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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Extension to the dynamic modeling of the large angle magnetic suspension test fixture

The Large Angle Magnetic Suspension Test Fixture (LAMSTF) is a laboratory scale proof-of-concept system. The configuration is unique in that the electromagnets are mounted in a circular planar array. A mathematical model of the system had previously been developed, but was shown to have inaccuracies. These inaccuracies showed up in the step responses. Eddy currents were found to be the major cause of the modeling errors. In the original system, eddy currents existed in the aluminum baseplate, iron cores, and the sensor support frame. An attempt to include the eddy current dynamics in the system model is presented. The dynamics of a dummy sensor ring were added to the system. Adding the eddy current dynamics to the simulation improves the way it compares to the actual experiment. Also presented is a new method of determining the yaw angle of the suspended element. From the coil currents the yaw angle can be determined and the controller can be updated to suspend at the new current. This method has been used to demonstrate a 360 degree yaw angle rotation.

Foster, Lucas E.↗
NASA NTRS2005

Nanomaterials Work at NASA-Johnson Space Center

Nanomaterials activities at NASA-Johnson Space Center focus on single wall carbon nanotube production, characterization and their applications for aerospace. Nanotubes are produced by arc and laser methods and the growth process is monitored by in-situ diagnostics using time resolved passive emission and laser induced fluorescence of the active species. Parametric study of both these processes are conducted to monitor the effect of production parameters including temperature, buffer gas, flow rate, pressure, laser fluence and arc current. Characterization of the nanotube material is performed using the NASA-JSC protocol developed by combining analytical techniques of SEM, TEM, UV-VIS-NIR absorption, Raman, and TGA. Efforts at JSC over the past five years in composites have centered on structural polymernanotube systems. Recent activities broadened this focus to multifunctional materials, supercapacitors, fuel cells, regenerable CO2 absorbers, electromagnetic shielding, radiation dosimetry and thermal management systems of interest for human space flight. Preliminary tests indicate improvement of performance in most of these applications because of the large surface area as well as high conductivity exhibited by SWCNTs.

Arepalli, Sivaram↗
NASA NTRS2003

Stabilizing an optoelectronic microwave oscillator with photonic filters

This paper compares methods of active stabilization of an optoelectronic microwave oscillator (OEO) based on insertion of a source of optical group delay into an OEO loop. The performance of an OEO stabilized with either a high- optical cavity or an atomic cell is analyzed. We show that the elements play a role of narrow-band microwave filters improving an OEO stability.

Atomic clocks electromagnetically induced transpar↗
NASA NTRS2003

Dynamic Spin Rig Upgraded With a Five- Axis-Controlled Three-Magnetic-Bearing Support System With Forward Excitation

The NASA Glenn Research Center Dynamic Spin Rig is used for experimental evaluation of vibration analysis methods and dynamic characteristics for rotating systems. Measurements are made while rotors are spun and vibrated in a vacuum chamber. The rig has been upgraded with a new active magnetic bearing rotor support and excitation system. This design is expected to provide operational improvements over the existing rig. The rig will be able to be operated in either the old or new configuration. In the old configuration, two ball bearings support the vertical shaft of the rig, with the test article located between the bearings. Because the bearings operate in a vacuum, lubrication is limited to grease. This limits bearing life and speed. In addition, the old configuration employs two voice-coil electromagnetic shakers to apply oscillatory axial forces or transverse moments to the rotor shaft through a thrust bearing. The excitation amplitudes that can be imparted to the test article with this system are not adequate for components that are highly damped. It is expected that the new design will overcome these limitations.

