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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Status of beamed power transmission technology and applications at 2.45 gigahertz

Demonstrations and unique components of the 2.45 GHz beamed power transmission technology are reviewed. Attention is given to the following projects and developments: a microwave power helicopter demonstration; certification of overall dc to dc efficiency of 54 percent in the laboratory; demonstration of the transmission of significant amounts of power over significant distances; the solar power satellite and beamed power transmission; the Canadian SHARP program; space applications; an equatorially based beam power transmission system; an all-electronic LEO to GEO transportation system; and an orbiting industrial park system.

Brown, William C.↗
NASA NTRS1989

Transmission overhaul and replacement predictions using Weibull and renewal theory

A method to estimate the frequency of transmission overhauls is presented. This method is based on the two-parameter Weibull statistical distribution for component life. A second method is presented to estimate the number of replacement components needed to support the transmission overhaul pattern. The second method is based on renewal theory. Confidence statistics are applied with both methods to improve the statistical estimate of sample behavior. A transmission example is also presented to illustrate the use of the methods. Transmission overhaul frequency and component replacement calculations are included in the example.

Savage, M.↗
NASA NTRS1989

Generation and tooth contact analysis of spiral bevel gears with predesigned parabolic functions of transmission errors

A new approach for determination of machine-tool settings for spiral bevel gears is proposed. The proposed settings provide a predesigned parabolic function of transmission errors and the desired location and orientation of the bearing contact. The predesigned parabolic function of transmission errors is able to absorb piece-wise linear functions of transmission errors that are caused by the gear misalignment and reduce gear noise. The gears are face-milled by head cutters with conical surfaces or surfaces of revolution. A computer program for simulation of meshing, bearing contact and determination of transmission errors for misaligned gear has been developed.

Litvin, Faydor L.↗
NASA NTRS1990

Assessment of worm gearing for helicopter transmissions

A high-efficiency hydrostatic worm gear drive for helicopter transmissions is assessed. The example given is for a large cargo helicopter with three 4000-kW engines and transmission reduction ratio of 110. Also contained are: an efficiency calculation, a description of the test stand for evaluating the feasibility of worm gear hydrostatic mesh, a weight calculation, and a comparison with conventional helicopter transmissions of the same power and transmission reduction ratio.

Chaiko, Lev↗
NASA NTRS1990

X-ray/VUV transmission gratings for astrophysical and laboratory applications

This paper describes the techniques used to fabricate deep-submicron-period transmission gratings for astrophysical and laboratory applications, with special attention given to the major steps involved in the transmission grating fabrication. These include the holographic lithography procedure used to pattern the master transmission grating, the fabrication of X-ray mask, the X-ray lithography step used to transfer the X-ray mask pattern into a substrate, and the electroplating of the substrate to form the final grating pattern. The various ways in which transmission gratings can be used in X-ray and VUV spectroscopy are discussed together with some examples of experiments reported in the literature.

Schattenburg, M. L.↗
NASA NTRS1990

A parameterization for the shortwave transmissivity of stratiform water clouds based on empirical data and radiative transfer theory

Surface measurements of solar flux and total integrated liquid-water content, radiosonde data, and infrared satellite images are analyzed in conjunction with radiative transfer calculations to derive an empirical parameterization for the shortwave transmissivity of continental stratiform water clouds. The data were collected near Denver, Colorado, over a period of six years. A multiple reflection radiative transfer model is employed to estimate stratus cloud transmissivity in terms of the measurable liquid-water path (LWP). A nonlinear fit of estimated transmissivities to the corresponding observations of LWP yields close agreement with a previous, more complicated parameterization. The derived expression for cloud transmissivity is used to predict mean daily surface fluxes for 61 days during which periods of stratiform clouds were observed over the Denver area. A comparison between predicted and measured fluxes shows agreement to within + or - 4 percent, with best agreement for clouds of moderate optical thickness. Potential sources of error are identified with sensitivity studies.

Derr, V. E.↗
NASA NTRS1990

Advanced Rotorcraft Transmission (ART) program review

This paper summarizes the work accomplished to date on the NASA/Army Advanced Rotorcraft Transmission (ART) program. A 23-percent weight reduction has been demonstrated for a high output reduction ratio split path transmission compared to an aggressive program goal of 25-percent. Greater than 10 dB noise reduction in the cabin is achieved by the use of high contact ratio spur and double helical gears. In addition, mean times between transmission removals have been increased by almost four fold. These performance gains have been achieved by application of advanced transmission technology concepts. Technology areas are being explored which offer high gain but at relatively high risk in such areas as composites, split power gear concepts, double helical gears, new gear materials, high speed spring clutches, and ceramic rolling element bearings.

Kish, Jules↗
NASA NTRS1992

Separation distance and static transmission error of involute spur gears

The effects of separation distance and deflection of gear teeth on the static transmission error of involute spur gears are investigated. In this paper, only low-contact-ratio gears with true involute profile are studied. Gear ratio and tooth addendum are varied to examine their effects on the separation distance and static transmission error. Results obtained from the investigation shows that the contact ratio and static transmission error are affected significantly if considering the separation distance. In general, the magnitude of contact ratio has been increased and the variation of static transmission error has been smoothed. The most significant change occurs for a gear pair with a theoretical contact ratio close to 1.95.

