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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 NTRS1980

Noise control prediction for high-speed, propeller-driven aircraft

An analytical study is described which explores add-on treatments and advanced concepts for the reduction of noise levels in three high-speed aircraft driven by propellers. Noise reductions of 25 to 28 dB are required to achieve a goal of an A-weighted sound level not greater than 80 dB. It is found that only a double-wall system, with a limp inner wall or trim panel, can achieve the required noise reductions. Weight penalties are estimated for the double-wall treatments. These penalties are 0.75% to 1.51% of the aircraft takeoff weight for the particular baseline designs selected.

Wilby, J. F.↗
NASA NTRS1979

Estimation of mean sea surfaces in the North Atlantic, the Pacific and the Indian Ocean using GEOS-3 altimeter data

The sea surface heights above the reference ellipsoid were determined for several regions of the world's ocean using data from the radar altimeter on board the GEOS-3 satellite in conjunction with precise orbital position information derived from laser data. The resolution of the estimated sea surfaces varied from 0.25 degrees off the east coast of the United States to about 2 degrees in the Indian Ocean near Australia. The rms crossover discrepancy after adjustment varied from 30 cm to 70 cm depending on geographic location. Comparison of the altimeter derived mean sea surface in the North Atlantic with the 5 x 5 ft GEM-8 detailed gravimetric geoid indicated a relative consistency of better than one meter.

Marsh, J. G.↗
NASA NTRS1981

High energy density batteries for satellite applications

The performance requirements of high-energy batteries for terrestrial applications were examined to establish whether or not these systems showed any promise in aerospace applications. The technology assessment is reported and consists of a battery technology evaluation, preliminary engineering studies, and system selection. Major candidate systems are compared and a program schedule is provided.

Marcoux, L.↗
NASA NTRS1980

Two-dimensional VLA maps of solar bursts at 15 and 23 GHz with arcsec resolution

Three small, impulsive solar-microwave bursts (peak fluxes 4.9, 3.0, and 0.4 sfu) were observed during 1979 September 7-9, using the Very Large Array (VLA) at 15.05 or 22.5 GHz. The data from 10 antennas distributed on three arms of the array provide the first two-dimensional burst images with spatial resolution as high as 1.0 x 0.75 arcsec. Comparison with optical data showed in the impulsive phase of all three flares, the microwave emission was dominated by a compact source located between the H-alpha kernels. In the post-impulsive phase, the microwave source was larger and elongated in a direction consistent with the orientation of the magnetic field lines joining the H-alpha kernels. These results are interpreted to imply that the initial energy release occurs near the top of the magnetic arch joining the H-alpha kernels.

Marsh, K. A.↗
NASA NTRS1980

VLA observations of impulsive solar flares at 4.9 GHz

A series of snapshot synthesis maps constructed as a function of time provided a complete mapping of source structure in one dimension and absolute location in two dimensions of five impulsive solar microwave bursts observed during July 15-18, 1978. It was found that all five flares were dominated by a single 12-18 arcsec source located between the H-alpha kernels, near the magnetic neutral line. Spectral data from Sagamore Hill (1.4-35 GHz) show that the spectral turnover at low frequencies results from the absorption by the ambient active region; these results, together with the observed magnetic configuration, suggest a model which could explain the evolution in source structure at 4.9 GHz in terms of magnetic reconnection which starts below the optical depth of the ambient active region equal to 1.

Marsh, K. A.↗
NASA NTRS1981

Seasat altimeter observations of dynamic topography in the Gulf Stream region

A straightforward approach to altimeter data analysis in the Gulf Stream system is presented, using a detailed geoid model to remove the gravitational component. The resulting sea surface height profiles compare remarkably well with independent oceanographic observations. Specific features such as cold rings, warm rings, and no anomaly regions are analyzed and it is shown that known positions of cyclonic and anticyclonic rings correspond with depressions and elevations, respectively, with amplitudes as large as 95 cm. The apparent fluctuation of the Gulf Stream is indicated by the results, as in the finding that on time scales of a few days, surface transport indicated by the sea surface height difference across the stream varied by nearly 30%

Cheney, R. E.↗
NASA NTRS1980

Precision orbit determination software validation experiment

This paper presents the results of an experiment which was designed to ascertain the level of agreement between GEODYN and UTOPIA, two completely independent computer programs used for precision orbit determination, and to identify the sources which limit the agreement. For a limited set of models and a seven-day data set arc length, the altitude components of the ephemeris obtained by the two programs agree at the sub-centimeter level throughout the arc.

