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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The statistical character of Pc 4 magnetic pulsations at synchronous orbit

A statistical study of 215 magnetic pulsation events identified on the basis of waveform and period as Pc 4 (45- to 150-s period) observed at synchronous orbit by ATS 6 is reported. The study was designed to be similar to that done with Pc 3 (10- to 45-s period) by Arthur et al. (1977). These Pc 4 are found to occur most often near 1800 local time but are observed at all local times. The dominant period is approximately 100 s, but a secondary peak in the distribution occurred at approximately 53 s. They tend to be nearly linearly polarized, principally transverse to the ambient magnetic field. The Pc 4 are found to divide naturally into two classes (radial and azimuthal) on the basis of the azimuth of the major axis of polarization. These classes divide further into low-frequency (less than or equal to 0.015 Hz) and high-frequency (greater than or equal to 0.015 Hz) classes. These four classes organize the remaining wave characteristics quite well. Division of the Pc 4 events into these classes does not lead to identification of a single source mechanism as it did with Pc 3. However, some correspondence between the classes and various proposed mechanisms does exist.

Arthur, C. W.↗
NASA NTRS1981

Ion propulsion for shared Shuttle, sun-synchronous missions

The configuration of an ion propulsion module (IPM) for use in the deployment and retrieval of sun-synchronous satellites on shared Shuttle flights is described. In addition to enabling shared Shuttle payloads requiring large orbital plane changes for achieving desired viewing conditions, the IPM makes over 10 kw available for payload power-sharing on orbit. The IPM also affords a large on-orbit propulsion capability. It has 2.8 x 10 to the 7th N-sec available at full propellant loading, of which less than half was needed for deploying and retrieving the representative spacecraft studied. Its remaining propulsion capability can be used for increasing payload or for additional propulsive functions on orbit.

Zafran, S.↗
NASA NTRS1975

Study of hollow corner retroreflectors for use in a synchronous orbit

The performance of a hollow corner cube retroreflector made up of three mutually perpendicular optically flat mirrors when undergoing the thermal-mechanical strains induced by a spacecraft environment was studied. Of particular interest was a device of 200 square centimeter optical aperture used on a satellite in a synchronous orbit. It was assumed that the reflector always faces the earth. The effects of direct solar irradiance, earthshine, and albedo were considered. The results included the maximum mirror surface temperature during the orbit as well as the worst-case loss of optical performance due to thermally-induced mirror distortions. It was concluded that a device made of three suitably coated flat ULE mirrors, optically contacted to each other and supported mechanically in a nonrigid mount, would be expected to concentrate over 80 percent of the theoretical maximum energy in the central of the far field diffraction pattern. Continued development of the device through a detailed design, fabrication, and test phase was recommended.

Yoder, P. R., Jr.↗
NASA NTRS1980

NASCAP charging calculations for a synchronous orbit satellite

The use of the NASA Charging Analyzer Program (NASCAP) for the computation of spacecraft charge up in the energetic plasma environment of geosynchronous orbits is described. Spacecraft modelling, materials parameters, and NASCAP charging analyses are described. The synchronous orbit plasma environment used in the stress analysis employs a two Maxwellian energy distribution to determine the fluxes. Several NASCAP runs performed to determine the location and magnitude of environmentally induced voltage stresses are analyzed.

Sanders, N. L.↗
NASA NTRS1982

Queueing analysis of synchronous time division multiplexing with individual source buffering

Synchronous time division multiplexing is analyzed. Packets of information arrive at the system as a compound Poisson process, and are transmitted only during individual periodic intervals. Packet arrivals are blocked (lost) if the system has a finite capacity and is congested. Using the theory of semiregenerative processes, the distribution of the number of packets in the system (system size) is found. This nonstationary distribution is used to determine the complete system behavior, including the delay distributions, the blocking probability, and the density of the system size at arrival instants. Numerical examples illustrate applications of the results given.

Clare, L.↗
NASA NTRS1982

General Theory of the Double Fed Synchronous Machine

Motor and generator operation of a double-fed synchronous machine were studied and physically and mathematically treated. Experiments with different connections, voltages, etc. were carried out. It was concluded that a certain degree of asymmetry is necessary for the best utilization of the machine.

El-Magrabi, M. G.↗
NASA NTRS1980

Open-loop nanosecond-synchronization for wideband satellite communications

A synchronization technique for use with an onboard processing satellite communication system is discussed. The satellite oscillator is used both as the system time reference and as the frequency source for all downlink carriers and data clocks. Downlink timing is established at each system earth terminal through a combination of carrier and data-clock tracking and a downlink timing epoch signal consisting of one bit per TDMA data burst. Uplink timing is established by an open-loop range prediction process using precision ephemerides calculated and distributed by the central control station. Overall timing accuracy of the uplink signal at the satellite receiver of + or - 7 nanoseconds permits unambiguous identification of each data bit position in a 128 Mbps TDMA burst. This is accomplished by means of simple, inexpensive terminal hardware using available crystal oscillators for time/frequency references and digital synthesis techniques that may be implemented in digital LSI chips.

Holmes, W. M., Jr.↗
NASA NTRS1982

Synchronized voltage contrast display analysis system

An apparatus and method for comparing internal voltage potentials of first and second operating electronic components such as large scale integrated circuits (LSI's) in which voltage differentials are visually identified via an appropriate display means are described. More particularly, in a first embodiment of the invention a first and second scanning electron microscope (SEM) are configured to scan a first and second operating electronic component respectively. The scan pattern of the second SEM is synchronized to that of the first SEM so that both simultaneously scan corresponding portions of the two operating electronic components. Video signals from each SEM corresponding to secondary electron signals generated as a result of a primary electron beam intersecting each operating electronic component in accordance with a predetermined scan pattern are provided to a video mixer and color encoder.

