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NASA NTRS1977

Theoretical aspects of sounder antenna operation

The fundamental problem of calculating the radiation from an electric dipole immersed in a magnetoplasma is one of solving Maxwell's equations coupled to the self-consistent field-particle equations describing the plasma. For very small applied antenna voltages, the plasma dynamics may be linearized, and the plasma reaction currents computed self-consistently in terms of the voltage on the antenna. Thus, the short dipole can be idealized as a point dipole of moment P sub o = C sub a, V sub o el, where C sub a is the antenna element-to-plasma capacitance for a sheath of dimensions roughly several plasma Debye lengths and el is the dipole element's length. In actual practice, it is at this point that the first difficulty with the antenna theory arises. Even for small signals, the sheath around such an antenna will exhibit a complex impedance. For larger signals, nonlinear effects appear. Attemps are made to solve this problem.

Fredricks, R. W.↗

NASA NTRS1977

Induced emission of Jupiter's decametric radiation by Io-accelerated electrons

A source mechanism for the Io-modulated component of the Jovian decametric radiation is proposed on the basis of the model where electrons in the Io flux tube (IFT) can be accelerated by Io's sheath. It is suggested that a significant fraction of the Io-sheath-accelerated electrons can have pitch angles greater than the atmospheric loss cone and therefore become trapped in the IFT. These electrons have flat helical orbits near their mirror points and can give rise to induced emission of extraordinary-mode radiation with frequencies close to the local electron gyrofrequency. The excitation mechanism is primarily due to the interaction of electromagnetic waves with the electrons via a relativistic gyroresonance which arises because of the momentum dependence of the gyrofrequency. Emphasis is put on the case of nearly perpendicular propagation because it is consistent with the observed source regions and beaming pattern of the decametric emissions. The energy requirement is satisfied within the context of the theory. It is also shown that emission occurs in regions close to the planet above the ionosphere.

Wu, C. S.↗

NASA NTRS1977

Numerical simulation of spacecraft charging phenomena

A numerical simulation program is being constructed having the following features: (1) infinite circular cylindrical geometry with angle-dependence, (2) inclusion of incident particles, photoelectrons, secondary electrons, backscattered electrons, any gun emissions, and any internal current pathways including surface conductive layers, (3) quasistatic time-dependent iteration, in which sheath potential changes during particle transit times are ignored, (4) use of approximate, locally-dependent space charge density expressions in solving Poisson's equation for sheath potentials, with use of numerical orbit-following to determine surface currents, and (5) incident particle velocity distributions isotropic or beam-like, or some superposition of these. Rationales for each of these features are discussed.

Laframboise, J. G.↗

NASA NTRS1977

Mariner 10 magnetic field observations of the Venus wake

Magnetic field measurements made over a 21-hour interval during the Mariner 10 encounter with Venus were used to study the down-stream region of the solar wind-Venus interaction over a distance of approximately 100 R sub v. For most of the day before closest approach the spacecraft was located in a sheath-like region which was apparently bounded by planetary bow shock on the outer side and either a planetary wake boundary or transient boundary-like feature on the inner side. The spacecraft made multiple encounters with the wake-like boundary during the 21-hour interval with an increasing frequency as it approached the planet. Each pass into the wake boundary from the sheath region was consistently characterized by a slight decrease in magnetic field magnitude, a marked increase in the frequency and amplitude of field fluctuations, and a systematic clockwise rotation of the field direction when viewed from above the plane of the planet orbit.

Lepping, R. P.↗

NASA NTRS1978

Segregation of acid plume pixels from background water pixels, signatures of background water and dispersed acid plumes, and implications for calculation of iron concentration in dense plumes

Two files of data, obtained with a modular multiband scanner, for an acid waste dump into ocean water, were analyzed intensively. Signatures were derived for background water at different levels of effective sunlight intensity, and for different iron concentrations in the dispersed plume from the dump. The effect of increased sunlight intensity on the calculated iron concentration was found to be relatively important at low iron concentrations and relatively unimportant at high values of iron concentration in dispersed plumes. It was concluded that the basic equation for iron concentration is not applicable to dense plumes, particularly because lower values are indicated at the very core of the plume, than in the surrounding sheath, whereas radiances increase consistently from background water to dispersed plume to inner sheath to innermost core. It was likewise concluded that in the dense plume the iron concentration would probably best be measured by the higher wave length radiances, although the suitable relationship remains unknown.

Bahn, G. S.↗

NASA NTRS1978

Silicon Sheet Growth Development for the Large Area Sheet Task of the Low Cost Solar Array Project. Heat Exchanger Method - Ingot Casting Fixed Abrasive Method - Multi-Wire Slicing

Solar cells fabricated from HEM cast silicon yielded up to 15% conversion efficiencies. This was achieved in spite of using unpurified graphite parts in the HEM furnace and without optimization of material or cell processing parameters. Molybdenum retainers prevented SiC formation and reduced carbon content by 50%. The oxygen content of vacuum cast HEM silicon is lower than typical Czochralski grown silicon. Impregnation of 45 micrometers diamonds into 7.5 micrometers copper sheath showed distortion of the copper layer. However, 12.5 micrometers and 15 micrometers copper sheath can be impregnated with 45 micrometers diamonds to a high concentration. Electroless nickel plating of wires impregnated only in the cutting edge showed nickel concentration around the diamonds. This has the possibility of reducing kerf. The high speed slicer fabricated can achieve higher speed and longer stroke with vibration isolation.

