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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 595 records · Page 33
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NASA NTRS1977

Tracking performance of symbol synchronizers for Manchester coded data

The implementation and tracking performance of symbol synchronizers for Manchester coded data is presented with motivation provided by maximum a posteriori (MAP) estimation theory. Certain physically relizable closed-loop structures, readily implemented in practice, are suggested by the theory for uncoded data symbols with arbitrary data transition probabilities. The tracking performance of these loops is optimized and comparisons are made among the various configurations over a wide range of system parameters. Although not the major intent of the paper, the acquisition problem is briefly addressed.

Simon, M. K.↗
NASA NTRS1976

Static inverter with synchronous output waveform synthesized by time-optimal-response feedback

Time-optimal-response 'bang-bang' or 'bang-hang' technique, using four feedback control loops, synthesizes static-inverter sinusoidal output waveform by self-oscillatory but yet synchronous pulse-frequency-modulation (SPFM). A single modular power stage per phase of ac output entails the minimum of circuit complexity while providing by feedback synthesis individual phase voltage regulation, phase position control and inherent compensation simultaneously for line and load disturbances. Clipped sinewave performance is described under off-limit load or input voltage conditions. Also, approaches to high power levels, 3-phase arraying and parallel modular connection are given.

Kernick, A.↗
NASA NTRS1977

A unified analysis of pseudonoise synchronization by envelope correlation

A relationship between coarse acquisition (coarse alignment of two pseudonoise codes to within approximately one code symbol) and fine acquisition (tracking) in a pseudonoise modulated spread spectrum communication system is studied. A convenient technique for determining mean acquisition time and hold-in time (mean time to lose lock) after acquisition, using a delay lock loop, is elaborated. An analysis procedure for handling the transition from search to lock is developed and applied to a problem containing representative Space Shuttle data (signal parameters and synchronizer parameters).

Hopkins, P. M.↗
NASA NTRS1976

Timesharing without synchronization

The capacity region of a multiple-access channel has recently been identified as the convex hull (barred K) of a certain set (K) of points in the first quadrant of the (R1,R2) plane. For a pair of rates in K, a more or less standard random-coding argument can be used to show the existence of a good pair of codes. But for points in barred K-K, it is apparently necessary for the two senders to use some form of time sharing to achieve the desired rates. However, in order to share time, at least one of the senders must have knowledge of the other's phase; and in many practical situations this knowledge does not exist. This paper investigates the problems which arise in coding for multiple-access channels when the senders cannot synchronize with each other.

Mceliece, R. J.↗
NASA NTRS1976

120 MB/S and 240 MB/S bit synchronizer-signal conditioners for NASA high data rate applications

Two bit synchronizer-signal conditioners (BSSC) developed for NASA high data rate applications such as earth resources monitoring are described. One BSSC is centered at 120 MB/s and the other at 240 Mb/s. These subsystems are featured out of the total hardware developed because the BSSC is such a key subsystem in determining overall system statistical performance. These units represent an evolution of high data rate BSSC's available at low data rates. Numerous inputs/outputs, control functions, indicators, plus the ability to minimize the effects of various signal perturbations are provided. Examples of allowed perturbations are input level variations, bit rate variance static and dynamic, baseline, transition density, bandlimiting, etc., as well as noise. Emphasis in the past has been primarily concerned only with noise.

Gray, J. S.↗
NASA NTRS1978

Digital phase shifter synchronizes local oscillators

Digital phase-shifting network is used as synchronous frequency multiplier for applications such as phase-locking two signals that may differ in frequency. Circuit has various phase-shift capability. Possible applications include data-communication systems and hybrid digital/analog phase-locked loops.

Ali, S. M.↗
NASA NTRS1978

Synchronous transfer circuits for redundant systems

Circuit arrangements for flip-flops, counters, and clock drivers in redundant systems ensure that control is synchronously transferred to surviving components when failure occurs. In addition to original application to spacecraft systems, redundant circuits have terrestrial uses in power generators, solar-energy converters, computers, vehicle controllers, and other systems demanding high reliability.

Nagano, S.↗
NASA NTRS1977

The optimization of self-phased arrays for diurnal motion tracking of synchronous satellites

The diurnal motion of a synchronous satellite necessitates mechanical tracking when a large aperture, high gain antenna is employed at the earth terminal. An alternative solution to this tracking problem is to use a self phased array consisting of a number of fixed pointed elements, each with moderate directivity. Non-mechanical tracking and adequate directive gain are achieved electronically by phase coherent summing of the element outputs. The element beamwidths provide overlapping area coverage of the satellite motion but introduce a diurnal variation into the array gain. The optimum element beamwidth and pointing direction of these elements can be obtained under the condition that the array gain is maximized simultaneously with the minimization of the diurnal variation.

Theobold, D. M.↗
NASA NTRS1976

The ATS-5 solar cell experiment after 6-1/2 years in synchronous orbit

Several types of solar cell/coverslide combinations were launched into synchronous orbit. The cells were 2 and 10 ohm-cm crucible-grown silicon with thicknesses of 0.2 and 0.3 mm. Coverslides were fused silica, ranging in thickness from 0.15 to 1.52 mm. The cells were mounted on two panels, one a rigid aluminum honeycomb structure, giving essentially infinite backshielding; the other was a thin Kapton-fiberglass substrate, offering minimal protection to the rear surface of the cells. The current-voltage curves of the cells were measured. Correction of cell electrical output to standard temperature and solar intensity was performed, using empirical radiation-dependent corrections. It is found that the cells on the flexible panel degrade much more rapidly than predicted, while the rigid panel cells follow the predictions fairly well. The anomalous behavior of the flexible panel cells is attributed to the deposition of a contaminant on the cell coverslides.

