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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

The effect of small-wave modulation on the electromagnetic bias

The effect of the modulation of small ocean waves by large waves on the physical mechanism of the EM bias is examined by conducting a numerical scattering experiment which does not assume the applicability of geometric optics. The modulation effect of the large waves on the small waves is modeled using the principle of conservation of wave action and includes the modulation of gravity-capillary waves. The frequency dependence and magnitude of the EM bias is examined for a simplified ocean spectral model as a function of wind speed. These calculations make it possible to assess the validity of previous assumptions made in the theory of the EM bias, with respect to both scattering and hydrodynamic effects. It is found that the geometric optics approximation is inadequate for predictions of the EM bias at typical radar altimeter frequencies, while the improved scattering calculations provide a frequency dependence of the EM bias which is in qualitative agreement with observation. For typical wind speeds, the EM bias contribution due to small-wave modulation is of the same order as that due to modulation by the nonlinearities of the large-scale waves.

Rodriguez, Ernesto↗
NASA NTRS1992

Small experiments for the maturation of orbital cryogenic transfer technologies

The no-vent method is a promising approach to handling the problems of low-g venting during propellant transfer. A receiver tank is first cooled to remove thermal energy from the tank wall and the resultant vapor vented overboard. The nozzles mix the incoming liquid and residual vapor in the tank maintaining a thermodynamic state which allows the tank to fill with liquid without venting. Ground based testing at NASA Lewis Research Center (LeRC) has demonstrated the no-vent fill process and attempted to bound its low-gravity performance. But, low-gravity testing is required to validate the method. As an alternative to using a dedicated spacecraft for validation, several small scale experiments to study no-vent fill in low-g were formulated. Cost goals quickly limited the search to two possibilities: a secondary payload on the space shuttle, or a small scale sounding rocket experiment. The key issues of small scale experimentation are discussed, and a conceptual design of a sounding rocket experiment with liquid hydrogen for studying the fill process is presented.

Chato, David J.↗
NASA NTRS1990

The effects of small ice crystals on the infrared radiative properties of cirrus clouds

To be successful in the development of satellite retrieval methodologies for the determination of cirrus cloud properties, we must have fundamental scattering and absorption data on nonspherical ice crystals that are found in cirrus clouds. Recent aircraft observations (Platt et al. 1989) reveal that there is a large amount of small ice particles, on the order of 10 micron, in cirrus clouds. Thus it is important to explore the potential differences in the scattering and absorption properties of ice crystals with respect to their sizes and shapes. In this study the effects of nonspherical small ice crystals on the infrared radiative properties of cirrus clouds are investigated using light scattering properties of spheroidal particles. In Section 2, using the anomalous diffraction theory for spheres and results from the exact spheroid scattering program, efficient parameterization equations are developed for calculations of the scattering and absorption properties for small ice crystals. Parameterization formulas are also developed for large ice crystals using results computed from the geometric ray-tracing technique and the Fraunhofer diffraction theory for spheroids and hexagonal crystals. This is presented in Section 3. Finally, applications to the satellite remote sensing are described in Section 4.

Takano, Y.↗
NASA NTRS1992

Small experiments for the maturation of orbital cryogenic transfer technologies

The no-vent fill method is a promising approach to handle the problems of low-g venting during propellant transfer. A receiver tank is first cooled to remove thermal energy from the tank wall and the resultant vapor vented overboard. Then nozzles mix the incoming liquid and residual vapor in the tank maintaining a thermodynamic state which allows the tank to fill with liquid without venting. Ground based testing at NASA Lewis Research Center (LeRC) has demonstrated the no-vent fill process and attempted to bound its low-gravity performance. But, low-gravity testing is required to validate the method. As an alternative to using a dedicated spacecraft for validation the authors have formulated several small scale experiments to study no-vent fill in low-g. Cost goals quickly limited the search to two possibilities: a secondary payload on the Space Shuttle, or a small scale sounding rocket experiment. This paper will discuss the key issues of small scale experimentation and present a conceptual design of a sounding rocket experiment with liquid hydrogen for studying the fill process.

