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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Ferroelectric Emission Cathodes for Low-Power Electric Propulsion

Low- or no-flow electron emitters are required for low-power electric thrusters, spacecraft plasma contactors, and electrodynamic tether systems to reduce or eliminate the need for propellant/expellant. Expellant-less neutralizers can improve the viability of very low-power colloid thrusters, field emission electric propulsion devices, ion engines, Hall thrusters, and gridded vacuum arc thrusters. The NASA Glenn Research Center (GRC) is evaluating ferroelectric emission (FEE) cathodes as zero expellant flow rate cathode sources for the applications listed above. At GRC, low voltage (100s to approx. 1500 V) operation of FEE cathodes is examined. Initial experiments, with unipolar, bipolar, and RF burst applied voltage, have produced current pulses 250 to 1000 ns in duration with peak currents of up to 2 A at voltages at or below 1500 V. In particular, FEE cathodes driven by RF burst voltages from 1400 to 2000 V peak to peak, at burst frequencies from 70 to 400 kHz, emitted average current densities from 0.1 to 0.7 A/sq cm. Pulse repeatability as a function of input voltage has been initially established. Reliable emission has been achieved in air background at pressures as high as 10(exp -6) Torr.

Kovaleski, Scott D.↗
NASA NTRS1972

Low intensity Balmer emissions from the interstellar medium and geocorona

Galactic and non-galactic components of the diffuse H-alpha and H-beta night sky emissions were resolved with a Fabry-Perot spectrometer. The non-galactic component of both lines accounts for most of the emission at galactic latitudes greater than 30 deg. The intensities of the galactic component yield values for the average ionization rate per hydrogen atom that are between 10 to the minus 15th power and 10 to the minus 14th power s sup minus 1 assuming steady state ionization.

Reynolds, R. J.↗
NASA NTRS1973

Low-intensity optical emissions from the interstellar medium

Spectrometric scans of faint optical emissions from interstellar gas are reported. Systematic variations along the galactic plane in both the intensity and radial velocity of the galactic H alpha suggest that the diffuse emission is strongly associated with three nearby galactic spiral arms.

Reynolds, R. J.↗
NASA NTRS1974

Acceleration, containment, and emission of very low energy solar flare particles

We present the first observations of protons down to 44 keV and electrons down to less than about 2 keV emitted in an impulsive solar particle event. The observations are from the Apollo 15 Subsatellite during a flare event which began on September 1, 1971. We obtain a lower limit estimate of the energy contained in protons above about 0.05 MeV in the flare. The effects of adiabatic deceleration in the interplanetary medium and dE/dx energy loss in the corona are discussed. We conclude that energetic protons may constitute a major energy release in large solar flares.

Lin, R. P.↗
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 NTRS1989

Observations of low-frequency radio emissions in the earth's magnetosphere

Electromagnetic radiation in the earth's magnetosphere was investigated for the frequency range between 10 kHz and 80 kHz, using data from the Minnesota Plasma Wave Experiment aboard the IMP 6 spacecraft. Two types of radio emissions were examined, the first being the nonthermal continuum radiation, and the second, much more impulsive, is the radiation which lies between 10 and 60 kHz. The first type of radiation was found to correlate with the enhancements of the magnetic substorm index AE and to follow the onset of the negative bay feature of the AU index by about 20 min. The second radiation was found to correlate with auroral kilometric radiation (AKR) on a time scale of about 1 min; this radiation was found to have a source direction very near that of the coincident AKR.

Filbert, Paul C.↗
NASA NTRS1990

Low-frequency radio emissions at Neptune

The Voyager 2 plasma wave receiver detected weak radio emissions from Neptune's magnetosphere in the frequency range of 3 - 60 kHz. The emissions occurred in bursts lasting for typically 1.5 hours, often occurring twice per planetary rotation. Most of these radio bursts were detected within several degrees of the magnetic equatorial plane. During the passage through the magnetosphere, electrostatic upper hybrid resonance bands were observed close to the magnetic equator in conjunction with intensifications of the radio emissions at frequencies close to and above the upper hybrid bands. Further, near closest approach, the radio emissions were observed to cross the right-hand cutoff frequency with no apparent attenuation. It is concluded that the Neptunian radio emissions below about 60 kHz are produced by mode conversion from the upper hybrid waves and propagate in the ordinary mode into beams within about 12 deg of the magnetic equator. There is also evidence of an extraordinary mode emission at about 60 kHz which is apparently generated by an entirely different source from the escaping continuum radiation.

