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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The Hubble Space Telescope extragalactic distance scale key project. 2: Photometry of WFC images of M81

The Extragalactic Distance Scale (H(sub o)) Key Project for Hubble Space Telescope (HST) aims to employ the Cepheid period-luminosity (P-L) relation to measure galaxy distances out as far as the Virgo Cluster. The vital steps in this program are (1) to obtain precise photometry of stellar images from the Wide Field Camera (WFC) exposures of selected galaxies, and (2) to calibrate this photometry to obtain reliable distances to these galaxies from the Cepheid P-L relation. We have used the DAOPHOT II and ALLFRAME programs to determine 28 instrumental magnitudes -- 22 of F555W (of about V) and six of F785LP (of about I) -- of all stars brighter than V of about 25 in each of two 2.56 arcmin x 2.56 arcmin WFC fields of M81. The reductions use a varying point-spread function to account for the field effects in the WFC optics and yield instrumental magnitudes with single epoch precision ranging from 0.09 to 0.24 mag, at V of about 21.8 to 23.8 -- the magnitude range of the 30 Cepheids that we have now identified in M81. For brighter stars (V of about 22), single epoch magnitudes are precise to 0.09 mag. The photometric calibration onto the Johnson V and Kron-Cousins I systems was determined from independent ground-based CCD observing at the Canada-France-Hawaii Telescope (CFHT) 3.6 m (confirmed by the Kitt Peak National Observatory (KPNO) 4.0 m) and from the Palomar 5.0 m (using the wide-field COSMIC camera) and 1.5 m telescopes. Secondary standards, taken from the COSMIC and CFHT frames, were established in each of the WFC fields in V and I, allowing a direct transformation from ALLFRAME magnitudes to calibrated V and I magnitudes, giving mean V of about 23 magnitudes accurate to of about +/- 0.1 mag. The stellar populations in M81 have been analyzed in terms of the luminosity functions and color magnitude diagrams (CMD) derived from these data, from which we identify numerous supergiants, and a CMD morphology similar to M33.

Hughes, Shaun M. G.↗
NASA NTRS1994

The HST Quasar Absorption-Line Key Project. 8: CCD imaging of Hubble Space Telescope quasar fields

We present an analysis of CCD images of more than 100 quasars; many of the objects have been or will be observed in the Hubble Space Telescope (HST) Key Project Quasar Absorption-Line Survey. The data set consists of B, g, and i photometry of 117 quasars and deeper g (limiting magnitude of approximately equal 22) images of 101 quasar fields. Positions accurate to approximately equal 1 sec, measured with the Space Telescope Science Institute's Astrometric Support Program, are listed for all of the quasars in this study. Positions, magnitudes, and classifications of stars and galaxies located within approximately equal 100 sec of the quasars are given for all of the deep g data. The positions of the stars and galaxies relative to the quasar are accurate to approximately equal 0.5 sec. The results presented here can be used to prepare spectroscopic programs designed to obtain redshifts of galaxies in the fields of these quasars.

Kirhakos, Sofia↗
NASA NTRS1995

Key design issues for user terminals operating with HEO satellites

Coverage of high-latitude areas in the northern hemisphere using geostationary satellites can not be achieved with good elevation angles, and highly inclined elliptical orbits (HEO) present one possible way to overcome this problem. The high elevation angles they achieve and the relative motion of the satellites across the sky, including satellite hand-over, present a specific set of requirements for the design of user terminals, be they for communication or broadcast-reception purposed. This paper reviews key design issues for user terminals operating with satellites in highly inclined elliptical orbits. While all aspects of user terminal design are broadly covered, special emphasis is given to the antenna and RF front-end design. The types of terminals discussed include communications terminals: the hand-held, the notebook, and the vehicle-mounted types, as well as the vehicle-mounted digital audio broadcasting (DAB) receiver terminal. A number of solutions are outlined, based on tradeoffs with respect to the most significant system interface parameters such as G/T and equivalent isotropically radiated power (EIRP). Candidate antenna and front-end configurations were studied, in particular patch and helical antennas with the principal aim of deriving low cost, yet effective solutions. Issues related to achieving best EIRP for the communications terminals are presented, taking into account radiation safety limits. The differences in the design of receive only versus receive/transmit RF front-ends for HEO system terminals are highlighted and solutions for both proposed. This paper summarizes the results of internal ESTEC studies and external ESA-sponsored work concerning major user terminal parameters and design aspects performed for Archimedes -- a HEO satellite constellation for multimedia broadcasting and communications.

