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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Venus ionosphere - Photochemical and thermal diffusion control of ion composition

The major photochemical sources and sinks for ten of the ions measured by the ion mass spectrometer on the Pioneer Venus bus and orbiter spacecraft that are consistent with the neutral gas composition measured on the same spacecraft are identified. The neutral gas temperature (as a function of solar zenith angle) derived from measured ion distributions in photochemical equilibrium is given. Above 200 kilometers, the altitude behavior of ions is generally controlled by plasma diffusion, with important modifications for minor ions due to thermal diffusion resulting from the observed gradients of plasma temperatures. The dayside equilibrium distributions of ions are sometimes perturbed by plasma convection, while lateral transport of ions from the dayside seems to be a major source of the nightside ionosphere.

Bauer, S. J.↗
NASA NTRS1985

Enhanced N(+) Sub 2 in the Shuttle Environment

Observations were made of the N2 first negative and Meinel emission bands with the Imaging Spectrometric Observatory (ISO) on Spacelab 1. These observations have revealed the presence of N2 emissions which exceed those expected on the basis of current ionospheric models by up to a factor of 10. If the emission is of terrestrial origin, large unidentified ionospheric sources of N2 ions must exist. On the other hand, if the source is local to the shuttle environment, a mechanism must be found which is capable of generating emissions of such unexpectedly large intensity. Charge exchange of ambient ionospheric O+ ions with shuttle environmental N2, followed by resonance scattering of sunlight, as a candidate were suggested. However, this model implies that a cloud of N2 gases must surround the vehicle in concentrations in excess of 10 to the 11 c.c. cm with a scale length of tens of meters. In addition, the N2 residence time must be of the order of 10 sec.

Torr, D. G.↗
NASA NTRS1985

Ion-acoustic-like waves excited by the reflected ions at the earth's bow shock

Some model distributions based on recent observations and simulations of the plasma at the earth's bow shock are found to be unstable to obliquely propagating electrostatic instabilities. The model distributions consist of either an ion beam or an ion velocity ring accompanied by a bi-Maxwellian background ion distribution and a flattop electron distribution. Ion anisotropies and nonthermal electrons are capable of significantly lowering the threshold of the ion beam instability. The generated waves share many properties in common with the ion acoustic waves that have been observed at the earth's bow shock. The results also indicate the importance of an anisotropy in the background ion velocity distribution in identifying sources of the ion-acoustic-like waves observed in the ion foreshock and the solar wind.

Akimoto, K.↗
NASA NTRS1986

Solar wind control of the Geomagnetic Mass Spectrometer

Evidence from Dynamics Explorer retarding-ion mass-spectrometer data collected between 1981 and 1983 for the mass dispersion of ionospheric plasma in the polar cap, known as the Geomagnetic Mass Spectrometer, is discussed, and implications of this new source of ionospheric ions for the magnetosphere are considered. A localized source of energization of ionspheric H(+), He(+), O(+) and N(+) ions in the polar cusp yields a source of upswelling plasma that is transported into the magnetosphere, and equal heating of the ion species results in field-aligned flow velocities which are inversely proportional to the square root of the ion mass. The present phenomenon is produced by the resulting velocity filter effect of solar-driven ExB ion convection. The influence of solar wind conditions on the outflow via the polar cap ExB convection pattern is also discussed.

Waite, J. H., Jr.↗
NASA NTRS1979

The catalysis of nucleotide polymerization by compounds of divalent lead

The nonenzymatic, nontemplate catalysis of nucleotide polymerization by Pb(2+) ions, a possible prebiotic catalyst, is reported. Adenosine and uridine phosphoimidazoles were reacted in buffered solutions of lead salts and products were analyzed by means of paper chromatography and electrophoresis. In the presence of Pb(2+) ion at pH 8.0 and 7.0 the reaction is found to progress rapidly with excellent yields of oligomers, with optimal yields observed at pH 8.0. Little temperature dependence in the range 0 to 30 C is observed, however hydrolysis of the reaction products is minimal when the reaction is carried out at 0 C. Results show that the yield of oligomers is insensitive to mixing or the source of lead ions, indicating that naturally occurring minerals or precipitates could be a source of Pb(2+) ions under prebiotic conditions.

Sleeper, H. L.↗
NASA NTRS1985

Explanation of the inward displacement of Io's hot plasma torus and consequences for sputtering sources

Radial profiles of the ion density and flux-tube content in the Io torus have peak values inside Io's orbit, even though Io is the effective source of these ions. Formation of an inward peak constrains either the velocity distributions or source regions of sputtered neutrals. A further constraint is that the ionization of neutrals on trapped trajectories that return to Io's surface must be limited. A dominant sulphur source is most easily reconciled with these constraints.

