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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Testing the DC-electric field model in a solar flare observed by Yohkoh and the Compton Gamma-Ray Observatory

We apply a DC-electric field model to the analysis of soft and hard X-ray observations of a solar flare observed by Yohkoh and the Compton Gamma Ray Observatory (CGRO) on 6 September 1992. The flare was observed simultaneously in the soft X-ray Ca XIX line by the Yohkoh Bragg Crystal Spectrometer (BCS) and in hard X-rays (greater than 50 keV) by the CGRO Burst and Transient Spectrometer Experiment (BATSE). A strong stationary component of Ca XIX emission was present at the start of impulsive hard X-ray emission indicating an extended phase of heating prior to the production of energetic nonthermal electrons. We interpret the preflare Ca XIX emission as a signature of Joule heating by field-aligned currents. We relate the temporal variation of impulsive hard X-ray emission to the rate of runaway electron acceleration by the DC-electric field associated with the current. We find that the initial rise in hard X-ray emission is consistent with electron acceleration by a DC-electric field that increased from a preflare value of less than approximately 10(exp -5) V/cm to approximately (9 +/- 1) x 10(exp -5) V/cm at the time of the first hard X-ray peak and then remained constant during the rest of the impulsive phase. We attribute the increase in electric field strength to the formation of a current sheet at the reconnection point of two loop structures. The decrease in hard X-ray emission after flare maximum is consistent with a reduction in the number of runaway electrons due to an increase in coronal density produced by chromospheric evaporation. The increased density quenches the runaway process by enhancing collisional thermalization of electrons. To avoid the generation of an unrealistically large magnetic field, the flaring region must be highly filamented into greater than approximately 10(exp 6) oppositely directed current channels of approximately 30 cm width with an initial preflare current of approximately 3 x 10(exp 10) A per channel.

Zarro, D. M.↗
NASA NTRS1987

Development of a new generation of high-temperature composite materials

There are ever-increasing demands to develop low-density materials that maintain high strength and stiffness properties at elevated temperatures. Such materials are essential if the requirements for advanced aircraft, space power generation, and space station plans are to be realized. Metal matrix composites and intermetallic matrix composites are currently being investigated at NASA Lewis for such applications because they offer potential increases in strength, stiffness, and use temperature at a lower density than the most advanced single-crystal superalloys presently available. Today's discussion centers around the intermetallic matrix composites proposed by Lewis for meeting advanced aeropropulsion requirements. The fabrication process currently being used at Lewis to produce intermetallic matrix composites will be reviewed, and the properties of one such composite, SiC/Ti3Al+Nb, will be presented. In addition, the direction of future research will be outlined, including plans for enhanced fabrication of aluminide composites by the arc spray technique and fiber development by the floating-zone process.

Brindley, Pamela K.↗
NASA NTRS1972

Remarks about X-rays from Eta Carinae.

Two current models for Eta Carinae are discussed. It is shown that the recently observed soft X-ray flux seems to indicate a surprisingly high density for the ambient gas around Eta Carinae, and that some useful constraints on models of this object may result from X-ray observations.

Davidson, K.↗
NASA NTRS1980

Microwave beamed power technology improvement

The magnetron directional amplifier was tested for (1) phase shift and power output as a function of gain, anode current, and anode voltage, (2) background noise and harmonics in the output, (3) long life potential of the magnetron cathode, and (4) high operational efficiency. Examples of results were an adequate range of current and voltage over which 20 dB of amplification could be obtained, spectral noise density 155 dB below the carrier, 81.7% overall efficiency, and potential cathode life of 50 years in a design for solar power satellite use. A fabrication method was used to fabricate a 64 slot, 30 in square slotted waveguide array module from 0.020 in thick aluminum sheet. The test results on the array are discussed.

Brown, W. C.↗
NASA NTRS1986

RF wave observations in beam-plasma discharge

The Beam Plasma Discharge (BPD) was produced in the large vacuum chamber at Johnson Space Center (20 x 30 m) using an energetic electron beam of moderately high perveance. A more complete expression of the threshold current I sub c taking into account the pitch angle injection dependence is given. Ambient plasma density inferred from wave measurements under various beam conditions are reported. Maximum frequency of the excited RF band behaves differently than the frequency of the peak amplitude. The latter shows signs of parabolic saturation consistent with the light data. Beam plasma state (pre-BPD or BPD) does not affect the pitch angle dependence. Unexpected strong modulation of the RF spectrum at half odd integer of the electron cyclotron frequency (n + 1/2)f sub ce is reported (5 n 10). Another new feature, the presence of wave emission around 3/2 f sub ce for I sub b is approximate I sub c is reported.

