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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Pervasive large-scale magnetic fields in the Venus nightside ionosphere and their implications

When the solar wind dynamic pressure at Venus was extraordinarily high during the primary mission of the Pioneer Venus Orbiter (PVO), 'disappearing ionospheres' occurred on the nightside, with accompanying pervasive near-periapsis magnetic fields of tens of nanoteslas. These nightside counterparts of the generally horizontal large-scale magnetic fields in the dayside ionosphere are found to exhibit some dependence of field magnitude on the solar wind pressure but not on solar zenith angle. Their statistical behavior suggests a global configuration in which the low-altitude field wraps around the planet, while the field at higher altitudes is draped like the induced magnetotail field. The toroidal low-altitude field geometry implies the possible existence of magnetic x points in the low-altitude wake.

Luhmann, J. G.↗
NASA NTRS1998

Unloading Versus Driven Processes Derived from Auroral Energy Deposition and Polar Cap Size

The intensity of far ultraviolet auroral emissions at all local times during the three substorm phases has been monitored by the Ultraviolet Imager (UVI) on the Polar spacecraft for many substorms. Changes in the energy flux and characteristic energy of the precipitating electrons can be derived from these observations by modeling of the spectral emission processes. The global and local energy deposition is a new parameter that can be used in substorm studies since it provides a measure of energy transfer from the tail to the ionosphere due to precipitating electrons at a time resolution of three minutes. The polar cap area and area of auroral emissions can also be determined at high time resolution during substorms from the UVI images. An example of a substorm that appears to be driven by solar wind dynamic pressure alone will be presented. The polar cap area and other parameters do not indicate a growth phase prior to substorm onset. In another example, the slow growth phase followed by a very rapid increase in energy deposition during the expansion phase will be shown. This substorm was preceded by a southward IMF orientation. In these two examples, the role the solar wind in determining polar cap area is discussed. The time development of the area of auroral emissions is also discussed in relation to substorm phase and energy deposition. If the auroral emissions occur on closed field lines then the area of auroral emissions may provide an indication of changes in the thickness of the plasma sheet during each substorm phase.

Brittnacher, M. J.↗
NASA NTRS1985

Latitude variation of recurrent fluxes in the outer solar system

Recurrent low energy (not less than 0.5 MeV) proton flux enhancements, reliable indicators of corotating plasma inteaction regions in interplanetary space, have been observed on the Voyager 1 and 2 and Pioneer 11 spacecraft in the heliographic latitude range 2 deg S to 23 deg N and the heliocentric radial range 11 to 20 AU. After a period of rather high correlation between fluxes at different latitudes in early 1983, distinct differences develop. The evolution of the fluxes appears to be related to the temporal and latitudinal dynamics of solar coronal holes, suggesting that information about the latitudinal structure of solar wind stream sources propagates to these distances.

Christon, S. P.↗
DOE OSTI2019

MESSENGER Observations of Disappearing Dayside Magnetosphere Events at Mercury

MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) measurements taken during passes over Mercury's dayside hemisphere indicate that on four occasions the spacecraft remained in the magnetosheath even though it reached altitudes below 300 km. During these disappearing dayside magnetosphere (DDM) events, the spacecraft did not encounter the magnetopause until it was at very high magnetic latitudes, ~66 to 80°. These DDM events stand out with respect to their extremely high solar wind dynamic pressures, P sw ~140 to 290 nPa, and intense southward magnetic fields, B z ~ -100 to -400 nT, measured in the magnetosheath. In addition, the bow shock was observed very close to the surface during these events with a subsolar altitude of ~1,200 km. It is suggested that DDM events, which are closely associated with coronal mass ejections, are due to solar wind compression and/or reconnection-driven erosion of the dayside magnetosphere. The very low altitude of the bow shock during these events strongly suggests that the solar wind impacts much of Mercury's sunlit hemisphere during these events. More study of these disappearing dayside events is required, but it is likely that solar wind sputtering of neutrals from the surface into the exosphere maximizes during these intervals.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Signatures of flux erosion from the dayside magnetosphere