Anspaugh, B.↗
NASA NTRS1977

VLBI clock synchronization

The potential accuracy of VLBI (very long baseline interferometry) for clock epoch and rate comparisons was demonstrated by results from long- and short-baseline experiments. It was found that atomic clocks at widely separated sites (several thousand kilometers apart) can be synchronized to within several nanoseconds from a few minutes of VLBI observations and to within one nanosecond from several hours of observations.

Counselman, C. C., III↗
NASA NTRS1978

Comparison of synchronization of primate circadian rhythms by light and food

It is a well-documented fact that cycles of light and dark (LD) are the major entraining agent or 'zeitgeber' for circadian rhythms and that cycles of eating and fasting (EF) are capable of synchronizing a few circadian rhythms in the squirrel monkey. In this paper, by contrasting how these rhythms are timed by LD and EF cycles, the differential coupling to the oscillating system within adult male squirrel monkeys is examined. The variables measured are the rhythms of drinking, colonic temperature, and urinary potassium and water excretion. Attention is given to a comparison of the reproducibility of the averaged waveforms of the rhythms, the stability of the timing of a phase reference point, and the rate of resynchronization of these rhythms following an abrupt 8-hr phase delay in the zeitgeber. It is shown that the colonic temperature rhythm is more tightly controlled by LD than EF cycles, and that the drinking and urinary rhythms are more tightly coupled to EF than LD cycles.

Sulzman, F. M.↗
NASA NTRS1978

Pitch angle dispersion of drifting energetic protons at synchronous orbit

The time of arrival at ATS 6 of substorm-associated energetic proton flux enhancements has been examined as a function of both energy and pitch angle by using electron-proton spectrometer data. The protons exhibit energy dispersion with the particles with the highest energy arriving first. This has generally been interpreted as evidence that these particles have gradient- and curvature-drifted to the spacecraft from an acceleration region on the nightside. In the evening quadrant, proton enhancements at 90 deg pitch angle arrived at the spacecraft prior to those at small pitch angles. However, on the dayside the increase occurs first at the smallest pitch angle (about 30 degrees). The difference between the arrival times of the 30 deg and 90 deg protons increases for more westward local times. For the highest energy range observed, drifting protons are rarely seen at large pitch angles. These observations place severe restrictions on the simple drift models. Since the pitch angle dependence of the particle drift velocity is a field geometric quantity, the observations require the modification of present magnetospheric magnetic field models. In particular, the models need to reproduce better the enhanced field observed on the dayside near synchronous orbit.

Walker, R. J.↗
NASA NTRS1978

Low-energy plasma observations at synchronous orbit

The University of California at San Diego Auroral Particles Experiment on the ATS 6 satellite in synchronous orbit has detected a low-energy plasma population which is separate and distinct from both the ring current and the plasma sheet populations. The density and temperature of this low-energy population are highly variable, with temperatures in the range kT = 1-30 eV and densities ranging from less than 1 per cu cm to more than 10 per cu cm. The occurrence of a dense low-energy plasma is most likely in the afternoon and dusk local time sectors, whereas n greater than 1 per cu cm is seen in the local night sector only during magnetically quiet periods. These observations suggest that this plasma is the outer zone of the plasmasphere. During magnetically active periods this low-energy plasma is often observed flowing sunward. In the dusk sector, strong sunward plasma flow is often observed for 1-2 hours prior to the onset of a substorm-associated particle injection.

Lennartsson, W.↗
NASA NTRS1978

Geomagnetic field fluctuations at synchronous orbit. II - Radial diffusion

Power spectra of geomagnetic-field variations measured at synchronous equatorial altitude (geomagnetic shell parameter about 6.6) in the magnetosphere are used to calculate the time dependence of the radial diffusion coefficient for particles in the radiation belts. The diffusion coefficients calculated are mainly applicable for relativistic electrons. The magnitudes of the derived diffusion coefficients using data only from local day observations are consistent with those reported from analyses of most particle observations and thus are slightly larger than those derived from magnetic sudden commencements. They are consistent with the diffusion coefficients calculated from power spectra of ground-based geomagnetic data measured near L = 4.

Lanzerotti, L. J.↗
NASA NTRS1980

Binary synchronous simulator

Flexible simulator for trouble-shooting data transmission system uses binary synchronous communications protocol to produce error-free transmission of data between two points. Protocol may be used to replace display generator or be directly fed to display generator.

Rogers, J. R., III↗
NASA NTRS1979

Design of a video teleconference facility for a synchronous satellite communications link

The system requirements, design tradeoffs, and final design of a video teleconference facility are discussed, including proper lighting, graphics transmission, and picture aesthetics. Methods currently accepted in the television broadcast industry are used in the design. The unique problems associated with using an audio channel with a synchronous satellite communications link are discussed, and a final audio system design is presented.

Richardson, M. D.↗
NASA NTRS1979

System for synchronizing synthesizers of communication systems

Frequency synthesizers at first and second stations that communicate with each other via a transmission link having a constant propagation delay time are started and synchronized by transmitting a tone from the first station to the second station via the link. The frequencies derived from the synthesizer at the second station are received at the first station and are combined with the frequencies derived from the synthesizer at the first station to derive a constant beat frequency as the two synthesizers are stepped.

Enriquez, E. A.↗