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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 1,207 records · Page 67

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NASA NTRS1992

Chemical vapor deposition modeling for high temperature materials

The formalism for the accurate modeling of chemical vapor deposition (CVD) processes has matured based on the well established principles of transport phenomena and chemical kinetics in the gas phase and on surfaces. The utility and limitations of such models are discussed in practical applications for high temperature structural materials. Attention is drawn to the complexities and uncertainties in chemical kinetics. Traditional approaches based on only equilibrium thermochemistry and/or transport phenomena are defended as useful tools, within their validity, for engineering purposes. The role of modeling is discussed within the context of establishing the link between CVD process parameters and material microstructures/properties. It is argued that CVD modeling is an essential part of designing CVD equipment and controlling/optimizing CVD processes for the production and/or coating of high performance structural materials.

Gokoglu, Suleyman A.↗

NASA NTRS1990

Reliability in CMOS IC processing

Critical CMOS IC processing reliability monitors are defined in this paper. These monitors are divided into three categories: process qualifications, ongoing production workcell monitors, and ongoing reliability monitors. The key measures in each of these categories are identified and prioritized based on their importance.

Shreeve, R.↗

NASA NTRS1993

General overview of an integrated lunar oxygen production/brickmaking system

On the moon, various processing systems would compete for the same resources, most notably power, raw materials, and perhaps human attention. Therefore, it may be advantageous for two or more processes to be combined such that the integrated system would require fewer resources than separate systems working independently. The synergistic marriage of two such processes--lunar oxygen production and the manufacture of bricks from sintered lunar regolith--is considered.

Altemir, D. A.↗

NASA NTRS1993

Design and specification of a centralized manufacturing data management and scheduling system

As was revealed in a previous study, the Materials and Processes Laboratory's Productivity Enhancement Complex (PEC) has a number of automated production areas/cells that are not effectively integrated, limiting the ability of users to readily share data. The recent decision to utilize the PEC for the fabrication of flight hardware has focused new attention on the problem and brought to light the need for an integrated data management and scheduling system. This report addresses this need by developing preliminary designs specifications for a centralized manufacturing data management and scheduling system for managing flight hardware fabrication in the PEC. This prototype system will be developed under the auspices of the Integrated Engineering Environment (IEE) Oversight team and the IEE Committee. At their recommendation the system specifications were based on the fabrication requirements of the AXAF-S Optical Bench.

Farrington, Phillip A.↗

NASA NTRS1992

HSCT airframe materials: The Boeing perspective

Vugraphs are presented on the effect of cruise Mach number on the maximum takeoff weight of the High Speed Commercial Transport (HSCT). Predictions are made of the service life of the aircraft, and the aging effects of various candidate materials are examined. The objective of the study is to develop and evaluate low cost airplane designs by examining alternate structural, material, and manufacturing concepts, for the purpose of advising material suppliers and NASA on desired materials, product forms, and processing techniques.

Grande, Donald L.↗

NASA NTRS1994

Analysis of phase distribution phenomena in microgravity environments

In the past one of NASA's primary emphasis has been on identifying single and multiphase flow experiments which can produce new discoveries that are not possible except in a microgravity environment. While such experiments are obviously of great scientific interest, they do not necessarily provide NASA with the ability to use multiphase processes for power production and/or utilization in space. The purpose of the research presented in this paper is to demonstrate the ability of multidimensional two-fluid models for bubbly two-phase flow to accurately predict lateral phase distribution phenomena in microgravity environments. If successful, this research should provide NASA with mechanistically-based analytical methods which can be used for multiphase space design and evaluation, and should be the basis for future shuttle experiments for model verification.

Lahey, Richard, Jr.↗

NASA NTRS1991

Boron-carbon-silicon polymers and the ceramic thereof

The present invention relates to a process for the production of an organoborosilicon preceramic polymer. The prepolymer is pyrolyzed to produce a ceramic article useful in high temperature (e.g., aerospace) or extreme environmental applications.

Riccitiello, Salvatore R.↗

NASA NTRS1994

The validation by measurement theory of proposed object-oriented software metrics

Moving software development into the engineering arena requires controllability, and to control a process, it must be measurable. Measuring the process does no good if the product is not also measured, i.e., being the best at producing an inferior product does not define a quality process. Also, not every number extracted from software development is a valid measurement. A valid measurement only results when we are able to verify that the number is representative of the attribute that we wish to measure. Many proposed software metrics are used by practitioners without these metrics ever having been validated, leading to costly but often useless calculations. Several researchers have bemoaned the lack of scientific precision in much of the published software measurement work and have called for validation of software metrics by measurement theory. This dissertation applies measurement theory to validate fifty proposed object-oriented software metrics (Li and Henry, 1993; Chidamber and Kemerrer, 1994; Lorenz and Kidd, 1994).

