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NASA NTRS1992

Measurement and analysis of operating system fault tolerance

This paper demonstrates a methodology to model and evaluate the fault tolerance characteristics of operational software. The methodology is illustrated through case studies on three different operating systems: the Tandem GUARDIAN fault-tolerant system, the VAX/VMS distributed system, and the IBM/MVS system. Measurements are made on these systems for substantial periods to collect software error and recovery data. In addition to investigating basic dependability characteristics such as major software problems and error distributions, we develop two levels of models to describe error and recovery processes inside an operating system and on multiple instances of an operating system running in a distributed environment. Based on the models, reward analysis is conducted to evaluate the loss of service due to software errors and the effect of the fault-tolerance techniques implemented in the systems. Software error correlation in multicomputer systems is also investigated.

Lee, I.↗

NASA NTRS1993

Fault-tolerant onboard digital information switching and routing for communications satellites

The NASA Lewis Research Center is developing an information-switching processor for future meshed very-small-aperture terminal (VSAT) communications satellites. The information-switching processor will switch and route baseband user data onboard the VSAT satellite to connect thousands of Earth terminals. Fault tolerance is a critical issue in developing information-switching processor circuitry that will provide and maintain reliable communications services. In parallel with the conceptual development of the meshed VSAT satellite network architecture, NASA designed and built a simple test bed for developing and demonstrating baseband switch architectures and fault-tolerance techniques. The meshed VSAT architecture and the switching demonstration test bed are described, and the initial switching architecture and the fault-tolerance techniques that were developed and tested are discussed.

Shalkhauser, Mary JO↗

NASA NTRS1990

Validated Fault Tolerant Architectures for Space Station

Viewgraphs on validated fault tolerant architectures for space station are presented. Topics covered include: fault tolerance approach; advanced information processing system (AIPS); and fault tolerant parallel processor (FTPP).

Lala, Jaynarayan H.↗

NASA NTRS1990

A Fault-tolerant RISC Microprocessor for Spacecraft Applications

Viewgraphs on a fault-tolerant RISC microprocessor for spacecraft applications are presented. Topics covered include: reduced instruction set computer; fault tolerant registers; fault tolerant ALU; and double rail CMOS logic.

Timoc, Constantin↗

NASA NTRS1993

Impact damage tolerance of thin wall composite struts

An experimental investigation was made to study the impact damage tolerance of thin wall composite struts made of both brittle epoxy and toughened epoxy based composite materials. Damage parameters such as barely visible surface damage and internal damage represented by the ultrasonic C-scan, and residual compressive strengths were evaluated against impact energy for two impactor sizes. From both a damage resistance (internal damage vs. impact energy) and a damage tolerance (residual compressive strength vs. internal damage) point of view, the toughened IM7/977-2 struts exhibited better performance than the brittle epoxy based T50/934 struts. This is attributed to the toughening mechanism in 977-2 which impedes delamination initiation from impact, and delamination growth and subsequent buckling under a compression loading. At barely visible damage thresholds, regardless of the impactor sizes, a maximum strength reduction of 45-55 percent was observed for the T50/934 struts, and approximately 10 percent for IM7/977-2 struts. This is of great interest for developing a damage tolerance design approach and risk assessment methodology in which the design allowable would be defined by the residual strength at the threshold of barely visible damage.

Chen, G.-S.↗

NASA NTRS1993

Hydrogen tolerance of a Ti3Al-based alloy

The Ti-24Al-11Nb (Ti-24-11) alloy heat-treated to the fine basketweave microstructure was shown previously to be hydrogen-tolerant. In order to assess its limit of hydrogen tolerance, the tensile, creep, fracture toughness, and sustained-load crack growth behaviors of this alloy were studied as a function of hydrogen content. The mechanical test results indicated that the fine basketweave microstructure was tolerant to hydride embrittlement for hydrogen contents up to about 1500 wppm. On the other hand, hydrogen charging experiments indicated that the Ti-24-11 alloy was severely cracked and pulverized under zero load when the hydrogen content exceeded 3000 wppm. X-ray diffraction results revealed that the dichotomous behaviors might be due to the formation of face-centered cubic (fcc) delta-type hydrides at higher hydrogen contents but face-centered tetragonal (fct) gamma-type hydrides at lower hydrogen contents.

