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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Direct conversion of light to radio frequency energy

A description is presented of the test results obtained with the latest models of the phototron. The phototron was conceived as a replacement for the high voltage solar cell-high power klystron combination for the solar power satellite concept. Physically, the phototron is a cylindrical evacuated glass tube with a photocathode, two grids, and a reflector electrode in a planar configuration. The phototron can be operated either in a biased mode where a low voltage is used to accelerate the electron beam produced by the photocathode or in an unbiased mode referred to as self-oscillation. The device is easily modulated by light input or voltage to broadcast in AM or FM. The range of operation of the present test model phototrons is from 2 to 200 MHz.

Freeman, J. W.↗
NASA NTRS1982

Dynamical features of moving double layers

Numerical simulations of the dynamics of double layers that form in response to an applied potential drop across a plasma are carried out for plasmas of lengths much greater than previously considered. The evolution of finite-size plasmas of lengths 100, 200 and 400 Debye lengths at the low-potential end of the simulation region was followed by the solution of the Vlasov and Poisson equations. Results show that the double layer moves towards the high-potential side of the layer, at a speed directly dependent on the length of the plasma. The moving double layer is accompanied by a moving density front which is similar to an ion acoustic shock created by the expansion of a high-density plasma into a low-density plasma, as well as plasma heating and evacuation, electron and ion current interruptions and recovery. Double layer formation, motion, and accompanying phenomena are found to repeat periodically. Results are in good agreement with laboratory experiments, and may be used to explain certain phenomena observed in auroral plasmas.

Singh, N.↗
NASA NTRS1981

The spontaneous concentration of magnetic field in the photosphere of the sun

The basic physics of magnetic flux tubes in the solar photosphere is reviewed, with areas still open to conjecture pointed out. The question of the concentration of individual small flux tubes to levels of 1-2 kilogauss, when the average solar surface magnetic field is on the order of 10 gauss, by processes of twisting and the formation of flux ropes made up of tubes wound around each other is considered together with the effects of turbulence on the flux tube. Mechanisms for tube compression by the evacuation of the gas contained within a flux tube are then examined, and the possibility of field concentration through the cooling of the gas within the tube in a superadiabatic process is suggested. Attention is then given to possible mechanisms serving to maintain the concentration of flux tubes far below the surface of the sun which gives rise to sunspots and pores as the flux tree emerges through the surface.

Parker, E. N.↗
NASA NTRS1984

Evaporation Tower With Prill Nozzles

Tower more efficient than conventional evaporation equipment. Liquids such as milk and fruit juice concentrated by passing them through tiny nozzle to form droplets, then allowing droplets to fall through evacuated tower with cooled walls.

Du Fresne, E. R.↗
NASA NTRS1984

Liquid-Oxygen-Compatible Cement for Gaskets

Fluorelastomer and metal bonded reliably by new procedure. To cure fluoroelastomer cement, metal plate/gasket assembly placed in vacuum bag evacuated to minimum vacuum of 27 inches (69 cm) of mercury. Vacuum maintained throughout heating process and until assembly returns to ambient room temperature. Used to seal gaskets and O-rings or used to splice layers of elastomer to form non-standard sized O-rings. Another possible use is to apply protective, liquid-oxygen-compatible coating to metal parts.

Elmore, N. L.↗
NASA NTRS1982

Ampoule sealing apparatus and process

An apparatus and process for sealing fused quartz ampoules housing a semiconductor growth charge under vacuum is described. An elongated fused quartz ampoule having an enlarged diameter open end and a reduced diameter closed end is vertically retained in a vacuum assembly. A semiconductor charge is disposed within the reduced diameter portion of the ampoule. A quartz plug of substantially the same diameter as the reduced diameter portion is suspended within the open and of the ampoule via a rotary vacuum feed. After evacuation of the ampoule a plug is lowered into the reduced diameter area and sealed therein while maintaining the vacuum on the ampoule. The charged ampoule area is then separated from the remaining structure by breaking along the scored line.

Debnam, W. J., Jr.↗
NASA NTRS1983

The measurement of solar spectral irradiances at wavelengths between 40 and 4000 A

Two 1/8-meter Ebert-Fastie spectrometers were refurbished and upgraded in order to measure the solar spectral irradiances between 1160 A and 3100 A. An evacuated 1/4-meter normal-incidence spectrometer was also fabricated for spectral irradiance measurements over the wavelength range from 1250 A to 250 A. Procedures were developed for the calibration of all three instruments utilizing standards at the National Bureau of Standards. The two 1/8-meter spectrometers were flown to measure the solar spectral irradiances near solar maximum on two different dates. Data from these flights were analyzed. The performance of the spectrometers, and the results of an analysis of the variabilities of the solar spectral irradiances over the solar cycles 20 and 21 are discussed.

