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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

AMPTE/CCE and SCATHA simultaneous observations of magnetic signatures associated with a substorm onset

Magnetic field signatures associated with a substorm onset event are examined by making use of simultaneous observations from the Active Magnetosphere Particle Tracer Explorer (AMPTE)/Charge Composition Explorer (CCE) and Spacecraft Charging AT High Altitude (SCATHA). The observations of the two satellites are discussed in relation to their differences and the relative positions of the satellites. Despite the small separation between the satellites, AMPTE/CCE observed the start of irregular magnetic field fluctuations a few tens of seconds earlier than SCATHA, indicating that the CCE was within, or closer to, the onset region. It was found that the amplitude of the fluctuations was largest in the north-south component. The results indicate that the magnetic field fluctuations were excited locally and the coherence length was less than a multiple of Larmor radius of thermal protons. It is suggested that the tail current disruption is described as a system of chaotic filamentary electric currents which flow in various directions, but preferentially anti-parallel to the cross-tail current, and that ions play an important role in the triggering of the tail current disruption.

Ohtani, S.↗
NASA NTRS2005

Propagation of Interplanetary Disturbances in the Outer Heliosphere

Contents include the following: 1. We have developed a one-dimensional, spherically symmetric, multi-fluid MHD model that includes solar wind protons and electrons, pickup ions, and interstellar neutral hydrogen. This model advances the existing solar wind models for the outer heliosphere in two important ways: one is that it distinguishes solar wind protons from pickup ions, and the other is that it allows for energy transfer from pickup ions to the solar wind protons. Model results compare favorably with the Voyager 2 observations. 2. 2. Solar wind slowdown and interstellar neutral density. The solar wind in the outer heliosphere is fundamentally different from that in the inner heliosphere since the effects of interstellar neutrals become significant. 3. ICME propagation from the inner to outer heliosphere. Large coronal mass ejections (CMEs) have major effects on the structure of the solar wind and the heliosphere. The plasma and magnetic field can be compressed ahead of interplanetary CMEs. 4. During the current solar cycle (Cycle 23), several major CMEs associated with solar flares produced large transient shocks which were observed by widely-separated spacecraft such as Wind at Earth and Voyager 2 beyond 60 AU. Using data from these spacecraft, we use the multi-fluid model to investigate shock propagation and interaction in the heliosphere. Specifically, we studied the Bastille Day 2000, April 2001 and Halloween 2003 events. 5. Statistical properties of the solar wind in the outer heliosphere. In a collaboration with L.F. Burlaga of GSFC, it is shown that the basic statistical properties of the solar wind in the outer heliosphere can be well produced by our model. We studied the large-scale heliospheric magnetic field strength fluctuations as a function of distance from the Sun during the declining phase of a solar cycle, using our numerical model with observations made at 1 AU during 1995 as input. 6. Radial heliospheric magnetic field events. The heliospheric magnetic field (HMF) direction, on average, conforms well to the Parker spiral.

Wang, Chi↗
NASA NTRS2011

MW-Class Electric Propulsion System Designs for Mars Cargo Transport

Multi-kilowatt electric propulsion systems are well developed and have been used on commercial and military satellites in Earth orbit for several years. Ion and Hall thrusters have also propelled robotic spacecraft to encounters with asteroids, the Moon, and minor planetary bodies within the solar system. High power electric propulsion systems are currently being considered to support piloted missions to near earth asteroids, as cargo transport for sustained lunar or Mars exploration, and for very high-power piloted missions to Mars and the outer planets. Using NASA Mars Design Architecture 5.0 as a reference, a preliminary parametric analysis was performed to determine the suitability of a nuclear powered, MW-class electric propulsion system for Mars cargo transport. For this initial analysis, high power 100-kW Hall thrusters and 250-kW VASIMR engines were separately evaluated to determine optimum vehicle architecture and estimated performance. The DRA 5.0 cargo mission closed for both propulsion options, delivering a 100 t payload to Mars orbit and reducing the number of heavy lift launch vehicles from five in the baseline DRA 5.0 architecture to two using electric propulsion. Under an imposed single engine-out mission success criteria, the VASIMR system took longer to reach Mars than did the Hall system, arising from the need to operate the VASIMR thrusters in pairs during the spiral out from low Earth orbit.