Chan, Kwai S.↗

NASA NTRS1994

Collection, processing, and reporting of damage tolerant design data for non-aerospace structural materials

This report describes the organization, format and content of the NASA Johnson damage tolerant database which was created to store damage tolerant property data for non aerospace structural materials. The database is designed to store fracture toughness data (K(sub IC), K(sub c), J(sub IC) and CTOD(sub IC)), resistance curve data (K(sub R) VS. delta a (sub eff) and JR VS. delta a (sub eff)), as well as subcritical crack growth data (a vs. N and da/dN vs. delta K). The database contains complementary material property data for both stainless and alloy steels, as well as for aluminum, nickel, and titanium alloys which were not incorporated into the Damage Tolerant Design Handbook database.

Huber, P. D.↗

NASA NTRS1994

Advanced information processing system: The Army Fault-Tolerant Architecture detailed design overview

The Army Avionics Research and Development Activity (AVRADA) is pursuing programs that would enable effective and efficient management of large amounts of situational data that occurs during tactical rotorcraft missions. The Computer Aided Low Altitude Night Helicopter Flight Program has identified automated Terrain Following/Terrain Avoidance, Nap of the Earth (TF/TA, NOE) operation as key enabling technology for advanced tactical rotorcraft to enhance mission survivability and mission effectiveness. The processing of critical information at low altitudes with short reaction times is life-critical and mission-critical necessitating an ultra-reliable/high throughput computing platform for dependable service for flight control, fusion of sensor data, route planning, near-field/far-field navigation, and obstacle avoidance operations. To address these needs the Army Fault Tolerant Architecture (AFTA) is being designed and developed. This computer system is based upon the Fault Tolerant Parallel Processor (FTPP) developed by Charles Stark Draper Labs (CSDL). AFTA is hard real-time, Byzantine, fault-tolerant parallel processor which is programmed in the ADA language. This document describes the results of the Detailed Design (Phase 2 and 3 of a 3-year project) of the AFTA development. This document contains detailed descriptions of the program objectives, the TF/TA NOE application requirements, architecture, hardware design, operating systems design, systems performance measurements and analytical models.

Harper, Richard E.↗

NASA NTRS1994

Failure tolerant operation of kinematically redundant manipulators

Redundant manipulators may compensate for failed joints with their additional degrees of freedom. In this paper such a manipulator is considered fault tolerant if it can guarantee completion of a task after any one of its joints has failed. This fault tolerance of kinematically redundant manipulators is insured here. Methods to analyze the manipulator's work space find regions inherently suitable for critical tasks because of their high level of failure tolerance. Constraints are then placed on the manipulator's range of motion to guarantee completion of a task.

Lewis, Christopher L.↗

NASA NTRS1994

FTAPE: A fault injection tool to measure fault tolerance

The paper introduces FTAPE (Fault Tolerance And Performance Evaluator), a tool that can be used to compare fault-tolerant computers. The tool combines system-wide fault injection with a controllable workload. A workload generator is used to create high stress conditions for the machine. Faults are injected based on this workload activity in order to ensure a high level of fault propagation. The errors/fault ratio and performance degradation are presented as measures of fault tolerance.

Tsai, Timothy K.↗

NASA NTRS1995

Measuring fault tolerance with the FTAPE fault injection tool

This paper describes FTAPE (Fault Tolerance And Performance Evaluator), a tool that can be used to compare fault-tolerant computers. The major parts of the tool include a system-wide fault-injector, a workload generator, and a workload activity measurement tool. The workload creates high stress conditions on the machine. Using stress-based injection, the fault injector is able to utilize knowledge of the workload activity to ensure a high level of fault propagation. The errors/fault ratio, performance degradation, and number of system crashes are presented as measures of fault tolerance.