Stojkovic, I.↗
NASA NTRS1996

Key Topics for High-Lift Research: A Joint Wind Tunnel/Flight Test Approach

Future high-lift systems must achieve improved aerodynamic performance with simpler designs that involve fewer elements and reduced maintenance costs. To expeditiously achieve this, reliable CFD design tools are required. The development of useful CFD-based design tools for high lift systems requires increased attention to unresolved flow physics issues. The complex flow field over any multi-element airfoil may be broken down into certain generic component flows which are termed high-lift building block flows. In this report a broad spectrum of key flow field physics issues relevant to the design of improved high lift systems are considered. It is demonstrated that in-flight experiments utilizing the NASA Dryden Flight Test Fixture (which is essentially an instrumented ventral fin) carried on an F-15B support aircraft can provide a novel and cost effective method by which both Reynolds and Mach number effects associated with specific high lift building block flows can be investigated. These in-flight high lift building block flow experiments are most effective when performed in conjunction with coordinated ground based wind tunnel experiments in low speed facilities. For illustrative purposes three specific examples of in-flight high lift building block flow experiments capable of yielding a high payoff are described. The report concludes with a description of a joint wind tunnel/flight test approach to high lift aerodynamics research.

Fisher, David↗
NASA NTRS1997

SSME Key Operations Demonstration

A Space Shuttle Main Engine (SSME) test program was conducted between August 1995 and May 1996 using the Technology Test Bed (TTB) Engine. SSTO vehicle studies have indicated that increases in the propulsion system operating range can save significant weight and cost at the vehicle level. This test program demonstrated the ability of the SSME to accommodate a wide variation in safe operating ranges and therefore its applicability to the SSTO mission. A total of eight tests were completed with four at Marshall Space Flight Center's Advanced Engine Test Facility and four at the Stennis Space Center (SSC) A-2 attitude test stand. Key demonstration objectives were: 1) Mainstage operation at 5.4 to 6.9 mixture ratio; 2) Nominal engine start with significantly reduced engine inlet pressures of 50 psia LOX and 38 psia fuel; and 3) Low power level operation at 17%, 22%, 27%, 40%, 45%, and 50% of Rated Power Level. Use of the highly instrumented TTB engine for this test series has afforded the opportunity to study in great detail engine system operation not possible with a standard SSME and has significantly contributed to a greater understanding of the capabilities of the SSME and liquid rocket engines in general.

Anderson, Brian↗
NASA NTRS1999

Infrared Space Observatory (ISO) Key Project: the Birth and Death of Planets

This program was designed to continue to analyze observations of stars thought to be forming protoplanets, using the European Space Agency's Infrared Space Observatory, ISO, as one of NASA Key Projects with ISO. A particular class of Infrared Astronomy Satellite (IRAS) discovered stars, known after the prototype, Vega, are principal targets for these observations aimed at examining the evidence for processes involved in forming, or failing to form, planetary systems around other stars. In addition, this program continued to provide partial support for related science in the WIRE, SOFIA and Space Infrared Telescope Facility (SIRTF) projects, plus approved ISO supplementary time observations under programs MCREE1 29 and VEGADMAP. Their goals include time dependent changes in SWS spectra of Long Period Variable stars and PHOT P32 mapping experiments of recognized protoplanetary disk candidate stars.

Stencel, Robert E.↗
NASA NTRS1999

Key Durability Issues with Mullite-Based Environmental Barrier Coatings for Si-Based Ceramics

Plasma-sprayed mullite (3Al2O3 central dot 2SiO2) and mullite/yttria-stabilized-zirconia (YSZ) dual layer coatings have been developed to protect silicon-based ceramics from environmental attack. Mullite-based coating systems show excellent durability in air. However, in combustion environments, corrosive species such as molten salt or water vapor penetrate through cracks in the coating and attack the Si-based ceramics along the interface, Thus modification of the coating system for enhanced crack-resistance is necessary for long-term durability in combustion environments. Other key durability issues include interfacial contamination and coating/substrate bonding. Interfacial contamination leads to enhanced oxidation and interfacial pore formation, while weak coating/substrate bonding leads to rapid attack of the interface by corrosive species, both of which can cause premature failure of the coating. Interfacial contamination can be minimized by limiting impurities in coating and substrate materials. The interface may be modified to improve the coating/substrate bond.

Lee, Kang N.↗
NASA NTRS2000

Application of ANFIS to Phase Estimation for Multiple Phase Shift Keying

The paper discusses a novel use of Adaptive Neuro-Fuzzy Inference Systems (ANFIS) for estimating phase in Multiple Phase Shift Keying (M-PSK) modulation. A brief overview of communications phase estimation is provided. The modeling of both general open-loop, and closed-loop phase estimation schemes for M-PSK symbols with unknown structure are discussed. Preliminary performance results from simulation of the above schemes are presented.

