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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Determination of calibration constants for the hole-drilling residual stress measurement technique applied to orthotropic composites. I - Theoretical considerations

The hole-drilling technique for the measurement of residual stresses using electrical resistance strain gages has been widely used for isotropic materials and has been adopted by the ASTM as a standard method. For thin isotropic plates, with a hole drilled through the thickness, the idealized hole-drilling calibration constants are obtained by making use of the well-known Kirsch's solution. In this paper, an analogous attempt is made to theoretically determine the three idealized hole-drilling calibration constants for thin orthotropic materials by employing Savin's (1961) complex stress function approach.

Prasad, C. B.↗
NASA NTRS1988

Measurement of the properties of lossy materials inside a finite conducting cylinder

Broadband, swept frequency measurement techniques were investigated for the evaluation of the electrical performance of thin, high temperature material coatings. Reflections and transmission measurements using an HP8510B Network Analyzer were developed for an existing high temperature test rig at NASA Lewis Research Center. Reflection measurements will be the initial approach used due to fixture simplicity even though surface wave transmission measurements would be more sensitive. The minimum goal is to monitor the electrical change of the material's performance as a function of temperature. If possible, the materials constitutive parameters, epsilon and muon will be found.

Dominek, A.↗
NASA NTRS1989

Optoelectronic Technique Eliminates Common-Mode Voltages

Small signals transmitted between circuits at large differences of potential. Technique lends itself to accurate measurement of any electrical parameter and display of value. Accommodates broad range of measured values from millivolts to hundreds of volts and provides unlimited electrical isolation. Measured parameter converted to duration, proportional to value, of pulse of light. Transmitted along optical fiber to or from isolated circuit. Applications include operation of traveling-wave tubes or other electron-gun devices including filaments at cathode potential and measurement of current from, or control of series stacked power supplies. Used for optimization and testing of depressed-collector/microwave-tube combinations.

Lesny, Gary G.↗
NASA NTRS1988

A high voltage power converter for space astronomy applications

A dc-dc low-power, high-voltage converter for use in space is described which furnishes a commandable, low-noise dc output in the range of 0 to -7500 V. The converter is suitable for biasing of detectors commonly employed in space astronomy, microchannel plates, photomultipliers, and gas discharge detectors. The converter's reliability has been demonstrated by accelerated life testing under thermal vacuum. The electrical and mechanical design, packaging, layout and fabrication techniques, and tests employed are described.

Ray, David C.↗
NASA NTRS1989

Electromagnetic properties of material coated surfaces

The electromagnetic properties of material coated conducting surfaces were investigated. The coating geometries consist of uniform layers over a planar surface, irregularly shaped formations near edges and randomly positioned, electrically small, irregularly shaped formations over a surface. Techniques to measure the scattered field and constitutive parameters from these geometries were studied. The significance of the scattered field from these geometries warrants further study.

Beard, L.↗
NASA NTRS1992

Screen Cage Ion Plating (SCIP) and scratch testing of polycrystalline aluminum oxide

A screen cage ion plating (SCIP) technique was developed to apply silver films on electrically nonconducting aluminum oxide. It is shown that SCIP has remarkable throwing power; surfaces to be coated need not be in direct line of sight with the evaporation source. Scratch tests, employing a diamond stylus with a 200 micro m radius tip, were performed on uncoated and on silver coated alumina. Subsequent surface analysis show that a significant amount of silver remains on the scratched surfaces, even in areas where high stylus load produced severe crack patterns in the ceramic. Friction coefficients were lowered during the scratch tests on the coated alumina indicating that this modification of the ion planting process should be useful for applying lubricating films of soft metals to electrical insulating materials. The very good throwing power of SCIP also strongly suggests general applicability of this process in other areas of technology, e.g., electronics, in addition to tribology.

Spalvins, Talivaldis↗
NASA NTRS1997

Growth of Bulk Wide Bandgap Semiconductor Crystals and Their Potential Applications

Developments in bulk crystal growth research for electro-optical devices in the Center for Photonic Materials and Devices since its establishment have been reviewed. Purification processes and single crystal growth systems employing physical vapor transport and Bridgman methods were assembled and used to produce high purity and superior quality wide bandgap materials such as heavy metal halides and II-VI compound semiconductors. Comprehensive material characterization techniques have been employed to reveal the optical, electrical and thermodynamic properties of crystals, and the results were used to establish improved material processing procedures. Postgrowth treatments such as passivation, oxidation, chemical etching and metal contacting during the X-ray and gamma-ray device fabrication process have also been investigated and low noise threshold with improved energy resolution has been achieved.

