Search NASA⌕ Search

SEARCH · Search NASA

Results for “common causes”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

An Efficient Approach for the Reliability Analysis of Phased-Mission Systems with Dependent Failures

We consider the reliability analysis of phased-mission systems with common-cause failures in this paper. Phased-mission systems (PMS) are systems supporting missions characterized by multiple, consecutive, and nonoverlapping phases of operation. System components may be subject to different stresses as well as different reliability requirements throughout the course of the mission. As a result, component behavior and relationships may need to be modeled differently from phase to phase when performing a system-level reliability analysis. This consideration poses unique challenges to existing analysis methods. The challenges increase when common-cause failures (CCF) are incorporated in the model. CCF are multiple dependent component failures within a system that are a direct result of a shared root cause, such as sabotage, flood, earthquake, power outage, or human errors. It has been shown by many reliability studies that CCF tend to increase a system's joint failure probabilities and thus contribute significantly to the overall unreliability of systems subject to CCF.We propose a separable phase-modular approach to the reliability analysis of phased-mission systems with dependent common-cause failures as one way to meet the above challenges in an efficient and elegant manner. Our methodology is twofold: first, we separate the effects of CCF from the PMS analysis using the total probability theorem and the common-cause event space developed based on the elementary common-causes; next, we apply an efficient phase-modular approach to analyze the reliability of the PMS. The phase-modular approach employs both combinatorial binary decision diagram and Markov-chain solution methods as appropriate. We provide an example of a reliability analysis of a PMS with both static and dynamic phases as well as CCF as an illustration of our proposed approach. The example is based on information extracted from a Mars orbiter project. The reliability model for this orbiter considers the various phases of Launch, Cruise, Mars Orbit Insertion, and Orbit. Some of the CCF for the orbiter in this mission include environmental effects, such as micrometeoroids, human operator errors, and software errors.

reliability analysis↗
NASA NTRS2015

Diverse Redundant Systems for Reliable Space Life Support

Reliable life support systems are required for deep space missions. The probability of a fatal life support failure should be less than one in a thousand in a multi-year mission. It is far too expensive to develop a single system with such high reliability. Using three redundant units would require only that each have a failure probability of one in ten over the mission. Since the system development cost is inverse to the failure probability, this would cut cost by a factor of one hundred. Using replaceable subsystems instead of full systems would further cut cost. Using full sets of replaceable components improves reliability more than using complete systems as spares, since a set of components could repair many different failures instead of just one. Replaceable components would require more tools, space, and planning than full systems or replaceable subsystems. However, identical system redundancy cannot be relied on in practice. Common cause failures can disable all the identical redundant systems. Typical levels of common cause failures will defeat redundancy greater than two. Diverse redundant systems are required for reliable space life support. Three, four, or five diverse redundant systems could be needed for sufficient reliability. One system with lower level repair could be substituted for two diverse systems to save cost.

life support↗
NASA NTRS2014

Sharepoint Team Site Configuration

The Data Mining project seeks to bring the capability of data visualization to NASA anomaly and problem reporting systems for the purpose of improving data trending, evaluations, and analyses. Currently NASA systems are tailored to meet the specific needs of its organizations. This tailoring has led to a variety of nomenclatures and levels of annotation for procedures, parts and anomalies making difficult the realization of the common causes for anomalies. Making significant observations and realizing the connection between these causes without a common way to view data is difficult to impossible. The Data Mining project is in its early stages of presenting a common visualization of normalized data through a web based portal. In this paper I detail what I have learned and what I have accomplished during my time as an intern toward the purpose of creating the project portal. I have gone through an iterative process of familiarization with the project and its goals, site design, research, modification and review on the road to creating a common method and location to view the visualized data created under this project.

iss↗
NASA NTRS2011

Breakdowns in Coordination Between Air Traffic Controllers

This talk outlines the complexity of coordination in air traffic control, introduces the NextGen technologies, identifies common causes for coordination breakdowns in air traffic control and examines whether these causes are likely to be reduced with the introduction of NextGen technologies. While some of the common causes of breakdowns will be reduced in a NextGen environment this conclusion should be drawn carefully given the current stage of development of the technologies and the observation that new technologies often shift problems rather than reduce them.

