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At least 613 records · Page 34

Development of stitched/RTM primary structures for transport aircraft

This report covers work accomplished in the Innovative Composite Aircraft Primary Structure (ICAPS) program. An account is given of the design criteria and philosophy that guides the development. Wing and fuselage components used as a baseline for development are described. The major thrust of the program is to achieve a major cost breakthrough through development of stitched dry preforms and resin transfer molding (RTM), and progress on these processes is reported. A full description is provided on the fabrication of the stitched RTM wing panels. Test data are presented.

Hawley, Arthur V.↗

Primary results from the Berkeley EUV airglow rocket spectrometer: O I and N2 FUV/EUV dayglow in the thermosphere and lower exosphere

The Berkeley extreme-ultraviolet airglow rocket spectrometer (BEARS) made spectroscopic measurements of far and extreme UV, atomic oxygen emissions from a Black Brandt XII (12.041 WT) sounding rocket launched from Wallops Island, Virginia, on September 30, 1988. BEARS' primary instrument, a near-normal Rowland mount spectrometer, measured several atomix oxygen and molecular nitrogen dayglow features at high spectral resolution (1.5 A): O I (989, 1027, 1304, and 1356 A); and N2 Lyman-Birge-Hopfield (4, 0) and (3, 0) bands at 1325 and 1354 A. The instrument collected over 800 s of data spanning altitudes of 150 - 963 km with look directions between 95 deg and 125 deg from zenith. We have analyzed the data using electrons and radiative transport models in a forward modeling approach. The model and data are generally in good agreement. However, there are some discrepancies, which are discussed in terms of remote sensing capabilities and improvements to the models.

Cotton, Daniel M.↗

Ground-based grasslands data to support remote sensing and ecosystem modeling of terrestrial primary production

Estimating terrestrial net primary production (NPP) using remote-sensing tools and ecosystem models requires adequate ground-based measurements for calibration, parameterization, and validation. These data needs were strongly endorsed at a recent meeting of ecosystem modelers organized by the International Geosphere-Biosphere Program's (IGBP's) Data and Information System (DIS) and its Global Analysis, Interpretation, and Modelling (GAIM) Task Force. To meet these needs, a multinational, multiagency project is being coordinated by the IGBP DIS to compile existing NPP data from field sites and to regionalize NPP point estimates to various-sized grid cells. Progress at Oak Ridge National Laboratory (ORNL) on compiling NPP data for grasslands as part of the IGBP DIS data initiative is described. Site data and associated documentation from diverse field studies are being acquired for selected grasslands and are being reviewed for completeness, consistency, and adequacy of documentation, including a description of sampling methods. Data are being compiled in a database with spatial, temporal, and thematic characteristics relevant to remote sensing and global modeling. NPP data are available from the ORNL Distributed Active Archive Center (DAAC) for biogeochemical dynamics. The ORNL DAAC is part of the Earth Observing System Data and Information System, of the US National Aeronautics and Space Administration.

Olson, R. J.↗

Experiment K-7-31: Studies of Vestibular Primary Afferents and Eye Movements in Normal, Hypergravity and Hypogravity - Axon Cosmos Flight 2044

Fourteen days of active head movements in microgravity appear to modify the gain and neural adaptation properties of the horizontal semicircular canals in the rhesus monkey. This is the first demonstration of adaptive plasticity in the sensory receptor. Reversing prisms, for example, do not modify the gain of the primary afferent response. Pulse yaw rotation, sinusoidal rotation, and sum of sinusoidal rotation testing during the first day following recovery revealed that the gain of a sample of afferents was significantly greater than the gain derived from afferent responses obtained during pre-flight and control monkey testing. There was no strong evidence of tilt sensitivity in the sample of afferents that we tested either during the pre-flight or control tests or during the first day post-flight. Two irregular afferents tested on postflight day 2 showed changes with tilt but the responses were not systematic. The spontaneous discharge did not change following flight. Mean firing rate and coefficient of variation remained constant during the post flight tests and was near the value measured during pre flight tests. The change in gain of horizontal canal afferents might be adaptive. The animals were required to look at a target for food. This required active head and eye movements. Active head movements have been shown to be hypometric and eye movements have been shown to be hypermetric during the first few days of past Cosmos flights (see introduction). It might be that the increased gain in the horizontal semicircular canals permit accurate target acquisition during hypometric head movements by driving the eyes to greater angles for smaller angles of head movement. The mechanism by which the semicircular canals recalibrate (increase their gain) is unknown. The efferent vestibular system is a logical candidate. Horizontal nystagmus during rotation about an earth vertical axis with the horizontal semicircular canals in the plane of rotation produced the same response during postflight day 1 and post-flight day 9. But when the head was pitched down 45? the nystagmus slow phase velocity was greater and the duration was about twice during post-flight day 1. Apparently, this response involving the interaction of the horizontal and vertical semicircular canals and the otoliths did not recalibrate during post-flight day 1. The 'DC' bias of the slow phase velocity of the horizontal nystagmus during constant velocity horizontal axis rotation was roughly 4 times for one flight monkey and roughly 2 times for the other on post-flight day 1 compared to post-flight day 9. These results suggest that the otolith mediated response during constant velocity rotation also did not recalibrate on post-flight day 1.

