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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

The heliopause

A Pioneer or Voyager spacecraft will soon pass through one of the last major frontiers in the solar system - the heliospheric terminal shock. Some unknown, but perhaps small, distance beyond the terminal shock is the heliopause, marking the final boundary between solar-wind and Galactic plasmas and the final goal of these spacecraft. This occasion offers an opportunity to obtain a wealth of information on the properties of the Galaxy, the interstellar medium, and the large-scale interactions of that medium with stellar winds. Several tentative remote detections of the shock place it just beyond the present spacecraft locations. However, uncertainties in the physical processes and parameters that determine the location of the boundary lead to equal uncertainties in predicting which of the spacecraft will reach it first.

Suess, Steven T.↗
NASA NTRS1983

Factors controlling the location of the Venus bow shock

The location of the Venus bow shock determined from magnetic field measurements during the first and third years of Pioneer Venus orbiter operation is examined and compared with nearly simultaneously obtained interplanetary solar wind data to determine those factors that control the size of the Venus bow shock. The location of the intersection of the bow shock with the terminator that is best determined by the data does not vary significantly between years 1979 and 1981 and is only 16 percent more distant than the Venera 9 and 10 shock when account is taken of solar wind aberration. Alfvenic Mach number and magnetosonic Mach number affect the size of the bow shock significantly. Solar wind dynamic pressure has a lesser effect. No significant asymmetries in the shock shape were found either as a result of the orientation of the clock angle of the IMF in the terminator plane or the angle of the IMF relative to the shock normal.

Tatrallyay, M.↗
NASA NTRS2016

Plasma Observations During the Mars Atmospheric Plume Event of March-April 2012

We present initial analysis and conclusions from plasma observations made during the reported Mars Dust plume event of March - April 2012. During this period, multiple independent amateur observers detected a localized, high-altitude plume over the Martian dawn terminator [Sanchez-Lavega7 et al., Nature, 2015, doi:10.1038nature14162], the origin of which remains to be explained. We report on in-situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by Mars Express, obtained over the surface region, but at the opposing terminator. We tentatively conclude that the formation and/or transport of this plume to the altitudes where it was observed could be due in part the result of a large interplanetary coronal mass ejection (ICME) encountering the Martian system. Interestingly, we note that a similar plume detection in May 1997 may also have been associated with a large ICME impact at Mars.

Plumes↗
DOE OSTI2024

Capacity contributions of Southern Oregon offshore wind to the Pacific Northwest and California

Variable renewable energy generation poses unique capacity challenges, which increasingly depend on weather events at varying timescales. Facilitated by transmission planning, geographic and technological diversity of the generation fleet may provide a mitigation to capacity shortfalls. In this work, offshore wind (OSW) energy is sited in the areas off the West Coast between Coos Bay, Oregon, and Crescent City, California. Three generation and transmission scenarios are modeled within the Western Interconnection: (i) 3.4 gigawatts (GW) of installed OSW capacity connected to Southern Oregon through a High Voltage Alternating Current (HVAC) Radial Topology in 2030; (ii) 12.9 GW of installed OSW capacity connected to Washington, Oregon, and California through a High Voltage Direct Current (HVDC) Radial Topology post-2030, and (iii) the same 12.9 GW connected to the same locations through a Multi-terminal DC (MTDC) Backbone Topology post-2030. Zonal dispatch simulations assuming coincident wind, solar, and hydropower production and loads over 18 meteorological years, accounting for temperature-dependent equipment derating and forced outages, serve as inputs to the Associated System Capacity Contribution (ASCC) methodology. The capacity credit is 33%, 25% and 34% for the 2030 HVAC Radial Topology, 2030+ HVDC Radial Topology, and 2030+ MTDC Backbone Topology, respectively. Transmission design is shown to mitigate the typical erosion of marginal capacity contribution as more OSW is developed, underscoring the opportunity for grid modernization while decarbonizing the generation mix.

