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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Development of a calibrated software reliability model for flight and supporting ground software for avionic systems

The object of this project was to develop and calibrate quantitative models for predicting the quality of software. Reliable flight and supporting ground software is a highly important factor in the successful operation of the space shuttle program. The models used in the present study consisted of SMERFS (Statistical Modeling and Estimation of Reliability Functions for Software). There are ten models in SMERFS. For a first run, the results obtained in modeling the cumulative number of failures versus execution time showed fairly good results for our data. Plots of cumulative software failures versus calendar weeks were made and the model results were compared with the historical data on the same graph. If the model agrees with actual historical behavior for a set of data then there is confidence in future predictions for this data. Considering the quality of the data, the models have given some significant results, even at this early stage. With better care in data collection, data analysis, recording of the fixing of failures and CPU execution times, the models should prove extremely helpful in making predictions regarding the future pattern of failures, including an estimate of the number of errors remaining in the software and the additional testing time required for the software quality to reach acceptable levels. It appears that there is no one 'best' model for all cases. It is for this reason that the aim of this project was to test several models. One of the recommendations resulting from this study is that great care must be taken in the collection of data. When using a model, the data should satisfy the model assumptions.

Lawrence, Stella↗
NASA NTRS1990

Redundant disk arrays: Reliable, parallel secondary storage

During the past decade, advances in processor and memory technology have given rise to increases in computational performance that far outstrip increases in the performance of secondary storage technology. Coupled with emerging small-disk technology, disk arrays provide the cost, volume, and capacity of current disk subsystems, by leveraging parallelism, many times their performance. Unfortunately, arrays of small disks may have much higher failure rates than the single large disks they replace. Redundant arrays of inexpensive disks (RAID) use simple redundancy schemes to provide high data reliability. The data encoding, performance, and reliability of redundant disk arrays are investigated. Organizing redundant data into a disk array is treated as a coding problem. Among alternatives examined, codes as simple as parity are shown to effectively correct single, self-identifying disk failures.

Gibson, Garth Alan↗
NASA NTRS1992

Analysis of nickel-cadmium battery reliability data containing zero failures

An analysis of reliability data on Nickel-Cadmium (NiCd) batteries (for use in spacecraft) is presented. The data were collected by Gates Aerospace and represent a substantial reliability database. The data were taken from the performance of 183 satellites which were in operation from between .1 and 22 years, for a total of 278 million cell-hours of operation.

Denson, William K.↗
NASA NTRS1992

The process group approach to reliable distributed computing

The difficulty of developing reliable distribution software is an impediment to applying distributed computing technology in many settings. Experience with the ISIS system suggests that a structured approach based on virtually synchronous process groups yields systems that are substantially easier to develop, exploit sophisticated forms of cooperative computation, and achieve high reliability. Six years of research on ISIS, describing the model, its implementation challenges, and the types of applications to which ISIS has been applied are reviewed.

Birman, Kenneth P.↗
NASA NTRS1991

Reliability analysis of ceramic matrix composite laminates

At a macroscopic level, a composite lamina may be considered as a homogeneous orthotropic solid whose directional strengths are random variables. Incorporation of these random variable strengths into failure models, either interactive or non-interactive, allows for the evaluation of the lamina reliability under a given stress state. Using a non-interactive criterion for demonstration purposes, laminate reliabilities are calculated assuming previously established load sharing rules for the redistribution of load as the failure of laminae occur. The matrix cracking predicted by ACK theory is modeled to allow a loss of stiffness in the fiber direction. The subsequent failure in the fiber direction is controlled by a modified bundle theory. Results using this modified bundle model are compared with previous models which did not permit separate consideration of matrix cracking, as well as to results obtained from experimental data.

Thomas, David J.↗
NASA NTRS1992

Structural system reliability calculation using a probabilistic fault tree analysis method

The development of a new probabilistic fault tree analysis (PFTA) method for calculating structural system reliability is summarized. The proposed PFTA procedure includes: developing a fault tree to represent the complex structural system, constructing an approximation function for each bottom event, determining a dominant sampling sequence for all bottom events, and calculating the system reliability using an adaptive importance sampling method. PFTA is suitable for complicated structural problems that require computer-intensive computer calculations. A computer program has been developed to implement the PFTA.