Bernstein, W.↗
NASA NTRS1987

Self-consistent analysis of gain saturation in channeled-substrate-planar double-heterojunction lasers

A self-consistent model for semiconductor lasers (using the channeled-substrate-planar (CSP) double-heterojunction (DH) laser as an example) which does not assume constant optical power along the laser axis is developed. This approach allows for the analysis of high-power lasers with low facet reflectivities which produce nonuniform photon densities along the propagation direction. Analytical equations for the modal gain coefficient, the threshold current density, and the radiated power for a specific CSP laser structure are obtained.

Butler, Jerome K.↗
NASA NTRS1990

Emerging applications of high temperature superconductors for space communications

Proposed space missions require longevity of communications system components, high input power levels, and high speed digital logic devices. The complexity of these missions calls for a high data bandwidth capacity. Incorporation of high temperature superconducting (HTS) thin films into some of these communications system components may provide a means of meeting these requirements. Space applications of superconducting technology has previously been limited by the requirement of cooling to near liquid helium temperatures. Development of HTS materials with transition temperatures above 77 K along with the natural cooling ability of space suggest that space applications may lead the way in the applications of high temperature superconductivity. In order for HTS materials to be incorporated into microwave and millimeter wave devices, the material properties such as electrical conductivity, current density, surface resistivity and others as a function of temperature and frequency must be well characterized and understood. The millimeter wave conductivity and surface resistivity were well characterized, and at 77 K are better than copper. Basic microwave circuits such as ring resonators were used to determine transmission line losses. Higher Q values than those of gold resonator circuits were observed below the transition temperature. Several key HTS circuits including filters, oscillators, phase shifters and phased array antenna feeds are feasible in the near future. For technology to improve further, good quality, large area films must be reproducibly grown on low dielectric constant, low loss microwave substrates.

Heinen, Vernon O.↗
NASA NTRS1990

Full custom VLSI - A technology for high performance computing

Full custom VLSI is presented as a viable technology for addressing the need for the computing capabilities required for the real-time health monitoring of spacecraft systems. This technology presents solutions that cannot be realized with stored program computers or semicustom VLSI; also, it is not dependent on current IC processes. It is argued that, while design time is longer, full custom VLSI produces the fastest and densest VLSI solution and that high density normally also yields low manufacturing costs.

Maki, Gary K.↗
NASA NTRS1993

Redshift space clustering of galaxies and cold dark matter model

The distorting effect of peculiar velocities on the power speturm and correlation function of IRAS and optical galaxies is studied. The observed redshift space power spectra and correlation functions of IRAS and optical the galaxies over the entire range of scales are directly compared with the corresponding redshift space distributions using large-scale computer simulations of cold dark matter (CDM) models in order to study the distortion effect of peculiar velocities on the power spectrum and correlation function of the galaxies. It is found that the observed power spectrum of IRAS and optical galaxies is consistent with the spectrum of an Omega = 1 CDM model. The problems that such a model currently faces may be related more to the high value of Omega in the model than to the shape of the spectrum. A low-density CDM model is also investigated and found to be consistent with the data.

Bahcall, Neta A.↗
NASA NTRS2005

Current Sheet Evolution in the Aftermath of a CME Event

We report on SOHO-UVCS observations of the coronal restructuring following a Coronal Mass Ejection (CME) on November 26,2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after a CME in the NW quadrant, UVCS began taking spectra at 1.7 solar radius, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6 x 10(exp 6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the Fe XVIII emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by Ulysses-SWICS throughout the magnetic cloud associated with the CME. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Bemporad, A.↗
NASA NTRS2005

Phase Contrast X-ray Imaging of Shuttle Insulating Foam

X-ray radiation has been widely used for imaging applications since Rontgen first discovered X-rays over a century ago. Its large penetration depth makes it ideal for the nondestructive visualization of internal structure of materials or objects unobtainable otherwise. Currently widely used nondestructive evaluation (NDE) tools-X-ray radiography and tomography are absorption-based, and work well in highly absorbing materials where density or composition variations due to internal structure or defects are high enough to be spatially distinguished in terms of absorption contrast. However, in many cases where materials such as insulating foam are light-weight, the conventional absorption-based X-ray methods for NDE become less effective. Indeed, the low-density shuttle insulating foam used for flight mission poses a great challenge to the standard NDE tools in that the absorption contrast arising from internal defects of such a low- density material is either weak or indistinguishable. In this presentation, the latest progress in phase contrast X-ray imaging of internal defects of insulating foam will be presented and discussed, demonstrating new opportunities to solve challenging issues involved in advanced materials development and processing for space exploration.

