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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 109 records · Page 6
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 NTRS2004

A Unified Fault-Tolerance Protocol

Davies and Wakerly show that Byzantine fault tolerance can be achieved by a cascade of broadcasts and middle value select functions. We present an extension of the Davies and Wakerly protocol, the unified protocol, and its proof of correctness. We prove that it satisfies validity and agreement properties for communication of exact values. We then introduce bounded communication error into the model. Inexact communication is inherent for clock synchronization protocols. We prove that validity and agreement properties hold for inexact communication, and that exact communication is a special case. As a running example, we illustrate the unified protocol using the SPIDER family of fault-tolerant architectures. In particular we demonstrate that the SPIDER interactive consistency, distributed diagnosis, and clock synchronization protocols are instances of the unified protocol.

Miner, Paul↗
NASA NTRS1993

Analysis of the eastern range multiplexed fiber optic IRIG B120 distribution system

A study was conducted to assess the effects of transmitting a precision clock synchronization signal over a commercial multiplexed fiber optic communication system. This study is an evaluation of the distortion and jitter introduced into the signal by this type of transmission system. An analysis comparing signal quality at the multiplexing and demultiplexing ends of the fiber optic communication system shows that the amplitude and phase distortion added to the clock synchronization signal by the transmission system is minimal.

Duncan, Michael J.↗
NASA NTRS1979

Clock synchronisation experiment in India using symphonie satellite

A recent clock synchronization experiment between the National Physical Laboratory (NPL), New Delhi and Space Applications Center (SAC), Ahemedabad, in India via geostationary satellite symphonie 2, stationed at 49 E longitude, is reported. A two-way transmission using a microwave transponder considered to provide the greatest precision in synchronization of two remote clocks is described.

Somayajulu, Y. V.↗
NASA NTRS1990

Preliminary error budget for an optical ranging system: Range, range rate, and differenced range observables

Future missions to the outer solar system or human exploration of Mars may use telemetry systems based on optical rather than radio transmitters. Pulsed laser transmission can be used to deliver telemetry rates of about 100 kbits/sec with an efficiency of several bits for each detected photon. Navigational observables that can be derived from timing pulsed laser signals are discussed. Error budgets are presented based on nominal ground stations and spacecraft-transceiver designs. Assuming a pulsed optical uplink signal, two-way range accuracy may approach the few centimeter level imposed by the troposphere uncertainty. Angular information can be achieved from differenced one-way range using two ground stations with the accuracy limited by the length of the available baseline and by clock synchronization and troposphere errors. A method of synchronizing the ground station clocks using optical ranging measurements is presented. This could allow differenced range accuracy to reach the few centimeter troposphere limit.

Folkner, W. M.↗
NASA NTRS1995

Time aspects of the European Complement to GPS: Continental and transatlantic experimental phases

The CNES project of a European Complement to GPS (CE-GPS) is conceived to fulfill the needs of Civil Aviation for a non-precise approach phase with GPS as sole navigation means. This generates two missions: a monitoring mission - alarm of failure - ,and a navigation mission - generating a GPS-like signal on board the geostationary satellites. The host satellites will be the Inmarsat constellation. The CE-GPS missions lead to some time requirements, mainly the accuracy of GPS time restitution and of monitoring clock synchronization. To demonstrate that the requirements of the CE-GPS could be achieved, including the time aspects, an experiment has been scheduled over the Last two years, using a part of the Inmarsat II F-2 payload and specially designed ground stations based on 10 channels GPS receivers. This paper presents a review of the results obtained during the continental phase of the CE-GPS experiment with two stations in France, along with some experimental results obtained during the transatlantic phase (three stations in France, French Guyana, and South Africa). It describes the synchronization of the monitoring clocks using the GPS Common-view or the C- to L-Band transponder of the Inmarsat satellite, with an estimated accuracy better than 10 ns (1 sigma).

Uhrich, Pierre J. M.↗
NASA NTRS1979

Ramp time synchronization

A new method of intercontinental clock synchronization has been developed and proposed for possible use by NASA's Deep Space Network (DSN), using a two-way/three-way radio link with a spacecraft. Analysis of preliminary data indicates that the real-time method has an uncertainty of 0.6 microsec, and it is very likely that further work will decrease the uncertainty. Also, the method is compatible with a variety of nonreal-time analysis techniques, which may reduce the uncertainty down to the tens of nanosecond range.

