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NASA NTRS1983

High-energy tail distributions and resonant wave particle interaction

High-energy tail distributions (k distributions) are used as an alternative to a bi-Lorentzian distribution to study the influence of energetic protons on the right- and left-hand cyclotron modes in a hot two-temperature plasma. Although the parameters are chosen to be in a range appropriate to solar wind or magnetospheric configurations, the results apply not only to specific space plasmas. The presence of energetic particles significantly alters the behavior of the electromagnetic ion cyclotron modes, leading to a wide range of unstable frequencies and increased growth rates. From the strongly enhanced growth rates it can be concluded that high-energy tail distributions should not show major temperature anisotropies, which is consistent with observations.

Leubner, M. P.↗

NASA NTRS1990

Transient particle acceleration associated with solar flares

Mechanisms that apply to solar flares are discussed, and their applicability to other astrophysical sites, where transient X-ray and gamma-ray bursts occur, is tested. Two different approaches are used to determine the characteristics of the charged particles, accelerated in association with solar flares: (1) measurement of the energy spectra and composition of charged particles observed in space and believed to be associated with a specific solar flare; and (2) recording of electromagnetic emissions in the visible, ultraviolet, soft X-ray, hard X-ray, and gamma-ray spectral regions, and also high-energy neutrons produced in the solar atmosphere by the particles accelerated in association with the solar flare. It is suggested that, at the present level of knowledge, regions where particle acceleration and interactions occur are unlikely to be specified.

Chupp, E. L.↗

NASA NTRS1993

Plasma contactor technology for Space Station Freedom

Hollow cathode plasma contactors have been baselined for Space Station Freedom to control the electrical potentials of surfaces to eliminate/mitigate damaging interactions with the space environment. The system represents a dual-use technology which is a direct outgrowth of the NASA electric propulsion program and in particular the technology development effort on ion thruster systems. Specific efforts include optimizing the design and configuration of the contactor, validating its required lifetime, and characterizing the contactor plume and electromagnetic interference. The plasma contactor subsystems include the plasma contactor unit, a power electronics unit, and an expellant management unit. Under this program these will all be brought to breadboard and engineering model development status. New test facilities have been developed, and existing facilities have been augmented, to support characterizations and life testing of contactor components and systems. This paper discusses the magnitude, scope, and status of the plasma contactor hardware development program now under way and preliminary test results on system components.

Patterson, Michael J.↗

NASA NTRS1993

Plasma contactor technology for Space Station Freedom

Hollow cathode plasma contactors were baselined for Space Station Freedom (SSF) to control the electrical potentials of surfaces to eliminate/mitigate damaging interactions with the space environment. The system represents a dual-use technology which is a direct outgrowth of the NASA electric propulsion program and in particular the technology development effort on ion thruster systems. Specific efforts include optimizing the design and configuration of the contactor, validating its required lifetime, and characterizing the contactor plume and electromagnetic interference. The plasma contact or subsystems include the plasma contact or unit, a power electronics unit, and an expellant management unit. Under this program these will all be brought to breadboard and engineering model development status. New test facilities were developed, and existing facilities were augmented, to support characterizations and life testing of contactor components and systems. The magnitude, scope, and status of the plasma contactor hardware development program now underway and preliminary test results on system components are discussed.