Gilland, James H.↗
NASA NTRS2016

Observations of the Minor Species Al and Fe in Mercury's Exosphere

We report here on the first observational evidence of Al and Fe in the exosphere of Mercury, based on measurements of resolved emission lines of these metals with Keck-1/HIRES. Al emission was observed on two separate runs, in 2008 and 2013, with tangent column densities of 3.1 +/- 1.0 and 4.0 +/-1.5 x 10(exp 7) Al atoms cm(exp - 2) at altitudes of 1185 and 1870 km (1.5 and 1.75 R(sub M). The Al radiative intensity was seen to increase where the slit crossed the planetary penumbral shadow, and then decrease monotonically with altitude. Fe emission has been observed once, in 2009, indicating an extended source. We also present observed 3- Sigma Ca(+) upper limits near Mercury's equatorial anti-solar limb, from which an abundance limit of 4.0 x 10(exp 6) cm(exp -2) at 1650 km altitude is derived for the Ca ion. A simple model for zenith column abundances of the neutral species yields 1.9 -5.2 x 10(exp 7) Al cm(exp -2) , and 8.2 x 10(exp 8) Fe cm(exp -2) . The observations appear to be consistent with production of these species by impact vaporization, with a large fraction of the Al ejecta in molecular form, and that for Fe in mixed atomic and molecular forms. The scale height of the Al gas is consistent with a kinetic temperature of 6100-8000 K. The apparent high temperature and low density of the Al gas would suggest that it may be produced by dissociation of molecules.

Mercury↗
NASA NTRS2023

Multiphysics Modeling of Electrode Dissolution under Hydrodynamic Conditions in Low Conductivity Water

Efficient plug-flow electrochemical reactors are characterized by their ability to effectively convert species with significant ionic strength and/or with the assistance of a well-behaved electrolyte. Because of the classic electroconductivity requirement, electrochemical reactors are not particularly attractive options for applications with low-conductivity conditions, especially for low-pressure feeds. However, these reactors can still find application in dedicated processes such as ultra-clean water conditioning and biological-coupled separation systems. Consequently, a multi-physics model was developed using COMSOL Multiphysics to characterize different reactor-design conditions based on the Tertiary Current Distribution which accounts for the effects of expected variations in electrolyte composition and ionic strength on the electrochemical process, as well as solution resistance and electrode kinetics. The modelling framework presented here employs single-phase laminar fluid flow, the Nernst-Planck equation, the water-based electroneutrality condition, and concentration-dependent overpotentials. This investigation particularly explores the electrolysis process of “anodic dissolution,” in which elemental species dissociate from the solid matrix of the electrode and enter the liquid phase of the electrolyte as soluble ions. The reactor configuration of interest has a rectangular parallel-electrode design and is operated galvanostatically. A series of parametric studies are carried out to inspect the response of the system when hydrodynamic, kinetic, and geometric conditions are changed. The parametric sweep resulted in variable effluent concentrations and system voltage, which reveal underlaying optimization patterns for electrode dissolution in low conductivity water.

Multiphysics↗
NASA NTRS1977

Ion Drive multi-asteroid rendezvous trajectories

The general characteristics of multiasteroid rendezvous missions are examined, taking into account a use of an improved solar electric propulsion system, called Ion Drive. The improvements are related to the development of light-weight solar cells, extensions to high thruster power levels with high exhaust velocity, and the attachment of solar concentrators to increase the power available beyond 1.5 AU. Flight times on the order of 500-800 days are generally required. It is assumed that a stay time of about 60 days at each asteroid is adequate. Attention is given to launch and spacecraft parameters, the search technique, and multiasteroid tours involving Ceres and Vesta. It is found that at least four asteroids in the main belt, generally selected from those with known characteristics, may be reached on a single mission with a 100-kg separable probe landed on each one.

Bender, D. F.↗
NASA NTRS2011

COMPASS Final Report: Enceladus Solar Electric Propulsion Stage

The results of the NASA Glenn Research Center (GRC) COllaborative Modeling and Parametric Assessment of Space Systems (COMPASS) internal Solar Electric Propulsion (SEP) stage design are documented in this report (Figure 1.1). The SEP Stage was designed to deliver a science probe to Saturn (the probe design was performed separately by the NASA Goddard Space Flight Center s (GSFC) Integrated Mission Design Center (IMDC)). The SEP Stage delivers the 2444 kg probe on a Saturn trajectory with a hyperbolic arrival velocity of 5.4 km/s. The design carried 30 percent mass, 10 percent power, and 6 percent propellant margins. The SEP Stage relies on the probe for substantial guidance, navigation and control (GN&C), command and data handling (C&DH), and Communications functions. The stage is configured to carry the probe and to minimize the packaging interference between the probe and the stage. The propulsion system consisted of a 1+1 (one active, one spare) configuration of gimbaled 7 kW NASA Evolutionary Xenon Thruster (NEXT) ion propulsion thrusters with a throughput of 309 kg Xe propellant. Two 9350 W GaAs triple junction (at 1 Astronomical Unit (AU), includes 10 percent margin) ultra-flex solar arrays provided power to the stage, with Li-ion batteries for launch and contingency operations power. The base structure was an Al-Li hexagonal skin-stringer frame built to withstand launch loads. A passive thermal control system consisted of heat pipes to north and south radiator panels, multilayer insulation (MLI) and heaters for the Xe tank. All systems except tanks and solar arrays were designed to be single fault tolerant.

