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NASA NTRS1991

Polarization model applied to Uranian radio emission

The total power and the degree of circular polarization as measured by the Planetary Radio Astronomy experiments on the Voyager spacecraft are modeled. For a source near the electron cyclotron frequency, the degree of circular polarization is determined by the angle between the wave vector and the field. It is shown that the observed strong circular polarization of Uranian smooth low-frequency (SLF) can be modeled as emission that is beamed along the direction of the magnetic field in a filled cone. The main observational constraints of SLF emission from Uranus are met by conjugate sources at about 21 deg from the magnetic equator.

Sawyer, C. B.↗

NASA NTRS1991

Amplitude and phase-shaping effects in beamwaveguides

Results are presented of an investigation on improvements in a geometrical optics (GO) design of a beam-waveguide antenna for operation at multiple frequency bands. Improvements might be possible by changing the design of the lower-frequency input pattern to the beam waveguide. The effects of amplitude and phase shaping the input pattern have been studied with an aperture diffraction model. Accurate vector near-field computations were made rapidly with a spherical wave expansion of the input and scattered fields. Numerical results indicate that for aperture sizes of less than 30 wavelengths, there is insufficient control on defocusing due to amplitude and phase shaping. Design tradeoffs on spillover loss and defocusing are possible by changing the amplitude and phase distribution of the input wavefront for larger size apertures.

Rengarajan, Sembiam R.↗

NASA NTRS1992

Three-dimensional compressible turbulent computations for a nondiffusing S-duct

The PARC3D code was used to compute the compressible turbulent flow within a three dimensional, nondiffusing S-duct. A frame of reference is provided for future computational fluid dynamics studies of internal flows with strong secondary flows and provides an understanding of the performance characteristics of a typical S-duct with attached flow. The predicted results, obtained with both H- and O-grids, are compared with the experimental wall pressure, static and total pressure fields, and velocity vectors. Additionally, computed boundary layer thickness, velocity profiles in wall coordinates, and skin friction values are presented.

Harloff, G. J.↗

NASA NTRS1992

Navier-Stokes analysis and experimental data comparison of compressible flow in a diffusing S-duct

Full three-dimensional Navier-Stokes computational results are compared with new experimental measurements for the flowfield within a round diffusing S-duct. The present study extends previous computational and experimental results for a similar smaller scale S-duct. Predicted results are compared with the experimental static and total pressure fields, and velocity vectors. Additionally, wall pressures, velocity profiles in wall coordinates, and skin friction values are presented. The CFD results employ algebraic and k-epsilon turbulence models. The CFD computed and experimentally determined separated flowfield is carefully examined.

Harloff, Gary J.↗

NASA NTRS1992

On neutralized currents in the solar corona

Using Ampere's integral law applied to vector magnetograph transverse field data, the current pattern in an active region associated with flaring activity is analyzed. The greater sensitivity of this integral formalism of Ampere's law may allow one to identify regions of weak return current around the actual positive current region. The effects of Faraday rotation on the inferred magnetic field measurements, and hence on the deduced current pattern, are discussed. It is concluded that the current patterns in the region consist either of a neutralized current system, well modeled by a coaxial cable, or of a potential field, with the apparent currents in the core an artifact induced by magneto-optical effects. In either case, the data do not convincingly show an unneutralized current system.

Wilkinson, Ladye K.↗

NASA NTRS1992

Navier-Stokes analysis and experimental data comparison of compressible flow in a diffusing S-duct

Harloff, Gary J.↗

NASA NTRS1992

Active region studies with coordinated SOHO, microwave, and magnetograph observations

The scientific justification for an observing campaign to study the quantitative magnetic and plasma properties of coronal loops in active regions is presented. The SOHO (Solar and Heliospheric Observatory) instruments of primary relevance are CDS (Coronal Diagnostic Spectrometer), EIT, SUMER (Solar Ultraviolet Measurement of Emitted Radiation), and MDI. The primary ground based instruments would be the VLA (Very Large Array), the Owens Valley Radio Observatory, and vector and longitudinal field magnetographs. Similar campaigns have successfully been carried out with the Solar Maximum Mission x-ray polychromator and the Soft X-ray Imaging Sounding Rocket Payload (CoMStOC '87), the Goddard Solar EUV Rocket Telescope and Spectrograph, the Lockheed Solar Plasma Diagnostics Experiment rocket payload, and the Soft X-ray Telescope in Yohkoh (CoMStoc '92). The scientific payoff from such a campaign is discussed in light of the results from these previous campaigns.