Chen, Kuo-Tong↗
NASA NTRS2003

Magnetic Flux Compression Experiments Using Plasma Armatures

Magnetic flux compression reaction chambers offer considerable promise for controlling the plasma flow associated with various micronuclear/chemical pulse propulsion and power schemes, primarily because they avoid thermalization with wall structures and permit multicycle operation modes. The major physical effects of concern are the diffusion of magnetic flux into the rapidly expanding plasma cloud and the development of Rayleigh-Taylor instabilities at the plasma surface, both of which can severely degrade reactor efficiency and lead to plasma-wall impact. A physical parameter of critical importance to these underlying magnetohydrodynamic (MHD) processes is the magnetic Reynolds number (R(sub m), the value of which depends upon the product of plasma electrical conductivity and velocity. Efficient flux compression requires R(sub m) less than 1, and a thorough understanding of MHD phenomena at high magnetic Reynolds numbers is essential to the reliable design and operation of practical reactors. As a means of improving this understanding, a simplified laboratory experiment has been constructed in which the plasma jet ejected from an ablative pulse plasma gun is used to investigate plasma armature interaction with magnetic fields. As a prelude to intensive study, exploratory experiments were carried out to quantify the magnetic Reynolds number characteristics of the plasma jet source. Jet velocity was deduced from time-of-flight measurements using optical probes, and electrical conductivity was measured using an inductive probing technique. Using air at 27-inHg vacuum, measured velocities approached 4.5 km/s and measured conductivities were in the range of 30 to 40 kS/m.

Turner, M. W.↗
NASA NTRS2007

Deep Space Transportation System Using the Sun-Earth L2 Point

Recently, various kinds of planetary explorations have become more feasible, taking the advantage of low thrust propulsion means such as ion engines that have come into practical use. The field of space activity has now been expanded even to the rim of the outer solar system. In this context, the Japan Aerospace Exploration Agency (JAXA) has started investigating a Deep Space Port built at the L2 Lagrange point in the Sun-Earth system. For the purpose of making the deep space port practically useful, there is a need to establish a method to making spaceship depart and return from/to the port. This paper first discusses the escape maneuvers originating from the L2 point under the restricted three-body problem. Impulsive maneuvers from the L2 point are extensively studied here, and using the results, optimal low-thrust escape strategies are synthesized. Furthermore, this paper proposes the optimal escape and acceleration maneuvers schemes using Electric Delta-V Earth Gravity Assist (EDVEGA) technique.

Matsumoto, Michihiro↗
NASA NTRS2009

A Real-Time Microwave Camera at K-Band (24 GHz)

Nondestructive testing (NDT) community has been moving towards effective and robust inspection systems that can provide real-time information about materials, geometrical, structural and mechanical characteristics of composite materials/structures. Moreover, in many applications it is desired to have an image of the structure, after which the information contained in the image is correlated to the above characteristics. Microwave signals penetrate inside of dielectric composite structures and their interaction with the interior of the structure renders critical information for NDT purposes. Subsequently, this information (i.e., magnitude and phase or reflected signal) may be used to produce an image of the interior of the structure revealing potential flaws or anomalies. Image processing and reconstruction techniques may also be incorporated to produce high-resolution images (i.e., synthetic-aperture, back-propagation, etc.). There are several different approaches for designing areal-time microwave camera system. One approach is based on modulated scatterer technique (MST), which is used to tag scattered electric field in a discrete two-dimensional (2D) spatial domain (e.g. a retina) resulting in the 2D magnitude and phase distribution of the scattered electric field which is required for producing an image of a material or structure under inspection. The ability to rapidly modulate resonant slot antennas in such a retina along with using receivers with fast responses provide for real-time image production capability. Design issue and criteria become more challenging at higher frequencies and for a relatively large retina size. This paper presents the basic design and challenges for a microwave camera with a retina size of 6" by 6" operating at a frequency of 24 GHz.

Ghasr, M. T.↗
NASA NTRS2015

Reconfigurable Very Long Instruction Word (VLIW) Processor

Future NASA missions will depend on radiation-hardened, power-efficient processing systems-on-a-chip (SOCs) that consist of a range of processor cores custom tailored for space applications. Aries Design Automation, LLC, has developed a processing SOC that is optimized for software-defined radio (SDR) uses. The innovation implements the Institute of Electrical and Electronics Engineers (IEEE) RazorII voltage management technique, a microarchitectural mechanism that allows processor cores to self-monitor, self-analyze, and selfheal after timing errors, regardless of their cause (e.g., radiation; chip aging; variations in the voltage, frequency, temperature, or manufacturing process). This highly automated SOC can also execute legacy PowerPC 750 binary code instruction set architecture (ISA), which is used in the flight-control computers of many previous NASA space missions. In developing this innovation, Aries Design Automation has made significant contributions to the fields of formal verification of complex pipelined microprocessors and Boolean satisfiability (SAT) and has developed highly efficient electronic design automation tools that hold promise for future developments.