Hietzke, W.↗
DOE OSTI2025

Hong-Ou-Mandel interference with a coexisting clock using transceivers for synchronization over deployed fiber

Interference between independently generated photons is a key step towards distributing entanglement over long distances, but it requires synchronization between the distantly-located photon sources. Synchronizing the clocks of such photon sources using coexisting two-way classical optical communications over the same fiber that transports the quantum photonic signals is a promising approach for achieving photon-photon interference over long distances, enabling entanglement distribution for quantum networking using the deployed fiber infrastructure. Here, we demonstrate photon-photon interference by observing the Hong-Ou-Mandel dip between two distantly-located sources: a weak coherent-state source obtained by attenuating the output of a laser and a heralded single-photon source. We achieve a maximum dip visibility of 0.58 +/- 0.04 when the two sources are connected via 4.3 km of deployed fiber. Dip visibilities > 0.5 are nonclassical and a first step towards achieving teleportation over the deployed fiber infrastructure. In our experiment, the classical optical communication is achieved with - 21 dBm of optical signal launch power, which is used to synchronize the clocks in the two independent, distantly-located photon sources. The impact of spontaneous Raman scattering from the classical optical signals is mitigated by appropriate choice of the quantum- and classical-channel wavelengths. All equipment used in our experiment (the photon sources and the synchronization setup) is commercially available. Finally, our experiment represents a scalable approach to enabling practical quantum networking with commercial equipment and coexistence with classical communications in optical fiber.

47 OTHER INSTRUMENTATION↗
NASA NTRS1974

Worldwide time and frequency synchronization by planned VLBI networks

Accurate baseline determinations and clock synchronization results obtained from the Quasar Patrol observations at X band with the Goldstone-Haystack baseline are presented. In addition, data from stations at Greenbank, West Virginia, and Onsala, Sweden were used. It was estimated that clock accuracy was on the order of 16 cm.

Coates, R. J.↗
NASA NTRS1977

DSN research and technology support

The ongoing activities at the Venus Station (DSS 13) and the Microwave Test Facility (MTF) discussed include: (1) equipment implementation for unattended operation at DSS 13; (2) salvaging of a 20-kW klystron, at a cost savings of several thousand dollars by the DSN High Power Transmitter Facility; (3) extensive tracking activities with the 26-m antenna including DSN Platform Parameters, Multistation Planetary Radar, Helios II Spectrum Broadening Analysis, VLBI Validation, Planetary Radio Astronomy, and Pulsar Rotation Constancy, for a total time of 219-1/4 observing hours; (4) clock synchronization transmissions from the DSS 13 master clock to the overseas 64-m antenna complexes and special implementation activities in support of PV-78; and (5) implementation of a hydrogen maser frequency standard and the pathfinder installation of a utility control system (UCS) and significant station modification and maintenance.

Jackson, E. B.↗
NASA NTRS2012

Model Checking A Self-Stabilizing Synchronization Protocol for Arbitrary Digraphs

This report presents the mechanical verification of a self-stabilizing distributed clock synchronization protocol for arbitrary digraphs in the absence of faults. This protocol does not rely on assumptions about the initial state of the system, other than the presence of at least one node, and no central clock or a centrally generated signal, pulse, or message is used. The system under study is an arbitrary, non-partitioned digraph ranging from fully connected to 1-connected networks of nodes while allowing for differences in the network elements. Nodes are anonymous, i.e., they do not have unique identities. There is no theoretical limit on the maximum number of participating nodes. The only constraint on the behavior of the node is that the interactions with other nodes are restricted to defined links and interfaces. This protocol deterministically converges within a time bound that is a linear function of the self-stabilization period. A bounded model of the protocol is verified using the Symbolic Model Verifier (SMV) for a subset of digraphs. Modeling challenges of the protocol and the system are addressed. The model checking effort is focused on verifying correctness of the bounded model of the protocol as well as confirmation of claims of determinism and linear convergence with respect to the self-stabilization period.

Malekpour, Mahyar R.↗
NASA NTRS2011

Analysis of Proximity-1 Space Link Interleaved Time Synchronization (PITS) Protocol

To synchronize clocks between spacecraft in proximity, the Proximity-1 Space Link Interleaved Time Synchronization (PITS) Protocol has been proposed. PITS is based on the NTP Interleaved On-Wire Protocol and is capable of being adapted and integrated into CCSDS Proximity-1 Space Link Protocol with minimal modifications. In this work, we will discuss the correctness and liveness of PITS. Further, we analyze and evaluate the performance of time synchronization latency with various channel error rates in different PITS operational modes.