Chato, David J.↗
NASA NTRS1992

Small-crack growth behavior in high-strength aluminum alloys - A NASA/CAE cooperative program

NASA and the Chinese Aeronautics Establishment have participated in a Fatigue and Fracture Mechanics Cooperative Program giving attention to small-crack effects in high-strength Al alloys. Experimental and analytical investigations studied crack initiation and growth behavior of small cracks in both bare 7075-T6 and clad LC9cs Al alloys, with a view to the improvement of their fracture-mechanics analyses in the cases of surface crack and corner crack configurations. It is also expected that superior life-prediction methods will be developed in order to correlate and predict small crack and large crack growth with various load histories.

Newman, J. C., Jr.↗
NASA NTRS1993

Atmospheric holes and small comets

Global images of Earth's UV dayglow as gained with an imaging photometer on board Dynamics Explorer 1 exhibit transient decreases, or atmospheric holes, in the dayglow intensities over areas with diameters about 50 km. Features of these atmospheric holes include (1) preferential motion in the east-to-west direction across the sunlit face of Earth, (2) similar diurnal variations in occurrence rates as those for radar meteors, (3) correlation of the occurrence rates with the nonshower rates as determined with forward scatter radar, and (4) larger angular diameters for these atmospheric holes when the spacecraft approaches Earth during its perigee passes. These atmospheric holes are interpreted in terms of obscuration of the dayglow by water clouds from the disruption and subsequent vaporization of small comets at low altitudes above the atmosphere. Supporting evidence for the existence of these small comets is given by their telescopic sighting at greater altitudes before disruption and the detection of water bursts in Earth's upper atmosphere. The small-comet hypothesis and its relationship to geophysical, lunar, and interplanetary phenomena are discussed.

Frank, L. A.↗
NASA NTRS1931

The effect of small variations in profile of airfoils

This report deals with the effect of small variations in ordinates specified by different laboratories for the airfoil section. This study was made in connection with a more general investigation of the effect of small irregularities of the airfoil surface on the aerodynamic characteristics of an airfoil. These tests show that small changes in airfoil contours, resulting from variations in the specified ordinates, have a sufficiently large effect upon the airfoil characteristics to justify the taking of great care in the specification of ordinates for the construction of models.

Ward, Kenneth E↗
NASA NTRS1993

Combustor technology for future small gas turbine aircraft

Future engine cycles proposed for advanced small gas turbine engines will increase the severity of the operating conditions of the combustor. These cycles call for increased overall engine pressure ratios which increase combustor inlet pressure and temperature. Further, the temperature rise through the combustor and the corresponding exit temperature also increase. Future combustor technology needs for small gas turbine engines is described. New fuel injectors with large turndown ratios which produce uniform circumferential and radial temperature patterns will be required. Uniform burning will be of greater importance because hot gas temperatures will approach turbine material limits. The higher combustion temperatures and increased radiation at high pressures will put a greater heat load on the combustor liners. At the same time, less cooling air will be available as more of the air will be used for combustion. Thus, improved cooling concepts and/or materials requiring little or no direct cooling will be required. Although presently there are no requirements for emissions levels from small gas turbine engines, regulation is expected in the near future. This will require the development of low emission combustors. In particular, nitrogen oxides will increase substantially if new technologies limiting their formation are not evolved and implemented. For example, staged combustion employing lean, premixed/prevaporized, lean direct injection, or rich burn-quick quench-lean burn concepts could replace conventional single stage combustors.

