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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Dye fading test for mission control operator console displays

A dye fading test of 40 days duration was conducted to determine the effect of mission control operator console and ambient lighting effects on a series of photographic products under consideration for use in mission console operator consoles. Six different display samples, each containing 36 windows of several different colors, were prepared and placed in the mission control consoles for testing. No significant changes were recorded during the testing period. All changes were attributed to a mechanical problem with the densitometer. Detailed results are given in graphs.

Lockwood, H. E.↗
NASA NTRS1978

Ultrasonic simulation of MSBLS multipath fading for orbiter landing configuration

The on-shuttle antenna pattern of the MSBLS receiver, and the azimuth and elevation beamwidths were simulated by their corresponding ultrasonic transducer beams. The scanning rate for the azimuth and elevation beams was 1.75 degrees/second. The results were adjusted for full-scale maximum sinusoidal scan rates of 691 and 377 deg/sec for AZ and EL respectively. The rain drops were simulated by air bubbles, with a similar size distribution, in water. The rain volume was created along a part of the propagation path, and not on the runway, because it was found difficult to avoid an accumulation of bubbles on the runway surface and surroundings simulated by the model surface. Multipath fading from the ground, and its possible degrading effect on the orbiter received beam shape and the associated landing guidance parameters is discussed.

Hayre, H. S.↗
NASA NTRS1978

Observations of auroral fading before breakup

The onset of auroral breakup was studied by means of a variety of instruments with time resolution of some tens of seconds. Rapid sequences of all-sky photographs and fast meridian scans by photometers show that breakup is usually preceded by moderate brightening which is followed by fading of the auroral brightness lasting one or two min, all occurring before the actual breakup. Data from the International Magnetospheric Study magnetometer network might indicate a correlated response by the local auroral and ionospheric currents. Riometer recordings show a slow decrease in ionospheric radio wave absorption over a period of about 10 min prior to breakup. The observations are discussed with reference to the trigger mechanism for the expansion phase of a magnetospheric substorm.

Pellinen, R. J.↗
NASA NTRS1981

Method for retarding dye fading during archival storage of developed color photographic film

Dye fading during archival storage of developed color photographic film is retarded by placing the film in a sealed, opaque vault, introducing a dry, pressurized inert gas into the vault while the latter is vented, and sealing the vault after the air within the vault has been purged and replaced by the inert gas. Preferably, the gas is nitrogen; and the vault is stored at a temperature below room temperature to preserve the color photographic emulsions on the film contained within the vault. For short-term storage, sodium thiocyanate pads charged with water are placed within the vault. For long term storage, the interior of the vault is kept at a low relative humidity.

Hoover, R. B.↗
NASA NTRS1982

Effects of the mode of storage on the capacity fading of the sintered nickel electrodes

A systematic investigation of the effect of temperature and two conditions of storage, shortened and open circuit, on the capacity fading of sintered nickel electrodes in NiCd batteries was conducted. All testing was done on sintered electrodes in flooded cells. Cycling tests to measure the capacity were performed at room temperature. The capacity out to one volt, a capacity useful for satellite applications. Test results indicated that: the shortened electrode showed a higher rate of loss than the open circuit electrodes; there was an increase in both modes with an increase in temperature; there was a loss of capacity with time of storage; a general degradation was observed as a function of time; shortened electrodes showed a higher end of charge than the open circuit ones; and at room temperature there was a lower loss in the open circuit electrode than in the shortened one.

Vyes, B.↗
NASA NTRS1980

Spectral parameter estimation of CAT radar echoes in the presence of fading clutter

The analysis technique and a part of the results obtained from CAT radar echoes from higher troposphere and lower stratosphere are presented. First, the effect of processing distortion caused by the periodogram method using FFT algorithm on the slowly fading ground clutter echo is discussed. It is shown that an extremely narrow clutter spectrum can spill over the entire frequency range if the data are truncated at a tie sorter than their correlation time affecting largely the estimation of the CAT spectrum contribution, especially when the latter is a few tens of dB weaker than the former. A nonlinear least squares fitting procedure is used to parameterize the observed power spectrum in terms of CAT echo power, Doppler shift, spectral width, and the parameters which specify the shape of the clutter component.

Sato, T.↗
NASA NTRS1982

Ice depolarization of the Comstar beacon at 28.56 GHz during low fades and correlation with radar backscatter

Radar correlation with significant ice depolarization events accompanied by low copolarization fades of the 28.56-GHz Comstar beacon signal are described for an experimental program at Wallops Island, VA. Using a Faraday switch at the front end of the receiver, the copolarization and cross-polarization levels of the 28.56-GHz beacon signal are sequentially monitored. A nearby high resolution S-band radar pointing along the earth-satellite path monitors the simultaneous ice and rain reflectivity. For a first case considered, excellent correlation is noted between the cross-polarization events and relatively large and extended ice reflectivities along a segment of the earth-satellite path at altitudes near and above the 0 C isotherm. In a second case, the radar and receiver data strongly suggest the cross-polarization mechanism is due to a hailshaft which intersects the path at altitudes well below the 0 deg isotherm.

