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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Generation of large scale field-aligned density irregularities in ionospheric heating experiments

Threshold and growth rate for stimulated Brillouin scattering are calculated for a uniform magnetoplasma. These are then compared with the threshold and growth rate of a new thermal instability in which the nonlinear Lorentz force felt by the electrons at the beat frequency of the two electromagnetic waves is replaced by a pressure force due to differential heating in the interference pattern of the pump wave and the generated electromagnetic wave. This thermal instability, which is still essentially stimulated Brillouin scattering, has a threshold which is especially low when the propagation vector of the beat wave is almost normal to the magnetic field. The threshold is then considerably lower than the threshold for normal stimulated Brillouin scattering and therefore this new instability is probably responsible for the generation of large scale field aligned irregularities and ionospheric spread F.

Fejer, J. A.↗
NASA NTRS1973

Two-component, self-aligning laser vector velocimeter

A newly developed laser Doppler velocimeter is described. The basic optical component of the instrument is a two-dimensional ultrasonic Bragg cell. It is shown that use of this Bragg cell simplifies the optics usually required for the more conventional velocimeters, allows measurement of two-vector components of velocity, requires no adjustment of alignment mirrors, and enables both velocity component signals to be detected with a single detector. Some results from experiments using this velocimeter in an atmospheric application are described.

Farmer, W. M.↗
NASA NTRS1974

Aligned magnetohydrodynamic solution for solar wind flow past the earth's magnetosphere

Exact numerical solutions of the MHD equations for a perfect dissipationless gas with aligned magnetic field are given for conditions representative of steady supersonic solar wind flow past an axisymmetric model of the earth's magnetosphere. The solution is based on use of a transformation that relates without approximation the equations of magnetohydrodynamics to those of gasdynamics of a pseudogas that has an unusual equation of state. The results confirm the applicability of the previously existing gasdynamic solutions for the typically modest intensities of the interplanetary magnetic field that lead to Alfven Mach numbers of about 10 or greater. For smaller values, however, significant effects are indicated with the flanks of the bow wave moving away from the earth and the nose moving toward the earth. The results are consistent with direct observations in space.

Spreiter, J. R.↗
NASA NTRS1975

Performance of graphite fiber-reinforced polyimide composites in self-aligning plain bearings to 315 C

A 50/50 (weight percent) composite of graphite fibers and polyimide was studied in self-aligning plain bearings oscillating + or - 15 degrees at 1 hz. The friction coefficient was 0.15 + or - 0.05 at 250 C, and 0.05 + or - 0.02 at 315 C. Best results were obtained with a molded composite liner with chopped graphite fibers randomly oriented in the composite. The specific wear rate is given. It was found that the dynamic unit load capacity was higher for a composite bushing (thin liner), than for a composite ball.

Sliney, H. E.↗
NASA NTRS1975

Field-aligned electric currents and their measurement by the incoherent backscatter technique

Field aligned electric currents flow in the magnetosphere in many situations of fundamental geophysical interest. It is shown here that the incoherent backscatter technique can be used to measure these currents when the plasma line can be observed. The technique provides a ground based means of measuring these currents which complements the rocket and satellite ones.

Bauer, P.↗
NASA NTRS1974

Axial alignment fixtures for tension tests of threaded specimens

Description of two axial alignment fixtures that are capable of providing very low load application eccentricity in tension tests of threaded notched cylindrical specimens. The described fixtures are simple in design, very compact, and free from the effects of friction. Also, an evaluation procedure is presented that can be used to qualify any fixture for use in sharp notch tensile tests.

Jones, M. H.↗
NASA NTRS1975

Rocket measurement of auroral electron fluxes associated with field-aligned currents

A rocket-borne experiment using an electron and proton energy spectrometer is described, with particular reference to calibration and data reduction procedures. An upper limit of the measured proton flux is found to be 1,000,000 protons per sq cm sec sr keV. The characteristics of particle precipitation observed during flight over the auroral band are evaluated. The electron flux in regions of maximum flux tends to be the most field-aligned in the energy interval with the highest intensity.

Pazich, P. M.↗
NASA NTRS1975

Observations of an intense field-aligned thermal ion flow and associated intense narrow band electric field oscillations

An investigation is conducted concerning the conditions encountered during a Javelin sounding rocket experiment conducted on Apr. 3, 1970 at Fort Churchill, Canada. Evidence is presented that near the equatorward edge of the auroral arc an intense beam of cold plasma ions was flowing parallel to the earth's magnetic field. The beam was associated with intense narrow band electric field oscillations near the local ion gyrofrequency. The data support the hypothesis that intense electrostatic ion cyclotron waves were driven unstable by field-aligned currents.

Bering, E. A.↗
NASA NTRS1976

Net field-aligned currents observed by Triad

The existence of a net current flowing into or away from the ionosphere in the current layer is inferred from the Triad-satellite magnetometer observation of a steplike level shift in the east-west component of the magnetic field at 800 km altitude. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side. The current layer is identified as the same layer that was observed by the Ogo 5 satellite at much higher altitudes. Thus, the field-aligned currents observed by Triad must be considered to be an important element in the electrodynamical coupling between the distant magnetosphere and the ionosphere.

Sugiura, M.↗
NASA NTRS1976

Field-aligned precipitation of greater than 30-keV electrons

A search through 2-3 months of data from Ogo 6 has revealed about 10 cases of field-aligned precipitation of electrons at energies greater than 30 keV. Brief descriptions are given of the four most spectacular of these events, in which the ratio between precipitated and trapped fluxes reached about 100 in one case. Preliminary indications are that such events occur mainly in the evening and midnight sectors and at high geomagnetic latitudes (usually at or above the trapping boundary for electrons with energies greater than 30 keV).

