Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “synchronization”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Minimizing selective availability error on Topex GPS measurements

GPS measurements made at Topex/Poseidon and the accompanying ground tracking sites will be affected by the selective availability. Although in principle the effects may be removed by differencing between receivers observing the same GPS satellites, this requires accurate synchronization of all receiver clocks. In the case of Topex/Poseidon application, there are two sources of imperfect clock synchronization. The first and larger is due to the constantly drifting clock onboard Topex, which may cause a residual effect as large as 10 cm on Topex carrier phase and 1 m on Topex pseudorange. The second is due to light-time differences between receivers observing the same GPS satellites, which may amount to a few mm error. In this paper a data reduction scheme which incorporates a low-order polynomial interpolation and carrier phase smoothing on pseudorange acquired at Topex and ground receivers is described; a simulation analysis is given demonstrating the effectiveness of the scheme for reducing the GPS S/A effects; and comparison with other schemes is discussed.

Wu, S. C.↗
NASA NTRS1991

System Decommutes And Displays Telemetry Data

TDPlus computer program software system for decommutation of pulse-code-modulation (PCM) telemetry signals. Provides synchronization, conversion into engineering units, and display of serial bit streams. Transforms IBM PC-compatible computer into PCM-telemetry-decommutation system. Synchronizes telemetric signals data and enables conversion back into such meaningful forms as voltage, current, pressure, and the like. Also controls operation of digital-to-analog converters to ship data to paper strip charts or to parallel digital ports for offloading to other computers. Software used to process actual data only when telemetry-data-processing computer modified in accordance with specifications contained in "TDPlus TM Data Processor" (GSC-13291). Written in Turbo C and 8088 Assembly language.

Massey, D. E.↗
NASA NTRS1990

Conservative parallel simulation of priority class queueing networks

A conservative synchronization protocol is described for the parallel simulation of queueing networks having C job priority classes, where a job's class is fixed. This problem has long vexed designers of conservative synchronization protocols because of its seemingly poor ability to compute lookahead: the time of the next departure. For, a job in service having low priority can be preempted at any time by an arrival having higher priority and an arbitrarily small service time. The solution is to skew the event generation activity so that the events for higher priority jobs are generated farther ahead in simulated time than lower priority jobs. Thus, when a lower priority job enters service for the first time, all the higher priority jobs that may preempt it are already known and the job's departure time can be exactly predicted. Finally, the protocol was analyzed and it was demonstrated that good performance can be expected on the simulation of large queueing networks.

Nicol, David M.↗
NASA NTRS1991

Satellite orbit considerations for a global change technology architecture trade study

A study was conducted to determine satellite orbits for earth observation missions aimed at obtaining data for assessing data global climate change. A multisatellite system is required to meet the scientific requirements for temporal coverage over the globe. The best system consists of four sun-synchronous satellites equally spaced in local time of equatorial crossing. This system can obtain data every three hours for all regions. Several other satellite systems consisting of combinations of sun-synchronous orbits and either the Space Station Freedom or a mid-altitude equatorial satellite can provide three to six hour temporal coverage, which is sufficient for measuring many of the parameters required for the global change monitoring mission. Geosynchronous satellites are required to study atmospheric and surface processes involving variations on the order of a few minutes to an hour. One or two geosynchronous satellites can be relocated in longitude to study processes over selected regions of earth.

Harrison, Edwin F.↗
NASA NTRS1990

Delivery and application of precise timing for a traveling wave powerline fault locator system

The Bonneville Power Administration (BPA) has successfully operated an in-house developed powerline fault locator system since 1986. The BPA fault locator system consists of remotes installed at cardinal power transmission line system nodes and a central master which polls the remotes for traveling wave time-of-arrival data. A power line fault produces a fast rise-time traveling wave which emanates from the fault point and propagates throughout the power grid. The remotes time-tag the traveling wave leading edge as it passes through the power system cardinal substation nodes. A synchronizing pulse transmitted via the BPA analog microwave system on a wideband channel sychronizes the time-tagging counters in the remote units to a different accuracy of better than one microsecond. The remote units correct the raw time tags for synchronizing pulse propagation delay and return these corrected values to the fault locator master. The master then calculates the power system disturbance source using the collected time tags. The system design objective is a fault location accuracy of 300 meters. BPA's fault locator system operation, error producing phenomena, and method of distributing precise timing are described.