Timothy, J. G.↗
NASA NTRS1983

Vibration isolation and pressure compensation apparatus for sensitive instrumentation

A system for attenuating the inherent vibration associated with a mechanical refrigeration unit employed to cryogenically cool sensitive instruments used in measuring chemical constituents of the atmosphere is described. A modular system including an instrument housing and a reaction bracket with a refrigerator unit floated there between comprise the instrumentation system. A pair of evacuated bellows that "float' refrigerator unit and provide pressure compensation at all levels of pressure from seal level to the vacuum of space. Vibration isolators and when needed provide additional vibration damping for the refrigerator unit. A flexible thermal strap (20 K) serves to provide essentially vibration free thermal contact between cold tip of the refrigerator unit and the instrument component mounted on the IDL mount. Another flexible strap (77 K) serves to provide vibration free thermal contact between the TDL mount thermal shroud and a thermal shroud disposed about the thermal shaft.

Averill, R. D.↗
NASA NTRS1983

Ar-39 recoil losses and presolar ages in Allende inclusions

Argon analyses were performed for five coarse-grained, Ca-Al-rich inclusions from the Allende meteorite. The samples were neutron-irradiated in evacuated ampuoles, and the Ar in the ampuoles and in the samples was analyzed. Up to 60 percent of Ar-39 was lost from the samples into the ampuoles due to recoil during neutron-irradiation; this loss resulted in substantial increases in the apparent Ar-40-Ar-39 ages of the samples. Substantial amounts of trapped Ar-36 of unknown origin were found in the inclusions, and the presence of trapped Ar-40 could not be ruled out. It is inferred that the interpretation of high Ar-40/K-40 ratios as very high (presolar) ages may be subject to question. It is noted that the degrees of Ar-39 recoil loss reported is comparable to recoil loss in terrestrial rocks and cannot be attributed to KCl contamination of the samples.

Villa, I. M.↗
NASA NTRS1982

Solidification studies of Nb-Ge alloys at large degrees of supercooling

A 32 meter evacuated drop tube has been used to investigate the solidification of Nb-Ge alloys after deep undercooling. Samples have been supercooled as much as 500 K below the liquidus by using free-fall conditions to eliminate crucible induced nucleation. Final microstructures are dependent on the quenching rates at the bottom of the drop tube with a striking extension of the beta phase solubility limit at the higher quenching rates.

Lacy, L. L.↗
NASA NTRS1982

Gravity-driven convection studies in compound semiconductor crystal growth by physical vapor transport

Experimental results are summarized, and it is pointed out that gravity-driven convection can alter the diffusive-advective mass transport behavior in the growth of crystals by physical vapor transport. Specially designed and constructed transparent furnaces are described which are being used to study the effects of gravity in the crystal growth of the compound semiconductors PbTe and CdTe. The theory underlying vapor transport behavior is reviewed, with attention given to the vapor-solid behavior of compound materials, to one-dimensional mass transport, and to gravity-induced (natural) convection. In the transparent furnaces, the quartz capillary tube mounted along the axis of the main quartz ampoule is used to measure the temperature at the growth surface (vapor-solid crystal interface) and the source, as well as the complete temperature profile along the axis of the tube. The light-pipe works to remove heat from the growth end of the ampoule by radiative heat transfer. The ampoules are sealed after being evacuated to the low 10 to the -8th torr range with a cryogenic vacuum pump.

Zoutendyk, J. A.↗
NASA NTRS1984

Preparation and cleanliness verifications of a space simulation chamber for contamination sensitive test specimens

Contamination sensitive optical devices were to be evaluated under thermal vacuum conditions. Test specifications called for an extremely clean chamber environment, ambient temperature chamber walls, and optical surface temperatures at approximately - 30 C. Chamber preparation included the replacement of diffusion pumps with cryopumps and the cleaning of the chamber walls to reduce contamination levels. Chamber cleaning using vacuum bake was tried and abandoned as time consuming and ineffective. Chemical cleaning and cleanliness verification methods were developed. Gas chromatograph analysis techniques were used extensively throughout the cleaning process to verify cleanliness levels prior to evacuating the chamber. A chamber cleanliness verification test using a thermoelectric quartz crystal microbalance and witness samples was performed to demonstrate that an appropriate cleanliness level was achieved.

Koch, W. R.↗
NASA NTRS1984

An analytical study of reusable flight-weight cryogenic propellant tank designs

Thermostructural analyses of reusable flight-weight cryogenic tanks for a vertically launched space vehicle have been conducted. An analytical procedure was developed for sizing the tank structure, cryogenic insulation, and thermal protection system. Unstiffened, integrally-stiffened, and honeycomb core sandwich tank skins using aluminum or stainless steel materials were compared for their ability to meet design criteria at least weight. Cryogenic insulation systems were also evaluated, including closed-cell cryogenic foams and evacuated honeycomb core. The results indicate that a 400 F foam-insulated unstiffened-skin aluminum tank structure is the lightest structure for either LOX or LH2 tanks that meet the selected design criteria, but only two to four percent lighter than a stiffened aluminum tank.