The rate of merging and the strength of the region 1 Birkeland currents increase during periods of southward interplanetary magnetic field (IMF). Fringe fields of the Birkeland currents depress dayside magnetospheric magnetic field strengths and remove magnetic flux from the dayside magnetophere, thereby allowing the dayside magnetopause to move inward and the cusp equatorward. We use previously derived fits to the magnetospause location as a function of IMF B(sub z), the condition of pressure balance at the magnetopause, and an idealized model of region 1 Birkeland currents to estimate that strong southward IMF turnings will produce approximately 13- to 26-nT depressions in the geosynchronous magnetic field strength over periods of 30-60 min. We then present three case studies of geosynchronous magnetic field strength variations during periods of nearly constant solar wind dynamic pressure and southward IMF. The dayside magnetospheric magnetic field strength was depressed approximately 10 nT during a period of strongly southward IMF (B(sub z) = -6 nT), but only approximately 5 nT during two more typical periods of slightly southward IMF (B(sub z) = -2 to -3 nT). The depressions correspond to periods of enhanced AL index, which we interpret as evidence for directly driven solar wind-magnetosphere interaction rather than the unloading of energy stored within the magnetotail. Dayside geosynchronous magnetic field strengths are weakly correlated with IMF B(sub z).

Sibeck, D. G.↗
NASA NTRS1995

A dynamic model of the three-fluid solar wind: Equilibrium structures and fluxes

We report results from a dynamic approach to equilibrium for a three fluid solar-wind model in spherical 1D. We advance the mass, momentum and energy transport equations for protons, alpha particles and electrons, with full interspecies coulomb coupling and the simplifications recommended by Burgi (1992). They include no ion heat conduction and an ambipolar electric field in place of the negligible electron momentum coupling. At the inner boundary (the solar surface) we specify the inflow velocity, mass flux, and temperature for each species, and at the outer boundary at large radius we allow the fluids to flow freely from the computational domain. Starting from an initial wind model (e.g.. single fluid) we evolve to a three-fluid steady state. We will describe comparisons with Burgi's static equilibrium results. and examine the stability of the discontinuities which appear in his derived parameter variations.

Ruden, S. P.↗
DOE OSTI2022

Physics-Informed Sparse Gaussian Process for Probabilistic Stability Analysis of Large-Scale Power System with Dynamic PVs and Loads

This work proposes a physics-informed sparse Gaussian process (SGP) for probabilistic stability assessment of large-scale power systems in the presence of uncertain dynamic PVs and loads. The differential and algebraic equations considering uncertainties from dynamic PVs and loads are reformulated to a nonlinear mapping relationship that allows the application of SGP. Thanks to the nonparametric characteristic of Gaussian process, the proposed framework does not require distributions of uncertain inputs and this distinguishes it from existing approaches. As the original Gaussian process is not scalable to large-scale systems with high dimensional uncertain inputs, this paper develops the SGP with a stochastic variational inference technique. It leads to approximately two orders of complex reduction. A data pre-processing step is also introduced to tackle the coexistence of stable and unstable cases by sample clustering and constructing separate SGPs. The probabilistic transient stability index is analyzed to assess system stability under different uncertain dynamics loads and PVs. Comparisons are performed with the sampling-based, the polynomial chaos expansion-based, and traditional Gaussian process-based methods on the modified IEEE 118-bus and Texas 2000-bus systems under various scenarios, including different levels of uncertainties and the existence of nonlinear correlations among dynamic PVs. The impacts of data quality and quantity issues are also investigated. It is shown that the proposed SGP achieves significantly improved computational efficiency while maintaining high accuracy with a limited number of data.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1986

Technology for Bayton-cycle powerplants using solar and nuclear energy

Brayton cycle gas turbines have the potential to use either solar heat or nuclear reactors for generating from tens of kilowatts to tens of megawatts of power in space, all this from a single technology for the power generating system. Their development for solar energy dynamic power generation for the space station could be the first step in an evolution of such powerplants for a very wide range of applications. At the low power level of only 10 kWe, a power generating system has already demonstrated overall efficiency of 0.29 and operated 38 000 hr. Tests of improved components show that these components would raise that efficiency to 0.32, a value twice that demonstrated by any alternate concept. Because of this high efficiency, solar Brayton cycle power generators offer the potential to increase power per unit of solar collector area to levels exceeding four times that from photovoltaic powerplants using present technology for silicon solar cells. The technologies for solar mirrors and heat receivers are reviewed and assessed. This Brayton technology for solar powerplants is equally suitable for use with the nuclear reactors. The available long time creep data on the tantalum alloy ASTAR-811C show that such Brayton cycles can evolve to cycle peak temperatures of 1500 K (2240 F). And this same technology can be extended to generate 10 to 100 MW in space by exploiting existing technology for terrestrial gas turbines in the fields of both aircraft propulsion and stationary power generation.

