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At least 631 records · Page 35

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NASA NTRS1980

Simultaneous observations of field-aligned currents and plasma drift velocities by Atmosphere Explorer C

The three-axis flux gate magnetometer on board the Atmosphere Explorer C (AE-C) has provided an additional magnetic field data set to the already broad spectrum of AE-C measurement. The results of an investigation into the feasibility of using the magnetometer for scientific purposes are described. It is shown that within the limitations inherent in the device and in the data reduction technique used, meaningful results can be obtained when the spacecraft is in the spinning mode. From a comparison between the field-aligned current signatures and the simultaneously observed ion convection velocity, it proved possible to locate regions of ionospheric conductivity gradients.

Bythrow, P. F.↗

NASA NTRS1981

Flow through axially aligned sequential apertures of the orifice and Borda types

Choked flow rate and pressure profile data were obtained and studied for two axially aligned sequential configurations consisting of four Borda type inlets of 1.9 1/D with two separation distances of 0.8 and 30 diameters and four orifice type inlets of 0.5 1/D with two separation distances of 0.66 and 32 diameters. Data were obtained using fluid nitrogen over the reduced inlet temperature and pressure range 0.68 T/T sub c gas and P/P sub c to 2. A flow coefficient reduced temperature plot can be used to represent the flow rate data for each geometry. At the larger separation distances, the pressure profiles dropped sharply at the entrance and partially recovered within each of the Borda and orifice inlet configurations; the exception being the last inlet where at low entrance temperatures, fluid jetting could occur. For the smaller spacings fluid jetting was prevalent throughout each of the inlet configurations at lower inlet temperatures. These results are in qualitative agreement with data of tubes with single Borda or sharp edge orifice type inlets to 105 1/D and water flow visualization studies.

Hendricks, R. C.↗

NASA NTRS1981

Some flow phenomena associated with aligned, sequential apertures with Borda-type inlets

Choked flow rate and pressure profile data were taken and studied for a configuration consisting of four axially aligned, sequential Borda tubes of 1.9 length diameter ratio with separation distances of 0.8 and 30 tube diameters. For either case the flow rate data could be represented by a flow coefficient reduced temperature plot. At a separation distance of 30 tube diameters the pressure profiles dropped sharply at the entrance and recovered within each Borda tube; except at low temperatures, where fluid jetting through the last Borda tube occurred. At a separation distance of 0.8 tube jetting was prevalent, and application of a significant backpressure did not alter the jetting. These results agree with other data for tubes with Borda or sharp edge orifice inlets and with a water flow visualization study reported herein.

Hendericks, R. C.↗

NASA NTRS1980

A seasonal change in the effect of field-aligned currents at synchronous orbit

The expected signature of substorm field-aligned currents is described for synchronous satellites near 10 deg magnetic latitude. The main effect is a positive D perturbation premidnight and a negative D perturbation postmidnight. This behavior is illustrated for two substorms near the fall equinox. A second pair of substorms taken from winter solstice do not show the expected behavior. The absence of this effect in winter observations is verified statistically by superposed epoch analysis. A simple explanation of this behavior based on the geometry of the plane of magnetic symmetry is presented. During disturbed times at winter solstice a synchronous satellite nominally at 10 deg magnetic latitude is effectively at the magnetic equator. This distortion of the magnetic equator must be considered in future models of the disturbed magnetospheric magnetic field.

Mcpherron, R. L.↗

NASA NTRS1980

Temperature gradients through EHD films and molecular alignment evidenced by infrared spectroscopy

Partial and complete emission band reversals have been observed in the infrared emission spectra from portions of operating sliding contacts. An elementary analysis has been carried out to show that partial reversals are due to temperature gradients in the fluid film - the film acts both as a radiation-emitter and absorber, and that total reversals - an emission spectrum appears as an absorption spectrum are likely to be due to a continuum source, such as hot solid asperities. The total energy radiated under the latter conditions exceeds that under the others. A decrease in gap width with increased load was accompanied by a dramatic spectral change in the case of 5P4E polyphenyl ether, which is indicative of molecular alignment.

King, V. W.↗

NASA NTRS1981

MAGSAT: Vector magnetometer absolute sensor alignment determination

A procedure is described for accurately determining the absolute alignment of the magnetic axes of a triaxial magnetometer sensor with respect to an external, fixed, reference coordinate system. The method does not require that the magnetic field vector orientation, as generated by a triaxial calibration coil system, be known to better than a few degrees from its true position, and minimizes the number of positions through which a sensor assembly must be rotated to obtain a solution. Computer simulations show that accuracies of better than 0.4 seconds of arc can be achieved under typical test conditions associated with existing magnetic test facilities. The basic approach is similar in nature to that presented by McPherron and Snare (1978) except that only three sensor positions are required and the system of equations to be solved is considerably simplified. Applications of the method to the case of the MAGSAT Vector Magnetometer are presented and the problems encountered discussed.