Holman, Gordon D.↗

NASA NTRS1993

Navier-Stokes analysis of three-dimensional S-ducts

Full 3D Navier-Stokes computational results are presented for compressible flows within nondiffusing and diffusing S-ducts. The present study provides an understanding of the performance characteristics of typical S-ducts with attached and separated flows and provides a frame of reference for future computational fluid dynamic studies of internal flows with strong secondary flows. The predicted results, which were obtained using both H- and O-grids, are compared with the experimental wall pressures, static and total pressure fields, and velocity vectors. In addition, computed boundary-layer thickness, velocity profiles in wall coordinates and skin friction values are presented. The inviscid contributions to the secondary flows are quantified. The S-duct entrance Mach number was 0.6, and the Reynolds number was 1.76 x 10 exp 6 based on the upstream duct diameter.

Harloff, G. J.↗

NASA NTRS1994

Euler potentials of current-free fields expressed in spherical harmonics

Given a magnetic field B = -del(vector differential operator)(sub gamma) with gamma expanded in spherical harmonics, it is shown that analytic Euler potentials may be derived for B if gamma is asymmetrical but contains only the contribution of a single index n. This work generalizes a result for sectorial harmonics with n = m, derived by Willis and Gardiner (1988).

Stern, David P.↗

NASA NTRS2004

Solar Magnetic Explosions, Spicules, and the Heliosphere

We present an example of each of the following observed characteristics of the magnetic origins of quiet-region coronal heating, spicules, macrospicules, and coronal mass ejections (CMEs). (1) In quiet regions, the luminosity of the corona is roughly proportional to the edge length of the underlying photospheric magnetic network. (2) Spicules and EUV explosive events are concentrated at the edges of the magnetic network. (3) Many macrospicules have the magnetic structure of a surge rooted around an inclusion of opposite-polarity magnetic flux. (4) CMEs and eruptive flares are driven by explosions of sheared magnetic fields rooted along polarity dividing lines (neutral lines) in the photospheric magnetic flux. These characteristics together suggest that the mainstay of the heliosphere, the corona/solar wind rooted in quiet regions and coronal holes, may be driven by myriads of tiny magnetic explosions at the network edges, explosions like those that drive CMEs but of vastly smaller scale. If so, the steady solar wind and the CMEs that disrupt it both have the same root cause: explosions of initially-closed, strongly-sheared, bipolar magnetic fields. The photospheric vector magnetograms, chromospheric filtergrams, EUV spectra, and coronal images from Solar-B are expected to have sufficient sensitivity, spatial resolution, and cadence to test this scenario for coronal heating in quiet regions and coronal holes. This work was supported by NASA/OSS through its Solar and Heliospheric Physics SR and T Program and Sun-Earth Connection GI Program.

Moore, Ronald L.↗

NASA NTRS1998

A remotely interrogatable sensor for chemical monitoring

A new type of continuously operating, in-situ, remotely monitored sensor is presented. The sensor is comprised of a thin film array of magnetostatically coupled, magnetically soft ferromagnetic thin film structures, adhered to or encased within a thin polymer layer. The polymer is made so that it swells or shrinks in response to the chemical analyte of interest, which in this case is pH. As the polymer swells or shrinks, the magnetostatic coupling between the magnetic elements changes, resulting in changes in the magnetic switching characteristics of the sensor. Placed within a sinusoidal magnetic field the magnetization vector of the coupled sensor elements periodically reverses directions, generating magnetic flux that can be remotely detected as a series of voltage spikes in appropriately placed pickup coils. one preliminary sensor design consists of four triangles, initially spaced approximately 50 micrometers apart, arranged to form a 12 mm x 12 mm square with the triangle tips centered at a common origin. Our preliminary work has focused on monitoring of pH using a lightly crosslinked pH sensitive polymer layer of hydroxyethylmethacrylate and 2-(dimethylamino) ethylmethacrylate. As the polymer swells or shrinks the magnetostatic coupling between the triangles changes, resulting in measurable changes in the amplitude of the detected voltage spirits.

