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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 325 records · Page 18

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NASA NTRS1984

Cathode degradation and erosion in high pressure arc discharges

The various processes which control cathode erosion and degradation were identified and evaluated. A direct current arc discharge was established between electrodes in a pressure-controlled gas flow environment. The cathode holder was designed for easy testing of various cathode materials. The anode was a water cooled copper collector electrode. The arc was powered by a dc power supply with current and voltage regulated cross-over control. Nitrogen and argon were used as propellants and the materials used were two percent thoriated tungsten, barium oxide impregnated porous tungsten, pure tungsten and lanthanum hexaboride. The configurations used were cylindrical solid rods, wire bundles supported by hollow molybdenum tubes, cylindrical hollow tubes, and hollow cathodes of the type used in ion thrusters. The results of the mass loss tests in nitrogen indicated that pure tungsten eroded at a rate more than 10 times faster than the rates of the impregnated tungsten materials. It was found that oxygen impurities of less than 0.5 percent in the nitrogen increased the mass loss rate by a factor of 4 over high purity nitrogen. At power levels less than 1 kW, cathode size and current level did not significantly affect the mass loss rate. The hollow cathode was found to be operable in argon and in nitrogen only at pressures below 400 and 200 torr, respectively.

Hardy, T. L.↗

NASA NTRS1987

Microwave performance of an optically controlled AlGaAs/GaAs high electron mobility transistor and GaAs MESFET

Direct current and also the microwave characteristics of optically illuminated AlGaAs/GaAs HEMT are experimentally measured for the first time and compared with that of GaAs MESFET. The results showed that the average increase in the gain is 2.89 dB under 1.7 nW/sq cm optical intensity at 0.83 microns. Further, the effect of illumination on S-parameters is more pronounced when the devices are biased close to pinch off. Novel applications of optically illuminated HEMT as a variable gain amplifier, high speed high frequency photo detector, and mixer are demonstrated.

Simons, Rainee N.↗

NASA NTRS1987

Method and apparatus for measuring minority carrier lifetime in a direct band-gap semiconductor

A direct band-gap semiconductor is exposed to intensity-modulated photon radiation having a characteristic energy at least as great as the energy gap of the semiconductor. This produces a time dependent concentration of excess charge carriers through the material, producing a luminescence signal modulated at the same frequency as the incident radiation but shifted in phase by an amount related to the lifetime of minority carriers. In a preferred embodiment, the phase shift of the luminescence signal is determined by transforming it to a modulated electrical signal and mixing the electrical signal with a reference signal modulated at the same frequency and having a phase which is known relative to the incident radiation. Minority carrier lifetime is calculated by integrating a direct current component of the mixed signal (F sub dc) over a 2 pi range in phase of the reference signal.

Vonroos, Oldwig↗

NASA NTRS1987

The NASA/USAF arcjet research and technology program

Direct current arcjets have the potential to provide specific impulses greater than 500 sec with storable propellants, and greater than 1000 sec with hydrogen. This level of performance can provide significant benefits for such applications as orbit transfer, station keeping, orbit change, and maneuvering. The simplicity of the arcjet system and its elements of commonality with state-of-the-art resistojet systems offer a relatively low risk transition to these enhanced levels of performance for low power (0.5 to 1.5 kW) station keeping applications. Arcjets at power levels of 10 to 30 kW are potentially applicable to orbit transfer missions. Furthermore, with the anticipated development of space nuclear power systems, arcjets at greater than 100 kW may become attractive. This paper describes the ongoing NASA/USAF program and describes major recent accomplishments.

Stone, James R.↗

NASA NTRS1987

DC electrical, thermal, and spectroscopic properties of various condensation polyimides containing surface cobalt oxide

Doping polyimides with cobalt ion causes the room temperature direct current electrical resistivity to decrease relative to the polymer alone, the reduction being most pronounced for the air-side of the cobalt modified polyimides. At a constant electrical field, resistivity for the volume, air-side and glass-side modes decreases yet further with an increase in temperature as expected for semiconductors and insulators. X-ray photoelectron spectroscopy indicates the air-side of the cobalt modified polyimides is predominantly Co3O4. The bulk resistivity of the air-side and activation energy of conduction for this surface are comparable to high purity sintered Co3O4. Charging characteristics at room temperature indicate a substantial polymer matrix contribution to both the glass-side and volume mode measurements but a negligible contribution to the air-side electrical properties. Volume electrical resistivity for similar additive levels is reduced by increasing the molecular flexibility of the host polymer.

Rancourt, J. D.↗

NASA NTRS1987

The NASA/USAF arcjet research and technology program

Stone, James R.↗

NASA NTRS1988

Test results of high-voltage, high-power, solid-state remote power controllers

This report discusses the results of testing high-voltage, high-power, solid-state remote power controllers (RPC) using RPCs designed and built by John C. Sturman at the Lewis Research Center, Cleveland, Ohio, and utilizing the Autonomously Managed Power Systems (AMPS) breadboard/test facility. These test results are used to determine usefulness of the RPCs for future applications in high-voltage direct-current space power.