Oleson, Steven R.↗
NASA NTRS2016

Magnetospheric Multiscale Mission Attitude Dynamics: Observations from Flight Data

Extensive flight data is being collected throughout the MMS mission that includes quantities that are of interest for attitude dynamics studies such as spin rate, spin axis orientation nutation rate, etc. One example of such data is the long-term evolution of the spin rates of the four spacecraft. Spikes in these rates are observed that are separated by the MMS orbital period (just under 24 hr) and occur around perigee due to gravity-gradient torque. Periodic discontinuities in spin rate are caused by the controller resetting the spin rate approximately to the nominal 3.1 RPM value at the time of each maneuver. In between, a slow decay in spin rate can be seen to occur. The paper will discuss various disturbance torque mechanisms that could potentially be responsible for this behavior: these include magnetic hysteresis, eddy currents, solar radiation pressure, and a possible interaction between gravity-gradient and wire boom flexibility effects. One additional disturbance mechanism is produced by the Active Spacecraft Potential Control (ASPOC) devices: these emit positive indium ions to keep the MMS spacecraft electrically neutral, so as not to corrupt the electric field observations that are made by some of the on-board instruments. The spin rate decays that could be produced by these various mechanisms will be quantified in the paper, and their signatures described. Comparing these with the observations from flight data then allow the most likely candidate to be determined.

DYNAMICS↗
NASA NTRS1973

Electric field observations by incoherent scatter radar in the auroral zone.

Analysis of ion drift velocity measurements, made for a 24-hour period in February 1972 by the incoherent scatter radar at Chatanika, Alaska (L = 5.7), provides a detailed view of electric fields and currents in the auroral zone. Large northward electric fields were seen in the evening sector, and an abrupt change to southward occurred at the start of a midnight sector substorm. The westward electric field was generally much smaller than the north-south electric field but showed a rapid increase at the time of a westward auroral surge. Study of global magnetograms and all-sky camera photographs has led to the identification of five substorms during the 24-hour observation period. These substorms were sufficiently separated in time to allow identification of the electric field and current variations in late afternoon, evening, and morning local time sectors.

Banks, P. M.↗
NASA NTRS1981

Cometary particulate analyzer design definition study

A concept for remotely determining the relative abundance of elements contained in cometary particulates collected by a spacecraft was conducted with very encouraging results. The technique utilizes a short high intensity burst of laser radiation to vaporize and ionize collected particulate material. Ions extracted from this laser-produced plasma are analyzed in a time of flight mass spectrometer to yield an atomic mass spectrum representative of the relative abundance of elements in the particulates. A prototype analyzer system was designed, constructed, and tested. Results show that: (1) energy-time focus performs as predicted in improving resolution; (2) power densities sufficient to produce usable ionization efficiencies can be obtained; (3) complex alloys such as stainless steel can be analyzed; and (4) a tiny, simple and reliable laser used in the demonstration easily meets spacecraft power and mass limitations. A mass resolution of 150 was experimentally demonstrated at mass 108, and an analytical extrapolation predicts a resolution sufficient to separate masses 250 and 251.

Utterback, N. G.↗
NASA NTRS1993

The Generation of Oblique Magnetosonic Waves

One of the outstanding issues regarding the excitation of magnetosonic waves has been the observational evidence that obliquely propagating waves are dominant at comets and planetary foreshocks despite the predictions of linear theory that maximum growth occurs at parallel propagation. To address this issue, we have conducted a detailed linear theory using a beam-ring distribution function. The results have shown that such distribution functions are associated with four separate instabilities. Two of these instabilities are similar to the right hand resonant ion/ion and the non-resonant instabilities which are also present in the case of a field aligned beam. The other two instabilities are associated with the presence of ring part of the distribution function. One of these instabilities excites magnetosonic waves with maximum growth in the oblique directions. The other excites Alfven waves with maximum growth in the oblique directions. The importance of the former instability is that it may explain the oblique nature of the magnetosonic waves observed at planetary foreshocks and comets. In order to understand the nonlinear properties of these various instabilities, we have also conducted 2-D hybrid (particle ions, fluid electrons) simulations. We have found that when the beam density is sufficiently large so that the non-resonant instability has the largest growth rate, these waves dominate the initial wave power in the system. At later times, however, the obliquely propagating magnetosonic waves become dominant. Another important finding was that when the two instabilities which excite magnetosonic waves have the largest growth rates, the system is dominated by the obliquely propagating magnetosonic waves. This is despite the fact that the largest growth rate for one of the instabilities occurs in the parallel direction. The exact cause of this is not currently understood and is under investigation.

