading alone. The changes induced by simulated weightlessness in the proximal tibia and humerus, however, were generally comparable. This evidence for systemic skeletal responses has drawn attention to endocrine factors.

Wronski, T. J.↗
NASA NTRS1976

Reduction of acoustic losses by outgassing

Heat treatment procedure at low pressure increases internal-friction quality factor of treated samples. Method can reduce propagation losses in porous ferroelectric ceramics by as much as a factor of 100.

Cirlin, E. H.↗
NASA NTRS1966

Flow losses in flexible hose.

Empirical method predicting flexible hose flow losses, with Fanning friction factor as Reynolds number and internal hose geometry function

FLEXIBLE BODY↗
NASA NTRS1971

Energy changes of cosmic rays in interplanetary space.

The observation reported by Murray et al. (1971), in which a feature or ?kink' in the kinetic-energy spectrum of solar cosmic rays from a solar burst was seen to decrease with time, is examined. By means of calculations based on a model for cosmic ray bursts, it is demonstrated that the observed rate cannot be interpreted immediately as the rate of loss of energy, and factors are indicated which must be considered in the interpretation of the data.

Gleeson, L. J.↗
NASA NTRS1975

An experimental investigation of compressor stall using an on-line distortion indicator and signal conditioner

The relation of the steady-state and dynamic distortions and the stall margin of a J85-13 turbojet engine was investigated. A distortion indicator capable of computing two distortion indices was used. A special purpose signal conditioner was also used as an interface between transducer signals and distortion indicator. A good correlation of steady-state distortion and stall margin was established. The prediction of stall by using the indices as instantaneous distortion indicators was not successful. A sensitivity factor that related the loss of stall margin to the turbulence level was found.

Costakis, W. G.↗
NASA NTRS1975

Electron angular distributions above the dayside auroral oval

An electrostatic analyzer was employed on the Ariel 4 satellite to determine pitch angle distributions of electron intensities over the dayside auroral oval. Two major precipitation zones were encountered: an equatorward zone of broad spectra with intensities of approximately 1000 electrons/(sq cm-sec-sr-eV) and a poleward zone, the polar cusp, with intensities typical of those of the magnetosheath. Angular distributions within the equatorward zone are generally isotropic outside of the atmospheric backscatter cone. The precipitation mechanism appears to be pitch angle scattering near the distant magnetic equator. In contrast, pitch angle distributions within the polar cusp are often found to be strongly field aligned with intensities within the atmospheric loss cone greater by factors of approximately 10 than the mirroring intensities. These distributions are qualititatively similar to those for the inverted V precipitation events at later local times, and probably share a common acceleration mechanism with the inverted V phenomenon.

Craven, J. D.↗
NASA NTRS1976

Electron angular distributions above the day side auroral oval

An electrostatic analyzer, a Lepedea, was employed on the low-altitude satellite Ariel 4 in order to gain pitch angle distributions of electron intensities with good temporal resolution within the energy range 205 eV to 12.5 keV over the day side auroral oval. Two major precipitation zones were encountered: an equatorward zone of broad spectra with intensities of about 10 to the 4th el/sq cm/s/sr/eV and a poleward zone, the polar cusp, with intensities typical of those of the magnetosheath. Angular distributions within the equatorward zone are generally isotropic outside of the atmospheric backscatter cone. The precipitation mechanism would appear to be pitch angle scattering near the distant magnetic equator. In contrast, pitch angle distributions within the polar cusp are often found to be strongly field aligned with intensities within the atmospheric loss cone greater by factors of about 10 than the mirroring intensities.

Craven, J. D.↗
NASA NTRS1977

A computer analysis of heterojunction and graded composition solar cells

The development and application of a variable composition solar cell computer analysis program is discussed. The basic device equations are derived and results of the computer analysis of several Al(x)Ga(1-x)As and GaAs(1-x)P(x) solar cell structures are presented along with a discussion of the effects of interface states and various composition and doping profiles on maximum solar cell efficiency. Interface states are found to be responsible for a severe reduction in the efficiency of GaAs(1-x)P(x) cells, but do not significantly affect the behavior of Al(x)Ga(1-x)As cells. The depth of the p-n junction below the wide bandgap window layer is a critical factor in determining the loss of minority carriers to interface recombination at the heterojunction.

