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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Explanation of the computer listings of Faraday factors for INTASAT users

Using a simplified form of the Appleton-Hartree formula for the phase refractive index, a relationship was obtained between the Faraday rotation angle along the angular path and the total electron content along the vertical path, intersecting the angular at the height of maximum electron density. Using the second mean value theorem of integration, the function B cosine theta second chi was removed from under the integral sign and replaced by a 'mean' value. The mean value factors were printed on the computer listing for 39 stations receiving signals from the INTASAT satellite during the specified time period. The data is presented by station and date. Graphs are included to demonstrate the variation of the Faraday factor with local time and season, with magnetic latitude, elevation and azimuth angles. Other topics discussed include a description of the bent ionospheric model, the earth's magnetic field model, and the sample computer listing.

Nesterczuk, G.↗
NASA NTRS1980

A modeling of magnetic field variations during magnetospheric substorms

Magnetic field variations in the noon-midnight plane during the magnetospheric substorm are studied in terms of changes of three current systems: the dynamo-driven current on the magnetopause, the cross-tail current and the field-aligned current-auroral electrojet system. The field-aligned current is assumed to be generated as a result of interruption and subsequent diversion of the cross-tail current to the ionosphere. It is concluded that the available observations are consistent with a large increase of the three currents.

Akasofu, S.-I.↗
NASA NTRS1986

An interplanetary magnetic field dependent model of the ionospheric convection electric field

An IMF-dependent model of the magnetospheric electric field at ionospheric altitudes has been developed based on published observations, qualitative models, and a limited understanding of the electric field source. The empirical inputs are discussed, and the model is presented in an ionospheric convection situation where corotation is an important ingredient. This leads to a description of sunward ionospheric plasma transport in the polar cap for northward IMF orientations. The validity of the model is discussed, and areas in which more empirical results are required are specified.

Sojka, J. J.↗
NASA NTRS1990

A theoretical model for magnetic field mapping as a means of broken fiber detection in graphite epoxy composites

A technique for location of broken fibers by imaging magnetic fields generated from currents injected in the fibers is presented. It is concluded that the magnetic field pattern drops abruptly near the axis of a hole, or a break in fibers. The magnetic image of a hole gives contours with the shape of an ellipse. By measuring the semimajor and semiminor axis of image it is possible to determine the ratios of the conductivities. These ratios depend on feedthrough at sites where fibers of the different directions of the layup can make electrical contact with other fibers in adjacent layers. The effects of delaminations should alter these values.

Yost, William T.↗
NASA NTRS2012

Application of the NASCAP Spacecraft Simulation Tool to Investigate Electrodynamic Tether Current Collection in LEO

Recent interest in using electrodynamic tethers (EDTs) for orbital maneuvering in Low Earth Orbit (LEO) has prompted the development of the Marshall ElectroDynamic Tether Orbit Propagator (MEDTOP) model. The model is comprised of several modules which address various aspects of EDT propulsion, including calculation of state vectors using a standard orbit propagator (e.g., J2), an atmospheric drag model, realistic ionospheric and magnetic field models, space weather effects, and tether librations. The natural electromotive force (EMF) attained during a radially-aligned conductive tether results in electrons flowing down the tether and accumulating on the lower-altitude spacecraft. The energy that drives this EMF is sourced from the orbital energy of the system; thus, EDTs are often proposed as de-orbiting systems. However, when the current is reversed using satellite charged particle sources, then propulsion is possible. One of the most difficult challenges of the modeling effort is to ascertain the equivalent circuit between the spacecraft and the ionospheric plasma. The present study investigates the use of the NASA Charging Analyzer Program (NASCAP) to calculate currents to and from the tethered satellites and the ionospheric plasma. NASCAP is a sophisticated set of computational tools to model the surface charging of three-dimensional (3D) spacecraft surfaces in a time-varying space environment. The model's surface is tessellated into a collection of facets, and NASCAP calculates currents and potentials for each one. Additionally, NASCAP provides for the construction of one or more nested grids to calculate space potential and time-varying electric fields. This provides for the capability to track individual particles orbits, to model charged particle wakes, and to incorporate external charged particle sources. With this study, we have developed a model of calculating currents incident onto an electrodynamic tethered satellite system, and first results are shown here.

