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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 1,567 records · Page 87

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NASA NTRS1975

Comparisons of ground-based monitor data with Pioneers 8, 9, 10 and 11 observations in 1968-1974

The paper examines ground-based neutron monitor data and the counting rates in different energy channels on the Pioneer 8, 9, 10 and 11 spacecraft to determine the scale size of the transient cosmic-ray variations (Forbush decreases) and the relationship of these variations to changes in the interplanetary magnetic field. Since the Pioneer spacecraft sampled the inner modulating region extensively, the spatial extent of Forbush decreases (Fd's) can be determined. In some cases the Fd modulating region was co-rotating and in others radially expanding. The azimuthal extent of the Fd region was variable but was typically about 45 deg in extent. These observations will be interpreted in terms of models proposed for Fds.

Lockwood, J. A.↗

NASA NTRS1976

A gated, wideband magnetic direction finder for lightning return strokes

A magnetic direction finder has been developed which utilizes only the initial few microseconds of wideband return stroke waveforms to provide accurate directions to the channel bases of lightning discharges to ground. Bearing errors are minimized because, near the ground, most channels tend to be straight and vertical with no large branches or horizontal sections. Tests on a number of lightning storms at distances of 10 to 100 km indicate the angular resolution is in the range 1-2 deg, with little or no systematic dependence on azimuth or distance.

Krider, E. P.↗

NASA NTRS1976

The nature of multiple solutions for surface wind speed over the oceans from scatterometer measurements

The satellite SEASAT-A will carry a radar scatterometer in order to measure microwave backscatter from the sea surface. From pairs of radar measurements at angles separated by 90 deg in azimuth the surface wind speed and direction may be inferred, though not uniquely. In this paper the character of the solutions for wind speed and direction is displayed, as well as the nature of the ambiguities of these solutions. An economical procedure for handling such data is described, plus a criterion for the need for conventional (surface) data in order to resolve the ambiguities of solutions.

Price, J. C.↗

NASA NTRS1976

Comparison of predictions and under-the-wing EBF noise data

Detailed three-dimensional free field noise data were obtained by NASA for an under-the-wing externally blown model three-flap wing, and for a similar slotless wing. Spatial (polar and azimuthal) and spectral characteristics of these data are presented. These data are compared with predictions from some published EBF noise calculation methods. Methods include the totally empirical ANOPP and GELAC procedures, and a semi-empirical noise component method. The latter method adds the separately computed dipole noise due to fluctuating lift and drag, trailing edge noise, and quadrupole noise due to the deflected jet. Each of these components is calculated for the local geometry and flow conditions.

Fink, M. R.↗

NASA NTRS1976

An analytic model illustrating the effects of rotation on a magnetosphere containing low-energy plasma

The structure of an isolated rapidly rotating magnetosphere containing low-energy plasma is treated analytically. The plasma is confined to a thin sheet lying in the equatorial plane. Its effects as far as the magnetosphere as a whole is concerned are equivalent to those of an azimuthal current sheet. When the current distribution is assumed to have a certain form, it is possible to describe the complete solution in terms of simple functions. It is shown that neutral points eventually appear in the magnetic-field configuration, indicating that the magnetosphere is unable to contain additional plasma with the assumed distribution.

Gleeson, L. J.↗

NASA NTRS1976

A note on correlation description

The paper suggests some modifications to definitions of correlation functions made by Freeman and Bennett (1974) specifically for comparing measured quantities with those predicted by rotor theories, with reference to rotorcraft flight simulation. Special attention is paid to the quality of correlation, determined by a quality factor relating the measured and computed entities. Correlation criteria (mean load and rotor performance, overall amplitude and phase, harmonic altitude and harmonic phase) are examined, along with phase angle correlation criteria (harmonic phase defined by sine-cosine relation and harmonic phase defined by a first positive peak rotor azimuth position)

Mccloud, J. L., III↗

NASA NTRS1975

Spiral structure produced by tidal interaction of galaxies

Simulation of a close passage of two galaxies where the self-gravity of the disk stars is taken into account was performed with the aid of a large-scale N-body model (Hohl and Hockney, 1969; Hohl, 1972). The calculation was performed by perturbing an initially stable axisymmetric disk consisting of 100,000 stars by the passage of a companion galaxy having one-fourth the mass of the primary galaxy. Parameters appropriate for M 51 and its companion NGC 5195 were used. The results show the evolution of a weak two arm spiral. The effect of large random velocities on the formation of spiral structure was studied by plotting the spatial distribution of stars for various velocity intervals. The spiral structure is quite pronounced for stars with the lower velocity dispersion, but it can hardly be detected for stars with higher velocities. The tidal interaction causes only slight changes in the azimuthally averaged density distribution.

