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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Multibeam antenna study, Phase 2

An antenna system concept for point to point communication between any two points in the Continental United States was developed using a synchronous orbit satellite. The design and fabrication of a two dimensional artificial dielectric lens contained in a parallel plate waveguide system is presented. The experimental pattern and voltage standing wave ratio results are listed from tests with four different lenses: a plano-convex natural dielectric (Teflon) lens, a plano-convex artificial dielectric lens, a two-point corrected Teflon lens, and a two-point corrected artificial dielectric lens. A computer simulated design of an operational two lens, 24 beam configuration is also presented. The computer design presents overlays of each beam onto the Continental United States from a fixed synchronous orbit satellite with a definition of these areas where beam-to-beam isolation is not sufficient to permit the reuse of frequency.

Byrnes, P. J.↗
DOE OSTI2016

Mode coupling in spin torque oscillators

A number of recent experimental works have shown that the dynamics of a single spin torque oscillator can exhibit complex behavior that stems from interactions between two or more modes of the oscillator, such as observed mode-hopping or mode coexistence. There has been some initial work indicating how the theory for a single-mode (macro-spin) spin torque oscillator should be generalized to include several modes and the interactions between them. In the present work, we rigorously derive such a theory starting with the Landau–Lifshitz–Gilbert equation for magnetization dynamics by expanding up to third-order terms in deviation from equilibrium. Here, our results show how a linear mode coupling, which is necessary for observed mode-hopping to occur, arises through coupling to a magnon bath. In conclusion, the acquired temperature dependence of this coupling implies that the manifold of orbits and fixed points may shift with temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

THREE-DIMENSIONAL MAGNETOHYDRODYNAMIC SIMULATIONS OF CIRCUMBINARY ACCRETION DISKS: DISK STRUCTURES AND ANGULAR MOMENTUM TRANSPORT

We present the first three-dimensional magnetohydrodynamic (MHD) simulations of a circumbinary disk surrounding an equal-mass binary. The binary maintains a fixed circular orbit of separation a. As in previous hydrodynamic simulations, strong torques by the binary can maintain a gap of radius {approx_equal} 2a. Streams curve inward from r {approx_equal} 2a toward the binary; some of their mass passes through the inner boundary, while the remainder swings back out to the disk. However, we also find that near its inner edge the disk develops both a strong m = 1 asymmetry and growing orbital eccentricity. Because the MHD stresses introduce more matter into the gap, the total torque per unit disk mass is {approx_equal} 14 times larger than found previously. The inner boundary accretion rate per unit disk mass is {approx_equal} 40 times greater than found from previous hydrodynamic calculations. The implied binary shrinkage rate is determined by a balance between the rate at which the binary gains angular momentum by accretion and loses it by gravitational torque. The large accretion rate brings these two rates nearly into balance, but in net, we find that a-dot /a < 0, and its magnitude is about 2.7 times larger than predicted by the earlier hydrodynamic simulations. If the binary comprises two massive black holes, the accretion rate may be great enough for one or both to be an active galactic nucleus, with consequences for the physical state of the gas both in the disk body and in its inner gap.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The 3D flow field around an embedded planet

3D modifications to the well-studied 2D flow topology around an embedded planet have the potential to resolve long-standing problems in planet formation theory. We present a detailed analysis of the 3D isothermal flow field around a 5 Earth-mass planet on a fixed circular orbit, simulated using our graphics processing unit hydrodynamics code PEnGUIn. We find that, overall, the horseshoe region has a columnar structure extending vertically much beyond the Hill sphere of the planet. This columnar structure is only broken for some of the widest horseshoe streamlines, along which high altitude fluid descends rapidly into the planet’s Bondi sphere, performs one horseshoe turn, and exits the Bondi sphere radially in the midplane. A portion of this flow exits the horseshoe region altogether, which we refer to as the “transient” horseshoe flow. The flow continues as it rolls up into a pair of up–down symmetric horizontal vortex lines shed into the wake of the planet. This flow, unique to 3D, affects both planet accretion and migration. It prevents the planet from sustaining a hydrostatic atmosphere due to its intrusion into the Bondi sphere, and leads to a significant corotation torque on the planet, unanticipated by 2D analysis. In the reported simulation, starting with a Σ∼r{sup −3/2} radial surface density profile, this torque is positive and partially cancels with the negative differential Lindblad torque, resulting in a factor of three slower planet migration rate. Finally, we report 3D effects can be suppressed by a sufficiently large disk viscosity, leading to results similar to 2D.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Tunable Mode Coupling in Nanocontact Spin-Torque Oscillators

Recent experiments on spin-torque oscillators have revealed interactions between multiple magneto-dynamic modes, including mode coexistence, mode hopping, and temperature-driven crossover between modes. The initial multimode theory indicates that a linear coupling between several dominant modes, arising from the interaction of the subdynamic system with a magnon bath, plays an essential role in the generation of various multimode behaviors, such as mode hopping and mode coexistence. In this work, we derive a set of rate equations to describe the dynamics of coupled magneto-dynamic modes in a nanocontact spin-torque oscillator. Here, expressions for both linear and nonlinear coupling terms are obtained, which allow us to analyze the dependence of the coupled dynamic behaviors of modes on external experimental conditions as well as intrinsic magnetic properties. For a minimal two-mode system, we further map the energy and phase difference of the two modes onto a two-dimensional phase space and demonstrate in the phase portraits how the manifolds of periodic orbits and fixed points vary with an external magnetic field as well as with the temperature.

