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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 253 records · Page 14

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NASA NTRS2003

Comparison of Ground-Penetrating Radar and Low-Frequency Electromagnetic Sounding for Detection and Characterization of Groundwater on Mars

Two orbital, ground-penetrating radars, MARSIS and SHARAD, are scheduled for Mars flight, with detection of groundwater a high priority. While these radars will doubtlessly provide significant new information on the subsurface of Mars, thin films of adsorbed water in the cryosphere will strongly attenuate radar signals and prevent characterization of any true aquifers, if present. Scattering from 10-m scale layering or wavelength-size regolith heterogeneities will also degrade radar performance. Dielectric contrasts are sufficiently small for low-porosity, deep aquifers that groundwater cannot be reliably identified. In contrast, low-frequency (mHz-kHz) soundings are ideally suited to groundwater detection due to their great depths of penetration and the high electrical conductivity (compared to cold, dry rock) of groundwater. A variety of low-frequency methods span likely ranges of mass, volume, and power resources, but all require acquisition at or near the planetary surface. Therefore the current generation of orbital radars will provide useful global reconnaissance for subsequent targeted exploration at low frequency. Introduction: Electromagnetic (EM) methods

R E Grimm↗

NASA NTRS1972

Water impact loads

Computer program to generate time history of load factor and pressure on conical body of revolution during impact with water is discussed. Program calculates depth of penetration, velocity, force, load factor, maximum pressure at water line, and average pressure. Program is written in FORTRAN 4 Level H for IBM 360/85/195 Release 20.1 computer.

Sanders, D. H.↗

NASA NTRS1972

Ring current particle distributions during the magnetic storms of 16-18 December 1971

In an effort to summarize the constrasting development of the stormtime ring currents during the December 16-18, 1971 magnetic storms, maps were drawn indicating the proton energy density spatial/temporal distributions. The maps contain distributions for the 5 to 138 keV protons for each of seven orbits. The first storm was not characteristic of a single substorm nor a fully developed magnetic storm, but it was comprised of a sudden commencement, a positive phase, and multiple substorms producing a small depression in the magnetic field. The second storm was classical in development with a short two hour growth phase. Energy density distribution constrasts for the two storms show the second storm displayed three dominant features over the first storm. They were: (1) the intensities were 2 1/2 times larger, (2) the depths of penetration were 1/2 to 1 Reynolds number lower, and (3) the distribution became symmetric.

Smith, P. H.↗

NASA NTRS1971

Brief review of thermoluminescence studies in lunar samples.

A weak thermoluminescence, due primarily to plagioclase feldspar, is found to exist in Apollo 11 and 12 lunar rock and topsoil samples. This effect increases with depth to about 10 cm below the surface and becomes relatively even in greater depth. The penetration of the diurnal temperature wave is traced to the rock thermoluminescence. Evidence is also found for the thermal draining of the surface rock.

Hoyt, H. P., Jr.↗

NASA NTRS1972

On multidisciplinary research on the application of remote sensing to water resources problems

This research is directed toward development of a practical, operational remote sensing water quality monitoring system. To accomplish this, five fundamental aspects of the problem have been under investigation during the past three years. These are: (1) development of practical and economical methods of obtaining, handling and analyzing remote sensing data; (2) determination of the correlation between remote sensed imagery and actual water quality parameters; (3) determination of the optimum technique for monitoring specific water pollution parameters and for evaluating the reliability with which this can be accomplished; (4) determination of the extent of masking due to depth of penetration, bottom effects, film development effects, and angle falloff, and development of techniques to eliminate or minimize them; and (5) development of operational procedures which might be employed by a municipal, state or federal agency for the application of remote sensing to water quality monitoring, including space-generated data.

Source record↗

NASA NTRS1974

Computer simulation of the Pioneer 10 microwave occultation experiment

As Pioneer 10 approaches the planet Jupiter, its trajectory will carry it behind the planet, as seen from the earth. The microwave telemetry signal from the spacecraft will then pass through the Jovian atmosphere on its way to the earth, and analysis of the effects of the atmosphere on the signal should yield information on the atmospheric structure. To help define the capabilities of this experiment and to aid the analysis of the real data, we have simulated the occultation experiment on a computer by using model Jovian atmospheres and a predicted trajectory. The results indicate that the useful depth of penetration of the microwave signal will be governed by ammonia absorption rather than superrefractivity. The experiment is apparently far more sensitive to variations in cloud-top temperature than to variations in the hydrogen-helium ratio. Characteristic 'flashes' in the attenuation record of the signal may yield information on the location of the top of the Jovian convective zone.