Patterson, Michael J.↗

NASA NTRS1995

Fast Multipole Methods for Three-Dimensional N-body Problems

We are developing computational tools for the simulations of three-dimensional flows past bodies undergoing arbitrary motions. High resolution viscous vortex methods have been developed that allow for extended simulations of two-dimensional configurations such as vortex generators. Our objective is to extend this methodology to three dimensions and develop a robust computational scheme for the simulation of such flows. A fundamental issue in the use of vortex methods is the ability of employing efficiently large numbers of computational elements to resolve the large range of scales that exist in complex flows. The traditional cost of the method scales as Omicron (N(sup 2)) as the N computational elements/particles induce velocities at each other, making the method unacceptable for simulations involving more than a few tens of thousands of particles. In the last decade fast methods have been developed that have operation counts of Omicron (N log N) or Omicron (N) (referred to as BH and GR respectively) depending on the details of the algorithm. These methods are based on the observation that the effect of a cluster of particles at a certain distance may be approximated by a finite series expansion. In order to exploit this observation we need to decompose the element population spatially into clusters of particles and build a hierarchy of clusters (a tree data structure) - smaller neighboring clusters combine to form a cluster of the next size up in the hierarchy and so on. This hierarchy of clusters allows one to determine efficiently when the approximation is valid. This algorithm is an N-body solver that appears in many fields of engineering and science. Some examples of its diverse use are in astrophysics, molecular dynamics, micro-magnetics, boundary element simulations of electromagnetic problems, and computer animation. More recently these N-body solvers have been implemented and applied in simulations involving vortex methods. Koumoutsakos and Leonard (1995) implemented the GR scheme in two dimensions for vector computer architectures allowing for simulations of bluff body flows using millions of particles. Winckelmans presented three-dimensional, viscous simulations of interacting vortex rings, using vortons and an implementation of a BH scheme for parallel computer architectures. Bhatt presented a vortex filament method to perform inviscid vortex ring interactions, with an alternative implementation of a BH scheme for a Connection Machine parallel computer architecture.

Koumoutsakos, P.↗

NASA NTRS2003

Imagine the Universe!

Welcome to the 2004 edition of the education CD from the Laboratory for High Energy Astrophysics at NASA Goddard Space Flight Center. We hope that you will find it to be an exciting and fun learning experience. We have tried very hard to make this CD as user-friendly as possible and along the way we have discovered some things that every user may need to know. Please read the README file found on the CD if you have any questions or problems using the disk. Then, after that, if you still have problems, email us at itu@athena.gsfc.nasa.gov. We will be happy to help you 'get going'! Below are links to all of the sites included on the CD. You will also find the addresses for the on-line version of each of these sites. If you have a good Internet connection available, we recommend that you view the sites on-line. There you will find the latest updated information, interactive activities, and active links to other sites. Included on the disk are: Imagine The Universe! This site is dedicated to a discussion about our Universe... what we know about it, how it is evolving, and the kinds of objects and phenomena it contains. Emphasizing the X-ray and gamma-ray parts of the electromagnetic spectrum, it also discusses how scientists know what they know, what mysteries remain, and how the answers to remaining mysteries may one day be found. Lots of movies, quizzes, and a special section for educators. Geared for ages 14 and up. This site can be viewed on-line at http://imagine.gsfc.nasa.gov/. StarChild: A learning center for young astronomers The 1998 Webby Award Winner for Best Education Website, StarChild is aimed at ages 4-14. It contains easy-to-understand information about our Solar System, the Universe, and space exploration. There are also activities, songs, movies, and puzzles! This site can be viewed on-line at http://starchild.gsfc.nasa.gov/. Astronomy Picture of the Day APOD offers a new astronomical image and caption each calendar day. We have captured the year 2003 entries of this award-winning site and included them on the disk. The images and information provide a wonderful resource for all ages. This site can be viewed on-line at http://apod.gsfc.nasa.gov/apod/astropix.html.

