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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

On Europa's Magnetospheric Interaction: A MHD Simulation of the E4 Flyby

The global three-dimensional interaction of Europa with the Jovian magnetosphere is modeled by using a complete set of ideal magnetohydrodynamic (MHD) equations. The model accounts for exospheric mass loading, ion-neutral charge exchange, recombination, and a possible intrinsic dipole magnetic field of Europa. The single-fluid MHD equations are solved by using a modem, finite volume, higher-order, Godunov-type method on an adoptively refined unstructured grid, which allows detailed modeling of the region near Europa while still resolving both the upstream region and the satellite's wake. The magnetic field and plasma density measured during Galileo's EGA flyby of December 19, 1996, are reproduced reasonably well in the simulation. We find the agreement between the data and our model particularly convincing if we assume that the plasma velocity during the EGA flyby deviated from the nominal corotation direction by approximately 20 deg. Evidence from the Galileo energetic particle detector also supports this assumption. In this case, we can fit the data using a dipole with orientation close to that of an induced dipole arising from the interaction of a hypothetical conducting subsurface layer on Europa with the periodically changing magnetic field of Jupiter. However, the magnitude of the dipole in our model is somewhat smaller (70%) than that suggested by Khurana et al. The total mass loading and ion-neutral charge exchange rates are consistent with the estimates of Europa's atmosphere and ionosphere.

Kabin, K.↗
NASA NTRS1984

Wave-particle interactions in the Venus wake and tail

The first descriptions of combined tail measurements from the Pioneer Venus plasma analyzer, magnetometer, and plasma wave detector are presented. The analysis concentrates on those orbits which are representative of the first tail passage. Summary plasma analyzer parameters are used to show that waves occurring at the boundary of the magnetotail can be identified as Doppler-shifted ion acoustic oscillations. High-density plasma distributions in the magnetotail region usually appear to be non-Maxwellian at the highest time resolution. These distorted distribution functions are generally accompanied by enhanced plasma wave signals and magnetic field reversals indicative of electric currents. A different time for the spacecraft entrance into the magnetotail from that previously defined is identified. It is shown that the wave activity in the Venus tail appears similar to the broadband noise identified in the earth's tail, except that at Venus the levels are usually higher.

Intriligator, D. S.↗
NASA NTRS1987

Plasma interactions in the Space Shuttle Orbiter environment

Attempts to measure the ambient ionospheric plasma environment in the vicinity of the payload bay of the Space Shuttle Orbiter have shown that the plasma is quite different, in a variety of characteristics, from the ionospheric plasma at low earth orbit altitudes. It appears that the large size, complex geometry and various outgassing characteristics of a typical Orbiter payload can all contribute to modifications of the plasma environment of the Space Shuttle Orbiter. The measurements indicate that the plasma is often quite turbulent and contains populations more energetic than the ambient ionospheric plasma. Pronounced wake and ram effects have been observed, and at times the data can be interpreted as plasma number density enhancements of an order of magnitude or greater over the ambient, undisturbed plasma concentration. There is evidence that this enhanced plasma concentration contains molecular ions, not occurring naturally at low earth orbit altitudes. In addition to describing the observations, the electrodynamics of enhanced Orbiter-generated plasma and its possible impact on optical measurements from the Space Shuttle Orbiter will be discussed.

Raitt, W. J.↗
NASA NTRS1982

The distant interplanetary wake of Venus - Plasma observations from Pioneer Venus

Observations by the Pioneer Vernus Orbiter plasma analyzer during passages through the Venus solar wind wake in June 1979 are reported. The spacecraft traveled 8-12 Venus radii behind the planet from the sun, detecting frequent, episodic disappearances of the plasma. The disappearance occurred inside the magnetotail, indicating a tattered, filamentary extension of the solar wind cavity. Positive oxygen ions were observed inside and outside of the magnetotail on some days, and were absent on others. The data indicate that the cavity contracts during high solar wind dynamic pressure, although the presence of 0(+) ions is not correlated well with the solar wind dynamic pressure. The most intense bursts originated from a flux of 10 million ions/sq cm per sec, with an 0(+) kinetic energy estimated to be 100,000-1,000,000 K.

