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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Solar power satellite microwave power transmission and reception system

The microwave power transmission and reception system of the Satellite Power System (SPS) has been intensively reviewed and assessed in a three-year concept development and evaluation program. This paper will review some concepts of SPS with particular emphasis on the design of the microwave power transmission and reception system. Technology requirements and proposals for meeting them will be discussed for various parts of the microwave system and to some degree for critical components such as power amplifiers. Specific subjects to be discussed are SPS concepts, antenna design, phase control, rectenna, and technology.

Finnell, W.↗
NASA NTRS1981

Modification to Scott's method for direct integration of gaseous transmission to improve speed and accuracy

Two limitations to the method of Scott for rapid direct integration of gaseous transmission in a finite spectral interval over an inhomogeneous optical path are discussed. One of these is the inability to use a precomputed form of the Voigt line shape, which can be parameterized via the linewidth alone. This is rectified using the Voigt shape approximation of Kielkopf, which involves a linear combination of three functions which can be pre-computed: the Lorentz shape, the Doppler shape and a correction function. The other limitation involves situations where lines must be treated individually, either line positions must be known with great precision or a uniform value for the widths of all lines in the spectral interval does not describe the transmission adequately. In this case, the strongest lines are treated individually, while the remainder are treated assuming uniform line widths and line positions coincident with positions on the frequency grid, i.e. following Scott's method directly.

Orton, G. S.↗
NASA NTRS1981

Acoustic transmission in lined flow ducts - A finite element eigenvalue problem

The problem of acoustical transmission in lined ducts with subsonic mean flow is of considerable practical interest in the context of fan noise attenuation in the ducted inlet regions of turbofan aircraft engines. If nonaxisymmetric liners are present, a loss of axial symmetry results, and the study of acoustic transmission involves the solution of a full two-dimensional eigenvalue problem. The reported investigation is concerned with such an eigenvalue problem. The employed method of solution is effectively a two-dimensional analog of an approach considered by Astley and Eversman (1979). The approach makes use of a Galerkin Finite Element Method whereby the weighting and basis functions are generated automatically by the discretization.

Astley, R. J.↗
NASA NTRS1983

Coding for Single-Line Transmission

Digital transmission code combines data and clock signals into single waveform. MADCODE needs four standard integrated circuits in generator and converter plus five small discrete components. MADCODE allows simple coding and decoding for transmission of digital signals over single line.

Madison, L. G.↗
NASA NTRS1984

Dual-Rate Transmission Reduces Weather Effects

Scheme ensures maximum data received on average. Dual-rate scheme for maximizing data returned during spacecraft mission, adaptable, as is or with modifications, to high-frequency terrestrial data transmission. Data rate fixed in advance at minimum value guarantees reasonable prospect of success during bad weather. Dualrate strategy yields net data rate 2.5 times best achievable with single transmission rate.

Posner, E. C.↗
NASA NTRS1984

Equations for Automotive-Transmission Performance

Curve-fitting procedure ensures high confidence levels. Threedimensional plot represents performance of small automatic transmission coasting in second gear. In equation for plot, PL power loss, S speed and T torque. Equations applicable to manual and automatic transmissions over wide range of speed, torque, and efficiency.

Chazanoff, S.↗
NASA NTRS1982

Gates to Gregg High Voltage Transmission Line Study

The usefulness of LANDSAT data in the planning of transmission line routes was assessed. LANDSAT digital data and image processing techniques, specifically a multi-date supervised classification aproach, were used to develop a land cover map for an agricultural area near Fresno, California. Twenty-six land cover classes were identified, of which twenty classes were agricultural crops. High classification accuracies (greater than 80%) were attained for several classes, including cotton, grain, and vineyards. The primary products generated were 1:24,000, 1:100,000 and 1:250,000 scale maps of the classification and acreage summaries for all land cover classes within four alternate transmission line routes.

