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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 NTRS1984

Effect of Interfacial characteristics of metal clad polymeric substrates on electrical high frequency interconnection performance

Etched metallic conductor lines on metal clad polymeric substrates are used for electronic component interconnections. Significant signal losses are observed for microstrip conductor lines used for interconnecting high frequency devices. At these frequencies, the electronic signal travels closer to the metal-polymer interface due to the skin effect. Copper-teflon interfaces were characterized by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to determine the interfacial properties. Data relating roughness of the copper film to signal losses was compared to theory. Films used to enhance adhesion are found, to contribute to these losses.

Bhasin, K. B.↗
NASA NTRS1983

Monolithic short wave infrared (SWIR) detector array

A monolithic self-scanned linear detector array was developed for remote sensing in the 1.1- 2.4-micron spectral region. A high-density IRCCD test chip was fabricated to verify new design approaches required for the detector array. The driving factors in the Schottky barrier IRCCD (Pdsub2Si) process development are the attainment of detector yield, uniformity, adequate quantum efficiency, and lowest possible dark current consistent with radiometric accuracy. A dual-band module was designed that consists of two linear detector arrays. The sensor architecture places the floating diffusion output structure in the middle of the chip, away from the butt edges. A focal plane package was conceptualized and includes a polycrystalline silicon substrate carrying a two-layer, thick-film interconnecting conductor pattern and five epoxy-mounted modules. A polycrystalline silicon cover encloses the modules and bond wires, and serves as a radiation and EMI shield, thermal conductor, and contamination seal.

Source record↗
NASA NTRS1985

Performance analysis of radiation cooled dc transmission lines for high power space systems

As space power levels increase to meet mission objectives and also as the transmission distance between power source and load increases, the mass, volume, power loss, and operating voltage and temperature become important system design considerations. This analysis develops the dependence of the specific mass and percent power loss on hte power and voltage levels, transmission distance, operating temperature and conductor material properties. Only radiation cooling is considered since the transmission line is assumed to operate in a space environment. The results show that the limiting conditions for achieving low specific mass, percent power loss, and volume for a space-type dc transmission line are the permissible transmission voltage and operating temperature. Other means to achieve low specific mass include the judicious choice of conductor materials. The results of this analysis should be immediately applicable to power system trade-off studies including comparisons with ac transmission systems.

Schwarze, G. E.↗
NASA NTRS1986

Spontaneous radiation emitted by moving tethered systems

Some concepts related to radiation emitted by a large conductor moving through a magnetoplasma are outlined and referred to the case of long tethers. Some recent results of a theoretical calculation of Alfven wings, their structure and the power associated with are shown. How the problem of radiation from TSS or for any large conductor moving through a magnetoplasma should be approached is presented. The approach is that of the theory of antennas in plasmas.

Dobrowolny, M.↗
NASA NTRS1985

Performance analysis of radiation cooled dc transmission lines for high power space systems

As space power levels increase to meet mission objectives and also as the transmission distance between power source and load increases, the mass, volume, power loss, and operating voltage and temperature become important system design considerations. This analysis develops the dependence of the specific mass and percent power loss on the power and voltage levels, transmission distance, operating temperature and conductor material properties. Only radiation cooling is considered since the transmission line is assumed to operate in a space environment. The results show that the limiting conditions for achieving low specific mass, percent power loss, and volume for a space-type dc transmission line are the permissible transmission voltage and operating temperature. Other means to achieve low specific mass include the judicious choice of conductor materials. The results of this analysis should be immediately applicable to power system trade-off studies including comparisons with ac transmission systems.

Schwarze, G. E.↗
NASA NTRS1987

Electrodynamic tether

Electrodynamic tethers hold promise for a variety of space applications. Electrodynamic tethers depend upon the interactions between a moving insulated conductor and the Earth's magnetic field. An electric field is generated along the tether as in a conductor moving in the magnetic field of a generator. If the circuit is closed to the ambient space plasma via a plasma gun or other equivalent device, a current is enabled to flow in the tether, and electric power is generated at the expense of orbital mechanical energy. The net effect is a decrease in the altitude of the orbiting tethered system. The situation can be reversed by driving current against the electric field via an external power supply such as a photovoltaic array.

Patterson, Michael↗
NASA NTRS1988

The application of high temperature superconductors to space electrical power distribution components

Some important space based electrical power distribution systems and components are examined to determine what might be achieved with the introduction of high temperature superconductors (HTS). Components that are compared in a before and after fashion include transformers, transmission lines, and capacitors. It is concluded that HTS has its greatest effect on the weight associated with transmission lines, where the weight penalty could be reduced by as much as 130 kg/kW/km of cable. Transformers, because 28 percent of their mass is in the conductor, are reduced in weight by the same factor. Capacitors are helped the least with only negligible savings possible. Finally, because HTS can relax the requirement to use alternating current in order to reduce conductor mass, it will be possible to generate significant savings by eliminating most transformers and capacitors.

