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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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NASA NTRS1976

Low-energy electron intensities at large distances over the earth's polar cap

The eccentric-orbiting satellite Imp 5 penetrated the distant polar magnetosphere at positions corresponding to those for magnetic field lines which intersect the earth's northern polar cap. Measurements of electron intensities with E not less than 250 eV in these regions of extremely low plasma densities were gained with an electrostatic analyzer. The observational period was January-October 1970. Electron intensities within the energy range 250 eV-50 keV were less by orders of magnitude than those typically encountered within the plasma sheet and over the auroral oval. However, dramatic temporal variations of average electron intensities in the polar cap region were found for orbit-to-orbit comparisons. The observed intensity variations showed a remarkable correlation with the polarity of the magnetic sector structure in the interplanetary medium: high intensities for 'away from the sun' sectors and low intensities for 'toward' sectors.

Yeager, D. Y.↗
NASA NTRS1985

Hydrogen spectrum in magnetic white dwarfs - H-alpha, H-beta and H-gamma transitions

Using the results of an accurate variational calculation, a graphical display of the wavelengths of the H-alpha H-beta, and H-gamma lines of hydrogen for magnetic field values ranging from 0 to 560 megagauss, which is believed to cover the range of fields found in magnetic white dwarfs. This is the first complete detailed compilation of such results.

Henry, R. J. W.↗
NASA NTRS1985

Polar cap photoionization and the ten-hour clock at Jupiter

It is shown that the clock-like modulation of the spectral index of energetic electrons (greater than 2 MeV) in the outer Jovian magnetosphere is due to a periodic shift of the particle energy spectrum toward higher and lower energies. This shift results in a modulation of the spectral index when the spectrum is not a pure power law in energy. It is suggested that the periodic energization is due to a periodic modulation of the magnetic field in the outer magnetosphere. This modulation is caused by a variation of the longitudinally averaged Pedersen conductivity due to the asymmetric solar illumination of the trace of the magnetodisk in the high-latitude ionospheres. Such a modulation requires the presence of a surface magnetic anomaly.

Goertz, C. K.↗
NASA NTRS1988

Simultaneous X-ray and radio observations of GX 13 + 1

The results of simultaneous X-ray and radio observations of GX 13 + 1, intrinsically one of the brightest Galactic bulge X-ray sources, are presented and possible models are discussed. No evidence is found for correlated X-ray and radio flux density variations. The variation of the 6-20 cm wavelength spectral index from +0.5 to -1.0 indicates that the radio flux is probably produced by a nonthermal emission mechanism. Application of an equipartition synchrotron model to the data suggests that the radio emission originates in a region with a magnetic field of about 1 gauss. If the radio flux density variations are due to injection of relativistic electrons, the equivalent nonthermal particle energy is 10 to the 36th - 10 to the 41st ergs/s.

Garcia, M. R.↗
NASA NTRS1976

Latitudinal changes of composition in the disturbed thermosphere from Esro 4 measurements

Densities of N2, O, Ar, and He at a height of 280 km, obtained from gas analyzer measurements aboard Esro-4, were analyzed to establish a global pattern for variations that are associated with geomagnetically induced disturbances. It is shown that during longer periods of sustained geomagnetic activity, thermospheric temperature increases with geomagnetic latitude, reaching a maximum in the region of the magnetic pole, while during short-lived magnetic storms, the maximum temperature may be reached in the auroral zones. The observed variations of composition in middle and high latitudes can be explained by assuming that temperature variations are accompanied by variations in the height of the homopause. In the equatorial region the four gases studied vary in phase with similar amplitudes during a magnetic storm, indicating a density wave proceeding from higher latitudes.

Jacchia, L. G.↗
NASA NTRS1994

Modelling and control of a rotor supported by magnetic bearings

In this paper we develop a dynamical model of a rotor and the active magnetic bearings used to support the rotor. We use this model to develop a stable state feedback control of the magnetic bearing system. We present the development of a rigid body model of the rotor, utilizing both Rotation Matrices (Euler Angles) and Euler Parameters (Quaternions). In the latter half of the paper we develop a stable state feedback control of the actively controlled magnetic bearing to control the rotor position under inbalances. The control law developed takes into account the variation of the model with rotational speed. We show stability over the whole operating range of speeds for the magnetic bearing system. Simulation results are presented to demonstrate the closed loop system performance. We develop the model of the magnetic bearing, and present two schemes for the excitation of the poles of the actively controlled magnetic bearing. We also present a scheme for averaging multiple sensor measurements and splitting the actuation forces amongst redundant actuators.

Gurumoorthy, R.↗
NASA NTRS1976

Ionospheric plasma cloud dynamics

Measurements of the thermospheric neutral wind and ionospheric drift made at Eglin AFB, Florida and Kwajalein Atoll are discussed. The neutral wind measurements at Eglin had little variation over a period of four years for moderate magnetic activity (Kp 4); the ionospheric drifts are small. Evidence is presented that indicates that increased magnetic activity has a significant effect on the neutral wind magnitude and direction at this midlatitude station. The neutral wind at dusk near the equator is generally small although in one case out of seven it was significantly larger. It is described how observations of large barium releases can be used to infer the degree of electrodynamic coupling of ion clouds to the background ionosphere. Evidence is presented that indicates that large barium releases are coupled to the conjugate ionosphere at midlatitudes.