Bergis, V.↗
NASA NTRS1983

Refinement and application of acoustic impulse technique to study nozzle transmission characteristics

An improved acoustic impulse technique was developed and was used to study the transmission characteristics of duct/nozzle systems. To accomplish the above objective, various problems associated with the existing spark-discharge impulse technique were first studied. These included (1) the nonlinear behavior of high intensity pulses, (2) the contamination of the signal with flow noise, (3) low signal-to-noise ratio at high exhaust velocities, and (4) the inability to control or shape the signal generated by the source, specially when multiple spark points were used as the source. The first step to resolve these problems was the replacement of the spark-discharge source with electroacoustic driver(s). These included (1) synthesizing on acoustic impulse with acoustic driver(s) to control and shape the output signal, (2) time domain signal averaging to remove flow noise from the contaminated signal, (3) signal editing to remove unwanted portions of the time history, (4) spectral averaging, and (5) numerical smoothing. The acoustic power measurement technique was improved by taking multiple induct measurements and by a modal decomposition process to account for the contribution of higher order modes in the power computation. The improved acoustic impulse technique was then validated by comparing the results derived by an impedance tube method. The mechanism of acoustic power loss, that occurs when sound is transmitted through nozzle terminations, was investigated. Finally, the refined impulse technique was applied to obtain more accurate results for the acoustic transmission characteristics of a conical nozzle and a multi-lobe multi-tube supressor nozzle.

Salikuddin, M.↗
NASA NTRS1982

Design of an advanced 500-HP helicopter transmission

A 500-hp Advanced Technology Demonstrator helicopter transmission was designed by an American aerospace company under a NASA contract. The project was mainly concerned with designing a 500-hp version of the OH-58C 317-hp transmission which would have the capabilities for a long, quiet life at a minimum increase in cost, weight, and space, which usually increase along with power increases. This objective was accomplished by implementing advanced technology which has been developed during the last decade and by making improvements dictated by field experience. The improvements are related to bearings made of cleaner gear steels, spiral bevel gears made of cleaner gear steels, high contact ratio spur gear teeth in the planetary which will reduce noise level and increase gear life, and modifications concerning the sun gear.

Braddock, C. E.↗
NASA NTRS1984

Two dimensional nonlinear analysis of sound transmission through a near-sonic throat flow

A two-dimensional nonlinear theory of sound transmission through a nonuniform duct carrying a near-sonic throat flow is described. The mean flow in the duct is treated according to a generalized quasi-one dimensional model, and the analysis of the unsteady perturbations is carried out using the Method of Matched Asymptotic Expansions. The linearized acoustic field in the subsonic regions of the duct is approximated by a Wave Envelope model which is matched asymptotically with a nonlinear inner solution valid in the near-sonic throat region. Numerical results are presented to illustrate the predictions of the theory. It is found that, in general, shock waves develop in the acoustic field during transmission through the near-sonic flow. Unlike previous one-dimensional theories, the current study shows that dispersion can play a major role in the propagation process.

Myers, M. K.↗
NASA NTRS1983

Spectroscopic measurements of the 8- to 13-micrometer transmission of the upper atmosphere following the El Chichon eruptions

Infrared transmission spectra of the atmosphere above 11-km altitude were obtained at latitudes from 2 deg S to 50 deg N in December 1982. A circular variable-interference filter spectrometer mounted in a Convair 990 (the Galileo II) aircraft was used to obtain spectra of the sun through different air masses. Comparisons of spectra through different air masses provide atmospheric transmission measurements that show not only normal absorption features, such as those from CO2 and O3, but also additional absorption near 8.5 microns consistent with H2SO4 aerosols. The average fractional absorption from latitude 10 deg N to 41 deg N at 8.5 microns was 0.02/air mass, half of which was attributable to aerosols.

Witteborn, F. C.↗
NASA NTRS1984

Development of large rotorcraft transmissions

The U.S. Army Heavy Lift Helicopter (HLH) represents a large rotorcraft which was developed by an American aerospace company. In the early 1970's with the HLH Advanced Technology Components (ATC) program, the development of large rotorcraft transmission and drive systems was started. Failures in the spiral bevel gearing were experienced in tests because the employed method of analysis had not considered the effect of rim bending. Consequently, new gears with strengthened rims were designed and fabricated. For a more accurate prediction of the load capacity of the gears, an extensive Finite Element Method (FEM) system was developed. The U.S. Army's XCH-62 HLH aft rotor transmission was finally successfully tested at full design torque and speed. A description of the test program is provided, and the analytical program is discussed. The analytical phase includes the development of a preprocessing program which aids in the review of calculated FEM stresses.

Samanich, N. E.↗
NASA NTRS1985

Continuously Variable Transmission

Chain slides along two cones, in novel transmission concept. Transmission includes chain drive between two splined shafts. Chain sprockets follow surfaces of two cones. As one chain sprocket moves toward smaller diameter other chain sprocket moves toward larger diameter, thereby changing "gear" ratio. Movement initiated by tension applied to chain by planetary gear mechanism. Device positive, simple, and efficient over wide range of speed ratios.

