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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Evaluation of silicon carbide fiber/titanium composites

Izod impact, tensile, and modulus of elasticity were determined for silicon carbide fiber/titanium composites to evaluate their potential usefulness as substitutes for titanium alloys or stainless steel in stiffness critical applications for aircraft turbine engines. Variations in processing conditions and matrix ductility were examined to produce composites having good impact strength in both the as-fabricated condition and after air exposure at elevated temperature. The impact strengths of composites containing 36 volume percent silicon carbide (SiC) fiber in an unalloyed (A-40) titanium matrix were found to be equal to unreinforced titanium-6 aluminum-4 vanadium alloy; the tensile strengths of the composites were marginally better than the unreinforced unalloyed (A-70) matrix at elevated temperature, though not at room temperature. At room temperature the modulus of elasticity of the composites was 48 percent higher than titanium or its alloys and 40 percent higher than that of stainless steel.

Jech, R. W.↗
NASA NTRS2018

Vehicle-Level System Impact of Boundary Layer Ingestion for the NASA D8 Concept Aircraft

The purpose of this study was to evaluate the vehicle-level impact of a boundary layer ingestion (BLI) propulsion system on a commercial transport aircraft concept. The NASA D8 (ND8) aircraft was chosen as the BLI concept aircraft to be studied. A power balance methodology developed by the Massachusetts Institute of Technology was adapted for use with the existing NASA sizing and performance tools to model the fuel consumption impact of BLI on the ND8. A key assumption for the BLI impact assessment was a 3.5% efficiency penalty associated with designing a fan for and operating in the distorted flow caused by BLI. The ND8 was compared to several other ND8-like aircraft that did not utilize BLI in order to determine the fuel consumption benefit attributable to BLI. Analytically “turning off” BLI on the ND8 without accounting for the physical requirements of redirecting the boundary layer or resizing the aircraft to meet the performance constraints resulted in a 2.8% increase in block fuel consumption to fly the design mission. When this non-physical aircraft was resized to meet the performance constraints, the block fuel consumption was 4.0% greater than the baseline ND8. The ND8 was also compared to an ND8-like aircraft with conventionally podded engines under the wing. This configuration had a 5.6% increase in block fuel consumption compared to the baseline ND8. This result is more reflective of the real world impact if BLI is not an available technology for the ND8 design. The BLI benefit results presented for this study should not be applied to other aircraft that have a propulsion-airframe integration design or BLI implementation different from the ND8.

Marien, Ty V.↗
NASA NTRS1985

Utilizing remote sensing of Thematic Mapper data to improve our understanding of estuarine processes and their influence on the productivity of estuarine-dependent fisheries

The purpose of the project is to refine and validate a probabilistic spatial computer model through the analyses of thematic mapper imagery. The model is designed to determine how the interface between marshland and water changes as marshland is converted to water in a disintegrating marsh. Coastal marshland in Louisiana is disintegrating at the rate of approximately 40 sq mi a year, and an evaluation of the potential impact of this loss on the landings of estuarine-dependent fisheries is needed by fisheries managers. Understanding how marshland-water interface changes as coastal marshland is lost is essential to the process of evaluating fisheries effects, because several studies suggest that the production of estuarine-dependent fish and shellfish may be more closely related to the interface between marshland and water than to acreage of marshland. The need to address this practical problem has provided an opportunity to apply some scientifically interesting new techniques to the analyses of satellite imagery. Progress with the development of these techniques is the subject of this report.

Browder, Joan A.↗
NASA NTRS1995

Impact Characteristics of Candidate Materials for Single-Stage-to-Orbit (SSTO) Technology

Four fiber/resin systems were compared for resistance to damage and damage tolerance. One toughened epoxy and three toughened bismaleimide (BMI) resins were used., all with IM7 carbon fiber reinforcement. A statistical design of experiments technique was used to evaluate the effects of impact energy, specimen thickness and tup diameter on the damage area and residual compression-after-impact (CAI) strength. Results showed that two of the BMI systems sustained relatively large damage areas yet had an excellent retention of CAI strength.