Schmid, F.↗

NASA NTRS1978

Resonant absorption of Alfvenic surface waves and the heating of solar coronal loops

A first-order mass- and energy-balance model is developed for steady-state EUV 'coronal rain' loops that are not associated with postflare events and are often seen over sunspot umbrae. The model disregards variations in a loop's thermodynamic and magnetic properties along magnetic-field lines and yields average properties of the resonant absorption sheath, the boundary layer, and the loop's interior. Both irreversible heating by Alfvenic surface waves and energy transport via induced boundary-layer convection are taken into account in the analysis. Results that include predictions of the temperatures of the sheath and the boundary-layer plasma, the temperature of the interior plasma, the radiative output of the loop, and the filling factor associated with this radiation are given in terms of the period and velocity amplitude of the relevant surface wave as well as various parameters that characterize a typical 'coronal rain' loop. These results are shown to be consistent with the observed minimum and maximum temperatures as well as the radiative output of typical 'coronal rain' loops.

Ionson, J. A.↗

NASA NTRS1979

Magnetosheath effects on cylindrical Langmuir probes

A study of the response of cylindrical Langmuir probes in magnetoplasmas focusing on the relative magnitudes of Larmor radius and sheath size is presented. The approach results in a classification of magnetic field effects which involves the magnetic field strength and plasma parameters of density, temperature, and the applied probe potential. It is shown that a 0.25 G field can have similar effects on the current collection properties of the probe in ionospheric plasma as a 30 kG field would have in a hot, dense laboratory plasma. The data also show: (1) the effects of probe orientation on electron current collection from magnetoplasmas; (2) that these effects can be important even when the electron Larmor radius is larger than the radius of the probe; and (3) that substantial magnetic field effects occur when the probe sheath is comparable to or greater than the Larmor radius.

Szuszczewicz, E. P.↗

NASA NTRS1980

Initial assessment of the effects of energetic ion injections in the magnetosphere due to the transport of satellite power system components from low earth orbit to geosynchronous earth orbit

Potentially serious environmental effects exist when cargo orbital transfer vehicle (COTV) ion propulsion is used on the scale proposed in the preliminary definition studies of the Satellite Power System. These effects of the large scale injections of ion propulsion exhaust in the plasmasphere and in the outer magnetosphere were shown to be highly model dependent with major differences existing in the predicted effects of two models, the ion cloud model and the ion sheath model. The expected total number density deposition of the propellant Ar(+) in the plasmasphere, the energy spectra of the deposited Ar(+) and time dependent behavior of the Ar(+) injected into the plasmasphere by a fleet of COTV vehicles differ drastically between the two models. The ion sheath model was demonstrated to be applicable to the proposed Ar(+) beam physics if the beam was divergent and turbulent whereas the ion cloud model was not a realistic approximation for such a beam because the "frozen-field" assumption on which it is based is not valid.

Curtis, S. A.↗

NASA NTRS1981

Theory and tests of a thermal ion detector sensitive only at Near-normal incidence

Measurements of thermal ions are influenced by factors such as spacecraft potential, velocity, angle of attack, and sheath size. A theory is presented for the response of an instrument which accepts ions only within a small angle of incidence from normal. Although a more general theory is available and forms the basis of this one, the small angle restriction allows a simpler formulation which does not depend on sheath size. Furthermore, practical instruments are easily designed around this restriction. Laboratory tests verify that such instruments respond as expected and they illustrate how design details influence perturbations from the ideal response characteristics.

Robinson, J. W.↗

NASA NTRS1982

Plasma and electric field boundaries at high and low altitudes on July 29, 1977

Hot plasma observations at high and low altitudes were compared. The plasma ion composition at high altitudes outside the plasmasphere was 0+. Heavy ions were also observed at low altitudes outside the plasmasphere. It is shown that at times these ions are found well below the plasmapause inside the plasmasphere. Comparisons of the low altitude plasma and dc electric fields show that the outer limits of the plasmasphere is not always corotating at the low L-shells. The corotation boundary, the estimated plasmapause boundary at the boundary of the inner edge of plasma sheet ions were at the same position. The inner edge of plasma sheet electrons is observed at higher latitudes than the plasmasphere boundary during disturbed times. The inner edge of the plasma sheaths shows a strong dawn to dusk asymmetry. At the same time the inner edge of the ring current and plasma sheath also moves to high latitudes reflecting an apparent inflation of the magnetosphere.

