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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Orbital debris and meteoroid population as estimated from LDEF impact data

Examination of LDEF's various surfaces shows numerous craters and holes due to hypervelocity impacts of meteoroids and man-made orbital debris. In this paper, the crater numbers as reported by Humes have been analyzed in an effort to understand the orbital debris and natural meteoroid environment in LEO. To determine the fraction of man-made to natural impacts, the side to top ratio of impacts and results of the Chemistry of Micrometeoroids Experiment are used. For craters in the 100 micron to 500 micron size range, about 25 percent to 30 percent of the impacts on the forward-facing surfaces and about 10 percent of the impacts on the trailing surfaces were estimated due to man-made orbital debris. A technique has been developed to convert crater numbers to particle fluxes, taking the fact into account that the distributions of impact velocity and incidence angle vary over the different surfaces of LDEF, as well as the ratio of the surface area flux to the cross-sectional area flux. Applying this technique, Humes' data concerning craters with limiting lip diameters of 100 micron, 200 micron and 500 micron have been converted into orbital debris and meteoroid fluxes ranging from about 20 micron to 200 micron particle diameter. The results exhibit good agreement with orbital debris model and meteoroid model. The converted meteoroid flux is slightly larger than Grun's model (by 40 to 70 percent). The converted orbital debris flux is slightly lower than Kessler's model for particle diameter smaller than about 30 micron and slightly larger than the model for particle diameter larger than about 40 micron. Taking also into account the IDE data point at about 0.8 micron particle diameter, it suggests to change the slope log (flux) versus log (diameter) of orbital debris flux in the 1 micron to 100 micron particle diameter range from 2.5 to 1.9.

Zhang, Jingchang↗
NASA NTRS1995

First lidar measurements of water vapor and aerosols from a high-altitude aircraft

Water vapor plays an important role in many atmospheric processes related to radiation, climate change, atmospheric dynamics, meteorology, the global hydrologic cycle, and atmospheric chemistry, and yet our knowledge of the global distribution of water vapor is very limited. The differential absorption lidar (DIAL) technique has the potential of providing needed high resolution water vapor measurements from aircraft and from space, and the Lidar Atmospheric Sensing Experiment (LASE) is a key step in the development of this capability. The LASE instrument is the first fully engineered, autonomous DIAL system, and it is designed to operate from a high-altitude aircraft (ER-2) and to make water vapor and aerosol profile measurements across the troposphere. The LASE system was flown from the NASA Wallops Flight Facility in a series of engineering flights during September 1994. This paper discusses the characteristics of the LASE system and presents the first LASE measurements of water vapor and aerosol profiles.

Browell, Edward V.↗
NASA NTRS1996

Data Analysis and Theoretical Studies of the Upper Mesosphere and Lower Thermosphere

Three separate tasks were proposed under this award. The first involved extending our continuing study of electrodynamical feedback between the thermosphere/ionosphere and the magnetosphere. The second was a model-experiment comparison study of global dynamics and the third was a 'spectral energetics' analysis of tidal dissipation and energy exchange mechanisms. The Earth's mesosphere and lower-thermosphere/ionosphere (MLTI), between approximately 60 and 180 km altitude, is the most poorly understood region of the Earth's atmosphere, primarily because of its relative inaccessibility. This lack of knowledge has been widely recognized and has provided important scientific rationale for the upcoming NASA TIMED mission. While the data gathered during the TIMED era will revolutionize our understanding of the MLTI region, much work can be done prior to the mission, both to develop data-analysis and modeling techniques and to study the more limited relevant experimental data from previous missions. The grant reported on here continues and extends an existing successful program of scientific research into the energetics, dynamics and electrodynamics of the MLTI, using available theoretical and data analysis tools.

Burns, Alan↗
NASA NTRS2000

Natural Hazards of the Space Environment

Spacecraft in Low Earth Orbit (LEO) are subject to numerous environmental hazards. Here I'll briefly discuss three environment factors that pose acute threats to the survival of spacecraft systems and crew: atmospheric drag, impacts by meteoroids and orbital debris, and ionizing radiation. Atmospheric drag continuously opposes the orbital motion of a satellite, causing the orbit to decay. This decay will lead to reentry if not countered by reboost maneuvers. Orbital debris is a by-product of man's activities in space, and consists of objects ranging in size from miniscule paint chips to spent rocket stages and dead satellites. Ionizing radiation experienced in LEO has several components: geomagnetically trapped protons and electrons (Van Allen belts); energetic solar particles; galactic cosmic rays; and albedo neutrons. These particles can have several types of prompt harmful effects on equipment and crew, from single-event upsets, latchup, and burnout of electronics, to lethal doses to crew.All three types of prompt threat show some dependence on the solar activity cycle. Atmospheric drag mitigation and large debris avoidance require propulsive maneuvers. M/OD and ionizing radiation require some form of shielding for crew and sensitive equipment. Limiting exposure time is a mitigation technique for ionizing radiation and meteor streams.