Drake, Jeffrey T.↗
NASA NTRS2000

North Atlantic Aerosol Properties and Direct Radiative Effects: Key Results from TARFOX and ACE-2

Aerosol effects on atmospheric radiative fluxes provide a forcing function that can change the climate In potentially significant ways. This aerosol radiative forcing is a major source of uncertainty in understanding the observed climate change of the past century and in predicting future climate. To help reduce this uncertainty, the International Global Atmospheric Chemistry Project (IGAC) has endorsed a series of multiplatform aerosol field campaigns. The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the second Aerosol Characterization Experiment (ACE-2) were the first IGAC campaigns to address the impact of anthropogenic aerosols, Both TARFOX and ACE-2 gathered extensive data sets on aerosol properties and radiative effects, TARFOX focused on the urban-industrial haze plume flowing from the eastern United States over the western Atlantic Ocean, whereas ACE-2 studied aerosols carried over the eastern Atlantic from both European urban/industrial and African mineral sources. These aerosols often have a marked influence on the top-of-atmosphere radiances measured by satellites. Shown there are contours of aerosol optical depth derived from radiances measured by the AVHRR sensor on the NOAA-11 satellite. The contours readily show that aerosols originating in North America, Europe, and Africa impact the radiative properties of air over the North Atlantic. However, the accurate derivation of flux changes, or radiative forcing, from the satellite measured radiances or retrieved optical depths remains a difficult challenge. In this paper we summarize key initial results from TARFOX and, to a lesser extent, ACE-2, with a focus on those results that allow an improved assessment of the flux changes caused by North Atlantic aerosols at middle latitudes.

Russell, P. B.↗
NASA NTRS2000

Key Durability Issues with Mullite-Based Environmental Barrier Coatings for Si-Based Ceramics

Plasma-sprayed mullite (3Al2O3.2SiO2) and mullite/yttria-stabilized-zirconia (YSZ) dual layer coatings have been developed to protect silicon -based ceramics from environmental attack. Mullite-based coating systems show excellent durability in air. However, in combustion environments, corrosive species such as molten salt or water vapor penetrate through cracks in the coating and attack the Si-based ceramics along the interface. Thus the modification of the coating system for enhanced crack-resistance is necessary for long-term durability in combustion environments. Other key durability issues include interfacial contamination and coating/substrate bonding. Interfacial contamination leads to enhanced oxidation and interfacial pore formation, while a weak coating/substrate bonding leads to rapid attack of the interface by corrosive species, both of which can cause a premature failure of the coating. Interfacial contamination can be minimized by limiting impurities in coating and substrate materials. The interface may be modified to improve the coating/substrate bond.

Lee, Kang N.↗
NASA NTRS1997

Petaflops Computing: The Key Algorithmic Challenges

The prospect of petaflops-class computers brings to the fore some important algorithmic issues that have been considered in the high performance computing community for several years. Key among them are (1) concurrency (whether the fundamental concurrency of an algorithm is sufficient to keep thousands of processors productively busy); (2) data locality; (3) latency tolerance; and (4) memory and operation count scaling. This introductory presentation will give an overview of these issues.

Bailey, David H.↗
NASA NTRS1998

North Atlantic Aerosol Properties and Direct Radiative Effects: Key Results from TARFOX and ACE-2

Aerosol effects on atmospheric radiative fluxes provide a forcing function that can change the climate in potentially significant ways. This aerosol radiative Forcing is a major source of uncertainty in understanding the observed climate change of the past century and in predicting, future climate. To help reduce this uncertainty, the International Global Atmospheric Chemistry Project (IGAC) has endorsed a series of multiplatform aerosol field campaigns. The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the second Aerosol Characterization Experiment (ACE-2) were the first IGAC campaigns to address the impact of anthropogenic aerosols. Both TARFOX and ACE-2 gathered extensive data sets on aerosol properties and radiative effects. TARFOX focused on the urban-industrial haze plume flowing from the eastern United States over the western Atlantic Ocean, whereas ACE-2 studied aerosols carried over the eastern Atlantic from both European urban/industrial and African mineral sources. These aerosols often have a marked influence on the top-of-atmosphere radiances measured by satellites, as illustrated in Figure 1. Shown there are contours of aerosol optical depth derived from radiances measured by the AVHRR sensor on the NOAA-11 satellite. The contours readily show that aerosols originating in North America, Europe, and Africa impact the radiative properties of air over the North Atlantic. However, the accurate derivation of flux chances, or radiative forcing, from the satellite-measured radiances or 'etrieved optical depths remains a difficult challenge. In this paper we summarize key Initial results from TARFOX and, to a lesser extent ACE-2, with a focus on those results that allow an improved assessment of the flux changes caused by North Atlantic aerosols at middle and high latitudes.