Fennell, J. F.↗

NASA NTRS1980

Effects of argon ion injections in the plasmasphere

In lifting massive space power system payloads from low Earth orbit to geosynchronous Earth orbit, Cargo Orbit Transfer (COTV) using ion propulsion will inject energetic beams of argon ions into the plasmasphere. The relationship of the beam velocity to Alfven and thermal velocities as a function of radial distance in the plasmasphere is given for positions near the Earth's equatorial plane. A beam sheath loss model is used which results in a deposition of argon ions and hence energy in the plasmasphere which is much less than that in models calling for clouds or plasma instabilities to rapidly stop the beam. A comparison is given of the cumulative fractional mass loss of an ion beam injected at 1.5 R for the ion cloud and the ion beam sheath loss process. The integrated difference of these two deposition models is shown for the construction of one SPS.

Curtis, S. A.↗

NASA NTRS1982

Magnetopause modeling - Flux transfer events and magnetosheath quasi-trapped distributions

Three-dimensional distribution functions for energetic ions are studied numerically in the magnetosphere, through the magnetopause, and in the magnetosheath using a simple one-dimensional quasi-static model and ISEE 1 magnetopause crossing data for November 10, 1977. Quasi-trapped populations in the magnetosheath observed near flux transfer events (FTEs) are investigated, and it is shown that the population in the sheath appears to sandwich the FTE distributions. These quasi-trapped distributions are due to slow, large pitch angle, outward moving particles left behind by the outward rush of the ions more field-aligned at the time the flux was opened. It is found that sheath convective flows can map along the connected flux tube without drastically changing the distribution function, and results suggest that localized tangential fields above the upper limit may exist.

Speiser, T. W.↗

NASA NTRS1983

Transducer Joint for Kidney-Stone Ultrasonics

Ultrasonic therapy for kidney stones improved by new way of connecting wire-probe ultrasonic waveguide to transducer. Improved mounting allows joint to last long enough for effective treatment. Sheath and rubber dampers constrain lateral vibration of wire waveguide. Combination of V-shaped mounting groove, sheath, and rubber dampers increases life expectancy of wire 15 times or more.

Angulo, E. D.↗

NASA NTRS1984

Oxidation Protection for Thermocouples

Thin platinum film on thermocouple sheath protects non-noble-metal thermocouples from deterioration in oxygen-rich atmosphere. Coating works on nickel-alloy sheathed thermocouples otherwise destroyed by corrosion in pure oxygen at 1,000 degrees C.

Richter, R.↗

NASA NTRS1980

Compression panel studies for supersonic cruise vehicles

Results of analytical and experimental studies are summarized for titanium, boron fiber reinforced aluminum matrix composite, Borsic fiber reinforced aluminum matrix composite, and titanium sheathed Borsic fiber reinforced aluminum matrix composite stiffened panels. The results indicate that stiffened panels with continuous joints (i.e., brazed, diffusion bonded or adhesive bonded joints) are more structurally efficient than geometrically similar panels with discrete joints (i.e., spotwelded or bolted joints). In addition, results for various types of fiber reinforced aluminum matrix stiffened panels indicate that titanium sheathed Borsic fiber reinforced aluminum matrix composite panels are the most structurally efficient. Analytical results are also presented for graphite fiber reinforced polyimide matrix composite stiffened panels and superplastically formed and diffusion bonded titanium sandwich panels.

Mcwithey, R. R.↗

NASA NTRS1982

Electric field observations of time constants related to charging and charge neutralization processes in the ionosphere

The Polar 5 electric field results are reviewed, and the transients from Polar 3 are presented. The phenomena are discussed from the standpoint of space charge. On the basis of the Polar 5 results, the large magnitude of the electric field from Polar 3 is seen as indicating that the observed space charge was probably within a few km or less of the payload. Reference is made to Cole's prediction (1960) that charges in the ionosphere would reach equilibrium with a time constant of the order of a few microsec. The processes involved in the two cases presented here require time constants of the order of ms. If the sheath dimensions are taken to be between 50 and 100 m, which is not considered unreasonable in view of the electric field measurements, then a qualitative estimate of the neutralization time would be the transit time for ions across the sheath. Since the kinetic velocity of a 1-eV proton is approximately 14 m/s, it would traverse the distance in 4 to 8 ms, assuming freedom of movement across magnetic field lines. This is the order of the decay times observed on Polar 5.

Maynard, N. C.↗

NASA NTRS1984

An investigation of the existence of a surface water layer on aircraft radomes during simulated flight in heavy precipitation

An experiment to investigate the electromagnetic attenuation effects of an impacting water spray on an aircraft weather radome was conducted in Langley's 4 X 7 m. wind tunnel equipped with a water spray system. Results indicate no significant liquid water film formed at the stagnation point of the radome under the test conditions. However, a water sheath was observed standing away from the radome surface, which could possibly have significant attenuation properties of its own. Due to the lack of fidelity in modeling both the natural environment with the tunnel apparatus and the water sheath, it is recommended that further studies be undertaken to better define the water distribution in the vicinity of the radome and measure its effect on weather radar performance.

Branstetter, J. R.↗