Aron, Paul R.↗
NASA NTRS1989

High-Performance Power-Semiconductor Packages

A 600-V, 50-A transistor and 1,200-V, 50-A diode in rugged, compact, lightweight packages intended for use in inverter-type power supplies having switching frequencies up to 20 kHz. Packages provide low-inductance connections, low loss, electrical isolation, and long-life hermetic seal. Low inductance achieved by making all electrical connections to each package on same plane. Also reduces high-frequency losses by reducing coupling into inherent shorted turns in packaging material around conductor axes. Stranded internal power conductors aid conduction at high frequencies, where skin effect predominates. Design of packages solves historical problem of separation of electrical interface from thermal interface of high-power semiconductor device.

Renz, David↗
NASA NTRS1989

Variable-Resistivity Material For Memory Circuits

Nonvolatile memory elements packed densely. Electrically-erasable, programmable, read-only memory matrices made with newly-synthesized organic material of variable electrical resistivity. Material, polypyrrole doped with tetracyanoquinhydrone (TCNQ), changes reversibly between insulating or higher-resistivity state and conducting or low-resistivity state. Thin film of conductive polymer separates layer of row conductors from layer of column conductors. Resistivity of film at each intersection and, therefore, resistance of memory element defined by row and column, increased or decreased by application of suitable switching voltage. Matrix circuits made with this material useful for experiments in associative electronic memories based on models of neural networks.

Nagasubramanian, Ganesan↗
NASA NTRS1989

Monolithic Solid Oxide Fuel Cell development

The Monolithic Solid Oxide Fuel Cell (MSOFC) is an oxide-ceramic structure in which appropriate electronic and ionic conductors are fabricated in a honeycomb shape similar to a block of corrugated paperboard. These electronic and ionic conductors are arranged to provide short conduction paths to minimize resistive losses. The power density achievable with the MSOFC is expected to be about 8 kW/kg or 4 kW/L, at fuel efficienceis over 50 percent, because of small cell size and low resistive losses in the materials. The MSOFC operates in the range of 700 to 1000 C, at which temperatures rapid reform of hydrocarbon fuels is expected within the nickel-YSZ fuel channels. Tape casting and hot roll calendering are used to fabricate the MSOFC structure. The performance of the MSOFC has improved significantly during the course of development. The limitation of this system, based on materials resistance alone without interfacial resistances, is 0.093 ohm-sq cm area-specific resistance (ASR). The current typical performance of MSOFC single cells is characterized by ASRs of about 0.4 to 0.5 ohm-sq cm. With further development the ASR is expected to be reduced below 0.2 ohm-sq cm, which will result in power levels greater than 1.4 W/sq cm. The feasibility of the MSOFC concept was proven, and the performance was dramatically improved. The differences in thermal expansion coefficients and firing shrinkages among the fuel cell materials were minimized. As a result of good matching of these properties, the MSOFC structure was successfully fabricated with few defects, and the system shows excellent promise for development into a practical power source.

Myles, K. M.↗
NASA NTRS1988

The application of high temperature superconductors to space electrical power distribution components

Some important space based electrical power distribution systems and components are examined to determine what might be achieved with the introduction of high temperature superconductors (HTS). Components that are compared in a before-and-after fashion include transformers, transmission lines, and capacitors. It is concluded that HTS has its greatest effect on the weight associated with transmission lines, where the weight penalty could be reduced by as much as 130 kg/kW/km of cable. Transformers, because 28 percent of their mass is in the conductor, are reduced in weight by the same factor. Capacitors are helped the least with only negligible savings possible. Finally, because HTS can relax the requirement to use alternating current in order to reduce conductor mass, it will be possible to generate significant savings by eliminating most transformers and capacitors.

Aron, Paul R.↗
NASA NTRS1988

Carbon dioxide electrolysis with solid oxide electrolyte cells for oxygen recovery in life support systems

The direct electrochemical reduction of carbon dioxide (CO2) is achieved without catalysts and at sufficiently high temperatures to avoid carbon formation. The tubular electrolysis cell consists of thin layers of anode, electrolyte, cathode and cell interconnection. The electrolyte is made from yttria-stabilized zirconia which is an oxygen ion conductor at elevated temperatures. Anode and cell interconnection materials are complex oxides and are electronic conductors. The cathode material is a composite metal-ceramic structure. Cell performance characteristics have been determined using varying feed gas compositions and degrees of electrochemical decomposition. Cell test data are used to project the performance of a three-person CO2-electrolysis breadboard system.

Isenberg, Arnold O.↗
NASA NTRS1989

Mesh-matrix analysis method for electromagnetic launchers

The mesh-matrix method is a procedure for calculating the current distribution in the conductors of electromagnetic launchers with coil or flat-plate geometry. Once the current distribution is known the launcher performance can be calculated. The method divides the conductors into parallel current paths, or meshes, and finds the current in each mesh by matrix inversion. The author presents procedures for writing equations for the current and voltage relations for a few meshes to serve as a pattern for writing the computer code. An available subroutine package provides routines for field and flux coefficients and equation solution.