Williams, D. J.↗
NASA NTRS1976

Ground state properties of solid and liquid spin-aligned atomic hydrogen

Calculations of the ground state energy in the solid phase were performed with the aid of a variational approach. The Morse potential form of the atomic triple potential computed by Kolos and Wolniewicz (1965) was employed for the calculations. The ground state energies of both the liquid and solid phases of spin-aligned atomic hydrogen around the volume of the transition are presented in a graph.

Danilowicz, R. L.↗
NASA NTRS1976

Simultaneous observations of field-aligned currents and particle fluxes in the post-midnight sector

The paper presents several examples of simultaneous measurements of electrons and positive ions (5 eV to 15 eV) and of magnetic field perturbations due to field-aligned currents made on the polar-orbiting ISIS-2 satellite at 1400 km altitude in the early morning local time (MLT) sector. There is a good general correspondence between changes in the gradient of the E-W component of the magnetic field along the spacecraft orbit and changes in the character of the low-energy electron fluxes. The equatorward region of outward current flow in this post-midnight sector is spatially coincident with the isotropic precipitation associated with the low-altitude plasma sheet. In cases examined, electron current density always exceeds positive ion current density by a factor of 10 and usually by a factor of over 100.

Klumpar, D. M.↗
NASA NTRS1977

Observation of a structured auroral field-aligned current system

A rocketborne experiment package was launched over a structured auroral arc from Poker Flat, Alaska, at 0722 UT on February 25, 1972. The results of the flight vector-magnetometer data have been detailed by Casserly and Cloutier (1975), who report the detection of a pair of oppositely directed Birkeland current sheets associated with the auroral band. This association has now been extensively investigated, and it has been shown that some observed structures in the arc due to the presence of a fold are also evident in the Birkeland current system. In particular, the field-aligned current to the east of the fold is at a higher geomagnetic latitude than the current to the west of the fold. Variations in other model current parameters are also shown to be well correlated with changes in the visual arc system.

Casserly, R. T., Jr.↗
NASA NTRS1978

Structural alignment sensor

Comparative Michelson interferometers are discussed as well as the operating range potential of a structural alignment sensor (SAS) which requires only one laser mode. Schematics are presented for the distance measurement logic, the basic SAS system, the SAS optical layout, the coarse measurement signal processor, and the measured range resolution.

Davis, L.↗
NASA NTRS1978

Structural Alignment Sensor Feasibility Demonstration

A structural alignment sensor (SAS) was developed for use with large deployable antenna systems for contour measurement and/or active control. The SAS is a laser ranging system using frequency modulation and accurate phase measurement to determine distance. Work was done with a CO2 and HeNe laser. The capability of the SAS to measure antenna rib contours was studied over ranges of 50 meters to a resolution of 100 microns. Initial resolution data was taken with the CO2 system. This data shows that it will indeed meet the SAS requirements. The development of the HeNe system was initiated because it offers substantial improvement in size, weight, and power over the CO2 system. The final demonstration was made with the HeNe system and it too showed that the SAS requirements could be met with this alternate approach. The projection of these results to a conceptual design for a flight system and its application are described.

Anderson, R. H.↗
NASA NTRS1979

Field-aligned currents and large-scale magnetospheric electric fields

The existence of field-aligned currents (FAC) at northern and southern high latitudes was confirmed by a number of observations, most clearly by experiments on the TRIAD and ISIS 2 satellites. The high-latitude FAC system is used to relate what is presently known about the large-scale pattern of high-latitude ionospheric electric fields and their relation to solar wind parameters. Recently a simplified model was presented for polar cap electric fields. The model is of considerable help in visualizing the large-scale features of FAC systems. A summary of the FAC observations is given. The simplified model is used to visualize how the FAC systems are driven by their generators.

Dangelo, N.↗
NASA NTRS1979

Field-aligned currents, convection electric fields, and ULF-ELF waves in the cusp

Nearly simultaneous observations from the Triad and Hawkeye satellites over the Southern Hemisphere, at low altitudes near the noon meridian and close to the usual polar cusp latitudes, show that in and near the polar cusp there exist several relationships between field-aligned currents (FACs), convection electric fields, ULF-ELF magnetic noise, broadband electrostatic noise and interplanetary magnetic fields. The most important findings are (1) the FACs directed into the ionosphere in the noon-to-dusk local time sector and directed away from the ionosphere in the noon-to-dawn local time sector and identified as region-1 permanent FACs (Iijima and Potemra, 1976a) and are located equatorward of the regions of antisunward (westward) convection; (2) the observations are consistent with a two-cell convection pattern symmetric in one case (throat positioned at noon) and asymmetric in another (throat located in a sector on the forenoon side in juxtaposition to the region of strong convection on the afternoon side); and (3) fine-structure FACs are responsible for the generation of ULF-ELF noise in the polar cusp.

Saflekos, N. A.↗
NASA NTRS1979

HF-induced parametric decay in presence of field-aligned irregularities

A nonlinear theory for the saturation of the HF-induced parametric decay instability is formulated in terms of the normal modes of a field-aligned plasma wave duct. Coupling coefficients between modes are derived, and a saturation spectrum is computed numerically for a typical irregularity. The computed spectrum shows that unstable waves may propagate at larger angles to the magnetic field than would be the case in a regular medium. The relevance of this work to the experiment of Muldrew and Showen (1977), concerning the height of the HF-induced plasma line at Arecibo, is discussed. A possible explanation is also found for the 'decay line' feature in comparison with the 'broad bump' in the observed backscatter spectrum.

Rypdal, K.↗