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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Ultrasonic and optical evaluation of surgical implant materials and devices. A durability study of pericardial bioprostheses

Laser Doppler Anemometry (LDA) and accelerated fatigue testing were used in an attempt to assess the durability of two cardiac value bioprostheses. The LDA system was used to monitor the function of the cardiac valves over time. This was done through flow characterization in an aortic flow chamber, designed to closely simulate in vivo conditions, both in the near vicinity (sinuses of valsalva region) and also somewhat downstream (aortic region) from the values. The accelerated fatigue tester was operated by opening and closing the valves at a rate of 1300 R.P.M., about 18 x the normal rate. The results from the two test valves indicate a definite change in the flow characteristics downstream from the valve after certain accelerated test intervals. The high velocity cross-sectional flow area seems to increase over time in use, causing a decrease in the peak velocity. The tissue became more flaccid in certain areas, and tears were apparent at about 9.4 million cycles for the Ionescu-Shiley valve and at 24 million cycles for the Carpentier-Edwards valve. The use of Doppler ultrasound as a technique for monitoring the function of bioprostheses over time in vivo is also discussed.

Schuster, P. R.↗
NASA NTRS2003

Long-Term Reliability of High Speed SiGe/Si Heterojunction Bipolar Transistors

Accelerated lifetime tests were performed on double-mesa structure Si/Si0.7Ge0.3/Si npn heterojunction bipolar transistors, grown by molecular beam epitaxy, in the temperature range of 175C-275C. Both single- and multiple finger transistors were tested. The single-finger transistors (with 5x20 micron sq m emitter area) have DC current gains approximately 40-50 and f(sub T) and f(sub MAX) of up to 22 GHz and 25 GHz, respectively. The multiple finger transistors (1.4 micron finger width, 9 emitter fingers with total emitter area of 403 micron sq m) have similar DC current gain but f(sub T) of 50 GHz. It is found that a gradual degradation in these devices is caused by the recombination enhanced impurity diffusion (REID) of boron atoms from the p-type base region and the associated formation of parasitic energy barriers to electron transport from the emitter to collector layers. This REID has been quantitatively modeled and explained, to the first order of approximation, and the agreement with the measured data is good. The mean time to failure (MTTF) of the devices at room temperature is estimated from the extrapolation of the Arrhenius plots of device lifetime versus reciprocal temperature. The results of the reliability tests offer valuable feedback for SiGe heterostructure design in order to improve the long-term reliability of the devices and circuits made with them. Hot electron induced degradation of the base-emitter junction was also observed during the accelerated lifetime testing. In order to improve the HBT reliability endangered by the hot electrons, deuterium sintered techniques have been proposed. The preliminary results from this study show that a deuterium-sintered HBT is, indeed, more resistant to hot-electron induced base-emitter junction degradation. SiGe/Si based amplifier circuits were also subjected to lifetime testing and we extrapolate MTTF is approximately 1.1_10(exp 6) hours at 125iC junction temperature from the circuit lifetime data.

Ponchak, George E.↗
NASA NTRS1980

Mechanisms of nitrogen heterocycle influence on turbine fuel stability

Lewis bases were extracted from a Utah COED syncrude via ligand exchange. Addition of this extract to Jet A at levels as low as 5 ppm N produced deterioration of stability in both JFTOT and accelerated storage tests (7 days at 394 K with 13:1air to fuel ratio). Comparable effects on Jet A stability were obtained by addition of pyridine and quinoline, while pyrrole and indole were less detrimental at the same concentration level. The weight of deposit produced accelerated storage tests was found to be proportional to the concentration of added nitrogen compound. Over the narrow temperature range accessible with the experimental method, Arrhenius plots obtained by assuming specific rate to be proportional to the weight of material deposited in seven days exhibit greater slopes in the presence of those nitrogen compounds producing the greater deposition rates. It is shown that despite variation in appearance the elemental composition and spectral characteristics of the deposits are unaffected by addition of the nitrogen compounds. The linearity of the Arrhenius plots and of a plot of Arrhenius slope versus intercept for all the compounds suggests a constancy of mechanism over the range of temperature and heterocycles studied.

