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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 NTRS1986

Avionics electromagnetic interference immunity and environment

Aircraft electromagnetic spectrum and radio frequency (RF) field strengths are charted, profiling the higher levels of electromagnetic voltages encountered by the commercial aircraft wiring. Selected military, urban, and rural electromagnetic field levels are plotted and provide a comparison of radiation amplitudes. Low frequency magnetic fields and electric fields from 400 H(Z) power systems are charted versus frequency and wire separation to indicate induced voltages on adjacent or neighboring circuits. Induced EMI levels and attenuation characteristics of electric, magnetic, RF fields, and transients are plotted and graphed for common types of wire circuits. The significance of wire circuit returns and shielding is emphasized to highlight the techniques that help block the paths of electromagnetic interference and maintain avionic interface signal quality.

Clarke, C. A.↗
NASA NTRS1971

Study of second breakdown in power transistors using infrared techniques

Infrared thermal maps pinpoint exact location where second breakdown will occur before phenomenon happens and before physical damage develops at hot spot. Crystal structure analysis at that point determines cause of fault. Absolute power of radiation emitted from hot spot is direct indication of voltage level at which second breakdown occurs

Source record↗
NASA NTRS1978

Controlled freezing of biological samples

Apparatus consists of thermocouple connected to semiconductor reference junction. Junction is connected to amplifier that boosts signal by 1,000. High-level signal is displayed on recorder and fed into second amplifier where it is compared with signal from potentiometer of programmed dc reference in bag-temperature programer. Difference in signals indicates output voltage. Remaining circuitry provides zero-phase, time-proportion control of heaters such that heater power is directly proportional to error signal.

Cygnarowicz, T. A.↗
NASA NTRS1977

Properties of TiO2 thin films and a study of the TiO2-GaAs interface

Titanium dioxide (TiO2) films prepared by chemical vapor deposition were investigated in this study for the purpose of the application in the GaAs metal-insulator-semiconductor field-effect transistor. The degree of crystallization increases with the deposition temperature. The current-voltage study, utilizing an Al-TiO2-Al MIM structure, reveals that the d-c conduction through the TiO2 film is dominated by the bulk-limited Poole-Frenkel emission mechanism. The dependence of the resistivity of the TiO2 films on the deposition environment is also shown. The results of the capacitance-voltage study indicate that an inversion layer in an n-type substrate can be achieved in the MIS capacitor if the TiO2 films are deposited at a temperature higher than 275 C. A process of low temperature deposition followed by the pattern definition and a higher temperature annealing is suggested for device fabrications. A model, based on the assumption that the surface state densities are continuously distributed in energy within the forbidden band gap, is proposed to interpret the lack of an inversion layer in the Al-TiO2-GaAs MIS structure with the TiO2 films deposited at 200 C.

Chen, C. Y.↗
NASA NTRS1981

Parasitic current losses due to solar electric propulsion generated plasmas

Solar electric propulsion is a leading candidate for many upcoming space missions. Under many circumstances plasma produced by charge-exchange reactions within the ion beam dominates the ambient environment near the spacecraft. The calculations presented here contain a predictive hydrodynamic model for the charge-exchange plasma expansion, and a fully three-dimensional model for the structure of the plasma sheath around the solar array wing. Results of calculations for several configurations and voltage levels indicate that with kilovolt biases power losses of approximately 10 percent or more are likely, even with only one engine in operation, and that ameliorative measures should focus on the inboard portion of the solar arrays.

Katz, I.↗
NASA NTRS1985

Direct-Current Unbalance Detector

Short circuits to ground indicated by voltage changes. Current transducer connected in bridge circuit with floating 30-Vdc power supply measures voltage unbalance between positive and negative powerlines and ground. Detection circuit output swings higher or lower than normal balanced condition voltage to signify unbalance toward positive or negative side respectively. Circuit configuration adaptable to monitor 4- to 20-mA current loops often found in industrial controls.

Wagner, A. P.↗
NASA NTRS1986

Carrier surface generation and recombination effects in photoconduction of HgI2 single crystals

Dc photoconductivity characteristics of HgI2 single crystals have been measured in the range of 1.75-2.75 eV, using CuI as a transparent electrical contact. Hole and electron photocurrents could be separately measured by applying different voltage polarities to the illuminated electrode. It is shown that charge carrier generation near the surface is highly extrinsic, as displayed by differences in the hole and electron photogeneration spectra. Analysis of the photoconductivity versus voltage characteristics indicates that the hole and electron bulk trapping times satisfy greater than 70 and 3 microsec, respectively. The hole and electron surface recombination velocities were 1.0 x 10 to the 4th cm/s and 8 x 10 to the 5th cm/s, respectively.

Burshtein, Z.↗
NASA NTRS1988

Pulse Coil Tester

Set of relays tested easily and repeatedly. Pulse coil tester causes coil under test to generate transient voltage; waveform indicates condition of coil. Tester accommodates assembly of up to four coils at a time.