Sutherland, J. E.↗
NASA NTRS1979

The potential of np GaAs solar cells for high efficiency concentrator applications

This communication considers the design of the front grid contact of np GaAs solar cells for high efficiency concentrator applications. This design involves shadowing, contact resistance, and active layer sheet resistance losses, and at high concentrations, the power loss due to voltage drop on the resistance of the grid fingers should be considered. Analysis of the performance can be calculated as a function of junction depth and surface recombination velocity. The junction depth can be optimized by considering its effect on the collection efficiency of the dark current-voltage characteristics or the open circuit voltage, and on the series resistance loss or the fill factor for material parameters. The choice of the material parameters, calculation of the short circuit current, the selection of the n layer thickness, and the cell maximum power and efficiency are discussed. It is concluded that optimized multi-grid structures should allow the use of 10 by 10 sq cm cells with good efficiencies at high concentration ratios, and efficiencies of 22 to 25% should be obtainable from large area cells at concentrations of 40 AM1.

Flat, A.↗
NASA NTRS1984

Transient components in the Lyman lines of hot stars Evidence for the ejection of shells or puffs on very short timescales

The existence of H I transient components in the stellar wind of Epsilon Per toward eight early type stars observed by the Copernicus satellite is systematically investigated. It is shown that such transient components are indeed present in the spectra of five of these stars and have characteristics very similar to the one found in the case of Epsilon Per. It is shown that such components can be interpreted in terms of coherent 'puffs' or shells of matter ejected by the stars. They would be caused by an increase of the stellar mass loss rate by a factor of 1.5 to 3 during one hour or less, and would be accelerated more slowly than the quiet wind. It is suggested that such events must be due to instabilities in these stars which are all slightly evolved stars ranging in spectral types between O9 and B1. The instabilities are probably similar to those in Beta Cephei stars, i.e., nonradial pulsations.

Gry, C.↗
NASA NTRS1985

Effects of wear on structure-sensitive magnetic properties of ceramic ferrite in contact with magnetic tape

Wear experiments and electron microscopy and diffraction studies were conducted to examine the wear and deformed layers in single-crystal Mn-Zn (ceramic) ferrite magnetic head material in contact with magnetic tape and the effects of that contact on magnetic properties. The crystalline state of the single-crystal magnetic head was changed drastically during the sliding process. A nearly amorphous structure was produced on its wear surface. Deformation in the surficial layer of the magnetic head was a critical factor in readback signal loss above 2.5 dB. The signal output level was reduced as applied normal load was increased. Considerable plastic flow occurred on the magnetic tape surface with sliding, and the signal loss due to the tape wear was approximately 1 dB.

Miyoshi, K.↗
NASA NTRS1987

Local heat/mass transfer and pressure drop in a two-pass rib-roughened channel for turbine airfoil cooling

The heat transfer characteristics of turbulent air flow in a multipass channel were studied via the naphthalene sublimation technique. The naphthalene-coated test section, consisting of two straight, square channels joined by a 180 deg turn, resembled the internal cooling passages of gas turbine airfoils. The top and bottom surfaces of the test channel were roughened by rib turbulators. The rib height-to-hydraulic diameter ratio (e/D) were 0.063 and 0.094, and the rib pitch-to-height ratio (P/e) were 10 and 20. The local heat/mass transfer coefficients on the roughened top wall and on the smooth divider and side walls of the test channel were determined for three Reynolds numbers of 15, 30, and 60, thousand, and for three angles of attack (alpha) of 90, 60, and 45 deg. Results showed that the local Sherwood numbers on the ribbed walls were 1.5 to 6.5 times those for a fully developed flow in a smooth square duct. The average ribbed-wall Sherwood numbers were 2.5 to 3.5 times higher than the fully developed values, depending on the rib angle of attack and the Reynolds number. The results also indicated that, before the turn, the heat/mass transfer coefficients in the cases of alpha = 60 and 45 deg were higher than those in the case of alpha=90 deg. However, after the turn, the heat/mass transfer coefficients in the oblique-rib cases were lower than those in the transverse rib case. Correlations for the average Sherwood number ratios for individual channel surfaces and for the overall Sherwood number ratios are reported. Correlations for the fully developed friction factors and for the loss coefficients are also provided.

Han, J. C.↗
NASA NTRS1989

Jupiter's radiation belt ions - A comparison of theory and observation

Radial profiles are constructed for the Jovian radiation belt flux-tube content Y-asterisk from the reported phase-space density of energetic particles obtained from Voyager 1 data over the range L = 6 to L = 9. These experimental profiles are compared with theoretical solutions for Y-asterisk from an interchange-diffusion model of the coupled radiation belt and Iogenic ion populations. Subject to certain limitations of the Voyager 1 data, the model solutions are found to be consistent with the data for a variety of input parameters. Model solutions are also found corresponding to radiation belt ions that are expected to be mainly responsible for the auroral energy input. Comparison of the present theoretical profiles with the data implies that the energetic radiation belt ions should have a peak loss rate within a factor of three of that for strong diffusion scattering.