Neal, Ralph D.↗

NASA NTRS1995

The Validation by Measurement Theory of Proposed Object-Oriented Software Metrics

Neal, Ralph D.↗

NASA NTRS1995

Neutral solar wind evolution during solar cycle

The time dependent model of the expected fluxes of the neutral H and He components of the solar wind in the inner heliosphere is discussed. The model takes into account typical temporal evolution of the distribution of neutral interstellar gases (hydrogen and helium) in the interplanetary space due to solar cycle effects and the long term variability of the solar wind. The contribution of different charge exchange processes to the production of particular NSW element is presented. The distribution of the NSW flux is analysed with respect to the heliocentric distance and azimuthal angle from the Interstellar Wind apex. It demonstrates significant, time-dependent upwind/downwind H and He flux asymmentries. It is shown that the most pronounced modulation of the NSW flux is expected around the solar maximum epoch, when a strong decrease of the energetic H flux by two three orders of magnitude at 1 AU is predicted. The computations show that in the inner solar system (approx. 1 AU) energetic helium atoms production in the downwind region usually dominates the production of the hydrogen component This leads to the conclusion that the NSW composition at the Earth orbit strongly depends on time and the position of the observation point in reference to the apex direction.

Bzowski, M.↗

NASA NTRS1996

A Software Quality Model and Metrics for Risk Assessment

A software quality model and its associated attributes are defined and used as the model for the basis for a discussion on risk. Specific quality goals and attributes are selected based on their importance to a software development project and their ability to be quantified. Risks that can be determined by the model's metrics are identified. A core set of metrics relating to the software development process and its products is defined. Measurements for each metric and their usability and applicability are discussed.

L Hyatt↗

NASA NTRS1996

The Validation by Measurement Theory of Proposed Object-Oriented Software Metrics

Neal, Ralph D.↗

NASA NTRS1996

Ionospheric Profiling using GPS/MET Data

A report on ionospheric profiling using GPS and MET data is presented. A description of the GPS occultation technique, some examples of GPS/MET data products, the data processing system and a preliminary validation of ionospheric profiles is discussed.

Hajj, George↗

NASA NTRS1997

Chondritic Meteorites: Nebular and Parent-Body Formation Process

Chondritic meteorites are the products of condensation, agglomeration and accretion of material in the solar nebula; these objects are the best sources of information regarding processes occurring during the early history of the solar system. We obtain large amounts of high-quality chemical and petrographic data and use them to infer chemical fractionation processes that occurred in the solar nebula and on meteorite parent bodies during thermal metamorphism, shock metamorphism and aqueous alteration. We compare diverse groups of chondrites and model their different properties in terms of processes that differed at different nebular locations or on different parent-bodies. In order to expand our set of geochemically important elements (particularly Si, C, P and S) and to distinguish the different oxidation states of Fe, Greg Kallemeyn spent three months (1 Sept. - 30 Nov. 1995) at the Smithsonian Institution to learn Eugene Jarosewich's wet chemical techniques. Key specimens from the recently established CK, CR and R chondrite groups were analyzed.

Rubin, Alan E.↗

NASA NTRS1997

The High-Energy Continuum Emission of the Gamma-Ray Blazar PKS 0528+134

We present Advanced Satellite for Cosmology and Astrophysics (ASCA) observations of the gamma-ray blazar PKS 0528 + 134, obtained at two separate epochs in 1994 August and 1995 March. These data represent the first measurement of the X-ray continuum emission of this source in the medium-hard X-ray band. Both ASCA spectra are consistent with a single power law with photon index GAMMA approximate 1.7-1.8 and column density N(sub H) approximately 5 x 10(exp 21) /sq cm, higher than Galactic. The X-ray flux increased by a factor of 4 in approximately 7 months without appreciable change of the spectral shape. During the lower state of 1994 August, PKS 0528 + 134 was observed simultaneously in the optical, X-rays, and at gamma-ray energies with EGRET. The gamma-ray intensity is the faintest detected thus far in the source, with a steep spectrum (GAMMA approximately 2.7). The extrapolation of the X-ray continuum to the gamma-ray range requires a sharp spectral break at approximately 10(exp 22) Hz. We discuss the radio through gamma-ray spectral energy distribution of PKS 0528 + 134, comparing the low state of 1994 August with the flare state of 1993 March. We show that in PKS 0528 + 134, a non-negligible contribution from the external radiation field is present and that, although synchrotron self-Compton scenarios cannot be ruled out, inverse Compton upscattering of thermal seed photons may be the dominant cooling process for the production of the high-energy continuum in this blazar.