Bearman, Chris↗
NASA NTRS1995

Evaluation of control parameters for Spray-In-Air (SIA) aqueous cleaning for shuttle RSRM hardware

HD-2 grease is deliberately applied to Shuttle Redesigned Solid Rocket Motor (RSRM) D6AC steel hardware parts as a temporary protective coating for storage and shipping. This HD-2 grease is the most common form of surface contamination on RSRM hardware and must be removed prior to subsequent surface treatment. Failure to achieve an acceptable level of cleanliness (HD-2 calcium grease removal) is a common cause of defect incidence. Common failures from ineffective cleaning include poor adhesion of surface coatings, reduced bond performance of structural adhesives, and failure to pass cleanliness inspection standards. The RSRM hardware is currently cleaned and refurbished using methyl chloroform (1,1,1-trichloroethane). This chlorinated solvent is mandated for elimination due to its ozone depleting characteristics. This report describes an experimental study of an aqueous cleaning system (which uses Brulin 815 GD) as a replacement for methyl chloroform. Evaluation of process control parameters for this cleaner are discussed as well as cleaning mechanisms for a spray-in-air process.

Davis, S. J.↗
NASA NTRS2014

Spacesuit Water Membrane Evaporator Integration with the ISS Extravehicular Mobility Unit

NASA has developed a Solid Water Membrane Evaporation (SWME) to provide cooling for the next generation spacesuit. The current spacesuit team has looked at this technology from the standpoint of using the ISS EMU to demonstrate the SWME technology while EVA, and from the standpoint of augmenting EMU cooling in the case of a fouled EMU cooling system. One approach to increasing the TRL of the system is to incorporate this hardware with the existing EMU. Several integration issues were addressed to support a potential demonstration of the SWME with the existing EMU. Systems analysis was performed to assess the capability of the SWME to maintain crewmember cooling and comfort as a replacement for sublimation. The materials of the SWME were reviewed to address compatibility with the EMU. Conceptual system placement and integration with the EMU via an EVA umbilical system to ensure crew mobility and Airlock egress were performed. A concept of operation for EVA use was identified that is compatible with the existing system. This concept is extensible as a means to provide cooling for the existing EMU. The cooling system of one of the EMUs on orbit has degraded, with the root cause undetermined. Should there be a common cause resident on ISS, this integration could provide a means to recover cooling capability for EMUs on orbit.

Margiott, Victoria↗
NASA NTRS2014

Spacesuit Water Membrane Evaporator Integration with the ISS Extravehicular Mobility

NASA has developed a Solid Water Membrane Evaporation (SWME) to provide cooling for the next generation spacesuit. One approach to increasing the TRL of the system is to incorporate this hardware with the existing EMU. Several integration issues were addressed to support a potential demonstration of the SWME with the existing EMU. Systems analysis was performed to assess the capability of the SWME to maintain crewmember cooling and comfort as a replacement for sublimation. The materials of the SWME were reviewed to address compatibility with the EMU. Conceptual system placement and integration with the EMU via an EVA umbilical system to ensure crew mobility and Airlock egress were performed. A concept of operation for EVA use was identified that is compatible with the existing system. This concept is extensible as a means to provide cooling for the existing EMU. The cooling system of one of the EMUs on orbit has degraded, with the root cause undetermined. Should there be a common cause resident on ISS, this integration could provide a means to recover cooling capability for EMUs on orbit.

Margiott, Victoria↗
NASA NTRS2016

We Can't Count on Repairing All Failures Going to Mars

Reliability analysis often assumes that a complex system can be kept operating indefinitely with scheduled maintenance and emergency repair using a stock of spare parts, as long as the spare parts are not depleted. This assumption seems justified for well-tested, widely used, long operational systems with a multigenerational history of failure, redesign, and reliability growth. It seems doubtful that newer, relatively untried, high technology space systems can always be repaired. We cannot assume space systems will have a low rate of random failures that can all be repaired with a few identical spares. New untried systems usually have a high initial failure rate, called infant mortality, due to errors in requirements, design, parts, materials, and operations planning. These problems can cause groups of related failures called Common Cause Failures (CCFs). The practical definition of a CCF is any failure mode that cannot be cured using identical redundant systems or spare parts. Systems with CCFs may fail repeatedly for the same reason. Can a life support system be kept operating on the way to Mars using only redundant systems and spare parts? The failure history of International Space Station (ISS) life support systems suggests that CCFs are likely to occur and will probably require design changes rather than being reparable with spare parts.

