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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Reliability improvements in tunable Pb1-xSnxSe diode lasers

Recent developments in the technology of Pb-salt diode lasers which have led to significant improvements in reliability and lifetime, and to improved operation at very long wavelengths are described. A combination of packaging and contacting-metallurgy improvements has led to diode lasers that are stable both in terms of temperature cycling and shelf-storage time. Lasers cycled over 500 times between 77 K and 300 K have exhibited no measurable changes in either electrical contact resistance or threshold current. Utilizing metallurgical contacting process, both lasers and experimental n-type and p-type bulk materials are shown to have electrical contact resistance values that are stable for shelf storage periods well in excess of one year. Problems and experiments which have led to devices with improved performance stability are discussed. Stable device configurations achieved for material compositions yielding lasers which operate continuously at wavelengths as long as 30.3 micrometers are described.

Linden, K. J.↗
NASA NTRS1982

Solar-Powered Supply Is Light and Reliable

DC supply originally intended for use in solar-powered spacecraft propulsion is lightweight and very reliable. Operates from 100-200 volt output of solar panels to produce 11 different dc voltages, with total demand of 3,138 watts. With exception of specially wound inductors and transformers, system uses readily available components.

Willis, A. E.↗
NASA NTRS1980

Spacecraft transmitter reliability

A workshop on spacecraft transmitter reliability was held at the NASA Lewis Research Center on September 25 and 26, 1979, to discuss present knowledge and to plan future research areas. Since formal papers were not submitted, this synopsis was derived from audio tapes of the workshop. The following subjects were covered: users' experience with space transmitters; cathodes; power supplies and interfaces; and specifications and quality assurance. A panel discussion ended the workshop.

Source record↗
NASA NTRS1981

Monolithic ceramic capacitors for high reliability applications

Monolithic multi-layer ceramic dielectric capacitors are widely used in high reliability applications in spacecraft, launch vehicles, and military equipment. Their relatively low cost, wide range of values, and package styles are attractive features that result in high usage in electronic circuitry in these applications. Design and construction of monolithic ceramic dielectric capacitors, defects that can lead to failure, and methods for defect detection that are being incorporated in military specifications are discussed.

Thornley, E. B.↗
NASA NTRS1981

Accelerated life testing and reliability of high K multilayer ceramic capacitors

The reliability of one lot of high K multilayer ceramic capacitors was evaluated using accelerated life testing. The degradation in insulation resistance was characterized as a function of voltage and temperature. The times to failure at a voltage-temperature stress conformed to a lognormal distribution with a standard deviation approximately 0.5.

Minford, W. J.↗
NASA NTRS1981

Reliability achievement in high technology space systems

The production of failure-free hardware is discussed. The elements required to achieve such hardware are: technical expertise to design, analyze, and fully understand the design; use of high reliability parts and materials control in the manufacturing process; and testing to understand the system and weed out defects. The durability of the Hughes family of satellites is highlighted.

Lindstrom, D. L.↗
NASA NTRS1981

Innovation and reliability of atomic standards for PTTI applications

Innovation and reliability in hyperfine frequency standards and clock systems are discussed. Hyperfine standards are defined as those precision frequency sources and clocks which use a hyperfine atomic transition for frequency control and which have realized significant commercial production and acceptance (cesium, hydrogen, and rubidium atoms). References to other systems such as thallium and ammonia are excluded since these atomic standards have not been commercially exploited in this country.

Kern, R.↗
NASA NTRS1981

A 100 microsec, reliable, 10 Hz pulsed supersonic molecular beam source

A 10-Hz repetition rate, 100-microsec duration, reliable pulsed supersonic molecular beam source is described. Mechanical and electrical design of the pulsed valve are given in detail. Characteristics of the supersonic expansion obtained using coherent anti-Stokes Raman spectroscopy in acetylene are presented. They include pulse shape, gas rotational and translational cooling as a function of distance from the nozzle, clustering effects, and shock heating at the leading edge of the pulse.

Byer, R. L.↗
NASA NTRS1983

Designing Glass Panels for Economy and Reliability

Analytical method determines probability of failure of rectangular glass plates subjected to uniformly distributed loads such as those from wind, earthquake, snow, and deadweight. Developed as aid in design of protective glass covers for solar-cell arrays and solar collectors, method is also useful in estimating the reliability of large windows in buildings exposed to high winds and is adapted to nonlinear stress analysis of simply supported plates of any elastic material.

Moore, D. M.↗
NASA NTRS1981

Reliability analysis of the F-8 digital fly-by-wire system

The F-8 Digital Fly-by-Wire (DFBW) flight test program intended to provide the technology for advanced control systems, giving aircraft enhanced performance and operational capability is addressed. A detailed analysis of the experimental system was performed to estimated the probabilities of two significant safety critical events: (1) loss of primary flight control function, causing reversion to the analog bypass system; and (2) loss of the aircraft due to failure of the electronic flight control system. The analysis covers appraisal of risks due to random equipment failure, generic faults in design of the system or its software, and induced failure due to external events. A unique diagrammatic technique was developed which details the combinatorial reliability equations for the entire system, promotes understanding of system failure characteristics, and identifies the most likely failure modes. The technique provides a systematic method of applying basic probability equations and is augmented by a computer program written in a modular fashion that duplicates the structure of these equations.