Nettles, Alan↗
NASA NTRS1984

Evaluating NASA Technology Programs in Terms of Private Sector Impacts

NASA is currently developing spacecraft technology for application to NASA scientific missions, military missions and commercial missions which are part of or form the basis of private sector business ventures. The justification of R&D programs that lead to spacecraft technology improvements encompasses the establishment of the benefits in terms of improved scientific knowledge that may result from new and/or improved NASA science missions, improved cost effectiveness of NASA and DOD missions and new or improved services that may be offered by the private sector (for example communications satellite services). It is with the latter of these areas that attention will be focused upon. In particular, it is of interest to establish the economic value of spacecraft technology improvements to private sector communications satellite business ventures. It is proposed to assess the value of spacecraft technology improvements in terms of the changes in cash flow and present value of cash flows, that may result from the use of new and/or improved spacecraft technology for specific types of private sector communications satellite missions (for example domestic point-to-point communication or direct broadcasting). To accomplish this it is necessary to place the new and/or improved technology within typical business scenarios and estimate the impacts of technical performance upon business and financial performance.

Greenberg, J. S.↗
NASA NTRS2010

Evaluation of Enhanced High Resolution MODIS/AMSR-E SSTs and the Impact on Regional Weather Forecast

Over the last few years, the NASA Short-term Prediction Research and Transition (SPoRT) Center has been generating a 1-km sea surface temperature (SST) composite derived from retrievals of the Moderate Resolution Imaging Spectroradiometer (MODIS) for use in operational diagnostics and regional model initialization. With the assumption that the day-to-day variation in the SST is nominal, individual MODIS passes aboard the Earth Observing System (EOS) Aqua and Terra satellites are used to create and update four composite SST products each day at 0400, 0700, 1600, and 1900 UTC, valid over the western Atlantic and Caribbean waters. A six month study from February to August 2007 over the marine areas surrounding southern Florida was conducted to compare the use of the MODIS SST composite versus the Real-Time Global SST analysis to initialize the Weather Research and Forecasting (WRF) model. Substantial changes in the forecast heat fluxes were seen at times in the marine boundary layer, but relatively little overall improvement was measured in the sensible weather elements. The limited improvement in the WRF model forecasts could be attributed to the diurnal changes in SST seen in the MODIS SST composites but not accounted for by the model. Furthermore, cloud contamination caused extended periods when individual passes of MODIS were unable to update the SSTs, leading to substantial SST latency and a cool bias during the early summer months. In order to alleviate the latency problems, the SPoRT Center recently enhanced its MODIS SST composite by incorporating information from the Advanced Microwave Scanning Radiometer-EOS (AMSR-E) instruments as well as the Operational Sea Surface Temperature and Sea Ice Analysis. These enhancements substantially decreased the latency due to cloud cover and improved the bias and correlation of the composites at available marine point observations. While these enhancements improved upon the modeled cold bias using the original MODIS SSTs, the discernable impacts on the WRF model were still somewhat limited. This paper explores several factors that may have contributed to this result. First, the original methodology to initialize the model used the most recent SST composite available in a hypothetical real ]time configuration, often matching the forecast initial time with an SST field that was 5-8 hours offset. To minimize the differences that result from the diurnal variations in SST, the previous day fs SST composite is incorporated at a time closest to the model initialization hour (e.g. 1600 UTC composite at 1500 UTC model initialization). Second, the diurnal change seen in the MODIS SST composites was not represented by the WRF model in previous simulations, since the SSTs were held constant throughout the model integration. To address this issue, we explore the use of a water skin-temperature diurnal cycle prediction capability within v3.1 of the WRF model to better represent fluctuations in marine surface forcing. Finally, the verification of the WRF model is limited to very few over-water sites, many of which are located near the coastlines. In order to measure the open ocean improvements from the AMSR-E, we could use an independent 2-dimensional, satellite-derived data set to validate the forecast model by applying an object-based verification method. Such a validation technique could aid in better understanding the benefits of the mesoscale SST spatial structure to regional models applications.

Schiferl, Luke D.↗
NASA NTRS2012

Full-field Deformation Measurement Techniques for a Rotating Composite Shaft

Test methods were developed to view global and local deformation in a composite tube during a test in which the tube is rotating at speeds and torques relevant to rotorcraft shafts. Digital image correlation (DIC) was used to provide quantitative displacement measurements during the tests. High speed cameras were used for the DIC measurements in order to capture images at sufficient frame rates and with sufficient resolution while the tube was rotating at speeds up to 5,000 rpm. Surface displacement data was resolved into cylindrical coordinates in order to measure rigid body rotation and global deformation of the tube. Tests were performed on both undamaged and impact damaged tubes in order to evaluate the capability to detect local deformation near an impact damaged site. Measurement of radial displacement clearly indicated a local buckling deformation near the impacted site in both dynamic and static tests. X-ray computed tomography (CT) was used to investigate variations in fiber architecture within the composite tube and to detect impact damage. No growth in the impact damage area was observed by DIC during dynamic testing or by x-ray CT in post test inspection of the composite tube.