Schutz, B. E.↗
NASA NTRS1980

Precision orbit analyses in support of the Seasat altimeter experiment

It is noted that major improvements have been made in the Goddard Space Flight Center (GSFC) geodynamic models for Seasat. It is pointed out that the dominant error source in Seasat ephemeris computation is currently the uncertainty in modeling the earth's gravity field. Attention is also given to significant errors arising from atmospheric drag and solar radiation pressure modeling. It is noted that a comparison of GSFC and Naval Surface Weapons Center (NSWC) Seasat ephemerides indicate the presence of an unexplained difference of about 4 m in the location of the center of mass along the Z axis. This difference is consistent with that obtained with earlier geoid and station coordinated comparisons performed by other investigators. It is expected that future combinations of Seasat and GEOS-3 altimeter data, together with laser and Unified S-Band tracking data, will ultimately produce a gravity field which allows computations of a global Seasat ephemeris with an rms radial accuracy of about 50 cm.

Marsh, J. G.↗
NASA NTRS1980

Resolving the percentage of component terrains within single resolution elements

An approximate maximum likelihood technique employing a widely available discriminant analysis program is discussed that has been developed for resolving the percentage of component terrains within single resolution elements. The method uses all four channels of Landsat data simultaneously and does not require prior knowledge of the percentage of components in mixed pixels. It was tested in five cases that were chosen to represent mixtures of outcrop, soil and vegetation which would typically be encountered in geologic studies with Landsat data. For all five cases, the method proved to be superior to single band weighted average and linear regression techniques and permitted an estimate of the total area occupied by component terrains to within plus or minus 6% of the true area covered. Its major drawback is a consistent overestimation of the pixel component percent of the darker materials (vegetation) and an underestimation of the pixel component percent of the brighter materials (sand).

Marsh, S. E.↗
NASA NTRS1983

Field Measurement of Thermal Inertia

Radiometric measurements determine thermal inertia for geologic materials. Measurements are correlated with data obtained by remote sensing, for discriminating varieties of rock encountered when exploring for minerals by aircraft or by satellites equipped with infrared scanners.

Kahle, A. B.↗
NASA NTRS1983

Control System Damps Vibrations

New control system damps vibrations in rotating equipment with help of phase-locked-loop techniques. Vibrational modes are controlled by applying suitable currents to drive motor. Control signals are derived from sensors mounted on equipment.

Kopf, E. H., Jr.↗
NASA NTRS1982

Solar pond power plant feasibility study for Davis, California

The feasibility of constructing a solar pond power plant at Davis, California was studied. Site visits, weather data compilation, soil and water analyses, conceptual system design and analyses, a material and equipment market survey, conceptual site layout, and a preliminary cost estimate were studied. It was concluded that a solar pond power plant is technically feasible, but economically unattractive. The relatively small scale of the proposed plant and the high cost of importing salt resulted in a disproportionately high capital investment with respect to the annual energy production capacity of the plant. Cycle optimization and increased plant size would increase the economical attractiveness of the proposed concept.

Wu, Y. C.↗
NASA NTRS1982

Recommendations for field measurements of aircraft noise

Specific recommendations for environmental test criteria, data acquisition procedures, and instrument performance requirements for measurement of noise levels produced by aircraft in flight are provided. Recommendations are also given for measurement of associated airplane and engine parameters and atmospheric conditions. Recommendations are based on capabilities which were available commercially in 1981; they are applicable to field tests of aircraft flying subsonically past microphones located near the surface of the ground either directly under or to the side of a flight path. Aircraft types covered by the recommendations include fixed-wing airplanes powered by turbojet or turbofan engines or by propellers. The recommended field-measurement procedures are consistent with assumed requirements for data processing and analysis.