Adams, Mitzi↗
NASA NTRS1973

Analysis of a model for transport of charged particles in a random magnetic field

A model for the transport of charged particles in a random magnetic field is a Volterra integrodifferential equation with a long-range kernel. The integrodifferential equation is solved numerically with the method of Bellman, Kalaba, and Lockett (1966). The results are shown to be in excellent agreement with analytical asymptotic results.-

Hanson, F. B.↗
NASA NTRS1996

Estimates of magnetic flux, and energy balance in the plasma sheet during substorm expansion

The energy and magnetic flux budgets of the magnetotail plasma sheet during substorm expansion are investigated. The possible mechanisms that change the energy content of the closed field line region which contains all the major dissipation mechanisms of relevance during substorms, are considered. The compression of the plasma sheet mechanism and the diffusion mechanism are considered and excluded. It is concluded that the magnetic reconnection mechanism can accomplish the required transport. Data-based empirical magnetic field models are used to investigate the magnetic flux transport required to account for the observed magnetic field dipolarizations in the inner magnetosphere. It is found that the magnetic flux permeating the current sheet is typically insufficient to supply the required magnetic flux. It is concluded that no major substorm-type magnetospheric reconfiguration is possible in the absence of magnetic reconnection.

Hesse, Michael↗
NASA NTRS1997

Ring Current Modeling in a Realistic Magnetic Field Configuration

A 3-dimensional kinetic model has been developed to study the dynamics of the storm time ring current in a dipole magnetic field. In this paper, the ring current model is extended to include a realistic, time-varying magnetic field model. The magnetic field is expressed as the cross product of the gradients of two Euler potentials and the bounce-averaged particle drifts are calculated in the Euler potential coordinates. A dipolarization event is modeled by collapsing a tail-like magnetosphere to a dipole-like configuration. Our model is able to simulate the sudden enhancements in the ring current ion fluxes and the corresponding ionospheric precipitation during the substorm expansion.

Fok, M.-C.↗
NASA NTRS1998

CIIs During the May 98 CMEs

The Thermal Ion Dynamics Experiment (TIDE) instrument on the ISTP/Polar spacecraft observed intense Cusp Ion Injections (CIIs) during the May 1998 series of Coronal Mass Ejections (CMEs). The energy signatures of the CIIs can be used to determine the magnetic field topology of the geomagnetic field and the Interplanetary Magnetic Field (IMF) at the reconnection site. Particle tracing using model magnetic fields and the TIDE on observations are used to locate the point of magnetopause crossing.

Chandler, Michael O.↗
NASA NTRS1981

An electrodynamic model of electric currents and magnetic fields in the dayside ionosphere of Venus

The electric current configuration induced in the ionosphere of Venus by the interaction of the solar wind has been calculated in previous papers (Cloutier and Daniell, 1973; Daniell and Cloutier, 1977; Cloutier and Daniell, 1979) for average steady-state solar wind conditions and interplanetary magnetic field. This model is generalized to include the effects of (1) plasma depletion and magnetic field enhancement near the ionopause, (2) velocity-shear-induced MHD instabilities of the Kelvin-Helmholtz type within the ionosphere, and (3) variations in solar wind parameters and interplanetary magnetic field. It is shown that the magnetic field configuration resulting from the model varies in response to changes in solar wind and interplanetary field conditions, and that these variations produce magnetic field profiles in excellent agreement with those seen by the Pioneer-Venus Orbiter. The formation of flux-ropes by the Kelving-Helmholtz instability is shown to be a natural consequence of the model, with the spatial distribution and size of the flux-ropes determined by the magnetic Reynolds number.

Cloutier, P. A.↗
NASA NTRS1966

Models of the Earth's magnetic field.

Geomagnetic field model based on definition of core field, crustal field, ionospheric currents and plasma pressures, examining trapped particle behavior

GEOMAGNETIC FIELD↗
NASA NTRS1984

The Z3 model of Saturns magnetic field and the Pioneer 11 vector helium magnetometer observations

Magnetic field observations obtained by the Pioneer 11 vector helium magnetometer are compared with the Z(sub 3) model magnetic field. These Pioneer 11 observations, obtained at close-in radial distances, constitute an important and independent test of the Z(sub 3) zonal harmonic model, which was derived from Voyager 1 and Voyager 2 fluxgate magnetometer observations. Differences between the Pioneer 11 magnetometer and the Z(sub 3) model field are found to be small (approximately 1%) and quantitatively consistent with the expected instrumental accuracy. A detailed examination of these differences in spacecraft payload coordinates shows that they are uniquely associated with the instrument frame of reference and operation. A much improved fit to the Pioneer 11 observations is obtained by rotation of the instrument coordinate system about the spacecraft spin axis by 1.4 degree. With this adjustment, possibly associated with an instrumental phase lag or roll attitude error, the Pioneer 11 vector helium magnetometer observations are fully consistent with the Voyager Z(sub 3) model.

