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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Collecting, analyzing and archiving of ground based infrared solar spectra obtained from several locations

The infrared solar spectrum as observed from the ground under high resolution contains thousands of absorption lines. The majority of these lines are due to compounds that are present in the Earth's atmosphere. Ground based infrared solar spectra contain information concerning the composition of the atmosphere at the time the spectra were obtained. The objective of this program is to record solar spectra from various ground locations, and to analyze and archive these spectra. The analysis consists of determining, for as many of the absorption lines as possible, the molecular species responsible for the absorption, and to verify that current models of infrared transmission match the observed spectra. Archiving is an important part of the program, since a number of the features in the spectra have not been identified. At some later time, when the features are identified, it will be possible to determine the amount of that compound that was present in the atmosphere at the time the spectrum was taken.

Murcray, David G.↗
NASA NTRS1992

Effect of lubricant jet location on spiral bevel gear operating temperatures

An experimental study was conducted to determine the effect of lubricant jet location on spiral bevel gear bulk temperatures. Transient surface temperatures were also measured. Tests were conducted on aircraft quality spiral bevel gears in a closed loop test facility. Thermocoupled pinions and an infrared microscope were used to collect the pertinent data. A single fan jet lubricated the test gears. Lubricant flow rate (lubricant jet pressure) and applied torque were also varied. The results showed that jet placement had a significant effect on the gear bulk temperatures.

Handschuh, Robert F.↗
NASA NTRS1992

Light-heavy ion measurements in CR-39 located on the Earth side of LDEF

The azimuthal angle distribution and the charge and energy spectra of selected light-heavy (3 less than or = Z less than or = 8) stopping particles were measured in a single layer of CR-39 plastic nuclear track detector (PNTD) from the stack of the A0015 experiment located on the Earth-end of the satellite. The directional incidence of the trapped protons is studied by comparing the azimuthal angle distribution of selected recoils, obtained in the LDEF detectors, to that obtained through calibrations of PNTDs with exposure performed with 200 MeV proton beams from different directions. Similar measurements will be performed in a CR-39 sample exposed on the space-end of the LDEF satellite for intercomparison. The experimental results will also be compared to theoretical calculations.

Csige, I.↗
NASA NTRS1992

Experimental and analytical study of the effects of floor location on response of composite fuselage frames

Experimental and analytical results are presented of the effects of floor placement on the structural response and strength of I-cross section, semi-circular fuselage frames constructed of graphite-epoxy composite material. The composite frame configuration is representative of current conventional aircraft design. Experimental strain distributions are presented from static loading tests of the composite frames and compared with finite element structural models and closed form solutions. An understanding of floor location effects can aid dynamists in predicting the crash behavior of these conventional structures, and may assist the designer in developing crashworthy structures for future aircraft.

Jones, Lisa E.↗
NASA NTRS1992

Comment on 'Solar wind control of the magnetopause shape, location, and motion' by D. G. Sibeck, R. E. Lopez, and E. C. Roelof

The methodology employed in the paper 'Solar wind control of the magnetopause shape, location, and motion' by Sibeck et al. (1991), which quantifies the magnetospheric response to solar wind dynamic pressure and interplanetary magnetic field variations, is commented on, with emphasis on how the shape and position of the magnetopause boundary can be specified, within some uncertainty, for particular simultaneous values of the solar wind pressure in the magnetic field. The reply of Sibeck et al. included a data set of 1821 magnetopause crossings, each associated with an hourly averaged solar wind dynamic pressure and/or north-south component of the interplanetary magnetic field. A least squares fit to an ellipsoid of revolution to subsets of the data was performed.

Dunlop, M. W.↗
NASA NTRS1992

Neptune's non-thermal radio emissions - Phenomenology and source locations

During the inbound and the outbound leg of Voyager 2's encounter with Neptune, the Planetary Radio Astronomy (PRA) experiment aboard the spacecraft detected short radio bursts at frequencies within the range of about 500-1300 kHz, and broad-banded smoothly varying emission patterns within the frequency range from about 40-800 kHz. Both emissions can be described in terms of a period of 16.1 hours determining Neptune's rotation period. Furthermore, just near closest approach, a narrow-banded smoothly varying radio component was observed occurring between 600 and 800 kHz. After giving a brief overview about some general characteristics of Neptune's nonthermal radio emission, the source locations of Neptune's emission components are determined, using an offset tilted dipole model for Neptune's magnetic field. Assuming that the emission originates near the electron gyrofrequency a geometrical beaming model is developed in order to fit the observed emission episodes.

