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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

A solid state converter for measurement of aircraft noise and sonic boom

The problems inherent in present systems of instrumentation for measuring aircraft noise and sonic boom include limited frequency response, expensive connecting cables, sensitivity to cable length and type, high sensitivity to environmental conditions, and additional limitations of individual system components. Furthermore, differing requirements have resulted in the use of two different systems for aircraft noise and sonic boom measurements respectively. To alleviate these difficulties a unified system of instrumentation suitable for both types of measurements was developed. The system features a new solid state converter connected to a zero drive amplifier. The system was found insensitive to cable length and type up to at least 1000 ft and requires no impedance matching networks. The converter itself has flat frequency response from dc to 28 kHz (- 3 db), dynamic range of 72 db, and noise floor of 50 db in the band 22.4 Hz to 22.4 kHz.

Zuckerwar, A. J.↗
NASA NTRS1972

Electrodes for the thermionic converters, phase 2 - 3

The characteristics of electrodes for thermionic converters are discussed. A metal/ceramic Marchuk tube was constructed and operated with a quiescent cesium vapor plasma corresponding to cesium liquid reservoir temperatures from 376 to 427 K. The work function characteristics of tantalum test emitters coated with anodic films were measured to evaluate the applicability of the materials as the collector surface in a plasma mode thermionic converter. Work function minimum values between 1.4 and 1.5 electron volts were observed. The effect of the electronegative surface layers was partially obscured by additive vapor impurities detected by the clean tantalum reference emitter.

Desteese, J. G.↗
NASA NTRS1972

Feasibility study of oxygen-dispensing emitters for thermionic converters, phase 1

A metal/ceramic Marchuk tube was used to measure work functions of oxygen-doped tantalum, to determine applicability of the material to plasma-mode thermionic converters. Oxygen-doped tantalum was shown to increase in work function monotonically with oxygen doping in the range 0.1 to 0.3 atomic percent. Oxygenated test emitters were run at an average temperature of 2165 K and a T/T sub Cs ratio -5.8 to observe the influence of oxygen depletion. Bare work function decreased with outgassing of oxygen. Projections were made based on outgassing kinetics and area/volume ratios to calculate the longevity of oxygen doping in a practical converter. Calculations indicated that the program goal of 10,000 hr could be achieved at 1800 K with an initial oxygen doping of 1 atomic percent and a practical emitter area/volume ratio.

Desteese, J. G.↗
NASA NTRS1973

ASDTIC control and standardized interface circuits applied to buck, parallel and buck-boost dc to dc power converters

Versatile standardized pulse modulation nondissipatively regulated control signal processing circuits were applied to three most commonly used dc to dc power converter configurations: (1) the series switching buck-regulator, (2) the pulse modulated parallel inverter, and (3) the buck-boost converter. The unique control concept and the commonality of control functions for all switching regulators have resulted in improved static and dynamic performance and control circuit standardization. New power-circuit technology was also applied to enhance reliability and to achieve optimum weight and efficiency.

Schoenfeld, A. D.↗
NASA NTRS1973

Design, development, and fabrication of a electronic analog microminiaturized electronic analog signal to discrete time interval converter

The microminiaturization of an electronic analog signal to discrete time interval converter is presented. Discrete components and integrated circuits comprising the converter were assembled on a thin-film ceramic substrate containing nichrome resistors with gold interconnections. The finished assembly is enclosed in a flat package measuring 3.30 by 4.57 centimeters. The module can be used whenever conversion of analog to digital signals is required, in particular for the purpose of regulation by means of pulse modulation. In conjunction with a precision voltage reference, the module was applied to control the duty cycle of a switching regulator within a temperature range of -55 C to +125 C, and an input voltage range of 10V to 35V. The output-voltage variation was less than + or - 300 parts per million, i.e., less than + or - 3mV for a 10V output.

Schoenfeld, A. D.↗
NASA NTRS1974

A solid-state converter for measurement of aircraft noise and sonic boom

A solid-state converter, used in a system of instrumentation for measuring aircraft noise and sonic boom, features a dual-gate FET mixer and an output stage designed for compatibility with a zero drive amplifier. With a half-inch condenser microphone the converter itself has an operating frequency range from dc-28 kHz (-3 dB), a dynamic range of 72 dB, and a noise floor of 50 dB in the band from 22.4 Hz to 22.4 kHz; the system requires no impedance matching networks and is insensitive to cable length up to at least 3000 ft.

Zuckerwar, A. J.↗
NASA NTRS1973

The 12 GHZ image and sum enhanced mixer diode converter

The development, fabrication, and testing of five image and sum frequency enhanced mixed diode converters are discussed. Design specifications include a RF band of 11.7 to 12.2 GHz, an IF band of 1.0 to 1.5 GHz, an IF return loss of 10 db, band center of 6.2 db, band edge of 6.7 db, LO frequency of 10.7 GHz, LO power of 20 dbm, and a conversion gain of 15.8 db. The converter is also capable of 30 db below desired signals for the third order intermodulation product level for twelve -75 dbm carriers.

Degenford, J. E.↗
NASA NTRS1975

Sequential color video to parallel color video converter

The engineering design, development, breadboard fabrication, test, and delivery of a breadboard field sequential color video to parallel color video converter is described. The converter was designed for use onboard a manned space vehicle to eliminate a flickering TV display picture and to reduce the weight and bulk of previous ground conversion systems.