Linker, J. A.↗
NASA NTRS1984

Ion cyclotron waves as a possible source of resonant auroral radar echoes

Some auroral radar Doppler data which show the presence of spectra not previously discussed are described. The data were obtained during highly distributed magnetic conditions with a relatively small 50 MHz radar pointed northeast of Ithaca, New York. The data are characterized by strong discrete echoes and display spectral peaks which are even narrower than type 1 and are centered at a considerably smaller Doppler shift. These echoes were present simultaneously with and adjacent in range to the commonly observed auroral spectra, and were probably obtained from a height of about 140 km or higher, well above the center of the auroral electrojet. The results are compared with existing electrojet instability theories, and other plasma instabilities which might be important are discussed. The Doppler shift suggests that the narrow spectra might be caused by ion cyclotron waves generated by field-aligned currents, but the observations cannot be fully explained by any of the theories.

Fejer, B. G.↗
NASA NTRS1990

Radial diffusion of low-energy plasma ions in Saturn's magnetosphere

Radial diffusion of low-energy plasma ions in Saturn's magnetosphere is investigated using a comprehensive set of equations for radial diffusion that incorporate distributed sources and sinks of ions. The results of calculations indicate that the radial-diffusion transport of low-energy O(+) ions with a source in the neutral H2O cloud of the satellites Dione and Tethys can account for Voyager observations of thermal heavy ions in Saturn's magnetosphere. The source rate was calculated to be about 10 to the 26th O(+) ions/sec, in good agreement with the sputtering calculations of Johnson et al. (1989). It is estimated that, due to fast radial diffusion, the residence time of O(+) ions in the Dione-Tethys torus is about 30 days, sufficiently short to account for the plasma density observed there. The densities of hot H(+) and N(+) resulting from the ionization and pickup of Titan's neutral clouds in the outer magnetosphere can also be accounted for within the framework of diffusive ion transport.

Barbosa, D. D.↗
NASA NTRS1982

Solutions to the equations for corotating magnetospheric convection

The equations of centrifugally driven convection appropriate to a treatment of the transport of Io plasma in Jupiter's magnetosphere are solved for two special cases of the source distribution. The results show that, in the corotating frame of Jupiter, the mass flows outward from the source, forming spirallike streamlines. It is found that the pitch of a spiral depends on the amount of resident mass and the ionospheric conductivity and that the outflow speed depends on the size of the source region, the resident mass, and the source strength of new ions. An example of a wide source and slow outflow is presented. It is noted that, in the limit of a narrow source, the outflow is rapid and the streamlines are nearly radial.

Summers, D.↗
NASA NTRS2001

Source Determination for Substorm-Related Ion Injections

The grant supported an effort to restore and analyze data from the Spacecraft Charging at High Altitude (SCATHA) spacecraft. This spacecraft, which was originally an Air Force mission, was launched into a near geo-synchronous orbit in early 1979 to, investigate the inner magnetosphere at altitudes where it was known that spacecraft can undergo significant charging events. SCATHA included an ion composition experiment (designated SC8) and in many ways was a precursor to other missions, such as the AMPTE Charge Composition Explorer.

Strangeway, Robert J.↗
NASA NTRS2005

Technical Consultation of the International Space Station (ISS) Internal Active Thermal Control System (IATCS) Cooling Water Chemistry

The Internal Active Thermal Control System (IATCS) coolant exhibited unexpected chemical changes during the first year of on-orbit operation following the launch and activation in February 2001. The coolant pH dropped from 9.3 to below the minimum specification limit of 9.0, and re-equilibrated between 8.3 and 8.5. This drop in coolant pH was shown to be the result of permeation of CO2 from the cabin into the coolant via Teflon flexible hoses which created carbonic acid in the fluid. This unexpected diffusion was the result of having a cabin CO2 partial pressure higher than the ground partial pressure (average 4.0 mmHg vs. less than 0.2 mmHg). This drop in pH was followed by a concurrent increasing coolant nickel concentration. No other metal ions were observed in the coolant and based on previous tests, the source of nickel ion was thought to be the boron nickel (BNi) braze intermetallics used in the construction of HXs and cold plates. Specifically, BNi2 braze alloy was used for the IATCS IFHX and BNi3 braze alloy was used for the IATCS Airlock Servicing and Performance Checkout Unit (SPCU) HX and cold plates. Given the failure criticality of the HXs, a Corrosion Team was established by the IATCS CWG to determine the impact of the nickel corrosion on hardware performance life.