Mars↗
NASA NTRS2019

High Reliability Requires More than Providing Spares

It is sometimes optimistically hoped that a space life support system can be kept working throughout a long duration mission by repairing failed components, as long as sufficient spares are flown. It is usually assumed that the components have constant known failure rates. Then the needed numbers of spares can be computed to have any particular probability that all failed components can be replaced by available spares. This approach can provide high reliability if its favorable assumptions, including constant known failure rates, are satisfied. Other favorable assumptions are that the failures are statistically independent, repair will be successful without causing further failures, and all failures are due to internal component failures. These assumptions are not usually justified. The failure rates may be estimates that are inadequately verified because of insufficient testing. Failure rates may change due to materials substitutions, manufacturing changes, redesigns to fix failures, and new failures caused by redesigns. Failures that are not statistically independent may result from one common cause, such as a design or manufacturing error or a cascade of cause and effect, possibly caused by an external event such as a power outage. Repair may be unsuccessful or cause damage. Many failures occur at component interfaces or at the overall systems level, not within isolated components. Other failures causes are completely external to the system, due to assembly, maintenance, and operational errors or to unexpected environmental challenges. Replacement with sufficient spares can compensate for expected internal component failures but may not be able to cope with unpredictable design and manufacturing flaws, human errors, and environmental impacts. Reliability estimates based on providing sufficient spares to compensate for expected failures may be far too high. They are essentially upper bounds on reliability that might be approached if many frequent but often unconsidered failure causes can be eliminated.

spares↗
NASA NTRS1993

Failure environment analysis tool applications

Understanding risks and avoiding failure are daily concerns for the women and men of NASA. Although NASA's mission propels us to push the limits of technology, and though the risks are considerable, the NASA community has instilled within, the determination to preserve the integrity of the systems upon which our mission and, our employees lives and well-being depend. One of the ways this is being done is by expanding and improving the tools used to perform risk assessment. The Failure Environment Analysis Tool (FEAT) was developed to help engineers and analysts more thoroughly and reliably conduct risk assessment and failure analysis. FEAT accomplishes this by providing answers to questions regarding what might have caused a particular failure; or, conversely, what effect the occurrence of a failure might have on an entire system. Additionally, FEAT can determine what common causes could have resulted in other combinations of failures. FEAT will even help determine the vulnerability of a system to failures, in light of reduced capability. FEAT also is useful in training personnel who must develop an understanding of particular systems. FEAT facilitates training on system behavior, by providing an automated environment in which to conduct 'what-if' evaluation. These types of analyses make FEAT a valuable tool for engineers and operations personnel in the design, analysis, and operation of NASA space systems.

Pack, Ginger L.↗
NASA NTRS1994

Failure environment analysis tool applications

Understanding risks and avoiding failure are daily concerns for the women and men of NASA. Although NASA's mission propels us to push the limits of technology, and though the risks are considerable, the NASA community has instilled within it, the determination to preserve the integrity of the systems upon which our mission and, our employees lives and well-being depend. One of the ways this is being done is by expanding and improving the tools used to perform risk assessment. The Failure Environment Analysis Tool (FEAT) was developed to help engineers and analysts more thoroughly and reliably conduct risk assessment and failure analysis. FEAT accomplishes this by providing answers to questions regarding what might have caused a particular failure; or, conversely, what effect the occurrence of a failure might have on an entire system. Additionally, FEAT can determine what common causes could have resulted in other combinations of failures. FEAT will even help determine the vulnerability of a system to failures, in light of reduced capability. FEAT also is useful in training personnel who must develop an understanding of particular systems. FEAT facilitates training on system behavior, by providing an automated environment in which to conduct 'what-if' evaluation. These types of analyses make FEAT a valuable tool for engineers and operations personnel in the design, analysis, and operation of NASA space systems.