17 WIND ENERGY↗
NASA NTRS1985

A model for the origin of high-energy cosmic rays

It is suggested that cosmic rays, up to the highest energies observed, originate in the Galaxy and are accelerated in astrophysical shock waves. If there is a galactic wind, in analogy with the solar wind, a hierarchy of shocks ranging from supernova shocks to the galactic wind termination shock is expected. This leads to a consistent model in which most cosmic rays, up to perhaps 10 to the 14th eV energy, are accelerated by supernova shocks, but that particles with energies of 10 to the 15th eV and higher are accelerated at the termination shock of the galactic wind. Intermediate energies may be accelerated by intermediate-scale shocks, and there may be larger scale shocks associated with the Local Group of galaxies.

Jokipii, J. R.↗
NASA NTRS1985

On the origin of high-energy cosmic rays

It is suggested that cosmic rays, up to the highest energies observed, originate in the Galaxy and are accelerated in astrophysical shock waves. If there is a galactic wind, in analogy with the solar wind, a hierarchy of shocks ranging from supernova shocks to the galactic wind termination shock is expected. This leads to a consistent model in which most cosmic rays, up to perhaps 10 to the 14th eV energy, are accelerated by supernova shocks, but that particles with energies of 10 to the 15th eV and higher are accelerated at the termination shock of the galactic wind. Intermediate energies may be accerelated by intermediate-scale shocks, and there may be larger scale shocks associated with the Local Group of galaxies.

Jokipii, J. R.↗
NASA NTRS1988

Model structure of a cosmic-ray mediated stellar or solar wind

An idealized hydrodynamic model is presented for the mediation of a free-streaming stellar wind by galactic cosmic rays or energetic particles accelerated at the stellar wind termination shock. The spherically-symmetric stellar wind is taken to be cold; the only body force is the cosmic ray pressure gradient. The cosmic rays are treated as a massless fluid with an effective mean diffusion coefficient k proportional to radial distance r. The structure of the governing equations is investigated both analytically and numerically. Solutions for a range of values of k are presented which describe the deceleration of the stellar wind and a transition to nearly incompressible flow and constant cosmic ray pressure at large r. In the limit of small k the transition steepens to a strong stellar wind termination shock. For large k the stellar wind is decelerated gradually with no shock transition. It is argued that the solutions provide a simple model for the mediation of the solar wind by interstellar ions as both pickup ions and the cosmic ray anomalous component which together dominate the pressure of the solar wind at large r.

Lee, M. A.↗
NASA NTRS1995

Locations of termination shock and heliopause based on Voyager plasma and magnetic field data

The locations of the termination shock and the heliopause are studied taking into account the effects of pickup protons. The study uses available plasma and magnetic field data from Voyagers over a 14-year period (1978-1991) and Voyager observation of the 1992-93 radio emission event. Outside 30 AU, pickup protons have a significant influence on dynamical structures of the outer heliosphere. The solar wind is treated as a mixture of electrons, solar wind protons, and interstellar pickup protons. If the magnitude of the interstellar magnetic field B(sub int) is given, one can quantitatively study the motion and location of the termination shock. The location is anti-correlated with the sun spot number and the shock has an average speed of approx. 24 km/s. Because B(sub int) is poorly known, additional information is needed in studying the termination shock. Cummings, et al. have used observations of anomalous cosmic rays to estimate the location of the shock. The observations of the 1991 GMIR and GMIR shock and the 1992-93 radio emission event provide another handle for the study of the termination shock and the heliopause. After its penetration through the termination shock, the GMIR shock continued to propagate in the subsonic region of the solar wind and eventually interacted with the heliopause. This interaction produces a transmitted shock propagating outward in the interstellar medium and a reflected shock propagating inward toward the sun in the subsonic solar wind. The plasma frequencies behind the reflected and the transmitted shock can be, respectively, responsible for the 2- and 3-kHz radio emissions. Taking into account the effects of pickup protons we found that the average locations of the termination shock and the heliopause in 1991-92 are at approximately 66 AU and 150 AU, respectively.

