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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 487 records · Page 27
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NASA NTRS1982

Determining spacecraft angular position with Delta VLBI - The Voyager demonstration

A demonstration of a new VLBI-based radio metric data type for interplanetary navigation has been conducted using the Voyager spacecraft on their approach to Saturn. Pseudo-range measurements from stations on intercontinental baselines were employed, in conjunction with interferometric observations of quasars, to obtain a precise measure of the spacecraft angular position. In addition to its high accuracy this technique requires significantly less station time than conventional range and Doppler and can be used in a downlink only mode. The paper describes the data type, acquisition system, and processing procedures. Anticipated measurement accuracy is established by analysis of various system error sources. Results obtained from Voyager observations are given to show that the system performance is in accordance with expectations.

Border, J. S.↗
NASA NTRS1982

Protostellar mass and angular momentum loss

Recent radio observations have indicated that appreciable, continuing mass loss is occurring from regions of star formation. The conditions under which massive protostellar objects may exhibit strong, rotationally driven winds are investigated. For plausible rotational velocities and magnetic field strengths, ejection of about 10,000 solar masses a year at speeds of 10-100 km/s can be maintained for time scales of about 0.0001 yr; these values are insensitive to the protostellar luminosity. An evolutionary scenario is sketched which suggests that protostellar clouds may be expected to be rapidly rotating and to possess substantial magnetic fields when the clouds have contracted to radii of about 10 to the 14th cm. The centrifugally driven winds proposed present an alternative to fragmentation for providing the angular momentum loss required in the phase of rapid cloud contraction.

Hartmann, L.↗
NASA NTRS1982

Linear force and moment equations for an annular smooth shaft seal perturbed both angularly and laterally

Coefficients are derived for equations expressing the lateral force and pitching moments associated with both planar translation and angular perturbations from a nominally centered rotating shaft with respect to a stationary seal. The coefficients for the lowest order and first derivative terms emerge as being significant and are of approximately the same order of magnitude as the fundamental coefficients derived by means of Black's equations. Second derivative, shear perturbation, and entrance coefficient variation effects are adjudged to be small.

Fenwick, J.↗
NASA NTRS1983

Precision optical angular position marker system for rotating machinery

An optical system is described which generates one or more markers of the angular shaft position of rotating machinery. The system consists of a light source, an optical cable, a machinery mounted lens assembly, a light detector, and a signal conditioner. Light reflected by targets on the rotor is converted to a digital output signal. The system is highly immune to extreme environments of vibration and temperature and achieved a 0.002 percent precision under operational test conditions.

Barranger, J. P.↗
NASA NTRS1982

Variations in atmospheric angular momentum and the length of day

Six years of twice daily global analyses were used to create and study a lengthy time series of high temporal resolution angular momentum values. Changes in these atmospheric values were compared to independently determined charges in the rotation rate of the solid Earth. Finally, the atmospheric data was examined in more detail to determine the time and space scales on which variations in momentum occur within the atmosphere and which regions are contributing most to the changes found in the global integral. The data and techniques used to derive the time series of momentum values are described.

Rosen, R. D.↗
NASA NTRS1982

Cosmic turbulence and the angular momenta of astronomical systems

It is suggested that gravitationally bound astronomical systems ranging from asteroids to galaxy superclusters may derive their rotation from a hierarchy of cosmic turbulence, thus explaining the empirical specific angular momentum-mass relationship (j approximately equal to M to the 3/4 power) exhibited by these systems. It is shown that many of the properties of these systems, e.g., the random orientation of their spin vectors, can be accounted for if astronomical objects form in a turbulent environment.

Fleck, R. C., Jr.↗
NASA NTRS1983

The latitude-height structure of 40-50 day variations in atmospheric angular momentum

Using five years of U.S. National Meteorological Center twice-daily global analyses, a description of the two-dimensional latitude-height structure of the winds responsible for quasi-periodic variations in the relative angular momentum of the atmosphere observed by Langley et al. (1981) is constructed. Cross-spectral and amplitude phase eigenvector techniques indicate that these variations are associated with wave-like motions in the tropical upper troposphere which propagate poleward and downward in phase within the tropics. The tropical component is suggested to be the zonally averaged part of the motions described by Madden and Julian (1971, 1972), while a Northern Hemisphere midlatitude component whose phase is essentially independent of height may be a direct response to the tropical motions. Alternatively, both motions may be the common response to an as yet unidentified tropical forcing.

Anderson, J. R.↗
NASA NTRS1984

Annihilation of angular momentum drift during spinning-up and thrusting maneuvers of rigid bodies

A very simple, yet accurate, heuristic solution for the spiral path of the angular momentum vector during spin-up and spin-down maneuvers of rigid body spacecraft is presented. A two-burn scheme is proposed consisting of a burn, a coast, and a second burn of the spin thruster. The appropriate burn times are found by a transcendental equation similar to Kepler's equation. Numerical results verify the accuracy of the burn, coast, and burn times given by closed form expressions. The scheme can also be applied to the problem of axial thrusting during constant spin.