Tse, David K.↗
NASA NTRS1993

Real-time transmission of digital video using variable-length coding

Huffman coding is a variable-length lossless compression technique where data with a high probability of occurrence is represented with short codewords, while 'not-so-likely' data is assigned longer codewords. Compression is achieved when the high-probability levels occur so frequently that their benefit outweighs any penalty paid when a less likely input occurs. One instance where Huffman coding is extremely effective occurs when data is highly predictable and differential coding can be applied (as with a digital video signal). For that reason, it is desirable to apply this compression technique to digital video transmission; however, special care must be taken in order to implement a communication protocol utilizing Huffman coding. This paper addresses several of the issues relating to the real-time transmission of Huffman-coded digital video over a constant-rate serial channel. Topics discussed include data rate conversion (from variable to a fixed rate), efficient data buffering, channel coding, recovery from communication errors, decoder synchronization, and decoder architectures. A description of the hardware developed to execute Huffman coding and serial transmission is also included. Although this paper focuses on matters relating to Huffman-coded digital video, the techniques discussed can easily be generalized for a variety of applications which require transmission of variable-length data.

Bizon, Thomas P.↗
NASA NTRS1994

Comparison of Transmission Error Predictions with Noise Measurements for Several Spur and Helical Gears

Measured sound power data from eight different spur, single and double helical gear designs are compared with predictions of transmission error by the Load Distribution Program. The sound power data was taken from the recent Army-funded Advanced Rotorcraft Transmission project. Tests were conducted in the NASA gear noise rig. Results of both test data and transmission error predictions are made for each harmonic of mesh frequency at several operating conditions. In general, the transmission error predictions compare favorably with the measured noise levels.

Houser, Donald R.↗
NASA NTRS1995

Nonlinear system guidance in the presence of transmission zero dynamics

An iterative procedure is proposed for computing the commanded state trajectories and controls that guide a possibly multiaxis, time-varying, nonlinear system with transmission zero dynamics through a given arbitrary sequence of control points. The procedure is initialized by the system inverse with the transmission zero effects nulled out. Then the 'steady state' solution of the perturbation model with the transmission zero dynamics intact is computed and used to correct the initial zero-free solution. Both time domain and frequency domain methods are presented for computing the steady state solutions of the possibly nonminimum phase transmission zero dynamics. The procedure is illustrated by means of linear and nonlinear examples.

Meyer, G.↗
NASA NTRS1995

Mid-infrared transmission spectra of crystalline and nanophase iron oxides/oxyhydroxides and implications for remote sensing of Mars

Ferric-iron-bearing materials play an important role in the interpretation of visible to near-IR Mars spectra, and they may play a similarly important role in the analysis of new mid-IR spacecraft spectral observations to be obtained over the next decade. We review exisiting data on mid-IR transmission spectra of ferric oxides/oxyhydroxides and present new transmission spectra for ferric-bearing materials spanning a wide range of mineralogy and crystallinity. These materials include 11 samples of well-crystallized ferric oxides (hematite, maghemite, and magnetite) and ferric oxyhydroxides (goethite, lepidocrocite). We also report the first transmission spectra for purely nanophase ferric oxide samples that have been shown to exhibit spectral similarities to Mars in the visible to near-IR and we compare these data to previous and new transmission spectra of terrestial palagonites. Most of these samples show numerous, diagnostic absorption features in the mid-IR due to Fe(3+) - 0(2-) vibrational transitions, structural and/or bound OH, and/or silicates. These data indicate that high spatial resolution, moderate spectral resolution mid-IR ground-based and spacecraft observations of Mars may be able to detect and uniquely discriminate among different ferric-iron-bearing phases on the Martian surface or in the airborne dust.

Bell, James F., III↗
NASA NTRS1997

Gear and Transmission Research at NASA Lewis Research Center

This paper is a review of some of the research work of the NASA Lewis Research Center Mechanical Components Branch. It includes a brief review of the NASA Lewis Research Center and the Mechanical Components Branch. The research topics discussed are crack propagation of gear teeth, gear noise of spiral bevel and other gears, design optimization methods, methods we have investigated for transmission diagnostics, the analytical and experimental study of gear thermal conditions, the analytical and experimental study of split torque systems, the evaluation of several new advanced gear steels and transmission lubricants and the evaluation of various aircraft transmissions. The area of research needs for gearing and transmissions is also discussed.

Townsend, Dennis P.↗
NASA NTRS1996

Ground Isolation Circuit for Isolating a Transmission Line from Ground Interference

This invention relates generally to a system for isolating ground interference from a transmission line, e.g., a ground isolation circuit for isolating a wideband transmission signal (such as a video signal) from ground by modulating the base signal on a carrier signal to permit the transmission signal to be isolated. In one embodiment, the circuit includes a pair of matched mixer circuits, each of which receives a carrier signal from the same oscillator circuit. The first mixer circuit also receives the baseband signal input, after appropriate conditioning, and modulates the baseband signal onto the carrier signal. In a preferred embodiment the carrier signal has a predetermined frequency which is at least two times the frequency of the baseband signal. The modulated signal (which can comprise an rf signal) is transmitted via an rf transmission line to the second mixer, which demodulates the rf signal to recover the baseband signal. Each port of the mixer connects to an isolation transformer to ensure isolation from ground interference. The circuit is considered to be of commercial value in that it can provide isolation between transmitting and receiving circuits, e.g., ground isolation for television circuits or high frequency transmitters, without the need for video transformers or optical isolators, thereby reducing the complexity, power consumption, and weight of the system.