Summers, Danny↗
NASA NTRS1990

Cellular structure of lean hydrogen flames in microgravity

Detailed, time-dependent, two-dimensional numerical simulations of premixed laminar flames have been used to study the initiation and subsequent development of cellular structures in lean hydrogen-air flames. The model includes detailed hydrogen-oxygen combustion with 24 elementary reactions of eight reactive species and a nitrogen diluent, molecular diffusion of all species, thermal conduction, viscosity, and convection. This model has been used to study the nonlinear evolution of cellular flame structure and shows that cell splitting, as observed in experiments, can be predicted numerically for sufficiently reactive mixtures. The structures that evolved also resembled the cellular structures observed in experiments. The present study shows that the 'cell-split limit' postulated from experimental observations is an intrinsic property of the mixture and that external factors such as heat losses are not necessary to cause this limit.

Patnaik, G.↗
NASA NTRS1992

Magnetic Resonance Imaging (MRI) of skeletal muscles in astronauts after 9 days of space flight

Skylab data indicated that prolonged exposure of human subjects to microgravity environment causes significant muscle atrophy accompanied by reduced muscle strength and fatigue resistance. The objective of this study was to determine decrements in muscle size, if any, in the soleus and gastrocnemius muscles of male and female astronauts after 9 days of space flight. Methods: Eight astronauts, one female and seven male, between the ages of 31 and 59 years 59-84 kg in body weight were examined by MRI 2-3 times preflight within 16 days before launch, and 2 days, (n=6) and seven days (n=3) after landing. The right leg muscles (gastroc-soleus) were imaged with a lower extremity coil in magnets operating at 1.0 or 1.5 Tsela. The imaging protocol consisted of spin echo with a Tr of 0.70 - 1.5 sec. Thirty to forty 3-5 mm thick slices were acquired in 256 x 128 or 256 x 256 matrices. Acquisition time lasted 20-40 minutes. Multiple slices were measured by computerized planimetry. Results: Compared to the preflight, the cross-sectoral areas (CSA) of the soleus, gastrocnemius, and the leg, at 2 days after landing were reduced (at least p less than 0.05) 8.9 percent, 13.2 percent, and 9.5 percent respectively. The soleus and the leg of three astronauts evaluated at 7 days postflight did not show full recovery compared to the preflight values. Conclusions: It is concluded that l9-days of space flight may cause significant decreases in CSA of the leg muscles. The factors responsible for this loss need further determination.

Jaweed, M.↗
NASA NTRS1994

A model for the spectroscopic variations of the peculiar symbiotic star MWC 560

In this note, we show that the ultraviolet and optical spectroscopic variability of this unique symbiotic star can be understood in terms of a time variable collimated stellar wind with a rapid acceleration near the source. Using the radial velocities observed during the ultraviolet bright phase, we find that a variation in the mass loss rate of a factor of ten can explain the ultraviolet spectral changes. The acceleration is far faster than normally observed in radiatively driven stellar winds and may be due to mechanical driving of the outflow from the disk.

Shore, Steven N.↗
NASA NTRS1995

Photoevaporating stellar envelopes observed with Rayleigh beacon adaptive optics

We present H-alpha and I-band images of a approximately 1 min diameter field centered on theta(sup 1) C Ori made with a unique adaptive optics system that uses either starlight or Rayleigh-backscattered laser light to correct for atmospheric wavefront distortion. Approximately one-half of the stars in this region are positionally associated with knots of ionized gas, which are interpreted as photoevaporating envelopes of low-mass stars. The acronyms 'partially ionized globule' (PIGs), external ionized (accretion) disks in the environs of radiation sources (EIDERs), or protoplanetary disks (ProPlyDs) all refer to these same knots. The H-alpha fluxes of the PIGs are proportional to their 2 cm radio continumm flux densities, and for nearly all the ionized knots, the 2 cm brightness temperatures are consistent with theta(sup 1) C Ori as the primary source of ionization. The comet-like morphology of the bright nebulosities is modeled as the result of an equilibrium between photoionization, recombination, and shadowing. The radii of the ionized 'head' of the cometary PIGs grow with distance from theta(sup 1) C Ori; the radii range from approximately less than or equal to 0.05 sec to approximately 0.25 sec. We interpret the size-distance relationship as evidence that the envelopes all have the same density profile and mass-loss rate within a factor of 2. Faint, arcuate wisps are observed 1 sec to 2 sec distance from some of the cometary nebulosities; these are modeled as bow shocks caused by the wind from theta(sup 1) C Ori. The positions of the stars associated with the PIGs in the observational H-R diagram indicate they are pre-main-sequence stars with masses less than approximately 3 solar mass, with approximately 1 solar mass being typical. Their medium I-K color is 2.9.

Mccullough, P. R.↗