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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Radio observations of interplanetary magnetic field structures out of the ecliptic

Observations of the out-of-ecliptic trajectories of type III solar radio bursts have been obtained from simultaneous direction-finding measurements in two independent satellite experiments, IMP-6 with spin plane in the ecliptic and RAE-2 with spin plane normal to the ecliptic. Burst-exciter trajectories were observed which originated at the active region and then crossed the ecliptic plane at about 0.8 AU. A considerable large-scale north-south component of the interplanetary magnetic field followed by the exciters is found. The apparent north-south and east-west angular source sizes observed by the two spacecraft are approximately equal, and range from 25 deg at 600 kHz to 110 deg at 80 kHz.

Fitzenreiter, R. J.↗
NASA NTRS1979

Low frequency radio emissions from Jupiter - Jovian kilometric radiation

A new component of the Jovian radio spectrum has been observed by the plasma wave instruments on Voyager 1 and 2 at frequencies ranging from about 10 to 56 kHz or higher. This Jovian kilometric radiation is characterized by storms of emissions lasting typically 45 minutes at 56.2 kHz, however some events persist for as long as four hours. The storms usually exhibit impulsive bursts with time scales of a few seconds to several minutes, although some events show smoothly varying intensities as a function of time. High resolution frequency-time spectrograms reveal a continuum-like background with more intense, narrowband features superimposed. The narrowband, or discrete, features tend to decrease in frequency with increasing time, falling about 1 kHz in 5 to 60 seconds. The maximum power emitted assuming an isotropic radiator near Jupiter and a bandwidth for the most intense bursts of about 10 kHz is about 10 to the 19th watts. The Jovian kilometric radiation is most likely observed within + or - 45 deg of 200 deg System III longitude, lambda III, although there is a secondary maximum near lambda III = 25 deg.

Kurth, W. S.↗
NASA NTRS1980

An exploratory survey of noise levels associated with a 100kW wind turbine

Noise measurements of a 125-foot diameter, 100 kW wind turbine are presented. The data include measurements as functions of distance from the turbine and directivity angle and cover a frequency range from 1 Hz to several kHz. Potential community impact is discussed in terms of A-weighted noise levels relative to background levels, and the intrasonic spectral content. Finally, the change in the sound power spectrum associated with a change in the rotor speed in described. The acoustic impact of this size wind turbine is judged to be minimal.

Balombin, J. R.↗
NASA NTRS1979

Planetary radio astronomy observations from Voyager 2 near Jupiter

The Voyager 2 Planetary Radio Astronomy experiment to Jupiter has confirmed and extended to higher zenomagnetic latitudes results from the identical experiment carried by Voyager 1. The kilometric emissions discovered by Voyager 1 often extended to 1 megahertz or higher on Voyager 2 and often consisted of negatively, or less frequently, positively drifting narrowband bursts. On the basis of tentative identification of plasma wave emissions similar to those detected by Voyager 1, the plasma torus associated with Io appeared somewhat denser to Voyager 2 than it did to Voyager 1. The paper reports on quasi-periodic sinusoidal or impulsive bursts in the broadcast band range of wavelengths (800 to 1800 kHz). A Faraday effect appears at decametric frequencies, which probably results from propagation of the radiation near its sources on Jupiter. Finally, the occurrence of decametric emission in homologous arc families is discussed.

Warwick, J. W.↗
NASA NTRS1980

An exploratory survey of noise levels associated with a 100 kW wind turbine

During performance tests of a 125-foot diameter, 100 kW wind turbine at the NASA Plum Brook Station near Sandusky, Ohio, the opportunity arose to make exploratory noise measurements and results of those surveys are presented. The data include measurements as functions of distance from the turbine, and directivity angle, and cover a frequency range from 1 Hz to several kHz. Potential community impact is discussed in terms of A-weighted noise levels relative to background levels, and the infrasonic spectral content. Finally, the change in the sound power spectrum associated with a change in the rotor speed is described. The acoustic impact of this size wind turbine is judged to be minimal.