Connerney, J. E. P.↗
NASA NTRS1992

Global and local current sheet thickness estimates during the late growth phase

The thinning and intensification of the cross tail current sheet during the substorm growth phase are analyzed during the CDAW 6 substorm (22 Mar. 1979) using two complementary methods. The magnetic field and current sheet development are determined using data from two spacecraft and a global magnetic field model with several free parameters. These results are compared with the local calculation of the current sheet location and structure previously done by McPherron et al. Both methods lead to the conclusion that an extremely thin current sheet existed prior to the substorm onset, and the thicknesses estimated by the two methods at substorm onset agree relatively well. The plasma data from the ISEE 1 spacecraft at 13 R(sub E) show an anisotropy in the low energy electrons during the growth phase which disappears just before the substorm onset. The global magnetic model results suggest that the field is sufficiently stretched to scatter such low energy electrons. The strong stretching may improve the conditions for the growth of the ion tearing instability in the near Earth tail at substorm onset.

Pulkkinen, T. I.↗
NASA NTRS1991

Gasdynamic modeling of the Venus magnetotail

A gasdynamic, convected magnetic field model of the solar wind interaction with Venus is used to model the steady state Venus magnetotail. The flow obstacle surface is approximated as a tangential discontinuity. An initial obstacle shape is defined by balancing a hydrostatic equilibrium approximation for the internal plasma pressure with an external flow pressure approximation. These approximations produce a cylindrical obstacle in the distant tail. A refined obstacle shape that attempts to balance this internal pressure with the calculated external flow pressure tapers inward toward the tail axis downstream of the terminator. The bulk plasma flow and magnetic field properties compare well with experimental observations. The model predicts central magnetotail oxygen plasma number densities of about 0.2/cu cm and temperatures on the order of 10 to the 6th K flowing tailward at speeds as low as 200 m/s.

Moore, K. R.↗
NASA NTRS1988

Auroral origin of a component of Jupiter's decametric radiation

Simultaneous observations at about 22 MHz of an Io-unrelated component of Jovian decametric radiation from Voyagers 1 and 2 and from a ground-based observatory are analyzed to investigate the beam structure of the radiation and to locate the radio-emitting region. It is concluded that the radiation of this component is emitted in quasi-continuous beams that corotate with the Jovian inner magnetosphere and that each beam can be approximated by a sector of a hollow cone. The source locations are geometrically determined by fitting a hollow-cone beam model, based on the O4 magnetic field model, to the observations. The result indicates that the radio sources lie above the northern hemisphere and on the field lines that are connected with the ultraviolet aurora of the so-called active sector.

Maeda, K.↗
NASA NTRS1989

Steady state magnetic field configurations for the earth's magnetotail

A two-dimensional, force-balance magnetic field model is presented. The theoretical existence of a steady state magnetic field configuration that is force-balanced and consistent with slow, lossless, adiabatic, earthward convection within the limit of the ideal MHD is demonstrated. A numerical solution is obtained for a two-dimensional magnetosphere with a rectangular magnetopause and nonflaring tail. The results are consistent with the convection time sequences reported by Erickson (1985).

Hau, L.-N.↗
NASA NTRS1993

Revised prediction of LDEF exposure to trapped protons

The Long Duration Exposure Facility (LDEF) spacecraft flew in a 28.5 deg inclination circular orbit with an altitude in the range from 319.4 to 478.7 km. For this orbital altitude and inclination, two components contribute most of the penetrating charge particle radiation encountered - the galactic cosmic rays and the geomagnetically trapped Van Allen protons. Where shielding is less than 1.0 g/sq cm geomagnetically trapped electrons make a significant contribution. The 'Vette' models together with the associated magnetic field models and the solar conditions were used to obtain the trapped electron and proton omnidirectional fluences reported previously. Results for directional proton spectra using the MSFC anisotropy model for solar minimum and 463 km altitude (representative for the LDEF mission) were also reported. The directional trapped proton flux as a function of mission time is presented considering altitude and solar activity variation during the mission. These additional results represent an extension of previous calculations to provide a more definitive description of the LDEF trapped proton exposure.

Watts, John W.↗