Kohlman, Lee W.↗
NASA NTRS2012

Using Remotely Sensed Data and Watershed and Hydrodynamic Models to Evaluate the Effects of Land Cover Land Use Change on Aquatic Ecosystems in Mobile Bay, AL

Alabama coastal systems have been subjected to increasing pressure from a variety of activities including urban and rural development, shoreline modifications, industrial activities, and dredging of shipping and navigation channels. The impacts on coastal ecosystems are often observed through the use of indicator species. One such indicator species for aquatic ecosystem health is submerged aquatic vegetation (SAV). Watershed and hydrodynamic modeling has been performed to evaluate the impact of land cover land use (LCLU) change in the two counties surrounding Mobile Bay (Mobile and Baldwin) on SAV stressors and controlling factors (temperature, salinity, and sediment) in the Mobile Bay estuary. Watershed modeling using the Loading Simulation Package in C++ (LSPC) was performed for all watersheds contiguous to Mobile Bay for LCLU scenarios in 1948, 1992, 2001, and 2030. Remotely sensed Landsat-derived National Land Cover Data (NLCD) were used in the 1992 and 2001 simulations after having been reclassified to a common classification scheme. The Prescott Spatial Growth Model was used to project the 2030 LCLU scenario based on current trends. The LSPC model simulations provided output on changes in flow, temperature, and sediment for 22 discharge points into the estuary. These results were inputted in the Environmental Fluid Dynamics Computer Code (EFDC) hydrodynamic model to generate data on changes in temperature, salinity, and sediment on a grid throughout Mobile Bay and adjacent estuaries. The changes in the aquatic ecosystem were used to perform an ecological analysis to evaluate the impact on SAV habitat suitability. This is the key product benefiting the Mobile Bay coastal environmental managers that integrates the influences of temperature, salinity, and sediment due to LCLU driven flow changes with the restoration potential of SAVs. Data products and results are being integrated into NOAA s EcoWatch and Gulf of Mexico Data Atlas online systems for dissemination to coastal resource managers and stakeholders. Objective 1: Develop and utilize Land Use scenarios for Mobile and Baldwin Counties, AL as input to models to predict the affects on water properties (temperature,salinity,)for Mobile Bay through 2030. Objective 2: Evaluate the impact of land use change on seagrasses and SAV in Mobile Bay. Hypothesis: Urbanization will significantly increase surface flows and impact salinity and temperature variables that effect seagrasses and SAVs.

Al-Hamdan, Mohammad↗
NASA NTRS2014

Human Exploration Science Office (KX) Overview

The Human Exploration Science Office supports human spaceflight, conducts research, and develops technology in the areas of space orbital debris, hypervelocity impact technology, image science and analysis, remote sensing, imagery integration, and human and robotic exploration science. NASA's Orbital Debris Program Office (ODPO) resides in the Human Exploration Science Office. ODPO provides leadership in orbital debris research and the development of national and international space policy on orbital debris. The office is recognized internationally for its measurement and modeling of the debris environment. It takes the lead in developing technical consensus across U.S. agencies and other space agencies on debris mitigation measures to protect users of the orbital environment. The Hypervelocity Impact Technology (HVIT) project evaluates the risks to spacecraft posed by micrometeoroid and orbital debris (MMOD). HVIT facilities at JSC and White Sands Test Facility (WSTF) use light gas guns, diagnostic tools, and high-speed imagery to quantify the response of spacecraft materials to MMOD impacts. Impact tests, with debris environment data provided by ODPO, are used by HVIT to predict risks to NASA and commercial spacecraft. HVIT directly serves NASA crew safety with MMOD risk assessments for each crewed mission and research into advanced shielding design for future missions. The Image Science and Analysis Group (ISAG) supports the International Space Station (ISS) and commercial spaceflight through the design of imagery acquisition schemes (ground- and vehicle-based) and imagery analyses for vehicle performance assessments and mission anomaly resolution. ISAG assists the Multi-Purpose Crew Vehicle (MPCV) Program in the development of camera systems for the Orion spacecraft that will serve as data sources for flight test objectives that lead to crewed missions. The multi-center Imagery Integration Team is led by the Human Exploration Science Office and provides expertise in the application of engineering imagery to spaceflight. The team links NASA programs and private industry with imagery capabilities developed and honed through decades of human spaceflight, including imagery integration, imaging assets, imagery data management, and photogrammetric analysis. The team is currently supporting several NASA programs, including commercial demonstration missions. The Earth Science and Remote Sensing Team is responsible for integrating the scientific use of Earth-observation assets onboard the ISS, which consist of externally mounted sensors and crew photography capabilities. This team facilitates collaboration on remote sensing and participates in research with academic organizations and other Government agencies, not only in conjunction with ISS science, but also for planetary exploration and regional environmental/geological studies. Human exploration science focuses on science strategies for future human exploration missions to the Moon, Mars, asteroids, and beyond. This function provides communication and coordination between the science community and mission planners. ARES scientists support the operation of robotic missions (i.e., Mars Exploration Rovers and the Mars Science Laboratory), contribute to the interpretation of returned mission data, and translate robotic mission technologies and techniques to human spaceflight.