Hohl, F.↗

NASA NTRS1976

Ion cyclotron instability of drifting plasma clouds

The paper is concerned with a quantitative study of the frequency dispersion characteristics of the ion cyclotron mode in a realistic dipole magnetosphere where the particles are allowed to drift azimuthally. The adopted model assumes that the particles are injected at a constant L shell in an extended region around local midnight. A drift-convoluted distribution function is used to study the spatial and temporal characteristics of the ion cyclotron instability. Two cases are examined: one in which the cold plasma density is constant and the other in which the cold particle density is allowed to vary. The resulting growth rates are presented in both the frequency versus coordinate space and the frequency versus time space. Possible inferences regarding wave emissions such as IPDP (intervals of pulsations of diminishing period) events are discussed. It is shown that the frequency dispersive effects can be produced by either the drift effects or changing the cold plasma density.

Lin, C. S.↗

NASA NTRS1976

The spiral structure of the interplanetary magnetic field

The Pioneer 10 data concerning the heliocentric radial variation of the interplanetary magnetic field are examined. Incorporating the systematic increase in solar wind velocity observed during the mission leads to much improved agreement between the usual Parker Archimedean spiral and the data. The effects of correlations between short-period fluctuations of speed and azimuthal field are discussed. It is concluded that during the period under study they did not substantially affect the average magnetic field.

Parker, G. D.↗

NASA NTRS1975

The SAS-3 X-ray observatory

The experiment section of the Small Astronomy Satellite-3 (SAS-3) launched in May 1975 is an X-ray observatory intended to determine the location of bright X-ray sources to an accuracy of 15 arc-seconds; to study a selected set of sources over a wide energy range, from 0.1 to 55 keV, while performing very specific measurements of the spectra and time variability of known X-ray sources; and to monitor the sky continuously for X-ray novae, flares, and unexpected phenomena. The improvements in SAS-3 spacecraft include a clock accurate to 1 part in 10 billion, rotatable solar panels, a programmable data format, and improved nutation damper, a delayed command system, improved magnetic trim and azimuth control systems. These improvements enable SAS-3 to perform three-axis stabilized observations of any point on the celestial sphere at any time of the year. The description of the experiment section and the SAS-3 operation is followed by a synopsis of scientific results obtained from the observations of X-ray sources, such as Vela X-1 (supposed to be an accreting neutron star), a transient source of hard X-ray (less than 36 min in duration) detected by SAS-3, the Crab Nebula pulsar, the Perseus cluster of galaxies, and the Vela supernova remnant.

Mayer, W. F.↗

NASA NTRS1976

Generalization and refinement of an automatic landing system capable of curved trajectories

Refinements in the lateral and longitudinal guidance for an automatic landing system capable of curved trajectories were studied. Wing flaps or drag flaps (speed brakes) were found to provide faster and more precise speed control than autothrottles. In the case of the lateral control it is shown that the use of the integral of the roll error in the roll command over the first 30 to 40 seconds of flight reduces the sensitivity of the lateral guidance to the gain on the azimuth guidance angle error in the roll command. Also, changes to the guidance algorithm are given that permit pi-radian approaches and constrain the airplane to fly in a specified plane defined by the position of the airplane at the start of letdown and the flare point.

Sherman, W. L.↗

NASA NTRS1976

Magnitude of 64-m elevation axis movements due to alidade temperature changes

In projected very-long baseline interferometry (VLBI) work a reference point for 64-m antennas is the intersection of the elevation and azimuth axes. A minimum-level effort at DSS 14 to determine the magnitude of the effect of diurnal changes in the temperature of the alidade legs on the height of the elevation axis is described. The thermal expansion between the lowest recorded temperature -3 C (27 F) and the highest, 36 C (97 F), over the period covered was 8.9 mm (0.35 in.).

Hung, N. T.↗

NASA NTRS1976

Radar systems for the water resources mission, volume 2

The application of synthetic aperture radar (SAR) in monitoring and managing earth resources was examined. The function of spaceborne radar is to provide maps and map imagery to be used for earth resource and oceanographic applications. Spaceborne radar has the capability of mapping the entire United States regardless of inclement weather; however, the imagery must have a high degree of resolution to be meaningful. Attaining this resolution is possible with the SAR system. Imagery of the required quality must first meet mission parameters in the following areas: antenna patterns, azimuth and range ambiguities, coverage, and angle of incidence.

