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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Design, performance, and evaluation of a direct-current contactor for space nuclear electrical systems

A direct-current contactor for use in large space power systems was designed, built, and tested. It was developed to be operational in an environment of 540 C and at a pressure of 0.0001 N/sq m or lower. The contactor is rated to pass 10 A continuously and to interrupt a 20-A current at 10,000 V. It was tested to determine the corona threshold level and the leakage current at different temperatures. Also, it was tested for its closing and interruption ability.

Mueller, L. A.↗
NASA NTRS1990

The theory of an auto-resonant field emission cathode relativistic electron accelerator for high efficiency microwave to direct current power conversion

A novel method of microwave power conversion to direct current is discussed that relies on a modification of well known resonant linear relativistic electron accelerator techniques. An analysis is presented that shows how, by establishing a 'slow' electromagnetic field in a waveguide, electrons liberated from an array of field emission cathodes, are resonantly accelerated to several times their rest energy, thus establishing an electric current over a large potential difference. Such an approach is not limited to the relatively low frequencies that characterize the operation of rectennas, and can, with appropriate waveguide and slow wave structure design, be employed in the 300 to 600 GHz range where much smaller transmitting and receiving antennas are needed.

Manning, Robert M.↗
NASA NTRS1992

Direct current electrical potential measurement of the growth of small cracks

The analytical and experimental aspects of the direct-current electrical potential difference (dcEPD) method for continuous monitoring of the growth kinetics of short (50 to 500 microns) fatigue cracks are reviewed, and successful applications of the deEPD method to study fatigue crack propagation in a variety of metallic alloys exposed to various environments are described. Particular attention is given to the principle of the dcEPD method, the analytical electrical potential calibration relationships, and the experimental procedures and equipment.

Gangloff, Richard P.↗
NASA NTRS1972

Determination of work functions near melting points of refractory metals by using a direct-current arc

Effective work functions of refractory metals at temperatures near their melting points were determined by using a direct-current arc. A metal wire connected as the cathode was melted by striking an arc discharge in an argon atmosphere. A melted sphere was formed with a definite emitting area which was calculated from the sphere diameter measured after terminating the arc. Effective work functions were calculated from the Richardson-Dushman equation by using this emission area. The procedure is experimentally advantageous because surface cleanliness of the specimen is not critical, high vacuum is not required, and the anode-cathode spacing is not critical.

Gordon, W. A.↗
NASA NTRS1965

Zener diode controls switching of large direct currents

High-current zener diode is connected in series with the positive input terminal of a dc supply to block the flow of direct current until a high-frequency control signal is applied across the zener diode. This circuit controls the switching of large dc signals.

Source record↗
NASA NTRS1985

Electrical measurements in the atmosphere and the Ionosphere over an active thunderstorm. II - Direct current electric fields and conductivity

On August 9, 1981, a series of three rockets was launched over an air mass thunderstorm off the eastern seaboard of Virginia while simultaneous stratospheric and ground-based electric field measurements were made. The conductivity was substantially lower at most altitudes than the conductivity profiles used by theoretical models. Direct current electric fields over 80 mV/m were measured as far away as 96 km from the storm in the stratosphere at 23 km altitude. No dc electric fields above 75 km altitude could be identified with the thunderstorm, in agreement with theory. However, vertical current densities over 120 pA/sq m were seen well above the classical 'electrosphere' (at 50 or 60 km). Frequent dc shifts in the electric field following lightning transients were seen by both balloon and rocket payloads. These dc shifts are clearly identifiable with either cloud-to-ground (increases) or intercloud (decreases) lightning flashes.

Holzworth, R. H.↗
NASA NTRS1990

Impulsive phase heating by uni-directional current systems in solar flares

The possibility of producing rapid heating of a substantial coronal volume by current dissipation, driven by a tearing instability associated with a single unidirectional current system, is investigated. For the fast tearing mode, it is found that, for initial growth rates gamma(f) equal or less than 0.3/s, the electron heating is offset by convective losses, resulting in a very slow temperature rise, and hard X-ray emitting temperatures are never realized. For the larger growth rates, heating from 10 to the 7th to 10 to the 8th K can be achieved in a few seconds; however, in this regime, the maximum volume heated is some three to five orders of magnitude less than the volume of heated material that is inferred from hard X-ray emission measures. The results suggest that to achieve the required heating for the fast tearing mode, a more complicated geometry involving multiple small-scale, oppositely directed current channels may be necessary.

La Rosa, T. N.↗
NASA NTRS1993

Direct-Current Monitor With Flux-Reset Transformer Coupling

Circuit measures constant or slowly-varying unidirectional electrical current using flux-reset transformer coupling. Measurement nonintrusive in sense that no need for direct contact with wire that carries load current to be measured, and no need to install series resistive element in load-current path. Toroidal magnetic core wrapped with coil of wire placed around load-current-carrying wire, acts as transformer core, load-current-carrying wire acts as primary winding of transformer, and coil wrapped on core acts as secondary winding.

Canter, Stanley↗
NASA NTRS1966

Standard arc welders provide high amperage direct current source

Standard arc welders or power supplies are hooked up in parallel or series connections to obtain an adequate supply of current or voltage for various purposes. This method provides maximum flexibility in a wide range of voltages and currents.

Beasley, W. D.↗