Acuna, M. H.↗

NASA NTRS1981

Flow through axially aligned sequential apertures of the orifice and Borda types

Choked flow rate and pressure profile data were taken and studied for two axially aligned sequential configurations consisting of: (1) Four Borda type inlets of 1.9 1/D with two separation distances of 0.8 and 30 diameters. (2) Four orifice type inlets of 0.5 1/D with two separation distances of 0.66 and 32 diameters. A flow-coefficient reduced-temperature plot can be used to represent the flow rate data for each geometry. At the larger separation distances, the pressure profiles dropped sharply at the entrance and partially recovered within each of the Borda and orifice inlet configurations; the exception being the last inlet where at low entrance temperatures, fluid jetting could occur. For the smaller spacings fluid jetting was prevalent throughout each of the inlet configurations at lower inlet temperatures. These results are in qualitative agreement with data of tubes with single Borda or sharp-edge orifice type inlets to 105 1/D and water flow visualization studies.

Hendricks, R. C.↗

NASA NTRS1982

Field-aligned ion streams in the earth's midnight region

Plasma measurements from the University of California at San Diego auroral particles experiment on the geosynchronous Applied Technology Satellite 6 in the midnight region show that the low-energy ion fluxes (1-100 eV) are field aligned and are well characterized as thermal populations (1-10 eV) with a streaming velocity of 30-100 km/s along the magnetic field line. The lowest energies are found prior to injections, on quiet days, with an increase of the streaming velocity evident when an injection occurs near the satellite. Multiple peaks in the ion distribution functions are attributed to the presence of different ions species (H/+/, He/+/, O/+/, O/2+/) streaming at similar velocities, both during quiet times and as the plasma velocity increases in response to an injection.

Olsen, R. C.↗

NASA NTRS1982

Observations of field-aligned currents, particles, and plasma drift in the polar cusps near solstice

Magnetic perturbations observed by the TRIAD magnetometer within two hours of an AE-C spacecraft pass provide field-aligned current data, from the same local time in the northern hemisphere, for a study of the polar cusp. The AE-C spinning mode has allowed the use of the Z-axis magnetometer for Birkeland current observations, in conjunction with particle and drift measurements. The average B(z) were found to be 1.9 nT and -1.1 nT during the first two hourly intervals on January 15, 1977. Measurements from the low energy electron experiment revealed intense fluxes of soft, cusp-like 100 eV Maxwellian electrons throughout the prenoon polar cap. The upward directed current can be identified as the dominant cusp current appropriate for B(y) values lower than zero, while the downward directed current, which has the appropriate sign of a dayside region 1 current, is observed to lie entirely within a westerly, antisunward-convecting plasma.

Bythrow, P. F.↗

NASA NTRS1982

Optimal sun-alignment techniques of large solar arrays in electric propulsion spacecraft

Optimum sun-alignment of large solar arrays in electric propulsion spacecraft operating in earth orbit requires periodic roll motions around the thrust axis, synchronized with the apparent conical motion of the sun line. This oscillation is sustained effectively with the aid of gravity gradient torques while only a small share of the total torque is being contributed by the attitude control system. Tuning the system for resonance requires an appropriate choice of moment-of-inertia characteristics. To minimize atmospheric drag at low orbital altitudes the solar array is oriented parallel, or nearly parallel, to the flight direction. This can increase the thrust-to-drag ratio by as much as an order of magnitude. Coupled with optimal roll orientation, this feathering technique will permit use of electric propulsion effectively at low altitudes in support of space shuttle or space station activities and in spiral ascent missions.

Meissinger, H. F.↗

NASA NTRS1983

Auroral electron interaction with the atmosphere in the presence of conjugate field-aligned electrostatic potentials

In the present investigation, both pitch angle and energy distributions of auroral electrons are obtained, for the first time, by rigorous numerical solutions of a multiangle transport equation at all energies in a realistic three component atmosphere in the presence of a conjugate field-aligned electrostatic potential. The results confirm all previous demonstrations of the validity of Evan's (1974, 1975, 1976) hypothesis concerning the origin of low energy auroral electrons from collisional interactions of the auroral primaries with the atmosphere. The existence of a collisionally populated field-perpendicular flux at energies near the beam energy is also demonstrated.

