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At least 595 records · Page 33

All sources NASA NTRS DOE OSTI

NASA NTRS1990

Location selection for vibration controllers in space crane as adaptive structures

It is assumed that the space crane is vibrating about a known configuration which is reached at the end of some maneuver. For this configuration, r actuator locations are to be determined in order to control the first q of the structural vibration modes of the system optimizing the energy dissipation rate. A modified version of the control stratagem of Chang (1980) is applied using the structural modes of the uncontrolled crane, followed by algorithms for the actuator placement problem.

Lu, L. Y.↗

NASA NTRS1990

Utilization of Landsat multispectral data in geobotanical investigations - The location of ironstone gravel in the Sam Houston National Forest, Texas

The location of ironstone gravel deposits by remote sensing (using Landsat MSS frames) over a heavily vegetated terrain is demonstrated. It is suggested that the spectral class exhibited on an analyzed Landsat frame (acquired during a protracted drought period) relates to water stressed regions within the upland pine forest type as a result of the near-surface geology of the areas where ironstone gravel is present. It is also suggested that the presence of both the ironstone aggregate and the associated plinthite hardpan layer may be responsible for the absence of longleaf pine on these sites of the Sam Houston National Forest, as compared to similar sites a few km away.

Cibula, William G.↗

NASA NTRS1990

A determination of the radio-planetary frame tie and the DSN tracking station locations

The orientation of the reference frame of radio source catalogs relative to that of planetary ephemerides is uncertain by 30 mas (150 nrad). At this level of uncertainty this orientation offset, or 'frame tie', can be a major systematic error source for interplanetary spacecraft orbit determination. This work presents a method of determining the radio-planetary frame tie from a comparison of Very Long Baseline Interferometry (VLBI) and Lunar Laser Ranging (LLR) station coordinate and earth orientation parameter estimates. Preliminary results are presented which indicate that accuracies of 5 mas or better may be achieved with this method. An important by-product of this method of frame tie determination is a set of Deep Space Network (DSN) station locations with 10 cm per component accuracy. This station set is in a geocentric coordinate system with known orientation relative to the radio and planetary frames.

Finger, Mark H.↗

NASA NTRS1990

Effect of location of aft-mounted nacelles on the longitudinal aerodynamic characteristics of a high-wing transport airplane

As part of a propulsion/airframe integration program at Langley Research Center, tests were conducted in the Langley 16-Foot Transonic Tunnel to determine the effects of locating flow-through mixed flow engine nacelles in several aft underwing positions on the longitudinal aerodynamics of a high wing transport airplane. D-shaped inlet nacelles were used in the test. Some configurations with antishock bodies and with nacelle toe-in were also tested. Data were obtained for a free stream Mach number range of 0.70 to 0.85 and a model angle-of-attack range from -2.5 to 4.0 degrees.

Abeyounis, William K.↗

NASA NTRS1991

Model correlation and damage location for large space truss structures: Secant method development and evaluation

On-orbit testing of a large space structure will be required to complete the certification of any mathematical model for the structure dynamic response. The process of establishing a mathematical model that matches measured structure response is referred to as model correlation. Most model correlation approaches have an identification technique to determine structural characteristics from the measurements of the structure response. This problem is approached with one particular class of identification techniques - matrix adjustment methods - which use measured data to produce an optimal update of the structure property matrix, often the stiffness matrix. New methods were developed for identification to handle problems of the size and complexity expected for large space structures. Further development and refinement of these secant-method identification algorithms were undertaken. Also, evaluation of these techniques is an approach for model correlation and damage location was initiated.

Smith, Suzanne Weaver↗

NASA NTRS1991

The effect of the Earth's oblate spheroid shape on the accuracy of a time-of-arrival lightning ground strike locating system

The algorithm used in previous technology time-of-arrival lightning mapping systems was based on the assumption that the earth is a perfect spheroid. These systems yield highly-accurate lightning locations, which is their major strength. However, extensive analysis of tower strike data has revealed occasionally significant (one to two kilometer) systematic offset errors which are not explained by the usual error sources. It was determined that these systematic errors reduce dramatically (in some cases) when the oblate shape of the earth is taken into account. The oblate spheroid correction algorithm and a case example is presented.

