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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Solar cycle variations in F-region Te in the vicinity of the midlatitude trough based on AE-C measurements at solar minimum and DE-2 measurements at solar maximum

Magnetospheric energy deposited in the plasmasphere produces large enhancements in the electron temperature in the nightside ionosphere at the foot of the geomagnetic L shell that traverses the plasmapause. This temperature peak, which is associated with the midlatitude trough in electron density, often has a great enough amplitude to produce 630 nm emission known as a Sar-arc. The Atmosphere Explorer-C measurements made at solar minimum and the Dynamics Explorer-2 measurements made at solar maximum are used to illustrate how this signature of F-region electron heating changes with solar activity. Global empirical models of the electron temperature and density have not been able to resolve these features thus far because of their large movements with geomagnetic activity and because of the large bin sizes used in the models. It is not yet clear how this major feature of the F-region temperature structure could be included easily in the IRI model.

Brace, Larry H.↗
NASA NTRS1975

The SAR arc event observed during the December 1971 magnetic storm

Observations from five separate experiments on the Isis 2 spacecraft are used to study the atmosphere/ionosphere during the magnetic storm of December 16-20, 1971. The data are most complete in the midlatitude region, permitting a study of the SAR arc (subauroral red arc) which developed during the night of December 17-18. Ion composition and temperature, electron temperature, electron-density height profiles from the spacecraft to the F region, and the intensity of the 6300-A oxygen emission are all presented for the region of interest. It is found that the H(+) concentration had sharp gradients near the SAR arc and that the plasma temperature was significantly enhanced over typical nighttime values, reaching nearly 7000 K at 1400 km on the field line which intersected the arc. A system of time-dependent equations for atmospheric/ionospheric composition and temperature is solved using boundary conditions which were selected so that the solutions are in agreement with the observations. From these solutions, an assessment is made of the influence of (1) the efflux of plasma from the ionosphere to the magnetosphere, (2) the decrease in O/N2 at the turbopause, (3) the increase in the loss coefficient as a result of an increase in the vibrational temperature of N2, and (4) the conduction of thermal energy into the ionosphere.

Maier, E. J.↗
NASA NTRS2005

NASA GRC and MSFC Space-Plasma Arc Testing Procedures

Tests of arcing and current collection in simulated space plasma conditions have been performed at the NASA Glenn Research Center (GRC) in Cleveland, Ohio, for over 30 years and at the Marshall Space flight Center (MSFC) for almost as long. During this period, proper test conditions for accurate and meaningful space simulation have been worked out, comparisons with actual space performance in spaceflight tests and with real operational satellites have been made, and NASA has achieved our own internal standards for test protocols. It is the purpose of this paper to communicate the test conditions, test procedures, and types of analysis used at NASA GRC and MSFC to the space environmental testing community at large, to help with international space-plasma arcing testing standardization. To be discussed are: 1. Neutral pressures, neutral gases, and vacuum chamber sizes. 2. Electron and ion densities, plasma uniformity, sample sizes, and Debye lengths. 3. Biasing samples versus self-generated voltages. Floating samples versus grounded. 4. Power supplies and current limits. Isolation of samples from power supplies during arcs. Arc circuits. Capacitance during biased arc-threshold tests. Capacitance during sustained arcing and damage tests. Arc detection. Preventing sustained discharges during testing. 5. Real array or structure samples versus idealized samples. 6. Validity of LEO tests for GEO samples. 7. Extracting arc threshold information from arc rate versus voltage tests. 8 . Snapover and current collection at positive sample bias. Glows at positive bias. Kapton pyrolization. 9. Trigger arc thresholds. Sustained arc thresholds. Paschen discharge during sustained arcing. 10. Testing for Paschen discharge thresholds. Testing for dielectric breakdown thresholds. Testing for tether arcing. 11. Testing in very dense plasmas (ie thruster plumes). 12. Arc mitigation strategies. Charging mitigation strategies. Models. 13. Analysis of test results. Finally, the necessity of testing will be emphasized, not to the exclusion of modeling, but as part of a complete strategy for determining when and if arcs will occur, and preventing them from occurring in space.

Ferguson, Dale C.a↗
NASA NTRS2000

Synthesis of Single Wall Carbon Nanotubes by Plasma Arc: Role of Plasma Parameters

Single wall carbon nanotubes (SWNT) are porous objects on the molecular scale and have a low density, which gives them potential applications as adsorbent for molecular hydrogen. Their H2 absorption capacity published in the literature varies from 4 to 10% by mass according to the purity of the materials and storage conditions. Optimization of production methods of SWNTs should permit improving these new materials for storage of hydrogen. In this article, we show the potential of using SWNTs in hydrogen storage. In particular, we pose problems associated with synthesis, purification, and opening up of the nanotubes. We present an electric arc process currently used at laboratory scale to produce single wall carbon nanotubes. We discuss, in particular, operating conditions that permit growth of nanotubes and some plasma parameters that assure control of the material. Analysis of the process is carried out with the aid of local measurements of temperature and scanning and transmission electron microscopy of the materials.