Sambruna, Rita M.↗

NASA NTRS1997

The High-energy Continuum Emission of the Gamma-Ray Blazar PKS 0528+134

We present Advanced Satellite for Cosmology and Astrophysics (ASCA) observations of the gamma-ray blazar PKS 0528 + 134, obtained at two separate epochs in 1994 August and 1995 March. These data represent the first measurement of the X-ray continuum emission of this source in the medium-hard X-ray band. Both ASCA spectra are consistent with a single power law with photon index GAMMA approx. = 1.7-1.8 and column density N(sub H) approx. = 5 x 10(exp 21)/ sq cm, higher than Galactic. The X-ray flux increased by a factor of 4 in approx. 7 months without appreciable change of the spectral shape. During the lower state of 1994 August, PKS 0528 + 134 was observed simultaneously in the optical, X-rays, and at gamma-ray energies with Energetic Gamma Ray Experiment Telescope (EGRET). The gamma-ray intensity is the faintest detected thus far in the source, with a steep spectrum (GAMMA approx. = 2.7). The extrapolation of the X-ray continuum to the gamma-ray range requires a sharp spectral break at approx. 10(exp 22) Hz. We discuss the radio through gamma-ray spectral energy distribution of PKS 0528 + 134, comparing the low state of 1994 August with the flare state of 1993 March. We show that in PKS 0528 + 134, a non-negligible contribution from the external radiation field is present and that, although synchrotron self-Compton scenarios cannot be ruled out, inverse Compton upscattering of thermal seed photons may be the dominant cooling process for the production of the high-energy continuum in this blazar.

Sambruna, Rita M.↗

NASA NTRS2000

PROPULSE 980: A Hydrogen Peroxide Enrichment System

The PROPULSE 980 unit is a transportable processing plant that enriches aerospace grade hydrogen peroxide from 90% to 98% final concentration. The unit was developed by Degussa-H Is, in cooperation with Orbital, NASA Marshall Space Center, and NASA Stennis Space Center. The system is a self-contained unit that houses all of the process equipment, instrumentation and controls to perform the concentration operation nearly autonomously. It is designed to produce non-bulk quantities of 98% hydrogen peroxide. The enrichment unit design also maintains system, personnel and environmental safety during all aspects of the enrichment process and final product storage. As part of the Propulse 980 checkout and final buyoff, it will be disassembled at the Degussa-H Is Corporation plant in Theodore, AL, transported to the Stennis Space Center, reassembled and subjected to a series of checkout tests to verify design objectives have been met. This paper will summarize the basic project elements and provide an update on the present status of the project.

Boxwell, Robert↗

NASA NTRS2001

Continued Investigations of the Accretion History of Extraterrestrial Matter over Geologic Time

This grant supported our ongoing project to characterize the accretion rate of interplanetary dust particles (IDPs) to Earth over geologic time using He-3 as a tracer. IDPs are derived from collisions in the asteroid belt and from disaggregation of active comets. Owing to their small size (few to few hundred micrometers diameter) these particles spiral into the sun under Poynting-Robertson drag typically in less than a few tens of kyrs. Thus IDPs must be continually resupplied to the zodiacal cloud, and because the processes of IDP production are likely to be sporadic, time variation in the IDP accretion rate to Earth is likely to be time-varying. For example, major asteroidal collisions and comet showers should greatly enhance the IDP accretion rate. Our ultimate objective (still ongoing) is to document this time variance so as to better understand the history of the solar system, the source of IDPs accreting to Earth, and the details of the mechanism by which particles are captured by Earth. To document variations in IDP accretion rate through time we use He-3 as a tracer. This isotope is in extremely low abundance in terrestrial matter, but IDPs have very high concentrations of He-3 from implantation of solar wind ions. By measuring He-3 in seafloor sediments, we can estimate the IDP accretion rate for at least the last few hundred Myrs. Under an earlier NASA grant we identified the existence of a large increase in He-3 flux in the Late Eocene (35 Myr ago), coincident with the two largest impact craters of the Cenozoic Era. The simplest interpretation of this observation is the occurrence of a shower of long period comets at that time, simultaneously increasing the impact cratering probability and accretion rate of IDPs to Earth (Farley et al., 1998). Comet showers produced by stellar perturbation of the Oort cloud should be fairly common in the geologic record, so this is not an unreasonable interpretation of our observations.

Farley, Kenneth↗