Tsai, Timothy K.↗

NASA NTRS1992

Application of damage tolerance methodology in certification of the Piaggio P-180 Avanti

The Piaggio P-180 Avanti, a twin pusher-prop engine nine-passenger business aircraft was certified in 1990, to the requirements of FAR Part 23 and Associated Special Conditions for Composite Structure. Certification included the application of a damage tolerant methodology to the design of the composite forward wing and empennage (vertical fin, horizontal stabilizer, tailcone, and rudder) structure. This methodology included an extensive analytical evaluation coupled with sub-component and full-scale testing of the structure. The work from the Damage Tolerance Analysis Assessment was incorporated into the full-scale testing. Damage representing hazards such as dropped tools, ground equipment, handling, and runway debris, was applied to the test articles. Additional substantiation included allowing manufacturing discrepancies to exist unrepaired on the full-scale articles and simulated bondline failures in critical elements. The importance of full-scale testing in the critical environmental conditions and the application of critical damage are addressed. The implication of damage tolerance on static and fatigue testing is discussed. Good correlation between finite element solutions and experimental test data was observed.

Johnson, Jerry↗

NASA NTRS1993

The combined effect of glass buffer strips and stitching on the damage tolerance of composites

Recent research has demonstrated that through-the-thickness stitching provides major improvements in the damage tolerance of composite laminates loaded in compression. However, the brittle nature of polymer matrix composites makes them susceptible to damage propagation, requiring special material applications and designs to limit damage growth. Glass buffer strips, embedded within laminates, have shown the potential for improving the damage tolerance of unstitched composite laminates loaded in tension. The glass buffer strips, less stiff than the surrounding carbon fibers, arrest crack growth in composites under tensile loads. The present study investigates the damage tolerance characteristics of laminates that contain both stitching and glass buffer strips.

Kullerd, Susan M.↗

NASA NTRS1995

FTAPE: A fault injection tool to measure fault tolerance

Tsai, Timothy K.↗

NASA NTRS1960

Centrifuge Study of Pilot Tolerance to Acceleration and the Effects of Acceleration on Pilot Performance

A research program the general objective of which was to measure the effects of various sustained accelerations on the control performance of pilots, was carried out on the Aviation Medical Acceleration Laboratory centrifuge, U.S. Naval Air Development Center, Johnsville, PA. The experimental setup consisted of a flight simulator with the centrifuge in the control loop. The pilot performed his control tasks while being subjected to acceleration fields such as might be encountered by a forward-facing pilot flying an atmosphere entry vehicle. The study was divided into three phases. In one phase of the program, the pilots were subjected to a variety of sustained linear acceleration forces while controlling vehicles with several different sets of longitudinal dynamics. Here, a randomly moving target was displayed to the pilot on a cathode-ray tube. For each combination of acceleration field and vehicle dynamics, pilot tracking accuracy was measured and pilot opinion of the stability and control characteristics was recorded. Thus, information was obtained on the combined effects of complexity of control task and magnitude and direction of acceleration forces on pilot performance. These tests showed that the pilot's tracking performance deteriorated markedly at accelerations greater than about 4g when controlling a lightly damped vehicle. The tentative conclusion was also reached that regardless of the airframe dynamics involved, the pilot feels that in order to have the same level of control over the vehicle, an increase in the vehicle dynamic stability was required with increases in the magnitudes of the acceleration impressed upon the pilot. In another phase, boundaries of human tolerance of acceleration were established for acceleration fields such as might be encountered by a pilot flying an orbital vehicle. A special pilot restraint system was developed to increase human tolerance to longitudinal decelerations. The results of the tests showed that human tolerance of longitudinal deceleration forces was considerably improved through use of the special restraint system.