Mihalov, J. D.↗
NASA NTRS1979

Plasma diffusion into the wake of Venus

A model of the diffusion of ionosheath plasma into the wake region of Venus is presented. It is shown that particle diffusion, which is assumed to be a consequence of the fluctuating magnetic field observed in the wake of Venus by Pioneer Venus and Veneras 9 and 10, can explain the plasma observations made in the wake by Veneras 9 and 10. The pressure due to these diffusing particles when balanced against the ionospheric pressure yield ionopause heights less than 1000 km for zenith angles less than about 135 deg. The model also predicts significant fluxes of low energy electrons and ions for zenith angles less than 135 deg, which are capable of producing the observed nightside ionosphere.

Gombosi, T.↗
NASA NTRS1981

Ultrarelativistic electromagnetic pulses in plasmas

The physical processes of a linearly polarized electromagnetic pulse of highly relativistic amplitude in an underdense plasma accelerating particles to very high energies are studied through computer simulation. An electron-positron plasma is considered first. The maximum momenta achieved scale as the square of the wave amplitude. This acceleration stops when the bulk of the wave energy is converted to particle energy. The pulse leaves behind as a wake a vacuum region whose length scales as the amplitude of the wave. The results can be explained in terms of a snow plow or piston-like action of the radiation on the plasma. When a mass ratio other than unity is chosen and electrostatic effects begin to play a role, first the ion energy increases faster than the electron energy and then the electron energy catches up later, eventually reaching the same value.

Ashour-Abdalla, M.↗
NASA NTRS1984

Measurements of the thermal plasma environment of the Space Shuttle

The paper presents some initial results on measurements of the thermal plasma environment obtained by a spherical retarding potential analyzer and a Langmuir probe flown on (STS-3) as part of the NASA Office of Space Science-1 payload in March 1982. One of the major effects observed is a higher degree of turbulence in the ambient plasma compared to what is observed from similar instruments flown on unmanned satellites. In addition we see the temperature of the thermal electrons elevated to values of 4000-5000 K. Associated with elevated electron temperatures are regions of enhanced plasma density resulting from the appearance of high densities of molecular ions. The thermal plasma data also show clear effects of an induced V x B.L potential at the location of the probes which matches that produced by an L vector linking the probes to the engine nozzles; thereby establishing the prime return current location on the Orbiter. The final observations discussed are the pronounced and complex wake effects resulting both from the main structure of the Orbiter and from the complex shapes of appendages attached to the Orbiter.

Raitt, W. J.↗
NASA NTRS1986

A plasma generator utilizing the high intensity ASTROMAG magnets

The magnet configuration for the proposed particle astrophysics magnet facility (ASTROMAG) on the space station includes a cusp magnetic field with an intensity of a few tesla. With these large magnets (or others) located in the outer ionosphere, many quite interesting and unique plasma physics experiments become possible. First there are studies utilizing the magnet alone to examine the supersonic, sub-Alfvenic interaction with the ambient medium; the scale length for the magnet perturbation is approx. 20 m. The magnetic field geometry when combined with the Earth's and their relative motion will give rise to a host of plasma phenomena: ring nulls, x-points, ion-acoustic and lower-hybrid shocks, electron heating (possible shuttle glow without a surface) launching of Alfvenwaves, etc. Second, active experiments are possible for a controlled study of fundamental plasma phenomena. A controlled variable species plasma can be made by using an RF ion source; use of two soft iron rings placed about the line cusp would give an adequate resonance zone (ECH or ICH) and a confining volume suitable for gas efficiency. The emanating plasma can be used to study free expansion of plasma along and across field lines (polar wind), plasma flows around the space platform, turbulent mixing in the wake region, long wavelength spectrum of convecting modes, plasma-dust interactions, etc.

Sullivan, James D.↗
NASA NTRS1986

The Venus magnetotail

The magnetic structure of the Venus magnetotail has been measured using 9 seasons of Pioneer Venus measurements in the distant wake region. The magnetotail region is about 4 Venus radii wide and about 3.2 Venus radii high at 12 Venus radii behind the planet. The tail contains about 2.3 Megawebers of flux, much of which closes across the tail. The J x B force associated with this cross tail component accelerates the tail plasma down the tail causing an ion loss rate of about 10 to the 26th ions per second. The Venus tail does respond to solar activity and contains significantly less magnetic flux at solar minimum.

Russell, C. T.↗
NASA NTRS1975

Laboratory observations of electron temperature in the wake of a sphere in a streaming plasma

A parametric study was performed of electron-temperature variation in the wake of a conducting sphere in a streaming plasma. The flow conditions were varied as follows: the ambient electron temperatures in the range from 850 to 2450 K; the ambient electron densities in the range from 0.0005 to 0.00007 per cu cm; and body potentials relative to plasma potential in the range from +1.7 to -2.8 V for an ion-beam energy of approximately 4 eV. Electron-temperature enhancements were observed which ranged up to 200 per cent above ambient in the nearest proximity of the body surface. The magnitude of the enhancement depends upon the ambient density, temperature, and body potential.