Longuski, J. M.↗
NASA NTRS1984

An El Nino signal in atmospheric angular momentum and earth rotation

Anomalously high values of atmospheric angular momentum and length of day were observed in late January 1983. This signal in the time series of these two coupled quantities appears to have been a consequence of the equatorial Pacific Ocean warming event of 1982-1983.

Rosen, R. D.↗
NASA NTRS1984

The lunar angular momentum problem

Formation of the Moon by classical Darwin-type fission of a rapidly spinning proto-Earth is discussed. The relationship of angular momentum to accretion disks is examined. The co-accretion scenario and Darwin-type fission are compared and evaluated.

Weidenschilling, S. J.↗
NASA NTRS1984

An experimental investigation of the angular scattering and backscattering behaviors of the simulated clouds of the outer planets

A cryogenic, 50 liter volume Planetary Cloud Simulation Chamber has been constructed to permit the laboratory study of the cloud compositions which are likely to be found in the atmospheres of the outer planets. On the basis of available data, clouds composed of water ice, carbon dioxide, and liquid and solid ammonia and methane, both pure and in various mixtures, have been generated. Cloud microphysical observations have been permitted through the use of a cloud particle slide injector and photomicrography. Viewports in the lower chamber have enabled the collection of cloud backscattering data using 633 and 838 nm laser light, including linear depolarization ratios and complete Stokes parameterization. The considerable technological difficulties associated with the collection of angular scattering patterns within the chamber, however, could not be completely overcome.

Sassen, K.↗
NASA NTRS1985

Shower disc sampling and the angular resolution of gamma-ray shower detectors

As part of the design study for the new UHE gamma ray detector being constsructed at Haverah Park, a series of experiments using scintillators operated side-by-side in 10 to the 15th power eV air showers are undertaken. Investigation of the rms sampling fluctuations in the shower disc arrival time yields an upper limit to the intrinsic sampling uncertainty, sigma sub rms = (1.1 + or - 0.1)ns, implying an angular resolution capability 1 deg for an inter-detector spacing of approximately 25 m.

Lambert, A.↗
NASA NTRS1985

Angular Resolution of an EAS Array for Gamma Ray Astronomy at Energies Greater Than 5 x 10 (13) Ev

A 24 detector extensive air shower array is being operated at Ootacamund (2300 m altitude, 11.4 deg N latitude) in southern India for a study of arrival directions of showers of energies greater than 5 x 10 to the 13th power eV. Various configurations of the array of detectors have been used to estimate the accuracy in determination of arrival angle of showers with such an array. These studies show that it is possible to achieve an angular resolution of better than 2 deg with the Ooty array for search for point sources of Cosmic gamma rays at energies above 5 x 10 to the 13th power eV.

Apte, A. R.↗
NASA NTRS1985

The angular resolution of air shower gamma ray telescopes

A crucial charactristic of air shower arrays in the field of high energy gamma-ray astronomy is their angular resolving power, the arrival directions being obtained by the time of flight measurements. A small air shower array-telescope is used to study the resolution in the definition of the shower front as a function of the shower size.

Morello, C.↗
NASA NTRS1985

A bi-directional charged particle telescope to observe flux, energy spectrum and angular distribution of relativistic and non-relativistic particles

A Charged Particle Telescope (CPT) was designed, fabricated and calibrated to make the following observations: (1) discrimination between various singly charged particles, e.g., electrons, muons and protons, in about 5 to 100 MeV energy range; (2) measurement of the flux and the energy of the charged particles incident to the telescope from two opposite directions and stopping in the telescope, thus obtaining flux and energy spectrum of downward and upward moving charged particles; and (3) measurement of the broad angular distribution of selected particles as a function of azimuthal angle. This telescope can be used to study low energy electron, muon and proton energy spectra. The experiment was flown in a high altitude balloon from Hyderabad, India, in December 1984. This same equipment is also useful in ground level electron, muon spectrum study.

Verma, S. D.↗
NASA NTRS1985

Angular distribution and multiplicity of backward hadrons in hFe interactions at 0.5-5.0 TeV energies (PION Experiment)

Based on the analysis of approximates 5 X 1000 events registered on the PION installation, data are obtained on the angular distribution and multiplicity of particles, flying back into the laboratory coordinate system (LCS) that are identified mainly as hadrons produced in the reactions of hFe yield h prime X type. The inclusively produced hadron energy is 200 MeV. The experimental data are compared to the results of the cumulative particle production in hA processes observed on accelerators at lower energies.

Avakian, V. V.↗