Source record↗
NASA NTRS1975

Spectral reflectance properties of electroplated and converted zinc for use as a solar selective coating

The spectral reflectance properties of electroplated and chemically converted zinc were measured for both chromate and chloride conversion coatings. The reflectance properties were measured for various times of conversion and for conversion at various chromate concentrations. The values of absorptance, integrated over the solar spectrum, and of infrared emittance, integrated over black body radiation at 250 F were then calculated from the measured reflectance values. The interdependent variations of absorptance and infrared emittance were plotted. The results indicate that the optimum combination of the highest absorptance in the solar spectrum and the lowest emittance in the infrared of the converted electroplated zinc is produced by chromate conversion at 1/2 concentration of the standard NEOSTAR chromate black solution for 0.50 minute or by chloride conversion for 0.50 minute.

Mcdonald, G. E.↗
NASA NTRS1976

Low work function silicon collector for thermionic converters

To improve the efficiency of present thermionic converters, single crystal silicon was investigated as a low work function collector material. The experiments were conducted in a test vehicle which resembled an actual thermionic converter. Work function as low as 1.0eV was obtained with an n-type silicon. The stabilities of the activated surfaces at elevated temperatures were tested by raising the collector temperature up to 829 K. By increasing the Cs arrival rate, it was possible to restore the originally activated low work function of the surface at elevated surface temperatures. These results, plotted in the form of Rasor-Warner curve, show a behavior similar to that of metal electrode except that the minimum work function was much lower with silicon than with metals.

Chang, K. H.↗
NASA NTRS1975

Spectral reflectance properties of electroplated and converted zinc for use as a solar selective coating

The spectral reflectance properties of electroplated and chemically converted zinc were measured for both chromate and chloride conversion coatings. The reflectance properties were measured for various times of conversion and for conversion at various chromate concentrations. The values of absorptance, alpha, integrated over the solar spectrum, and of infrared emittance, epsilon, integrated over black body radiation at 250 F were then calculated from the measured reflectance values. The interdependent variations of alpha and epsilon were plotted. The results indicate that the optimum combination of the highest absorptance in the solar spectrum and the lowest emittance in the infrared of the converted electroplated zinc is produced by chromate conversion at 1/2 concentration of the standard NEOSTAR chromate black solution for 0.50 minute or by chloride conversion for 0.50 minute.

Mcdonald, G. E.↗
NASA NTRS1977

Nuclear thermionic converter

Efficient nuclear reactor thermionic converter units are described which can be constructed at low cost and assembled in a reactor which requires a minimum of fuel. Each converter unit utilizes an emitter rod with a fluted exterior, several fuel passages located in the bulges that are formed in the rod between the flutes, and a collector receiving passage formed through the center of the rod. An array of rods is closely packed in an interfitting arrangement, with the bulges of the rods received in the recesses formed between the bulges of other rods, thereby closely packing the nuclear fuel. The rods are constructed of a mixture of tungsten and thorium oxide to provide high power output, high efficiency, high strength, and good machinability.

Phillips, W. M.↗
NASA NTRS1977

High efficiency thermionic converter studies

Research in thermionic energy conversion technology is reported. The objectives were to produce converters suitable for use in out of core space reactors, radioisotope generators, and solar satellites. The development of emitter electrodes that operate at low cesium pressure, stable low work function collector electrodes, and more efficient means of space charge neutralization were investigated to improve thermionic converter performance. Potential improvements in collector properties were noted with evaporated thin film barium oxide coatings. Experiments with cesium carbonate suggest this substance may provide optimum combinations of cesium and oxygen for thermionic conversion.

Huffman, F. N.↗
NASA NTRS1977

Analog to digital converter for two-dimensional radiant energy array computers

The analog to digital converter stage derives a bit array of digital radiant energy signals representative of the amplitudes of an input radiant energy analog signal array and derives an output radiant energy analog signal array to serve as an input to succeeding stages. The converter stage includes a digital radiant energy array device which contains radiant energy array positions so that the analog array is less than a predetermined threshold level. A scaling device amplifies the radiant signal levels of the input array and the digital array so that the radiant energy signal level carried by the digital array corresponds to the threshold level. An adder device adds the signals of the scaled input and digital arrays at corresponding array positions to form the output analog array.

Shaefer, D. H.↗
NASA NTRS1976

N2-Cs thermionic converter development

The possibility of using molecular nitrogen gas additive as an energy storage which in turn produces cesium ionization in advanced thermionic converter is first described theoretically. Experimental data confirmed for the first time such cesium ionization by vibrationally excited molecular nitrogen. Based on these experimental observations, the use of this scheme for the verification of validity of the recent Lam's theory and its application for the development of an advanced flowing thermionic converter are discussed.

Shaw, D. T.↗
NASA NTRS1977

Results of metallographical diagnostic examination of Navy half-watt thermoelectric converters degraded by accelerated tests

To verify the 15-year reliability of the Navy half-watt radioisotope thermoelectric generator (RTG), bismuth-telluride thermoelectric converters were submitted to testing at high temperatures which accelerated the degradation and caused failure of the converters. Metallographic diagnostic examination of failed units verified failure mechanisms. Results of diagnostic examinations are presented.

Rosell, F. E., Jr.↗
NASA NTRS1977

Status of research on advanced thermionic converters

It is shown that it is possible to controllably and continuously elevate the electron temperature in the plasmatron thermionic energy converter from the emitter temperature to the maintenance electron temperature for the diode arc mode. This ability and the apparent validity of an elementary analytical model of the plasma should make possible the optimization and evaluation of operation under strong ionization conditions for which the plasma resistance should be acceptably low. Measurement of the vacuum space charge arising from the emission from a surface in cesium vapor indicates the presence of a substantial negative ion emission current. Apparatus has been constructed for identifying and directly measuring the flux of positive, negative and neutral species emitted from an electrode surface in a cesium vapor diode. The primary purpose of the investigation is to determine the influence of negative ion emission on the effective work function of thermionic converter electrodes. Initial data indicate the presence of H(-), Cs(-) and possibly C(-) and CH(-).

Hatch, G. L.↗