Oran, W. A.↗
NASA NTRS1984

Interactions between the orbiting Space Shuttle and the ionosphere

This paper presents an analysis of interactions between the Space Shuttle Orbiter and the ionosphere based on thermal plasma data obtained from a Spherical Retarding Potential Analyzer (SRPA) and a Langmuir Probe (LP) flown on the third Space Shuttle flight (STS-3) in March 1982. While previous work on spacecraft-plasma interactions has dealt with wake effects, the present work deals with effects that are seen in ram conditions that have not been previously discussed. One observation is a higher degree of plasma turbulence than has been reported from unmanned spacecraft measurements that manifests itself as a frequency component at 2.2 kHz in the SRPA signal. Also seen are unusually high number densities of what appear to be ions with a mass of at least 30 or 32 amu and a temperature in the range 2000-3000 K. Coincident with the enhanced molecular ion species, the temperature of the thermal electrons is seen elevated to above 5000 K. It is hypothesized that these measurements are evidence for a plasma instability resulting from the motion of the outgassing Orbiter through the ionosphere.

Siskind, D. E.↗
NASA NTRS2008

ISS Charging Hazards and Low Earth Orbit Space Weather Effects

Current collection by high voltage solar arrays on the International Space Station (ISS) drives the vehicle to negative floating potentials in the low Earth orbit daytime plasma environment. Pre-flight predictions of ISS floating potentials Phi greater than |-100 V| suggested a risk for degradation of dielectric thermal control coatings on surfaces in the U.S. sector due to arcing and an electrical shock hazard to astronauts during extravehicular activity (EVA). However, hazard studies conducted by the ISS program have demonstrated that the thermal control material degradation risk is effectively mitigated during the lifetime of the ISS vehicle by a sufficiently large ion collection area present on the vehicle to balance current collection by the solar arrays. To date, crew risk during EVA has been mitigated by operating one of two plasma contactors during EVA to control the vehicle potential within Phi less than or equal to |-40 V| with a backup process requiring reorientation of the solar arrays into a configuration which places the current collection surfaces into wake. This operation minimizes current collection by the solar arrays should the plasma contactors fail. This paper presents an analysis of F-region electron density and temperature variations at low and midlatitudes generated by space weather events to determine what range of conditions represent charging threats to ISS. We first use historical ionospheric plasma measurements from spacecraft operating at altitudes relevant to the 51.6 degree inclination ISS orbit to provide an extensive database of F-region plasma conditions over a variety of solar cycle conditions. Then, the statistical results from the historical data are compared to more recent in-situ measurements from the Floating Potential Measurement Unit (FPMU) operating on ISS in a campaign mode since its installation in August, 2006.

Minow, Joseph↗
NASA NTRS1987

Corona anemometry for qualitative measurement of reversing surface flow with application to separation control by external excitation

An corona anemometer which detects gas flow by the displacement of an ion beam is described, and experiments are performed using the anemometer to investigate the active control of diffusor separation by periodic forcing. The apparatus is applied to the separated flow over a rearward facing ramp. An oscillating vane is attached to the surface near the separation point. It is suggested that the enhancement in turbulent energy produced by the oscillating vane is due to drastic modification of the wake shear flow, and not to vane-produced turbulence.

Durbin, P. A.↗
NASA NTRS2003

Plasma Sheath Behavior of the ProSEDS Delta II

The Propulsive Small Expendable Deployer System (ProSEDS) mission is a demonstration of the orbit lowering capabilities of an electrodynamic tether. The system is sequenced through various electrical modes, involving both open circuit and closed circuit configurations, so that the performance capabilities of the system can be studied. Ionospheric electrons are collected on the upper end of the bare tether, conducted through the tether, and returned to the ionosphere at the lower end (Delta I1 2nd stage) via the operation of a Hollow Cathode Plasma Contactor (HCPC). The working gas of the HCPC is xenon. Environmental plasma measurements and sheath potential are obtained from the Differential Ion Flux Probe w/Mass Analysis (DIFPM) and Langmuir Probe and Spacecraft Potential (LPSP) instruments. Each instrument has three sensors symmetrically placed about the strut section of the Delta 2nd stage. A magnetometer is also included in the ProSEDS instrumentation suite. An initial analysis of the rocket stage sheath behavior as a function of ProSEDS configuration (open or closed circuit), ambient ionospheric density, orientation to velocity vector (ram-wake influence), and magnetic field orientation is presented. An initial assessment on how well the plasma contactor grounded the rocket stage is also presented.