Morrison, Carlos R.↗
NASA NTRS1998

Integrated Advanced Microwave Sounding Unit-A (AMSU-A). Test Report, Electromagnetic Interference (EMI)/Electromagnetic Radiation(EMR) and Electromagnetic Capability (EMC) for the EOS/AMSU-A1

This document contains the procedure and the test results of the Advanced Microwave Sounding Unit-A (AMSU-A) Earth Observing System (EOS) Project, assembly part number 1356008-1, serial number 202, Electromagnetic Interference (EMI) and Electromagnetic Susceptibility (EMC) qualification test. The test was conducted in accordance with the approved EMI/EMC Test Plan/Procedure, Specification number AE-26151/8B, dated 10 September 1998. Aerojet intends that the presentation and submittal of this document, prepared in accordance with the objectives established by the aforementioned Test Plan/Procedure, document number AE-26151/8B, will satisfy the data requirement with respect to the AMSU-A/EOS instrument operational compliance of the EMI/EMC test requirement. Test for the AMSU-A/EOS instrument have been completed and all the requirements per General Interface Requirement Document (GIRD), GSFC 422-11-12-01, for EOS Common Spacecraft/Instruments, paragraph 10.11, were met with the exceptions of the test methods CE03, RE01, and RE02, as described in this document.

Paliwoda, L.↗
NASA NTRS2017

A Closer Look at the ABI on the GOES-R Series

The Advanced Baseline Imager (ABI) on board the Geostationary Operational Environmental Satellite-R (GOES-R) is America's next-generation geostationary advanced imager. GOES-R launched on 19 November 2016. The ABI is a state-of-the-art 16-band radiometer, with spectral bands covering the visible, near-infrared, and infrared portions of the electromagnetic spectrum. Many attributes of the ABI-such as spectral, spatial, and temporal resolution; radiometrics; and image navigation/registration-are much improved from the current series of GOES imagers. This paper highlights and discusses the expected improvements of each of these attributes. From ABI data many higher-level-derived products can be generated and used in a large number of environmental applications. The ABI's design allows rapid-scan and contiguous U.S. imaging automatically interleaved with full-disk scanning. In this paper the expected instrument attributes are covered, as they relate to signal-to-noise ratio, image navigation and registration, the various ABI scan modes, and other parameters. There will be several methods for users to acquire GOES-R imagery and products depending on their needs. These include direct reception of the imagery via the satellite downlink and an online-accessible archive. The information from the ABI on the GOES-R series will be used for many applications related to severe weather, tropical cyclones and hurricanes, aviation, natural hazards, the atmosphere, the ocean, and the cryosphere.

GOES-R↗
NASA NTRS2018

Levitation Experiments on ISS: Science and Applications

Levitation experiments on the International Space Station (ISS) are ongoing. The European Space Agency (ESA) Materials Science Laboratory Electromagnetic Levitator (MSL-EML) has been in operation since 2015. US investigators are on several of the European Topical Teams and have been heavily involved with the experiments since 2009. The experiments include magneto-hydrodynamic (MHD) modeling of macro-convection, the effects of convection on microstructure, investigation of metallic glass formation, and much more. Recently NASA selected four proposals to the MaterialsLab NASA Research Announcement (NRA) for experiments on the Japan Aerospace eXploration Agency (JAXA) Electrostatic Levitation Furnace (ELF), which was launched to the ISS in 2015. It is estimated that the four US investigators will have flight experiments on ELF within the next few years. The experiments range from a novel method to measure interfacial tension to investigations of thermophysical properties of metals, metal oxides, and non-linear optical materials. Using the MSL-EML and ELF, US investigators are studying a wide range of NASA exploration-relevant materials. Levitation experiments enable exploration in many ways. For example, high quality thermophysical properties of high-temperature materials are critical to develop accurate models of casting, welding, and metal additive manufacturing, which could lead to more efficient and more reliable production of metallic parts for exploration, commercial, and industrial applications. High-quality thermophysical properties could also lead to the development of functional oxide glass and optical materials. In many cases, the accuracy of available property data is the limiting factor in the predictive capabilities of the models. Many thermophysical properties can be measured in a levitator on Earth, but with convective contamination. This contamination plays a significant role in the formation of the intermediate phases. In particular, nucleation and viscosity measurements demand quiescent conditions that can only be attained in microgravity-based levitation systems. A brief overview of the ongoing and planned levitation experiments on the ISS will be presented, followed by the exploration-relevance.