Velev, Miroslav N.↗
NASA NTRS2017

A Novel Solid State Ultracapacitor

Novel dielectric materials were researched to develop an internal barrier layer capacitor that is fully solid state. These materials included reduced nanoparticles of barium titanate that were coated with various atomic layer deposited oxides. The nanoparticle powders were then densified into pellets and characterized using a dielectric test fixture over a frequency range of 20 Hz to 2 MHz. Densification and sintering were evaluated using scanning electron microscopic techniques. Ultimately, the samples showing the most promising electrical characteristics of permittivity, dissipation factor and equivalent series resistance were chosen to manufacture devices for subsequent testing.

Cortes-Pena, A. Y.↗
NASA NTRS1989

Combining electric field and aurora observations from DE 1 and 2 with ground magnetometer records to estimate ionospheric electromagnetic quantities

Global distribution of electric fields and currents in the high-latitude ionosphere was estimated using data from the ground-based network of magnetometers and from nearly simultaneous observations with DE 1 and DE 2 satellites. The electric field and current distributions at high altitudes were calculated from instantaneous ionospheric conductivity (estimated from the DE 1 auroral data), using the Kamide et al. (1981) magnetogram inversion technique; an optimum conductivity was then chosen iteratively so that the resultant electric fields would become consistent with electric field deduced from ion drifts measured along the DE-2 orbit. It is demonstrated that, when analyzing the large-scale electrodynamics of individual substorms, statistical conductivity models are not fully adequate for use with the magnetogram inversion technique.

Kamide, Y.↗
NASA NTRS2004

Probabilistic Physics-Based Risk Tools Used to Analyze the International Space Station Electrical Power System Output

This paper describes the methods employed to apply probabilistic modeling techniques to the International Space Station (ISS) power system. These techniques were used to quantify the probabilistic variation in the power output, also called the response variable, due to variations (uncertainties) associated with knowledge of the influencing factors called the random variables. These uncertainties can be due to unknown environmental conditions, variation in the performance of electrical power system components or sensor tolerances. Uncertainties in these variables, cause corresponding variations in the power output, but the magnitude of that effect varies with the ISS operating conditions, e.g. whether or not the solar panels are actively tracking the sun. Therefore, it is important to quantify the influence of these uncertainties on the power output for optimizing the power available for experiments.

Patel, Bhogila M.↗
NASA NTRS2011

Detecting Cracks in Ceramic Matrix Composites by Electrical Resistance

The majority of damage in SiC/SiC ceramic matrix composites subjected to monotonic tensile loads is in the form of distributed matrix cracks. These cracks initiate near stress concentrations, such as 90o fiber tows or large matrix pores and continue to accumulate with additional stress until matrix crack saturation is achieved. Such damage is difficult to detect with conventional nondestructive evaluation techniques (immersion ultrasonics, x-ray, etc.). Monitoring a specimen.s electrical resistance change provides an indirect approach for monitoring matrix crack density. Sylramic-iBN fiber- reinforced SiC composites with a melt infiltrated (MI) matrix were tensile tested at room temperature. Results showed an increase in resistance of more than 500% prior to fracture, which can be detected either in situ or post-damage. A relationship between resistance change and matrix crack density was also determined.

Smith, Craig↗
NASA NTRS1994

A New Electromagnetic Instrument for Thickness Gauging of Conductive Materials

Eddy current techniques are widely used to measure the thickness of electrically conducting materials. The approach, however, requires an extensive set of calibration standards and can be quite time consuming to set up and perform. Recently, an electromagnetic sensor was developed which eliminates the need for impedance measurements. The ability to monitor the magnitude of a voltage output independent of the phase enables the use of extremely simple instrumentation. Using this new sensor a portable hand-held instrument was developed. The device makes single point measurements of the thickness of nonferromagnetic conductive materials. The technique utilized by this instrument requires calibration with two samples of known thicknesses that are representative of the upper and lower thickness values to be measured. The accuracy of the instrument depends upon the calibration range, with a larger range giving a larger error. The measured thicknesses are typically within 2-3% of the calibration range (the difference between the thin and thick sample) of their actual values. In this paper the design, operational and performance characteristics of the instrument along with a detailed description of the thickness gauging algorithm used in the device are presented.

Fulton, J. P.↗
NASA NTRS2011

Detecting Damage in Ceramic Matrix Composites Using Electrical Resistance

The majority of damage in SiC/SiC ceramic matrix composites subjected to monotonic tensile loads is in the form of distributed matrix cracks. These cracks initiate near stress concentrations, such as 90 deg fiber tows or large matrix pores and continue to accumulate with additional stress until matrix crack saturation is achieved. Such damage is difficult to detect with conventional nondestructive evaluation techniques (immersion ultrasonics, x-ray, etc.). Monitoring a specimen.s electrical resistance change provides an indirect approach for monitoring matrix crack density. Sylramic-iBN fiber- reinforced SiC composites with a melt infiltrated (MI) matrix were tensile tested at room temperature. Results showed an increase in resistance of more than 500% prior to fracture, which can be detected either in situ or post-damage. A relationship between resistance change and matrix crack density was also determined.

Smith, Craig E.↗