Wright, K. H.↗
NASA NTRS1981

Evidence for the acceleration of ionospheric O/+/ in the magnetosheath of Venus

Plasma spectra from 12 orbits of the Pioneer-Venus Orbiter are reported which suggest the presence of ionospheric material in the magnetosheath plasma near and sunward of the terminator plane. Each spectrum shows a high E/q peak, consistent with O(+) moving at a speed lower than or comparable to that of the ambient magnetosheath plasma. It is pointed out that even though the data set is limited, the most intense heavy-ion fluxes clearly occur at altitudes less than a few thousand km. With the identification of the energetic component at O(+), the data reveal a trend for the speed of O(+) near the planet to be lower than the local magnetosheath speed, whereas the two speeds are comparable at altitudes above a few thousand km. These data, in combination with related observations that indicate O(+) moving at ambient speed in the distant wake, suggest that ionospheric material is swept up by the magnetosheath, accelerated to ambient speed within a few thousand km, and carried back through the wake region.

Mihalov, J. D.↗
NASA NTRS1999

Electric Field Double Probe Measurements on Satellites with Very Low Perigees

Measurements of DC and AC electric Fields at low altitudes (less than 150 km) in the Earth's ionosphere address a wide array of important scientific questions including Joule Heating, the closure of field aligned currents, and the deviation of E x B electron velocities from ion velocity vectors influenced by collisions. Double probes represent a well-proven technique for gathering high quality DC and AC electric field measurements for which the design of the boom system is of critical importance for the success of the experiment. In general, ionospheric DC electric field instruments that achieve accuracies of 0.1 mV/m or better, place sensors at large distances from the spacecraft body in order to extend well beyond the spacecraft wake and sheath and to achieve the large signal-to-noise ratios for DC and long wavelength measurements. Additional sets of sensors inboard of the primary, outermost sensors provide useful additional information, both for diagnostics of the plasma contact potentials, which particularly enhance the DC electric field measurements on non-spinning spacecraft, and for wavelength and phase velocity measurements that use the spaced receiver or "Interferometer" technique. Accurate attitude knowledge enables V x B contributions to be subtracted from the measured potentials, and permits the measured components to be rotated into meaningful geophysical reference frames. This presentation discusses the expected performance of electric field double probe experiments and their boom mechanisms on both spinning and non-spinning satellite platforms with very low perigees. Careful selection of probe surface materials, such as titanium nitride, for the low perigee environment, as well as thermal considerations are also discussed.

Pfaff, R. F., Jr.↗
NASA NTRS1975

Results of magnetospheric barium ion cloud experiment of 1971

The barium ion cloud experiment involved the release of about 2 kg of barium at an altitude of 31 482 km, a latitude of 6.926 N., and a longitude of 74.395 W. Significant erosion of plasma from the main ion core occurred during the initial phase of the ion cloud expansion. From the motion of the outermost striational filaments, the electric field components were determined to be 0.19 mV/m in the westerly direction and 0.68 mV/m in the inward direction. The differences between these components and those measured from balloons flown in the proximity of the extremity of the field line through the release point implied the existence of potential gradients along the magnetic field lines. The deceleration of the main core was greater than theoretically predicted. This was attributed to the formation of a polarization wake, resulting in an increase of the area of interaction and resistive dissipation at ionospheric levels. The actual orientation of the magnetic field line through the release point differed by about 10.5 deg from that predicted by magnetic field models that did not include the effect of ring current.

Adamson, D.↗
NASA NTRS1982

Measurements by the plasma diagnostics package on STS-3

A comprehensive set of measurements about the orbiter environment are provided by the plasma diagnostics package (PDP). Ion and electron particle densities, energies, and spatial distribution functions; ion mass for identification of particular molecular ion species; and magnetic fields, electric fields and electromagnetic waves over a broad frequency range are studied. Shuttle environmental measurements will be made both on the pallet and, by use of the remote manipulator system (RMS), the PDP will be maneuvered in and external to the bay area to continue environmental measurements and to carry on a joint plasma experiment with the Utah State University fast-pulsed electron generator. Results of orbiter environment EMI measurements and S-band field strengths as well as preliminary results from wake search operations indicating wake boundary identifiers are reported.

Shawhan, S. D.↗