Johnston, M. F.↗
NASA NTRS1983

Timing subsystem development: Network synchronization experiments

This paper describes a program in which several experimental timing subsystem prototypes were designed, fabricated, and field tested using a small network of troposcatter and microwave digital communication links. This equipment was responsible for modem/radio interfacing, time interval measurement, clock adjustment and distribution, synchronization technique, and node to node information exchange. Presented are discussions of the design approach, measurement plan, and performance assessment methods. Recommendations are made based on the findings of the test program and an evaluation of the design of both the hardware and software elements of the timing subsystem prototypes.

Backe, K. R.↗
NASA NTRS1982

Pc 1-2 observations of heavy ion effects by synchronous satellite ATS-6

Ion cyclotron waves generated in the magnetosphere by the ion cyclotron instability of protons are thought to be the origin of Pc 1-2 geomagnetic pulsations. Propagation characteristics of these waves have been measured using ATS-6 synchronous satellite magnetometer wave data. Of particular interest are the wave spectra, polarization properties, and wave diagnostics; all are characteristic of propagation in a cool ambient magnetospheric plasma containing He(+) and O(+) heavy ions.

Fraser, B. J.↗
NASA NTRS1983

Satellite observations of Pi 2 activity at synchronous orbit

An attempt is made to characterize Pi 2 activity at synchronous orbit, on the basis of magnetic field data recorded in September, 1974. Pi 2 bursts are primarily seen in the nighttime sector, probably near 2100 LT, and are usually simultaneous with the Pi 2 bursts seen at midlatitude ground stations. Three main event types are noted at the data-gathering satellite: a 100-sec irregular oscillation in all field components, an additional 100-sec irregular oscillation which, unlike the first, is not accompanied by high frequency oscillations, and a much rarer, quasi-sinusoidal oscillation in the east-west component of the field. The dominant period of Pi 2 bursts is about 100 sec, and tends to be shorter as the level of activity measured by field changes at the satellite increases.

Sakurai, T.↗
NASA NTRS1985

Synchronously Deployable Truss

Double-layered truss structure compactly packaged and sychronously deployed. Synchronously deployable truss constructed of two surface layers of struts, arranged in triangles, connected by "tripods" of equal-length core struts. Mechanism powered by passive spring and damped by hydraulic-damping cylinder. When released, spring drives slider linked to core and surface struts. Variety of truss geometries, including curved structures, comtemplated.

Bush, H. G.↗
NASA NTRS1984

Structural Analysis of the Support System for a Large Compressor Driven by a Synchronous Electric Motor

For economic reasons, the steam drive for a large compressor was replaced by a large synchronous electric motor. Due to the resulting large increase in mass and because the unit was mounted on a steel frame approximately 18 feet above ground level, it was deemed necessary to determine if a steady state or transient vibration problem existed. There was a definite possibility that a resonant or near resonant condition could be encountered. The ensuing analysis, which led to some structural changes as the analysis proceeded, did not reveal any major steady state vibration problems. However, the analysis did indicate that the system would go through several natural frequencies of the support structure during start-up and shutdown. This led to the development of special start-up and shutdown procedures to minimize the possibility of exciting any of the major structural modes. A coast-down could result in significant support structure and/or equipment damage, especially under certain circumstances. In any event, dynamic field tests verified the major analytical results. The unit has now been operating for over three years without any major vibration problems.

Winter, J. R.↗
NASA NTRS1983

Synchronization of magnetic stars in binary systems

Asynchronous rotation of magnetic stars in close binary systems drives substantial field-aligned electrical currents between the magnetic star and its companion. The resulting magnetohydrodynamic torque is able to account for the heretofore unexplained synchronous rotation of the strongly magnetic degenerate dwarf component in systems like AM Her, VV Pup, AN UMa, and EF Eri as well as the magnetic A type component in systems like HD 98088 and 41 Tauri. The electric fields produced by even a small asynchronism are large and may accelerate some electrons to high energies, producing radio emission. The total energy dissipation rate in systems with degenerate dwarf spin periods as short as 1 minute may reach 10 to the 33rd ergs/s. Total luminosities of this order may be a characteristic feature of such systems.

Lamb, F. K.↗
NASA NTRS1985

Synchronization for Optical PPM Signals

Method based on statistical properties of weak pulse-positionmodulated (PPM) signal enables synchronization of receiver clock with received-signal time base. Method applies to weak optical M-ary PPM signals, for which there is only one pulse of length Tp transmitted during one of timeslots of length T in each successive interval of M timeslots. Method requires small dead time, Td, at beginning and end of each timeslot, during which pulse amplitude is zero.

Vilnrotter, V. A.↗
NASA NTRS1985

Reed-solomon Code Synchronization Revisited

A concatenated coding consisting of an inner (7, 1/2) convolutional code and an outer (255, 223) Reed-Solomon code was recommended by the Consultative Committee for Space Data Systems for cross-supported space missions. The Reed-Solomon code that was chosen makes use of the Berlekamp encoding algorithm. Some peculiarities of this code that could give rise to synchronization problems are examined. Suggestions are given to alleviate these problems.

Deutsch, L. J.↗
NASA NTRS1985

Synchronizing Heavily Encoded Data in Bad Weather

Deep space missions choose a data rate to ensure reliable communication under most conditions. Certain critical data can be more heavily encoded, to be decoded under particularly bad atmospheric conditions. It is shown that, in such a system, finding and synchronizing critical data will not be a problem.

Swanson, L.↗