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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Potential for EMU Fabric Damage by Electron Beam and Molten Metal During Space Welding for the International Space Welding Experiment

As a consequence of preparations concerning the International Space Welding Experiment (ISWE), studies were performed to better understand the effect of molten metal contact and electron beam impingement with various fabrics for space suit applications. The question arose as to what would occur if the electron beam from the Ukrainian Universal Hand Tool (UHT) designed for welding in space were to impinge upon a piece of Nextel AF-62 ceramic cloth designed to withstand temperatures up to 1427 C. The expectation was that the electron beam would lay down a static charge pattern with no damage to the ceramic fabric. The electron beam is capable of spraying the fabric with enough negative charge to repel further electrons from the fabric before significant heating occurs. The static charge pattern would deflect any further charge accumulation except for a small initial amount of leakage to the grounded surface of the welder. However, when studies were made of the effect of the electron beam on the insulating ceramic fabric it was surprisingly found that the electron beam did indeed burn through the ceramic fabric. It was also found that the shorter electron beam standoff distances had longer burnthrough times than did some greater electron beam standoff distances. A possible explanation for the longer burnthrough times for the small electron beam standoff distance would be outgassing of the fabric which caused the electron beam hand-tool to cycle on and off to provide some protection for the cathodes. The electron beam hand tool was observed to cycle off at the short standoff distance of two inches likely due to vapors being outgassed. During the electron beam welding process there is an electron leakage, or current leakage, flow from the fabric. A static charge pattern is initially laid down by the electron beam current flow. The static charge makes up the current leakage flow which initially slightly heats up the fabric. The initially laid down surface charge leaks a small amount of current. The rate at which the current charge leaks from the fabric controls how fast the fabric heats up. As the ceramic fabric is heated it begins to outgass primarily from contamination/impurities atoms or molecules on and below the fabric surface. The contaminant gases ionize to create extra charge carriers and multiply a current of electrons. The emitted gas which ionized in the electron leakage flow promotes further leakage. Thus, the small leakage of charge from the fabric surface is enhanced by outgassing. When the electron beam current makes up the lost current, the incoming electrons heat the fabric and further enhance the outgassing. The additional leakage promotes additional heating up of the ceramic fabric. The electrons bound to the ceramic fabric surface leak off more and more as the surface gets hotter promoting even greater leakage. The additional electrons that result also gain energy in the field and produce further electrons. Eventually the process becomes unstable and accelerates to the point where a hole is burned through the fabric.

Fragomeni, James M.↗
NASA NTRS1997

Comparison of N2O Emissions from Soils at Three Temperate Agricultural Sites

Nitrous oxide (N2O) flux simulations by four models were compared with year-round field measurements from five temperate agricultural sites in three countries. The field sites included an unfertilized, semi-arid rangeland with low N2O fluxes in eastern Colorado, USA; two fertilizer treatments (urea and nitrate) on a fertilized grass ley cut for silage in Scotland; and two fertilized, cultivated crop fields in Germany where N2O loss during the winter was quite high. The models used were daily trace gas versions of the CENTURY model, DNDC, ExpertN, and the NASA-Ames version of the CASA model. These models included similar components (soil physics, decomposition, plant growth, and nitrogen transformations), but in some cases used very different algorithms for these processes. All models generated similar results for the general cycling of nitrogen through the agro-ecosystems, but simulated nitrogen trace gas fluxes were quite different. In most cases the simulated N20 fluxes were within a factor of about 2 of the observed annual fluxes, but even when models produced similar N2O fluxes they often produced very different estimates of gaseous N loss as nitric oxide (NO), dinitrogen (N2), and ammonia (NH3). Accurate simulation of soil moisture appears to be a key requirement for reliable simulation of N2O emissions. All models simulated the general pattern of low background fluxes with high fluxes following fertilization at the Scottish sites, but they could not (or were not designed to) accurately capture the observed effects of different fertilizer types on N2O flux. None of the models were able to reliably generate large pulses of N2O during brief winter thaws that were observed at the two German sites. All models except DNDC simulated very low N2O fluxes for the dry site in Colorado. The US Trace Gas Network (TRAGNET) has provided a mechanism for this model and site intercomparison. Additional intercomparisons are needed with these and other models and additional data sets; these should include both tropical agro-ecosystems and new agricultural management techniques designed for sustainability.

