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NASA NTRS2011

A Self-Stabilizing Distributed Clock Synchronization Protocol for Arbitrary Digraphs

This report presents a self-stabilizing distributed clock synchronization protocol in the absence of faults in the system. It is focused on the distributed clock synchronization of an arbitrary, non-partitioned digraph ranging from fully connected to 1-connected networks of nodes while allowing for differences in the network elements. 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. 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. We present an outline of a deductive proof of the correctness of the protocol. A model of the protocol was mechanically verified using the Symbolic Model Verifier (SMV) for a variety of topologies. Results of the mechanical proof of the correctness of the protocol are provided. The model checking results have verified the correctness of the protocol as they apply to the networks with unidirectional and bidirectional links. In addition, the results confirm the claims of determinism and linear convergence. As a result, we conjecture that the protocol solves the general case of this problem. We also present several variations of the protocol and discuss that this synchronization protocol is indeed an emergent system.

Malekpour, Mahyar R.↗

NASA NTRS2004

Automated Static Culture System Cell Module Mixing Protocol and Computational Fluid Dynamics Analysis

This report is a documentation of a fluid dynamic analysis of the proposed Automated Static Culture System (ASCS) cell module mixing protocol. The report consists of a review of some basic fluid dynamics principles appropriate for the mixing of a patch of high oxygen content media into the surrounding media which is initially depleted of oxygen, followed by a computational fluid dynamics (CFD) study of this process for the proposed protocol over a range of the governing parameters. The time histories of oxygen concentration distributions and mechanical shear levels generated are used to characterize the mixing process for different parameter values.

Kleis, Stanley J.↗

NASA NTRS1995

Network time synchronization servers at the US Naval Observatory

Responding to an increased demand for reliable, accurate time on the Internet and Milnet, the U.S. Naval Observatory Time Service has established the network time servers, tick.usno.navy.mil and tock.usno.navy.mil. The system clocks of these HP9000/747i industrial work stations are synchronized to within a few tens of microseconds of USNO Master Clock 2 using VMEbus IRIG-B interfaces. Redundant time code is available from a VMEbus GPS receiver. UTC(USNO) is provided over the network via a number of protocols, including the Network Time Protocol (NTP) (DARPA Network Working Group Report RFC-1305), the Daytime Protocol (RFC-867), and the Time protocol (RFC-868). Access to USNO network time services is presently open and unrestricted. An overview of USNO time services and results of LAN and WAN time synchronization tests will be presented.

Schmidt, Richard E.↗

NASA NTRS2011

Model Checking a Self-Stabilizing Distributed Clock 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.

Malekpour, Mahyar R.↗

NASA NTRS2011

Correctness Proof of a Self-Stabilizing Distributed Clock Synchronization Protocol for Arbitrary Digraphs

This report presents a deductive proof of a self-stabilizing distributed clock synchronization protocol. It is focused on the distributed clock synchronization of an arbitrary, non-partitioned digraph ranging from fully connected to 1-connected networks of nodes while allowing for differences in the network elements. This protocol does not rely on assumptions about the initial state of the system, and no central clock or a centrally generated signal, pulse, or message is used. 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. We present a deductive proof of the correctness of the protocol as it applies to the networks with unidirectional and bidirectional links. We also confirm the claims of determinism and linear convergence.

Malekpour, Mahyar R.↗

NASA NTRS2012

Model Checking A Self-Stabilizing Synchronization Protocol for Arbitrary Digraphs

Malekpour, Mahyar R.↗

NASA NTRS2001

Mars Sample Handling Protocol Workshop Series

This report provides a record of the proceedings and recommendations of Workshop 3 of the Series, which was held in San Diego, California, March 19-21, 2001. Materials such as the Workshop agenda and participant lists as well as complete citations of all references and a glossary of terms and acronyms appear in the Appendices. Workshop 3 builds on the deliberations and findings of the earlier workshops in the Series, which have been reported separately. During Workshop 3, five individual sub-groups were formed to discuss the following topics: (1) Unifying Properties of Life, (2) Morphological organization and chemical properties, (3) Geochemical and geophysical properties, (4) Chemical Method and (5) Cell Biology Methods.