Street, Michael A.↗
NASA NTRS1989

Transportable telemetry workstation

The goal was to complete the design of a prototype for a Transportable Telemetry Workstation (TTW). The Macintosh 2 is used to provide a low-cost system which can house real-time cards mounted on the NuBus inside the Macintosh 2 plus provide a standardized user interface on the Macintosh 2 console. Prior to a telemetry run, the user will be able to configure his real-time telemetry processing functions from the Macintosh 2 console. During a telemetry run, the real-time cards will store the telemetry data directly on a hard disk while permitting viewing of the data cards on the Macintosh 2 console on various selectable formats. The user will view the cards in terms of the functions they perform and the selectable paths through the cards, it is not required to become involved directly in hardware issue except in terms of the functional configuration of the system components. The TTW will accept telemetry data from an RS422 serial input data bus, pass it through a frame synchronizer card and on to a real time controller card via a telemetry backplane bus. The controller card will then route the data to a hard disk through a SCSI interface, and/or to a user interface on the Macintosh 2 console by way of the Macintosh 2 NuBus. The three major components to be designed, therefore, are the TTW Controller Card, the TTW Synchronizer Card, and the NuBus/Macintosh 2 User Interface. Design and prototyping of this state-of-the-art, transportable, low-cost, easy-to-use multiprocessor telemetry system is continuing. Other functions are planned for the future.

Collins, Aaron S.↗
NASA NTRS1989

A comparative study of seminiferous tubular epithelium from rats flown on Cosmos 1887 and SL3

Space flight, with its unique environmental constraints such as immobilization, decreased and increased pressures, and radiation, is known to affect testicular morphology and spermatogenesis. Among the several biological experiments and animals on board COSMOS 1887 Biosputnik flight were 10 rats, from which were collected testicular tissue. Average weights of flight tests were 6.4 pct. below that of the vivarium control when normalized for weight loss/100 grams body weight. Counts of surviving spermatogonia per tubule cross section indicated an average of 39 spermatogonia for flight animals, 40 for synchronous controls and 44 for the vivarium controls. Serum testosterone was significantly decreased when compared to basal controls but the decrease was not significant when compared in vivarium and synchronous control groups. The significant decrease in spermatogonia and the decrease in serum testosterone are similar to that in animals flown on Space Lab 3 (Challenger Shuttle).

Sapp, Walter J.↗
NASA NTRS1989

Solving the BM Camelopardalis puzzle

BM Camelopardalis (=12 Cam) is a chromospherically active binary star with a relatively large orbital eccentricity. Systems with large eccentricities usually rotate pseudosynchronously. However, BM Cam has been a puzzle since its observed rotation rate is virtually equal to its orbital period indicating synchronization. All available photometry data for BM Cam have been collected and analyzed. Two models of modulated ellipticity effect are proposed, one based on equilibrium tidal deformation of the primary star and the other on a dynamical tidal effect. When the starspot variability is removed from the data, the dynamical tidal model was the better approximation to the real physical situation. The analysis indicates that BM Cam is not rotating pseudosynchronously but rotating in virtual synchronism after all.

Teke, Mathias↗
NASA NTRS1991

COSMOS 2044: Lung morphology study, experiment K-7-28

Researchers examined the effect of microgravity during spaceflight on lung tissue. The ultrastructure of the left lungs of 5 Czechoslovakian Wister rats flown on the 13 day, 19+ hour Cosmos 2044 mission was examined and compared to 5 vivarium and 5 synchronous controls at 1-g conditions, and 5 rats exposed to 14 days of tail suspension. Pulmonary hemorrage and alveolar adema of unknown origin occurred to a greater extent in the flight, tail-suspended, and synchronous control animals, and in the dorsal regions of the lung when compared with the vivarium controls. The cause of these changes, which are possibly due to an increase in pulmonary vascular pressure, requires further investigation.