Frolking, S. E.↗
NASA NTRS2003

The 2002 NASA Faculty Fellowship Program Research Reports

Contents include the following: System Identification of X-33. Neural Network Advanced Ceramic Technology for Space Applications at NASA MSFC. Developing a MATLAB-Based Tool for Visualization and Transformation. Subsurface Stress Fields in Single Crystal (Anisotropic). Contacts Our Space Future: A Challenge to the Conceptual Artist Concept Art for Presentation and Education. Identification and Characterization of Extremophile Microorganisms. Significant to Astrobiology. Mathematical Investigation of Gamma Ray and Neutron. Absorption Grid Patterns for Homeland Defense-Related Fourier Imaging Systems. The Potential of Microwave Radiation for Processing Martian Soil. Fuzzy Logic Trajectory Design and Guidance for Terminal Area.

Bland, J.↗
NASA NTRS2003

Mapping a Better Vintage

Vineyards such as those located in California's Napa Valley tend to be subdivided into relatively large fields or blocks that often encompass heterogeneous physical conditions. Since growers typically treat the entire block as a single minimum management unit for cultivation and harvest, mapping and monitoring the variability within a block is a concern. Over the last decade, an increasing number of vineyard managers have utilized digital remote sensing and geographic information systems (GIS) to visualize the variability within their blocks. With computer software designed to overlay remotely sensed imagery with environmental and agronomic geographic data on a map, GIS helps growers recognize and explain patterns that might not have been obvious otherwise. GIS can also serve as a valuable archiving mechanism for future reference. To further develop the use of image technology and GIS for vineyard management support, NASA's Earth Science Enterprise partnered with the U.S. wine and commercial remote sensing industries for a project known as the Viticultural Integration of NASA Technologies for Assessment of the Grapevine Environment (VINTAGE). With project investigators from NASA's Ames Research Center, the California State University at Monterey Bay, and the University of Montana, several prototype products have been developed to support agricultural decisions concerning canopy management and irrigation practice. One key VINTAGE aspect involved the evaluation of satellite and airborne multispectral imagery for delineation of sub-block management zones within a vineyard.

Source record↗
NASA NTRS1997

W-Band On-Wafer Measurement of Uniplanar Slot-Type Antennas

Uniplanar slot-type antennas such as coplanar waveguide fed single- and dual-polarized slot-ring antennas and double folded-slot antennas are characterized using a millimeter-wave network analyzer and on-wafer measurement techniques. The antennas are designed to be mounted on a dielectric lens to minimize power loss into substrate modes and realize high-gain antenna patterns. On-wafer measurements are performed by placing the antenna wafer on a thick dielectric spacer of similar e(sub t) and eliminating the reflection from the probe station chuck with time-domain gating. The measured results agree well with method-of-moments simulations.

Raman, Sanjay↗
NASA NTRS2009

Wide-Angle-Scanning Reflectarray Antennas Actuated by MEMS

An effort to develop large-aperture, wide-angle-scanning reflectarray antennas for microwave radar and communication systems is underway. In an antenna of this type as envisioned, scanning of the radiated or incident microwave beam would be effected through mechanical rotation of the passive (reflective) patch antenna elements, using microelectromechanical systems (MEMS) stepping rotary actuators typified by piezoelectric micromotors. It is anticipated that the cost, mass, and complexity of such an antenna would be less than, and the reliability greater than, those of an electronically scanned phased-array antenna of comparable beam-scanning capability and angular resolution. In the design and operation of a reflectarray, one seeks to position and orient an array of passive patch elements in a geometric pattern such that, through constructive interference of the reflections from them, they collectively act as an efficient single reflector of radio waves within a desired frequency band. Typically, the patches lie in a common plane and radiation is incident upon them from a feed horn.