Daniel, S. R.↗
NASA NTRSDate not supplied

Stress Testing of Chip Aluminum Polymer Capacitors

Layered aluminum polymer capacitors (APC) may be viable replacements to current chip tantalum capacitors due to their lower ESR, weight, and smaller size. So far, there is a lack of information regarding the reliability of these parts. Available technical literature is mostly related to the effect on humidity. Although APCs have a limited moisture resistance, it may be contained to the level sufficient for space applications. In this work, seven types of commercial APCs manufactured by four vendors and rated to voltages from 6.3 to 35 V were used to evaluate reliability of the parts under environmental stresses and highly accelerated life tests. Characteristics of the parts, including breakdown voltages, the level of anomalous charging currents (ACC), capacitance, DF, ESR and leakage currents were measured in the process of storage at high-temperatures (from 100 to 150 °C) and high humidity at 85 °C. Monitored highly accelerated life tests have been carried out at temperatures of 85 °C and 125 °C and voltages varying from 1.2 to 1.9 times the rated voltage. Degradation processes and reliability of APCs have been analyzed and compared to polymer tantalum capacitors.

Alexander Teverovsky↗
NASA NTRS1978

The 5200 cycle test of an 8-cm diameter Hg ion thruster

An accelerated cycle test was conducted in which an 8-cm Engineering Model Thruster (EMT) prototype successfully completed 5200 on-off cycles and a total of more than 1300hours of thruster operation at a 4.5 mN thrust level. Cathode tip heater powers required for starting and keeper voltages remained well within acceptable limits. The discharge chamber utilization and electrical efficiency were nearly constant over the duration of the test. It was concluded that on-off cyclic operation by itself does not appreciably degrade starting capability or performance of the 8-cm EMT.

Mantenieks, M. A.↗
NASA NTRS1981

Outdoor and laboratory testing of photovoltaic modules

An overview of outdoor and laboratory testing being applied to terrestrial photovoltaic modules is presented. Descriptions of the test procedures, examples of results, and discussion of the advantages and shortcomings of each approach are included. The test program consists of real-time outdoor testing of systems, modules and materials, and accelerated outdoor testing and laboratory testing of modules. The test results suggest that the various types of tests complement each other and contribute toward the objective of verifying the environmental suitability of the product. A description of representative photovoltaic systems operational in the U.S. in 1981 is presented, along with an identification, description, and physical inspection summary of JPL test module sites and a summary of degradation and failure data for the modules.

Hoffman, A.↗
NASA NTRS1985

Determining The Life Expectancy of Photovoltaic Systems

Several tests used to determine adequacy of photovoltaic systems, their modules, and materials to survive in real environments. Tests include outdoor testing of systems, real-time and accelerated outdoor testing of modules and materials, and laboratory testing of modules and materials.

Hoffman, A. R.↗
NASA NTRS2022

Useful Life of Tantalum Capacitors

Currently, the major reliability characteristic of tantalum capacitors is the failure rate, which is a constant used to characterize random failures of electronic components. However, contemporary MnO2 and polymer tantalum capacitors have both infant mortality (IM) and wear-out (WO) failures. This requires assessments of the useful life of the parts that is limited by the time of inception of WO failures that can be determined using an adequate reliability model and results of highly accelerated life testing (HALT). In this presentation, a modified time dependent dielectric breakdown (TDDB) model is used to describe both IM and WO failures during HALT. Specifics of physical processes resulting in degradation and failures in polymer and MnO2 tantalum capacitors are discussed, and the increase of IM failures with the level of stress is explained. The model justifies exponential dependence of the acceleration factors on voltage and predicts higher values of the voltage acceleration constant for IM compared to WO failures.

tantalum capacitors↗
NASA NTRS1980

Investigation of reliability attributes and accelerated stress factors on terrestrial solar cells

Three tasks were undertaken to investigate reliability attributes of terrestrial solar cells: (1) a study of the electrical behavior of cells in the second (reverse) quadrant; (2) the accelerated stress testing of three new state-of-the-art cells; and (3) the continued bias-temperature testing of four block 2 type silicon cells at 78 C and 135 C. Electrical characteristics measured in the second quadrant were determined to be a function of the cell's thermal behavior with breakdown depending on the initiation of localized heating. This implied that high breakdown cells may be more fault tolerant when forced to operate in the second quadrant, a result contrary to conventional thinking. The accelerated stress tests used in the first (power) quadrant were bias-temperature, bias-temperature-humidity, temperature-humidity, thermal shock, and thermal cycle. The new type cells measured included an EFG cell, a polycrystalline cell, and a Czochralski cell. Significant differences in the response to the various tests were observed between cell types. A microprocessed controlled, short interval solar cell tester was designed and construction initiated on a prototype.