Evans, Steven W.↗
NASA NTRS2000

Satellite and Ground-based Radiometers Reveal Much Lower Dust Absorption of Sunlight than Used in Climate Models

The ability of dust to absorb solar radiation and heat the atmosphere is one of the main uncertainties in climate modeling and the prediction of climate change. Dust absorption is not well known due to limitations of in situ measurements. New techniques to measure dust absorption are needed in order to assess the impact of dust on climate. Here we report two new independent remote sensing techniques that provide sensitive measurements of dust absorption. Both are based on remote sensing. One uses satellite spectral measurements, the second uses ground based sky measurements from the AERONET network. Both techniques demonstrate that Saharan dust absorption of solar radiation is several times smaller than the current international standards. Dust cooling of the earth system in the solar spectrum is therefore significantly stronger than recent calculations indicate. We shall also address the issue of the effects of dust non-sphericity on the aerosol optical properties.

Kaufman, Y. J.↗
NASA NTRS2003

Surface Tension and Viscosity of SCN and SCN-acetone Alloys at Melting Points and Higher Temperatures Using Surface Light Scattering Spectrometer

Succinonitrile has been and is being used extensively in NASA's Microgravity Materials Science and Fluid Physics programs and as well as in several ground-based and microgravity studies including the Isothermal Dendritic Growth Experiment (IDGE). Succinonitrile (SCN) is useful as a model for the study of metal solidification, although it is an organic material, it has a BCC crystal structure and solidifies dendriticly like a metal. It is also transparent and has a low melting point (58.08 C). Previous measurements of succinonitrile (SCN) and alloys of succinonitrile and acetone surface tensions are extremely limited. Using the Surface Light Scattering technique we have determined non invasively, the surface tension and viscosity of SCN and SCN-Acetone Alloys at different temperatures. This relatively new and unique technique has several advantages over the classical methods such as, it is non invasive, has good accuracy and measures the surface tension and viscosity simultaneously. The accuracy of interfacial energy values obtained from this technique is better than 2% and viscosity about 10 %. Succinonitrile and succinonitrile-acetone alloys are well-established model materials with several essential physical properties accurately known - except the liquid/vapor surface tension at different elevated temperatures. We will be presenting the experimentally determined liquid/vapor surface energy and liquid viscosity of succinonitrile and succinonitrile-acetone alloys in the temperature range from their melting point to around 100 C using this non-invasive technique. We will also discuss about the measurement technique and new developments of the Surface Light Scattering Spectrometer.

Tin, Padetha↗
NASA NTRS2001

In-Flight Edge Response Measurements for High Spatial Resolution Remote Sensing Systems

In-flight measurement of spatial resolution were conducted as part of the ASA Scientific Data Purchase (SDP) Validation and Verification (V&V) process. Characterization included remote sensing systems with ground sample distance (GSD) of 1 meter or less, such as the panchromatic imager on-board the ICONOS satellite and the airborne ADAR System 5500 multispectral instrument. Final image products were used to evaluate the effect of both the image acquisition system (e.g., optics, electronics, motion, jitter, atmosphere) and image post-processing (e.g., resampling, modulation trasfer function (MTF) compensator). Spatial resolution was characterized by full width at half maximum (FWHM) of an edge response-derived line spread function. This was found to be a more robust measure of spatial resolution than the value of NTF at Nyquist frequency The edge responses were analysed using the tilted-edge technique that ovecomes the spatial sampling limitations of the digital imaging systems. As an enhancement to existing algorithms, the slope of the edge response and the orientation of the edge target were determined by a single computational process. Adjacent black and white square panels, either painted on a flat surface or deployed as traps, formed the ground-based edge targets used in the tests. Orientation of the deployable tarps was optimized beforehand, based on simulations of the imaging system. Numerous edge target images were analyzed for each of the tested sensors. The effect of such factors as acquisition geometry, temporal variability, MTF compensation, and GSD on spatial resolution were investigated.