Race, Margaret S.↗

NASA NTRS2005

Automating CapCom Using Mobile Agents and Robotic Assistants

We have developed and tested an advanced EVA communications and computing system to increase astronaut self-reliance and safety, reducing dependence on continuous monitoring and advising from mission control on Earth. This system, called Mobile Agents (MA), is voice controlled and provides information verbally to the astronauts through programs called personal agents. The system partly automates the role of CapCom in Apollo-including monitoring and managing EVA navigation, scheduling, equipment deployment, telemetry, health tracking, and scientific data collection. EVA data are stored automatically in a shared database in the habitat/vehicle and mirrored to a site accessible by a remote science team. The program has been developed iteratively in the context of use, including six years of ethnographic observation of field geology. Our approach is to develop automation that supports the human work practices, allowing people to do what they do well, and to work in ways they are most familiar. Field experiments in Utah have enabled empirically discovering requirements and testing alternative technologies and protocols. This paper reports on the 2004 system configuration, experiments, and results, in which an EVA robotic assistant (ERA) followed geologists approximately 150 m through a winding, narrow canyon. On voice command, the ERA took photographs and panoramas and was directed to move and wait in various locations to serve as a relay on the wireless network. The MA system is applicable to many space work situations that involve creating and navigating from maps (including configuring equipment for local topology), interacting with piloted and unpiloted rovers, adapting to environmental conditions, and remote team collaboration involving people and robots.

Clancey, William J.↗

NASA NTRS2006

Delay Tolerant Networking - Bundle Protocol Simulation

In this paper, we report on the addition of MACHETE models needed to support DTN, namely: the Bundle Protocol (BP) model. To illustrate the useof MACHETE with the additional DTN model, we provide an example simulation to benchmark its performance. We demonstrate the use of the DTN protocol and discuss statistics gathered concerning the total time needed to simulate numerous bundle transmissions.

licklider protocol↗

NASA NTRS2004

Low-earth-orbit Satellite Internet Protocol Communications Concept and Design

This report presents a design concept for a low-Earth-orbit end-to-end Internet-Protocol- (IP-) based mission. The goal is to maintain an up-to-date communications infrastructure that makes communications seamless with the protocols used in terrestrial computing. It is based on the premise that the use of IPs will permit greater interoperability while also reducing costs and providing users the ability to retrieve data directly from the satellite. However, implementing an IP-based solution also has a number of challenges, since wireless communications have different characteristics than wired communications. This report outlines the design of a low-Earth-orbit end-to-end IP-based mission; the ideas and concepts of Space Internet architectures and networks are beyond the scope of this document. The findings of this report show that an IP-based mission is plausible and would provide benefits to the user community, but the outstanding issues must be resolved before a design can be implemented.

Slywezak, Richard A.↗

NASA NTRSDate not supplied

Nasa Exploration Atmosphere Tests 3 & 4: Development and Validation of Planetary Extravehicular Activity Prebreathe Protocols for Alternate Atmospheres and Suit Pressures

INTRODUCTION: Space suits operate at low pressures to optimize astronauts’ performance. The drop in pressure from the habitat environment to the suit carries a risk of decompression sickness (DCS), which is mitigated by a 95% O2 prebreathe protocol. Prebreathe protocols for the lunar surface have a significantly higher risk compared to International Space Station microgravity Extravehicular Activities (EVA). In previous studies, we validated a prebreathe protocol from a 56.5 kPa 34% O2 cabin to a 29.6 kPa EVA pressure; however, the enriched oxygen cabin environment poses a flammability risk that requires significant changes to material design and selections. Here, we report outcomes for prebreathe protocols from a sub-30% O2 cabin and associated changes necessary to control DCS risk critical to upcoming lunar missions. METHODS: Fourteen volunteers completed 11-day hypobaric chamber studies with an “alternate exploration atmosphere” of 66.2kPa, 28.5% O2. Subjects acclimated for 48 hrs and then participated in five 6-hour simulated EVAs at 29.6 or 35.6kPa, 95% O2. Prior to EVA, subjects underwent a 20, 90, or 150-minute prebreathe. The EVA simulation was designed to be representative of future planetary EVAs, proportionate to the subject’s VO2max. Decompression stress was monitored by real-time doppler and echocardiograph alternating every 15 min, as well as clinical monitoring for DCS signs/symptoms. Venous gas emboli (VGE) and DCS outcomes were verified against NASA-STD-3001 acceptance criteria. RESULTS AND DISCUSSION: Venous gas emboli (VGE) were identified during all EVAs. A neurological DCS case was identified in the 90-min/29.6kPa prebreathe, terminating further testing of this protocol. No DCS cases were identified in the 150 min/29.6kPa protocol. The 20 min/36.5kPa protocol was rejected due to a Type II DCS case. All DCS symptoms resolved with treatment, with no sequelae post initial treatment of DCS. These various test points highlighted to the significant benefit of elevated suit pressure to shorten prebreathe protocols, but also the difficulty in assessing and managing DCS during sustained EVA operations in remote planetary surfaces.