Fang, Houfei↗
NASA NTRS2010

Combustion Stability Analyses of Coaxial Element Injectors with Liquid Oxygen/Liquid Methane Propellants

Liquid rocket engines using oxygen and methane propellants are being considered by the National Aeronautics and Space Administration (NASA) for in-space vehicles. This propellant combination has not been previously used in a flight-qualified engine system, so limited test data and analysis results are available at this stage of early development. NASA has funded several hardware-oriented activities with oxygen and methane propellants over the past several years with the Propulsion and Cryogenic Advanced Development (PCAD) project, under the Exploration Technology Development Program. As part of this effort, the NASA Marshall Space Flight Center has conducted combustion stability analyses of several of the configurations. This paper presents test data and analyses of combustion stability from the recent PCAD-funded test programs at the NASA MSFC. These test programs used swirl coaxial element injectors with liquid oxygen and liquid methane propellants. Oxygen was injected conventionally in the center of the coaxial element, and swirl was provided by tangential entry slots. Injectors with 28-element and 40-element patterns were tested with several configurations of combustion chambers, including ablative and calorimeter spool sections, and several configurations of fuel injection design. Low frequency combustion instability (chug) occurred with both injectors, and high-frequency combustion instability occurred at the first tangential (1T) transverse mode with the 40-element injector. In most tests, a transition between high-amplitude chug with gaseous methane flow and low-amplitude chug with liquid methane flow was readily observed. Chug analyses of both conditions were conducted using techniques from Wenzel and Szuch and from the Rocket Combustor Interactive Design and Analysis (ROCCID) code. The 1T mode instability occurred in several tests and was apparent by high-frequency pressure measurements as well as dramatic increases in calorimeter-measured heat flux throughout the chamber. Analyses of the transverse mode were conducted with ROCCID and empirical methods such as Hewitt d/V. This paper describes the test hardware configurations, test data, analysis methods, and presents results of the various analyses.

Hulka, J. R.↗
NASA NTRS2016

State of the Carbon Cycle - Consequences of Rising Atmospheric CO2

The rise of atmospheric CO2, largely attributable to human activity through fossil fuel emissions and land-use change, has been dampened by carbon uptake by the ocean and terrestrial biosphere. We outline the consequences of this carbon uptake as direct and indirect effects on terrestrial and oceanic systems and processes for different regions of North America and the globe. We assess the capacity of these systems to continue to act as carbon sinks. Rising CO2 has decreased seawater pH; this process of ocean acidification has impacted some marine species and altered fundamental ecosystem processes with further effects likely. In terrestrial ecosystems, increased atmospheric CO2 causes enhanced photosynthesis, net primary production, and increased water-use efficiency. Rising CO2 may change vegetation composition and carbon storage, and widespread increases in water use efficiency likely influence terrestrial hydrology and biogeochemical cycling. Consequences for human populations include changes to ecosystem services including cultural activities surrounding land use, agricultural or harvesting practices. Commercial fish stocks have been impacted and crop production yields have been changed as a result of rising CO2. Ocean and terrestrial effects are contingent on, and feedback to, global climate change. Warming and modified precipitation regimes impact a variety of ecosystem processes, and the combination of climate change and rising CO2 contributes considerable uncertainty to forecasting carbon sink capacity in the ocean and on land. Disturbance regime (fire and insects) are modified with increased temperatures. Fire frequency and intensity increase, and insect lifecycles are disrupted as temperatures move out of historical norms. Changes in disturbance patterns modulate the effects of rising CO2 depending on ecosystem type, disturbance frequency, and magnitude of events. We discuss management strategies designed to limit the rise of atmospheric CO2 and reduce uncertainty in forecasts of decadal and centennial feedbacks of rising atmospheric CO2 on carbon storage.