Rabl, Gerald K. F.↗
NASA NTRS1993

Locating Damaged Truss Members From Responses To Vibrations

Method of on-orbit assessment for location of damage based on use of capabilities of vibration-control system to measure vibrations in structure. Experiment involved use of laboratory scale-model truss structure exhibiting expected characteristics of truss structures proposed for large spacecraft. Vibrations excited in truss, and measurements of responses of structure used in series of two identification algorithms to produce mathematical model of structure in current condition, possibly containing damage. Similar methods considered for examining buildings for damage by earthquakes.

Smith, S. W.↗
NASA NTRS1993

Locating Electron Traps In A CCD

"Pocket pumping" is technique for mapping sizes of electron-trapping defects and picture elements within which traps located in charge-coupled device (CCD). Two kinds of traps: forward and reverse. Pocket pumping relies on fact that in terms of charges measurable by external circuitry, forward traps affect only forward, while reverse traps affect only reverse, transfer of charge along row or column of picture elements. Charges in picture elements shifted back and forth many times to amplify trapping effect by repetition. Traps smaller than 1 electron detected by this method.

Janesick, James↗
NASA NTRS1992

The choice of the location of the lunar base

The development of modern methods of remote sensing of the lunar surface and data from lunar studies by space vehicles make it possible to assess scientifically the expediency of the location of the lunar base in a definite region on the Moon. The preliminary choice of the site is important for tackling a range of problems associated with ensuring the activity of a manned lunar base and with fulfilling the research program. Based on astronomical data, we suggest the Moon's western hemisphere, specifically the western part of Oceanus Procellarum, where natural, scientifically interesting objects have been identified, as have surface rocks with enhanced contents of ilmenite, a possible source of oxygen. A comprehensive evaluation of the region shows that, as far as natural features are concerned, it is a key one for solving the main problems of the Moon's origin and evolution.

Schevchenko, V. V.↗
NASA NTRS1993

The effect of clock, media, and station location errors on Doppler measurement accuracy

Doppler tracking by the Deep Space Network (DSN) is the primary radio metric data type used by navigation to determine the orbit of a spacecraft. The accuracy normally attributed to orbits determined exclusively with Doppler data is about 0.5 microradians in geocentric angle. Recently, the Doppler measurement system has evolved to a high degree of precision primarily because of tracking at X-band frequencies (7.2 to 8.5 GHz). However, the orbit determination system has not been able to fully utilize this improved measurement accuracy because of calibration errors associated with transmission media, the location of tracking stations on the Earth's surface, the orientation of the Earth as an observing platform, and timekeeping. With the introduction of Global Positioning System (GPS) data, it may be possible to remove a significant error associated with the troposphere. In this article, the effect of various calibration errors associated with transmission media, Earth platform parameters, and clocks are examined. With the introduction of GPS calibrations, it is predicted that a Doppler tracking accuracy of 0.05 microradians is achievable.

Miller, J. K.↗
NASA NTRS1993

Light-heavy ion measurements in CR-39 located on the Earth side of LDEF

The azimuthal angle distribution and the charge and energy spectra of selected light-heavy (5 less than or equal to Z less than or equal to 8) stopping particles were measured in a single layer of CR-39 plastic nuclear track detector (PNTD) from the stack of the A0015 experiment located on the Earth-end of the LDEF satellite. The directional incidence of the trapped protons is studied by comparing the azimuthal angle distribution of selected recoils, obtained in the LDEF detectors, to that obtained through calibrations of PNTD's with exposures performed with 200 MeV proton beams from different directions.

Csige, I.↗
NASA NTRS1992

Measured effect of step axial location on labyrinth seal leakage

An advanced, finite volume code has been extensively used in a parametric design study of simple stepped seals, in order to ascertain a leakage-minimizing optimal design and test it, in conjunction with the baseline case of the wear-ring seal of a high pressure pump. It is found that a significant leakage effect arises from this shifting of the rotor and stator sealing surfaces; at extremely low rpm, a significant shaft speed effect occurs for the optimized design in some shaft locations.

Morrison, G. L.↗
NASA NTRS1992

Momentum, water vapor, and carbon dioxide exchange at a centrally located prairie site during FIFE

Eddy correlation measurements were taken of momentum, water vapor, sensible heat, and CO2 at a centrally located plateau site in the FIFE study area from May to October 1987. Approximately 82 percent of the vegetation at the site was composed of several C4 grass species, with the remainder being C3 grasses, forbs, wedges, and woody plants. Precipitation was about normal during the study period, except for a three week dry period in late July to early August that caused moisture stress conditions.