Whang, Y. C.↗
NASA NTRS2000

Winds From Luminous Late-Type Stars: The Effects of Nonlinear Alfven Waves - 1

We present the results of magnetohydrodynamic (MHD) modeling of winds from luminous late-type stars using a 2.5-dimensional, nonlinear MHD computer code. We assume that the wind is generated within an initially hydrostatic atmosphere and is driven by torsional Alfven waves generated at the stellar surface. Two cases of atmospheric topology are considered: case I has longitudinally uniform density distribution and isotropic radial magnetic field over the stellar surface, and case II has an isotropic, radial magnetic field with a transverse density gradient, which we refer to as an "atmospheric hole." We use the same set of boundary conditions for both models. The calculations are designed to model a cool luminous star, for which we assume an initial hydrostatic pressure scale height of 0.072 Stellar Radius, an Alfven wave speed of 92 km/s at the surface, and a wave period of 76 days, which roughly corresponds with the convective turnover time. For case I the calculations produce a wind with terminal velocity of about 22 km/s and a mass loss rate comparable to the expected value of 10(exp -6) Solar Mass/yr. For case II we predict a two-component wind: a fast (25 km/s) and relatively dense wind outside of the atmospheric hole and a slow (1.5 km/s), rarefied wind inside of the hole.

Airapetian, V. S.↗
NASA NTRS1985

Dependence of Venus ionopause altitude and ionospheric magnetic field on solar wind dynamic pressure

The shape of the dayside Venus ionopause, and its dependence on solar wind parameters, is examined using Pioneer Venus Orbiter field and particle data. The ionopause is defined here as the altitude of pressure equality between magnetosheath pressure and ionospheric thermal pressure; its typical altitudes range from about 300 km near the subsolar point to about 900 km near the terminator. A strong correlation between ionopause altitude and magnetosheath magnetic pressure is demonstrated; correlation between magnetic pressure and the normally incident component of solar wind dynamic pressure is also evident. The data support the hypothesis of control of the ionopause altitude by solar wind dynamic pressure, manifested in the sheath as magnetic pressure. The presence of large scale magnetic fields in the ionosphere is observed primarily when dynamic pressure is high and the ionopause is low.

Phillips, J. L.↗
NASA NTRS1973

On the extent of the Martian ionosphere.

The boundary of the Martian ionosphere just above the photochemical layer, where solar-wind induced convection becomes important, is estimated. The Martian ionosphere is expected to terminate at an altitude of approximately 300 km.

Bauer, S. J.↗
NASA NTRS1994

Gasdynamic models of the solar wind/interstellar medium interaction

The interaction between the solar wind and the interstellar medium is modeled self-consistently using numerical solutions of the time-dependent gasdynamic equations in spherical and cylindrical coordinates. For the results presented here it is assumed that the solar system moves through the surrounding medium with a supersonic velocity. After an initial (nonequilibrium) state has been specified, the numerical solution follows the evolution in time until the interaction relaxes to a dynamic equilibrium. As would be expected, the solutions show the formation of a bow shock upstream of the traveling solar system to deflect the interstellar plasma around the cavity created by the solar wind. A terminiation shock also forms to slow and compress the solar wind plasma. For the simulation in spherical coordinates, the downstream portion of the termination shock reaches equilibrium more than three times further from the Sun than the equilibrium distance to the termination shock on the upstream side.

Steinolfson, R. S.↗
NASA NTRS2011

The Solar Wind in the Outer Heliosphere and Heliosheath

The solar wind environment has a large influence on the transport of cosmic rays. This chapter discusses the observations of the solar wind plasma and magnetic field in the outer heliosphere and the heliosheath. In the supersonic solar wind, interaction regions with large magnetic fields form barriers to cosmic ray transport. This effect, the "CR-B" relationship, has been quantified and is shown to be valid everywhere inside the termination shock (TS). In the heliosheath, this relationship breaks down, perhaps because of a change in the nature of the turbulence. Turbulence is compressive in the heliosheath, whereas it was non-compressive in the solar wind. The plasma pressure in the outer heliosphere is dominated by the pickup ions which gain most of the flow energy at the TS. The heliosheath plasma and magnetic field are highly variable on scales as small as ten minutes. The plasma flow turns away from the nose roughly as predicted, but the radial speeds at Voyager 1 are much less than those at Voyager 2, which is not understood. Despite predictions to the contrary, magnetic reconnection is not an important process in the inner heliosheath with only one observed occurrence to date.

