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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 271 records · Page 15

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NASA NTRS1983

Solar wind control of the low-latitude asymmetric magnetic disturbance field

The extent to which the low latitude dawn-dusk magnetic asymmetry is controlled by the dawn-dusk solar wind motional electric field VBs and/or substorm processes measured by the westward auroral electrojet index AL is studied using the technique of empirical linear prediction filters. A new index, (ASYM), defined as the difference between dawn and dusk deviations in the X (geomagnetic Northward) magnetic field component, is used to measure the dawn-dusk asymmetry. Quantitative information which characterizes the coupling processes are provided by the empirically determined filters obtained from this analysis. Results indicate that some currents are directly driven by the solar wind-magnetosphere interaction and that their magnetic perturbations contribute to both the AL and ASYM indices. However, a portion of the AL index that is uncorrelated with VBs is correlated with ASYM which suggests that internal magnetospheric processes also contribute to AL and ASYM.

Clauer, C. R.↗

NASA NTRS1984

Magnetopause merging site asymmetries

Regions where a draped model magnetosheath magnetic field is nearly antiparallel to a model geomagnetic field are shown to be asymmetric for an interplanetary magnetic field (IMF) at the garden hose angle, as suggested by Heelis. When the IMF has a southward component, the asymmetry favors the dawn region for both IMF polarities. The dusk region is favored when the IMF has a northward component. If the regions of antiparallel fields are assumed to be sites of maximum magnetic merging, then the asymmetry is consistent with observed seasonal variations of geomagnetic activity and with dawn-displaced magnetospheric phenomena. In the alternate merging geometry of a line passing through the subsolar region, the asymmetry is predominantly north-south rather than dawn-dusk. Merging line geometry is consistent with the seasonal variations but not with the dawn-displaced phenomena.

Crooker, N. U.↗

NASA NTRS1985

Magnetopause merging site asymmetries

Crooker, N. U.↗

NASA NTRS1993

On nonsinusoidal waves at the Earth's magnetopause

We have examined International Sun Earth Explorer (ISEE) 1 and 2 data during an interval of multiple magnetopause crossings along the flanks of the tail on January 22, 1978. During the event the interplanetary magnetic field was mainly northward. We found that the surface waves on the magnetopause were nonsinusoidal with steepened sunward facing surfaces. This result is consistent with observations reported for an analogous event by Chen et al. (1993). The dawn-dusk electric field E in the low-latitude boundary layer was approx. 10 kV/R(sub E), which is much greater than the approx. 1 kV/R(sub E) dawn-dusk E field typical of the sunward convecting plasma sheet plasma. The ratio of the dawn-dusk E field in the LLBL to the dusk-dawn E in the magnetosheath was approx. 1/3. We propose that the magnetic field in the magnetosheath modulates the wave form in a way that may result in an anomalous transport of momentum across the magnetopause.

Chen, S.-H.↗

NASA NTRS2010

Simulation and 'TWINS Observations of the 22 July 2009 Storm

TWINS is the first mission to perform stereo imaging of the Earth's ring current. The magnetic storm on 22 July 2009 is the largest storm observed since TWINS began routine stereo imaging in June 2008. On 22 July 2009, the Dst dropped to nearly -80nT at 7:00 and 10:00 UT. During the main phase and at the peak of the storm, TWINS 1 and 2 were near apogee and moving from pre-dawn to post-dawn local time. The energetic neutral atom (ENA) imagers on the 2 spacecraft captured the storm intensification and the formation of the partial ring current. The peak of the ENA emissions was seen in the midnight-to-dawn local-time sector. The development of this storm has been simulated using the Comprehensive Ring Current Model (CRCM) to understand and interpret the observed signatures. We perform CRCM runs with constant and time-varying magnetic field. The model calculations are validated by comparing the simulated ENA and ion flux intensities with TWINS ENA images and in-situ ion data from THEMIS satellites. Simulation with static magnetic field produces a strong shielding electric field that skews the ion drift trajectories toward dawn. The model's corresponding peak ENA emissions are always eastward than those in the observed TWINS images. On the other hand, simulation with a dynamic magnetic field gives better spatial agreements with both ENA and insitu particle data, suggesting that temporal variations of the geomagnetic field exert a significant influence upon global ring current ion dynamics.