Correia, M. J.↗

Bend stress relaxation and tensile primary creep of a polycrystalline alpha-SiC fiber

Understanding the thermomechanical behavior (creep and stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high temperature applications. It is important to understand and model the total creep of fibers at low strain levels where creep is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance. The objective of this paper is to compare and analyze bend stress relaxation and tensile creep data for alpha-SiC fibers produced by the Carborundum Co. (Niagara Falls, NY). This fiber is of current technical interest and is similar in composition to bulk alpha-SiC which has been studied under compressive creep conditions. The temperature, time, and stress dependences will be discussed for the stress relaxation and creep results. In addition, some creep and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable creep components of these materials. The data will be presented in order to model the deformation behavior and compare relaxation and/or creep behavior for relatively low deformation strain conditions of practical concern. Where applicable, the tensile creep results will be compared to bend stress relaxation data.

Hee Man, Yun↗

Chondrule formation, metamorphism, brecciation, an important new primary chondrule group, and the classification of chondrules

The recently proposed compositional classification scheme for meteoritic chondrules divides the chondrules into groups depending on the composition of their two major phases, olivine (or pyroxene) and the mesostasis, both of which are genetically important. The scheme is here applied to discussions of three topics: the petrographic classification of Roosevelt County 075 (the least-metamorphosed H chondrite known), brecciation (an extremely important and ubiquitous process probably experienced by greater than 40% of all unequilibrated ordinary chondrites), and the group A5 chondrules in the least metamorphosed ordinary chondrites which have many similarities to chondrules in the highly metamorphosed 'equilibrated' chondrites. Since composition provides insights into both primary formation properties of the chondruies and the effects of metamorphism on the entire assemblage it is possible to determine the petrographic type of RC075 as 3.1 with unique certainty. Similarly, the near scheme can be applied to individual chondrules without knowledge of the petrographic type of the host chondrite, which makes it especially suitable for studying breccias. Finally, the new scheme has revealed the existence of chondrules not identified by previous techniques and which appear to be extremely important. Like group A1 and A2 chondrules (but unlike group B1 chondrules) the primitive group A5 chondruies did not supercool during formation, but unlike group A1 and A2 chondrules (and like group B1 chondrules) they did not suffer volatile loss and reduction during formation. It is concluded that the compositional classification scheme provides important new insights into the formation and history of chondrules and chondrites which would be overlooked by previous schemes.

Sears, Derek W. G.↗

Piloted Simulation Tests of Propulsion Control as Backup to Loss of Primary Flight Controls for a B747-400 Jet Transport

Partial failures of aircraft primary flight control systems and structural damages to aircraft during flight have led to catastrophic accidents with subsequent loss of lives (e.g. DC-10, B-747, C-5, B-52, and others). Following the DC-10 accident at Sioux City, Iowa in 1989, the National Transportation Safety Board recommended 'Encourage research and development of backup flight control systems for newly certified wide-body airplanes that utilize an alternate source of motive power separate from that source used for the conventional control system.' This report describes the concept of a propulsion controlled aircraft (PCA), discusses pilot controls, displays, and procedures; and presents the results of a PCA piloted simulation test and evaluation of the B747-400 airplane conducted at NASA Ames Research Center in December, 1996. The purpose of the test was to develop and evaluate propulsion control throughout the full flight envelope of the B747-400 including worst case scenarios of engine failures and out of trim moments. Pilot ratings of PCA performance ranged from adequate to satisfactory. PCA performed well in unusual attitude recoveries at 35,000 ft altitude, performed well in fully coupled ILS approaches, performed well in single engine failures, and performed well at aft cg. PCA performance was primarily limited by out-of-trim moments.