Lyons, Valerie J.↗
NASA NTRS1993

Relief of some small landforms on Venus

Three sets of radar images have been acquired under different viewing conditions by the Magellan synthetic aperture radar: (1) left-looking with varied incidence angles (cycle 1); (2) right-looking with nearly constant incidence angles (cycle 2); and (3) left-looking with varied incidence angles, most of which were smaller than those in (1) except for those acquired on passes across Maxwell Montes with incidence angles larger than those in (1) (cycle 3). Image displacements in the radar images that are caused by the relief of landforms provide several methods of estimating this relief: (1) monoscopic measurements of foreshortening of landforms that are symmetrical in the plane of the look-direction of the radar (includes radial symmetry); (2) stereoscopic measurements of parallax in same-side image pairs (cycles 1-2 and 3); and (3) measurements of parallax in opposite-side image pairs (cycles 1-2 and/or 2-3). Success in methods 2 and 3 (especially 3) depends on identifying conjugate image points in the two images. Here, we report our preliminary results for five impact craters, seven small volcanic edifices, and two lava flows. The three methods mentioned above lead to the interesting result that Venusian impact craters have depth-diameter ratios like those on Mars rather than those on Earth, but some appear partly filled. Our results for de Lalande and Melba also suggest filling, but there may be other causes for their relatively small depth-diameter ratios. A host of small volcanic edifices have relief that can be crudely estimated using the above methods. Relief/diameter ratios for our cratered cones are about the same as those of Icelandic lava shields; some Venusian cones resemble the Martian shields of Mareotis-Tempe and Ceraunius Fossae, but the Venusian relief diameter ratios are larger. The smallest cratered dome is similar in size and profile to a Martian dome north of Uranius Patera; the smallest cratered cone resembles one in Chryse Planitia. Lava flows on Venus that are thick enough to measure are rare, but we have applied methods 1 and 3 to the huge flow of Ovda Regio and flows of an unusual volcano, Mahuea Tholus.

Moore, H. J.↗
NASA NTRS1993

Small spacecraft for planetary exploration

There is need for lower cost, more frequent planetary science missions to compliment the 'once a decade' large multidisciplinary missions. The Solar System Exploration Division of NASA's Office of Space Science and Applications has initiated a program of planetary missions using small spacecraft. This program is called Discovery. Conceptual designs of small spacecraft (100 to 500 kg) for potential Discovery missions to near Earth asteroids are summarized. Another class of spacecraft that could be used for Discovery missions are called microspacecraft. Microspacecraft would be compatible with small launch vehicles such as Pegasus. The term 'microspacecraft' is used here for spacecraft concepts whose mass is about 10 kg. A study of a microspacecraft for a mission to near Earth asteroids is also summarized.

Jones, Ross M.↗
NASA NTRS1993

Utilization of Shuttle small payload accommodations in the DOD Space Test Program

Over the past 27 years, the U.S. Air Force, as executive agent for the Department of Defense (DOD) Space Test Program, has flown approximately 325 space experiments for the Army, Navy, Air Force, and other DOD agencies. These experiments have made significant contributions to the improvement of military technology and operations. Flight of Space Test Program experiments has been carried out utilizing free flyer spacecraft, the Space Shuttle crew cabin, and the Space Shuttle cargo bay. This paper will concentrate on those experiments which have been flown by the NASA Space Shuttle small payload flight systems, e.g., GAS, uprated GAS (CAP), and Hitchhiker flight systems. Discussions of Space Test Program experiments flown by Space Shuttle small payloads flight systems will include the experiment objectives, the accommodations and services provided by the flight systems, experiment results, and lessons learned from the planning and conduct of the flight. Particular emphasis will be placed on those experiments which required and were provided with a new and unique capability by the small payloads flight systems. These capabilities include the first use of the GAS opening lid, the first use of the GAS payload ejection capability, and the first use of the Hitchhiker cross bay carrier.

Hagler, Thomas↗
NASA NTRS1993

Heterogeneity in small aliquots of Apolllo 15 olivine-normative basalt: Implications for breccia clast studies