Kurth, W. S.↗
NASA NTRS1991

Low-frequency radio emissions in the outer heliosphere

Progress is reported toward a model for the 2 and 3 kHz radio waves observed by Voyagers 1 and 2 during the 1983-1987 interval at radial distances from the sun of 17 and 13 AU, respectively. The brightness temperature and range of the volume emissivity for the radiation are calculated, and the results are compared with the characteristics of known radiation at multiples of the plasma frequency. The derived brightness temperatures are used to constrain the source of the Langmuir waves required to generate the observed emission and to rule out certain emission mechanisms. Minimum values of 3-30 micro-V/m are derived for the Langmuir wave electric field intensity and are found to be in reasonable agreement with observed values at planetary bow shocks. Path lengths required for the radiation to reach the observed levels are derived and discussed. The relevance of these ideas to possible direct observations of heliospheric boundaries is addressed.

Macek, W. M.↗
NASA NTRS1989

Low frequency acoustic emissions from large horizontal axis wind turbines

Available test data and theoretical predictions of LF noise from large wind turbines of the type to be used for energy generation are briefly summarized. The main LF noise sources are identified as tower-wake/blade interactions and rotor-plane inflow gradients. Sound-pressure time histories, measured and calculated narrow-band and rotational noise spectra, and noise radiation patterns for the WTS-4 and WWG-0600 wind turbines are presented graphically.

Hubbard, Harvey H.↗
NASA NTRS1994

Search for effects of Comet S-L 9 fragment impacts on low radio frequency emission from Jupiter

Decametric radio observations of Jupiter were made before, during, and after the impacts of the fragments of the comet S-L 9 with the planet, from the University of Florida Radio Observatory, the Maipu Radio Astronomy Observatory of the University of Chile, and the Owens Valley Radio Observatory of the California Institute of Technology. The decametric radiation was monitored at frequencies from 16.7 to 32 MHz. The minimum detectable flux densities were on the order of 30 kJy, except for that of the large 26.3 MHz array in Florida, which was about 1 kJy. There was no significant enhancement or suppression of the decametric L-burst or S-burst emission with respect to normal activity patterns that might be attributed to the fragment entries. A burst of left-hand elliptically polarized radiation having a considerably longer duration than an L-burst was observed almost simultaneously with the impact of the large fragment Q2, and another with right-hand elliptical polarization was observed simultaneously with Q1. We consider the possibility that these two bursts were emitted just above the local electron cyclotron frequencies from the southern and northern ends, respectively, of magnetic flux tubes that had been excited in some way by the proximity of fragments Q2 and Q1. A search was conducted for possible comet-enhanced Jovian synchrotron radiation at 45 MHz using a large dipole antenna array at the observatory in Chile.

Carr, T. D.↗
NASA NTRS1994

Method and apparatus for producing a substrate with low secondary electron emissions

The present invention is directed to a method and apparatus for producing a highly-textured surface on a copper substrate with only extremely small amounts of texture-inducing seeding or masking material. The texture-inducing seeding material is delivered to the copper substrate electrically switching the seeding material in and out of a circuit loop.

Jensen, Kenneth A.↗
NASA NTRS1998

Method and Apparatus for Producing a Substrate with Low Secondary Electron Emissions

The present invention is directed to a method and apparatus for producing a highly-textured surface on a copper substrate with only extremely small amounts of texture-inducing seeding of masking material. The texture-inducing seeding material is delivered to the copper substrate electrically switching the seeding material in and out of a circuit loop.

Jensen, Kenneth A.↗