Source record↗
NASA NTRS1993

Identification of an interstellar oxide grain from the Murchison meteorite by ion imaging

We report here the first use of a new ion-imaging system to locate a rare interstellar aluminum oxide grain in a Murchison acid residue. While several types of carbon-rich interstellar grains, including graphite, diamond, SiC, and TiC, have previously been found, isotopically anomalous interstellar oxide grains have proven more elusive. We have developed an ion imaging system which allows us to map the isotopic composition of large numbers of grains relatively quickly and is, thus, ideally suited to search for isotopically exotic subsets of grains. The system consists of a PHOTOMETRICS CCD camera coupled to the microchannel plate/fluorescent screen of the WU modified CAMECA IMS-3F ion microprobe. Isotopic images of the sample surface are focused on the CCD and digitized. Subsequent image processing identifies individual grains in the images and determines isotopic ratios for each. For the present work, we have imaged in O-16 and O-18; negligible contributions of (17)OH(-) and (16)OH2(-) signals to the O-18 signal allow the use of low mass resolution, simplifying the measurements. Repeated imaging runs on terrestrial corundum particles showed that the system measures isotopic ratios reproducibly to about +/- 40%. Each imaging run took about six minutes to complete, and for this study there were on average 5-15 grains in each image. We have conducted imaging searches in 2-4 micron size separates of both Orgueil and Murchison.

Nittler, L. R.↗
NASA NTRS2010

FIB-NanoSIMS-TEM Coordinated Study of a Wark-Lovering Rim in a Vigarano Type A CAI

Wark-Lovering (WL) rims are thin multi layered mineral sequences that surround most Ca, Al-rich inclusions (CAIs). Unaltered WL rims are composed of the same primary high temperature minerals as CAIs, such as melilite, spinel, pyroxene, hibonite, perovskite, anorthite and olivine. It is still unclear whether the rim minerals represent a different generation formed by a separate event from their associated CAIs or are a byproduct of CAI formation. Several models have been proposed for the origins of WL rims including condensation, flashheating, reaction of a CAI with a Mg-Si-rich reservoir (nebular gas or solid); on the basis of mineralogy, abundances of trace elements, O and Mg isotopic studies. Detailed mineralogical characterizations of WL rims at micrometer to nanometer scales have been obtained by TEM observations, but so far no coordinated isotopic - mineralogical studies have been performed. Thus, we have applied an O isotopic imaging technique by NanoSIMS 50L to investigate heterogeneous distributions of O isotopic ratios in minerals within a cross section of a WL rim prepared using a focused ion beam (FIB) instrument. After the isotopic measurements, we determine the detailed mineralogy and microstructure of the same WL FIB section to gain insight into its petrogenesis. Here we present preliminary results from O isotopic and elemental maps by NanoSIMS and mineralogical analysis by FE-SEM of a FIB section of a WL rim in the Vigarano reduced CV3 chondrite.

Cai, A.↗
NASA NTRS2004

Traveling Wave Tube (TVT) RF Power Combining Demonstration for use in the Jupiter Icy Moons Orbiter (JIMO)

The Jupiter Icy Moons Orbiter (JIMO) is set to launch between the years 2012 and 2015. It will possibly utilize a nuclear reactor power source and ion engines as it travels to the moons of Jupiter. The nuclear reactor will produce hundreds of kilowatts of power for propulsion, communication and various scientific instruments. Hence, the RF amplification devices aboard will be able to operate at a higher power level and data rate. The initial plan for the communications system is for an output of 1000 watts of RF power, a data rate of at least 10 megabits a second, and a frequency of 32 GHz. A higher data rate would be ideal to fully utilize the instruments aboard JIMO. At NASA Glenn, one of our roles in the JIMO project is to demonstrate RF power combining using multiple traveling wave tubes (TWT). In order for the power of separate TWT s to be combined, the RF output waves from each must be in-phase and have the same amplitude. Since different tubes act differently, we had to characterize each tube using a Network Analyzer. We took frequency sweeps and power sweeps to characterize each tube to ensure that they will behave similarly under the same conditions. The 200 watt Dornier tubes had been optimized to run at a lower power level (120 watts) for their extensive use in the ACTS program, so we also had to experiment with adjusting the voltage settings on several internal components (helix, anode, collector) of the tubes to reach the full 200 watt potential. from the ACTS program. Phase shifters and power attenuators were placed in the waveguide circuit at the inputs to the tubes so that adjustments could be made individually to match them exactly. A magic tee was used to route and combine the amplified electromagnetic RF waves on the tube output side. The demonstration of 200 watts of combined power was successful with efficiencies greater than 90% over a 500 MHz bandwidth. The next step will be to demonstrate the use of three amplifiers using two magic tees by adding a 200 watt Dornier tube to the Varian and Logimetrics combined setup for a total of 400 watts. After that we will use two 200 watt Dorniers for 400 watts and eventually four 200 watt Dornier tubes to demonstrate 800 watts. After demonstrating the success of power combining, we will need to verify the integrity of a modulated signal sent through the combined tubes. The purpose will be to see what effects separating and recombining will have on the modulated signal and also what effect it will have on combining efficiency. A Bit Error Rate (BER) will be determined by a Bit Error Rate Tester (BERT) by comparing the random information it transmits to what it receives back. The process began with two 100 watt tubes, a Varian and a Logimetrics, salvaged