Most of the recent advances in lunar petrology are the direct result of breccia pull-apart studies, which have identified a wide array of new highland and mare basalt rock types that occur only as clasts within the breccias. These rocks show that the lunar crust is far more complex than suspected previously, and that processes such as magma mixing and wall-rock assimilation were important in its petrogenesis. These studies are based on the implicit assumption that the breccia clasts, which range in size from a few mm to several cm across, are representative of the parent rock from which they were derived. In many cases, the aliquot allocated for analysis may be only a few grain diameters across. While this problem is most acute for coarse-grained highland rocks, it can also cause considerable uncertainty in the analysis of mare basalt clasts. Similar problems arise with small aliquots of individual hand samples. Our study of sample heterogeneity in 9 samples of Apollo 15 olivine normative basalt (ONB) which exhibit a range in average grain size from coarse to fine are reported. Seven of these samples have not been analyzed previously, one has been analyzed by INAA only, and one has been analyzed by XRF+INAA. Our goal is to assess the effects of small aliquot size on the bulk chemistry of large mare basalt samples, and to extend this assessment to analyses of small breccia clasts.

Lindstrom, Marilyn M.↗
NASA NTRS1993

A small satellite design for deep space network testing and training

With the continuing exploration of the Solar System and the reemphasis on Earth focused missions, the need for faster data transmission rates has grown. Ka-band could allow a higher data delivery rate over the current X-band, however the adverse effects of the Earth's atmosphere on Ka are as yet unknown. The Deep Space Network and Jet Propulsion Lab have proposed to launch a small satellite that would simultaneously transmit X and Ka signals to test the viability of switching to Ka-band. The Mockingbird Design Team at the University of Texas at Austin applied small satellite design principles to achieve this objective. The Mockingbird design, named BATSAT, incorporates simple, low-cost systems designed for university production and testing. The BATSAT satellite is a 0.64 m diameter, spherical panel led satellite, mounted with solar cells and omni-directional antennae. The antennae configuration negates the need for active attitude control or spin stabilization. The space-frame truss structure was designed for 11 g launch loads while allowing for easy construction and solar-panel mounting. The communication system transmits at 1 mW by carrying the required Ka and X-band transmitters, as well as an S band transmitter used for DSN training. The power system provides the 8.6 W maximum power requirements via silicon solar arrays and nickel-cadmium batteries. The BATSAT satellite will be lofted into an 1163 km, 70 deg orbit by the Pegasus launch system. This orbit fulfills DSN dish slew rate requirements while keeping the satellite out of the heaviest regions of the Van Allen radiation belts. Each of the three DSN stations capable of receiving Ka-band (Goldstone, Canberra, and Madrid) will have an average of 85 minutes of view-time per day over the satellites ten year design life. Mockingbird Designs hopes that its small satellite design will not only be applicable to this specific mission scenario, but that it could easily be modified for instrument capability for university, government, and/or commercial research.

Mcwilliams, Dennis↗
NASA NTRS1993

A diagnostic model to estimate winds and small-scale drag from Mars Observer PMIRR data

Theoretical and modeling studies indicate that small-scale drag due to breaking gravity waves is likely to be of considerable importance for the circulation in the middle atmospheric region (approximately 40-100 km altitude) on Mars. Recent earth-based spectroscopic observations have provided evidence for the existence of circulation features, in particular, a warm winter polar region, associated with gravity wave drag. Since the Mars Observer PMIRR experiment will obtain temperature profiles extending from the surface up to about 80 km altitude, it will be extensively sampling middle atmospheric regions in which gravity wave drag may play a dominant role. Estimating the drag then becomes crucial to the estimation of the atmospheric winds from the PMIRR-observed temperatures. An interative diagnostic model based upon one previously developed and tested with earth satellite temperature data will be applied to the PMIRR measurements to produce estimates of the small-scale zonal drag and three-dimensional wind fields in the Mars middle atmosphere. This model is based on the primitive equations, and can allow for time dependence (the time tendencies used may be based upon those computed in a Fast Fourier Mapping procedure). The small-scale zonal drag is estimated as the residual in the zonal momentum equation; the horizontal winds having first been estimated from the meridional momentum equation and the continuity equation. The scheme estimates the vertical motions from the thermodynamic equation, and thus needs estimates of the diabatic heating based upon the observed temperatures. The latter will be generated using a radiative model. It is hoped that the diagnostic scheme will be able to produce good estimates of the zonal gravity wave drag in the Mars middle atmosphere, estimates that can then be used in other diagnostic or assimilation efforts, as well as more theoretical studies.