Moore, R. K.↗

NASA NTRS1976

Radar systems for the water resources mission. Volume 4: Appendices E-I

The use of a scanning antenna beam for a synthetic aperture system was examined. When the resolution required was modest, the radar did not use all the time the beam was passing a given point on the ground to build a synthetic aperture, so time was available to scan the beam to other positions and build several images at different ranges. The scanning synthetic-aperture radar (SCANSAR) could achieve swathwidths of well over 100 km with modest antenna size. Design considerations for a SCANSAR for hydrologic parameter observation are presented. Because of the high sensitivity to soil moisture at angles of incidence near vertical, a 7 to 22 deg swath was considered for that application. For snow and ice monitoring, a 22 to 37 deg scan was used. Frequencies from X-band to L-band were used in the design studies, but the proposed system operated in C-band at 4.75 GHz. It achieved an azimuth resolution of about 50 meters at all angles, with a range resolution varying from 150 meters at 7 deg to 31 meters at 37 deg. The antenna required an aperture of 3 x 4.16 meters, and the average transmitter power was under 2 watts.

Moore, R. K.↗

NASA NTRS1977

Electron dynamics in a plasma focus

Results are presented of a numerical integration of the three-dimensional relativistic equations of motion of electrons subject to given electric and magnetic fields deduced from experiments. Fields due to two different models are investigated. For the first model, the fields are those due to a circular distribution of axial current filaments. As the current filaments collapse toward the axis, large azimuthal magnetic and axial electric fields are induced. These fields effectively heat the electrons to a temperature of approximately 8 keV and accelerate electrons within the radius of the filaments to high axial velocities. Similar results are obtained for the current-reduction phase of focus formation. For the second model, the fields are those due to a uniform current distribution. Both the current-reduction and the compression phases were studied. These is little heating or acceleration of electrons during the compression phase because the electrons are tied to the magnetic field. However, during the current-reduction phase, electrons near the axis are accelerated toward the center electrode and reach energies of 100 keV. A criterion is obtained which limits the runaway electron current to about 400 A.

Hohl, F.↗

NASA NTRS1976

Accident investigation: Analysis of aircraft motions from ATC radar recordings

A technique was developed for deriving time histories of an aircraft's motion from air traffic control (ATC) radar records. This technique uses the radar range and azimuth data, along with the downlinked altitude data (from an onboard Mode-C transponder), to derive an expanded set of data which includes airspeed, lift, thrust-drag, attitude angles (pitch, roll, and heading), etc. This method of analyzing aircraft motions was evaluated through flight experiments which used the CV-990 research aircraft and recordings from both the enroute and terminal ATC radar systems. The results indicate that the values derived from the ATC radar records are for the most part in good agreement with the corresponding values obtained from airborne measurements. In an actual accident, this analysis of ATC radar records can complement the flight-data recorders, now onboard airliners, and provide a source of recorded information for other types of aircraft that are equipped with Mode-C transponders but not with onboard recorders.

Wingrove, R. C.↗

NASA NTRS1977

Design study for LANDSAT-D attitude control system

The gimballed Ku-band antenna system for communication with TDRS was studied. By means of an error analysis it was demonstrated that the antenna cannot be open loop pointed to TDRS by an onboard programmer, but that an autotrack system was required. After some tradeoffs, a two-axis, azimuth-elevation type gimbal configuration was recommended for the antenna. It is shown that gimbal lock only occurs when LANDSAT-D is over water where a temporary loss of the communication link to TDRS is of no consequence. A preliminary gimbal control system design is also presented. A digital computer program was written that computes antenna gimbal angle profiles, assesses percent antenna beam interference with the solar array, and determines whether the spacecraft is over land or water, a lighted earth or a dark earth, and whether the spacecraft is in eclipse.

Iwens, R. P.↗

NASA NTRS1977

Application of standard photogeologic techniques to LANDSAT imagery for mineral exploration in the basin and range province of Utah and Nevada

The author has identified the following significant results. Standard photogeologic techniques were applied to LANDSAT imagery of the basin and range province of Utah and Nevada to relate linear, tonal, textural, drainage, and geomorphic features to known mineralized areas in an attempt to develop criteria for the location of mineral deposits. No consistent correlation was found between lineaments, mapped according to specified criteria, and locations of mines, mining districts, or intrusive outcrops. Tonal and textural patterns were more closely related to geologic outcrop patterns than to mineralization. A statistical study of drainage azimuths of various length classes as measured on LANDSAT showed significant correlation with mineralized districts in the length class of 3-6 km. Alignments of outcrops of basalt, a rock type highly visible on LANDSAT imagery, appear to be colinear with acidic and intermediate intrusive centers in some areas and may assist on the recognition of regional fracture systems for mineral exploration.

Lattman, L. H.↗