Elliott, David G.↗
NASA NTRS1989

Simulation of radial expansion of an electron beam injected into a background plasma

A 2-D electrostatic particle code was used to study the beam radial expansion of a nonrelativistic electron beam injected from an isolated equipotential conductor into a background plasma. The simulations indicate that the beam radius is generally proportional to the beam electron gyroradius when the conductor is charged to a large potential. The simulations also suggest that the charge buildup at the beam stagnation point causes the beam radial expansion. From a survey of the simulation results, it is found that the ratio of the beam radius to the beam electron gyroradius increases with the square root of beam density and decreases inversely with beam injection velocity. This dependence is explained in terms of the ratio of the beam electron Debye length to the ambient electron Debye length. These results are most applicable to the SEPAC electron beam injection experiments from Spacelab 1, where high charging potential was observed.

Koga, J.↗
NASA NTRS1990

Solar array arcing in plasmas

Solar cells in space plasma conditions are known to arc into the plasma when the interconnects are at a negative potential of a few hundred volts, relative to plasma potential. For cells with silver-coated interconnects, a threshold voltage for arcing exists at about -230 V, as found in both ground and LEO experiments. The arc rate beyond the threshold voltage depends nearly linearly on plasma density, but has a strong power-law dependence on voltage, such that for small increments in operating voltage there is a large increment in arc rate. The arcs generate broadband radio interference and visible light. In ground tests, interconnects have been damaged by arcs in cells having insufficient isolation from a source of high current. Models for the arcs are highly dependent on the choice of interconnect conductor material exposed to the plasma and possibly on the geometry and choice of adjacent insulator material. Finally, new technology solar cells use copper for the cell interconnects, a material which may have a lower arcing threshold voltage than silver. It is expected, from ground tests of simulated solar cells, that any junction of conductor and insulator exposed to space plasma conditions will arc into the plasma at a few hundred volts negative potential, relative to the local plasma.

Ferguson, Dale C.↗
NASA NTRS1990

Solving time-dependent two-dimensional eddy current problems

Transient eddy current calculations are presented for an EM wave-scattering and field-penetrating case in which a two-dimensional transverse magnetic field is incident on a good (i.e., not perfect) and infinitely long conductor. The problem thus posed is of initial boundary-value interface type, where the boundary of the conductor constitutes the interface. A potential function is used for time-domain modeling of the situation, and finite difference-time domain techniques are used to march the potential function explicitly in time. Attention is given to the case of LF radiation conditions.

Lee, Min Eig↗
NASA NTRS1991

The effects of the exhaust plume on the lightning triggering conditions for launch vehicles

Apollo 12 and Atlas Centaur 67 are two launch vehicles that have experienced triggered lightning strikes. Serious consequences resulted from the events; in the case of Atlas Centaur 67, the vehicle and the payload were lost. These events indicate that it is necessary to develop launch rules which would prevent such occurrences. In order to develop valid lightning related rules, it is necessary to understand the effects of the plume. Some have assumed that the plume can be treated as a perfect conductor, and have computed electric field enhancement factors on that basis. The authors have looked at the plume, and believe that these models are not correct, because they ignore the fluid motion of the conducting plates. The authors developed a model which includes this flow character. In this model, the external field is excluded from the plume as it would be for any good conductor, but, in addition, the charge must distribute so that the charge density is zero at some location in the exhaust. When this condition is included in the calculation of triggering enhancement factors, they can be two to three times larger than calculated by other methods which include a conductive plume but don't include the correct boundary conditions. Here, the authors review the relevant features of rocket exhausts for the triggered lightning problem, present an approach for including flowing conductive gases, and present preliminary calculations to demonstrate the effect that the plume has on enhancement factors.

Eriksen, Frederick J.↗
NASA NTRS1991

The physics of the oscillating lightning

The lightning is proposed to start in a limited region of electric breakdown field. A growing charge pool in a cumulonimbus cloud is likely to produce such a field in its outer layers. When the field is not aligned with the potential surfaces, the electric force pushes positive charge in one direction and negative in the opposite. Self inductance develops and an embryo open electric circuit is born. Oscillations swiftly grow in strength when potential energy of the cloud is released. The channel extends in steps during those cycle stages where charge is crammed into the channel terminals. Electrostatic consequences of a narrow conductor among the cloud charges are computed. The conductor is charged by influence to such a degree that the charge is bound to leak out to the ambient air and appear as a charge sheath some distance off the channel. Ample energy is released to sustain the oscillations. The period increases with channel length and agrees well with observed time between steps. A ground strike leads to a shock pulse travelling up the channel.

Storebo, Per B.↗