decompression sickness↗

NASA NTRS2000

Mars Sample Handling Protocol Workshop Series

This document is the report resulting from the first workshop of the series on development of the criteria for a Mars sample handling protocol. Workshop 1 was held in Bethesda, Maryland on March 20-22, 2000. This report serves to document the proceedings of Workshop 1; it summarizes relevant background information, provides an overview of the deliberations to date, and helps frame issues that will need further attention or resolution in upcoming workshops. Specific recommendations are not part of this report.

Rummel, John D.↗

NASA NTRS2007

Model Checking a Byzantine-Fault-Tolerant Self-Stabilizing Protocol for Distributed Clock Synchronization Systems

This report presents the mechanical verification of a simplified model of a rapid Byzantine-fault-tolerant self-stabilizing protocol for distributed clock synchronization systems. This protocol does not rely on any assumptions about the initial state of the system. This protocol tolerates bursts of transient failures, and deterministically converges within a time bound that is a linear function of the self-stabilization period. A simplified model of the protocol is verified using the Symbolic Model Verifier (SMV) [SMV]. The system under study consists of 4 nodes, where at most one of the nodes is assumed to be Byzantine faulty. The model checking effort is focused on verifying correctness of the simplified model of the protocol in the presence of a permanent Byzantine fault as well as confirmation of claims of determinism and linear convergence with respect to the self-stabilization period. Although model checking results of the simplified model of the protocol confirm the theoretical predictions, these results do not necessarily confirm that the protocol solves the general case of this problem. Modeling challenges of the protocol and the system are addressed. A number of abstractions are utilized in order to reduce the state space. Also, additional innovative state space reduction techniques are introduced that can be used in future verification efforts applied to this and other protocols.

Malekpour, Mahyar R.↗

NASA NTRS1974

MSFC Skylab extravehicular activity development report

The development activities are presented in a chronological order and cover the EVA hardware design from initial concept to final flight configuration. Major concepts which were considered, and the criteria for design are identified. The reasons for the acceptance or rejection of these concepts are discussed. The report concludes that developmental protocol of interleaving analyses and simulations on an iterative basis provided a conservative, flexible and simple EVA system, which was effective not only for the nominal Skylab mission but for many contingency activities as well.