Creer, Brent Y.↗

NASA NTRS1998

NASA's Microgravity Fluid Physics Program: Tolerability to Residual Accelerations

An overview of the NASA microgravity fluid physics program is presented. The necessary quality of a reduced-gravity environment in terms of tolerable residual acceleration or g levels is a concern that is inevitably raised for each new microgravity experiment. Methodologies have been reported in the literature that provide guidance in obtaining reasonable estimates of residual acceleration sensitivity for a broad range of fluid physics phenomena. Furthermore, a relatively large and growing database of microgravity experiments that have successfully been performed in terrestrial reduced gravity facilities and orbiting platforms exists. Similarity of experimental conditions and hardware, in some cases, lead to new experiments adopting prior experiments g-requirements. Rationale applied to other experiments can, in principle, be a valuable guide to assist new Principal Investigators, PIs, in determining the residual acceleration tolerability of their flight experiments. The availability of g-requirements rationale from prior (mu)g experiments is discussed. An example of establishing g tolerability requirements is demonstrated, using a current microgravity fluid physics flight experiment. The Fluids and Combustion Facility (FCF) which is currently manifested on the US Laboratory of the International Space Station (ISS) will provide opportunities for fluid physics and combustion experiments throughout the life of the ISS. Although the FCF is not intended to accommodate all fluid physics experiments, it is expected to meet the science requirements of approximately 80% of the new PIs that enter the microgravity fluid physics program. The residual acceleration requirements for the FCF fluid physics experiments are based on a set of fourteen reference fluid physics experiments which are discussed.

Skarda, J. Raymond↗

NASA NTRS2000

COTS-Based Fault Tolerance in Deep Space: Qualitative and Quantitative Analyses of a Bus Network Architecture

Using COTS products, standards and intellectual properties (IPs) for all the system and component interfaces is a crucial step toward significant reduction of both system cost and development cost as the COTS interfaces enable other COTS products and IPs to be readily accommodated by the target system architecture. With respect to the long-term survivable systems for deep-space missions, the major challenge for us is, under stringent power and mass constraints, to achieve ultra-high reliability of the system comprising COTS products and standards that are not developed for mission-critical applications. The spirit of our solution is to exploit the pertinent standard features of a COTS product to circumvent its shortcomings, though these standard features may not be originally designed for highly reliable systems. In this paper, we discuss our experiences and findings on the design of an IEEE 1394 compliant fault-tolerant COTS-based bus architecture. We first derive and qualitatively analyze a -'stacktree topology" that not only complies with IEEE 1394 but also enables the implementation of a fault-tolerant bus architecture without node redundancy. We then present a quantitative evaluation that demonstrates significant reliability improvement from the COTS-based fault tolerance.

Tai, Ann T.↗

NASA NTRS2000

Software Fault Tolerance: A Tutorial

Because of our present inability to produce error-free software, software fault tolerance is and will continue to be an important consideration in software systems. The root cause of software design errors is the complexity of the systems. Compounding the problems in building correct software is the difficulty in assessing the correctness of software for highly complex systems. After a brief overview of the software development processes, we note how hard-to-detect design faults are likely to be introduced during development and how software faults tend to be state-dependent and activated by particular input sequences. Although component reliability is an important quality measure for system level analysis, software reliability is hard to characterize and the use of post-verification reliability estimates remains a controversial issue. For some applications software safety is more important than reliability, and fault tolerance techniques used in those applications are aimed at preventing catastrophes. Single version software fault tolerance techniques discussed include system structuring and closure, atomic actions, inline fault detection, exception handling, and others. Multiversion techniques are based on the assumption that software built differently should fail differently and thus, if one of the redundant versions fails, it is expected that at least one of the other versions will provide an acceptable output. Recovery blocks, N-version programming, and other multiversion techniques are reviewed.

Torres-Pomales, Wilfredo↗