English, R. E.↗
NASA NTRS2018

Orbital Characterization of GJ1108A System, and Comparison of Dynamical Mass with Model-Derived Mass for Resolved Binaries

We report an orbital characterization of GJ1108Aab that is a low-mass binary system in the pre-main-sequence phase. Via the combination of astrometry using adaptive optics and radial velocity measurements, an eccentric orbital solution of e = 0.63 is obtained, which might be induced by the Kozai–Lidov mechanism with a widely separated GJ1108B system. Combined with several observed properties, we confirm that the system is indeed young. Columba is the most probable moving group, to which the GJ1108A system belongs, although its membership to the group has not been established. If the age of Columba is assumed for GJ1108A, the dynamical masses of both GJ1108Aa and GJ1108Ab (M(sub dynamical,GJ1108Aa) = 0.72 ± 0.04 Solar Mass and M(sub dynamical,GJ1108Ab) = 0.30 ± 0.03 Solar Mass) are more massive than what an evolutionary model predicts based on the age and luminosities. We consider that the discrepancy in mass comparison can be attributed to an age uncertainty; the system is likely older than stars in Columba, and effects that are not implemented in classical models such as accretion history and magnetic activity are not preferred to explain the mass discrepancy. We also discuss the performance of the evolutionary model by compiling similar low-mass objects in the evolutionary state based on the literature. Consequently, it is suggested that the current model on average reproduces the mass of resolved low-mass binaries without any significant offsets.

Mizuki, T.↗
DOE OSTI2018

Heliosphere Responds to a Large Solar Wind Intensification: Decisive Observations from IBEX

Our heliosphere—the bubble in the local interstellar medium produced by the Sun's outflowing solar wind—has finally responded to a large increase in solar wind output and pressure in the second half of 2014. NASA's Interstellar Boundary Explorer ( IBEX ) mission remotely monitors the outer heliosphere by observing energetic neutral atoms (ENAs) returning from the heliosheath, the region between the termination shock and heliopause. IBEX observed a significant enhancement in higher energy ENAs starting in late 2016. While IBEX observations over the previous decade reflected a general reduction of ENA intensities, indicative of a deflating heliosphere, new observations show that the large (~50%), persistent increase in the solar wind dynamic pressure has modified the heliosheath, producing enhanced ENA emissions. The combination of these new observations with simulation results indicate that this pressure is re-expanding our heliosphere, with the termination shock and heliopause already driven outward in the locations closest to the Sun. The timing between the IBEX observations, a large transient pressure enhancement seen by Voyager 2 , and the simulations indicates that the pressure increase propagated through the heliosheath, reflected off the heliopause, and the enhanced density of the solar wind filled the heliosheath behind it before generating significantly enhanced ENA emissions. As a result, the coming years should see significant changes in anomalous cosmic rays, galactic cosmic radiation, and the filtration of interstellar neutral atoms into the inner heliosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2005

Seismic Study of the Solar Interior: Inferences from SOI/MDI Observations During Solar Activity

Work on the structure, asphericity and dynamics of the solar interior from p-mode frequencies and frequency splittings was carried out primarily in collaboration with Dr. Eff-Darwich (University of La Laguna, Tenerife). This ongoing collaboration produced new results for the inversion of the internal solar rotation rate and further development in inversion methodologies. It also resulted in inferences on the solar stratification. Substantial progress towards the characterization of high-degree p-modes has been achieved. In collaboration with Drs. Rabello-Soares and Schou (Stanford University), we have gained a clear conceptual understanding of the various elements that affect the leakage matrix of the SOI/MDI instrument. This work has precise implications on the properties and the characterization of the HMI instrument being developed for the SDO mission.