Marsh, A. H.↗
NASA NTRS1981

High resolution interferometric observations of the solar limb at 4.9 and 10.7 GHz during the solar eclipse of October, 1977

The radial intensity profile of the quiet solar limb has been measured at high spatial resolution using the VLA at 4.9 GHz and the Owens Valley solar interferometer at 10.7 GHz during the partial solar eclipse of October 12, 1977. The spatial resolution (13.8 arcsec at 4.9 GHz and 7.4 arcsec at 10.7 GHz) was provided primarily by the lunar limb. Substantial limb brightening at 4.9 GHz was found with a peak brightness temperature corresponding to an 80% increase over the disk value, and a possible small limb enhancement at 10.7 GHz. The results are consistent with a simple model consisting of a uniform disk (provided by a thoroughly roughened transition zone) overlaid by a corona in hydrostatic equilibrium with a density of 5 x 10 to the 8th at its base. The lack of the secant-like variation in the microwave intensity from center to limb is explained by a corona contained in loop structures rather than in spherically symmetric layers.

Marsh, K. A.↗
NASA NTRS1981

The systems impact of a concentrated solar array on a Jupiter orbiter

Results of a study are presented suggesting that a Galileo Jupiter orbiting mission could be performed with a concentrated solar array power source. A baseline spacecraft design using concentrated arrays is given, and the overall spacecraft implications for attitude control, propulsion, power conditioning and the resultant spacecraft mass are examined. It is noted that while the concentrated array concept still requires extensive development effort, no insurmountable system level barriers preclude the use of a concentrated solar array on this difficult mission, with its stressing radiation environment, its lengthy periods of spacecraft shadowing as it passes behind Jupiter, and, finally, its large delta v burn required for orbital insertion.

Rockey, D. E.↗
NASA NTRS1981

Oceanic eddy variability measured by GEOS 3 altimeter crossover differences

Eddy statistics of sea height variations associated with dynamic ocean currents, gathered by GEOS 3 altimetry (25 cm), are discussed. Time variable flow is noted to be measureable using altimeter height and orbit information by means of three techniques: collinear tracks, where rms variability can be determined for mesoscale phenomena measured along parallel tracks; mean surfaces, using a 3-dimensional mapping of the sea surface for an accurate representation of the surface undulations; and crossover differences, such as between data tracks from GEOS and Seasat which have reduced ephemeris error over scales of a few thousand km. Mesoscale energetics have been found suitable for tracing meandering ocean currents by the crossover method. Possible sources of error are considered, including altimeter noise, orbit error, short wavelength continental shelf tides, etc., and it is determined that observations of mesoscale sea height appear to be limited only by uncertainties in the altimetry, which for Seasat was 5 cm over 60% of the world's oceans.

Cheney, R. E.↗
NASA NTRS1981

Properties of solar flare electrons, deduced from hard X-ray and spatially resolved microwave observations

An important question concerning an understanding of impulsive solar flares is related to the energetic electrons responsible for the microwave and the hard X-ray emission. A description is presented of an investigation in which spatially resolved microwave observations of an impulsive flare and hard X-ray data from the Solar Maximum Mission (SMM) are used to test the hypothesis that the two types of emission come from the same basic electron population. The considered observations are found to imply that the microwaves and hard X-rays were not produced by a common population of electrons with either a Maxwellian or single power-law energy distribution. It is suggested that the calculations should be repeated when observations of stronger events become available, for which a better determination of the X-ray spectrum is possible. The possibility is considered that microwaves and moderately hard X-rays come from spatially different regions.

Marsh, K. A.↗
NASA NTRS1982

Detection of microwave emission from both components of the red dwarf binary EQ Pegasi

The detection at 4.9 GHz of the late main sequence binary EQ Pegasi (dM3.5e + dM4.5e) with the VLA is reported. Both components were detected, as flux levels of 0.69 mJy and 0.4 mJy, respectively. Thermal gyroresonance emission from the quiescent coronae of these stars appears to explain observations of the authors, as it does those of Gary and Linsky (1981) for chi Ori and UV Ceti, provided coronal magnetic fields in excess of 300 gauss exist over a region that has a length scale of at least twice the radii of these stars. Support for this model is provided by the unlikelihood of both stars flaring simultaneously, and by the fact that the emission was confined to each star within the observational uncertainty of a few AU.

Topka, K.↗