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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The origin of the Kirkwood gaps - A mapping for asteroidal motion near the 3/1 commensurability

A mapping of the phase space onto itself with the same low-order resonance structure as the 3/1 commensurability in the planar-elliptic restricted three-body problem is obtained. This mapping is about 1,000 times faster than the usual method of numerically integrating the averaged equations of motion. It exhibits some surprising behavior that might provide a key to the origin of the Kirkwood gaps. It is noted that a test asteroid placed in the gap may evolve for a million years with low eccentricity (less than 0.05) and then suddenly jump to large eccentricity (greater than 0.3), becoming a Mars crosser. The removal of the asteroid by a close encounter with Mars would then be possible. As a first test of this hypothesis, a distribution of 300 test asteroids in the area of the 3/1 commensurability was evolved for two million years. When the Mars crossers are removed, the distribution of initial conditions reveals a gap at the location of the 3/1 Kirkwood gap.

Wisdom, J.↗
NASA NTRS1982

Flight measurements of tile gap heating on the Space Shuttle

Data are presented from Space Shuttle flight measurements of the temperature distribution within the gaps of the reusable surface insulation tiles. This is the first of a series of flight measurements in which the gap width and tile surface edge radius will be systematically varied. The data show several interesting features including the time and effect of boundary-layer transition. The local heating rates into the gap surfaces are calculated from the measured temperature distribution down the gap at two locations.

Pitts, W. C.↗
NASA NTRS1983

Gage Measures Recessed Gaps

New tool measures separation between recessed parallel surfaces. Tiles have overhanging edges, tool designed to slip into gap from end so it extends through 0.040-inch crack. Measure gaps between 0.200 and 0.400 inch so gap fillers of proper thickness can be selected. Useful in numerous industrial situation involving gap measurements in inaccessable places.

Zepeda, J. L.↗
NASA NTRS1983

Aerothermal environment in control surface gaps in hypersonic flow: An overview

Experimental and analytical research to develop an understanding of the fluid and thermal environment in control surface gaps such as the spanwise gap of the wing elevon and chordwise gap of a split elevon configuration typical of the Space Shuttle are summarized. Although the experimental and analytical studies were initiated too late to significantly impact the Shuttle design they do provide a fundamental understanding of the basic fluid/thermal environment in control surface gaps and help to establish a firm data base for vehicle design.

Wieting, A. R.↗
NASA NTRS1983

Analysis of gap heating due to stepped tiles in the shuttle thermal protection system

Analytical methods used to investigate entry gap heating in the Shuttle orbiter thermal protection system are described. Analytical results are given for a fuselage lower-surface location and a wing lower-surface location. These are locations where excessive gap heating occurred on the first flight of the Shuttle. The results of a study to determine the effectiveness of a half-height ceramic fiber gap filler in preventing hot-gas flow in the tile gaps are also given.

Petley, D. H.↗
NASA NTRS1983

Aerothermal environment in control surface gaps in hypersonic flow - An overview

Experimental and analytical research by the NASA Langley Research Center to develop an understanding of the fluid and thermal environment in control surface gaps such as the spanwise gap of the wing elevon and chordwise gap of a split elevon configuration typical of the Space Shuttle are summarized. Although the experimental and analytical studies were initiated too late to significantly impact the basic Shuttle design they do provide a fundamental understanding of the basic fluid/thermal environment in control surface gaps and help to establish a firm data base for future vehicle design.

Wieting, A. R.↗
NASA NTRS1985

Hand-Held Electronic Gap-Measuring Tools

Repetitive measurements simplified by tool based on LVDT operation. With fingers in open position, Gap-measuring tool rests on digital readout instrument. With fingers inserted in gap, separation alters inductance of linear variable-differential transformer in plastic handle. Originally developed for measuring gaps between surface tiles of Space Shuttle orbiter, tool reduces measurement time from 20 minutes per tile to 2 minutes. Also reduces possibility of damage to tiles during measurement. Tool has potential applications in mass production; helps ensure proper gap dimensions in assembly of refrigerator and car doors and also used to measure dimensions of components and to verify positional accuracy of components during progressive assembly operations.