Fok, Mei-Ching↗

NASA NTRS2014

Vesta's Elemental Composition

Many lines of evidence (e.g. common geochemistry, chronology, O-isotope trends, and the presence of different HED rock types in polymict breccias) indicate that the howardite, eucrite, and diogenite (HED) meteorites originated from a single parent body. Meteorite studies show that this protoplanet underwent igneous differentiation to form a metallic core, an ultramafic mantle, and a basaltic crust. A spectroscopic match between the HEDs and 4 Vesta along with a plausible mechanism for their transfer to Earth, perhaps as chips off V-type asteroids ejected from Vesta's southern impact basin, supports the consensus view that many of these achondritic meteorites are samples of Vesta's crust and upper mantle. The HED-Vesta connection was put to the test by the NASA Dawn mission, which spent a year in close proximity to Vesta. Measurements by Dawn's three instruments, redundant Framing Cameras (FC), a Visible-InfraRed (VIR) spectrometer, and a Gamma Ray and Neutron Detector (GRaND), along with radio science have strengthened the link. Gravity measurements by Dawn are consistent with a differentiated, silicate body, with a dense Fe-rich core. The range of pyroxene compositions determined by VIR overlaps that of the howardites. Elemental abundances determined by nuclear spectroscopy are also consistent with HED-compositions. Observations by GRaND provided a new view of Vesta inaccessible by telescopic observations. Here, we summarize the results of Dawn's geochemical investigation of Vesta and their implications.

Prettyman, T. H.↗

NASA NTRS2013

30-kW SEP Spacecraft as Secondary Payloads for Low-Cost Deep Space Science Missions

The Solar Array System contracts awarded by NASA's Space Technology Mission Directorate are developing solar arrays in the 30 kW to 50 kW power range (beginning of life at 1 AU) that have significantly higher specific powers (W/kg) and much smaller stowed volumes than conventional rigid-panel arrays. The successful development of these solar array technologies has the potential to enable new types of solar electric propulsion (SEP) vehicles and missions. This paper describes a 30-kW electric propulsion vehicle built into an EELV Secondary Payload Adapter (ESPA) ring. The system uses an ESPA ring as the primary structure and packages two 15-kW Megaflex solar array wings, two 14-kW Hall thrusters, a hydrazine Reaction Control Subsystem (RCS), 220 kg of xenon, 26 kg of hydrazine, and an avionics module that contains all of the rest of the spacecraft bus functions and the instrument suite. Direct-drive is used to maximize the propulsion subsystem efficiency and minimize the resulting waste heat and required radiator area. This is critical for packaging a high-power spacecraft into a very small volume. The fully-margined system dry mass would be approximately 1120 kg. This is not a small dry mass for a Discovery-class spacecraft, for example, the Dawn spacecraft dry mass was only about 750 kg. But the Dawn electric propulsion subsystem could process a maximum input power of 2.5 kW, and this spacecraft would process 28 kW, an increase of more than a factor of ten. With direct-drive the specific impulse would be limited to about 2,000 s assuming a nominal solar array output voltage of 300 V. The resulting spacecraft would have a beginning of life acceleration that is more than an order of magnitude greater than the Dawn spacecraft. Since the spacecraft would be built into an ESPA ring it could be launched as a secondary payload to a geosynchronous transfer orbit significantly reducing the launch costs for a planetary spacecraft. The SEP system would perform the escape from Earth and then the heliocentric transfer to the science target.

Dawn spacecraft↗

DOE OSTI2024

Impact of the Out‐Of‐Plane Flow Shear on Magnetic Reconnection at the Flanks of Earth's Magnetopause

Abstract Magnetic reconnection changes the magnetic field topology and facilitates the energy and particle exchange at magnetospheric boundaries such as the Earth's magnetopause. The flow shear perpendicular to the reconnecting plane prevails at the flank magnetopause under southward interplanetary magnetic field conditions. However, the effect of the out‐of‐plane flow shear on asymmetric reconnection is an open question. In this study, we utilize kinetic simulations to investigate the impact of the out‐of‐plane flow shear on asymmetric reconnection. By systematically varying the flow shear strength, we analyze the flow shear effects on the reconnection rate, the diffusion region structure, and the energy conversion rate. We find that the reconnection rate increases with the upstream out‐of‐plane flow shear, and for the same upstream conditions, it is higher at the dusk side than at the dawn side. The diffusion region is squeezed in the outflow direction due to magnetic pressure which is proportional to the square of the Alfvén Mach number of the shear flow. The out‐of‐plane flow shear increases the energy conversion rate , and for the same upstream conditions, the magnitude of is larger at the dusk side than at the dawn side. This study reveals that out‐of‐plane flow shear not only enhances the reconnection rate but also significantly boosts energy conversion, with more pronounced effects on the dusk‐side flank than on the dawn‐side flank. These insights pave the way for better understanding the solar wind‐magnetosphere interactions.