Ungar, S. G.↗

NASA NTRS1977

Impact cratering phenomenon for the Ries multiring structure based on constraints of geological, geophysical, and petrological studies and the nature of the impacting body

In the present paper, an attempt is made to delineate, on the basis of field and laboratory data, the phenomenon of formation of the Ries multiring basin - the best preserved very large terrestrial impact structure. The model proposed conforms to constraints imposed by geological, geophysical, and petrological studies and by the nature of the postulated impacting body. It is also based on the impact features of a stony meteorite measuring 3 km in diameter at an impact velocity of 15 km/sec. The schematic reconstruction shows that critical to the production of a shallow crater is shallow impact penetration (shallow depth of burst). This and the nonballistic ejection of excavated material appear to be genetically related, i.e., if extensive nonballistic transport is recognized, then the associated crater must be a shallow structure and vice versa. This also means the shallow configuration of a crater may not have anything to do with postcratering readjustment.

Chao, E. C. T.↗

NASA NTRS1978

Lunar Seismology: the Internal Structure of the Moon

The direct P and S wave arrival times are the primary data set that can be measured on the seismograms of natural lunar seismic events. Polarization filtering techniques allow the enhancement of secondary body wave arrivals and record curves to identify the secondary phases and deduce structural information. Finally, shear wave amplitude vs. distance curves yield information on the location and magnitude of seismic velocity gradients in the interior. The results of these analyses show that the moon appears to have a two-layer crust at all four seismic stations: a 20 km upper crust that seems to be constant at all sites and a lower crust that is 40 km thick at stations 12 and 14 (mare), 55 + or - 10 km at station 16 (highland), and tentatively either 40 km or 70 km at station 15. The lower mantle extends from 480 km to at least 1100 km depth which is the maximum depth of penetration of all but a few seismic waves used as data. No definitive evidence for or against a lunar core exists.

Goins, N. R.↗

NASA NTRS1980

Observations from earth orbit and variability of the polar aurora on Jupiter

Spatially resolved spectra of Jupiter taken with the International Ultraviolet Explorer satellite show enhanced emissions from the polar regions at H L-alpha (1216 A) and in the Lyman and Werner bands of H2 (1175-1650 A). Two types of variability in emission brightness have been observed in these aurorae: an increase in the observed emission as the auroral oval rotates with Jupiter's magnetic pole to face toward the earth and a general variation in brightness of more than an order of magnitude under nearly identical observing conditions. In addition, the spectral character of these aurorae (determined by the ratio of H L-alpha to H2 brightnesses) appears variable, indicating that the depth of penetration of the auroral particles is not constant.

Clarke, J. T.↗

NASA NTRS1981

Electromagnetic deep-probing (100-1000 KMS) of the Earth's interior from artificial satellites: Constraints on the regional emplacement of crustal resources

Model simulations show that induction in a spherical Earth by distant magnetospheric sources can contribute magnetic field fluctuations at MAGSAT altitudes which are 30 to 40 percent of the external field amplitudes. When the characteristic dimensions (e.g. depth of penetration, etc) of a particular situations are small compared with the Earth's radius, the Earth can be approximated by a plane horizontal half space. In this case, electromagnetic energy is reflected with close to 100 percent efficiency from the Earth's surface. This implies that the total horizontal field is twice the source field when the source is above the satellite, but is reduced to values which are much smaller than the source field when the source is below the satellite. This latter effect tends to enhance the signature of gross electrical discontinuities in the lithosphere when observed at satellite altitudes.

Hermance, J. F.↗

NASA NTRS1982

Medium energy proton radiation damage to (AlGa)As-GaAs solar cells

The performance of (AlGa)As-GaAs solar cells irradiated by medium energy 2, 5, and 10 MeV protons was evaluated. The Si cells without coverglass and a number of GaAs solar cells with 12 mil coverglass were irradiated simultaneously with bare GaAs cells. The cell degradation is directly related to the penetration of depth of protons with GaAs. The influence of periodic and continuous thermal annealing on the GaAs solar cells was investigated.

Loo, R. Y.↗

NASA NTRS1981

Atmospheric breakup of terrestrial impactors

Aerodynamic stresses are large enough to crush large meteoriods entering the earth's atmosphere. The fragments are dispersed after breakup, changing the shape and effective density of the meteoroid. This decreases the depth of penetration of the meteoroid when it strikes the ground and may influence the size and morphology of the resulting impact crater. This paper shows that meteoroids up to a kilometer in diameter may be significantly affected by this process when they enter the earth's atmosphere. Meteoroids up to ten kilometers in diameter are affected on Venus. The degree of fragment dispersion is independent of the meteoroid's velocity or altitude of breakup (if it is higher than about three scale heights); it depends mainly upon the meteoroid's initial diameter and the angle of atmospheric entry.