36 MATERIALS SCIENCE↗
NASA NTRS1970

Skylab program CSM verification analysis report

The application of the SINDA computer program for the transient thermodynamic simulation of the Apollo fuel cell/radiator system for the limit condition of the proposed Skylab mission is described. Results are included for the thermal constraints imposed upon the Pratt and Whitney fuel cell power capability by the Block 2 EPS radiator system operating under the Skylab fixed attitude orbits.

Schaefer, J. L.↗
NASA NTRS1974

In-situ observations of irregular ionospheric structure associated with the plasmapause

Additional studies of the ion composition results obtained from the OGO-6 satellite support earlier observations of irregularities in the distribution of H(+) and He(+) within the light ion trough near L = 4, which has been associated with the plasmapause. These irregularities are in the form of sub-troughs superimposed upon the major midlatitude decrease of the light ions. In the sub-troughs, ionization depletions and recoveries of as much as an order of magnitude are observed within a few degrees of latitude, usually exhibited in a pattern which changes significantly with longitude as the earth rotates beneath the relatively fixed satellite orbit. The location and properties exhibited by these sub-troughs appear to be consistent with the concept of a plasmasphere distortion in the form of 'plasmatails' resulting from the combined effects of magnetospheric convection plus corotation.

Taylor, H. A., Jr.↗
NASA NTRS1977

On the perihelion precession as a Machian effect

A Lagrangian is constructed which gives Newtonian gravity in the lowest-order approximation in an isotropic universe and also predicts the correct advance of the perihelion with the proper choice of a constant governing the ratio of inertial to gravitational mass. The situation considered is that of a test particle orbiting a central body with external mass at rest and distributed isotropically at large distances from the central body. In the theory developed, the perihelion advance is due to a small contribution to the test-particle inertial mass by the central attracting body rather than to a failure of the inverse-square law of attraction. Some interesting Machian features of this theory are that: (1) the local value of the gravitational constant is determined by the mass distribution of the external matter; (2) the orbits are fixed, and the perihelion advances unambiguously with respect to the external-mass distribution; (3) there are no vestiges of absolute space; (4) the perihelion precession arises from the inertial interaction of the test particle with the central mass; (5) the local rest mass is really determined by the mass distribution of the rest of the universe; and (6) a limited form of the equivalence principle is inherent in one of the equations.

Eby, P. B.↗
NASA NTRS1991

Enhanced winds and tidal streams in massive X-ray binaries

The tidal effects created by the presence of a compact companion are expected to induce a stream of enhanced wind from the early-type primary star in massive X-ray binary systems. In this paper, two-dimensional gasdynamical simulations of such streams are presented. It is found that the wind enhancement is a sensitive function of the binary separation, and develops into a tidal stream as the primary approaches its critical surface. For typical system parameters, the Coriolis force deflects the stream sufficiently that it does not impact directly on the compact companion but passes behind it. The density in the stream can reach values of 20-30 times the ambient wind density, leading to strong attenuation of the X-ray flux that passes through the tidal stream, providing a possible explanation of the enhanced absorption events seen at later phases in the X-ray observations of massive X-ray binary systems such as Vela X-1. In contrast to the time-variable accretion wake, the tidal stream is relatively stationary, producing absorption features that should remain fixed from orbit to orbit. For systems with a strong tidal stream, the large asymmetry in the accreting wind results in the accretion of angular momentum of constant sign, as opposed to systems without streams, where the sign of the accreted angular momentum can change.

Blondin, John M.↗
NASA NTRS1997

Effects of Weightlessness on Vestibular Development of Quail

The lack of gravity is known to alter vestibular responses in developing and adult vertebrates. One cause of these altered responses may be changes in the connections between the vestibular receptor and the brain. Therefore we propose to investigate the effects of gravity on the formations of connections between the gravity receptors of the ear and the brain in developing quail incubated in space beginning at an age before these connections are established (incubation day three) until near the time of hatching, when they are to some extent functional. This investigation will make use of a novel technique, the diffusion of a lipophilic dye, DiI, in fixed tissue. This technique can thus be used to analyze the connections in specimens fixed in orbit, thus eliminating changes due to the earth's gravity. The evaluation of the data will enable us to detect gross deviations from normal patterns as well as detailed quantitative deviations.

Fritzsch, Bernd↗
NASA NTRS2001

The Future of Instrument Technology for Space-based Remote Sensing

The current paradigm for space-based remote sensing relies upon frequency-specific measurements in pre-defined orbits with fixed or narrowly variable apertures. The suites of Earth observing instruments currently deployed or planned for deployment within the next 3 years typify this paradigm. To enable NASA's Earth Science vision, the future paradigm of remote sensing must employ frequency-agile measurements capable of multi-scene observations. Real-time, autonomous adaptive sensing and taskability will be critical. Advanced capabilities will include: (1) Miniaturized observatories. (2) Robust, compact instrument architectures. (3) Miniaturized/programmable components. (4) Aperture synthesis. (5) Deployable apertures. (6) Low cost production.