Farhart, Samir↗
NASA NTRS2014

AVCOAT Density Characterization for Orion Multi-Purpose Crew Vehicle

The Orion Multi-Purpose Crew Vehicle (MPCV) will transport four crew members to and from lunar-class orbital destinations. The first orbital Exploration Flight Test (EFT-1) is scheduled for December 2014 and will provide valuable data on several systems, including the heat shield. The heat shield material is AvcoatTM, a mid-density ablator. Specifically, the heat shield contains a fiberglass-phenolic honeycomb structure filled with an ablative epoxy novolac resin. Post-flight characterization of the EFT-1 thermal protection system will be conducted in order to study the material response and measure the char front of the material. Avcoat density profiling will be conducted to study three critical material zones: char, pyrolysis, and virgin states as a function of material depth. As part of a ground test campaign, Avcoat coupons are tested at the NASA Ames Research Center Arc Jet Complex. The test campaign is set forth to study material response based on environments, perform Avcoat material density characterization, and compare the char depths from the HEAT sensor and density profiling studies. These investigations will then be compared to flight data in order to improve upon TPS material response models.

AVCOAT↗
NASA NTRS1986

Threshold determining mechanisms for discharges in high voltage solar arrays

A theory is developed to account for the observed properties of discharges of solar arrays immersed in plasma. The theory is based on the assumption that a thin layer of insulating contaminant covers any metallic surface exposed to the plasma. Quantities derivable from the theory include a voltage threshold for arcing. The existence of the threshold and its predicted weak dependence on plasma density appear consistent with experimental results.

Parks, D. E.↗
NASA NTRS2008

Controlling Charging and Arcing on a Solar Powered Auroral Orbiting Spacecraft

The Global Precipitation Measurement satellite (GPM) will be launched into a high inclination (65 degree) orbit to monitor rainfall on a global scale. Satellites in high inclination orbits have been shown to charge to high negative potentials, with the possibility of arcing on the solar arrays, when three conditions are met: a drop in plasma density below approximately 10,000 cm(exp -3), an injection of energetic electrons of energy more that 7-10 keV, and passage through darkness. Since all of these conditions are expected to obtain for some of the GPM orbits, charging calculations were done using first the Space Environment and Effects (SEE) Program Interactive Spacecraft Charging Handbook, and secondly the NASA Air-force Spacecraft Charging Analyzer Program (NASCAP-2k). The object of the calculations was to determine if charging was likely for the GPM configuration and materials, and specifically to see if choosing a particular type of thermal white paint would help minimize charging. A detailed NASCAP-2k geometrical model of the GPM spacecraft was built, with such a large number of nodes that it challenged the capability of NASCAP-2k to do the calculations. The results of the calculations were that for worst-case auroral charging conditions, charging to levels on the order of -120 to -230 volts could occur on GPM during night-time, with differential voltages on the solar arrays that might lead to solar array arcing. In sunlit conditions, charging did not exceed -20 V under any conditions. The night-time results were sensitive to the spacecraft surface materials chosen. For non-conducting white paints, the charging was severe, and could continue unabated throughout the passage of GPM through the auroral zone. Somewhat conductive (dissipative) white paints minimized the night-time charging to levels of -120 V or less, and thus were recommended for GPM thermal control. It is shown that the choice of thermal control paints is important to prevent arcing on high inclination orbiting spacecraft solar arrays as well as for GEO satellites, even for solar array designs chosen to minimize arcing.

Ferguson, Dale C.↗
NASA NTRS2005

Thruster Plume Plasma Diagnostics: A Ground Chamber Experiment for a 2-Kilowatt Arcjet