Casper, Paul W.↗

NASA NTRS1991

Comparison of lightning location data and polarisation radar observations of clouds

Simultaneous observations of both the precipitation and the lightning associated with thunderstorms show that the lightning is within 3 km of the maximum precipitation echo. The intensity and type of the precipitation is observed with 500 m spatial accuracy using an S-band polarization radar and the position of the lightning is inferred from a low frequency magnetic direction finding location system. Empirical adjustment to the angles using the redundancy of the lightning data reduce this error. Radar echoes above 45dBZ may be caused by soft hail or hailstones, but similarly intense echoes may result from melting snow. The data show that a new polarization radar parameter, the linear depolarization ratio, can distinguish between soft hail and melting snow, and that the intense radar echoes associated with melting snow pose no threat of lightning. A lightning risk only exists when the radar indicates that the clouds contain soft hail or hailstones.

Illingworth, A. J.↗

NASA NTRS1991

Continuous wave coherent laser radar - Calculation of measurement location and volume

The SNR equation of a CW, monostatic, coherent laser radar system is examined for the case of a distributed aerosol target. General analytic equations are derived which explicitly describe the contribution to total SNR from each range interval along the optic axis, the range resolution of the measurement, and the atmospheric volume contributing to the measurement. Plots are presented showing the location in range and the volume of the laser radar measurement.

Kavaya, Michael J.↗

NASA NTRS1991

The location of the source of high-frequency solar acoustic oscillations

Recently Libbrecht and Jefferies et al. have reported regular peaks in the solar oscillation power spectrum extending well above 5.3 mHz, the maximum frequency of trapped acoustic modes. Kumar et al. argued that these peaks are primarily due to the interference of traveling waves which are excited due to acoustic emission from turbulent convection. In contrast with the standing wave P-mode frequencies below 5.3 mHz, the positions of the high-frequency interference peaks (HIPs) are dependent on the location of the source of the acoustic oscillations. In the present work, Kumar et al.'s argument is strengthened, and more importantly, use is made of the above dependence to determine the acoustic source strength as a function of depth. It is found that the acoustic source profile, and thus the convective velocity, is peaked about 200 km deeper than what is expected from standard mixing length theory.

Kumar, Pawan↗

NASA NTRS1991

Investigative techniques used to locate the liquid hydrogen leakage on the Space Shuttle Main Propulsion System

Standard leak detection methods at ambient temperature have been developed in order to prevent excessive leakage from the Space Shuttle liquid oxygen and liquid hydrogen Main Propulsion System. Unacceptable hydrogen leakage was encountered on the Columbia and Atlantis flight vehicles in the summer of 1990 after the standard leak check requirements had been satisfied. The leakage was only detectable when the fuel system was exposed to subcooled liquid hydrogen during External Tank loading operations. Special instrumentation and analytical tools were utilized during a series of propellant tanking tests in order to identify the sources of the hydrogen leakage. After the leaks were located and corrected, the physical characteristics of the leak sources were analyzed in an effort to understand how the discrepancies were introduced and why the leakage had evaded the standard leak detection methods. As a result of the post-leak analysis, corrective actions and leak detection improvements have been implemented in order to preclude a similar incident.

Hammock, William R., Jr.↗

NASA NTRS1992

Magnetic Location Indicator

Ferrofluidic device indicates point of highest magnetic-flux density in workspace. Consists of bubble of ferrofluid in immiscible liquid carrier in clear plastic case. Used in flat block or tube. Axes of centering circle on flat-block version used to mark location of maximum flux density when bubble in circle. Device used to find point on wall corresponding to known point on opposite side of wall.

Stegman, Thomas W.↗

NASA NTRS1991

Estimation of geopotential differences over intercontinental locations using satellite and terrestrial measurements

An error analysis study was conducted in order to assess the current accuracies and the future anticipated improvements in the estimation of geopotential differences over intercontinental locations. An observation/estimation scheme was proposed and studied, whereby gravity disturbance measurements on the Earth's surface, in caps surrounding the estimation points, are combined with corresponding data in caps directly over these points at the altitude of a low orbiting satellite, for the estimation of the geopotential difference between the terrestrial stations. The mathematical modeling required to relate the primary observables to the parameters to be estimated, was studied for the terrestrial data and the data at altitude. Emphasis was placed on the examination of systematic effects and on the corresponding reductions that need to be applied to the measurements to avoid systematic errors. The error estimation for the geopotential differences was performed using both truncation theory and least squares collocation with ring averages, in case observations on the Earth's surface only are used. The error analysis indicated that with the currently available global geopotential model OSU89B and with gravity disturbance data in 2 deg caps surrounding the estimation points, the error of the geopotential difference arising from errors in the reference model and the cap data is about 23 kgal cm, for 30 deg station separation.

Pavlis, Nikolaos K.↗

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.↗