SanSoucie, Michael P.↗
NASA NTRS1987

A review of research and development on the microwave-plasma electrothermal rocket

The microwave-plasma electrothermal rocket (MWPETR) shows promise for spacecraft propulsion and maneuvering, without some of the drawbacks of competitive electric propulsion systems. In the MWPETR, the electric power is first converted to microwave-frequency radiation. In a specially-designed microwave cavity system, the electromagnetic energy of the radiation is transferred to the electrons in a plasma sustained in the working fluid. The resulting high-energy electrons transfer their energy to the atoms and molecules of the working fluid by collisions. The working fluid, thus heated, expands through a nozzle to generate thrust. In the MWPETR, no electrodes are in contact with the working fluid, the energy is transferred into the working fluid by nonthermal mechanisms, and the main requirement for the materials of construction is that the walls of the plasma chamber be insulating and transparent to microwave radiation at operating conditions. In this survey of work on the MWPETR, several experimental configurations are described and compared. Diagnostic methods used in the study are described and compared, including titration, spectroscopy, calorimetry, electric field measurements, gas-dynamic methods, and thrust measurements. Measured and estimated performance efficiencies are reported. Results of computer modeling of the plasma and of the gas flowing from the plasma are summarized.

Hawley, Martin C.↗
NASA NTRS2003

Review of Work Done with Professor Nussenzveig Regarding the Mie Theory

Prof. Nussenzveig has dedicated part of his career to a surprising and unusual pursuit harking back to the heyday of classical physics: Mie theory, or the scattering of electromagnetic radiation by a homogeneous sphere. M e theory was not put forward until around 1908 (nearly simultaneously by Debye in a different form) and was quickly forgotten in the rush to the then-new quantum mechanics. It remained somewhat of a backwater until Prof. Nussenzveig brought it back by adapting complex angular momentum ideas from Regge pole theory, which had originally been invented for quantum mechanics. Since 1960, he has made fundamental contributions to actually understanding (as opposed to merely calculating) Mie theory. I became involved with this work in 1978 by inviting Prof. Nussenzveig to visit me at the National Center for Atmospheric Research. Since then we have written several papers together on approximate methods for Mie cross-sections, bubble scattering, and other subjects. This lecture will review that work, ending with his recent work on Mie resonances. The emphasis will be on the applications in atmospheric sciences.

Wiscombe, W.↗
NASA NTRS2016

In-Flight Calibration Methods for Temperature-Dependent Offsets in the MMS Fluxgate Magnetometers

During the first dayside season of the Magnetospheric Multiscale (MMS) mission, the in-flight calibration process for the Fluxgate magnetometers (FGM) implemented an algorithm that selected a constant offset (zero-level) for each sensor on each orbit. This method was generally able to reduce the amplitude of residual spin tone to less than 0.2 nT within the region of interest. However, there are times when the offsets do show significant short-term variations. These variations are most prominent in the nighttime season (phase 1X), when eclipses are accompanied by offset changes as large as 1 nT. Eclipses are followed by a recovery period as long as 12 hours where the offsets continue to change as temperatures stabilize. Understanding and compensating for these changes will become critical during Phase 2 of the mission in 2017, when the nightside will become the focus of MMS science. Although there is no direct correlation between offset and temperature, the offsets are seen for the period of any given week to be well-characterized as function of instrument temperature. Using this property, a new calibration method has been developed that has proven effective in compensating for temperature-dependent offsets during phase 1X of the MMS mission and also promises to further refine calibration quality during the dayside season.

