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At least 631 records · Page 35

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NASA NTRS1973

The development and test of a long-life, high reliability solar array drive actuator

To meet the life and reliability requirements of five to ten year space missions, a new solar array drive mechanism for 3-axis stabilized vehicles has been developed and is undergoing life testing. The drive employs a redundant lubrication system to increase its reliability. An overrunning clutch mechanism is used to permit block redundant application of two or more drives to a common array drive shaft. Two prototype actuator and clutch assemblies, in continuous vacuum life test under load at 10 to the minus 8th power torr for more than sixteen months, have each accumulated more than 34,000 output revolutions without anomaly, the equivalent of more than seven years of operation in a 1000 km orbit or nearly ninety-five years at synchronous altitude.

Kirkpatrick, D. L.↗

NASA NTRS1971

Optimization of life support systems and their systems reliability

The identification, analysis, and optimization of life support systems and subsystems have been investigated. For each system or subsystem that has been considered, the procedure involves the establishment of a set of system equations (or mathematical model) based on theory and experimental evidences; the analysis and simulation of the model; the optimization of the operation, control, and reliability; analysis of sensitivity of the system based on the model; and, if possible, experimental verification of the theoretical and computational results. Research activities include: (1) modeling of air flow in a confined space; (2) review of several different gas-liquid contactors utilizing centrifugal force: (3) review of carbon dioxide reduction contactors in space vehicles and other enclosed structures: (4) application of modern optimal control theory to environmental control of confined spaces; (5) optimal control of class of nonlinear diffusional distributed parameter systems: (6) optimization of system reliability of life support systems and sub-systems: (7) modeling, simulation and optimal control of the human thermal system: and (8) analysis and optimization of the water-vapor eletrolysis cell.

Fan, L. T.↗

NASA NTRS1973

Feasibility model of a high reliability five-year tape transport, Volume 1

The development, performance, and test results for the spaceborne magnetic tape transport are discussed. An analytical model of the tape transport was used to optimize its conceptual design. Each of the subsystems was subjected to reliability analyses which included structural integrity, maintenance of system performance within acceptable bounds, and avoidance of fatigue failure. These subsystems were also compared with each other in order to evaluate reliability characteristics. The transport uses no mechanical couplings. Four drive motors, one for each reel and one for each of two capstans, are used in a differential mode. There are two hybrid, spherical, cone tapered-crown rollers for tape guidance. Storage of the magnetic tape is provided by a reel assembly which includes the reel, a reel support structure and bearings, dust seals, and a dc drive motor. A summary of transport test results on tape guidance, flutter, and skew is provided.

Eshleman, R. L.↗

NASA NTRS1973

Reliability after inspection

Flaws are occasionally overlooked during non-destructive inspections, and consequently the products are not 100 percent reliable. The quantitative relationships among the probability of having manufacturing defects, the probability of detecting a flaw, and final reliability are established. Several specific situations are considered: where a flaw might be present; where a random number of flaws are randomly scattered throughout the piece; where some parts of the product are not accessible for inspection; and a general case where various portions are more easily inspected than others, more or less likely to contain flaws than others, or are not inspectable while other portions are.

Davidson, J. R.↗

NASA NTRS1974

Design of a GN and C system to meet reliability goals

This paper analyzes the reliability of the guidance, navigation, and control (GNC) portion of an avionics system for the Space Shuttle Orbiter. This analysis shows how the GNC design is affected by the need to achieve an acceptable probability of successful completion of a mission and of safe return to an airport. It varies the redundancy of the inertial measurement unit (IMU), computers, and other time-critical elements. It also includes the reliability of the flight control electronics and of the nontime-critical sensors on a phase-by-phase basis. It shows that quadruple redundancy in certain subsystems, high quality parts, and cross-strapping on orbit are required.

Kayton, M.↗

NASA NTRS1974

New development in high reliability strapdown platforms using TDF sensors

New development in high reliability strapdown navigation platform using two-degree-of-freedom sensors and redundancy concept is presented in this paper. The development is based on the assumption that each axis of the sensor can fail without affecting the remaining axis. The systems reliability is investigated, the optimum redundancy configurations are proposed, a technique of sensor performance management is developed for the proposed systems.

Tsuei, Y. D.↗

NASA NTRS1974

Spaceflight tracking and data network operational reliability assessment for Skylab

Data on the spaceflight communications equipment status during the Skylab mission were subjected to an operational reliability assessment. Reliability models were revised to reflect pertinent equipment changes accomplished prior to the beginning of the Skylab missions. Appropriate adjustments were made to fit the data to the models. The availabilities are based on the failure events resulting in the stations inability to support a function of functions and the MTBF's are based on all events including 'can support' and 'cannot support'. Data were received from eleven land-based stations and one ship.

Seneca, V. I.↗

NASA NTRS1974

Adaptations of advanced safety and reliability techniques to petroleum and other industries

The underlying philosophy of the general approach to failure reduction and control is presented. Safety and reliability management techniques developed in the industries which have participated in the U.S. space and defense programs are described along with adaptations to nonaerospace activities. The examples given illustrate the scope of applicability of these techniques. It is indicated that any activity treated as a 'system' is a potential user of aerospace safety and reliability management techniques.

Purser, P. E.↗

NASA NTRS1975

Impact of coverage on the reliability of a fault tolerant computer

A mathematical reliability model is established for a reconfigurable fault tolerant avionic computer system utilizing state-of-the-art computers. System reliability is studied in light of the coverage probabilities associated with the first and second independent hardware failures. Coverage models are presented as a function of detection, isolation, and recovery probabilities. Upper and lower bonds are established for the coverage probabilities and the method for computing values for the coverage probabilities is investigated. Further, an architectural variation is proposed which is shown to enhance coverage.