network time protocol↗
DOE OSTI2021

White Rabbit Time Synchronization for Radiation Detector Readout Electronics

As radiation detector arrays in nuclear physics applications become larger and physically more separated, the time synchronization and trigger distribution between many channels of detector readout electronics become more challenging. Clocks and triggers are traditionally distributed through dedicated cabling, but newer methods such as the IEEE 1588 Precision Time Protocol and White Rabbit allow clock synchronization through the exchange of timing messages over Ethernet. Consequently, we report here the use of White Rabbit in a new detector readout module, the Pixie-Net XL. Herein, the White Rabbit core, data capture from multiple digitizing channels, and subsequent pulse processing for pulse height and constant fraction timing are implemented in a Kintex 7 FPGA. The detector data records include White Rabbit time stamps and are transmitted to storage through the White Rabbit core's gigabit Ethernet data path or a slower diagnostic/control link using an embedded Zynq processor. The performance is characterized by time-of-flight style measurements and by time correlation of high energy background events from cosmic showers in detectors separated by longer distances. Software for the Zynq processor can implement "software triggering", for example to limit recording of data to events where a minimum number of channels from multiple modules detect radiation at the same time.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Libpanda: A High Performance Library for Vehicle Data Collection

Cyber-Physical Systems (CPS) generally involve time-critical components due to physical dynamics, therefore necessitating high-performance subsystems. This is also true in data collection scenarios to infer physical phenomena. This paper covers Libpanda as an example of a component that has been designed to address performance issues in CPS implementations. Libpanda is a C++ library that interfaces software with a Comma.ai Panda device. Pandas are used for installation in modern vehicles to read the vehicle CAN bus, providing rich sensor data and limited vehicle control through message injection. The motivation to design lib-panda stems from the lack of performance in Python-based code that runs on inexpensive hardware like a Raspberry Pi. In such situations, Python code would result in utilizing 92% CPU while also dropping around 40% of the CAN packet due to bottlenecks. Without using different tools, inconsistent data collection means a loss of time-based vehicle state interpretation. Libpanda addresses these issues through implementation in a different language and implementation of different design paradigms involving asynchronous calls and multithreading. The Panda also features a GPS module that allows multiple instances to synchronize clocks for large-scale data collection scenarios. Libpanda has been designed with time-synchronization in mind to aid in the measurement of inter-vehicle dynamics. The performance improvements of libpanda have resulted in it becoming an important component in automotive dynamics research that requires a higher technical performance in large-scale experiments.

Bunting, Matthew↗
DOE OSTI2024

Proton Improvement Plan II (PIP-II) Clock and Timing

The PIP-II timing system is planned to be a two-part system consisting of a global timing system (referred to as ACLK) that provides high level, event-based timing for the whole Fermilab accelerator complex while the second part is a RF synchronized clock system unique to the PIP-II Linac itself (referred to as LCLK). The ACLK System will make use of an external 10 MHz GPS based signal source as a reference for its 650 MHz phase lock as it is the reference frequency for the TCLK output of the system (needed to support legacy hardware around complex). The LCLK System will use a PIP-II Linac RF reference (162.5 MHz) from the Linac LLRF system to allow beam synchronized event placement. Both the ACLK and LCLK systems will have a clock output with a data frame of 16 event bits + 32 data bits with frames broadcast at 650 MHz, phase locked to the 10MHz reference in the case of ACLK and the PIP-II LLRF sourced 162.5 MHz reference in the case of LCLK.

43 PARTICLE ACCELERATORS↗
NASA NTRS1995

Relativistic theory for syntonization of clocks in the vicinity of the Earth

A well known prediction of Einstein's general theory of relativity states that two ideal clocks that move with a relative velocity, and are submitted to different gravitational fields will, in general, be observed to run at different rates. Similarly the rate of a clock with respect to the coordinate time of some spacetime reference system is dependent on the velocity of the clock in that reference system and on the gravitational fields it is submitted to. For the syntonization of clocks and the realization of coordinate times (like TAI) this rate shift has to be taken into account at an accuracy level which should be below the frequency stability of the clocks in question, i.e. all terms that are larger than the instability of the clocks should be corrected for. We present a theory for the calculation of the relativistic rate shift for clocks in the vicinity of the Earth, including all terms larger than one part in 10(exp 18). This, together with previous work on clock synchronization (Petit & Wolf 1993, 1994), amounts to a complete relativistic theory for the realization of coordinate time scales at picosecond synchronization and 10(exp -18) syntonization accuracy, which should be sufficient to accommodate future developments in time transfer and clock technology.

Wolf, Peter↗