Magnetic field reconnection↗
NASA NTRS1994

Electromagnetic probe technique for fluid flow measurements

The probes described herein, in various configurations, permit the measurement of the volume fraction of two or more fluids flowing through a pipe. Each probe measures the instantaneous relative dielectric constant of the fluid in immediate proximity. As long as separation of the relative dielectric constant of the fluid is possible, several or even many fluids can be measured in the same flow stream. By using multiple probes, the velocity of each fluid can generally be determined as well as the distribution of each constituent in the pipe. The values are determined by statistical computation. There are many potential applications for probes of this type in industry and government. Possible NASA applications include measurements of helium/hydrazine flow during rocket tests at White Sands, liquid/gas flow in hydrogen or oxygen lines in Orbiter engines, and liquid/gaseous Freon flow in zero gravity tests with the KS135 aircraft at JSC. Much interest has been shown recently by the oil industry. In this a good method is needed to measure the fractions of oil, water, and natural gas flowing in a pipeline and the velocity of each. This particular problem involves an extension of what has been developed to date and our plans to solve this problem will be discussed herein.

Arndt, G. D.↗
NASA NTRS1994

Electromagnetic Probe Technique for Fluid Flow Measurements

The probes described herein, in various configurations, permit the measurement of the volume fraction of two or more fluids flowing through a pipe. Each probe measures the instantaneous relative dielectric constant of the fluid in immediate proximity. As long as separation of the relative dielectric constants of each fluid is possible, several or even many fluids can be measured in the same flow steam. By using multiple probes, the velocity of each fluid can generally be determined as well as the distribution of each constituent in the pipe. The values are determined by statistical computation. There are many potential applications for probes of this type in industry and government. Possible NASA applications include measurements of helium/hydrazine flow during rocket tests at White Sands, liquid/gas flow in hydrogen or oxygen lines in Orbiter engines, and liquid/gaseous Freon flow in zero gravity tests with the KS135 aircraft at JSC. Much interest has been shown recently by the oil industry. In this industry, a good method is needed to measure the fractions of oil, water, and natural gas flowing in a pipeline and the velocity of each. This particular problem involves an extension of what has been developed to date and our plans and program to solve this problem will be discussed herein.

Arndt, G. D.↗
NASA NTRS1994

Magnetically driven jets and winds: Exact solutions

We present a general class of self-similar solutions of the full set of MHD equations that include matter flow, electromagnetic fields, pressure, and gravity. The solutions represent axisymmetric, time-independent, nonrelativistic, ideal, magnetohydrodynamic, collimated outflows (jet and winds) from magnetized accretion disks around compact objects. The magnetic field extracts angular momentum from the disk, accelerates the outflows perpedicular to the disk, and provides collimation at large distances. The terminal outflow velocities are of the order of or greater than the rotational velocity of the disk at the base of the flow. When a nonzero electric current flows along the jet, the outflow radius oscillates with axial distance, whereas when the total electric current is zero (with the return current flowing across the jet's cross section), the outflow radius increase to a maximum and then decreases. The method can also be applied to relativistic outflows.

Contopoulos, J.↗
NASA NTRS1992

Scattering from dielectric structures above impedance surfaces and resistive sheets

Interest in understanding of electromagnetic interaction with rough surfaces has prompted the study of scattering from typical dielectric humps over impedance surfaces. It is shown that the Green's function of the problem for a resistive sheet resembles that of the impedance surface. Hence both problems are considered here. A numerical solution for the scattered field of a two-dimensional dielectric object, possibly inhomogeneous, with arbitrary cross section above the impedance surface or resistive sheet is sought. First the Green's function of the problem is derived based on the exact image theory. This form of the Green's function is amenable to numerical computation. Then the induced polarization currents are calculated by casting the integral equations into a matrix equation via the method of moments. Numerical problems in calculation of the Green's function when both source and observation points are close to the surface are discussed. Comparison of numerical results with a perturbation solution shows excellent agreement between the two methods.