Carbon Cycle↗
NASA NTRS2018

Overcoming Pitfalls When Using HDF5 Compression

Compression of large datasets in S-NPP, JPSS and other HDF5 data files may substantially reduce their size, in turn reducing disk space requirements and file download time. However, mismatches between the layout of the files' datasets, the HDF5 instance's cache settings, choice of compression algorithm, and the access pattern of applications using the data can sometimes result in poor performance or exhausting machine resources when running the application. Whether designed in advance or modified in response to encountered problems, applications can be tuned to optimize efficiency of data access, avoid unnecessary repeated decompression, and reduce the amount of memory used. Examples will be given of problems that may be encountered, how to use available tools to diagnose or work around them, changing cache settings to conserve memory, and designing access strategies to avoid both performance and memory issues when creating or modifying applications.

performance↗
NASA NTRS1993

Demonstrating damage tolerance of composite airframes

Commercial transport aircraft operating in the United States are certified by the Federal Aviation Authority to be damage tolerant. On 28 April 1988, Aloha Airlines Flight 243, a Boeing 727-200 airplane, suffered an explosive decompression of the fuselage but landed safely. This event provides very strong justification for the damage tolerant design criteria. The likely cause of the explosive decompression was the linkup of numerous small fatigue cracks that initiated at adjacent fastener holes in the lap splice joint at the side of the body. Actually, the design should have limited the damage size to less than two frame spacings (about 40 inches), but this type of 'multi-site damage' was not originally taken into account. This cracking pattern developed only in the high-time airplanes (many flights). After discovery in the fleet, a stringent inspection program using eddy current techniques was inaugurated to discover these cracks before they linked up. Because of concerns about safety and the maintenance burden, the lap-splice joints of these high-time airplanes are being modified to remove cracks and prevent new cracking; newer designs account for 'multi-site damage'.

Poe, Clarence C., Jr.↗
NASA NTRS1985

Adaptive antenna arrays for satellite communications: Design and testing

When two separate antennas are used with each feedback loop to decorrelate noise, the antennas should be located such that the phase of the interfering signal in the two antennas is the same while the noise in them is uncorrelated. Thus, the antenna patterns and spatial distribution of the auxiliary antennas are quite important and should be carefully selected. The selection and spatial distribution of auxiliary elements is discussed when the main antenna is a center fed reflector antenna. It is shown that offset feeds of the reflector antenna can be used as auxiliary elements of an adaptive array to suppress weak interfering signals. An experimental system is designed to verify the theoretical analysis. The details of the experimental systems are presented.

Gupta, I. J.↗
NASA NTRS1975

Physiological mass measurements on Skylab 1/2 and 1/3

Mass measurements of crewmen and objects were made for the first time in space during Skylab. A description of the new devices designed for such measurements and of the technique of their use is detailed. Results from ground-based chamber simulation tests and from those during Skylab II and III show similar patterns of simple metabolic deficits, of a rapid loss during the first few days of flight followed by a reciprocal gain for the first few postflight days, and other transient changes. It is concluded that two major causes of weight loss are present: (1) a fluid redistribution and loss, and (2) metabolic losses. Added to these are short-term changes from transient stress. Smaller, simpler, and cheaper devices have since been designed which should allow mass measurements on virtually any object in almost any spacecraft.

Thornton, W.↗
NASA NTRS1994

Practical guidelines for workload assessment

The practical problems that might be encountered in carrying out workload evaluations in work settings have been outlined. Different approaches have been distinguished that may determine the type of research design used and provide assistance in the difficult choice between workload assessment techniques. One approach to workload assessment is to examine the short-term consequences of combining various tasks. Theoretical models of attention allocation will underpin specific studies of interference and the consequences of task demand and task conflict for performance. A further approach with a different temporal orientation may lead us to a better understanding of the relationships between work demands and strain through the analysis of individual differences in cognitive control processes. The application of these processes may depend on individual differences in long term styles and short term strategies, but may be used to prevent decrements in work performance under difficult conditions. However, control may attract costs as well as benefits in terms of changes in effective state and physiological activity. Thus, strain associated with work demands may only be measurable in the form of tradeoffs between performance and other domains of individual activity. The methodological implications are to identify patterns of adjustment to workload variations using repeated measures and longitudinal sampling of performance as well as subjective and physiological measures. Possible enhancements to workplace design must take into account these human factors considerations of workload in order to avoid potential decrements in individual performance and associated organizational problems.

