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At least 1,369 records · Page 76

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NASA NTRS1989

Measurements of vertical motions by the Saskatoon MF radar (1983-1985): Relationships with horizontal winds and gravity waves

The continuing series of horizontal wind measurements by the spaced-antenna real time winds (RTW) method was supplemented by a phase coherent system for two years. Vertical motions are inferred from the complex autocorrelation functions, and an RTW system provides 5 min samples from 60 to 110 km. Comparisons with full interferometric 3-D velocity measurements confirm the validity of this approach. Following comparisons and corrections with the horizontal winds, mean summer and winter (24 h) days of vertical motions are shown. Tidal fluctuations are evident. In summer the motions are downward, consistent with data from Poker Flat, and the suggestion of Coy et al. (1986) that these represent Eulerian motions. The expected upward Lagrangian motion then results from adding up upward Stokes' drift. The winter motions are more complex, and are discussed in the context of gravity wave fluxes and possible meridional cells. The divergence of the vertical flux of zonal momentum is also calculated and found to be similar to the coriolis torque due to the meridional winds.

Manson, A. H.↗

NASA NTRS1988

Chemistry and petrology of the Apennine Front, Apollo 15. I - KREEP basalts and plutonic rocks. II - Impact melt rocks

The mineralogy, petrology, and chemistry of rock fragments for the Apennine Front coarse fines (10-4 and 4-2 mm) have been determined. The data are consistent with a single eruptive event that produced several flows. It is found that most of the plutonic rocks are ferroan in nature, with a few belonging to the Mg-suite. The mineral and bulk chemistry of KREEP basalts and the composition of ferroan anorthosites are discussed. Petrographic studies of 21 impact melts are also presented, showing a variety of textures. It is found that the Apollo 15 impact melts are mixtures of low-K Fra Mauro, KREEP, and plutonic components. The Ni/Ir ratios of the melt rocks are shown to be greater than chondritic values, indicating ancient and/or iron meteorite components.

Simon, S. B.↗

NASA NTRS1988

Wavelike perturbations observed in the neutral thermosphere of Venus

Wavelike perturbations are evident in the neutral thermosphere measurements of He, N, O, N2, and CO2 by the Pioneer Venus orbiter neutral mass spectrometer. In the wavelength range from 100 to 600 km, the amplitudes of the various species are comparable in magnitude, with CO2 having the largest amplitude, and with helium out of phase with respect to the heavier species. On the dayside, the small-scale variations of CO2 and N2 increase with increasing altitude from 170 to 210 km, with CO2 having the largest slope. Simple and complex wave structures are observed, including wave trains and pulselike events. There is more activity during nighttime than during daytime, and larger values of the activity occur in the vicinity of the predawn and postdusk terminator sectors. Below 160 km, the standard deviation of the CO2 density on the nightside is 12 percent, about 3 times the daytime value. The data are consistent with the interpretation that the density perturbation are due to gravity waves propagating upward from the lower thermosphere.

Kasprzak, W. T.↗

NASA NTRS1988

An imaging observation of SN 1987A at gamma-ray energies

The Caltech imaging gamma-ray telescope was launched by balloon from Alice Springs, Australia for observations of SN 1987A during November 1987. The preliminary results presented here are derived from 8200 s of instrument live time on the supernova and 2500 s on the Crab Nebula and pulsar at a float altitude of 36 km. Images of the SN 1987A region at gamma-ray energies confirming that the bulk of the gamma-ray emission comes from the supernova and not from LMC X-1. These flux measurements are compared to recent predictions concerning the distribution of Co-56 in the supernova ejecta. The data are consistent with models invoking moderate mixing of core material into the envelope.

Cook, W. R.↗

NASA NTRS1988

VLSI high speed packet processor

The Goddard Space Flight Center Mission Operations and Data Systems Directorate has developed a packet processor card utilizing semicustom very large scale integration (VLSI) devices, microprocessors, and programmable gate arrays to support the implementation of multichannel telemetry data capture systems. This card will receive synchronized error corrected telemetry transfer frames and output annotated application packets derived from this data. An adaptable format capability is provided by the programmability of three microprocessors while the throughput capability of the packet processor is achieved by a data pipeline consisting of two separate RAM systems controlled by specially designed semicustom VLSI logic.

Grebowsky, Gerald J.↗

NASA NTRS1989

Closure of the Africa-Eurasia-North America plate motion circuit and tectonics of the Gloria fault

The current motions of the African, Eurasian, and North American plates are examined. The problems addressed include whether there is resolvable motion of a Spitsbergen microplate, the direction of motion between the African and North American plates, whether the Gloria fault is an active transform fault, and the implications of plate circuit closures for rates of intraplate deformation. Marine geophysical data and magnetic profiles are used to construct a model which predicts about 4 mm/yr slip across the Azores-Gibraltar Ridge, and west-northwest convergence near Gibraltar. The analyzed data are consistent with a rigid plate model with the Gloria fault being a transform fault.