Prasad, S. S.↗

NASA NTRS1983

The formation of aligned spheres in miscibility gap systems

The development of regularly sized and spaced rods or spheres in a monotectic system is presently considered in terms of interface breakdown and capillary instability mechanisms between two liquid phases. The most important relationship, which governs the rod-to-aligned spheres transition, is the temperature gradient-to-growth rate ratio that determines the depth of the intercellular nodes. Rods will develop when these nodes are shallow by comparison to rod circumference, and spheres will develop when they are deep.

Schafer, C.↗

NASA NTRS1983

Spatial relationship of field-aligned currents, electron precipitation, and plasma convection in the auroral oval

Observations reported by Winningham et al. (1975) have established that the auroral oval mapped to the magnetosphere along closed field lines divided the oval into two distinct regions of particle precipitation. In order to determine relationships between field-aligned current, convection, and particle precipitation, simultaneous measurements of all quantities are needed. The studies of Bythrow et al. (1980, 1981) have utilized Atmosphere Explorer C data for sunlit passes of the high-latitude ionosphere. The addition of magnetometer information for the eclipsed high-latitude passes of the Atmospheric Explorer C spacecraft makes it possible to make simultaneous measurements of Birkeland currents, plasma convection, and electron precipitation in the nightside auroral oval and polar cap. The present investigation provides the results of such observations, discusses the observed relationships, and attempts to correlate boundaries.

Coley, W. R.↗

NASA NTRS1983

Electrical self-aligning connector

A self-aligning electrical connector device includes a receptacle component having a conically contoured interior and a plug component having a correspondingly contoured conical body receivable in the receptacle component. The plug component has a number of spaced conductive ring elements with a mating face and the receptacle component includes corresponding spaced conductive ring elements providing mating interface with the mating face of the ring elements of the plug component when connected to it. Each ring element of the receptacle component has several segmented portions which defect downwardly when the plug component is inserted. A biasing force is asserted against the face of the ring elements of the plug component providing positive electrical contact and connection between the ring elements of the components.

Clark, K. H.↗

NASA NTRS1984

Rapid Test Bed Concentrator (TBC) Alignment Techniques

A new, labor and cost saving method was developed to eliminate the procedure of covering all (220) mirrors and uncovering then one-by-one in sequence to adjust each to the focal plane. This latest method being used to align mirrors of a parabolic solar concentrator utilizes a computer-derived target of discreet images made up of individual mirror reflections on a plane in front of the intended, nominal, focal point. Incorporating this computer technique increases accuracy and gives potential to develop flux distributions required by different receiver designs.

Argoud, M. J.↗

NASA NTRS1983

Field-aligned ion beams upstream of the earth's bow shock Evidence for a magnetosheath source

High time resolution ISEE-1 and -2 observations of upstream field-aligned ion beams at several crossings of the earth's bow shock indicate that some beams are due to high energy magnetosheath particles leaking through the shock into the upstream region. The distribution immediately downstream of these oblique shocks consists of a 'core' of directly transmitted, slightly heated ions, plus a crescent-shaped, high-velocity distribution, centered roughly on the magnetic field in the direction toward the upstream region, with a fairly well defined low velocity cutoff.

Thomsen, M. F.↗

NASA NTRS1984

On the relationship between morning sector irregular magnetic pulsations and field aligned currents

For three magnetically disturbed days in early 1980, data from south polar masses of the Magsat satellite are compared with data from search coil magnetometer, riometer, and photometer instrumentation at Siple, Antarctica. It is found that during each Magsat polar pass in the morning sector, the level of Pi 1 activity correlates well with the intensities of three-dimensional current systems. Fine structure is often observed in the field-aligned currents during periods of intense Pi activity. Among the Birkeland currents are 2-s to 10-s (16-80 km) structured perturbations; these are evident in the transverse components of the field and are thought to indicate filamentary currents. Pi 1 amplitudes are found to be considerably larger when region 2 Birkeland currents are overhead than when they are not. In one case, detailed features are identified in the high-resolution Magsat magnetic field data that may be current fluctuations related to asymmetric Pi 1.

Engebretson, M. J.↗

NASA NTRS1984

Field-aligned currents observed in the vicinity of a moving auroral arc

The sounding rocket Porcupine F4 was launched into an auroral arc and the field aligned currents were independently deduced from magnetic field measurements; the horizontal current deduced from the electric field measurements and height integrated conductivity calculations; and measurements of electron fluxes. Above the arc the different methods agree. The magnetosphere acts as generator and the ionosphere as load. North of the arc, the first two methods disagree, possibly due to an Alfven wave carrying the observed magnetic field perturbation. The energy flow is out of the ionosphere. Here the ionosphere acts as generator and the magnetosphere as load.

Goertz, C. K.↗