Korzennik, Sylvain G.↗
NASA NTRS2022

Effect of an Interplanetary Coronal Mass Ejection on Saturn’s Radio Emission

The Saturn Kilometric Radiation (SKR) was observed for the first time during the flyby of Saturn by the Voyager spacecraft in 1980. These radio emissions, in the range of a few kHz to 1 MHz, are emitted by electrons travelling around auroral magnetic field lines. Their study is useful to understand the variability of a magnetosphere and its coupling with the solar wind. Previous studies have shown a strong correlation between the solar wind dynamic pressure and the SKR intensity. However, up to now, the effect of an Interplanetary Coronal Mass Ejection (ICME) has never been examined in detail, due to the lack of SKR observations at the time when an ICME can be tracked and its different parts be clearly identified. In this study, we take advantage of a large ICME that reached Saturn mid-November 2014 (Witasse et al., J. Geophys. Res. Space Physics, 2017, 122, 7865–7890). At that time, the Cassini spacecraft was fortunately travelling within the solar wind for a few days, and provided a very accurate timing of the ICME structure. A survey of the Cassini data for the same period indicated a significant increase in the SKR emissions, showing a good correlation after the passage of the ICME shock with a delay of ∼13 h and after the magnetic cloud passage with a delay of 25–42 h.

B. Cecconi↗
NASA NTRSDate not supplied

Investigation of the Alfven Wave Turbulence on the Dynamics of SEPs

Solar energetic particles (SEPs) are high-energy particles originating from the Sun that pose potential risks to space missions, especially those outside Earth's protective magnetosphere. Understanding their behavior within the heliosphere and Earth's magnetosphere is vital for the safety and functionality of space exploration. The study focuses on how the pitch angle scattering, the angle change between a particle's velocity and the magnetic field due to interactions with magnetic irregularities, impacts the decay phase of SEP events. By solving the focused transport equation, the study models the transport of SEPs along magnetic field lines, extending these lines up to 5 AU (Astronomical Units) to understand their behavior even beyond the typical proximity to the Sun. Incorporating the effects of pitch angle scattering at such vast distances is crucial for understanding the decay dynamics of a SEP event. This modeling of SEPs is integrated with simulations of other vital space phenomena: the solar wind, interplanetary magnetic field, and Alfven wave turbulence. This presentation covers the modeling approach used in this research and the role of pitch angle scattering at various heliocentric distances on the dynamics of the SEP events' decay phase.

solar energetic particles↗
NASA NTRS1998

Study of Magnetic Structure in the Solar Photosphere and Chromosphere

This grant funded an observational and theoretical program to study the structure and dynamics of the solar photosphere and low chromosphere, and the spectral signatures that result. The overall goal is to learn about mechanisms that cause heating of the overlying atmosphere, and produce variability of solar emission in spectral regions important for astrophysics and space physics. The program exploited two new ground-based observational capabilities: one using the Swedish Solar Telescope on La Palma for very high angular resolution observations of the photospheric intensity field (granulation) and proxies of the magnetic field (G-band images); and the other using the Near Infrared Magnetograph at the McMath-Pierce Solar Facility to map the spatial variation and dynamic behavior of the solar temperature minimum region using infrared CO lines. We have interpreted these data using a variety of theoretical and modelling approaches, some developed especially for this project. Previous annual reports cover the work done up to 31 May 1997. This final report summarizes our work for the entire period, including the period of no-cost extension from 1 June 1997 through September 30 1997. In Section 2 we discuss observations and modelling of the photospheric flowfields and their consequences for heating of the overlying atmosphere, and in Section 3 we discuss imaging spectroscopy of the CO lines at 4.67 mu.

Noyes, Robert W.↗
NASA NTRS1972

Testing relativistic gravity theories using radio tracking data from planetary orbiting spacecraft.

We present a thorough analysis of a computational method for determining the numerical values of the relativity and other related dynamical parameters using two-way Doppler and ranging data from planetary orbiting spacecraft. The computational method consists of two parts. From Doppler data we first determine the earth-planet components of the position of the orbiting spacecraft relative to the center of gravity of the planet to high accuracy; adding the observed spacecraft range yields a range value to the center of the planet. These constructed earth-planet range data, referred to as normal points, are then treated as raw data in a regression analysis combined with planetary radar delay and meridian circle measurements to solve for the significant solar system dynamical parameters. The major errors sources in the planetary orbiter process are enumerated and their individual effects on the overall accuracy of the normal point accuracies are presented. The accuracies of the parameter estimates as a function of time, data sampling, and a priori assumptions are illustrated.