White, N.↗

NASA NTRS2001

ISS And Space Environment Interactions Without Operating Plasma Contactor

The International Space Station (ISS) will be the largest, highest power spacecraft placed in orbit. Because of this the design of the electrical power system diverged markedly from previous systems. The solar arrays will operate at 160 V and the power distribution voltage will be 120 V. The structure is grounded to the negative side of the solar arrays so under the right circumstances it is possible to drive the ISS potential very negative. A plasma contactor has been added to the ISS to provide control of the ISS structure potential relative to the ambient plasma. The ISS requirement is that the ISS structure not be greater than 40 V positive or negative of local plasma. What are the ramifications of operating large structures with such high voltage power systems? The application of a plasma contactor on ISS controls the potential between the structure and the local plasma, preventing degrading effects. It is conceivable that there can be situations where the plasma contactor might be non-functional. This might be due to lack of power, the need to turn it off during some of the build-up sequences, the loss of functionality for both plasma contactors before a replacement can be installed, similar circumstances. A study was undertaken to understand how important it is to have the contactor functioning and how long it might be off before unacceptable degradation to ISS could occur. The details of interaction effects on spacecraft have not been addressed until driven by design. This was true for ISS. If the structure is allowed to float highly negative impinging ions can sputter exposed conductors which can degrade the primary surface and also generate contamination due to the sputtered material. Arcing has been known to occur on solar arrays that float negative of the ambient plasma. This can also generate electromagnetic interference and voltage transients. Much of the ISS structure and pressure module surfaces exposed to space is anodized aluminum. The anodization thickness is very thin to provide the required solar absorptance and emittance. For conditions where ISS structure can charge negative a large percentage of the array voltage, the dielectric strength of this layer is low, and dielectric breakdown (arcing) can occur. The energy stored capacitively in the structure can be delivered to the arc. The mechanisms by which this energy is delivered and how much of the energy is available hasn't been fully quantified. Questions have been raised regarding the possibility of whether a sustained arc might result due to current collected by the solar arrays from local plasma. It was postulated that even if dielectric breakdown didn't occur, impacts due to micrometeoroids and space debris could penetrate thin layers of dielectric on ISS and initiate an arc due to the coupling provided by the dense local plasma produced by the impact. This was proven in experiments conducted jointly by MSFC and Auburn University. A target chamber with a simulated ionospheric plasma and a biased, anodized aluminum plate and a 1-microfarad capacitor was used. The plate was then impacted by 75-micron particles accelerated to orbital velocity. Arc discharges were sustained for higher voltages but a threshold appears below which no discharge was initiated. Most items without an exposed power system will float electrically near the local plasma potential. This is true of the Space Shuttle, an Astronaut on EVA, and similar items. The structure of ISS might be at a large negative voltage. Therefore, capacitively stored energy can be transferred during docking, installing external boxes and equipment and Astronaut contact with ISS structure. The circumstances of when this can happen and the resulting effects are evaluated in this study. Also, a crewmember on EVA might be in the vicinity of an arc. All safety aspects of such an encounter including charging, molten particles from the arc site and EMI have been evaluated. This paper will report on the total results of this study focussed on the 4A configuration, scheduled to be complete in November, 2000. Interactions such as arcing, debris induced arcs, sustained arcs, sputtering, contamination from sputtering and arcing, docking interactions and Astronaut safety issues will all be addressed.

Carruth, M. R., Jr.↗

NASA NTRS1991

A dynamic analysis of the radiation excitation from the activation of a current collecting system in space

Current collecting systems moving in the ionosphere will induce electromagnetic wave radiation. The commonly used static analysis is incapable of studying the situation when such systems undergo transient processes. A dynamic analysis has been developed, and the radiation excitation processes are studied. This dynamic analysis is applied to study the temporal wave radiation from the activation of current collecting systems in space. The global scale electrodynamic interactions between a space-station-like structure and the ionospheric plasma are studied. The temporal evolution and spatial propagation of the electric wave field after the activation are described. The wave excitations by tethered systems are also studied. The dependencies of the temporal Alfven wave and lower hybrid wave radiation on the activation time and the space system structure are discussed. It is shown that the characteristics of wave radiation are determined by the matching of two sets of characteristic frequencies, and a rapid change in the current collection can give rise to substantial transient radiation interference. The limitations of the static and linear analysis are examined, and the condition under which the static assumption is valid is obtained.

Wang, J.↗

NASA NTRS1996

Low Frequency Waves in the Plasma Environment Around the Shuttle

As a part of the SAMPIE (The Solar Array Module Plasma Interaction Experiment) program, the Langmuir probe (LP) was employed to measure plasma characteristics during the flight of STS-62. The whole set of data could be divided into two parts: (1) low frequency sweeps to determine voltage-current characteristics and to find the electron temperature and number density; (2) high frequency turbulence (HFT) data caused by electromagnetic noise around the Shuttle. Broadband noise was observed at 250-20,000 Hz frequencies. Measurements were performed in ram conditions; thus, it seems reasonable to believe that the influence of spacecraft operations on plasma parameters was minimized. It is shown that ion acoustic waves were observed, and two kinds of instabilities are suggested for explanation of the origin of these waves. According to the purposes of SAMPIE, samples of solar cells were placed in the cargo bay of the Shuttle, and high negative bias voltages were applied to them to initiate arcing between these cells and the surrounding plasma. The arcing onset was registered by special counters, and data were obtained that included the amplitudes of current, duration of each arc, and the number of arcs per one experiment. The LP data were analyzed for two different situations: with arcing and without arcing. Electrostatic noise spectra for both situations and a theoretical explanation of the observed features are presented in this paper.