Richardson, J. D.↗
NASA NTRS1990

Plasma observations of the solar wind interaction with Mars

Measurements with the plasma analyzers on the Mars-2, 3 and 5 spacecraft show that Mars deflects a large fraction of the incoming solar wind flow to form a strong bow shock. The bow shock is about 1.41 Rm from the center of the planet at the subsolar point and about 2.40 Rm at the terminator. These distances are similar to those for Venus at times of moderate solar activity. The inferred effective obstacle altitude is about 400-700 km. An ion cushion has been found which is similar in its properties to the Venus magnetic barrier. The formation of this cushion appears to cause the deflection of the solar wind. Inside the cushion but well above the ionosphere is found a region where the ions are at the background, the electrons are cool and the magnetic pressure dominates. This region may resemble a planetary magnetosphere.

Vaisberg, O. L.↗
NASA NTRS1982

Structure and dynamics of the ionosphere

The structure of the Venus ionosphere and the major processes occurring within it are summarized. The daytime ionosphere is created by solar EUV radiation incident on the thermosphere; it is in photochemical equilibrium near its peak at about 142 km, where O2(+) is the major ion, and near diffusive equilibrium in its upper regions, where the major ion is O(+). The day-to-night plasma pressure gradient across the terminator drives a nightward ion flow which, together with electron precipitation, contributes to the formation of the nighttime ionosphere. Large-scale radial holes or plasma depletions extending downwards to nearly the ionization peak in the antisolar region are also observed which are associated with regions of strong radial magnetic fields. The ionopause is a highly dynamic and complex surface, extending from an average altitude of 290 km at the subsolar point to about 1000 km at the terminator and from 200 to over 3000 km on the nightside. A variety of solar wind interaction products are observed in the mantle, a transition region between the ionospheric plasma and the flowing shocked solar wind.

Nagy, A. F.↗
NASA NTRS1999

GHRS Observations of Cool, Low-Gravity Stars: The Outer Atmosphere and Wind of the Nearby K Supergiant Lambda Velorum - 5

UV spectra of lambda Velorum taken with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope are used to probe the structure of the outer atmospheric layers and wind and to estimate the mass-loss rate from this K5 lb-II supergiant. VLA radio observations at lambda = 3.6 cm are used to obtain an independent check on the wind velocity and mass-loss rate inferred from the UV observations, Parameters of the chromospheric structure are estimated from measurements of UV line widths, positions, and fluxes and from the UV continuum flux distribution. The ratios of optically thin C II] emission lines indicate a mean chromospheric electron density of log N(sub e) approximately equal 8.9 +/- 0.2 /cc. The profiles of these lines indicate a chromospheric turbulence (v(sub 0) approximately equal 25-36 km/s), which greatly exceeds that seen in either the photosphere or wind. The centroids of optically thin emission lines of Fe II and of the emission wings of self-reversed Fe II lines indicate that they are formed in plasma approximately at rest with respect to the photosphere of the star. This suggests that the acceleration of the wind occurs above the chromospheric regions in which these emission line photons are created. The UV continuum detected by the GHRS clearly traces the mean flux-formation temperature as it increases with height in the chromosphere from a well-defined temperature minimum of 3200 K up to about 4600 K. Emission seen in lines of C III] and Si III] provides evidence of material at higher than chromospheric temperatures in the outer atmosphere of this noncoronal star. The photon-scattering wind produces self-reversals in the strong chromospheric emission lines, which allow us to probe the velocity field of the wind. The velocities to which these self-absorptions extend increase with intrinsic line strength, and thus height in the wind, and therefore directly map the wind acceleration. The width and shape of these self-absorptions reflect a wind turbulence of approximately equal 9-21 km/s. We further characterize the wind by comparing the observations with synthetic profiles generated with the Lamers et al. Sobolev with Exact Integration (SEI) radiative transfer code, assuming simple models of the outer atmospheric structure. These comparisons indicate that the wind in 1994 can be described by a model with a wind acceleration parameter beta approximately 0.9, a terminal velocity of 29-33 km/s, and a mass-loss rate approximately 3 x 10(exp -9) solar M/yr. Modeling of the 3.6 cm radio flux observed in 1997 suggests a more slowly accelerating wind (higher beta) and/or a higher mass-loss rate than inferred from the UV line profiles. These differences may be due to temporal variations in the wind or from limitations in one or both of the models. The discrepancy is currently under investigation.