Torng, T. Y.↗
NASA NTRS1991

Fatigue crack growth reliability by probabilistic finite elements

Fusion of the probabilistic finite-element method and reliability analysis for probabilistic fatigue-crack growth is presented. A comprehensive method for determining the probability of fatigue failure for mixed-mode cyclic loading is also presented. The loading is mixed-mode with randomness in the initial and final crack lengths, initial crack angle and position, material properties, crack-growth law, crack-direction law, and loading. The methodology consists of calculating the reliability index via an optimization procedure which is used to calculate the probability of fatigue failure. Performance of the methodology presented is demonstrated on a classical mode-I fatigue problem.

Besterfield, Glen H.↗
NASA NTRS1992

Estimation and enhancement of real-time software reliability through mutation analysis

A simulation-based technique for obtaining numerical estimates of the reliability of N-version, real-time software is presented. An extended stochastic Petri net is employed to represent the synchronization structure of N versions of the software, where dependencies among versions are modeled through correlated sampling of module execution times. Test results utilizing specifications for NASA's planetary lander control software indicate that mutation-based testing could hold greater potential for enhancing reliability than the desirable but perhaps unachievable goal of independence among N versions.

Geist, Robert↗
NASA NTRS1992

A decomposition method for optimization of large-system reliability

This paper considers a decomposition approach for optimization of the reliability of a large system with a general network structure. A 3-level methodology is developed for optimal allocation of available resources among subsystems in order to ensure maximization of system-reliability. The decentralized nature of this methodology greatly reduces the complexity of the large problem and facilitates seeking the optimal solution. Two examples show that the complexity of a large system can be greatly reduced by solving several smaller-dimensional sub-problems iteratively. Sub-problems whose dimensions are small can be efficiently solved by any existing nonlinear programming method. Another important feature of this approach is the possible simplification of the objective function during the solution. This leads in some cases to an analytic solution for the lower-level optimization problems in a 3-level decomposition solution.

Li, Duan↗
NASA NTRS1991

A low maintenance and highly reliable fly-by-light architecture

This paper proposes a highly reliable distributed architecture for use in a commercial transport. Fly-By-Light characteristics of the architecture are a serial fiber optic backplane and redundant fiber optic data bus. The fiber optic bus is fault tolerant and Byzantine resilient. A distributed architecture (both physically and logically) can be realized by utilizing several processing clusters on the data bus. A processing cluster is composed of one or more processing units. The processing units consist of several modules. The modules of the processing unit are connected via a serial fiber optic backplane. Fault tolerance is implemented at the backplane to increase reliability and availability.

Dan Palumbo↗
NASA NTRS1993

Computing Reliabilities Of Ceramic Components

CARES/PC computer program performs statistical analysis of data obtained from fracture of simple, uniaxial tensile or flexural specimens of ceramics and estimates Weibull and Batdorf material parameters from these data. CARES/PC is subset of Ceramics Analysis and Reliability Evaluation of Structures (CARES) program (LEW-15168), which calculates fast-fracture reliabilities or failure probabilities of ceramic components by use of Batdorf and Weibull models to describe effects of multiaxial stress states on strengths of materials. CARES/PC written and compiled with the Microsoft FORTRAN v5.0 compiler.

Szatmary, S. A.↗
NASA NTRS1992

Software reliability through fault-avoidance and fault-tolerance

Accomplishments in the following research areas are summarized: structure based testing, reliability growth, and design testability with risk evaluation; reliability growth models and software risk management; and evaluation of consensus voting, consensus recovery block, and acceptance voting. Four papers generated during the reporting period are included as appendices.

Vouk, Mladen A.↗
NASA NTRS1992

Using software metrics and software reliability models to attain acceptable quality software for flight and ground support software for avionic systems

This paper is concerned with methods of measuring and developing quality software. Reliable flight and ground support software is a highly important factor in the successful operation of the space shuttle program. Reliability is probably the most important of the characteristics inherent in the concept of 'software quality'. It is the probability of failure free operation of a computer program for a specified time and environment.