Lathrop, J. W.↗
NASA NTRS1975

Solutions for discharge chamber sputtering and anode deposit spalling in small mercury ion thrusters

Proposed solutions to the problems of sputter erosion and sputtered material spalling in the discharge chamber of small mercury ion thrusters are presented. The accelerated life test evaluated three such proposed solutions: (1) the use of tantalum as a single low sputter yield material for the exposed surfaces of the discharge chamber components subject to sputtering, (2) the use of a severely roughened anode surface to improve the adhesion of the sputter-deposited coating, and (3) the use of a wire cloth anode surface in order to limit the size of any coating flakes which might spall from it. Because of the promising results obtained in the accelerated life test with anode surfaces roughened by grit-blasting, experiments were carried out to optimize the grit-blasting procedure. The experimental results and an optimal grit-blasting procedure are presented.

Power, J. L.↗
NASA NTRS1971

Accelerated battery-life testing - A concept

Test program, employing empirical, statistical and physical methods, determines service life and failure probabilities of electrochemical cells and batteries, and is applicable to testing mechanical, electrical, and chemical devices. Data obtained aids long-term performance prediction of battery or cell.

Mccallum, J.↗
NASA NTRS1973

Controlled porosity and pore size substrates for nickel-cadmium cells

A novel process for the preparation of improved cadmium electrode plaques with precisely controlled pore size and porosity is described. The requirements for these plaques include far better uniformity, reproducibility, and life than is currently available with conventional materials. The key features of the work were preparation of plaques via a powder metallurgical technique which consisted of isostatically compacting a blend of a nickel powder with a fugitive pore-former and subsequently sintering the 'green' compact. Cadmium electrodes were prepared from these materials and were cycle tested in negative-limited cells using an accelerated, torturous test regime. Results were obtained which showed the new structures yielded electrodes that were superior to the conventional structures in mechanical properties and performance.

Gordy, D. J.↗
NASA NTRS1983

Long life communication satellites: Electric power supply during the eclipse period

The electric batteries, essentially nickel-cadmium for French satellites such as D1 A, D1 C, D1 D, D2 B, D5 A, D5 B, etc. and the batteries for such satellites as Symphonie, ANS, INTASAT, ESRO 4, and COS-B are discussed. The experience obtained led to the development of long lifetime batteries for communication satellites. Real simulation tests showed a lifetime of four years and accelerated lifetime tests of twelve years. These batteries will be applied in OTS, METEOSAT, and Marots. At the same time, new batteries are being developed, based on nickel-hydrogen or on silver-hydrogen, which should provide longer lifetime and better reliability.

Font, S.↗
NASA NTRS1998

Summary of Rocketdyne Engine A5 Rocket Based Combined Cycle Testing

Rocketdyne Propulsion and Power (RPP) has completed a highly successful experimental test program of an advanced rocket based combined cycle (RBCC) propulsion system. The test program was conducted as part of the Advanced Reusable Technology program directed by NASA-MSFC to demonstrate technologies for low-cost access to space. Testing was conducted in the new GASL Flight Acceleration Simulation Test (FAST) facility at sea level (Mach 0), Mach 3.0 - 4.0, and vacuum flight conditions. Significant achievements obtained during the test program include 1) demonstration of engine operation in air-augmented rocket mode (AAR), ramjet mode and rocket mode and 2) smooth transition from AAR to ramjet mode operation. Testing in the fourth mode (scramjet) is scheduled for November 1998.

Ketchum. A.↗
NASA NTRS2001

Accomplishments of the Advanced Reusable Technologies (ART) RBCC Project at NASA/Marshall Space Flight Center