Argus, Donald F.↗

NASA NTRS1989

Optical studies of hydrogen above 200 gigapascals - Evidence for metallization by band overlap

Direct optical observations of solid hydrogen to pressures in the 250-gigapascal range at 77 K are reported. Hydrogen samples appear nearly opaque at the maximum pressures. Measurements of absorption and Raman spectra provide evidence that electronic excitations in the visible region begin at about 200 gigapascals. The optical data are consistent with a band-overlap mechanism of metallization.

Mao, N. K.↗

NASA NTRS1989

Plasma wave, magnetic field and energetic ion observations in the ion pick-up region of Comet Giacobini-Zinner

Simultaneous plasma wave, magnetic field, and energetic ion observations made by the ICE spacecraft in the extended ion pick-up region surrounding comet Giacobini-Zinner are examined to determine the conditions under which two characteristic wave emissions, electrostatic waves at a few kHz, and electromagnetic waves at a few tens of Hz, are generated. The data are consistent with the view that the kHz electrostatic emissions result from an instability of the pick-up photoelectron 'beam' produced when the angle alpha between the magnetic field and the solar wind velocity vector is less than about 60 deg, while the behavior of the tens of Hz electromagnetic waves suggests that they are generated by the pick-up ion 'ring' which is present when alpha exceeds about 60 deg.

Richardson, I. G.↗

NASA NTRS1989

On the source conditions for herringbone structure in type II solar radio bursts

An investigation is made of the correlation of the occurrence of the herringbone phenomenon in type II solar radio bursts with various flare properties. It is shown that herringbone is strongly correlated with the intensity of the type II burst: whereas about 21 percent of all type II bursts show herringbone, about 60 percent of the most intense bursts contain herringbone. This fact can explain most of the correlations between herringbone and other properties such as intense type III bursts, type IV emission, and high type II starting frequencies. It is also shown that when this is taken into account, there is no need to postulate two classes of type II burst in order to explain why there appears to be a difference in herringbone occurrence between the set of type II bursts associated with the leading edges of coronal mass ejections, and those not so associated. It is argued that the data are consistent with the idea that all coronal type II bursts are due to blast waves from flares.

Cane, H. V.↗

NASA NTRS1989

High-resolution microwave images of Saturn

An analysis of high-resolution microwave images of Saturn and Saturn's individual rings is presented. Radio interferometric observations of Saturn taken at the Very Large Array in New Mexico at wavelengths of 2 and 6 centimeters reveal interesting new features in both the atmosphere and rings. The resulting maps show an increase in brightness temperature of about 3 K from equator to pole at both wavelengths, while the 6-centimeter map shows a bright band at northern midlatitudes. The data are consistent with a radiative transfer model of the atmosphere that constrains the well-mixed, fully saturated, NH3 mixing ratio to be 0.00012 in a region just below the NH3 clouds, while the observed bright band indicates a 25 percent relative decrease of NH3 in northern midlatitudes. Brightness temperatures for the classical rings are presented. Ring brightness shows a variation with azimuth and is linearly polarized at an average value of about 5 percent. The variations in ring polarization suggest that at least 20 percent of the ring brightness is the result of a single scattering process.

Grossman, A. W.↗

NASA NTRS1990

Remote Maintenance Monitoring

Automated system gives new life to aging network of computers. Remote maintenance monitoring system developed to diagnose problems in large distributed computer network. Consists of data links, displays, controls, software, and more than 200 computers. Uses sensors to collect data on failures and expert system to examine data, diagnose causes of failures, and recommend cures. Designed to be retrofitted into launch processing system at Kennedy Space Center. Reduces downtime, lowers workload and expense of maintenance, and makes network less dependent on human expertise.

Owens, Richard C.↗

NASA NTRS1990

Bone growth and calcium balance during simulated weightlessness in the rat

Rats, age 28 days, experiencing tail suspension in modified metabolic cages for 1, 2, and 3 wk were compared with littermate controls. Food and water consumption, urinary and fecal Ca excretion, and serum Ca were measured; hearts, fore- and hindlimb bones, skulls, and mandibles were removed for determination of wet, dry, and ash weights and Ca concentration and for histological examination. Weight gain and Ca intake and excretion were the same for both groups; both displayed net Ca gain. Suspended rats had significantly lower wet, dry, and ash weights of femora and tibiae. Dry weights of the humeri and radii/ulnae were moderately higher, and the skull and mandible dry and ash weights were significantly higher in suspended than in control rats. Cortical thickness of the femur, but not humerus, was less in suspended rats. The data are consistent with the hypothesis that bone growth is influenced by the cardiovascular changes associated with tail suspension.