Bavuso, S. J.↗

NASA NTRS1974

Combined bending-torsion fatigue reliability of AISI 4340 steel shafting with K sub t = 2.34

Results generated by three, unique fatigue reliability research machines which can apply reversed bending loads combined with steady torque are presented. Six-inch long, AISI 4340 steel, grooved specimens with a stress concentration factor of 2.34 and R sub C 35/40 hardness were subjected to various combinations of these loads and cycled to failure. The generated cycles-to-failure and stress-to-failure data are statistically analyzed to develop distributional S-N and Goodman diagrams. Various failure theories are investigated to determine which one represents the data best. The effect of the groove and of the various combined bending-torsion loads on the S-N and Goodman diagrams are determined. Three design applications are presented. The third one illustrates the weight savings that may be achieved by designing for reliability.

Kececioglu, D.↗

NASA NTRS1975

A reliability tradeoff study of interconnecting power processors to mercury ion thrusters

A Monte Carlo mission simulation program has been developed to optimize the solar electric propulsion (SEP) thrust subsystem configuration for an Encke comet rendezvous mission. This program examines several possible options for interconnecting power processors to the mercury ion thrusters in order to enhance mission reliability and to reduce SEP subsystem weight. The quantity of power processors and ion thrusters required to perform the mission successfully depends not only on the total required thrust, but also on the individual thruster and power processor performance and reliability. Based on these considerations, it was necessary to determine the quantity of the active power processors and ion thrusters required at any time and the means of providing redundancy. The results provide the basis for selecting an optimum SEP thrust subsystem for this mission and other missions.

Costogue, E. N.↗

NASA NTRS1975

Reliability after inspection

The investigation is concerned with the derivation of relationships between the probability of having manufacturing defects, the probability of detecting a flaw, and the final reliability. Equations for the simple situation in which only one flaw can be present are used to introduce the relationships in a Bayes' theorem approach to the assessment of the final reliability. Situations which are prevalent in composites manufacturing are considered. Attention is given to a case involving the random occurrence of flaws on a laminate surface.

Davidson, J. R.↗

NASA NTRS1975

Automatic documentation system extension to multi-manufacturers' computers and to measure, improve, and predict software reliability

The DOMONIC system has been modified to run on the Univac 1108 and the CDC 6600 as well as the IBM 370 computer system. The DOMONIC monitor system has been implemented to gather data which can be used to optimize the DOMONIC system and to predict the reliability of software developed using DOMONIC. The areas of quality metrics, error characterization, program complexity, program testing, validation and verification are analyzed. A software reliability model for estimating program completion levels and one on which to base system acceptance have been developed. The DAVE system which performs flow analysis and error detection has been converted from the University of Colorado CDC 6400/6600 computer to the IBM 360/370 computer system for use with the DOMONIC system.

Simmons, D. B.↗

NASA NTRS1976

Avionics design for reliability bibliography

A bibliography with abstracts was presented in support of AGARD lecture series No. 81. The following areas were covered: (1) program management, (2) design for high reliability, (3) selection of components and parts, (4) environment consideration, (5) reliable packaging, (6) life cycle cost, and (7) case histories.

Source record↗

NASA NTRS1976

A methodology for producing reliable software, volume 1

An investigation into the areas having an impact on producing reliable software including automated verification tools, software modeling, testing techniques, structured programming, and management techniques is presented. This final report contains the results of this investigation, analysis of each technique, and the definition of a methodology for producing reliable software.

Stucki, L. G.↗

NASA NTRS1976

The F-12 series aircraft approach to design for control system reliability

The F-12 series aircraft control system design philosophy is reviewed as it pertains to functional reliability. The basic control system, i.e., cables, mixer, feel system, trim devices, and hydraulic systems are described and discussed. In addition, the implementation of the redundant stability augmentation system in the F-12 aircraft is described. Finally, the functional reliability record that has been achieved is presented.

Schenk, F. L.↗

NASA NTRS1976

Assessment of NDE Reliability Data

Twenty sets of relevant Nondestructive Evaluation (NDE) reliability data have been identified, collected, compiled, and categorized. A criterion for the selection of data for statistical analysis considerations has been formulated. A model to grade the quality and validity of the data sets has been developed. Data input formats, which record the pertinent parameters of the defect/specimen and inspection procedures, have been formulated for each NDE method. A comprehensive computer program has been written to calculate the probability of flaw detection at several confidence levels by the binomial distribution. This program also selects the desired data sets for pooling and tests the statistical pooling criteria before calculating the composite detection reliability. Probability of detection curves at 95 and 50 percent confidence levels have been plotted for individual sets of relevant data as well as for several sets of merged data with common sets of NDE parameters.

Yee, B. G. W.↗

NASA NTRS1976

Large-scale systems - Stability, complexity, reliability

This paper establishes the connective stability concept in the framework of the comparison principle and vector Liapunov functions, as a natural setting for resolving the complexity vs reliability problem in the control of large-scale dynamic systems. The central result is the following: a stable complex system when composed as a competitive structure of the interconnected stable subsystems remains stable despite the on-off participation of the subsystems. This result is important in that it can be used efficiently to synthesize reliable complex systems by multilevel feedback control.

Siljak, D. D.↗