Carpenter, Kenneth G.↗
NASA NTRS2008

Electrostatic Charging of Lunar Dust by UV Photoelectric Emissions and Solar Wind Electrons

The ubiquitous presence of dust in the lunar environment with its high adhesive characteristics has been recognized to be a major safety issue that must be addressed in view of its hazardous effects on robotic and human exploration of the Moon. The reported observations of a horizon glow and streamers at the lunar terminator during the Apollo missions are attributed to the sunlight scattered by the levitated lunar dust. The lunar surface and the dust grains are predominantly charged positively by the incident UV solar radiation on the dayside and negatively by the solar wind electrons on the night-side. The charged dust grains are levitated and transported over long distances by the established electric fields. A quantitative understanding of the lunar dust phenomena requires development of global dust distribution models, based on an accurate knowledge of lunar dust charging properties. Currently available data of lunar dust charging is based on bulk materials, although it is well recognized that measurements on individual dust grains are expected to be substantially different from the bulk measurements. In this paper we present laboratory measurements of charging properties of Apollo 11 & 17 dust grains by UV photoelectric emissions and by electron impact. These measurements indicate substantial differences of both qualitative and quantitative nature between dust charging properties of individual micron/submicron sized dust grains and of bulk materials. In addition, there are no viable theoretical models available as yet for calculation of dust charging properties of individual dust grains for both photoelectric emissions and electron impact. It is thus of paramount importance to conduct comprehensive measurements for charging properties of individual dust grains in order to develop realistic models of dust processes in the lunar atmosphere, and address the hazardous issues of dust on lunar robotic and human missions.

Abbas, Mian M.↗
NASA NTRS2022

Modeling the Lunar Wake Response to a CME Using a Hybrid PIC Model

In the solar wind, a low-density wake region forms downstream of the nightside lunar surface. In this study, we use a series of 3D hybrid particle-in-cell simulations to model the response of the lunar wake to a passing coronal mass ejection (CME). Average plasma parameters are derived from the Wind spacecraft located at 1 au during three distinct phases of a passing halo (Earth-directed) CME on 2015 June 22. Each set of plasma parameters, representing the shock/plasma sheath, a magnetic cloud, and plasma conditions we call the mid-CME phase, are used as the time-static upstream boundary conditions for three separate simulations. These simulation results are then compared with results that use nominal solar wind conditions. Results show a shortened plasma void compared to nominal conditions and a distinctive rarefaction cone originating from the terminator during the CME's plasma sheath phase, while a highly elongated plasma void reforms during the magnetic cloud and mid-CME phases. Developments of electric and magnetic field intensification are also observed during the plasma sheath phase along the central wake, while electrostatic turbulence dominates along the plasma void boundaries and 2–3 lunar radii RM downstream in the central wake during the magnetic cloud and mid-CME phases. The simulations demonstrate that the lunar wake responds in a dynamic way with the changes in the upstream solar wind during a CME.

Anthony P. Rasca↗