Taylor, A. H.↗
NASA NTRS1984

Heat pipe applications in aircraft propulsion

Heat pipes for improving the cycle efficiency and/or thrust-to-weight ratio of aircraft gas turbines are examined. A heat pipe employs a capillary structure, a wick, and an evacuated chamber to transfer heat between condensor and evaporator ends. Heat absorbed at the evaporator is transported to the condensor. In an aircraft, the heat pipe can be stationary or rotating, can be used for cooling stators and rotors, and is amenable to shapes such as cylinders, cones, and flat plates. Heat pipes in aircraft gas turbines can be applied for intercooling between stages, regeneration, reheat, and blade cooling. Improvements are projected in the cycle efficiency, thrust and thrust specific fuel consumption in the fanjet by using heat pipes. Consideration is also given to heat pipe heat exchangers with high axial heat transfer for stationary heat pipes and high heat transport for rotating heat pipes.

Beltran, M. R.↗
NASA NTRS1985

Improved Exhaust Diffuser for Jet-Engine Testing

High-altitude simulator reduced power requirements. Test cell uses its exhaust-capture duct only to remove gases from engine; cooling air evacuated through separate path by auxiliary suction system. This way, capture duct cross-sectional area kept close to exhaust jet area, leading to greatly improved recovery performance.

Parikh, P. G.↗
NASA NTRS1984

Research relative to the development of a cryogenic microwave cavity gradiometer for orbital use

The noncryogenic, single axis, gravity gradiometer which is characterized by a sensitivity of the order of 10 to the minus 2 power Eovos Units in a few sec integration time was investigated. The prototype of testing gradiometer on the earth surface by the free fall in vacuo method was expanded. An existing free fall tower facility and the possibility of adding inside the falling elevator cabin an air tight, sealed, cylindrical container with inside pressure or = -0.001 Torr were examined to test the gradiometer in free fall conditions inside this evacuated container. Earth's gravity anomalies are simulated with masses of suitable shape, weight, and location. The attitude of the falling gradiometer is monitored by a three axis gyro package mounted on the instrument package. It is concluded that the free fall testing of the gradiometer is both feasible and practical.

Grossi, M. D.↗
NASA NTRS1984

Design concept definition study for an improved shuttle waste collection subsystem

A no-risk approach for developing an Improved Waste Collection Subsystem (WCS) for the shuttle orbiter is described. The GE Improved WCS Concept builds on the experience of 14 Shuttle missions with over 400 man-days of service. This concept employs the methods of the existing flight-proven mature design, augmenting them to eliminate foreseen difficulties and to fully comply with the design requirements. The GE Improved WCS Concept includes separate storage for used wipes. Compaction of the wipes provides a solution to the capacity problem, fully satisfying the 210 man-day storage requirement. The added feature of in-flight serviceable storage space for the wipes creates a variable capacity feature which affords redundancy in the event of wipes compaction system failure. Addition of features permitting in-flight servicing of the feces storage tank creates a variable capacity WCS with easier post-flight servicing to support rapid turnaround of the Shuttle orbiter. When these features are combined with a vacuum pump to evacuate wipes and fecal storage tanks through replaceable odor/bacteria filters to the cabin, the GE Improved WCS satisfies the known requirements for Space Station use, including no venting to space.

Source record↗
NASA NTRS1985

Operating characteristics of a 0.87 kW-hr flywheel energy storage module

Discussion is given of the design and loss characteristics of 0.87 kW-hr (peak) flywheel energy storage module suitable for aerospace and automotive applications. The maraging steel flywheel rotor, a 46-cm- (18-in-) diameter, 58-kg (128-lb) tapered disk, delivers 0.65 kW-hr of usable energy between operating speeds of 10,000 and 20,000 rpm. The rotor is supported by 20- and 25-mm bore diameter, deep-groove ball bearings, lubricated by a self-replenishing wick type lubrication system. To reduce aerodynamic losses, the rotor housing was evacuated to vacuum levels from 40 to 200 millitorr. Dynamic rotor instabilities uncovered during testing necessitated the use of an elastometric-bearing damper to limit shaft excursions. Spindown losses from bearing, seal, and aerodynamic drag at 50 millitorr typically ranged from 64 to 193 W at 10,000 and 20,000 rpm, respectively. Discharge efficiency of the flywheel system exceeded 96 percent at torque levels greater than 21 percent of rated torque.

Loewenthal, S. H.↗