Liang, Haoming↗

NASA NTRS1972

Electron plasma oscillations in the near-earth solar wind: Preliminary observations and interpretations

Preliminary results and conclusions of a study of electric field oscillations in the upstream solar wind are reported. The OGO-5 orbits are on the dusk (three) and on the dawn (one) sides of the earth-sun line. It is concluded that there are electron streams produced at or near the bow shock. These streams penetrate the incoming solar wind plasma, and generate quasi-electromagnetic waves. The streams (as inferred from the wave levels) occur without regard to dawn-dusk location, as opposed to the low-frequency MHD upstream disturbances driven by backstreaming protons, which show a definitely strong preference for the dawn-noon sector. The presence of the suprathermal electron streams and associated wave turbulence indicates that some near-earth electron distributions are probably not representative of true solar wind distributions far away from the earth.

Fredricks, R. W.↗

NASA NTRS1973

Magnetospheric field morphology at magnetically quiet times

Review of the magnetospheric morphology, using the method of the Delta B topology, where Delta B is the difference between the observed and a reference field. It is confirmed that Delta B continuously decreases inward to close distances from the earth at all local times. Extrapolating the statistical relation between Dst at the ground and the equatorial Delta B obtained from OGO-5 near perigee, it is shown that Dst is 54 gammas, when Delta B is zero at approximately 2 to 3 earth radii. Conversely, for a magnetically quiet condition as defined by Dst = 0, the average equatorial Delta B at these distances is -45 gammas. These results demonstrate the significance of the effects of the magnetospheric equatorial current that exists even at quiet times. A preliminary study of inclination shows that the field lines on the dusk side are more stretched out than on the dawn side. A comparison of declination on both sides indicates that the bending of the field lines toward the tail is greater near dusk than near dawn. These results suggest an appreciable dawn-dusk asymmetry in the configuration of the inner magnetospheric field.

Sugiura, M.↗

NASA NTRS1975

Bow shock protons in the lunar environment

Protons from the earth's bow shock are observed by the suprathermal ion detector experiment (SIDE) in two regions of the lunar orbit. The dawn region begins at the dawn-side bow-shock crossing and ends about 5 days later, the dusk region begins at about 2 days prior to entering the dusk-side magnetosheath and ends at the inbound bow-shock crossing. Dusk and dawn refer to a terrestrial coordinate system. The dominant contribution to the ion spectra observed by the SIDE in these regions is from particles with energies between about 750 eV/q and 3500 eV/q. Analysis of simultaneous data from the Explorer 35 magnetometer and the SIDE indicates that the observability of bow-shock protons at the lunar distance is dependent on the configuration of the interplanetary magnetic field.

Benson, J.↗

NASA NTRS1977

Simultaneous observations of substorm electrons - Explorer 45 and ATS 5

Simultaneous observations of substorm-associated electron flux variations made on the satellites Explorer 45 and ATS 5 are used to infer the value of the dawn-dusk electric field present during a substorm. The observations were made during a substorm which occurred on December 17, 1971, while the two satellites were in the evening local time sector, within the plasma sheet. It is found that a dawn-dusk electric field of about 11 kV/R-E (about 2 mV/m) was present during the substorm. It is shown that the observations made at the two satellites are compatible with the model of a uniform enhanced dawn-dusk electric field acting upon a particle source which is spatially uniform in the region from which particles are convected to synchronous orbit.

Barfield, J. N.↗

NASA NTRS1979

Comparison of 2.8- and 21-cm microwave radiometer observations over soils with emission model calculations

An airborne experiment was conducted under NASA auspices to test the feasibility of detecting soil moisture by microwave remote sensing techniques over agricultural fields near Phoenix, Arizona at midday of April 5, 1974 and at dawn of the following day. Extensive ground data were obtained from 96 bare, sixteen hectare fields. Observations made using a scanning (2.8 cm) and a nonscanning (21 cm) radiometer were compared with the predictions of a radiative transfer emission model. It is shown that (1) the emitted intensity at both wavelengths correlates best with the near surface moisture, (2) surface roughness is found to more strongly affect the degree of polarization than the emitted intensity, (3) the slope of the intensity-moisture curves decreases in going from day to dawn, and (4) increased near surface moisture at dawn is characterized by increased polarization of emissions. The results of the experiment indicate that microwave techniques can be used to observe the history of the near surface moisture. The subsurface history must be inferred from soil physics models which use microwave results as boundary conditions.