Non-NASA Center↗

NASA NTRS2014

A Vortical Dawn Flank Boundary Layer for Near-Radial IMF: Wind Observations on 24 October 2001

We present an example of a boundary layer tailward of the dawn terminator which is entirely populated by rolled-up flow vortices. Observations were made by Wind on 24 October 2001 as the spacecraft moved across the region at the X plane approximately equal to −13 Earth radii. Interplanetary conditions were steady with a near-radial interplanetary magnetic field (IMF). Approximately 15 vortices were observed over the 1.5 hours duration of Wind's crossing, each lasting approximately 5 min. The rolling up is inferred from the presence of a hot tenuous plasma being accelerated to speeds higher than in the adjoining magnetosheath, a circumstance which has been shown to be a reliable signature of this in single-spacecraft observations. A blob of cold dense plasma was entrained in each vortex, at whose leading edge abrupt polarity changes of field and velocity components at current sheets were regularly observed. In the frame of the average boundary layer velocity, the dense blobs were moving predominantly sunward and their scale size along the X plane was approximately 7.4 Earth radii. Inquiring into the generation mechanism of the vortices, we analyze the stability of the boundary layer to sheared flows using compressible magnetohydrodynamic Kelvin-Helmholtz theory with continuous profiles for the physical quantities. We input parameters from (i) the exact theory of magnetosheath flow under aligned solar wind field and flow vectors near the terminator and (ii) the Wind data. It is shown that the configuration is indeed Kelvin-Helmholtz (KH) unstable. This is the first reported example of KH-unstable waves at the magnetopause under a radial IMF.

Magnetosheath↗

NASA NTRS2016

Optical Measurement Techniques for Rocket Engine Testing and Component Applications: Digital Image Correlation and Dynamic Photogrammetry

NASA Marshall Space Flight Center (MSFC) has been advancing dynamic optical measurement systems, primarily Digital Image Correlation, for extreme environment rocket engine test applications. The Digital Image Correlation (DIC) technology is used to track local and full field deformations, displacement vectors and local and global strain measurements. This technology has been evaluated at MSFC through lab testing to full scale hotfire engine testing of the J-2X Upper Stage engine at Stennis Space Center. It has been shown to provide reliable measurement data and has replaced many traditional measurement techniques for NASA applications. NASA and AMRDEC have recently signed agreements for NASA to train and transition the technology to applications for missile and helicopter testing. This presentation will provide an overview and progression of the technology, various testing applications at NASA MSFC, overview of Army-NASA test collaborations and application lessons learned about Digital Image Correlation.

Gradl, Paul↗

NASA NTRS1979

Application of the minimum correlation technique to the correction of the magnetic field measured by magnetometers on spacecraft

Some aspects of the problem of obtaining precise, absolute determination of the vector of low magnetic fields existing in the interplanetary medium are addressed. In the case of a real S/C, there is always the possibility of a spurious field which includes the spacecraft residual field and/or possible field from the sensors, due to both electronic drifts or changes of the magnetic properties of the sensor core. These latter effects may occur during storage of the sensors prior to launching and/or in-flight. The reliability is demonstrated for a method which postulates that there should be no correlation between changes in measured field magnitude and changes in the measured inclination of the field with respect to any one of three fixed Cartesian component directions. Application of this minimum correlation technique to data from IMP-8 and Helios 1-2 shows it is appropriate for determination of the zero offset corrections of triaxial magnetometers. In general, a number of the order of 1000 consecutive data points is sufficient for a good determination.