Balombin, J. R.↗
NASA NTRS1981

Shock-associated noise reduction from inverted-velocity-profile coannular jets

The reduction of shock-associated noise in inverted velocity profile coannular jets is investigated and quantified by making optical and acoustic measurements as a function of outer and inner stream pressure ratio combinations and interpreting noise results with the aid of new theoretical models. Schlieren photographs are obtained in three series of test conditions with a varying primary stream pressure ratio, and acoustic experiments are conducted on a polar arc radius of 3.05 m over a frequency range of 200 Hz to 80 kHz. A constant-thrust comparison is made, and data are plotted and discussed with emphasis on the variation of jet noise levels with primary stream Mach number and equivalent single jets on an absolute basis. It is shown that shock noise from the outer stream is almost eliminated when the inner stream is operated at a Mach number above unity at inverted and normal velocity profile conditions, and optical measurements indicate that for a fixed supercritical fan stream pressure ratio, the repetitive shock structure in the outer stream is minimized when the primary stream ratio becomes supercritical.

Tanna, H. K.↗
NASA NTRS1984

Noise-reduction measurements of stiffened and unstiffened cylindrical models of an airplane fuselage

Noise-reduction measurements are presented for a stiffened and an unstiffened model of an airplane fuselage. The cylindrical models were tested in a reverberant-field noise environment over a frequency range from 20 Hz to 6 kHz. An unstiffened metal fuselage provided more noise reduction than a fuselage having the same sidewall weight divided between skin and stiffening stringers and ring frames. The addition of acoustic insulation to the models tended to smooth out the interior-noise spectrum by reducing or masking the noise associated with the structural response at some of the resonant frequencies.

Willis, C. M.↗
NASA NTRS1984

Frequency encoded auditory display of the critical tracking task

The use of auditory displays for selected cockpit instruments was examined. In auditory, visual, and combined auditory-visual compensatory displays of a vertical axis, critical tracking task were studied. The visual display encoded vertical error as the position of a dot on a 17.78 cm, center marked CRT. The auditory display encoded vertical error as log frequency with a six octave range; the center point at 1 kHz was marked by a 20-dB amplitude notch, one-third octave wide. Asymptotic performance on the critical tracking task was significantly better when using combined displays rather than the visual only mode. At asymptote, the combined display was slightly, but significantly, better than the visual only mode. The maximum controllable bandwidth using the auditory mode was only 60% of the maximum controllable bandwidth using the visual mode. Redundant cueing increased the rate of improvement of tracking performance, and the asymptotic performance level. This enhancement increases with the amount of redundant cueing used. This effect appears most prominent when the bandwidth of the forcing function is substantially less than the upper limit of controllability frequency.

Stevenson, J.↗
NASA NTRS1984

The plasma wave environment of an auroral arc - Electrostatic ion cyclotron waves in the diffuse aurora

Electric field plasma wave observations were made with a sounding rocket payload in and near a quiet auroral arc. This payload was launched on March 9, 1978 from Poker Flat, Alaska. The payload trajectory was close to the magnetic meridian and passed over a 40 kR auroral arc. The present investigation is concerned with ac electric field observations in the ELF and lower VLF covering a frequency range from 2.5 Hz to 8 kHz. Attention is given to aspects of instrumentation, the general situation, a data analysis, and the obtained results. Waves were observed at low altitude in a region of downward parallel current and diffuse aurora. These waves had properties consistent with those expected for hydrogen and oxygen electrostatic ion cyclotron (EIC) waves.

Bering, E. A.↗
NASA NTRS1985

Thermionic noise measurements for on-line dispenser cathode diagnostics for linear beam microwave tubes

A test stand has been set up to measure the current fluctuation noise properties of B- and M-type dispenser cathodes in a typical TWT gun structure. Noise techniques were used to determine the work function distribution on the cathode surfaces. Significant differences between the B and M types and significant changes in the work function distribution during activation and life are found. In turn, knowledge of the expected work function can be used to accurately determine the cathode-operating temperatures in a TWT structure. Noise measurements also demonstrate more sensitivity to space charge effects than the Miram method. Full automation of the measurements and computations is now required to speed up data acquisition and reduction. The complete set of equations for the space charge limited diode were programmed so that given four of the five measurable variables (J, J sub O, T, D, and V) the fifth could be computed. Using this program, we estimated that an rms fluctuation in the diode spacing d in the frequency range of 145 Hz about 20 kHz of only about 10 to the -5 power A would account for the observed noise in a space charge limited diode with 1 mm spacing.