Sugg, F. E.↗
NASA NTRS1985

GaAsP on GaP top solar cells

GaAsP on GaP top solar cells as an attachment to silicon bottom solar cells are being developed. The GaAsP on GaP system offers several advantages for this top solar cell. The most important is that the gallium phosphide substrate provides a rugged, transparent mechanical substrate which does not have to be removed or thinned during processing. Additional advantages are that: (1) gallium phosphide is more oxidation resistant than the III-V aluminum compounds, (2) a range of energy band gaps higher than 1.75 eV is readily available for system efficiency optimization, (3) reliable ohmic contact technology is available from the light-emitting diode industry, and (4) the system readily lends itself to graded band gap structures for additional increases in efficiency.

Mcneely, J. B.↗
NASA NTRS1986

Satellite 'wakes' and the orbit of the Encke Gap moonlet

A general model is developed for the quasi-periodic optical depth fluctuations observed in photopolarimeter and radio occultation profiles near the Encke Gap of Saturn's rings, which may be the gravitational 'wakes' of a moonlet orbiting within the same gap. The results obtained are used to estimate the moonlet's orbit and mass from the occultation data. In view of the present treatment's neglect of particle collisions and self-gravity, the longitude is consistent with other estimates based on a photopolarimeter scan exterior to the gap. The consistency of the orbit parameters inferred from photopolarimeter, radio, and wavy edge data strongly suggests that a single, dominant moonlet orbits within the gap.

Showalter, M. R.↗
NASA NTRS1985

The effect on the transmission loss of a double wall panel of using helium gas in the gap

The possibility of increasing the sound-power transmission loss of a double panel by using helium gas in the gap is investigated. The transmission loss of a panel is defined as ten times the common logarithm of the ratio of the sound power incident on the panel to the sound power transmitted to the space on the other side of the panel. The work is associated with extensive research being done to develop new techniques for predicting the interior noise levels on board high-speed advanced turboprop aircraft and reducing the noise levels with a minimum weight penalty. Helium gas was chosen for its inert properties and its low impedance compared with air. With helium in the gap, the impedance mismatch experienced by the sound wave will be greater than that with air in the gap. It is seen that helium gas in the gap increases the transmission loss of the double panel over a wide range of frequencies.

Atwal, M. S.↗
NASA NTRS1986

High band gap 2-6 and 3-5 tunneling junctions for silicon multijunction solar cells

A multijunction silicon solar cell of high efficiency is provided by providing a tunnel junction between the solar cell junctions to connect them in series. The tunnel junction is comprised of p+ and n+ layers of high band gap 3-5 or 2-6 semiconductor materials that match the lattice structure of silicon, such as GaP (band gap 2.24 eV) or ZnS (band gap 3.6 eV). Each of which has a perfect lattice match with silicon to avoid defects normally associated with lattice mismatch.

Daud, Taher↗
NASA NTRS1989

High Temperature Gas-Gap Thermal Switch

Device set to allow heat to flow across gap (switch "on") or decrease rate of transfer of heat to relatively low value (switch "off"). Operates at temperatures in approximate range of 100 to 1,500 degree C. Central cylindrical object thermally connected to (or disconnected from) environment by filling gap between inner and outer sleeves of switch (or evacuating gap) to increase (or decrease) thermal conduction across gap.

Bard, Steven↗
NASA NTRS1990

Finding Platinum-Coating Gaps On Titanium Anodes

Simple procedure makes gaps visible to eye. New gap-detection method consists of plating thin layer of non-silver-colored metal like copper or gold on anode. Contrast in color between plated metal and bare anode material makes gaps stand out. If anode passes inspection, copper or gold plate removable by reversal of test-plating current. Remains to be determined whether test plating and removal damages anode. New method simpler and more economical than previous attempts to identify gaps in platinum.