Bull, John↗

Toward Describing the Effects of Ozone Depletion on Marine Primary Productivity and Carbon Cycling

This project was aimed at improved predictions of the effects of UVB and ozone depletion on marine primary productivity and carbon flux. A principal objective was to incorporate a new analytical description of photosynthesis as a function of UV and photosynthetically available radiation (Cullen et. al., Science 258:646) into a general oceanographic model. We made significant progress: new insights into the kinetics of photoinhibition were used in the analysis of experiments on Antarctic phytoplankton to generate a general model of UV-induced photoinhibition under the influence of ozone depletion and vertical mixing. The way has been paved for general models on a global scale.

Cullen, John J.↗

Propulsion Options for Primary Thrust and Attitude Control of Microspacecraft

Order of magnitude decreases in the size of scientific satellites and spacecraft could provide concurrent decreases in mission costs because of lower launch and fabrication costs. Although many subsystems are amenable to dramatic size reductions, miniaturization of the propulsion subsystems is not straightforward. There are a range of requirements for both primary and attitude control propulsion, dictated by mission requirements, satellite size, and power restrictions. Many of the established propulsion technologies can not currently be applied to microspacecraft. Because of this, micro-electromechanical systems (MEMS) fabrication technology is being explored as a path for miniaturization.

deGroot, W. A.↗

Structural Modeling of the Next Generation Space Telescope's Primary Mirror

In recent years, astronomical observations made with space telescopes have dramatically increased our understanding of the history of the universe. In particular, the cosmic Background Explorer (COBE) and the Hubble Space Telescope (HST) have yielded observations that cannot be achieved at ground-based observatories. We now have views of the universe before galaxies existed (from COBE) and views of young galaxies (from HST). But none of the existing observatories can provide views of the period in which the galaxies were born, about 100 million to one billion years after the "big bang". NASA expects the Next Generation Space Telescope (NGST) to fill this gap. An investigation into the structural modeling of the primary mirror of the NGST, its methodology and results are presented.

Boulet, J. A. M.↗

Improved Li/BCX Primary Cells for Space Applications

Li/BCX (bromine chloride in thionyl chloride) primary cells have been qualified for flight aboard the space shuttle for over fifteen years. These cells provide high energy density while maintaining an excellent safety record. Recently, changes to the electrolyte have resulted in an improved Li/BCX II system with a lower self-discharge rate. The use of low molarity electrolytes in programs unique to NASA have improved the safety hazards tolerance of these cells while maintaining or increasing their energy density.

Spillman, David M.↗

A Deployable Primary Mirror for Space Telescopes

NASA Langley Research Center, Composite Optics, Inc., and Nyma/ADF have developed jointly a deployable primary mirror for space telescopes that combines over five years of research on deployment of optical-precision structures and over ten years of development of fabrication techniques for optical-precision composite mirror panels and structures. The deployable mirror is directly applicable to a broad class of non-imaging "lidar" (Light direction and ranging) telescopes whose figure-error requirements are in the range of one to ten microns RMS. Furthermore, the mirror design can be readily modified to accommodate imaging-quality reflector panels and active panel-alignment control mechanisms for application to imaging telescopes. The present paper: 1) describes the deployable mirror concept; 2) explains the status of the mirror development; and 3) provides some technical specifications for a 2.55- m-diameter, proof-of-concept mirror.

Lake, Mark S.↗

A Deployable Primary Mirror for Space Telescopes

NASA Langley Research Center, Composite Optics, Inc., and Nyma/ADF have developed jointly a deployable primary mirror for space telescopes that combines over five years of research on deployment of optical-precision structures and over ten years of development of fabrication techniques for optical-precision composite mirror panels and structures. The deployable mirror is directly applicable to a broad class of non-imaging "lidar" (light direction and ranging) telescopes whose figure-error requirements are in the range of one to ten microns RMS. Furthermore, the mirror design can be readily modified to accommodate imaging-quality reflector panels and active panel-alignment control mechanisms for application to imaging telescopes. The present paper: 1) describes the deployable mirror concept; 2) explains the status of the mirror development; and 3) provides some technical specifications for a 2.55-m-diameter, proof-of-concept mirror.