Although detailed near field (0 to 3 cm) information regarding the exhaust plume of a two kilowatt arc jet is available (refs. 1 to 6), there is virtually little or no information (outside of theoretical extrapolations) available concerning the far field (2.6 to 6.1 m). Furthermore real information about the plasma at distances between (3 to 6 m) is of critical importance to high technology satellite companies in understanding the effect of arc jet plume exhausts on space based power systems. It is therefore of utmost importance that one understands the exact nature of the interaction between the arc jet plume, the spacecraft power system and the surrounding electrical plasma environment. A good first step in understanding the nature of the interactions lies in making the needed plume parameter measurements in the far field. All diagnostic measurements are performed inside a large vacuum system (12 m diameter by 18 m high) with a full scale arc jet and solar array panel in the required flight configuration geometry. Thus, necessary information regarding the plume plasma parameters in the far field is obtained. Measurements of the floating potential, the plasma potential, the electron temperature, number density, density distribution, debye length, and plasma frequency are obtained at various locations about the array (at vertical distances from the arc jet nozzle: 2.6, 2.7, 2.8, 3.2, 3.6, 4.0, 4.9, 5.0, 5.4, 5.75, and 6.14 m). Plasma diagnostic parameters are measured for both the floating and grounded configurations of the arc jet anode and array. Spectroscopic optical measurements are then acquired in close proximity to the nozzle, and contamination measurements are made in the vicinity of the array utilizing a mass spectrometer and two Quartz Crystal Microbalances (QCM's).

Galofaro, Joel T.↗
NASA NTRS2016

Extreme Asymmetry in the Polarized Disk of V1247 Orionis

We present the first near-infrared scattered-light detection of the transitional disk around V1247 Ori, which was obtained using high-resolution polarimetric differential imaging observations with Subaru/HiCIAO. Our imaging in the H band reveals the disk morphology at separations of approx.0.14-0.86 (54-330 au) from the central star. The polarized intensity image shows a remarkable arc-like structure toward the southeast of the star, whereas the fainter northwest region does not exhibit any notable features. The shape of the arm is consistent with an arc of 0.28 +/- 0.09 in radius (108 au from the star), although the possibility of a spiral arm with a small pitch angle cannot be excluded. V1247 Ori features an exceptionally large azimuthal contrast in scattered, polarized light; the radial peak of the southeastern arc is about three times brighter than the northwestern disk measured at the same distance from the star. Combined with the previous indication of an inhomogeneous density distribution in the gap at 46 au, the notable asymmetry in the outer disk suggests the presence of unseen companions and/or planet-forming processes ongoing in the arc.

azimuthal contrast↗
NASA NTRS1992

Arcing in space structures in low Earth orbit

This report describes results of an experimental and theoretical program to investigate arcing of structures containing dielectric and conducting materials when they are biased negatively with respect to a plasma. An argon ion source generated Ar(+) ions of directed energy 20 to 40 eV and density approximately 10(exp 7) cm(exp -3) that impinged upon samples containing a dielectric material on top of a negatively biased Kovar plate. Arcing events were studied for bias voltages between -300 and -1000V with respect to the ion beam. The samples were Dow Corning 93-500 adhesive on Kovar, fused silica cover slips bonded on Kovar, and silicon solar cells mounted on Kovar. Measurements of discharge current, Kovar plate voltage, and radiation from the arc versus time were carried out. Microsecond duration exposure images and optical spectra in the 0.24 to 0.40 micron band were also acquired during arcing events. Arcing events were found to be associated with exposed adhesive and means were found to eliminate arcing altogether. The charging of a silica cover plate and the fields around the plate were calculated using a particle-in-cell code. Models were developed to explain the ignition of the arc and the physical processes occurring during the discharge.

Upschulte, B. L.↗
NASA NTRS1972

The ionosphere during a subauroral red arc

The enhancements of the red 6300A line in the midlatitudes during maximum solar activity are discussed. From Explorer 31 and OGO-4 satellite data, electron and ion temperatures were obtained at altitudes of 880km and 2500km. It was found that there is an increased plasma temperature in the region of the optical emissions, a difference of 1000k between the plasma temperature at 880km and that at 2100km, and the ion temperatures are less than the electron temperatures. It is concluded that red arcs are observed only when there is heat flow from above, combined with decreased density caused by composition changes at the lower boundary.

Maier, E.↗
NASA NTRS1978

Some properties of low-vapor-pressure braze alloys for thermionic converters

Density, dc electrical resistivity, thermal conductivity, and linear thermal expansion are measured for arc-melted rod-shaped samples of binary eutectics of Zr, Hf, Ru, Nb, Ir, Mo, Ta, Os, Re, and W selected as very-low-pressure braze fillers for thermionic converters. The first two properties are measured at 296 K for Zr-21.7 at% Ru, Zr-13 wt% W, Zr-19 wt% W, Zr-22.3 at% Nb, Nb-66.9 at% Ru, Hf-25.3 wt% Re, Zr-25.7 at% Ta, Hf-22.5 at% W, and Nb-35 wt% Mo. The last property is measured from 293 K to 2/3 melting point for specified alloys of different compositions. Resistivities of 0.000055 to 0.000181 ohm-cm are observed with the alloys having resistivities about ten times that of the less resistive constituent metal and about three times that of the more resistive constituent metal, except for Zr-19 wt% W and Nb-35 wt% Mo (greater resistivities). Thermal expansion coefficients vary from 0.000006 to 0.0000105/K. All brazes exhibit linear thermal expansion near that of their constituent metals.