Heckman, R. T.↗

NASA NTRS2001

Mars Sample Handling Protocol Workshop Series: Workshop 2

Numerous NASA reports and studies have identified Planetary Protection (PP) as an important part of any Mars sample return mission. The mission architecture, hardware, on-board experiments, and related activities must be designed in ways that prevent both forward- and back-contamination and also ensure maximal return of scientific information. A key element of any PP effort for sample return missions is the development of guidelines for containment and analysis of returned sample(s). As part of that effort, NASA and the Space Studies Board (SSB) of the National Research Council (NRC) have each assembled experts from a wide range of scientific fields to identify and discuss issues pertinent to sample return. In 1997, the SSB released its report on recommendations for handling and testing of returned Mars samples. In particular, the NRC recommended that: a) samples returned from Mars by spacecraft should be contained and treated as potentially hazardous until proven otherwise, and b) rigorous physical, chemical, and biological analyses [should] confirm that there is no indication of the presence of any exogenous biological entity. Also in 1997, a Mars Sample Quarantine Protocol workshop was convened at NASA Ames Research Center to deal with three specific aspects of the initial handling of a returned Mars sample: 1) biocontainment, to prevent 'uncontrolled release' of sample material into the terrestrial environment; 2) life detection, to examine the sample for evidence of organisms; and 3) biohazard testing, to determine if the sample poses any threat to terrestrial life forms and the Earth's biosphere. In 1999, a study by NASA's Mars Sample Handling and Requirements Panel (MSHARP) addressed three other specific areas in anticipation of returning samples from Mars: 1) sample collection and transport back to Earth; 2) certification of the samples as non-hazardous; and 3) sample receiving, curation, and distribution. To further refine the requirements for sample hazard testing and the criteria for subsequent release of sample materials from quarantine, the NASA Planetary Protection Officer convened an additional series of workshops beginning in March 2000. The overall objective of these workshops was to develop comprehensive protocols to assess whether the returned materials contain any biological hazards, and to safeguard the purity of the samples from possible terrestrial contamination. This document is the report of the second Workshop in the Series. The information herein will ultimately be integrated into a final document reporting the proceedings of the entire Workshop Series along with additional information and recommendations.

Rummel, John D.↗

NASA NTRS1996

Data Transfer Efficiency Over Satellite Circuits Using a Multi-Socket Extension to the File Transfer Protocol (FTP)

In several experiments using NASA's Advanced Communications Technology Satellite (ACTS), investigators have reported disappointing throughput using the transmission control protocol/Internet protocol (TCP/IP) protocol suite over 1.536Mbit/sec (T1) satellite circuits. A detailed analysis of file transfer protocol (FTP) file transfers reveals that both the TCP window size and the TCP 'slow starter' algorithm contribute to the observed limits in throughput. In this paper we summarize the experimental and and theoretical analysis of the throughput limit imposed by TCP on the satellite circuit. We then discuss in detail the implementation of a multi-socket FTP, XFTP client and server. XFTP has been tested using the ACTS system. Finally, we discuss a preliminary set of tests on a link with non-zero bit error rates. XFTP shows promising performance under these conditions, suggesting the possibility that a multi-socket application may be less effected by bit errors than a single, large-window TCP connection.

Allman, Mark↗

NASA NTRS2011

A Study of an Optical Lunar Surface Communications Network with High Bandwidth Direct to Earth Link

A lunar surface systems study explores the application of optical communications to support a high bandwidth data link from a lunar relay satellite and from fixed lunar assets. The results show that existing 1-m ground stations could provide more than 99% coverage of the lunar terminal at 100Mb/s data rates from a lunar relay satellite and in excess of 200Mb/s from a fixed terminal on the lunar surface. We have looked at the effects of the lunar regolith and its removal on optical samples. Our results indicate that under repeated dust removal episodes sapphire rather than fused silica would be a more durable material for optical surfaces. Disruption tolerant network protocols can minimize the data loss due to link dropouts. We report on the preliminary results of the DTN protocol implemented over the optical carrier.

lunar optical communications↗

NASA NTRS1997

The Simulation of Read-time Scalable Coherent Interface

Scalable Coherent Interface (SCI, IEEE/ANSI Std 1596-1992) (SCI1, SCI2) is a high performance interconnect for shared memory multiprocessor systems. In this project we investigate an SCI Real Time Protocols (RTSCI1) using Directed Flow Control Symbols. We studied the issues of efficient generation of control symbols, and created a simulation model of the protocol on a ring-based SCI system. This report presents the results of the study. The project has been implemented using SES/Workbench. The details that follow encompass aspects of both SCI and Flow Control Protocols, as well as the effect of realistic client/server processing delay. The report is organized as follows. Section 2 provides a description of the simulation model. Section 3 describes the protocol implementation details. The next three sections of the report elaborate on the workload, results and conclusions. Appended to the report is a description of the tool, SES/Workbench, used in our simulation, and internal details of our implementation of the protocol.

Li, Qiang↗