Holland, C.↗
NASA NTRS1986

Sporadic narrowband radio emissions from Uranus

Among several different types of radio emissions discovered at Uranus during the Voyager 2 encounter in January 1986 is a very sporadic, bursty signal which consists of very narrow bands lying in the frequency range from about 3 to 10 kHz. The bursty emission was virtually undetectable from the dayside portion of the Voyager 2 trajectory, but was observed out to beyond 300 R(U) during the outbound trajectory through the predawn sector. While the narrowband tones making up this emission are reminiscent of escaping continuum radiation observed near earth, Jupiter, and Saturn, the Uranian signals show large amplitude variations on time scales of 1 s, suggesting a very different type of generation mechanism.

Kurth, W. S.↗
NASA NTRS1987

AMPTE IRM observations of waves associated with flux transfer events in the magnetosphere

The AMPTE IRM wave instrument has been applied to the study of flux transfer events (FTE's). This initial investigation concentrates on FTE's observed in the magnetosphere during the fall of 1984. The wave morphology consists of four significant features: at frequencies below the ion gyrofrequency, magnetic fluctuations occur with amplitudes of the order of 1 nT; at frequencies from a few hertz to a few hundred hertz, electric field fluctuations are observed which have a broadband amplitude of a few millivolts per meter, which are perpendicularly polarized at the lowest frequencies, and which are partly electrostatic and partly electromagnetic; in the frequency range from 100 Hz to 10 kHz, broadband spikelike waves occur with a time-averaged amplitude of about 0.1 mV/m; and near the electron plasma frequency, bursts of waves occur at the boundaries of FTE's. In none of the 25 events surveyed does the total broadband amplitude of all the waves exceed a few millivolts per meter, an amplitude far too small to provide the dissipation required by 'traditional' reconnection models in which the dissipation region has a thickness the order of an ion gyroradius. Thus, either all of the FTE's are observed at some distance from the diffusion region, or the observable waves play no significant role in the diffusion process, or 'traditional' reconnection models do not apply to reconnection in FTE's.

Labelle, J.↗
NASA NTRS1988

Plasma wave turbulence around the shuttle - Results from the Spacelab-2 flight

During the Spacelab-2 flight, which occurred from July 29, to August 6, 1985, a spacecraft called the Plasma Diagnostics Package (PDP) was released from the shuttle to explore the plasma environment around the shuttle. The plasma wave instrument on the PDP detected a region of intense broadband turbulence around the shuttle at frequencies extending from a few Hz to about 10 kHz. The noise has broadband intensities ranging from 1 to 5 mV/m and was observed at distances of up to 400 m from the shuttle. The highest intensities occurred in the region downstream of the shuttle and along magnetic field lines passing near the shuttle. The intensities also tended to increase during periods of high thruster activity, which provides strong evidence that the noise is caused by an interaction of the ionosphere with gaseous emissions from the shuttle, similar in many respects to the interaction of a comet with the solar wind. Antenna interference patterns observed in the wideband data show that the wavelength of the turbulence is very short, a few meters or less.

Gurnett, D. A.↗
NASA NTRS1990

Continuum radiation at Uranus

One Uranian radio emission which has thus far escaped attention is an analog of continuum radiation at earth, Jupiter, and Saturn. The emission is found to be propagating in the ordinary mode in the range of one to a few kHz on the inbound leg of the Voyager 2 encounter, shortly after the magnetopause crossing. The Uranian continuum radiation is notably weak, making it more like that detected at Saturn than the extremely intense Jovian continuum radiation. The Uranian emission shows some evidence for narrow-band components lying in the same frequency regime as the continuum, completing the analogy with the other planets, which also show narrow-band components superimposed on the continuum spectrum. It is argued that the low intensity of the Uranian continuum is most likely related to the lack of a density cavity within the Uranian magnetosphere that is deep relative to the solar wind plasma density.