Jordan, J. F.↗
NASA NTRS1994

Auroral activity associated with Kelvin-Helmholtz instability at the inner edge of the low-latitude boundary layer

Auroral activity occurred in the late afternoon sector (approx. 16 MLT) in the northern hemisphere during the passage at Earth of an interplanetary magnetic cloud on January 14, 1988. The auroral activity consisted of a very dynamic display which was preceded and followed by quiet auroral displays. During the quiet displays, discrete rayed arcs aligned along the geomagnetic L shells were observed. In the active stage, rapidly evolving spiral forms centered on magnetic zenith were evident. The activity persisted for many minutes and was characterized by the absence of directed motion. They were strongly suggestive of intense filaments of upward field-aligned currents embedded in the large-scale region 1 current system. Distortions of the flux ropes as they connect from the equatorial magnetosphere to the ionosphere were witnessed. We assess as possible generating mechanisms three nonlocal sources known to be associated with field-aligned currents. Of these, partial compressions of the magnetosphere due to variations of solar wind dynamic pressure seem an unlikely source. The possibility that the auroral forms are due to reconnection is investigated but is excluded because the active aurora were observed on the closed field line region just equatorward of the convection reversal boundary. To support this conclusion further, we apply recent results on the mapping of ionospheric regions to the equatorial plane based on the Tsyganenko 1989 model (Kaufmann et al., 1993). We find that for comparable magnetic activity the aurora map to the equatorial plane at X(sub GSM) = approx. 3 R(sub E) and approx. 2 R(sub E) inward of the magnetopause, that is, the inner edge of the boundary layer close to dusk. Since the auroral forms are manifestly associated with magnetic field shear, a vortical motion at the equatorial end of the flux rope is indicated, making the Kelvin-Helmholtz instability acting at the inner edge of the low-latitude boundary layer the most probable generating source.

Farrugia, C. J.↗
DOE OSTI2017

The Characteristic Response of Whistler Mode Waves to Interplanetary Shocks

Magnetospheric whistler mode waves play a key role in regulating the dynamics of the electron radiation belts. Recent satellite observations indicate a significant influence of interplanetary (IP) shocks on whistler mode wave power in the inner magnetosphere. In this study, we statistically investigate the response of whistler mode chorus and plasmaspheric hiss to IP shocks based on Van Allen Probes and THEMIS satellite observations. Immediately after the IP shock arrival, chorus wave power is usually intensified, often at postmidnight to prenoon sector, while plasmaspheric hiss wave power predominantly decreases near the dayside but intensifies near the nightside. We conclude that chorus wave intensification outside the plasmasphere is probably associated with the suprathermal electron flux enhancement caused by the IP shock. Through a simple ray tracing modeling assuming the scenario that plasmaspheric hiss is originated from chorus, we find that the solar wind dynamic pressure increase changes the magnetic field configuration to favor ray penetration in the nightside and promote ray refraction away from the dayside, potentially explaining the magnetic local time–dependent responses of plasmaspheric hiss waves following IP shock arrivals.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Tracing the Origin of Moving Groups. III. Detecting Moving Groups in LAMOST DR7

We revisit the moving groups (MGs) in the solar neighborhood with a sample of 91,969 nearby stars constructed from LAMOST DR7. Using the wavelet technique and Monte Carlo simulations, five MGs together with a new candidate located at $V$ ≃ -130 KM s -1 are detected simultaneously in $V$ - $\sqrt{U^2 + 2V^2}$ space. Taking into account the other known MGs, we conclude that MGs in the Galactic disk are spaced by approximately 15–25 km s -1 along $V$ velocity. Furthermore, the origin of detected MGs is analyzed through the distributions of [Fe/H]-[Mg/Fe] and ages. Our results support attributing the origin to the continuous resonant mechanisms probably induced by the bar or spiral arms of the Milky Way.

79 ASTRONOMY AND ASTROPHYSICS↗