Johnson, Yvette Binford↗

NASA NTRS1987

Microwave performance of an optically controlled AlGaAs/GaAs high electron mobility transistor and GaAs MESFET

Direct current and also the microwave characteristics of optically illuminated AlGaAs/GaAs HEMT are experimentally measured for the first time and compared with that of GaAs MESFET. The results showed that the average increase in the gain is 2.89 dB under 1.7 mW optical intensity at 0.83 microns. Further, the effect of illumination on S-parameters is more pronounced when the devices are biased close to pinch off. Novel applications of optically illuminated HEMT as a variable gain amplifier, high speed high frequency photodetector, and mixer are demonstrated.

Simons, Rainee N.↗

NASA NTRS1988

Rugged low-resistance contacts to YBa2Cu3O(x)

Rugged low-resistance contacts to a high-T(c) superconductor YBa2Cu3O(x) were made by melting gold onto the sample surface, where it diffused into the sample pores making a strong mechanical contact in the form of a bead. Contact resistances lower than 50 microohm were obtained, allowing passage, without heating, of a direct current of about 5 A while the sample remained in the superconducting state at 20 K. Results of SEM and of contact-resistance, critical-current, and shear-strength measurements on these contacts are included.

Caton, R.↗

NASA NTRS1988

Automatic Detection of Electric Power Troubles (ADEPT)

ADEPT is an expert system that integrates knowledge from three different suppliers to offer an advanced fault-detection system, and is designed for two modes of operation: real-time fault isolation and simulated modeling. Real time fault isolation of components is accomplished on a power system breadboard through the Fault Isolation Expert System (FIES II) interface with a rule system developed in-house. Faults are quickly detected and displayed and the rules and chain of reasoning optionally provided on a Laser printer. This system consists of a simulated Space Station power module using direct-current power supplies for Solar arrays on three power busses. For tests of the system's ability to locate faults inserted via switches, loads are configured by an INTEL microcomputer and the Symbolics artificial intelligence development system. As these loads are resistive in nature, Ohm's Law is used as the basis for rules by which faults are located. The three-bus system can correct faults automatically where there is a surplus of power available on any of the three busses. Techniques developed and used can be applied readily to other control systems requiring rapid intelligent decisions. Simulated modelling, used for theoretical studies, is implemented using a modified version of Kennedy Space Center's KATE (Knowledge-Based Automatic Test Equipment), FIES II windowing, and an ADEPT knowledge base. A load scheduler and a fault recovery system are currently under development to support both modes of operation.

Wang, Caroline↗

NASA NTRS1988

Automatic Detection of Electric Power Troubles (ADEPT)

Automatic Detection of Electric Power Troubles (A DEPT) is an expert system that integrates knowledge from three different suppliers to offer an advanced fault-detection system. It is designed for two modes of operation: real time fault isolation and simulated modeling. Real time fault isolation of components is accomplished on a power system breadboard through the Fault Isolation Expert System (FIES II) interface with a rule system developed in-house. Faults are quickly detected and displayed and the rules and chain of reasoning optionally provided on a laser printer. This system consists of a simulated space station power module using direct-current power supplies for solar arrays on three power buses. For tests of the system's ablilty to locate faults inserted via switches, loads are configured by an INTEL microcomputer and the Symbolics artificial intelligence development system. As these loads are resistive in nature, Ohm's Law is used as the basis for rules by which faults are located. The three-bus system can correct faults automatically where there is a surplus of power available on any of the three buses. Techniques developed and used can be applied readily to other control systems requiring rapid intelligent decisions. Simulated modeling, used for theoretical studies, is implemented using a modified version of Kennedy Space Center's KATE (Knowledge-Based Automatic Test Equipment), FIES II windowing, and an ADEPT knowledge base.

Wang, Caroline↗

NASA NTRS1989

Isotopic study of oxygen diffusion in oxide coatings

Diffusion of oxygen in thin films of silicon dioxide was studied using oxygen isotopically enriched in oxygen of atomic mass 18 (O-18). This subject is of interest because thin films of dielectrics such as SiO2 are proposed for use as a protective coatings for solar mirrors in low Earth orbit, which is a strongly oxidizing environment. Films of this material were prepared with a direct current magnetron using reactive sputtering techniques. To produce (O-18)- enriched SiO2, a standard 3.5-in.-diameter silicon wafer was reactively sputtered using (O-18)-enriched (95 percent) oxygen as the plasma feed gas. The films were characterized using Rutherford backscattering and Secondary Ion Mass Spectrometer (SIMS) to establish stoichiometry and purity. Subsequently, the films were exposed to an air-derived oxygen plasma in a standard laboratory plasma reactor for durations of up to 10 hr. The concentration ratio of O-16 as a function of depth was determined using SIMS profiling and compared to a baseline, nonplasma exposed sample. A value for the diffusivity of oxygen near the surface of these films was obtained and found to be about 10(-15)sq cm/sec.