Simon, Richard A.↗
NASA NTRS1997

International Space Station Cathode Life Testing

Four hollow cathode assembly (HCA) life tests were initiated at operating conditions simulating on-orbit operation of the International Space Station plasma contactor. The objective of these tests is to demonstrate the mission-required 18,000 hour lifetime with high-fidelity development model HCAS. HCAs are operated with a continuous 6 sccm xenon flow rate and 3 A anode current. On-orbit emission current requirements are simulated with a square waveform consisting of 50 minutes at a 2.5 A emission current and 40 minutes with no emission current. One HCA test was terminated after approximately 8,000 hours so that a destructive analysis could be performed. The analysis revealed no life-limiting processes and the ultimate lifetime was projected to be greater than the mission requirement. Testing continues for the remaining three HCAs which have accumulated approximately 8,000 hours, 10,000 hours, and 11,000 hours, respectively, as of June 1997. Anode and bias voltages, strong indicators of cathode electron emitter condition, are within acceptable ranges and have exhibited no life- or performance-limiting phenomena to date.

Soulas, George C.↗
NASA NTRS1998

Thermal Control using Electrochromism

The applicability of a charge balanced electrochromic device to modulate the frequencies in the thermal infrared region is examined in this study. The device consisted of a transparent conductor, WO3 anode, PMMA/LiClO4 electrolyte, V2O5 cathode and transparent conductor. The supporting structure in the device is SnO2 coated glass and the edges are sealed with epoxy to reduce moisture absorption. The performance evaluation comprised of cyclic voltammetric measurements and determination of transmittance at various wavelengths. The device was subjected to anodic and cathodic polarization by sweeping the potential at a rate of 10 mV/sec from -0.8V to 1.8V. The current versus voltage profile indicated no reaction between -0.5 and +0.5 V. The device is colored green at 1.8V with a transmittance of 5% at a wavelength, lambda=900 nm and colorless at -0.8V with a transmittance of 74% at lambda=500 nm. The optical modulation is limited to 400-1500 nm and there is no activity in the thermal infrared. The switching time is 75 seconds for transmittance to decrease from 74% to 50%. The device yielded reproducible values for transmittance when cycled between colored and bleached states by application of 1.8V and -0.8V, respectively.

Vaidyanathan, Hari↗
NASA NTRS1998

Thermal Control Using Electrochromism

The applicability of a charge balanced electrochromic device to modulate the frequencies in the thermal infra red region is examined in this study. The device consisted of a transparent conductor, WO3 anode, PMMA/LiClO4, electrolyte, V2O5, cathode and transparent conductor. The supporting structure in the device is SnO2 coated glass and the edges are sealed with epoxy to reduce moisture absorption. The performance evaluation comprised of cyclic voltammetric measurements and determination of transmittance at various wavelengths. The device was subjected to anodic and cathodic polarization by sweeping the potential at a rate of 10 mV/sec from -0.8 V to 1.8 V. The current versus voltage profile indicated no reaction between -0.5 and +0.5 V. The device is colored green at 1.8 V with a transmittance of 5% at a wavelength, lambda = 900 nm and colorless at -0.8 V with a transmittance of 74% at X = 500 nm. The optical modulation is limited to 400-1500 nm and there is no activity in the thermal infrared. The switching time is 75 seconds for transmittance to decrease from 74% to 50%. The device yielded reproducible values for transmittance when cycled between colored and bleached states by application of 1.8 V and -0.8 V, respectively.

Vaidyanathan, Hari↗
NASA NTRS1999

Thermal Control Using Electrochromism

The applicability of a charge balanced electrochromic device to modulate the frequencies in the thermal infrared region is examined in this study. The device consisted of a transparent conductor, WO3, anode, PMMA/LiClO4 electrolyte, V2O5 cathode and transparent conductor. The supporting structure in the device is SnO2 coated glass and the edges are sealed with epoxy to reduce moisture absorption. The performance evaluation comprised of cyclic voltammetric measurements and determination of transmittance at various wavelengths. The device was subjected to anodic and cathodic polarization by sweeping the potential at a rate of 10 mV/sec from -0.8V to 1.8V. The current versus voltage profile indicated no reaction between -0.5 and +0.5 V. The device is colored green at 1.8 V with a transmittance of 5% at a wavelength, lambda = 900 nm and colorless at -0.8 V with a transmittance of 74% at lambda = 500 nm. The optical modulation is limited to 400-1500 nm and there is no activity in the thermal infrared. The switching time is a function of temperature and time for coloring reaction was slower than the bleaching reaction. The device yielded reproducible values for transmittance when cycled between colored and bleached states by application of 1.8V and -0.8V, respectively.