Source record↗
NASA NTRS1978

Physical parameters defining the changing structure of a coronal hole

The S-056 X-ray data have been used to determine significant quantitative values for physical parameters defining the changing structure of a coronal hole. A new active region (McMath 12363) developed near a large coronal hole late on 1973 June 1. As the new bipolar region developed, a distinct decrease (channel) occurred in a nearby X-ray emission source. Quantitative values are given for the change in X-ray flux, average electron density, and temperature in the channel, and these variations are related to the corresponding photospheric and coronal magnetic fields in the region. The observations show that the decrease in X-ray flux resulted from a reduction in electron density rather than from cooling. The study suggests that changes in a coronal hole may be explained by the loss of material along weakened, less-confining magnetic field lines in the corona.

Vorpahl, J. A.↗
NASA NTRS1980

Energetic particles at interplanetary shock waves - The April 29, 1978 event

On April 29, 1978 a low-energetic particle event originating from a 3B flare at N22 E38 was observed by HELIOS 1 at 0.31 AU and W 38 and by HELIOS 2 at 0.29 AU and W 67 simultaneously with an interplanetary shock wave. Using plasma and magnetic field data these shocks were classified; the time variations were examined along with the angular and spectral distributions in the ecliptic plane of the intensities of 80 or more keV ions.

Richter, A. K.↗
NASA NTRS1982

Relationships between the Birkeland currents, ionospheric currents, and electric fields

Currents and electric fields in the ionosphere are calculated using a global model of the electron density including conjugate coupling along field lines. Incoherent scatter and rocket measurements of high-latitude electron densities are used to derive realistic variations of the polar conductivities as a function of magnetic activity. The Birkeland currents are specified in terms of three indices, and the relationship between these parameters and the auroral electrojets indices is examined along with the polar cap potential and the electric field at lower latitudes. A mathematical model of the currents, electric fields, and energy inputs produced by field aligned currents is developed, which is consistent with and specifiable in terms of measured geophysical indices.

Bleuler, E.↗
NASA NTRS1982

Overshoots in planetary bow shocks

The parametric variation with solar wind conditions in the overshoot in magnetic field strength observed in planetary bow shocks and believed to be associated with the ion reflection process is examined based on both terrestrial and planetary bow shock data. The combined data from Venus, earth, Jupiter and Saturn cover a wider range of solar wind densities, magnetic field strength, electron and proton temperatures, Mach numbers, beta, spiral angle, and scale lengths than observable from earth alone. The bow shock structure, particularly the magnitude of the post-shock field strength overshoot, is found to depend principally on plasma beta and the magnetosonic Mach number with a continuously increasing overshoot strength associated with increasing beta and Mach number.

Russell, C. T.↗
NASA NTRS1987

Radial force balance within Jupiter's dayside magnetosphere

A local field stress technique, developed previously in a study of the Saturnian magnetosphere, is introduced to the problem of determining the radial force balance characteristics of Jupiter's magnetosphere. The near-equatorial, radial magnetic force densities are estimated using the data obtained by Voyager 1 principally on the dayside (inbound) portion of its trajectory. Using the low-energy charged particle data (greater than about 30 keV) and other published data, ways in which the field forces might be balanced are explored. Inside 22 Jupiter radii, the magnetic radial forces match, in both magnitude and radial variation, the hot particle pressure gradient forces, assuming a mix of H(+) and O(n+) ions. Outside 22 Jupiter radii, a previously reported force balance problem is confirmed qualitatively, and two possible solutions are suggested.

Mauk, B. H.↗
NASA NTRS1989

The response of the thermospheric nitric oxide to an auroral storm. I - Low and middle latitudes

The response of low- and mid-latitude NO to the September 19, 1984 magnetic storm is studied. In particular, the effect of variations in the temperature and composition of the lower thermosphere on NO is investigated. Much of the observed NO response is adequately explained by including these variations in a photochemical model. In particular, Joule heating at auroral latitudes can cause temperature enhancements at nonauroral latitudes, which in turn can lead directly to an increase in the NO. The NO is most directly sensitive to heating at altitude above 120 km. Below 120 km, NO increased through downward diffusion from above. Sensitivity studies were performed to investigate the effect that uncertainties in the NO chemical scheme and in the state of the neutral atmosphere can have on the comparison of the model to the data. It is shown that the best fit to the midlatitude American orbit data is for O/O2 ratio twice that in the original TGCM simulation and for an N(2D) quenching value of 5 x 10 to the -13th.

Siskind, D. E.↗
NASA NTRS1990

The ultraviolet and visible light variability of BP Tauri - Possible clues for the origin of T Tauri star activity

BP Tau is a moderate-strength T Tauri star, which has previously been studied photometrically by Vrba et al. (1986, 1989) and shown to have a 7.6-day light cycle. Here, BP Tau was reobserved in order to monitor this star with the IUE satellite. In conjunction with the UV spectroscopy, nearly simultaneous ground-based optical photometry was also obtained. At optical wavelengths, the star was initially found to be varying with a period of 7.6 days. This variability suddenly vanished and was followed by a quiescent state that lasted about 11 days. The star then resumed its variability with a period of about 6.1 days. The UV continuum and most of the UV emission lines appeared to vary in phase with the optical flux. No variations were observed on the very short timescales ranging from several hours to half a day, expected on the basis of axisymmetric, quasi-steady-state accretion disk models of T Tauri stars. However, the nearly week-long variations that were observed may be consistent with a magnetically buffered accretion model, which has been proposed by Uchida and Shibata.

Simon, Theodore↗