Sarabandi, Kamal↗
NASA NTRS2003

The Design and Implementation of Instruments for Low-Frequency Electromagnetic Sounding of the Martian Subsurface

Low-frequency electromagnetic soundings of the subsurface can identify liquid water at depths ranging from hundreds of meters to approx. 10 km in an environment such as Mars. Among the tools necessary to perform these soundings are low-frequency electric and magnetic field sensors capable of being deployed from a lander or rover such that horizontal and vertical components of the fields can be measured free of structural or electrical interference. Under a NASA Planetary Instrument Definition and Development Program (PIDDP), we are currently engaged in the prototype stages of low frequency sensor implementations that will enable this technique to be performed autonomously within the constraints of a lander platform. Once developed, this technique will represent both a complementary and alternative method to orbital radar sounding investigations, as the latter may not be able to identify subsurface water without significant ambiguities. Low frequency EM methods can play a crucial role as a ground truth measurement, performing deep soundings at sites identified as high priority areas by orbital radars. Alternatively, the penetration depth and conductivity discrimination of low-frequency methods may enable detection of subsurface water in areas that render radar methods ineffective. In either case, the sensitivity and depth of penetration inherent in low frequency EM exploration makes this tool a compelling candidate method to identify subsurface liquid water from a landed platform on Mars or other targets of interest.

G T Delory↗
NASA NTRS1994

3D Electromagnetic Plasma Particle Simulations on the Intel Delta Parallel Computer

A three-dimensional electromagnetic PIC code has been developed on the 512 node Intel Touchstone Delta MIMD parallel computer. This code is based on the General Concurrent PIC algorithm which uses a domain decomposition to divide the computation among the processors. The 3D simulation domain can be partitioned into 1-, 2-, or 3-dimensional subdomains. Particles must be exchanged between processors as they move among the subdomains.

PIC↗
NASA NTRS1994

Superconducting axisymmetric finite elements based on a gauged potential variational principle. Part 1: Formulation

The present work is part of a research program for the numerical simulation of electromagnetic (EM) fields within conventional Ginzburg-Landau (GL) superconductors. The final goal of this research is to formulate, develop and validate finite element (FE) models that can accurately capture electromagnetic thermal and material phase changes in a superconductor. The formulations presented here are for a time-independent Ginzburg-Landau superconductor and are derived from a potential-based variational principle. We develop an appropriate variational formulation of time-independent supercontivity for the general three-dimensional case and specialize it to the one-dimensional case. Also developed are expressions for the material-dependent parameters alpha and beta of GL theory and their dependence upon the temperature T. The one-dimensional formulation is then discretized for finite element purposes and the first variation of these equations is obtained. The resultant Euler equations contain nonlinear terms in the primary variables. To solve these equations, an incremental-iterative solution method is used. Expressions for the internal force vector, external force vector, loading vector and tangent stiffness matrix are therefore developed for use with the solution procedure.

Schuler, James J.↗
NASA NTRS2011

High Resolution Rapid Response Observations of Compact Radio Sources with the Ceduna Hobart Interferometer (CHI)

Context. Frequent, simultaneous observations across the electromagnetic spectrum are essential to the study of a range of astrophysical phenomena including Active Galactic Nuclei. A key tool of such studies is the ability to observe an object when it flares i.e. exhibits a rapid and significant increase in its flux density. Aims. We describe the specific observational procedures and the calibration techniques that have been developed and tested to create a single baseline radio interferometer. that can rapidly observe a flaring object. This is the only facility that is dedicated to rapid high resolution radio observations of an object south of -30 degrees declination. An immediate application is to provide rapid contemporaneous radio coverage of AGN flaring at y-ray frequencies detected by the Fermi Gamma-ray Space Telescope. Methods. A single baseline interferometer was formed with radio telescopes in Hobart, Tasmania and Ceduna, South Australia. A software correlator was set up at the University of Tasmania to correlate these data. Results. Measurements of the flux densities of flaring objects can be made using our observing strategy within half an hour of a triggering event. These observations can be calibrated with amplitude errors better than 20%. Lower limits to the brightness temperatures of the sources can also be calculated using CHI. Key words. instrumentation:interferometers - galaxies:active - galaxies:jets - galaxies:nuclei quasars:general gamma rays:galaxies- 1.

Blanchard, Jay M.↗