Vaidyanathan, Hari↗
NASA NTRS2005

n/p/n Tunnel Junction InGaAs Monolithic Interconnected Module (MIM)

The Monolithic Interconnected Module (MIM), originally introduced at the First NREL thermophotovoltaic (TPV) conference, consists of low-bandgap indium gallium arsenide (InGaAs) photovoltaic devices, series interconnected on a common semi-insulating indium phosphide (inP) substrate. An infrared reflector is deposited on the back surface of the substrate to reflect photons, which were not absorbed in the first pass through the structure. The single largest optical loss in the current device occurs int he heavily doped p-type emitter. A new MIM design (pat.pend.) has been developed which flips the polarity of the conventional MIM cell (i.e., n/p rather than p/n), eliminating the need for the high conductivity p-type emitter. The p-type base of the cell is connected to the n-type lateral conduction layer through a thin InGaAs tunnel junction. 0.58 eV and 0.74 eV InGaAs devices have demonstrated reflectances above 90% for wavelengths beyond the bandgap (greater than 95% for unprocessed structures). Electrical measurements indicate minimal voltage drops across the tunnel junction (less than mV/junction under 1200K-blackbody illumnination) and fill factors that are above 70% at current densities (J(sub sc)) above 8 Angstroms per square centimeters for the 0.74eV devices.

Wilt, David M.↗
NASA NTRS2008

Preliminary Development and Testing of a Self-Injecting Gallium MPD Thruster

Discharge current and terminal voltage measurements were performed on a gallium electromagnetic thruster at discharge currents in the range of 20-54 kA. It was found that the arc impedance has a value of 6-7 m(Omega) at peak current. The absence of high-frequency oscillations in the terminal voltage trace indicates lack of the "onset" condition often seen in MPD arcs, suggesting that a sufficient number of charge carriers are present for current conduction. The mass ablated per pulse was not measured experimentally; however the mass flow rate was calculated using an ion current assumption and an anode power balance. Measurement of arc impedance predicts a temperature of 3.5 eV which from Saha equilibrium corresponds to Z = 2.0 - 3.5, and assuming Z = 2 yields an Isp of 3000 s and thrust efficiency of 50%.

Thomas, Robert E.↗
NASA NTRS2011

Two-axis direct fluid shear stress sensor

A micro sized multi-axis semiconductor skin friction/wall shear stress induced by fluid flow. The sensor design includes a shear/strain transduction gimble connected to a force collecting plate located at the flow boundary surface. The shear force collecting plate is interconnected by an arm to offset the tortional hinges from the fluid flow. The arm is connected to the shear force collecting plate through dual axis torsional hinges with piezoresistive torsional strain gauges. These gauges are disposed on the tortional hinges and provide a voltage output indicative of applied shear stress acting on the force collection plate proximate the flow boundary surface. Offsetting the torsional hinges creates a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from small shear stress, or small displacement of the collecting plate. The design also isolates the torsional sensors from exposure to the fluid flow.

Bajikar, Sateesh↗
NASA NTRS2014

Operational Status of the International Space Station Plasma Contactor Hollow Cathode Assemblies from July 2011 to May 2013

The International Space Station has onboard two Aerojet Rocketdyne developed plasma contactor units that perform the function of charge control. The plasma contactor units contain NASA Glenn Research Center developed hollow cathode assemblies. NASA Glenn Research Center monitors the onorbit operation of the flight hollow cathode assemblies. As of May 31, 2013, HCA.001-F has been ignited and operated 123 times and has accumulated 8072 hours of operation, whereas, HCA.003-F has been ignited and operated 112 times and has accumulated 9664 hours of operation. Monitored hollow cathode ignition times and anode voltage magnitudes indicate that they continue to operate nominally.

International Space Station↗
NASA NTRS2013

Operational Status of the International Space Station Plasma Contactor Hollow Cathode Assemblies July 2001 to May 2013

The International Space Station has onboard two Aerojet Rocketdyne developed plasma contactor units that perform the function of charge control. The plasma contactor units contain NASA Glenn Research Center developed hollow cathode assemblies. NASA Glenn Research Center monitors the on-orbit operation of the flight hollow cathode assemblies. As of May 31, 2013, HCA.001-F has been ignited and operated 123 times and has accumulated 8072 hours of operation, whereas, HCA.003-F has been ignited and operated 112 times and has accumulated 9664 hours of operation. Monitored hollow cathode ignition times and anode voltage magnitudes indicate that they continue to operate nominally.

Kamhawi, Hani↗
NASA NTRS1995

Preventing Overcharge And Overdischarge Of Lithium Cells

Secondary lithium cells operating at ambient temperature protected against overcharge and overdischarge by use of cathode additives acting as sources and sinks of electroactive chemical species, which is lithium. Additive in cathode limits excursion of voltage of cell during both overcharge and overdischarge. In addition to protecting cell, also serves as part of state-of-charge indicator: attainment of greater or lesser limiting voltage indicates end of charge or end of discharge, respectively. Concept applied to Li/TiS2 system, and also applicable to such other lithium systems as Li/MoS2, Li/NbSe3, and Li/V2O5.

Huang, Chen-Kuo↗