Blonski, Slawomir↗
NASA NTRS2004

Laser-Induced Breakdown Spectroscopy of Trace Metals

An alternative approach for laser-induced breakdown spectroscopy (LIBS) determination of trace metal determination in liquids is demonstrated. The limits of detection (LOD) for the technique ranged from 10 ppb to 10 ppm for 15 metals metals (Mg, Al, Si, Ca, Ti, Cr, Fe, Co, Ni, Cu, Zn, As, Cd, Hg, Pb) tested.

Simons, Stephen↗
NASA NTRS2001

Automated quantification of mitral valve regurgitation based on normalized centerline velocity distribution

Previous echocardiographic techniques for quantifying valvular regurgitation are limited by factors including uncertainties for orifice location and a hemispheric convergence assumption that often results in over- and underestimation of flow rate and regurgitant orifice area. Using computational fluid dynamics simulations, these factors were eliminated, allowing a more accurate assessment of regurgitation. A model was developed to allow automated quantification of regurgitant orifice diameter based on the centerline velocity data available from color M-mode echocardiography. The model, validated using in vitro unsteady flow data, demonstrated improved accuracy for orifice diameter (y=0.95x + 0.38, r=0.96) and volume (y=1.18x - 4.72, r=0.93).

NASA Program Biomedical Research and Countermeasur↗
NASA NTRS2003

Renal vascular responses to static handgrip: role of muscle mechanoreflex

During exercise, the sympathetic nervous system is activated, which causes vasoconstriction. The autonomic mechanisms responsible for this vasoconstriction vary based on the particular tissue being studied. Attempts to examine reflex control of the human renal circulation have been difficult because of technical limitations. In this report, the Doppler technique was used to examine renal flow velocity during four muscle contraction paradigms in conscious humans. Flow velocity was divided by mean arterial blood pressure to yield an index of renal vascular resistance (RVR). Fatiguing static handgrip (40% of maximal voluntary contraction) increased RVR by 76%. During posthandgrip circulatory arrest, RVR remained above baseline (2.1 +/- 0.2 vs. 2.8 +/- 0.2 arbitrary units; P < 0.017) but was only 40% of the end-grip RVR value. Voluntary biceps contraction increased RVR within 10 s of initiation of contraction. This effect was not associated with an increase in blood pressure. Finally, involuntary biceps contraction also raised RVR. We conclude that muscle contraction evokes renal vasoconstriction in conscious humans. The characteristic of this response is consistent with a primary role for mechanically sensitive afferents. This statement is based on the small posthandgrip circulatory arrest response and the vasoconstriction that was observed with involuntary biceps contraction.

NASA Discipline Neuroscience↗
NASA NTRS2002

Artificial cells: prospects for biotechnology

A variety of techniques can now be used to alter the genome of a cell. Although these techniques are very powerful, they have limitations related to cost and efficiency of scale. Artificial cells designed for specific applications combine properties of biological systems such as nanoscale efficiency, self-organization and adaptability at relatively low cost. Individual components needed for such structures have already been developed, and now the main challenge is to integrate them in functional microscopic compartments. It will then become possible to design and construct communities of artificial cells that can perform different tasks related to therapeutic and diagnostic applications.

Review↗
NASA NTRS1993

Formal Methods for Life-Critical Software

The use of computer software in life-critical applications, such as for civil air transports, demands the use of rigorous formal mathematical verification procedures. This paper demonstrates how to apply formal methods to the development and verification of software by leading the reader step-by-step through requirements analysis, design, implementation, and verification of an electronic phone book application. The current maturity and limitations of formal methods tools and techniques are then discussed, and a number of examples of the successful use of formal methods by industry are cited.

Butler, Ricky W.↗
NASA NTRS2005

Higher-Order Spectral Analysis of F-18 Flight Flutter Data

Royal Australian Air Force (RAAF) F/A-18 flight flutter test data is presented and analyzed using various techniques. The data includes high-quality measurements of forced responses and limit cycle oscillation (LCO) phenomena. Standard correlation and power spectral density (PSD) techniques are applied to the data and presented. Novel applications of experimentally-identified impulse responses and higher-order spectral techniques are also applied to the data and presented. The goal of this research is to develop methods that can identify the onset of nonlinear aeroelastic phenomena, such as LCO, during flutter testing.

