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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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Design and evaluation of cylindrical out-of-pile thermionic converter test vehicle to determine performance of tungsten emitters with preferred crystal orientation
High work function stable faceted W thermionic emitter surface preparation by electroetching and vapor deposition
Calorimetric measurements determining total hemispheric emittance of thin gold films as function of temperature, demonstrating film thickness effect
Thermal and electrical characteristics of two nuclear type cylindrical converters with nonuniform emitter temperature
Chemically vapor deposited deep etched tungsten emitter for high performance cylindrical thermionic converter
Total emittance measurements by portable IR reflectometer, tabulating nongray error effects
Substrate emitter monolithic inverted transistor structure for low-power high-current gain application
Radiometric measurement of total normal emittances of real surfaces at cryogenic temperatures
Bipolar junction transistor doping effects on bandgap decrease and emitter efficiency, explaining current gain temperature dependence
The performance of a fixed-space planar miniature diode (diminiode) with a guarded collector has been mapped using a computerized data acquisition facility. The electrode materials consisted of a tantalum alloy emitter and a Nb-1Zr collector; the electrode gap was 0.254 mm.
Measurements of spectral emittance in the IR region from 6.8 to 13.3 microns were made with an airborne spectrometer on flights at 650 m above the olivine basalt flows at Pisgah Crater in the southern Californian desert. Readings were taken at a rate of six spectra per second. The spectra show chemical and mineralogical differences that can be related to differences in the terrain below the aircraft.
Calorimetric measurements of the total hemispherical emittance of a section of polished aluminum support tubing from the Surveyor 3 spacecraft are reported. The values found, 0.090 at 25 C and 0.089 at 50 C, are lower than was expected from a visual estimate but are in good agreement with an estimate based upon scanning electron microscopy of the tubing.
The sizes, shapes, and complex refractive indices of particles are calculated in a study of the IR spectral reflectance of a semiinfinite medium composed of irregular particles of different materials. Geometric optics techniques with corrections for additional absorption due to particle edges and asperities is used in scattering and absorption calculations for particles larger than the wavelength. A Lorentz-Lorenz model is used to derive the averaged complex index of the medium, assuming that its individual particles are ellipsoids. Experimental results obtained on a Michelson interferometer for the spectral emittance of particulate mineral materials are compared with theoretical results. Good agreement between the experimental and theoretical results suggests the applicability, in remote IR spectroscopy, of the theoretical concepts applied in this study.
A comprehensive program to develop low solar absorptance/high emittance coatings, to be successful, must coordinate basic materials preparation, coatings technology, environmental simulation, production, and flight-test evaluation. The prime criteria for 'white' thermal-control coatings are low solar absorptance and, most importantly, solar-absorptance stability. Many variables affect the solar absorptance and its stability. These effects must be discerned and evaluated. The factors involved, however, are not entirely independent; accordingly, the present paper emphasizes the major variables, the relationships among them, and how important they are in improving the properties and performance of the coatings.
Simple addition to ceramic insulating tiles provides backup properties that minimize transfer of heat through tiles when their surfaces become damaged. Addition of 3 percent by weight of 320- or 600-grit silicon carbide powder to ceramic during production results in impregnated tile material that resists overheating. Silicon carbide increases emittance and decreases transmittance of ceramic.
Conceptual transistor embedded in photovoltaic diode promises to increase efficiency to more than 20 percent. Solar-cell transistor has front-surface contact, rear contact, and floating emitter. Variety of other contact and junction configurations possible, but do not offer ease of fabrication in combination with high performance.
The use of liquid dopants and liquid masks for p-n junction formation in dendritic web solar cells was investigated and found to be equivalent to the use of gaseous dopants and CVD SiO2 masks previously used. This results in a projected cost reduction of 0.02 1980$/Watt for a 25 MW/year production line, and makes possible junction formation processes having a higher throughput than more conventional processes. The effect of a low-energy (0.4 keV) hydrogen ion implant on dendritic web solar cells was also investigated. Such an implant was observed to improve Voc and Jsc substantially. Measurements of internal quantum efficiency suggest that it is the base of the cell, rather than the emitter, which benefits from the hydrogen implant. The diffusion length for electrons in the p-type base increased from 53 microns to 150 microns in one case, with dendritic web cell efficiency being boosted to 15.2 percent. The mechanism by which low-energy hydrogen ions can penetrate deeply into the silicon to effect the observed improvement is not known at this time.
Signal-to-noise ratio of radiometer system calculated. Publication from NASA's Jet Propulsion Laboratory presents calculations of power radiated from natural emitter on Earth to microwave collecting aperture on aircraft or spacecraft. Analysis develops power-transfer criteria for detection of emitting object by collecting aperture (that is, by antenna and its receiver). Resulting formulas used in design of radiometer systems.