Elliott, Ann R.↗
NASA NTRS1991

A carrier-arraying demonstration at Goldstone for receiving Pioneer 11 signals

A carrier arraying technique was demonstrated at Goldstone. The Block III receivers of two 34-m antennas, Deep Space Station 12 and 15, were arrayed together to receive S band (2.3 GHz) signals from the Pioneer 11 spacecraft. Carrier phases in the two receivers were synchronized by the analog phase lock loops, and carrier signals were added at an intermediate frequency to enhance tracking performance. The receiver at DSS 15, which has been unable to lock up and track the Pioneer 11 signal by itself due to a wider tracking loop bandwidth and a higher system temperature, was now able to track the carrier and produce usable baseband signals. The receiver at DSS 12 achieved a reduction of the rms phase error, increasing the telemetry symbol SNR by an average of 0.35 dB. The baseband signals from both antennas were then synchronized and combined using the existing Baseband Assembly, thereby achieving a total symbol SNR increase of 2.5 + or - 0.7 dB relative to DSS 12 alone. A more comprehensive model is presented to permit evaluation of both thermal and phase noise effects. The analysis agrees well with observed data.

Pham, T. T.↗
NASA NTRS1990

The Galileo Orbiter - Command and telemetry subsystems on their way to Jupiter

An overview is given of the Galileo command and telemetry subsystems, which exemplify the rigid time-synchronized systems required by TDM (time division multiplexing). The spacecraft clock is examined, along with some of the rationale for the development of the clock structure and timing to give a sense of the design imperatives for rigidly synchronized systems. Additional subjects include the structure of the science and engineering frames, emphasizing the subcommutated structure of the engineering frame and its relationship to the spacecraft clock; ground processing for and basic uses of the telemetry; the various message types used to transmit commands to the spacecraft; and the generation processes for the command message types.

Erickson, James K.↗
NASA NTRS1990

Evolution of starspots in the long-period RS CVN binary V1817 Cygni = HR 7428

Photometry between 1982 and 1989, published and unpublished, is analyzed. The ellipticity effect produces variability with a full amplitude of 0.033 m in V. A recent time of light minimum (JD 2445988.0 + or - 0.3 d) combined with an old spectroscopic time of conjunction from the 1920's yields a much improved orbital period (108.854 + or - 0.003). Removal of the ellipticity effect reveals starspot variability. Four different spots were observed at various times, two of them present simultaneously in the light curve during 1985. Mean spot lifetimes were around 2 years and the largest amplitude attributed to starspots was 0.04 m in V during 1986. Derived rotation periods for two spots were 5.3 + or - 1.2 percent slower than synchronous and 3.0 + or - 0.4 percent faster. The differential rotation coefficient for the K2 giant is k = 0.25 + or - 0.04, compared to k = 0.186 for the sun. V1817 Cygni has the longest orbital period of any binary known to execute synchronous rotation.

Hall, Douglas S.↗
NASA NTRS1991

On the radial structure of Saturn's B ring

Voyager observations have revealed that the Saturnian B ring is much more structured than previously anticipated. Some of these structures occur on radial scale lengths of less than 15 km. In the visible the ring an optical depth minimum at a small distance outside of synchronous orbit. It is suggested in this paper that the electromagnetically induced radial transport of angular momentum associated with radial transport of charged submicron-size dust particles may explain these features. This mechanism induces an instability which produces, over geological times, significant radial structuring of the ring. Mass contained in particles less than about 1 cm in size is transported away from the synchronous orbit. This produces the optical depth minimum there. A simulation, starting with a radially uniform mass and number density, yields a radial optical depth profile which is similar to what is observed. It is found that it takes about 400-800 million yr to produce the observed structure. This estimate for the age of B ring agrees with some other independent estimates.