Lawrence, Stella↗
NASA NTRS1992

Reliability analysis of External Tank Attack Ring (ETA)

The present study is restricted to External Tank Attachment Rings (ETA), but the concepts discussed are general in nature and can be applied to any structural component. The objective of this research work is to use some of the existing probabilistic methods to calculate the reliability of ETA Rings at various critical sections for the limit state of stress. This is done both in terms of the traditional probability of failure and reliability levels as well as the well known safety indices (beta) which have become a commonly accepted measure of safety.

Putcha, Chandra S.↗
NASA NTRS1992

What makes a family reliable?

Asteroid families are clusters of asteroids in proper element space which are thought to be fragments from former collisions. Studies of families promise to improve understanding of large collision events and a large event can open up the interior of a former parent body to view. While a variety of searches for families have found the same heavily populated families, and some searches have found the same families of lower population, there is much apparent disagreement between proposed families of lower population of different investigations. Indicators of reliability, factors compromising reliability, an illustration of the influence of different data samples, and a discussion of how several investigations perceived families in the same region of proper element space are given.

Williams, James G.↗
NASA NTRS1993

Solid Propulsion Integrity Program (SPIP) for verifiable enhanced solid rocket motor reliability

To increase the success rate of U.S. built Rocket Motors (SRM), the approach taken is: (1) set common reliability goals for nozzles, cases, bondline, propellant, and insulation; (2) build a common engineering data base to support standard industry-wide reliability assessment models; (3) structure or enhance existing industry/government/user term to develop the tools, methods needed, and the data to support them; and (4) areas where unreliabilities are found must be improved.

Butler, Barry L.↗
NASA NTRS1993

A dual output pressure, high reliability, long storage life gas delivery vessel assembly

A Gas Vessel Assembly has been developed that delivers purified, very low moisture content gas at two different output pressures. High pressure gas is delivered at up to 6,700 psi, and low pressure gas regulated to 130 psi is also delivered via a second outlet over a wide range of flow rates. The device is extremely lightweight (less than 1 lb) and compact, affords maximum mechanical integrity, high reliability (0.9999 at 95 percent confidence level), and offers extremely long storage life. Specialized design and fabrication techniques are employed that guarantee gas purity and negligible leakage for more than 20 years, in widely varying conditions of storage temperature, humidity, altitude, and vibration environments. The technology offers unique advantages in fast, high pressure discharge applications. For example, when combined with a cryostat, cryogenic temperatures can be achieved such as those used in missile seeker technology. The technology has many additional applications such as: emergency power sources for safety devices such as those needed in nuclear power plants, refineries, collision cushioning devices, superconductor cooling devices, emergency egress systems, miniature mechanical devices that employ gas bearings, and other areas where long storage, extremely high reliability and/or high energy density sources are required.

Maya, Isaac↗
NASA NTRS1992

Reliable vision-guided grasping

Automated assembly of truss structures in space requires vision-guided servoing for grasping a strut when its position and orientation are uncertain. This paper presents a methodology for efficient and robust vision-guided robot grasping alignment. The vision-guided grasping problem is related to vision-guided 'docking' problems. It differs from other hand-in-eye visual servoing problems, such as tracking, in that the distance from the target is a relevant servo parameter. The methodology described in this paper is hierarchy of levels in which the vision/robot interface is decreasingly 'intelligent,' and increasingly fast. Speed is achieved primarily by information reduction. This reduction exploits the use of region-of-interest windows in the image plane and feature motion prediction. These reductions invariably require stringent assumptions about the image. Therefore, at a higher level, these assumptions are verified using slower, more reliable methods. This hierarchy provides for robust error recovery in that when a lower-level routine fails, the next-higher routine will be called and so on. A working system is described which visually aligns a robot to grasp a cylindrical strut. The system uses a single camera mounted on the end effector of a robot and requires only crude calibration parameters. The grasping procedure is fast and reliable, with a multi-level error recovery system.

Nicewarner, Keith E.↗