Burke, W. J.↗

NASA NTRS1983

Exit of boundary layer plasma from the distant magnetotail

It is pointed out that the boundary layer plasma must somehow leave the magnetospheric system. It is proposed that the boundary layers on the dawn and dusk flanks are continued into the far magnetotail, becoming joined together far downstream, still on closed magnetic field lines. Within the combined layer there would be a dusk to dawn electric field for antisunward convection (as is the case for the boundary layers on the dawn and dusk flanks nearer to the earth). It is suggested that the boundary layer flow is so massive that the flow itself can generate the right electric field for continued flow. Most of the plasma in the mantle over the polar caps would also be convected out in a similar manner, rather feeding the plasma sheet. There would be a stagnation point inside the magnetotail, with any boundary or mantle plasma diffusing earthward of this point becoming the plasma sheet. It is deduced that no steady state solution is possible.

Heikkila, W. J.↗

NASA NTRS1985

Diurnal modulation of the quiet time penetrating electron flux

Three sounding rocket measurements of energetic electron precipitation in the 65 to 80 km altitude range above Siple Station, Antarctica suggest a possible diurnal modulation of the precipitation. Flights made on January 10 and 11, 1981, to investigate this possibility showed that no electrons were present after local noon, while a significant flux of penetrating electrons was observed the following day near local dawn, even though the level of magnetic activity was higher during the postnoon flight. A prevous flight from Siple Station also observed a large flux of penetrating electrons near local dawn. Calculations of electron drift trajectories in a model magnetic field indicate that moderate values of the convection electric field could cause significant local time variations in the penetrating electron flux at the western edge of the South Atlantic anomaly. These calculations indicate that Siple Station is shadowed by eastern Siberia when it is at local noon, but not when it is at local dawn.

Sheldon, W. R.↗

NASA NTRS1985

Configuration of the high-latitude thermosphere neutral circulation for IMF B(y) negative and positive

Asymmetries in the Northern Hemisphere neutral circulation that are dependent on the sign of the east-west 'B(y)' component of the IMF are presently illustrated by measurements of the neutral wind in the polar F-region which were conducted by the DE-2 spacecraft. The data thus obtained are categorized according to the sign of the hourly averaged IMF B(y) component measured by ISEE-3 for the hour preceding the DE-2 measurements. It is noted that there is (1) an asymmetry in the polar cap neutral flow velocity, with the region of most rapid antisunward flow shifting from the dawn side to the dusk side of the polar cap as B(y) changes from positive to negative; (2) a shift occurs in the magnetic local time of the region of entry of neutral gas into the polar cap, from a location on the dawn side of the moon-midnight meridian for B(y) positive to one more biased, for B(y) negative; and (3) there is an enhancement of velocities associated with the dawn anticlockwise neutral vortex for B(y) negative relative to those observed for B(y) positive.

Mccormac, F. G.↗

NASA NTRS1986

Ion neutral coupling in the high latitude thermosphere, part 1

Measurements of the neutral wind in the polar F region from Dynamics Explorer-2 (DE-2) were used to illustrate asymmetries in the neutral circulation that are dependent on the sign of the B sub y component of the interplanetary magnetic field (IMF). Individual DE-2 orbits and averaged data sets from different Universal times are presented. The data are categorized according to the sign of the hourly averaged IMF B sub y component measured by ISEE-3 for the hour preceding the DE-2 measurement. The major features observed are: (1) an asymmetry in the polar cap neutral flow velocity with the region of most rapid antisunward flow shifting from the dawn side to the dusk side of the polar cap as B sub y changes from positive to negative; (2) a shift in magnetic local time of the region of entry of neutral gas into the polar cap from a location on the dawn side of the noon-midnight meridian for B sub y positive to one more biased towards the dusk side for B sub y negative; (3) an enhancement in the velocities associated with the dawn, anti-clockwise neutral vortex B suby y negative relative to those observed for B sub y positive. The B sub y neutral wind asymmetries can be explained by similar asymmetries, previously observed, in the polar ion convection pattern. They imply a direct causal relationship between solar wind/magnetosphere coupling and neutral thermospheric dynamics.

Killeen, T. L.↗

NASA NTRS1986

The spatial distribution of energetic ions and electrons in the magnetotail

The spatial distributions of energetic ion and electron bursts on the IMP 7 and 8 satellites in the earth's magnetotail were studied. It was found that the ion bursts were more frequently detected in the dusk than in the dawn quarter of the neutral sheet whereas the electron bursts, more frequently in the dawn than the dusk quarter. The degree of dawn-dusk asymmetry is however energy dependent; the distribution for higher energy particle bursts exhibits higher degree of asymmetry. The morphologies of the distributions manifest themselves as seasonal variations of the most probable solar ecliptic latitudes at which the ion and electron bursts were observed. The amplitudes of the variations are about 25 deg with the seasonal variation for ions leading that for electrons by about 2 months.

Xu, R.-L.↗