Pack, Ginger L.↗
NASA NTRS1986

The use of flight test techniques in aircraft accident investigations

Wind shear is a serious safety hazard to commercial aviation. Low level wind shear (downburst) was the cause of the takeoff accident in New Orleans, July 9, 1982, and the landing accident in Dallas, Aug. 2, 1985. Shear layer instability is a common cause of clear air turbulence (CAT) at cruising altitudes. A number of encounters with severe CAT, in which passengers were injured, have recently occurred (Hannibal, MO, April 1981; Morton, WY, July 1982; etc.). Improved accident investigation techniques can lead to a better understanding of the nature of the wind environment associated with downbursts and CAT and to better detection and avoidance procedures. For the past several years, NASA-Ames has worked closely with the National Transportation Safety Board in the investigation of wind related accidents.

Parks, E. K.↗
NASA NTRS2013

The SEEDS Direct Imaging Survey for Planets and Scattered Dust Emission in Debris Disk Systems

Debris disks around young main-sequence stars often have gaps and cavities which for a long time have been interpreted as possibly being caused by planets. In recent years, several giant planet discoveries have been made in systems hosting disks of precisely this nature, further implying that interactions with planets could be a common cause of such disk structures. As part of the SEEDS high-contrast imaging survey, we are surveying a population of debris disk-hosting stars with gaps and cavities implied by their spectral energy distributions, in order to attempt to spatially resolve the disk as well as to detect any planets that may be responsible for the disk structure. Here we report on intermediate results from this survey. Five debris disks have been spatially resolved, and a number of faint point sources have been discovered, most of which have been tested for common proper motion, which in each case has excluded physical companionship with the target stars. From the detection limits of the 50 targets that have been observed, we find that beta Pic b-like planets (approximately 10M(sub jup) planets around G-A-type stars) near the gap edges are less frequent than 15-30%, implying that if giant planets are the dominant cause of these wide (27 AU on average) gaps, they are generally less massive than beta Pic b.

high-contrast imaging↗
NASA NTRS1989

Multi-version software reliability through fault-avoidance and fault-tolerance

A number of experimental and theoretical issues associated with the practical use of multi-version software to provide run-time tolerance to software faults were investigated. A specialized tool was developed and evaluated for measuring testing coverage for a variety of metrics. The tool was used to collect information on the relationships between software faults and coverage provided by the testing process as measured by different metrics (including data flow metrics). Considerable correlation was found between coverage provided by some higher metrics and the elimination of faults in the code. Back-to-back testing was continued as an efficient mechanism for removal of un-correlated faults, and common-cause faults of variable span. Software reliability estimation methods was also continued based on non-random sampling, and the relationship between software reliability and code coverage provided through testing. New fault tolerance models were formulated. Simulation studies of the Acceptance Voting and Multi-stage Voting algorithms were finished and it was found that these two schemes for software fault tolerance are superior in many respects to some commonly used schemes. Particularly encouraging are the safety properties of the Acceptance testing scheme.

Vouk, Mladen A.↗
NASA NTRS1976

Quasi-biennial geomagnetic variation caused by the sun

Clear evidence for the existence of a quasi-biennial geomagnetic variation is shown by an analysis of annual averages of the horizontal (H) component of the geomagnetic field observed at five observatories. The analysis uses a numerical filter, which is equivalent to taking the second order time derivative of the time series. The cause for the variation is external to the earth because its amplitude depends on magnetic activity. The second order time derivative of H is well correlated with the corresponding time derivatives of the relative sunspot number and 10.7 cm solar flux. It is suggested that quasi-biennial oscillations observed in the geomagnetic field, cosmic rays, stratospheric zonal wind and temperature, total ozone, and other meteorological parameters could be produced by a common cause on the sun.