Silva, Walter A.↗
NASA NTRS2005

Small Portable PEM Fuel Cell Systems for NASA Exploration Missions

Oxygen-Hydrogen PEM-based fuel cell systems are being examined as a portable power source alternative in addition to advanced battery technology. Fuel cell power systems have been used by the Gemini, Apollo, and Space Shuttle programs. These systems have not been portable, but have been integral parts of their spacecraft, and have used reactants from a separate cryogenic supply. These systems typically have been higher in power. They also have had significant ancillary equipment sections that perform the pumping of reactants and coolant through the fuel cell stack and the separation of the product water from the unused reactant streams. The design of small portable fuel cell systems will be a significant departure from these previous designs. These smaller designs will have very limited ancillary equipment, relying on passive techniques for reactant and thermal management, and the reactant storage will be an integral part of the fuel cell system. An analysis of the mass and volume for small portable fuel cell systems was done to evaluate and quantify areas of technological improvement. A review of current fuel cell technology as well as reactant storage and management technology was completed to validate the analysis and to identify technology challenges

Burke, Kenneth A.↗
NASA NTRS1993

A Simple Theory of Capillary-Gravity Wave Turbulence

Employing a recently proposed 'multi-wave interaction' theory [JFM, 243, 623-625], spectra of capillary-gravity waves are derived. This case is characterized by a rather high degree of nonlinearity and a complicated dispersion law. The resultant absence of scale invariance makes this and some other problems of wave turbulence (e.g., nonlinear Rossby waves) intractable by small-perturbation techniques, even in the weak turbulence limit. The analytical solution obtained in the present work is shown to be in good agreement with experimental data. Its low- and high-frequency limits yield power-laws characterizing spectra of purely gravity and capillary waves, respectively. In the limits of weak and strong linearity, these reduce of the Zakharov-Filonenko and Phillips spectra, respectively.

Glazman, Roman E.↗
NASA NTRS2008

Vibroacoustic Response of the NASA ACTS Spacecraft Antenna to Launch Acoustic Excitation

The Advanced Communications Technology Satellite was an experimental NASA satellite launched from the Space Shuttle Discovery. As part of the ground test program, the satellite s large, parabolic reflector antennas were exposed to a reverberant acoustic loading to simulate the launch acoustics in the Shuttle payload bay. This paper describes the modelling and analysis of the dynamic response of these large, composite spacecraft antenna structure subjected to a diffuse acoustic field excitation. Due to the broad frequency range of the excitation, different models were created to make predictions in the various frequency regimes of interest: a statistical energy analysis (SEA) model to capture the high frequency response and a hybrid finite element-statistical energy (hybrid FE-SEA) model for the low to mid-frequency responses. The strengths and limitations of each of the analytical techniques are discussed. The predictions are then compared to the measured acoustic test data and to a boundary element (BEM) model to evaluate the performance of the hybrid techniques.

Larko, Jeffrey M.↗
NASA NTRS2010

Boundary Layer Measurements in a Supersonic Wind Tunnel Using Doppler Global Velocimetry

A modified Doppler Global Velocimeter (DGV) was developed to measure the velocity within the boundary layer above a flat plate in a supersonic flow. Classic laser velocimetry (LV) approaches could not be used since the model surface was composed of a glass-ceramic insulator in support of heat-transfer measurements. Since surface flare limited the use of external LV techniques and windows placed in the model would change the heat transfer characteristics of the flat plate, a novel approach was developed. The input laser beam was divided into nine equal power beams and each transmitted through optical fibers to a small cavity within the model. The beams were then directed through 1.6-mm diameter orifices to form a series of orthogonal beams emitted from the model and aligned with the tunnel centerline to approximate a laser light sheet. Scattered light from 0.1-micron diameter water condensation ice crystals was collected by four 5-mm diameter lenses and transmitted by their respective optical fiber bundles to terminate at the image plane of a standard two-camera DGV receiver. Flow measurements were made over a range from 0.5-mm above the surface to the freestream at Mach 3.51 in steady state and heat pulse injected flows. This technique provides a unique option for measuring boundary layers in supersonic flows where seeding the flow is problematic or where the experimental apparatus does not provide the optical access required by other techniques.

Meyers, James F.↗
NASA NTRS2010

Real-Time Exponential Curve Fits Using Discrete Calculus

An improved solution for curve fitting data to an exponential equation (y = Ae(exp Bt) + C) has been developed. This improvement is in four areas -- speed, stability, determinant processing time, and the removal of limits. The solution presented avoids iterative techniques and their stability errors by using three mathematical ideas: discrete calculus, a special relationship (be tween exponential curves and the Mean Value Theorem for Derivatives), and a simple linear curve fit algorithm. This method can also be applied to fitting data to the general power law equation y = Ax(exp B) + C and the general geometric growth equation y = Ak(exp Bt) + C.

Rowe, Geoffrey↗