Hu, Zhengwei↗
NASA NTRS1990

Observation of a stationary, current-free double layer in a plasma

A stationary, current-free, potential double layer is formed in a two-electron-population plasma due to self-consistent separation of the two electron species. The position and amplitude of the double layer are controlled by the relative densities of the two electron populations. The steady-state double layer traps the colder electrons on the high potential side, and generates a neutralized, monoenergetic ion beam on the low potential side. The field-aligned double layer is annihilated when an electron current is drawn through the plasma.

Hairapetian, G.↗
NASA NTRSDate not supplied

Spacecraft Charging as an Asset to Interplanetary Small Spacecraft

Small spacecraft operate on a far more limited power budget than their larger counterparts, a problem compounded for interplanetary spacecraft in the outer solar system. The reduced solar flux beyond Earth’s orbit makes solar panels less effective for spacecraft exploring the gas giants and can they are susceptible to damage by intense radiation belts. Radioisotope thermoelectric generators are expensive and bulky compared to their power output. Interplanetary small satellite missions benefit from both alternative energy sources and low-power electronics to power their buses and scientific payloads. Traditionally, spacecraft engineers treat the space environment as a hazard, but it nevertheless offers a potential solution. Currents from space plasmas charge spacecraft to high potentials and can cause electrical arcing to occur between differentially charged surfaces. The spacecraft can harvest a small amount of power —<10 mW/m2at Jupiter — from the electric field between these surfaces to do useful work, either by charging a battery or directly powering an instrument or actuator. While using the energy directly has limited use due to the low electron density and temperature of most space plasmas, it can nevertheless be used in situations where solar panels are not desirable, such as high radiation environments. Two applications — a Langmuir probe and an attitude control actuator — exploit the disparate current-voltage characteristics between surfaces with different material properties and require minimal input power to operate.

Spacecraft↗
NASA NTRSDate not supplied

Spacecraft Charging as an Asset to Interplanetary Small Spacecraft

Small spacecraft operate on a far more limited power budget than their larger counterparts, a problem compounded for interplanetary spacecraft in the outer solar system. The reduced solar flux beyond Earth’s orbit makes solar panels less effective for spacecraft exploring the gas giants and they are susceptible to damage by intense radiation belts. Radioisotope thermoelectric generators are expensive and bulky compared to their power output. Interplanetary small satellite missions benefit from both alternative energy sources and low-power electronics to power their buses and scientific payloads. Traditionally, spacecraft engineers treat the space environment as a hazard, but it nevertheless offers a potential solution. Currents from space plasmas charge spacecraft to high potentials and can cause electrical arcing to occur between differentially charged surfaces. The spacecraft can harvest a small amount of power —<10 mW/m2at Jupiter — from the electric field between these surfaces to do useful work, either by charging a battery or directly powering an instrument or actuator. While using the energy directly has limited use due to the low electron density and temperature of most space plasmas, it can nevertheless be used in situations where solar panels are not desirable, such as high radiation environments. Two applications — a Langmuir probe and an attitude control actuator — exploit the disparate current-voltage characteristics between surfaces with different material properties and require minimal input power to operate.

spacecraft charging↗
NASA NTRS1995

The Thermal Ion Dynamics Experiment and Plasma Source Instrument

The Thermal Ion Dynamics Experiment (TIDE) and the Plasma Source Instrument (PSI) have been developed in response to the requirements of the ISTP Program for three-dimensional (3D) plasma composition measurements capable of tracking the circulation of low-energy (0-500 eV) plasma through the polar magnetosphere. This plasma is composed of penetrating magnetosheath and escaping ionospheric components. It is in part lost to the downstream solar wind and in part recirculated within the magnetosphere, participating in the formation of the diamagnetic hot plasma sheet and ring current plasma populations. Significant obstacles which have previously made this task impossible include the low density and energy of the outflowing ionospheric plasma plume and the positive spacecraft floating potentials which exclude the lowest-energy plasma from detection on ordinary spacecraft. Based on a unique combination of focusing electrostatic ion optics and time of flight detection and mass analysis, TIDE provides the sensitivity (seven apertures of about 1 cm squared effective area each) and angular resolution (6 x 18 degrees) required for this purpose. PSI produces a low energy plasma locally at the POLAR spacecraft that provides the ion current required to balance the photoelectron current, along with a low temperature electron population, regulating the spacecraft potential slightly positive relative to the space plasma. TIDE/PSI will: (a) measure the density and flow fields of the solar and terrestrial plasmas within the high polar cap and magnetospheric lobes; (b) quantify the extent to which ionospheric and solar ions are recirculated within the distant magnetotail neutral sheet or lost to the distant tail and solar wind; (c) investigate the mass-dependent degree energization of these plasmas by measuring their thermodynamic properties; (d) investigate the relative roles of ionosphere and solar wind as sources of plasma to the plasma sheet and ring current.