Mariani, F.↗

NASA NTRS1975

Preliminary model studies of the magnetosphere of Jupiter: Pioneer 10

Observations of the Jovian magnetic field and its interaction with the solar wind plasma were made while the Pioneer 10 spacecraft was within about 100 R sub j of the planet. The magnetosphere was found to be severely stretched due to the presence of an intense current sheet, which was particularly evident during the outbound passage of Pioneer 10 near the dawn terminator. Plots of the angle between the orientation of the outbound field and the radius vector from the planet to the spacecraft showed a strong tendency for the field to become radial at large distances from the planet. A similar trend has also been seen in both the inbound and outbound Pioneer 11 data. Preliminary work on a mathematical model of the magnetosphere of Jupiter is given, based upon the Pioneer 10 outbound data. Some of the implications of the radial field configuration inferred from the Pioneer 10 and 11 data are also discussed.

Jones, D. E.↗

NASA NTRS1993

Flight-path estimation in passive low-altitude flight by visual cues

A series of experiments was conducted, in which subjects had to estimate the flight path while passively being flown in straight or in curved motion over several types of nominally flat, textured terrain. Three computer-generated terrain types were investigated: (1) a random 'pole' field, (2) a flat field consisting of random rectangular patches, and (3) a field of random parallelepipeds. Experimental parameters were the velocity-to-height (V/h) ratio, the viewing distance, and the terrain type. Furthermore, the effect of obscuring parts of the visual field was investigated. Assumptions were made about the basic visual-field information by analyzing the pattern of line-of-sight (LOS) rate vectors in the visual field. The experimental results support these assumptions and show that, for both a straight as well as a curved flight path, the estimation accuracy and estimation times improve with the V/h ratio. Error scores for the curved flight path are found to be about 3 deg in visual angle higher than for the straight flight path, and the sensitivity to the V/h ratio is found to be considerably larger. For the straight motion, the flight path could be estimated successfully from local areas in the far field. Curved flight-path estimates have to rely on the entire LOS rate pattern.

Grunwald, Arthur J.↗

NASA NTRS2005

Attitude-Independent Magnetometer Calibration for Spin-Stabilized Spacecraft

The paper describes a three-step estimator to calibrate a Three-Axis Magnetometer (TAM) using TAM and slit Sun or star sensor measurements. In the first step, the Calibration Utility forms a loss function from the residuals of the magnitude of the geomagnetic field. This loss function is minimized with respect to biases, scale factors, and nonorthogonality corrections. The second step minimizes residuals of the projection of the geomagnetic field onto the spin axis under the assumption that spacecraft nutation has been suppressed by a nutation damper. Minimization is done with respect to various directions of the body spin axis in the TAM frame. The direction of the spin axis in the inertial coordinate system required for the residual computation is assumed to be unchanged with time. It is either determined independently using other sensors or included in the estimation parameters. In both cases all estimation parameters can be found using simple analytical formulas derived in the paper. The last step is to minimize a third loss function formed by residuals of the dot product between the geomagnetic field and Sun or star vector with respect to the misalignment angle about the body spin axis. The method is illustrated by calibrating TAM for the Fast Auroral Snapshot Explorer (FAST) using in-flight TAM and Sun sensor data. The estimated parameters include magnetic biases, scale factors, and misalignment angles of the spin axis in the TAM frame. Estimation of the misalignment angle about the spin axis was inconclusive since (at least for the selected time interval) the Sun vector was about 15 degrees from the direction of the spin axis; as a result residuals of the dot product between the geomagnetic field and Sun vectors were to a large extent minimized as a by-product of the second step.

Natanson, Gregory↗

NASA NTRS1972

The earth's bow shock in an oblique interplanetary field.

The pressure, magnetic field, temperature, particle density, and stream velocity throughout the magnetosheath have been calculated in the plane containing the interplanetary field and solar wind velocity vector for various orientations of the interplanetary magnetic field and various assumed ratios of specific heats of the compressed solar wind. Jump conditions at the bow shock gave initial conditions in the shocked plasma from which the appropriate hydromagnetic equations (for blunt bodies in the subsonic region near the subsolar point and for the method of characteristics in the supersonic region back in the tail) were integrated numerically back to the surface of the magnetosphere. Explicit consideration of the magnetic field shows that a net asymmetrical force on the magnetopause produces a side force, or 'lift' in addition to the well-known drag on the magnetosphere.

Shen, W.-W.↗