Verma, Shashi B.↗
NASA NTRS1992

Vision-based recursive estimation of rotorcraft obstacle locations

The authors address vision-based passive ranging during nap-of-the-earth (NOE) rotorcraft flight. They consider the problem of estimating the relative location of identifiable features on nearby obstacles, assuming a sequence of noisy camera images and imperfect measurements of the camera's translation and rotation. An iterated extended Kalman filter is used to provide recursive range estimation. The correspondence problem is simplified by predicting and tracking each feature's image within the Kalman filter framework. Simulation results are presented which show convergent estimates and generally successful feature point tracking. Estimation performance degrades for features near the optical axis and for accelerating motions. Image tracking is also sensitive to angular rate.

Leblanc, D. J.↗
NASA NTRS1993

Shear and compression buckling analysis for anisotropic panels with centrally located elliptical cutouts

An approximate analysis for buckling of biaxial- and shear-loaded anisotropic panels with centrally located elliptical cutouts is presented in the present paper. The analysis is composed of two parts, a prebuckling analysis and a buckling analysis. The prebuckling solution is determined using Lekhnitskii's complex variable equations of plane elastostatics combined with a Laurent series approximation and a boundary collocation method. The buckling solution is obtained using the principle of minimum potential energy. A by-product of the minimum potential energy equation is an integral equation which is solved using Gaussian quadrature. Comparisons with documented experimental results and finite element analyses indicate that the approximate analysis accurately predicts the buckling loads of square biaxial- and shear-loaded panels having elliptical cutouts with major axes up to sixty percent of the panel width. Results of a parametric study are presented for shear- and compression-loaded rectangular anisotropic panels with elliptical cutouts. The effects of panel aspect ratio, cutout shape, cutout size, cutout orientation, laminate anisotropy, and combined loading on the buckling load are examined.

Britt, V. O.↗
NASA NTRS1992

Preliminary burst location calibration results for the BATSE instrument on CGRO

Preliminary results pertaining to burst location using BATSE Large Area Detector measurements of solar flares are presented. These solar flare measurements are currently being used to fine tune the calibration of our data analysis software. The current status of techniques for identifying and eliminating systematic errors from the data analysis tools is discussed. Data revealing the effects of the atmospheric scattering algorithm that will be implemented in the data analysis software are presented.

Pendleton, G. N.↗
NASA NTRS1990

Accurate GPS measurement of the location and orientation of a floating platform

This article describes the design and initial tests of the GPS portion of a system for making seafloor geodesy measurements. In the planned system, GPS antennas on a floating platform will be used to measure the location of an acoustic transducer, attached below the platform, which interrogates an array of transponders on the seafloor. Since the GPS antennas are necessarily some distance above the transducer, a short-baseline GPS interferometer consisting of three antennas is used to measure the platform's orientation. A preliminary test of several crucial elements of the system was performed. The test involved a fixed antenna on the pier and a second antenna floating on a buoy about 80 m away. GPS measurements of the vertical component of this baseline, analyzed independently by two groups using different software, agree with each other and with an independent measurement within a centimeter. The first test of an integrated GPS/acoustic system took place in the Santa Cruz Basin off the coast of southern California in May 1990. In this test a much larger buoy, designed and built at SIO, was equipped with three GPS antennas and an acoustic transducer that interrogated a transponder on the ocean floor. Preliminary analysis indicates that the horizontal position of the transponder can be determined with a precision of about a centimeter.

Purcell, G. H., Jr.↗
NASA NTRS1993

Sizes and locations of coronal mass ejections - SMM observations from 1980 and 1984-1989

A statistical description of the sizes and locations of 1209 mass ejections observed with the SMM coronagraph/polarimeter in 1980 and 1984-1989 is presented. The average width of the coronal mass ejections detected with this instrument was close to 40 deg in angle for the entire period of SMM observations. No evidence was found for a significant change in mass ejection widths as reported by Howard et al. (1986). There is clear evidence for changes in the latitude distribution of mass ejections over this epoch. Mass ejections occurred over a much wider range of latitudes at the times of high solar activity (1980 and 1989) than at times of low activity (1985-1986).

Hundhausen, A. J.↗