Davidson, Craig A.↗
NASA NTRS1995

Mid-infrared transmission spectra of crystalline and nanophase iron oxides/oxyhydroxides and implications for remote sensing of Mars

Ferric-iron-bearing materials play an important role in the interpretation of visible to near-IR Mars spectra, and they may play a similarly important role in the analysis of new mid-IR spacecraft spectral observations to be obtained over the next decade. We review existing data on mid-IR transmission spectra of ferric oxides/oxyhydroxides and present new transmission spectra for ferric-bearing materials spanning a wide range of mineralogy and crystallinity. These materials include 11 samples of well-crystallized ferric oxides (hematite, maghemite, and magnetite) and ferric oxyhydroxides (goethite, lepidocrocite). We also report the first transmission spectra for purely nanophase ferric oxide samples that have been shown to exhibit spectral similarities to Mars in the visible to near-IR and we compare these data to previous and new transmission spectra of terrestrial palagonites. Most of these samples show numerous, diagnostic absorption features in the mid-IR due to Fe(3+)-O(2-) vibrational transitions, structural and/or bound OH, and/or silicates. These data indicate that high spatial resolution, moderate spectral resolution mid-IR ground-based and spacecraft observations of Mars may be able to detect and uniquely discriminate among different ferric-iron-bearing phases on the Martian surface or in the airborne dust.

Bell, James F., III↗
NASA NTRS1999

RF Transmission Lines on Silicon Substrates

A review of RF transmission lines on silicon substrates is presented. Through measurements and calculated results, it is shown that attenuation is dominated by conductor loss if silicon substrates with a resistivity greater than 2500 Ohm-cm are used. Si passivation layers affect the transmission line attenuation; however, measured results demonstrate that passivation layers do not necessarily increase attenuation. If standard, low resistivity Si wafers must be used, alternative transmission lines such as thin film microstrip and Co-Planar Waveguide (CPW) on thick polyimide layers must be used. Measured results presented here show that low loss per unit length is achievable with these transmission lines.

Ponchak, George E.↗
NASA NTRS2000

Experimental Analysis of Mast Lifting and Bending Forces on Vibration Patterns Before and After Pinion Reinstallation in an OH-58 Transmission Test Rig

As part of a collaborative research program between NASA Ames Research Center (ARC), NASA Glenn Research Center (GRC), and the US Army Laboratory, a series of experiments is being performed in GRC's 500 HP OH-58 Transmission Test Rig facility and ARC's AH-I Cobra and OH-58c helicopters. The findings reported in this paper were drawn from Phase-I of a two-phase test-rig experiment, and are focused on the vibration response of an undamaged pinion gear operating in the transmission test rig. To simulate actual flight conditions, the transmission system was run at three torque levels, as well as two mast lifting and two mast bending levels. The test rig was also subjected to disassembly and reassembly of the main pinion housing to simulate the effect of maintenance operations. An analysis of variance based on the total power of the spectral distribution indicates the relative effect of each experimental factor, including Wong interactions with torque. Reinstallation of the main pinion assembly is shown to introduce changes in the vibration signature, suggesting the possibility of a strong effect of maintenance on HUMS design and use. Based on these results, further research will be conducted to compare these vibration responses with actual OH58c helicopter transmission vibration patterns.

Huff, Edward M.↗
NASA NTRS2000

Performance Evaluation of the NASA/KSC Transmission System

NASA-KSC currently uses three bridged 100-Mbps FDDI segments as its backbone for data traffic. The FDDI Transmission System (FTXS) connects the KSC industrial area, KSC launch complex 39 area, and the Cape Canaveral Air Force Station. The report presents a performance modeling study of the FTXS and the proposed ATM Transmission System (ATXS). The focus of the study is on performance of MPEG video transmission on these networks. Commercial modeling tools - the CACI Predictor and Comnet tools - were used. In addition, custom software tools were developed to characterize conversation pairs in Sniffer trace (capture) files to use as input to these tools. A baseline study of both non-launch and launch day data traffic on the FTXS is presented. MPEG-1 and MPEG-2 video traffic was characterized and the shaping of it evaluated. It is shown that the characteristics of a video stream has a direct effect on its performance in a network. It is also shown that shaping of video streams is necessary to prevent overflow losses and resulting poor video quality. The developed models can be used to predict when the existing FTXS will 'run out of room' and for optimizing the parameters of ATM links used for transmission of MPEG video. Future work with these models can provide useful input and validation to set-top box projects within the Advanced Networks Development group in NASA-KSC Development Engineering.

Christensen, Kenneth J.↗