Vayner, Boris V.↗

NASA NTRS2003

Magnetogasdynamic Power Extraction and Flow Conditioning for a Gas Turbine

An extension of the Russian AJAX concept to a turbojet is being explored. This magnetohydrodynamic (MHD) energy bypass engine cycle incorporating conventional gas turbine technology has MHD flow conditioning at the inlet to electromagnetically extract part of the inlet air kinetic energy. The electrical power generated can be used for various on-board vehicle requirements including plasma flow control around the vehicle or it may be used for augmenting the expanding flow in the high speed nozzle by MHD forces to generate more thrust. In order to achieve this interaction, the air needs to be ionized by an external means even up to fairly high flight speeds, and the leading candidates may be classified as electrical discharge devices. The present kinetic modeling calculations suggest that the use of electron beams with characteristics close to the commercially available e-beam systems (electron energy approx. 60 keV, beam current approx. 0.2 mA/sq cm) to sustain ionization in intermediate pressure, low-temperature (P = 0.1 atm, T = 300 K) supersonic air flows allows considerable reduction of the flow kinetic energy (up to 10 to 20 percent in M = 3 flows). The calculations also suggest that this can be achieved at a reasonable electron beam efficiency (eta approx. 5), even if the e-beam window losses are taken into account. At these conditions, the exit NO and O atom concentrations due to e-beam initiated chemical reactions do not exceed 30 ppm. Increasing the beam current up to approx. 2 mA/sq cm, which corresponds to a maximum electrical conductivity of sigma(sub max) approx. 0.8 mho/m at the loading parameter of K = 0.5, would result in a much greater reduction of the flow kinetic energy (up to 30 to 40 percent). The MHD channel efficiency at these conditions would be greatly reduced (to eta approx. 1) due to increased electron recombination losses in the channel. At these conditions, partial energy conversion from kinetic energy to heat would result in a significant total pressure loss (P(sub 0)/P(sub 0i) approx. 0.3). The total pressure loss can be reduced operating at the loading parameter closer to unity, at the expense of the reduced electrical power output. Raising the beam current would also result in the increase of the exit O atom concentrations (up to 600 ppm) and NO (up to 150 ppm).

Adamovich, Igor V.↗

NASA NTRS2004

COSMOG: Cosmology Oriented Sub-mm Modeling of Galactic Foregrounds

With upcoming missions in mid- and far-Infrared there is a need for software packages to reliably simulate the planned observations. This would help in both planning the observation and scanning strategy and in developing the concepts of the far-off missions. As this workshop demonstrated, many of the new missions are to be in the far-IR range of the electromagnetic spectrum and at the same time will map the sky with a sub-arcsec angular resolution. We present here a computer package for simulating foreground maps for the planned sub-mm and far-IR missions. such as SPECS. The package allows to study confusion limits and simulate cosmological observations for specified sky location interactively and in real time. Most of the emission at wavelengths long-ward of approximately 50 microns is dominated by Galactic cirrus and Zodiacal dust emission. Stellar emission at these wavelengths is weak and is for now neglected. Cosmological sources (distant and not-so-distant) galaxies for specified cosmologies will be added. Briefly, the steps that the algorithm goes through is described.

Kashlinsky, A.↗

NASA NTRS2014

Atomic Layer Deposition of Chemical Passivation Layers and High Performance Anti-Reflection Coatings on Back-Illuminated Detectors

A back-illuminated silicon photodetector has a layer of Al2O3 deposited on a silicon oxide surface that receives electromagnetic radiation to be detected. The Al2O3 layer has an antireflection coating deposited thereon. The Al2O3 layer provides a chemically resistant separation layer between the silicon oxide surface and the antireflection coating. The Al2O3 layer is thin enough that it is optically innocuous. Under deep ultraviolet radiation, the silicon oxide layer and the antireflection coating do not interact chemically. In one embodiment, the silicon photodetector has a delta-doped layer near (within a few nanometers of) the silicon oxide surface. The Al2O3 layer is expected to provide similar protection for doped layers fabricated using other methods, such as MBE, ion implantation and CVD deposition.