Melosh, H. J.↗

NASA NTRS1983

Eddy-Current Damage Test for Carbon Composites

Nondestructive test method detects cracks in materials of low conductivity. Test setup includes eddycurrent unit with frequency of 2 to 20 MHz/ and storage oscilloscope. High frequency required to assure depth of penetration less than substrate thickness, to prevent thickness from influencing reading. Eddy-current analysis confirmed by visual inspection as damaged area was sectioned and evaluated.

Hamilton, A. B.↗

NASA NTRS1983

A microwave systems approach to measuring root zone soil moisture

Computer microwave satellite simulation models were developed and the program was used to test the ability of a coarse resolution passive microwave sensor to measure soil moisture over large areas, and to evaluate the effect of heterogeneous ground covers with the resolution cell on the accuracy of the soil moisture estimate. The use of realistic scenes containing only 10% to 15% bare soil and significant vegetation made it possible to observe a 60% K decrease in brightness temperature from a 5% soil moisture to a 35% soil moisture at a 21 cm microwave wavelength, providing a 1.5 K to 2 K per percent soil moisture sensitivity to soil moisture. It was shown that resolution does not affect the basic ability to measure soil moisture with a microwave radiometer system. Experimental microwave and ground field data were acquired for developing and testing a root zone soil moisture prediction algorithm. The experimental measurements demonstrated that the depth of penetration at a 21 cm microwave wavelength is not greater than 5 cm.

Newton, R. W.↗

NASA NTRS1985

Histological and compositional responses of bone to immobilization and other experimental conditions

Histological techniques were utilized for evaluating progressive changes in tibial compact bone in adult male monkeys during chronic studies of immobilization-associated osteopenia. The animals were restrained in a semirecumbent position which reduces normally occurring stresses in the lower extremities and results in bone mass loss. The longest immobilization studies were of seven months duration. Losses of haversian bone tended to occur predominatly in the proximal tibia and were characterized by increased activation with excessive depth of penetration of osteoclastic activity. There was no apparent regulation of the size and orientation of resorption cavities. Rapid bone loss seen during 10 weeks of immobilization appeared to be due to unrestrained osteoclastic activity without controls and regulation which are characteristic of adaptive systems. The general pattern of loss persisted throughout 7 months of immobilization. Clear cut evidence of a formation phase in haversian bone was seen only after two months of reambulation.

Brown, R. J.↗

NASA NTRS1985

A possible EAS array above the Soudan 2 detector

Multiple high energy muons, when studied with a large area detector, can be useful in the study of the composition of cosmic rays at energies approx. 10 14 eV. The Soudan II detector, primarily designed to detect nucleon decay, is located approx. 600 m deep underground and has dimensions of 16m x 8m x 5m (height), and is made up of drift tubes. The minimum muon energy needed to penetrate that depth is approximately 500 GeV. A set of simulated cosmic ray showers was set up to calculate the rate of muon associated events, using a trigger array with the number of detectors varying from 37 to 127 (the radius of acceptance varying from 50m to 100m). The number used in the calculations is given. The association rate is seen to be a strong function of the multiplicity of muons in the detector. The difference in the rates of association of proton and nuclei induced showers rises rapidly with multiplicity.

Sivaprasad, K.↗

NASA NTRS1986

Immobilization-associated osteoporosis in primates

Osteopenic changes in the tibial compact bone of fifteen adult male monkeys immobilized for up to 7 months are examined histologically. Osteonal formation in the proximal tibia is analyzed. The analysis reveals the loss of haversian bone in the proximal tibia, increased activation with excessive depth of penetration of osteoclastic activity, rapid bone loss, and resorption cavities of irregular size and orientation. Osteonal formation following reambulation is examined; the recovery of cortical is a repair and rejuvenation process characterized by refilling of resorption cavities and remodeling activities.

Young, D. R.↗

NASA NTRS1988

Interactions of planetesimals with protoplanetary atmospheres

The 'core instability' mechanism presently postulated for the interaction of planetesimals with the envelopes of growing giant planets involves core growth through the accretion of solid bodies in the solar nebula; the core thereby becomes more effective in the gravitational attraction of gas from the surrounding nebula into an envelope, until a runaway accretion stage is reached. Two-body trajectory curves of planetesimals through this envelope are computed which demonstrate the depth of penetration and the cross-sections for capture of icy and rocky planetesimals.

Podolak, Morris↗