Kurth, W. S.↗
NASA NTRS1990

Ground based studies of the vibrational and rotational dynamics of acoustically levitated drops and shells

A substantial amount of experimental data can be gathered on the dynamics of acoustically positioned liquids in a ground-based laboratory and during short duration low-gravity parabolic flights of the KC-135. The preliminary results of a set of measurements of the static shape, of the vibrational spectrum, and the rotation equilibrium shapes of simple drops and liquid shells carried out using ultrasonic levitators working between 19 and 40 kHz is presented. The droplet diameter ranges between 1 and 5 mm, the surface tension of the liquid used varies between 25 and 70 dynes/cm, and the viscosity is changed between 1 to 1,000 cP. Of particular interest is the variation of the frequency of the fundamental mode of shape oscillation with various factors, and the effects of static drop shape deformation on the limit of stability of the axisymmetric shape of a drop in solid-body rotation.

Trinh, E. H.↗
NASA NTRS1992

Evaluation of high temperature dielectric films for high voltage power electronic applications

Three high temperature films, polyimide, Teflon perfluoroalkoxy and poly-P-xylene, were evaluated for possible use in high voltage power electronic applications, such as in high energy density capacitors, cables and microelectronic circuits. The dielectric properties, including permittivity and dielectric loss, were obtained in the frequency range of 50 Hz to 100 kHz at temperatures up to 200 C. The dielectric strengths at 60 Hz were determined as a function of temperature to 250 C. Confocal laser microscopy was performed to diagnose for voids and microimperfections within the film structure. The results obtained indicate that all films evaluated are capable of maintaining their high voltage properties, with minimal degradation, at temperatures up to 200 C. However, above 200 C, they lose some of their electrical properties. These films may therefore become viable candidates for high voltage power electronic applications at high temperatures.

Suthar, J. L.↗
NASA NTRS1992

Plasma wave observations at Neptune

Phenomena detected by the plasma wave instrument during the Voyager 2 flyby of Neptune are reviewed. Particular attention given to radio emissions, electron plasma oscillations in the solar wind upstream of the bow shock, electrostatic electron cyclotron waves and upper hybrid resonance (UHR) waves, whistler mode noise, and dust impacts. The radio emissions which occur in a broad range of about 5 to 50 kHz are considered to be generated by mode conversion from UHR waves at the magnetic equator. The inner magnetosphere has relatively low plasma wave intensities (less than 100 microV/m). Many small micron-sized dust particles which were detected striking the spacecraft had the maximum impact rate of about 280 impacts per sec at the bound ring plane crossing, and about 110 impacts per sec at the outbound ring plane crossing. Most of the particles were concentrated in a dense disk, about one thousand km thick, near the equatorial plane.

Gurnett, D. A.↗
NASA NTRS1992

A miniature high-resolution accelerometer utilizing electron tunneling

New methods have been developed to implement high-resolution position sensors based on electron tunneling. These methods allow miniaturization while utilizing the position sensitivity of electron tunneling to give high resolution. A single-element tunneling accelerometer giving a displacement resolution of 0.002 A/sq rt Hz at 10 Hz, corresponding to an acceleration resolution of 5 x 10 exp -8 g/sq rt Hz, is described. A new dual-element tunneling structure which overcomes the narrow bandwidth limitations of a single-element structure is described. A sensor with an operating range of 5 Hz to 10 kHz, which can have applications as an acoustic sensor, is discussed. Noise is analyzed for fundamental thermal vibration of the suspended masses and is compared to electronic noise. It is shown that miniature tunnel accelerometers can achieve resolution such that thermal noise in the suspended masses is the dominant cause of the resolution limit. With a proof mass of order 100 mg, noise analysis predicts limiting resolutions approaching 10 exp -9 g/sq rt Hz in a 300 Hz band and 10 exp -8 g/sq rt Hz at 1 kHz.

Rockstad, Howard K.↗