Goldhirsh, J.↗
NASA NTRS1986

Fade-Free Mobile Communication

Scheme for mobile communication reduces multipath fading and interference between adjacent channels. Proposed communication system lends itself to almost completely digital implementation, eliminating costly and bulky crystal filters. Scheme suitable for satellite-aided or terrestrial mobile communication, including cellular mobile telephony, at frequencies in 150-to-900-MHz range.

Stevenson, C. R.↗
NASA NTRS1987

Trellis-Coded Modulation for Fading Channels

In proposed communication system, digital signals transmitted efficiently over fading channel by combination of trellis coding and multiple-phase-shift keying with addition of asymmetry to signal set. Coding and modulation schemes not designed separately as in previous systems but integrated to yield bandwidth-efficient modulation and forward-error-correction coding. Helps to satisfy need for reliable high-quality transmission of voice and data between land-mobile units via satellites, where limitations of power and bandwidth imposed simultaneously. Also applicable to ionospheric communications between fixed or mobile units.

Simon, Marvin K.↗
NASA NTRS1987

Equations For Fading-Memory Filters

Report discusses simplified recursive solutions for equations of class of fading-memory filters. Under appropriate assumptions regarding noise and exponential decay of effects of previous states, filter equations reduced to analytic formulas in closed form.

Statman, J. I.↗
NASA NTRS1986

Combined coding and delay-throughput analysis for fading channels of mobile satellite communications

This paper presents the analysis of using the punctured convolutional code with Viterbi decoding to improve communications reliability. The punctured code rate is optimized so that the average delay is minimized. The coding gain in terms of the message delay is also defined. Since using punctured convolutional code with interleaving is still inadequate to combat the severe fading for short packets, the use of multiple copies of assignment and acknowledgment packets is suggested. The performance on the average end-to-end delay of this protocol is analyzed. It is shown that a replication of three copies for both assignment packets and acknowledgment packets is optimum for the cases considered.

Wang, C. C.↗
NASA NTRS1985

Land mobile satellite transmission measurements at 869 MHz. A comparison of error probabilities for various message block durations and fade margins as a function of vegetation shadowing

In order to give vehicles travelling in rural areas of the U.S. access to the telephone network, a Land Mobile Satellite System is being planned. Previously presented data by the author were analyzed for the probability that the received signal level dropped below a threshold during short time blocks of various signal durations and the conditional probability that such an event would reoccur after a given delay. If it assumed that a fade threshold crossing of even 1 msec would produce an error in the transmission, then the derived quantities can be considered error probabilities. Extensive tables and graphs are presented with the results from the analysis. They can be used to devise communication strategies which will provide improved link availability in the presence of vegetation shadowing.

Vogel, Wolfhard J.↗
NASA NTRS1988

Modulation and coding for fast fading mobile satellite communication channels

The performance of Gaussian baseband filtered minimum shift keying (GMSK) using differential detection in fast Rician fading, with a novel treatment of the inherent intersymbol interference (ISI) leading to an exact solution is discussed. Trellis-coded differentially coded phase shift keying (DPSK) with a convolutional interleaver is considered. The channel is the Rician Channel with the line-of-sight component subject to a lognormal transformation.

Mclane, P. J.↗
NASA NTRS1991

A statistical rain attenuation prediction model with application to the advanced communication technology satellite project. 3: A stochastic rain fade control algorithm for satellite link power via non linear Markow filtering theory

The dynamic and composite nature of propagation impairments that are incurred on Earth-space communications links at frequencies in and above 30/20 GHz Ka band, i.e., rain attenuation, cloud and/or clear air scintillation, etc., combined with the need to counter such degradations after the small link margins have been exceeded, necessitate the use of dynamic statistical identification and prediction processing of the fading signal in order to optimally estimate and predict the levels of each of the deleterious attenuation components. Such requirements are being met in NASA's Advanced Communications Technology Satellite (ACTS) Project by the implementation of optimal processing schemes derived through the use of the Rain Attenuation Prediction Model and nonlinear Markov filtering theory.

Manning, Robert M.↗
NASA NTRS1990

Acoustic echo cancellation for full-duplex voice transmission on fading channels

This paper discusses the implementation of an adaptive acoustic echo canceler for a hands-free cellular phone operating on a fading channel. The adaptive lattice structure, which is particularly known for faster convergence relative to the conventional tapped-delay-line (TDL) structure, is used in the initialization stage. After convergence, the lattice coefficients are converted into the coefficients for the TDL structure which can accommodate a larger number of taps in real-time operation due to its computational simplicity. The conversion method of the TDL coefficients from the lattice coefficients is derived and the DSP56001 assembly code for the lattice and TDL structure is included, as well as simulation results and the schematic diagram for the hardware implementation.

Park, Sangil↗
NASA NTRS1990

New 16-PSK trellis codes for fading channels

Growth in satellite mobile communications leads to increasing requirements for high data rate transmission that can be met by more efficient modulation schemes (M greater than 8). The 16-PSK trellis coded modulation technique is a very promising solution. A class of new 16-PSK trellis codes with improved error rate are designed based on the criteria on fading channels.

Du, Jun↗
NASA NTRS1993

NiH2 capacity fade during early cycling

Tests were conducted on nickel hydrogen batteries to determine the charge efficiency of the nickel electrode as a function of rate and temperature, cell discharge capacity, and capacity fade. Test procedures and results are presented in outline and graphic form.

Zagrodnik, Jeffrey P.↗