Grana, D. C.↗
NASA NTRS1984

The Spectrophotometric Method of Determining the Transmission of Solar Energy in Salt Gradient Solar Ponds

In order to predict the thermal efficiency of a solar pond it is necessary to know total average solar energy reaching the storage layer. One method for determining this energy for water containing dissolved colored species is based upon spectral transmission measurements using a laboratory spectrophotometer. This method is examined and some of the theoretical ground work needed to discuss the measurement of transmission of light water. Results of in situ irradiance measurements from oceanography research are presented and the difficulties inherent in extrapolating laboratory data obtained with ten centimeter cells to real three dimensional pond situations is discussed. Particular emphasis is put on the need to account for molecular and particulate scattering in measurements done on low absorbing solutions. Despite these considerations it is expected that attenuation calculations based upon careful measurements using a dual beam spectrophotometer technique combined with known attenuation coefficients will be useful in solar pond modeling and monitoring for color buildup. Preliminary results using the CSM method are presented.

Giulianelli, J.↗
NASA NTRS1985

Land mobile satellite transmission measurements at 869 MHz: Selected results from the dedicated stratospheric balloon experiment of November 12 and 13, 1984

Satellite transmissions were simulated by placing an 869 MHz and a 1501 MHz transmitter aboard a stratospheric balloon. The balloon was followed on the ground by a van equipped with receivers and data acquisition equipment capable of creating a permanent record of the variations of the received signal amplitude and phase at the two signal frequencies. Results from simulated satellite transmission measurements at 869 MHz are presented. The data show that attenuation by roadside trees can be a limiting factor in systems with a 5 dB fade margin, if 84% availability is not acceptable. In less extreme environments, fading is much less severe. Without fading present, the signal power density function often could be described as Ricean with direct to scattered ratio power ratios of about 100. Phase fluctuations were apparent whenever the signal amplitude fluctuated. The duration of the fades and nonfades tended to cluster close to one wavelength. The power spectrum of both the amplitude and the phase show that most of the fluctuations occur at frequencies below the Doppler shift.

Vogel, W. J.↗
NASA NTRS1985

Modal response and noise transmission of composite panels

Noise transmission through flat, angular, fiber-reinforced composite panels is investigated experimentally and analytically. A modal decomposition technique was used to obtain solutions to the governing differential equation of motion. Experimental modal analysis was performed in order to confirm the theoretical results. The test specimens were cross-ply and angle-ply composite panels made of various concentrations of fiberglass, graphite, or aramid fibers embedded in epoxy resion. The experimental results showed good agreement with the theoretical calculations. Graphs of the transmission loss characteristics of the different composite panels are provided.

Grosveld, F. W.↗
NASA NTRS1985

Application of High Order Acoustic Finite Elements to Transmission Losses and Enclosure Problems

A family of acoustic finite elements was developed based on C continuity (acoustic pressure being the nodal variable) and the no-flow condition. The family include triangular, quadrilateral and hexahedral isoparametric elements with linear quadratic and cubic variation in modelling and distortion. Of greatest use in problems with irregular boundaries are the cubic isoparametric elements: the 32 node hexahedral element for three-dimensional systems; and the twelve node quadrilateral and ten node triangular elements for two-dimensional/axisymmetric applications. These elements were applied to problems involving cavity resonances, transmission loss in silencers and the study of end effects, using a Floating Point Systems 164 attached array processor accessed through an Amdahl 5860 mainframe. The elements are presently being used to study the end effects associated with duct terminations within finite enclosures. The transmission losses with various silencers and sidebranches in ducts is also being studied using the same elements.

Craggs, A.↗
NASA NTRS1986

Investigation of potential driver modules and transmission lines for a high frequency power system on the space station

The objective was to assess the feasibility of using the Series Resonant inverter as the driver module for the high frequency power system on the Space Station. This study evaluates the performance of the Series Resonant driver when it was operated with a dc input voltage and run through a series of tests to determine its start-up performance, response to load changes, load regulation, and efficiency. Also, this study compares the Series Resonant driver to another kind of driver that uses a Power Transistor snubber. An investigation of the various types of transmission lines is initiated. In particular, a simplified approach is utilized to describe the optimal transmission line.

Brush, H. T.↗