Moore, T. E.↗
NASA NTRS1990

High-T(sub c) squid application in medicine and geophysics

In the Laboratory a high-T(sub c) one-hole squid was built from Y1Ba2Cu3O(7-x) ceramics obtained by a standard procedure of solid state reaction. The ceramics with critical current density J(sub c) is greater than 100 A/sq cm was selected. In the middle of 10 x 10 x 2 mm ceramics pellet a 0.8 mm hole was drilled in which superconducting loop of the squid was located. Between the hole and the edge of the pellet a cut was mechanically filed out with a bridge inside it connecting the superconducting ring. A scheme of the magnetometer is presented. The resonant frequency shift of the tank circuit, the connection of the squid with this circuit, and the squid inductance are evaluated. One of the most interesting fields of the squid-based magnetometer application is biomagnetism, particularly, the human heart magnetocardiogram measuring. The low-temperature squids were used in this area and many interesting and important scientific results have been obtained. The observations have shown that the main noise contribution was not due to the squid but to the Earth's magnetic field variations, industrial inductions, and mainly to the vibrations caused by liquid nitrogen boiling and by vibrations of the box. Further attempts are needed to reduce the magnetic noise inductions. Nevertheless, the estimations promise the maximum signal/noise relation of the high-T(sub c) squid-magnetocardiometer to be not less than 10:1 in a bandwidth of 60 Hz. Apparently, such resolution would be enough not only for steady cardiogram reading but even for thin structure investigation at average technique application.

Polushkin, V. N.↗
NASA NTRS2010

Use of Data Comm by Flight Crew in High-Density Terminal Areas

This paper describes a collaborative FAA and NASA experiment using 22 commercial airline pilots to determine the effect of using Datalink Communication (Data Comm) to issue messages in busy, terminal area operations. Four conditions were defined that span current day to future flight deck equipage levels (voice communication only, Data Comm only, Data Comm with Moving Map Display, Data Comm with Moving Map displaying taxi route), and each condition was used to create an arrival and a departure scenario at the Boston Logan Airport. These eight scenarios were repeated twice for a total of 16 scenarios for each of the eleven crews. Quantitative data was collected on subject reaction time and eye tracking information. Questionnaires collected subjective feedback on workload and acceptability to the flight crew for using Data Comm in a busy terminal area. 95% of the Data Comm messages were responded to by the flight crew within one minute; however, post experiment debrief comments revealed almost unanimous consensus that two minutes was a reasonable expectation for crew response. Eye tracking data indicated an insignificant decrease in head-up time for the Pilot Flying when Data Comm was introduced; however, the Pilot Monitoring had significantly less head-up time. Data Comm workload was rated as operationally acceptable by both crew members in all conditions in flight at any altitude above the Final Approach Fix in terms of response time and workload. Results also indicate the use of Data Comm during surface operations was acceptable, the exception being the simultaneous use of voice, Data Comm, and audio chime required for an aircraft to cross an active runway. Many crews reported they believed Data Comm messages would be acceptable after the Final Approach Fix or to cross a runway if the message was not accompanied by a chime and there was not a requirement to immediately respond to the uplink message.

Baxley, Brian T.↗
NASA NTRS1974

Electron beam fluorescence system to measure gas density in impulse facilities

Very rapid measurements, ranging from a few microsecond to milliseconds in duration, characterize studies made in shock regions or behind them. A system to measure gas density under such conditions in a 15.24-cm (6-in.) expansion tube is described. The basic elements are an electron beam of moderate energy and high current capability, an optical detector, and the associated electronics and data readout equipment. A heated-cathode electron gun, capable of pulsed operation and delivering up to 200 milliamperes current, provides the source of electrons. Optics include a simple collector lens, aperture, collimator lens, filters, and a photomultiplier tube. The photomultiplier output signal was recorded by means of photographed oscilloscope traces for pulsed beam operation.

Hoppe, J. C.↗