Lake, Mark S.↗

The Use of Multi-Source Satellite and Geospatial Data to Study the Effect of Urbanization of Primary Productivity in the United States

Data from two different satellites, a digital land cover map, and digital census data were analyzed and combined in a geographic information system to study the effect of urbanization on photosynthetic vegetation productivity in the United States. Results show that urbanization can have a measurable but variable impact on the primary productivity of the land surface. Annual productivity can be reduced by as much as 20 days in some areas, but in resource limited regions, photosynthetic production can be enhanced by human activity. Overall, urban development reduces the productivity of the land surface and those areas with the highest productivity are directly in the path of urban sprawl.

Imhoff, M. L.↗

Full 3D Analysis of the GE90 Turbofan Primary Flowpath

The multistage simulations of the GE90 turbofan primary flowpath components have been performed. The multistage CFD code, APNASA, has been used to analyze the fan, fan OGV and booster, the 10-stage high-pressure compressor and the entire turbine system of the GE90 turbofan engine. The code has two levels of parallel, and for the 18 blade row full turbine simulation has 87.3 percent parallel efficiency with 121 processors on an SGI ORIGIN. Grid generation is accomplished with the multistage Average Passage Grid Generator, APG. Results for each component are shown which compare favorably with test data.

Turner, Mark G.↗

Fabrication and Thermo-Optical Properties of the MLS Composite Primary Reflector

The Microwave Limb Sounder (MLS) is a limb-sounding radiometer sensing emissions in the millimeter and sub-millimeter range. MLS will contribute to an understanding of atmospheric chemistry by assessing stratospheric and tropospheric ozone depletion, climate forcings and volcanic effects. The heart of the antenna is the primary reflector, constructed from graphite/cyanate composites in a facesheet/core construction. The reflector has an aperture of one square meter, a mass of 8.7 kilos and final figure accuracy of 4.37 microns rms. The surface is also modified to ensure RF reflectivity, prevent solar concentration and provide thermal balance to the spacecraft The surface is prepared by precision beadblasting, then coated with vapor deposited aluminum (VDA) and finally a layer of silicon suboxide (SiO(x)) to control the infrared emissivity. The resulting surface has a solar absorptance of 0.43 and an absorptance/emittance ratio of 1.3. BRDF analysis shows that 93% of the incident thermal energy is reflected outside a 10 degree angle of cone. For its mass and aperture, we believe this reflector to have the highest figure accuracy yet achieved in a composite antenna construction.

Willis, Paul B.↗

Compression Strength of Composite Primary Structural Components

The focus of research activities under NASA Grant NAG-1-2035 was the response and failure of thin-walled structural components. The research is applicable to the primary load carrying structure of flight vehicles, with particular emphasis on fuselage and wing'structure. Analyses and tests were performed that are applicable to the following structural components an aft pressure bulkhead, or a composite pressure dome, pressure cabin damage containment, and fuselage frames subject to crash-type loads.

Johnson, Eric R.↗

Using the World Primary Standard Dobson Spectrometer to Monitor the Stability of a Multi-Instrument Satellite Ozone Dataset

NASA is creating a long term satellite ozone time series by combining data from multiple instruments: Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) (1978 - 1993), Meteor 3 TOMS (1991 - 1994), Earth Probe TOMS (1996 - present), Nimbus 7 SB-JV (1978 - 1990), NOAA-9 Solar Backscatter UV Spectrometer (SBUV/2) (1984 - 1997), NOAA-11 SBUV/2 (1989 - 1994), and NOAA-14 SBUV/2 (1995 - present). The stability of individual data sets and possible instrument-to-instrument differences are best checked by comparison with ground-based measurements. We have examined the time dependence of the calibrations of these instruments by comparing satellite derived ozone with that measured by the world primary standard Dobson spectrometer No. 83. This instrument has been maintained since 1962 as a standard for total ozone to an uncertainty of plus or minus 0.5%. Measurements of AD pair ozone made with instrument No. 83 at Mauna Loa observatory most summers since 1979 were compared with coincident TOMS and SBUV(/2) ozone measurements. The comparison shows that the various instruments were stable relative to instrument No. 83 to within about plus or minus 1%, but that there are instrument-to-instrument biases of as much as 3%. Earth Probe TOMS, for example, is 1% to 2% high relative to Nimbus 7 TOMS when the world standard instrument is used as a transfer standard. Similar results are seen when comparisons are made with an ensemble of 41 Dobson stations throughout the world, demonstrating that the ensemble as a whole is stable despite the fact that many instruments within the ensemble have clear calibration changes.

McPeters, R.D.↗