Calhoun, Tracy A.↗
NASA NTRS1996

Final Tier 2 Environmental Impact Statement for International Space Station

The Final Tier 2 Environmental Impact Statement (EIS) for the International Space Station (ISS) has been prepared by the National Aeronautics and Space Administration (NASA) and follows NASA's Record of Decision on the Final Tier 1 EIS for the Space Station Freedom. The Tier 2 EIS provides an updated evaluation of the environmental impacts associated with the alternatives considered: the Proposed Action and the No-Action alternative. The Proposed Action is to continue U.S. participation in the assembly and operation of ISS. The No-Action alternative would cancel NASA!s participation in the Space Station Program. ISS is an international cooperative venture between NASA, the Canadian Space Agency, the European Space Agency, the Science and Technology Agency of Japan, the Russian Space Agency, and the Italian Space Agency. The purpose of the NASA action would be to further develop human presence in space; to meet scientific, technological, and commercial research needs; and to foster international cooperation.

Source record↗
NASA NTRS1995

Draft Tier 2 Environmental Impact Statement for International Space Station

The Draft Tier 2 Environmental Impact Statement (EIS) for the International Space Station (ISS) has been prepared by the National Aeronautics and Space Administration (NASA) and follows NASA's Record of Decision on the Final Tier 1 EIS for the Space Station Freedom. The Tier 2 EIS provides an updated evaluation of the environmental impacts associated with the alternatives considered: the Proposed Action and the No-Action alternative. The Proposed Action is to continue U.S. participation in the assembly and operation of ISS. The No-Action alternative would cancel NASA's participation in the Space Station Program. ISS is an international cooperative venture between NASA, the Canadian Space Agency, the European Space Agency, the Science and Technology Agency of Japan, the Russian Space Agency, and the Italian Space Agency. The purpose of the NASA action would be to further develop a human presence in space; to meet scientific, technological, and commercial research needs; and to foster international cooperation.

Source record↗
NASA NTRS1994

Fatigue resistance of unnotched and post impact(+/- 30 deg/0 deg) 3-D braided composites

The fatigue resistance of a multiaxial braided (3-D) graphite/expoxy composite in both unnotched and post impacted conditions has been evaluated. The material tested is a (+/- 30/0 deg) multiaxial braid constructed from AS4/12K tow graphite fibers and British Petroleum E905L epoxy resin. These materials were braided as dry preforms and the epoxy was added using a resin transfer molding process (RTM). The unnotched and post-impact specimens were tested in compression-compression fatigue at 10 Hz with a stress ratio of R=10. The unnotched tension-tension fatigue specimens were tested at S Hz with a stress ration of R=0.1. Damage initiation and growth was documented through the application of radiography and ultrasonic through transmission (C-scans). Visible inspection of surface and edge damage was also noted to describe the initiation and progression of damage in these materials. The mechanisms leading to damage initiation were established and failure modes were determined. Stiffness and strength degradation were measured as a function of applied cycles. These 3-D braided composite results were compared to strain levels currently used to design primary structure in commercial aircraft composite components made from prepreg tape and autoclave cured.

Portanova, Marc A.↗
NASA NTRS2005

Foreign Object Damage Resistance of Uncoated SiC/SiC Composites

2-D woven SiC/SiC composites fabricated by melt infiltration method were impact tested at room temperature and at 1316 C in air using 1.59 mm steel-ball projectiles at projectile velocities ranging from 110 m/s to 400 m/s. The extent of substrate damage with increasing projectile velocity was imaged and analyzed using optical microscopy and nondestructive evaluation (NDE) methods. The impacted specimens were flexure and tensile tested at room temperature to determine their residual mechanical properties. Results indicate that as the projectile velocity increases, internal damage in the target material also increases and the mechanical properties degrade. At velocities > 300 m/s, the projectile penetrates through the target material, but it still retains approx. 50% ultimate strength of the as-fabricated composites and exhibits non-brittle failure.