Russell, P. B.↗
NASA NTRS2000

Regulation of sucrose metabolism in higher plants: localization and regulation of activity of key enzymes

Sucrose (Suc) plays a central role in plant growth and development. It is a major end product of photosynthesis and functions as a primary transport sugar and in some cases as a direct or indirect regulator of gene expression. Research during the last 2 decades has identified the pathways involved and which enzymes contribute to the control of flux. Availability of metabolites for Suc synthesis and 'demand' for products of sucrose degradation are important factors, but this review specifically focuses on the biosynthetic enzyme sucrose-phosphate synthase (SPS), and the degradative enzymes, sucrose synthase (SuSy), and the invertases. Recent progress has included the cloning of genes encoding these enzymes and the elucidation of posttranslational regulatory mechanisms. Protein phosphorylation is emerging as an important mechanism controlling SPS activity in response to various environmental and endogenous signals. In terms of Suc degradation, invertase-catalyzed hydrolysis generally has been associated with cell expansion, whereas SuSy-catalyzed metabolism has been linked with biosynthetic processes (e.g., cell wall or storage products). Recent results indicate that SuSy may be localized in multiple cellular compartments: (1) as a soluble enzyme in the cytosol (as traditionally assumed); (2) associated with the plasma membrane; and (3) associated with the actin cytoskeleton. Phosphorylation of SuSy has been shown to occur and may be one of the factors controlling localization of the enzyme. The purpose of this review is to summarize some of the recent developments relating to regulation of activity and localization of key enzymes involved in sucrose metabolism in plants.

NASA Discipline Plant Biology↗
NASA NTRS2005

Key Reliability Drivers of Liquid Propulsion Engines and A Reliability Model for Sensitivity Analysis

This paper is to address the in-flight reliability of a liquid propulsion engine system for a launch vehicle. We first establish a comprehensive list of system and sub-system reliability drivers for any liquid propulsion engine system. We then build a reliability model to parametrically analyze the impact of some reliability parameters. We present sensitivity analysis results for a selected subset of the key reliability drivers using the model. Reliability drivers identified include: number of engines for the liquid propulsion stage, single engine total reliability, engine operation duration, engine thrust size, reusability, engine de-rating or up-rating, engine-out design (including engine-out switching reliability, catastrophic fraction, preventable failure fraction, unnecessary shutdown fraction), propellant specific hazards, engine start and cutoff transient hazards, engine combustion cycles, vehicle and engine interface and interaction hazards, engine health management system, engine modification, engine ground start hold down with launch commit criteria, engine altitude start (1 in. start), Multiple altitude restart (less than 1 restart), component, subsystem and system design, manufacturing/ground operation support/pre and post flight check outs and inspection, extensiveness of the development program. We present some sensitivity analysis results for the following subset of the drivers: number of engines for the propulsion stage, single engine total reliability, engine operation duration, engine de-rating or up-rating requirements, engine-out design, catastrophic fraction, preventable failure fraction, unnecessary shutdown fraction, and engine health management system implementation (basic redlines and more advanced health management systems).

Huang, Zhao-Feng↗
NASA NTRS2003

Multiple bit differential detection of offset quadrature phase-shift-keying

Analogous to multiple symbol differential detectionof quadrature phase-shift-keying (QPSK), a multiple bit differential detection scheme is described for offset QPSK that also exhibits continuous improvement in performance with increasing observation interval. Being derived from maximum-likelihood (ML) considerations, the proposed scheme is purported to be the most power efficient scheme for such a modulation and detection method. Extension of the results to shaped offset QPSK is also possible.

Digital communications offset quadriphase modulati↗
NASA NTRS1998

Key Factors on CSP Assembly Reliability

Although the weakest link of CSP assembly reliability has been often internal package failure, solder joint fatigue is still considered to be the key factor for reliability.

CSP assembly reliability solder joints↗
NASA NTRS1996

The Extragalactic Distance Scale Key Project VIII. The Discovery of Cepheids and a New Distance to NGC 3621 Using the Hubble Space Telescope

We report on the discovery of Cepheids in the field spiral galaxy NGC3621, based on observations made with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 3621 is one of 18 galaxies observed as part of the HST Key Project on the Extragalctic Distance Scale, which aims to measure the Hubble Constant to 10 percent accuracy.

galaxies NGC 3621 stars cepheids Hubble constant↗