Sugiura, M.↗
NASA NTRS1990

Multiversion software reliability through fault-avoidance and fault-tolerance

In this project we have proposed to investigate a number of experimental and theoretical issues associated with the practical use of multi-version software in providing dependable software through fault-avoidance and fault-elimination, as well as run-time tolerance of software faults. In the period reported here we have working on the following: We have continued collection of data on the relationships between software faults and reliability, and the coverage provided by the testing process as measured by different metrics (including data flow metrics). We continued work on software reliability estimation methods based on non-random sampling, and the relationship between software reliability and code coverage provided through testing. We have continued studying back-to-back testing as an efficient mechanism for removal of uncorrelated faults, and common-cause faults of variable span. We have also been studying back-to-back testing as a tool for improvement of the software change process, including regression testing. We continued investigating existing, and worked on formulation of new fault-tolerance models. In particular, we have partly finished evaluation of Consensus Voting in the presence of correlated failures, and are in the process of finishing evaluation of Consensus Recovery Block (CRB) under failure correlation. We find both approaches far superior to commonly employed fixed agreement number voting (usually majority voting). We have also finished a cost analysis of the CRB approach.

Vouk, Mladen A.↗
NASA NTRS2013

Conical Seat Shut-Off Valve

A moveable valve for controlling flow of a pressurized working fluid was designed. This valve consists of a hollow, moveable floating piston pressed against a stationary solid seat, and can use the working fluid to seal the valve. This open/closed, novel valve is able to use metal-to-metal seats, without requiring seat sliding action; therefore there are no associated damaging effects. During use, existing standard high-pressure ball valve seats tend to become damaged during rotation of the ball. Additionally, forces acting on the ball and stem create large amounts of friction. The combination of these effects can lead to system failure. In an attempt to reduce damaging effects and seat failures, soft seats in the ball valve have been eliminated; however, the sliding action of the ball across the highly loaded seat still tends to scratch the seat, causing failure. Also, in order to operate, ball valves require the use of large actuators. Positioning the metal-to-metal seats requires more loading, which tends to increase the size of the required actuator, and can also lead to other failures in other areas such as the stem and bearing mechanisms, thus increasing cost and maintenance. This novel non-sliding seat surface valve allows metal-to-metal seats without the damaging effects that can lead to failure, and enables large seating forces without damaging the valve. Additionally, this valve design, even when used with large, high-pressure applications, does not require large conventional valve actuators and the valve stem itself is eliminated. Actuation is achieved with the use of a small, simple solenoid valve. This design also eliminates the need for many seals used with existing ball valve and globe valve designs, which commonly cause failure, too. This, coupled with the elimination of the valve stem and conventional valve actuator, improves valve reliability and seat life. Other mechanical liftoff seats have been designed; however, they have only resulted in increased cost, and incurred other reliability issues. With this novel design, the seat is lifted by simply removing the working fluid pressure that presses it against the seat and no external force is required. By eliminating variables associated with existing ball and globe configurations that can have damaging effects upon a valve, this novel design reduces downtime in rocket engine test schedules and maintenance costs.

Farner, Bruce↗
NASA NTRS2014

Large Charge Moment Change Lightning in an Oklahoma Mesoscale Convective System

On 31 May 2013, a line of severe thunderstorms developed during the local afternoon in central Oklahoma, USA. One of the supercells produced the El Reno tornado, which caused significant damage and killed several people. During the 2300 UTC hour (during the mature supercell stage and just after the tornado began), the storm produced several positive cloud-to-ground (+CG) lightning strokes that featured large (> 100 C km) impulse charge moment changes (iCMCs; charge moment during the first 2 ms after the return stroke). These discharges occurred mainly in convection, in contrast to the typical pattern of large-CMC and sprite-parent +CGs occurring mainly in stratiform precipitation regions. After this time, the line of thunderstorms evolved over several hours into a large mesoscale convective system (MCS). By the 0700 UTC hour on 1 June 2013, the large-CMC pattern had changed markedly. Large-CMC negative CGs, which were absent early in the storm's lifetime, occurred frequently within convection. Meanwhile, large-CMC +CGs had switched to occurring mainly within the broad stratiform region that had developed during the intervening period. The evolution of the large-CMC lightning in this case will be examined using a mix of national mosaics of radar reflectivity, the Oklahoma Lightning Mapping Array (OKLMA), the Charge Moment Change Network (CMCN), and the National Lightning Detection Network (NLDN). A major goal of this study is understanding how storm structure and evolution affected the production of large-CMC lightning. It is anticipated that this will lead to further insight into how and why storms produce the powerful lightning that commonly causes sprites in the upper atmosphere.

Lang, Timothy J.↗