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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Global distribution of stratospheric aerosols by satellite measurements

A description is given of the first-ever global stratospheric aerosol climatology which is being developed by the earth-orbiting SAM II and SAGE satellite-based sensors. These sensors use the technique of solar occulation; that is, for every spacecraft sunrise and sunset, the modulation of solar intensity caused by the intervening earth-limb is measured. These data are mathematically inverted to yield vertical profiles of aerosol extinction coefficients with 1 km resolution. The data show seasonal variations which are similar in each hemisphere, with strong correlation between aerosol extinction and the corresponding temperature field. Typical values of extinction in the stratosphere are found to be about 0.0001 to 0.0002 per km at 1 micrometer; stratospheric optical depths at this wavelength are about 0.002. The peak extinction in the stratospheric aerosol layer follows the tropopause with altitude, with peak extinction ratios about 10 km above the local tropopause.

Mccormick, M. P.↗
NASA NTRS1980

Time-dependent lunar density models

Simple models of the geochemical and geophysical evolution of the moon were constructed with the particular aim of investigating the mass density distribution within the moon as a function of time. The strongly inverted (densest material on top) density distribution resulting from fractional crystallization of the lunar magma ocean was found to rearrange itself into a highly stable stratification. Density stratification due to compositional variation dominated gravitational stability; thus, thermally driven convection was found to be suppressed in regions with relaxed (rearranged so as to minimize the gravitational potential energy) compositional density variation. The suppression of convection as a heat transfer process results in considerable modification of thermal evolution. The models produced sufficient density segregation from magma oceans of a few hundred km thickness, such that relaxation to the most stable rearrangement yielded a polar moment of inertia approximating that measured for the present-day moon. Thus, lunar models matching moment-of-inertia constraints but lacking a metallic core are motivated.

Herbert, F.↗
NASA NTRS1981

Review of auroral particle precipitation

An attempt to establish the precipitation signal of an auroral arc based on data gathered by sounding rockets and satellites is presented. Rocket sounding is useful for altitudes up to a few thousand km, the S3-3 satellite from 4000-8000 km, and satellites in GEO for the equatorial plane. Inverted V structures have been observed down to a few km in width by rockets, and occur on open as well as closed field lines. Observations of bursts of field-aligned electrons, simultaneous ion and electron precipitation, counter-streaming electrons and conics have been interpreted as indicating ac phenomena. The S3-3 has recorded the presence of upward flowing ions, beams, and conics, downward flowing ions, and counter-streaming electrons in the 4000-8000 km region. Finally, plasma injections at synchronous orbit have been identified as the equatorial plane signature of any auroral substorm.

Arnoldy, R. L.↗
NASA NTRS1981

Formation of auroral arcs by plasma sheet processes

It is noted that, in the distant plasma sheet, it is likely that curvature drift is the most important source of drift parallel to the electric field, leading to what is commonly called Fermi acceleration of the particles. The energization mechanism here is proportional to the neutral sheet current density. It is a form of field-aligned acceleration, with rapid lowering of mirror points, caused by the transverse electric field in the plasma sheet. It is noted that the process will work for both negative and positive particles. A filamentation of the neutral current sheet is postulated. Here, the maximum energization by curvature drift and the accompanying intense precipitation will form an auroral band or arc along the sheet of magnetic field lines that maps out to the local enhancement of the crosstail current, explaining inverted V events.

Heikkila, W. J.↗
NASA NTRS1981

Observations pertaining to the generation of auroral kilometric radiation

Auroral kilometric radiation (AKR) observations that have determined the propagation mode or polarization of the radiation and the detailed intensity distribution of the AKR emission cone are discussed. Attention is also given to correlations between AKR with discrete field-aligned currents. It is noted that these observations have helped to identify the auroral particle population most likely responsible for the generation of AKR and the possible sources of the free energy that drives the instability. Thus far, AKR has not been observed simultaneously with large electrostatic waves. Auroral zone current systems are thought to be intimately involved in the generation of AKR. In particular, the most probable source of energy for AKR is the precipitating inverted-V auroral electron distribution.

Green, J. L.↗
NASA NTRS1981

Solar-pumped electronic-to-vibrational energy transfer lasers

The possibility of using solar-pumped lasers as solar energy converters is examined. The absorbing media considered are halogens or halogen compounds, which are dissociated to yield excited atoms, which then hand over energy to a molecular lasing medium. Estimates of the temperature effects for a Br2-CO2-He system with He as the cooling gas are given. High temperatures can cause the lower energy levels of the CO2 laser transition to be filled. The inverted populations are calculated and lasing should be possible. However, the efficiency is less than 0.001. Examination of other halogen-molecular lasant combinations (where the rate coefficients are known) indicate efficiencies in all cases of less than 0.005.