The focus of the NASA / Marshall Space Flight Center (MSFC) Advanced Reusable Technologies (ART) project is to advance and develop Rocket-Based Combined-Cycle (RBCC) technologies. The ART project began in 1996 as part of the Advanced Space Transportation Program (ASTP). The project is composed of several activities including RBCC engine ground testing, tool development, vehicle / mission studies, and component testing / development. The major contractors involved in the ART project are Aerojet and Rocketdyne. A large database of RBCC ground test data was generated for the air-augmented rocket (AAR), ramjet, scramjet, and ascent rocket modes of operation for both the Aerojet and Rocketdyne concepts. Transition between consecutive modes was also demonstrated as well as trajectory simulation. The Rocketdyne freejet tests were conducted at GASL in the Flight Acceleration Simulation Test (FAST) facility. During a single test, the FAST facility is capable of simulating both the enthalpy and aerodynamic conditions over a range of Mach numbers in a flight trajectory. Aerojet performed freejet testing in the Pebble Bed facility at GASL as well as direct-connect testing at GASL. Aerojet also performed sea-level static (SLS) testing at the Aerojet A-Zone facility in Sacramento, CA. Several flight-type flowpath components were developed under the ART project. Aerojet designed and fabricated ceramic scramjet injectors. The structural design of the injectors will be tested in a simulated scramjet environment where thermal effects and performance will be assessed. Rocketdyne will be replacing the cooled combustor in the A5 rig with a flight-weight combustor that is near completion. Aerojet's formed duct panel is currently being fabricated and will be tested in the SLS rig in Aerojet's A-Zone facility. Aerojet has already successfully tested a cooled cowl panel in the same facility. In addition to MSFC, other NASA centers have contributed to the ART project as well. Inlet testing and parametrics were performed at NASA / Glenn Research Center (GRC) and NASA / Langley Research Center (LaRC) for both the Aerojet and Rocketdyne concepts. LaRC conducted an Air-Breathing Launch Vehicle (ABLV) study for several vehicle concepts with RBCC propulsion systems. LaRC is also performing a CFD analysis of the ramjet mode for both flowpaths based on GASL test conditions. A study was performed in 1999 to investigate the feasibility of performing an RBCC flight test on the NASA / Dryden Flight Research Center (DFRC) SR-71 aircraft. Academia involvement in the ART project includes parametric RBCC flowpath testing by Pennsylvania State University (PSU). In addition to thrust and wall static pressure measurements, PSU is also using laser diagnostics to analyze the flowfield in the test rig. MSFC is performing CFD analysis of the PSU rig at select test conditions for model baseline and validation. Also, Georgia Institute of Technology (GT) conducted a vision vehicle study using the Aerojet RBCC concept. Overall, the ART project has been very successful in advancing RBCC technology. Along the way, several major milestones were achieved and "firsts" accomplished. For example, under the ART project, the first dynamic trajectory simulation testing was performed and the Rocketdyne engine A5 logged over one hour of accumulated test time. The next logical step is to develop and demonstrate a flight-weight RBCC engine system.

Nelson, Karl W.↗
NASA NTRS2000

Accelerated thermal and mechanical testing of CSP assemblies

Chip Scale Packages (CSP) are now widely used for many electronic applications including portable and telecommunication products. A test vehicle (TV-1) with eleven package types and pitches was built and tested by the JPL MicrotypeBGA Consortium during 1997 to 1999. Lessons learned by the team were published as a guidelines document for industry use. The finer pitch CSP packages which recently became available were indluded in the next test vehicle of the JPL CSP Consortium.

Chip Scale Package CSP thermal cycle fatigue solde↗
NASA NTRS2004

Reducing the Time and Cost of Testing Engines

Producing a new aircraft engine currently costs approximately $1 billion, with 3 years of development time for a commercial engine and 10 years for a military engine. The high development time and cost make it extremely difficult to transition advanced technologies for cleaner, quieter, and more efficient new engines. To reduce this time and cost, NASA created a vision for the future where designers would use high-fidelity computer simulations early in the design process in order to resolve critical design issues before building the expensive engine hardware. To accomplish this vision, NASA's Glenn Research Center initiated a collaborative effort with the aerospace industry and academia to develop its Numerical Propulsion System Simulation (NPSS), an advanced engineering environment for the analysis and design of aerospace propulsion systems and components. Partners estimate that using NPSS has the potential to dramatically reduce the time, effort, and expense necessary to design and test jet engines by generating sophisticated computer simulations of an aerospace object or system. These simulations will permit an engineer to test various design options without having to conduct costly and time-consuming real-life tests. By accelerating and streamlining the engine system design analysis and test phases, NPSS facilitates bringing the final product to market faster. NASA's NPSS Version (V)1.X effort was a task within the Agency s Computational Aerospace Sciences project of the High Performance Computing and Communication program, which had a mission to accelerate the availability of high-performance computing hardware and software to the U.S. aerospace community for its use in design processes. The technology brings value back to NASA by improving methods of analyzing and testing space transportation components.

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