Gulino, Daniel A.↗

NASA NTRS1989

CSM research: Testbed development

The Computational Structural Mechanics (CSM) Activity at Langley Research Center is developing methods for structural analysis on modern computers. To facilitate that research effort, a Testbed Development environment is being constructed. It is the purpose of the Testbed to insulate researchers from differences in the computer operating systems of modern computer systems and permit concentrated effort on the analytical problem rather than the analytical tools required to solve that problem. While modern computers enable the solution of larger problems of increasing complexity, they do so at a cost. Distributed computer environments, vector processing hardware and multiple processors dominate the current computer environment and threaten to overwhelm future analysis software. The systems software for current computers becomes more complex in order to manage the increasing complexity. The applications developer is caught between conflicting goals. They must take advantage of the computing power of new computer systems while maintaining a stable software development system. The CSM Testbed is being developed to address this problem for the computational structural analysis research community. The Langley CSM activity was initiated in October 1984. The current directions for the Testbed Development Team of the Langley CSM activity are discussed.

Gillian, Ronnie E.↗

NASA NTRS1988

Carbon doping in molecular beam epitaxy of GaAs from a heated graphite filament

Carbon doping of GaAs grown by molecular beam epitaxy has been obtained for the first time by use of a heated graphite filament. Controlled carbon acceptor concentrations over the range of 10 to the 17th-10 to the 20th/cu cm were achieved by resistively heating a graphite filament with a direct current power supply. Capacitance-voltage, p/n junction and secondary-ion mass spectrometry measurements indicate that there is negligible diffusion of carbon during growth and with postgrowth rapid thermal annealing. Carbon was used for p-type doping in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors. Current gains greater than 100 and near-ideal emitter heterojunctions were obtained in transistors with a carbon base doping of 1 x 10 to the 19th/cu cm. These preliminary results indicate that carbon doping from a solid graphite source may be an attractive substitute for beryllium, which is known to have a relatively high diffusion coefficient in GaAs.

Malik, R. J.↗

NASA NTRS1989

Theoretical and material studies of thin-film electroluminescent devices

Thin-film electroluminescent (TFEL) devices are studied for a possible means of achieving a high resolution, light weight, compact video display panel for computer terminals or television screens. The performance of TFEL devices depends upon the probability of an electron impact exciting a luminescent center which in turn depends upon the density of centers present in the semiconductor layer, the possibility of an electron achieving the impact excitation threshold energy, and the collision cross section itself. Efficiency of such a device is presently very poor. It can best be improved by increasing the number of hot electrons capable of impact exciting a center. Hot electron distributions and a method for increasing the efficiency and brightness of TFEL devices (with the additional advantage of low voltage direct current operation) are investigated.

Summers, C. J.↗

NASA NTRS1989

Liquid Rocket Booster (LRB) for the Space Transportation System (STS) systems study. Appendix C: Battery report for the liquid rocket booster TVC actuators

The actuators for control of engine valves and gimbals for a booster require 165 kW or more peak power at 270 volts direct current (VDC) during the 2 or 3 minutes of first stage ascent; other booster devices require much less power at 28 VDC. It is desired that a booster supply its own electrical power and satisfy redundancy requirements of the Solid Rocket Booster Shuttle, when applicable. The power of a Liquid Rocket Booster is therefore provided by two subsystems: Actuator Battery Power (270 VDC) Subsystem for the engine actuators, and Electrical Power and Distribution (28 VDC) Subsystem, to power everything else. Boosters will receive no electrical power from Orbiter, only commands and data, according to current plans. It was concluded that nine 30 volt silver-zinc batteries-in-series be used to provide the 270 volt, 37 kW average (165 kW peak).

Source record↗

NASA NTRS1989

A high efficiency motor/generator for magnetically suspended flywheel energy storage system

The authors discuss the theory and design of a brushless direct current motor for use in a flywheel energy storage system. The motor design is optimized for a nominal 4.5-in outside diameter operating within a speed range of 33,000-66,000 revolutions per minute with a 140-V maximum supply voltage. The equations which govern the motor's operation are used to compute a series of acceptable design parameter combinations for ideal operation. Engineering tradeoffs are then performed to minimize the irrecoverable energy loss while remaining within the design constraint boundaries. A final integrated structural design whose features allow it to be incorporated with the 500-Wh magnetically suspended flywheel is presented.

Niemeyer, W. L.↗

NASA NTRS1990

Statistical analysis of upflowing ion beam and conic distributions at DE 1 altitudes

Upflowing ion (UFI), beam, conic, and hybrid pitch angle distribution data obtained in the 8000-23,000-km altitude range by the energetic ion composition spectrometer of the DE 1 satellite during September 1981-June 1986 have been statistically analyzed. It is found that the source and transport mechanisms largely confine UFI to auroral field lines; no obvious one-to-one relationship is found between current direction and UFI source characteristics. O(+) is more efficiently accelerated than H(+) at the higher K(p) values.

Kondo, T.↗