Tattersall, Andrew J.↗
NASA NTRS2006

Measurement of Flow Pattern Within a Rotating Stall Cell in an Axial Compressor

Effective active control of rotating stall in axial compressors requires detailed understanding of flow instabilities associated with this compressor regime. Newly designed miniature high frequency response total and static pressure probes as well as commercial thermoanemometric probes are suitable tools for this task. However, during the rotating stall cycle the probes are subjected to flow direction changes that are far larger than the range of probe incidence acceptance, and therefore probe data without a proper correction would misrepresent unsteady variations of flow parameters. A methodology, based on ensemble averaging, is proposed to circumvent this problem. In this approach the ensemble averaged signals acquired for various probe setting angles are segmented, and only the sections for probe setting angles close to the actual flow angle are used for signal recombination. The methodology was verified by excellent agreement between velocity distributions obtained from pressure probe data, and data measured with thermoanemometric probes. Vector plots of unsteady flow behavior during the rotating stall regime indicate reversed flow within the rotating stall cell that spreads over to adjacent rotor blade channels. Results of this study confirmed that the NASA Low Speed Axial Compressor (LSAC) while in a rotating stall regime at rotor design speed exhibits one stall cell that rotates at a speed equal to 50.6 percent of the rotor shaft speed.

Lepicovsky, Jan↗
NASA NTRS2010

Analysis of a Transonic Alternating Flow Phenomenon Observed During Ares Crew Launch Vehicle Wind Tunnel Tests

A transonic wind tunnel test of the Ares I-X Rigid Buffet Model (RBM) identified a Mach number regime where unusually large buffet loads are present. A subsequent investigation identified the cause of these loads to be an alternating flow phenomenon at the Crew Module-Service Module junction. The conical design of the Ares I-X Crew Module and the cylindrical design of the Service Module exposes the vehicle to unsteady pressure loads due to the sudden transition from separated to attached flow about the cone-cylinder junction with increasing Mach number. For locally transonic conditions at this junction, the flow randomly fluctuates back and forth between a subsonic separated flow and a supersonic attached flow. These fluctuations produce a square-wave like pattern in the pressure time histories which, upon integration result in large amplitude, impulsive buffet loads. Subsequent testing of the Ares I RBM found much lower buffet loads since the evolved Ares I design includes an ogive fairing that covers the Crew Module-Service Module junction, thereby making the vehicle less susceptible to the onset of alternating flow. An analysis of the alternating flow separation and attachment phenomenon indicates that the phenomenon is most severe at low angles of attack and exacerbated by the presence of vehicle protuberances. A launch vehicle may experience either a single or, at most, a few impulsive loads since it is constantly accelerating during ascent rather than dwelling at constant flow conditions in a wind tunnel. A comparison of a wind-tunnel-test-data-derived impulsive load to flight-test-data-derived load indicates a significant over-prediction in the magnitude and duration of the buffet load

Sekula, Martin K.↗
NASA NTRS1972

Lineaments that are artifacts of lighting, part G

Apollo 15 orbital photographs, particularly those taken at low sun elevation angles, are examined revealing grid patterns of lineaments. Preliminary results of experiments demonstrate that spurious lineaments and grid patterns can be produced and that the directions are dependent in part upon the position of the light source. The experiments were designed to duplicate the effect of bright sunlight reflecting from a hummocky surface with little or no diffuse light in the shadowed areas.

Howard, K. A.↗
NASA NTRS1973

A technique for designing active control systems for astronomical telescope mirrors

This paper considers the problem of designing a control system to achieve and maintain the required surface accuracy of the primary mirror of a large space telescope. Control over the mirror surface is obtained through the application of a corrective force distribution by actuators located on the rear surface of the mirror. The design procedure is an extension of a model control technique developed for distributed parameter plants with known eigenfunctions to include plants whose eigenfunctions must be approximated by numerical techniques. Instructions are given for constructing the mathematical model of the system, and a design procedure is developed for use with. typical numerical data in selecting the number and location of the actuators. Examples of actuator patterns and their effect on various errors are given.

Active optics↗