Harries, W. L.↗
NASA NTRS1982

Ion distribution effects of turbulence on a kinetic auroral arc model

An inverted-V auroral arc structure plasma-kinetic model is extended to phenomenologically include the effects of electrostatic turbulence, with k-parallel/k-perpendicular being much less than unity. It is shown that, unless plasma sheet ions are very much more energetic than the electrons, anomalous resistivity is not a large contributor to parallel electrostatic potential drops, since the support of the observed potential drop requires a greater dissipation of energy than can be provided by the plasma sheet. Wave turbulence can, however, be present, with the ion cyclotron turbulence levels suggested by the ion resonance broadening saturation mechanism of Dum and Dupree (1970) being comparable to those observed on auroral field lines. The diffusion coefficient and net growth rate are much smaller than estimates based solely on local plasma properties.

Cornwall, J. M.↗
NASA NTRS1981

Flame structure in a swirl stabilized combustor inferred by radiant emission measurements

Results of measurements of time-averaged chemiluminescent emissions from CH, OH, and CO2 and of Na tracer emissions along lateral lines-of-sight through a cylindrical premixed, swirl-stabilized combustor are reported. Assuming axial symmetry and small optical depth, raw data are inverted to obtain local emission levels from these species as a function of radius. The chemiluminescent emissions are interpreted as signatures of chemical reaction and used in determining the regions of reactions and heat release in the combustor. The data are compared with composition and velocity data obtained in the combustor for identical operating conditions. The results demonstrate that reaction occurs in a relatively narrow, turbulent flame-like combustion zone which begins upstream of the time-averaged location of the swirl-induced recirculation zone and propagates around and laterally away from the recirculation zone into the unburned gas.

Beyler, C. L.↗
NASA NTRS1982

An equivalent layer magnetization model for the United States derived from Magsat data

Long wavelength anomalies in the total magnetic field measured by Magsat over the United States and adjacent areas are inverted to an equivalent layer crustal magnetization distribution. The model is based on an equal area dipole grid at the earth's surface. Model resolution, defined as the closest dipole spacing giving a resolution having physical significance, is about 220 km for Magsat data in the elevation range 300-500 km. The magnetization contours correlate well with large-scale tectonic provinces.

Mayhew, M. A.↗
NASA NTRS1982

Satellite observations of suprathermal electron bursts

Data from the ISIS 2 satellite are used to study the spatial distribution of the suprathermal electron bursts discovered by high-altitude sounding rockets. It is found that the bursts form an integral part of the boundary plasma sheet and are linked with the formation of discrete auroral arcs. The maximum energy of the bursts is always below the peak energy in neighboring discrete forms, and it appears that if the bursts fail to reach the minimum energy found to be necessary to sustain a discrete arc they collapse within a few seconds. It is suggested that in a pass across the auroral oval the overall envelope of the maximum energy in bursts and the peak energy in discrete auroral forms reflect the variation of the available acceleration (perhaps a parallel electric potential) across the auroral oval while the energy structure in individual forms is a function of the nonlinear processes which sustain them. This explanation appears to resolve the apparent discrepancy in scale thickness between rocket and satellite inverted V's.

Johnstone, A. D.↗
NASA NTRS1982

An equivalent layer magnetization model for the United States derived from satellite altitude magnetic anomalies

Long wavelength magnetic anomalies measured by the Pogo series satellites at altitudes 400-700 km over the United States and adjacent areas are inverted to an equivalent layer magnetization model based on an equal area dipole source array at the earth's surface. Minimum source spacing giving a stable solution and a physically meaningful magnetization distribution is 300 km, and a scheme is presented for effectively sampling the distribution on a grid twice as fine. The model expresses lateral variation in the vertical integral of magnetization and is a starting point for models of lateral variation in the form of the magnetization-depth curve in the magnetic crust. The magnetization model contours correlate with large-scale tectonic features, and in the western part of the country, probably reflect Curie isotherm undulations.

Mayhew, M. A.↗
NASA NTRS1982

Collisional narrowing in the optically pumped CH3OH and CH3F lasers

The gain linewidth of the optically pumped CH3F laser is observed to narrow and rebroaden with the addition of He. In addition, the same effect is observed in the CH3OH laser with the addition of the polyatomic buffer gases SF6 and CS2. These results offer conclusive evidence of the Dicke narrowing phenomena in these inverted pure rotational transitions. The effect is observed using a high harmonic mixing technique in a Schottky barrier diode.