Barnes, J. R.↗
NASA NTRS1994

Initiation and propagation of small corner cracks

The behaviour of small corner cracks, inclined or perpendicular to loading direction, is presented. There are two aspects to this investigation: initiation of small cracks and monitoring their subsequent growth. An initial pre-cracking procedure under cyclic compression is adopted to minimize the residual damage at the tip of the growing and self-arresting crack under cyclic compression. A final fatigue specimen, cut from the larger pre-cracked specimen, has two corner flaws. The opening load of corner flaw is monitored using a novel strain gauge approach. The behaviour of small corner cracks is described in terms of growth rate relative to the size of the crack and its shape.

Ellyin, Ferdnand↗
NASA NTRS1993

Lightning protection technology for small general aviation composite material aircraft

An on going NASA (Small Business Innovative Research) SBIR Phase II design and development program will produce the first lightning protected, fiberglass, General Aviation aircraft that is available as a kit. The results obtained so far in development testing of typical components of the aircraft kit, such as the wing and fuselage panels indicate that the lightning protection design methodology and materials chosen are capable of protecting such small composite airframes from lightning puncture and structural damage associated with severe threat lightning strikes. The primary objective of the program has been to develop a lightening protection design for full scale test airframe and verify its adequacy with full scale laboratory testing, thus enabling production and sale of owner-built, lightning-protected, Stoddard-Hamilton Aircraft, Inc. Glasair II airplanes. A second objective has been to provide lightning protection design guidelines for the General Aviation industry, and to enable these airplanes to meet lightening protection requirements for certification of small airplanes. This paper describes the protection design approaches and development testing results obtained thus far in the program, together with design methodology which can achieve the design goals listed above. The presentation of this paper will also include results of some of the full scale verification tests, which will have been completed by the time of this conference.

Plumer, J. A.↗
NASA NTRS1995

Dust in the Small Magellanic Cloud

We discuss simultaneous dust model fits to our extinction and polarization data for the Small Magellanic Cloud (SMC) using existing dust models. Dust model fits to the wavelength dependent polarization are possible for stars with small lambda(sub max). They generally imply size distributions which are narrower and have smaller average sizes compared to those in the Galaxy. The best fits for the extinction curves are obtained with a power law size distribution. The typical, monotonic SMC extinction curve can be well fit with graphite and silicate grains if a small fraction of the SMC carbon is locked up in the grains. Amorphous carbon and silicate grains also fit the data well.

Rodrigues, C. V.↗
NASA NTRS1995

Dust in the small Magellanic Cloud. 2: Dust models from interstellar polarization and extinction data

We study the dust in the Small Magellanic Cloud using our polarization and extinction data (Paper 1) and existing dust models. The data suggest that the monotonic SMC extinction curve is related to values of lambda(sub max), the wavelength of maximum polarization, which are on the average smaller than the mean for the Galaxy. On the other hand, AZV 456, a star with an extinction similar to that for the Galaxy, shows a value of lambda(sub max) similar to the mean for the Galaxy. We discuss simultaneous dust model fits to extinction and polarization. Fits to the wavelength dependent polarization data are possible for stars with small lambda(sub max). In general, they imply dust size distributions which are narrower and have smaller mean sizes compared to typical size distributions for the Galaxy. However, stars with lambda(sub max) close to the Galactic norm, which also have a narrower polarization curve, cannot be fit adequately. This holds true for all of the dust models considered. The best fits to the extinction curves are obtained with a power law size distribution by assuming that the cylindrical and spherical silicate grains have a volume distribution which is continuous from the smaller spheres to the larger cylinders. The size distribution for the cylinders is taken from the fit to the polarization. The 'typical', monotonic SMC extinction curve can be fit well with graphite and silicate grains if a small fraction of the SMC carbon is locked up in the grain. However, amorphous carbon and silicate grains also fit the data well. AZV456, which has an extinction curve similar to that for the Galaxy, has a UV bump which is too blue to be fit by spherical graphite grains.

Rodrigues, C. V.↗