Peri, Frank↗
NASA NTRS1961

Determination of the Required Number of Randomly Spaced Communication Satellites

An investigation has been made f o r determining the minimum number of passive satellites i n near-earth orbits required t o provide given percentages of communication time between two selected ground stations. The study is limited to the geometrical and probability aspects of the problem. An application of the analysis i s made f o r an assumed transatlantic communication system. The satellites are considered t o be i n circular, randomly spaced orbits with fixed inclination and altitude considered range from 1,000 t o 3,000 statute miles.

Bennett, Floyd V.↗
NASA NTRS1999

Early root cap development and graviresponse in white clover (Trifolium repens) grown in space and on a two-axis clinostat

White clover (Trifolium repens) was germinated and grown in microgravity aboard the Space Shuttle (STS-60, 1994; STS-63, 1995), on Earth in stationary racks and in a slow-rotating two-axis clinostat. The objective of this study was to determine if normal root cap development and early plant gravity responses were dependent on gravitational cues. Seedlings were germinated in space and chemically fixed in orbit after 21, 40, and 72 h. Seedlings 96 h old were returned viable to earth. Germination and total seedling length were not dependent on gravity treatment. In space-flown seedlings, the number of cell stories in the root cap and the geometry of central columella cells did not differ from those of the Earth-grown seedlings. The root cap structure of clinorotated plants appeared similar to that of seedlings from microgravity, with the exception of three-day rotated plants, which displayed significant cellular damage in the columella region. Nuclear polarity did not depend on gravity; however, the positions of amyloplasts in the central columella cells were dependent on both the gravity treatment and the age of the seedlings. Seedlings from space, returned viable to earth, responded to horizontal stimulation as did 1 g controls, but seedlings rotated on the clinostat for the same duration had a reduced curvature response. This study demonstrates that initial root cap development is insensitive to either chronic clinorotation or microgravity. Soon after differentiation, however, clinorotation leads to loss of normal root cap structure and plant graviresponse while microgravity does not.

manned↗
NASA NTRS2017

Improving Magnetosphere In Situ Observations Using Solar Sails

Past and current magnetosphere missions employ conventional spacecraft formations for in situ observations of the geomagnetic tail. Conventional spacecraft flying in inertially fixed Keplerian orbits are only aligned with the geomagnetic tail once per year, since the geomagnetic tail is always aligned with the Earth-Sun line, and therefore, rotates annually. Solar sails are able to artificially create sunsynchronous orbits such that the orbit apse line remains aligned with the geomagnetic tail line throughout the entire year. This continuous presence in the geomagnetic tail can significantly increase the science phase for magnetosphere missions. In this paper, the problem of solar sail formation design is explored using nonlinear programming to design optimal two-craft, triangle, and tetrahedron solar sail formations, in terms of formation quality and formation stability. The designed formations are directly compared to the formations used in NASA's Magnetospheric Multi-Scale mission.

Sails↗
NASA NTRS1974

Orbit-spectrum sharing between the fixed-satellite and broadcasting-satellite services with applications to 12 GHz domestic systems

A systematic, tutorial analysis of the general problem of orbit-spectrum sharing among inhomogeneous satellite system is presented. Emphasis is placed on extrapolating and applying the available data on rain attenuation and on reconciling differences in the results of various measurements of the subjective effects of interference on television picture quality. An analytic method is presented for determining the approximate values of the intersatellite spacings required to keep mutual interference levels within prescribed limits when many dissimilar satellites share the orbit. A computer model was developed for assessing the interference compatibility of arbitrary configurations of large numbers of geostationary satellite systems. It is concluded that the band from 11.7 c GHz can be shared effectively by broadcasting-satellite and fixed-satellite systems. Recommendations for future study are included.

Reinhart, E. E.↗
NASA NTRS1987

Computation and analyses of averaged monthly zonal albedos at the top of the atmosphere using Nimbus-7 ERB observed data

The Nimbus-7 ERB experiment measures the Earth's albedo from a satellite in a fixed Sun synchronous orbit. The data is obtained at a fixed time of the day for each latitude observed. For Earth Radiation Budget studies it is normally assumed that the observed scene is invariant during the day and that the albedo varies only with the solar zenith angle. This paper presents a technique for computing mean zonal albedos as a function of the albedo (A sub s) of cloud free atmosphere, the albedo (A sub c) of cloudy atmosphere and of the cloud fractions. The values of A sub s and A sub c are obtained from radiation transfer theory and climatological values of the surface and cloud albedos. The albedos are a function of the solar zenith angle, latitude and solar declination. The cloud fractions are measured from the Nimbus-7 ERB albedos. The present study shows the importance of taking into account latitude variations in surface types and in cloud cover.

Dhuria, Harbans↗