Shan, Lin-Hua↗
NASA NTRS1990

RF/optical interference design for optical intersatellite links

A design approach for the RF/optical link interface for a data relay satellite is described. The flexibility of forward and return links in future data acquisition satellites in handling varying missions and data rates to 1 Gbit/s is considered. Attention is focused on requirements for the NASA Tracking and Data Acquisition System. System components are described including the return link multiplexer, the return link transmultiplexer, the forward link multiplexer, the forward link demultiplexer, and the frontside/backside switch. Ping-pong buffers, which provide rate buffering for each input data stream, are discussed and justification bits, which handle variations due to Doppler shift and local oscillator variation, are considered. The time-division multiplexed streams consist of a unique synchronization word for frame synchronization, and control words associated with each data burst to identify the presence or absence of a justification bit. Redundant data paths are described for both forward and return data streams.

Garlow, Ronald K.↗
NASA NTRS1991

Technologies for unattended network operations

The necessary network management functions for a telecommunications, navigation and information management (TNIM) system in the framework of an extension of the ISO model for communications network management are described. Various technologies that could substantially reduce the need for TNIM network management, automate manpower intensive functions, and deal with synchronization and control at interplanetary distances are presented. Specific technologies addressed include the use of the ISO Common Management Interface Protocol, distributed artificial intelligence for network synchronization and fault management, and fault-tolerant systems engineering.

Jaworski, Allan↗
NASA NTRS1992

Control Circuit For Reed-Solomon Encoder

Control circuit designed for use with commercially available AHA4610 Reed-Solomon encoder. Needed to select depth of interleaving and to synchronize input and output blocks of data and parity bits with suitable clock signals. Circuit provides synchronizing and control signals for Reed-Solomon encoder. Encoder can operate with asynchronous input and output data streams at rates up to 80 Mb/s. Interleaving depth selectable, and accommodation to input data rate automatic.

Ross, Douglas↗
NASA NTRS1991

Improved accuracies for satellite tracking

A charge coupled device (CCD) camera on an optical telescope which follows the stars can be used to provide high accuracy comparisons between the line of sight to a satellite, over a large range of satellite altitudes, and lines of sight to nearby stars. The CCD camera can be rotated so the motion of the satellite is down columns of the CCD chip, and charge can be moved from row to row of the chip at a rate which matches the motion of the optical image of the satellite across the chip. Measurement of satellite and star images, together with accurate timing of charge motion, provides accurate comparisons of lines of sight. Given lines of sight to stars near the satellite, the satellite line of sight may be determined. Initial experiments with this technique, using an 18 cm telescope, have produced TDRS-4 observations which have an rms error of 0.5 arc second, 100 m at synchronous altitude. Use of a mosaic of CCD chips, each having its own rate of charge motion, in the focal place of a telescope would allow point images of a geosynchronous satellite and of stars to be formed simultaneously in the same telescope. The line of sight of such a satellite could be measured relative to nearby star lines of sight with an accuracy of approximately 0.03 arc second. Development of a star catalog with 0.04 arc second rms accuracy and perhaps ten stars per square degree would allow determination of satellite lines of sight with 0.05 arc second rms absolute accuracy, corresponding to 10 m at synchronous altitude. Multiple station time transfers through a communications satellite can provide accurate distances from the satellite to the ground stations. Such observations can, if calibrated for delays, determine satellite orbits to an accuracy approaching 10 m rms.

Kammeyer, P. C.↗
NASA NTRS1991

Satellite orbit considerations for a global change technology architecture trade study

A study was conducted to determine satellite orbits for Earth observation missions aimed at obtaining data for assessing global climate change. A multisatellite system is required to meet the scientific requirements for temporal coverage over the globe. The best system consists of four Sun-synchronous satellites equally spaced in local time of equatorial crossing. This system can obtain data every three hours for all regions. Several other satellite systems consisting of combinations of Sun-synchronous orbits and either the Space Station Freedom or a mid-latitude equatorial satellite can provide three to six hour temporal coverage, which is sufficient for measuring many of the parameters required for the global change monitoring mission. Geosynchronous satellites are required to study atmospheric and surface processes involving variations on the order of a few minutes to an hour. Two or more geosynchronous satellites can be relocated in longitude to study processes over selected regions of Earth.

Harrison, Edwin F.↗