Hoenk, Michael E.↗

NASA NTRS2022

Multiple Scattering Effects of Trees on L-band Microwave Using a Hybrid Method

The multiple scattering of electromagnetic waves in forests is studied using a two-step hybrid method. First, the T-matrix of a single tree is calculated based on its far-field computed with the full-wave simulations of the FEKO software. The T-matrix captures the multiple scattering caused by the tree structure. Second, the the interactions among different trees are considered using the T-matrices of the individual trees and the Foldy-Lax equations. The result of the two-step hybrid method is validated with FEKO by solving scattering from two trees directly. The multiple scattering effects are illustrated by the field solutions.

Yueh, Simon↗

NASA NTRS1982

Interpretation methodology and analysis of in-flight lightning data

A methodology is presented whereby electromagnetic measurements of inflight lightning stroke data can be understood and extended to other aircraft. Recent measurements made on the NASA F106B aircraft indicate that sophisticated numerical techniques and new developments in corona modeling are required to fully understand the data. Thus the problem is nontrivial and successful interpretation can lead to a significant understanding of the lightning/aircraft interaction event. This is of particular importance because of the problem of lightning induced transient upset of new technology low level microcircuitry which is being used in increasing quantities in modern and future avionics. Inflight lightning data is analyzed and lightning environments incident upon the F106B are determined.

Rudolph, T.↗

NASA NTRS1983

A theory of Jovian decameter radiation

A theory of the Jovian decameter radiation is presented based on the assumed existence of beams of energetic electrons in the inner Jovian magnetosphere. Beam-like electron distributions are shown to be unstable to the growth of both upper hybrid and lower hybrid electrostatic waves. The upconversion of these waves to fast extraordinary mode electromagnetic radiation is calculated by using a fluid model. Two possibilities are considered. First, a random phase approximation is made which leads to a very conservative estimate of intensity that can be expected in decameter radiation. The alternative possibility is also considered, viz, that the upconversion process is coherent. A comparison of both processes suggests that an incoherent interaction may be adequate to account for the observed intensity of decametric radiation, except perhaps near the peak of the spectrum (8 MHz). The coherent process is intrinsically more efficient and can easily produce the observed intensity near 8 MHz if only 0.01% of the energy in the beam is converted to electrostatic energy.

Goldstein, M. L.↗

NASA NTRS1995

Design and Development of High Voltage Direct Current (DC) Sources for the Solar Array Module Plasma Interaction Experiment

Two programmable, high voltage DC power supplies were developed as part of the flight electronics for the Solar Array Module Plasma Interaction Experiment (SAMPIE). SAMPIE's primary objectives were to study and characterize the high voltage arcing and parasitic current losses of various solar cells and metal samples within the space plasma of low earth orbit (LEO). High voltage arcing can cause large discontinuous changes in spacecraft potential which lead to damage of the power system materials and significant Electromagnetic Interference (EMI). Parasitic currents cause a change in floating potential which lead to reduced power efficiency. These primary SAMPIE objectives were accomplished by applying artificial biases across test samples over a voltage range from -600 VDC to +300 VDC. This paper chronicles the design, final development, and test of the two programmable high voltage sources for SAMPIE. The technical challenges to the design for these power supplies included vacuum, space plasma effects, thermal protection, Shuttle vibrations and accelerations.

Bibyk, Irene K.↗

NASA NTRS2021

Mathematical Model Development and Experimental Verification of Electromagnetic Force Actuators for use in Space Applications

This technical memorandum shows the development of the mathematics needed to model several types of electromagnetic force actuators that may be of interest for use in space applications. The actuators described are capable of providing attractive, repulsive, and longitudinal forces between the actuator and a variety of metal surfaces. Potential applications for these propellant free actuators include spacecraft docking, in-space fabrication, robotic spacecraft inspection and servicing, deflection of metallic debris, and interaction with iron core asteroids (e.g., landing, repelling, and relocating).

Robert C. Youngquist↗

NASA NTRS1984

Radio Science

Radio science experiments use electromagnetic waves to probe or study the solar system. Three major research areas were identified within this discipline: radio astronomy, radar astronomy, and celestial mechanics. Radio astronomy (or radiometry) is the detection and measurement of naturally produced radio frequency emissions. Sources include surfaces, atmospheres, rings, and plasmas. Radar astronomy is the observation of man-made signals after their interaction with a target. Both imaging and non-imaging results. Celestial mechanics includes all studies related to the motions of (and gravity fields of) bodies within the solar system. These should not be considered rigid separations, but aid in the discussion of the data sets.

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