Gentz, Steven J.↗
NASA NTRS2010

Sources and Losses of Ring Current Ions

During geomagnetic quiet times, in-situ measurements of ring current energetic ions (few to few tens of keVs) from THEMIS spacecraft often exhibit multiple ion populations at discrete energies that extend from the inner magnetosphere to the magnetopause at dayside or plasma sheet at nightside. During geomagnetic storm times, the levels of fluxes as well as the mean energies of these ions elevated dramatically and the more smooth distributions in energies and distances during quiet times are disrupted into clusters of ion populations with more confined spatial extends. This reveals local plasma heating processes that might have come into play. Several processes have been proposed. Magnetotail dipolarization, sudden enhancement of field-aligned current, local current disruptions, and plasma waves are possible mechanisms to heat the ions locally as well as strong convections of energetic ions directly from the magnetotail due to reconnections. We will examine two geomagnetic storms on October 11, 2008 and July 22, 2009 to reveal possible heating mechanisms. We will analyze in-situ plasma and magnetic field measurements from THEMIS, GOES, and DMSP for the events to study the ion pitch angle distributions and magnetic field perturbations in the auroral ionosphere and inner magnetosphere where the plasma heating processes occur.

Chen, Sheng-Hsien↗
NASA NTRS2016

Delay Tolerant Networking on NASA's Space Communication and Navigation Testbed

This presentation covers the status of the implementation of an open source software that implements the specifications developed by the CCSDS Working Group. Interplanetary Overlay Network (ION) is open source software and it implements specifications that have been developed by two international working groups through IETF and CCSDS. ION was implemented on the SCaN Testbed, a testbed located on an external pallet on ISS, by the GRC team. The presentation will cover the architecture of the system, high level implementation details, and issues porting ION to VxWorks.

communication networks↗
NASA NTRS1979

Distribution of energetic positive ion species above a diffuse midnight aurora

The present paper deals with species-identifying distribution function measurements of auroral primary particles, made during a magnetically quiet presubstorm period above a hydrogen-associated diffuse aurora. Only ions identified as H(+) and He(++) were detected. In the mass spectrum data, the He(++) was not clearly above background. At energies between 2.5 and 12 keV, the He(++)/H(+) intensity ratio had an upper limit of 2 to 4 percent. The same upper limit applies to all other ions, such as He(+) and O(+). Though this would suggest a solar wind source for these ions, an admixture including an appreciable fraction of polar wind protons is not precluded. This situation contrasts sharply with a number of recently reported observations of large intensities of precipitating O(+) ions during magnetic storms, and may be characteristic of undisturbed periods.

Moore, T. E.↗
NASA NTRS1987

Laser magnetic resonance in supersonic plasmas - The rotational spectrum of SH(+)

The rotational spectrum of v = 0 and v = 1X3Sigma(-)SH(+) was measured by laser magnetic resonance. Rotationally cold (Tr = 30 K), vibrationally excited (Tv = 3000 K) ions were generated in a corona excited supersonic expansion. The use of this source to identify ion signals is described. Improved molecular parameters were obtained; term values are presented from which astrophysically important transitions may be calculated. Accurate hyperfine parameters for both vibrational levels were determined and the vibrational dependence of the Fermi contact interaction was resolved. The hyperfine parameters agree well with recent many-body perturbation theory calculations.

Hovde, David C.↗
NASA NTRS1985

The cleft ion fountain - A two-dimensional kinetic model

The transport of ionospheric ions from a source in the polar cleft ionosphere through the polar magnetosphere is investigated using a two-dimensional, kinetic, trajectory-based code. The transport model includes the effects of gravitation, longitudinal magnetic gradient force, convection electric fields, and parallel electric fields. Individual ion trajectories as well as distribution functions and resulting bulk parameters of density, parallel average energy, and parallel flux for a presumed cleft ionosphere source distribution are presented for various conditions to illustrate parametrically the dependences on source energies, convection electric field strengths, ion masses, and parallel electric field strengths. The essential features of the model are consistent with the concept of a cleft-based ion fountain supplying ionospheric ions to the polar magnetosphere, and the resulting plasma distributions and parameters are in general agreement with recent low-energy ion measurements from the DE 1 satellite.

Horwitz, J. L.↗
NASA NTRS1991

A comprehensive magnetohydrodynamic model of the Venus ionosphere

The MHD Venus ionospheric model of Shinegawa and Cravens (1988) is improved here by including the energy equations for ions and electrons in a self-consistent manner. This new model reproduces observed electron density and magnetic field profiles very well, while the basic MHD process of the Venus ionosphere remain virtually unchanged. The results indicate that including energetics does not significantly alter the density and magnetic field profiles. Under unmagnetized conditions, heat fluxes for both ions and electrons must be imposed to reproduce the observed plasma temperature profiles. A heat source for the ions is probably present at higher altitudes in the magnetized ionosphere. Heating processes do not play a significant role in the dynamics at low altitudes.

Shinagawa, H.↗