Roer, Robert D.↗

NASA NTRS1990

The spectra of relativistic accretion disks - Application to A0620-00

The X-ray flux emitted from a geometrically thin, relativistic accretion disk in the steady state approximation is investigated in order to place limits on the quiescent state mass flow rate in the soft X-ray transient black hole candidate source A0620-00. Specific attention is focused on the effects associated with gravitational redshifts, Doppler shifts, and on the enhancement of the apparent accretion disk area due to gravitational light bending on the continuum spectrum. It is found that the upper limit to the mass flow rate within the inner regions of the disk, constrained by the lack of soft X-rays in the quiescent state, is about 2.8 x 10 to the -11th solar mass/yr for black hole masses greater than about 5.4 solar mass. The optical data are consistent with these upper limits provided that the inclination angle of the binary system is less than about 65 deg. The upper limits and the lack of a hard X-ray flux, together, suggest that the soft X-ray transient model based upon a mass transfer instability situated in the stellar envelope of the companion is inapplicable to A0620-00.

Fu, Albert↗

NASA NTRS1990

The peculiar velocity field in the Perseus-Pisces supercluster

Results are reported from a program to study peculiar motions of galaxies in the Per-Psc supercluster. The data set consists of newly obtained CCD photometry and published 21-cm line widths for 320 spiral galaxies. The peculiar velocities of these objects are estimated using the Tully-Fisher relation, calibrated with respect to an independent sample of cluster galaxies. Analysis shows that the principal feature of the velocity field in the Per-Psc region is a coherent streaming toward the Local Group. Nearly all the galaxies well in the foreground (cz less than about 2000 km/sec) have negtive peculiar velocities of amplitude about 1000 km/sec. A great majority of objects in the background of the supercluster, out to redshifts of about 7000 km/sec, also have very large negative peculiar velocities. The supercluster ridge itself, at a redshift or about 5000 km/sec, appears to consist of positive and negative peculiar-velocity groups of galaxies, but with negative peculiar velocities predominating both in amplitude and in number of objects involved.

Willick, Jeffrey A.↗

NASA NTRS1989

The use of models to predict potential contamination aboard orbital vehicles

A model of fungal growth on air-exposed, nonnutritive solid surfaces, developed for utilization aboard orbital vehicles is presented. A unique feature of this testable model is that the development of a fungal mycelium can facilitate its own growth by condensation of water vapor from its environment directly onto fungal hyphae. The fungal growth rate is limited by the rate of supply of volatile nutrients and fungal biomass is limited by either the supply of nonvolatile nutrients or by metabolic loss processes. The model discussed is structurally simple, but its dynamics can be quite complex. Biofilm accumulation can vary from a simple linear increase to sustained exponential growth, depending on the values of the environmental variable and model parameters. The results of the model are consistent with data from aquatic biofilm studies, insofar as the two types of systems are comparable. It is shown that the model presented is experimentally testable and provides a platform for the interpretation of observational data that may be directly relevant to the question of growth of organisms aboard the proposed Space Station.

Boraas, Martin E.↗

NASA NTRS1990

Optical backscatter characteristics of Arctic polar stratospheric clouds

Airborne lidar measurements have been made of polar stratospheric clouds (PSCs) during the Airborne Arctic Stratospheric Expedition in January-February 1989. These show the existence of a systematic relationship between the backscatter depolarization ratio and the (aerosol + molecular)/molecular backscatter ratio. The data are consistent with a two population PSC particle model.

Kent, G. S.↗

NASA NTRS1990

Chemical differences between small subsamples of Apollo 15 olivine-normative basalts

Results are presented on the chemical and petrological characterization of nine samples of an Apollo 15 mare basalt suite. The results show that all nine samples are low-silica olivine normative basalts (ONBs) similar to those described earlier for low-silica ONBs from Apollo 15 site. The samples were found to vary in texture and grain size, from fine-grained intergranular or subophitic basalts to coarse-grained granular 'microgabbros'. Several displayed macroscopic heterogeneity. Variation diagrams show that the overall trend of the data is consistent with the fractionation of olivine (plus minor Cr-spinel) from a high-MgO parent magma.

Shervais, J. W.↗

NASA NTRS1990

Sensitivity study of Space Station Freedom operations cost and selected user resources

The results of sensitivity studies performed to estimate probable ranges for four key Space Station parameters using the Space Station Freedom's Model for Estimating Space Station Operations Cost (MESSOC) are discussed. The variables examined are grouped into five main categories: logistics, crew, design, space transportation system, and training. The modification of these variables implies programmatic decisions in areas such as orbital replacement unit (ORU) design, investment in repair capabilities, and crew operations policies. The model utilizes a wide range of algorithms and an extensive trial logistics data base to represent Space Station operations. The trial logistics data base consists largely of a collection of the ORUs that comprise the mature station, and their characteristics based on current engineering understanding of the Space Station. A nondimensional approach is used to examine the relative importance of variables on parameters.

Accola, Anne↗