Bair, V. L.↗
NASA NTRS1986

Comet P/Halley 1910, 1986: An objective-prism study

V. M. Slipher of the Lowell Obs. collected a large amount of spectroscopic data during the 1910 apparition of Halley's comet. Three of his post perihelion objective-prism plates were selected, digitized, and subjected to modern digital data reduction procedures. Some of the important steps in the analysis where: (1) Density to intensity conversion for which was used 1910 slit spectra of Fe-arc lamp on similar plates (Sigma) and derived an average characteristic curve; (2) Flux calibration using the fact that during the period June 2 to 7 1910 P/Halley was very close (angular distance) to the bright star Alpha Sex (A0III, V-4.49), and the spectra of both star and comet were recorded on the same plates. The flux distribution of Alpha Sex was assumed to be similar to that of the standard star 58 Aql and derived a sensitivity curve for the system; (3) Atmospheric extinction using the standard curve for the Lowell Obs.; (4) Solar continuum subtraction using the standard solar spectrum binned to the spectral resolution. An example of a flux-calibrated spectrum of the coma (integrated over 87,000km) before the subtraction of solar continuum is presented.

Carsenty, U.↗
NASA NTRS1988

The terrestrial plasma source - A new perspective in solar-terrestrial processes from Dynamics Explorer

The geospace environment has been viewed as a mixing bowl for plasmas of both solar and terrestrial origin. The present perspective on the nature of the supply mechanisms has undergone a radical evolution over the past decade, particularly during the five years of the Dynamics Explorer mission. During this period, the terrestrial source has increased in importance in both magnitude and character of ionospheric outflow. These outflows include the classical polar wind, the cleft ion fountain, the auroral ion fountain, and the polar cap. The earth can be envisioned as a multifaceted fountain which ejects particles from different spatial locations spread around the globe. These particles exhibit a range of masses from 1 to 32 amu and a range of energies from 1 eV to 10 keV. The total flux of this ionospheric outflow is very large: adequate to supply the entire magnetospheric particle population. And the implications of the outflow are significant across a broad spectrum of solar-terrestrial processes ranging from sources of magnetospheric plasmas, to influences on ionospheric density and temperature structure, to energy transfer in phenomena such as stable auroral red arcs. The Dynamics Explorer mission has made a major contribution in the characterization of the terrestrial plasma source.

Chappell, Charles R.↗
NASA NTRS1994

Development of lightweight ceramic ablators and arc-jet test results

Lightweight ceramic ablators (LCA's) were recently developed at Ames to investigate the use of low density fibrous substrates and organic resins as high temperature, high strength ablative heat shields. Unlike the traditional ablators, LCA's use porous ceramic/carbon fiber matrices as substrates for structural support, and polymeric resins as fillers. Several substrates and resins were selected for the initial studies, and the best performing candidates were further characterized. Three arcjet tests were conducted to determine the LCA's thermal performance and ablation characteristics in a high enthalpy, hypersonic flow environment. Mass loss and recession measurements were obtained for each sample at post test, and the recession rates were determined from high speed motion films. Surface temperatures were also obtained from optical pyrometers.

Tran, Huy K.↗
NASA NTRS1984

Aircraft penetrations of arc cloud lines

Results of a NOAA/NASA research field program (1982-1983) which focused on dynamic and thermodynamic characterization of arc cloud lines are discussed. The program combines research aircraft flights with rapid-scan (3-minute interval) GOES imagery and covers the subcloud layer above and below the density surge line. Strong differences in the dynamic characteristics of air are noted to exist within and above the density surge line (DSL); air motions within the DSL are much more turbulent, with stronger upward and downward motions, than in the subcloud layer above the DSL. The arc cloud lines and the associated DSL regions are concluded to pose an extreme potential hazard to aircraft and Space Shuttle operations.

Sinclair, P. C.↗
NASA NTRS1973

A technique for measuring hypersonic flow velocity profiles

A technique for measuring hypersonic flow velocity profiles is described. This technique utilizes an arc-discharge-electron-beam system to produce a luminous disturbance in the flow. The time of flight of this disturbance was measured. Experimental tests were conducted in the Langley pilot model expansion tube. The measured velocities were of the order of 6000 m/sec over a free-stream density range from 0.000196 to 0.00186 kg/cu m. The fractional error in the velocity measurements was less than 5 percent. Long arc discharge columns (0.356 m) were generated under hypersonic flow conditions in the expansion-tube modified to operate as an expansion tunnel.

Gartrell, L. R.↗