Bodemeijer, Ronnald↗
NASA NTRS1990

InAsSbBi, a direct band-gap, III-V, LWIR material

In the last several years Dr. Stringfellow's group at the University of Utah has reported success in incorporating over 3 percent Bi in InAs and 1.5 percent in InAsSb using Organometallic Vapor Phase Epitaxy (OMVPE) growth techniques. For InAs the lattice constant increase is linear with a=6.058+0.966x (InAs(1-x)Bi(x)), and a decrease in band gap energy of dEg / dx = -55meV / at a percentage Bi. Extrapolating this to the ternary minimum band gap at InAs(0.35)Sb(0.65), an addition of 1 to 2 percent Bi should drop the band gap to the 0.1 to 0.05eV range (10 to 20 microns). These alloys are direct band gap semiconductors making them candidates for far IR detectors. The current status of the InAsSbBi alloys is that good crystal morphology and x ray diffraction data has been obtained for up to 3.4 percent Bi. The Bi is metastable at these concentrations but the OMVPE grown material has been able to withstand the 400 C growth temperature for several hours without phase separation.

Stringfellow, G. B.↗
NASA NTRS1992

Large-gap magnetic suspension systems

The classification of magnetic suspension devices into small-gap and large-gap categories is addressed. The relative problems of position sensing, control systems, power supplies, electromagnets, and magnetic field or force analysis are discussed. The similarity of all systems from a controls standpoint is qualified. Some applications where large-gap technology is being applied to systems with a physically small air-gap are mentioned. Finally, the applicability of some other suspension approaches, such as electrodynamic or superconducting are briefly addressed.

Britcher, Colin P.↗
NASA NTRS1992

Lattice-matched heteroepitaxy of wide gap ternary compound semiconductors

A variety of applications are identified for heteroepitaxial structures of wide gap I-III-VI2 and II-IV-V2 semiconductors, and are assessed in comparison with ternary III-V alloys and other wide gap materials. Non-linear optical applications of the I-III-VI2 and II-IV-V2 compound heterostructures are discussed, which require the growth of thick epitaxial layers imposing stringent requirements on the conditions of heteroepitaxy. In particular, recent results concerning the MOCVD growth of ZnSi(x)Ge(1-x)P2 alloys lattice-matching Si or GaP substrates are reviewed. Also, heterostructures of Cu(z)Ag(1-z)GaS2 alloys that lattice-match Si, Ge, GaP or GaAs substrates are considered in the context of optoelectronic devices operating in the blue wavelength regime. Since under the conditions of MOCVD, metastable alloys of the II-IV-V2 compounds and group IV elements are realized, II-IV-V2 alloys may also serve as interlayers in the integration of silicon and germanium with exactly lattice-matched tetrahedrally coordinated compound semiconductors, e.g. ZnSi(x)Ge(1-x)P2.

Bachmann, Klaus J.↗
NASA NTRS1992

Remote plasma enhanced chemical vapor deposition of GaP with in situ generation of phosphine precursors

Thin homoepitaxial films of gallium phosphide (GaP) have been grown by remote plasma enhanced chemical vapor deposition utilizing in situ-generated phosphine precursors. The GaP forming reaction is kinetically controlled with an activation energy of 0.65 eV. The increase of the growth rate with increasing radio frequency (RF) power between 20 and 100 W is due to the combined effects of increasingly complete excitation and the spatial extension of the glow discharge toward the substrate; however, the saturation of the growth rate at even higher RF power indicates the saturation of the generation rate of phosphine precursors at this condition. Slight interdiffusion of P into Si and Si into GaP is indicated from GaP/Si heterostructures grown under similar conditions as the GaP homojunctions.

Choi, S. W.↗
NASA NTRS1993

Remote plasma enhanced chemical vapor deposition of GaP with in situ generation of phosphine precursors

Thin homoepitaxial films of gallium phosphide (GaP) were grown by remote plasma enhanced chemical vapor deposition utilizing in situ generated phosphine precursors. The GaP forming reaction is kinetically controlled with an activation energy of 0.65 eV. The increase of the growth rate with increasing radio frequency (rf) power between 20 and 100 W is due to the combined effects of increasingly complete excitation and the spatial extension of the glow discharge toward the substrate, however, the saturation of the growth rate at even higher rf power indicates the saturation of the generation rate of phosphine precursors at this condition. Slight interdiffusion of P into Si and Si into GaP is indicated from GaP/Si heterostructures grown under similar conditions as the GaP homojunctions.

Choi, S. W.↗