Bhatt, R. T.↗
NASA NTRS1993

Micrometeoroid/space debris effects on materials

The Long Duration Exposure Facility (LDEF) micrometeoroid/space debris impact data has been reduced in terms that are convenient for evaluating the overall quantitative effect on material properties. Impact crater flux has been evaluated as a function of angle from velocity vector and as a function of crater size. This data is combined with spall data from flight and ground testing to calculate effective solar absorption and emittance values versus time. Results indicate that the surface damage from micrometeoroid/space debris does not significantly affect the overall surface optical thermal physical properties. Of course the local damage around impact craters radically alter optical properties. Damage to composites and solar cells on an overall basis was minimal.

Zwiener, James M.↗
NASA NTRS1976

Fiber composite fan blade impact improvement

The improved foreign object damage resistance of a metal matrix advanced composite fan blade was demonstrated. The fabrication, whirl impact test and subsequent evaluation of nine advanced composite fan blades of the "QCSEE" type design were performed. The blades were designed to operate at a tip speed of 282 m/sec. The blade design was the spar/shell type, consisting of a titanium spar and boron/aluminum composite airfoils. The blade retention was designed to rock on impact with large birds, thereby reducing the blade bending stresses. The program demonstrated the ability of the blades to sustain impacts with up to 681 g slices of birds at 0.38 rad with little damage (only 1.4 percent max weight loss) and 788 g slices of birds at 0.56 rad with only 3.2 percent max weight loss. Unbonding did not exceed 1.1 percent of the post-test blade area during any of the tests. All blades in the post-test condition were judged capable of operation in accordance with the FAA guidelines for medium and large bird impacts.

Graff, J.↗
NASA NTRS1999

Impact of Aircraft Emissions on Reactive Nitrogen over the North Atlantic Flight Corridor Region

The impact of aircraft emissions on reactive nitrogen in the upper troposphere (UT) and lowermost stratosphere (LS) was estimated using the NO(y)-O3 correlation obtained during the SASS Ozone and NO(x) Experiment (SONEX) carried out over the US continent and North Atlantic Flight Corridor (NAFC) region in October and November 1997. To evaluate the large scale impact, we made a reference NO(y)-O3 relationship in air masses, upon which aircraft emissions were considered to have little impact. For this purpose, the integrated input of NO(x) from aircraft into an air mass along a 10-d back trajectory (DELTA-NO(y)) was calculated based on the ANCAT/EC2 emission inventory. The excess NO(y) (dNO(y)) was calculated from the observed NO(y) and the reference NO(y)-O3 relationship. As a result, a weak positive correlation was found between the dNO(y) and DELTA-NO(y), and dNO(y) and NO(x)/NO(y) values, while no positive correlation between the dNO(y) and CO values was found, suggesting that dNO(y) values can be used as a measure of the NO(x) input from aircraft emissions. The excess NO(y) values calculated from another NO(y)-O3 reference relationship made using in-situ CN data also agreed with these dNO(y) values, within the uncertainties. At the NAFC region (45 N - 60 N), the median value of dNO(y) in the troposphere increased with altitude above 9 km and reached 70 pptv (20% of NO(y)) at 11 km. The excess NO(x) was estimated to be about half of the dNO(y) values, corresponding to 30% of the observed NO(x) level. Higher dNO(y) values were generally found in air masses where O3 = 75 - 125 ppbv, suggesting a more pronounced effect around the tropopause. The median value of dNO(y) in the stratosphere at the NAFC region at 8.5 - 11.5 km was about 120 pptv. The higher dNO(y) values in the LS were probably due to the accumulated effect of aircraft emissions, given the long residence time of affected air in the LS. Similar dNO(y) values were also obtained in air masses sampled over the US continent.

Koike, M.↗
NASA NTRS2011

The Effects of Foam Thermal Protection System on the Damage Tolerance Characteristics of Composite Sandwich Structures for Launch Vehicles

For any structure composed of laminated composite materials, impact damage is one of the greatest risks and therefore most widely tested responses. Typically, impact damage testing and analysis assumes that a solid object comes into contact with the bare surface of the laminate (the outer ply). However, most launch vehicle structures will have a thermal protection system (TPS) covering the structure for the majority of its life. Thus, the impact response of the material with the TPS covering is the impact scenario of interest. In this study, laminates representative of the composite interstage structure for the Ares I launch vehicle were impact tested with and without the planned TPS covering, which consists of polyurethane foam. Response variables examined include maximum load of impact, damage size as detected by nondestructive evaluation techniques, and damage morphology and compression after impact strength. Results show that there is little difference between TPS covered and bare specimens, except the residual strength data is higher for TPS covered specimens.

Nettles, A. T.↗