Lawandy, N. M.↗
NASA NTRS1981

Satellite profile measurements of stratospheric ozone

A description is presented of preliminary results obtained in connection with the Stratospheric Aerosol and Gas Experiment (SAGE). SAGE, which uses a limb scanning solar radiometer, is an experiment aboard the Applications Explorer Mission 2 spacecraft which was launched on February 18, 1979. The instrument utilizes the technique of solar occultation to measure limb-path atmospheric extinction profiles which are inverted to yield vertical profiles of various atmospheric constituents in the latitude range from 79 deg South to 79 deg North. The ozone spectral channel is centered at 0.60 micrometers in the middle of the Chappuis absorption band. The general characteristics of the ozone profile measurements are shown in a graph. Each profile represents a day's average of approximately 15 measurements at the latitude band indicated. The SAGE ozone measurements are generating a highly detailed picture of the stratospheric ozone distribution.

Mccormick, M. P.↗
NASA NTRS1982

Simulation, flight performance and control of Dynamics Explorers-A and -B spacecraft

This paper presents the results obtained from a study conducted to evaluate the dynamic behavior of Dynamics Explorers-A and -B spacecraft. The effects of environmental torques on the spacecraft motion, momentum buildup due to these torques, and the long appendages on the main body motion are studied using numerical simulations. The numerical results are compared with flight data and are found to be in good agreement. A control philosophy for DE-B to minimize the pitch axis drift is developed. The performance of DE-B in inverted mode and during the inversion maneuver as well as in the normal mode are studied. The spin ripple effect on DE-A due to the long appendages is analyzed and the results are correlated with flight data.

Sellappan, R. G.↗
NASA NTRS1982

A large normal-fault earthquake at the junction of the Tonga trench and the Louisville ridge

Long-period vertical-component Rayleigh waves are inverted in order to determine the source mechanism of the October 10, 1977 earthquake that occurred in the oceanic plate at the junction of the Tonga-Kermadec trench systems with the aseismic Louisville ridge. The cause was predominantly normal faulting on a plane striking roughly parallel to the trench, with a seismic moment of 1.7 x 10 to the 27th dyn cm. A focal depth of 20 km is determined by waveform modeling, but the actual rupture may have extended to 30 or 40 km. Two sources separated by 16 s comprised the event, which experienced an inferred rupture velocity of 3.5 km/sec. The interpretation that the earthquake was caused by gravitational pull due to the sinking slab implies that the Louisville ridge causes some degree of local decoupling between the plates. This event may be associated with the breakup of the Osbourn seamount. Alternatively, the earthquake may have resulted from tensional plate bending stress, as implied by its relatively shallow depth.

Eissler, H.↗
NASA NTRS1981

Large-area silicon-on-ceramic substrates for low-cost solar cells

The SCIM (Silicon-Coating-By-Inverted Meniscus) process to produce SOC (silicon-on-ceramic) substrates has been investigated for various growth conditions and substrate velocities (4-30 cm/min). Slotted mullite-based substrates (10-cm-wide by 100-cm-long) have been coated with smooth, continuous silicon layers, with thicknesses in the range from 100 to 300 microns. Thermal stress (which can be a problem at low velocities) is prevented by proper thermal design. The highest SCIM-coated SOC cell efficiencies to date are 7.5% (AM1, AR) as compared to 10.5% (AM1, AR) for dip-coated SOC cells. Substantial improvements in cell efficiency are expected when high purity parts are installed in the SCIM-coater.

Schuldt, S. B.↗
NASA NTRS1982

Two-dimensional inversion technique for satellite airglow data

A technique is described which inverts satellite airglow data producing volume emission rates as functions of altitude and position. The inversion is applied to data obtained when the spacecraft spins in the orbital plane. The altitude and height resolutions are constrained by the geometry chosen to simplify the inversion. The limitations of the method and its implementation on data from the Visual Airglow Experiment onboard the Atmosphere Explorer satellite are discussed. Sample maps of brightness and volume emission rates are shown.

Fesen, C. G.↗
NASA NTRS1983

Reduced Aircraft-Engine Noise

Shock structure modified to eliminate associated noise. Shock wave repeats in supersonic flow adjoining subsonic flow layer. When supersonic layer is added, shock wave is partially transmitted at interface. Result is almost total elimination of shock pattern after one or two reflections. Technique applicable to inverted as well as to normal-velocity-profile coannular jets and used to eliminate or reduce shock noise of turbojet engines.

Tanna, H. K.↗