Downey, Joseph A.↗
NASA NTRS1982

Anomalous phase separation behavior of gel-derived soda-silica glasses

The effects of retained bound hydroxyl groups on amorphous immiscibility behavior and on the kinetics of phase separation were studied in glasses containing from 10 to 19 percent sodium oxide preparaed by the gel process. Differences in behavior as functions of preliminary thermal treatment of the gel precursor and of melting conditions were studied, employing IR spectroscopy, SAXS and WAXD to monitor the variation in glass microstructure. Both the initial gel treatment and the OH concentration in the prepared glasses were found to affect the immiscibility temperatures, and the magnitude of the maximum temperature increase was also a function of the sodium oxide concentration. It is suggested that the variation in thermodynamic behavior may be caused by the structural arrangement attained by the OH groups during the gel condensation process, which in turn affects the extent of hydrogen bonding to nonbridging oxygen ions.

Neilson, G. F.↗
NASA NTRS1985

Gas chromatography: Possible application of advanced instrumentation developed for solar system exploration to space station cabin atmospheres

Gas chromatography (GC) technology was developed for flight experiments in solar system exploration. The GC is a powerful analytical technique with simple devices separating individual components from complex mixtures to make very sensitive quantitative and qualitative measurements. It monitors samples containing mixtures of fixed gases and volatile organic molecules. The GC was used on the Viking mission in support of life detection experiments and on the Pioneer Venus Large Probe to determine the composition of the venusian atmosphere. A flight GC is under development to study the progress and extent of STS astronaut denitrogenation prior to extravehicular activity. Advanced flight GC concepts and systems for future solar system exploration are also studied. Studies include miniature ionization detectors and associated control systems capable of detecting from ppb up to 100% concentration levels. Further miniaturization is investigated using photolithography and controlled chemical etching in silicon wafers. Novel concepts such as ion mobility drift spectroscopy and multiplex gas chromatography are also developed for future flight experiments. These powerful analytical concepts and associated hardware are ideal for the monitoring of cabin atmospheres containing potentially dangerous volatile compounds.

Carle, G. C.↗
NASA NTRS2003

Wave and Particle Interactions in the High and Low-Altitude Auroral Region During Rising Solar Activity

The project has resulted in four separate investigations, which are each in various stages of publication in the refereed scientific journals. The first investigation was of the generation of electrostatic electron cyclotron waves observed by the Polar spacecraft throughout the auroral regions, dayside cusp, and polar magnetosphere. We have since discovered that these waves are also present within the magnetopause and magnetosheath, which is one of the topics of a second study, entitled: 'Polar observations of plasma waves in and near the dayside magnetopause/magnetosheath.' A third study of plasma waves focussed on kilometric continuum (KC) emission. This work is reported in a paper entitled 'Near-source and Remote Observations of Kilometric Continuum Radiation From Multi-spacecraft Observations'.The final investigation of this program concerns the possible transverse heating of auroral ions by impulsive wave structures. We summarize that substantial transverse ion heating has already occurred at lower altitudes. Abstracts of the above four studies are included in the Appendix to this final report.

Gurnett, Donald A.↗
NASA NTRS2001

Proportional counter as neutron detector

A technique to separate out the dose, and lineal energy spectra of neutrons and charged particles is described. It is based on using two proportional counters, one with a wall, and the other with similar characteristics but wall made from a non-hydrogen containing material. Results of a calibration in a neutron field are also shown. c2001 Elsevier Science Ltd. All rights reserved.

NASA Center JSC↗