Brock, L. D.↗
NASA NTRS1981

Reliable aerial thermography for energy conservation

A method for energy conservation, the aerial thermography survey, is discussed. It locates sources of energy losses and wasteful energy management practices. An operational map is presented for clear sky conditions. The map outlines the key environmental conditions conductive to obtaining reliable aerial thermography. The map is developed from defined visual and heat loss discrimination criteria which are quantized based on flat roof heat transfer calculations.

Jack, J. R.↗
NASA NTRS1981

Reliability study of refractory gate gallium arsenide MESFETS

Refractory gate MESFET's were fabricated as an alternative to aluminum gate devices, which have been found to be unreliable as RF power amplifiers. In order to determine the reliability of the new structures, statistics of failure and information about mechanisms of failure in refractory gate MESFET's are given. Test transistors were stressed under conditions of high temperature and forward gate current to enhance failure. Results of work at 150 C and 275 C are reported.

Yin, J. C. W.↗
NASA NTRS1982

Experience with modified aerospace reliability and quality assurance method for wind turbines

The SR&QA approach assures that the machine is not hazardous to the public or operating personnel, can operate unattended on a utility grid, demonstrates reliability operation, and helps establish the quality assurance and maintainability requirements for future wind turbine projects. The approach consisted of modified failure modes and effects analysis (FMEA) during the design phase, minimal hardware inspection during parts fabrication, and three simple documents to control activities during machine construction and operation. Five years experience shows that this low cost approach works well enough that it should be considered by others for similar projects.

Klein, W. E.↗
NASA NTRS1982

TIGER reliability analysis in the DSN

The TIGER algorithm, the inputs to the program and the output are described. TIGER is a computer program designed to simulate a system over a period of time to evaluate system reliability and availability. Results can be used in the Deep Space Network for initial spares provisioning and system evaluation.

Gunn, J. M.↗
NASA NTRS1982

High rate, high reliability Li/SO2 cells

The use of the lithium/sulfur dioxide system for aerospace applications is discussed. The high rate density in the system is compared to some primary systems: mercury zinc, silver zinc, and magnesium oxide. Estimates are provided of the storage life and shelf life of typical lithium sulfur batteries. The design of lithium cells is presented and criteria are given for improving the output of cells in order to achieve high rate and high reliability.

Chireau, R.↗
NASA NTRS1981

Software models: A Bayesian approach to parameter estimation in the Jelenski-Moranda software reliability model

Maximum likelihood estimation procedures for the Jelinski-Moranda software reliability model often give misleading answers. A reparameterization and a Bayesian analysis eliminate some of the problems incurred by MLE methods and often give better predictions on sets of real and simulated data. Practical difficulties in estimating the initial number of errors N and the failure rate of each error phi by the method of maximum likelihood are: N, the MLE of N, is occasionally infinite (i.e., the routines for calculating N and phi do not converge). It is shown that N is finite sub i only if the regression line of the interevent times t sub i vs. i has positive slope. A serious problem is that often N approximates n, the sample size, and sometimes N = n. Thus the MLE predicts that the program is perfect even when it is far from being so. Only when almost all failures have been removed can N and phi be trusted near the end of debugging.

Littlewood, B.↗
NASA NTRS1982

The implementation and use of Ada on distributed systems with high reliability requirements

The use and implementation of Ada in distributed environments in which the hardware components are assumed to be unreliable is investigated. The possibility that a distributed system can be programmed entirely in Ada so that the individual tasks of the system are unconcerned with which processor they are executing on, and that failures can occur in the underlying hardware is considered. The reduced cost of computer hardware and the advantages of distributed processing (for example, increased reliability through redundancy and greater flexibility) indicate that many aerospace computer systems can be distributed. The use of Ada and distributed systems is a good combination for aerospace embedded systems.

Knight, J. C.↗
NASA NTRS1982

Reliability of the finite element method for calculating free edge stresses in composite laminates

The interlaminar normal stress distributions along the interface between the +45 deg and -45 deg plies of a graphite/epoxy laminate, obtained by various investigators, were found to disagree in both magnitude and sign. The reliability of the displacement-formulated finite element method in analyzing the edge-stress problem of a composite laminate is investigated. The history of the edge-stress problem is reviewed, and two well-known elasticity problems, one involving a stress discontinuity and one a singularity, are analyzed. The finite element analysis in these problems yields accurate stress distributions everywhere except in two elements closest to the stress discontinuity or singularity. Stress distributions for a + or -45 deg ply laminate near the singularity were similar to those of the two elasticity problems, demonstrating the methods, accuracy for calculating interlaminar stresses in composite laminates. The disagreement between the numerical methods was attributed to the unsymmetric stress tensor at singularity.

Whitcomb, J. D.↗