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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13

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NASA NTRS1980

Graphite composite truss welding and cap section forming subsystems. Volume 1: Executive summary

A rolltrusion process was developed for forming of a hybrid, single-ply woven graphite and glass fiber cloth, impregnated with a polysulfone resin and coated with TI02 pigmented P-1700 resin into strips for the on-orbit fabrication of triangular truss segments. Ultrasonic welding in vacuum showed no identifiable effects on weld strength or resin flow characteristics. An existing bench model cap roll forming machine was modified and used to roll form caps for the prototype test truss and for column test specimens in order to test local buckling and torsional instability characteristics.

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NASA NTRS1980

The Farley-Buneman instability in the polar cap ionosphere

Data on the Farley-Buneman instability in the E region of the polar cap are discussed. It is then shown how it is possible to use the instability as a diagnostic tool for polar cap electric fields and, hence, solar wind electric fields.

Dangelo, N.↗

NASA NTRS1981

The CAMEO barium release - E/parallel/ fields over the polar cap

Four successive thermite barium releases at an altitude of 965 km over polar cap invariant latitudes 84 to 76 deg near magnetic midnight were conducted from the orbiting second stage of the vehicle that launched Nimbus 7; the releases were made as part of the CAMEO (Chemically Active Material Ejected in Orbit) program. This was the first opportunity to observe the behavior of conventional barium release when conducted at orbital velocity in the near-earth magnetic field. The principal unexpected characteristic in the release dynamics was the high, 1.4 to 2.6 km/s, initial Ba(+) expansion velocity relative to an expected velocity of 0.9 km/s. Attention is also given to neutral cloud expansion, initial ion cloud expansion, convective motion, and the characteristics of field-aligned motion. The possibility of measuring parallel electric fields over the polar cap by observing perturbations in the motion of the visible ions is assessed.

Heppner, J. P.↗

NASA NTRS1981

Estimates of total quantity of meteorites in the East Antarctic ice cap

Based on a steady-state model of the East Antarctic ice cap, and current estimates of meteorite influx, a model is developed which predicts that the steady-state number of meteorites being carried in or on the ice is at least 760,000. This large meteorite population does not require unusual influx conditions, since the cold, dry climate preserves virtually all meteorites that fall with the exception of the fragile, porous carbonaceous chondrites. Application of the model to the Greenland ice cap yields a steady-state population of about 61,000 meteorites.

Olsen, E. J.↗

NASA NTRS1981

Dependence of polar cap potential drop on interplanetary parameters

The convection potential drop across the polar cap is computed from data obtained on high-inclination low-altitude satellites. Potential measurements are correlated with various combinations of parameters measured simultaneously in the upstream solar wind. Most of the potential drop is successfully predicted by merging theory, although a significant background potential drop of 35 kV does not depend on IMF parameters and is attributed to a process other than merging. Results indicate that small values of the IMF are amplified by a factor of 5-10 at the dayside magnetopause, which, when taken into account, improves correlations between IMF parameters and polar cap potential drop. Potential drop is better correlated with IMF parameters than with geomagnetic indices, due to nonlinear response of the magnetosphere affecting geomagnetic activity indices.

Reiff, P. H.↗

NASA NTRS1983

Ultrastructure of the root cap of Arabidopsis Thaliana L. Heynh under spaceflight conditions

Peculiarities of the ultrastructural organization of Arabidopsis root cap cells grown from the stage of two cotyledonous leaves in the Svetoblok-1 apparatus aboard the Salyut 6 research orbital station and in the laboratory are assessed. It is established that under conditions of real space flight vacuolization of the root cap cells increses considerably compared to the control variant. Changes in the topography and ulstrastructure of amyloplasts as well as lysis of cell walls are observed in the material under study. An assumption is advanced on analogous cell responses observed at the ultrastructural level to weightlessness and clinostatic conditions.

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NASA NTRS1982

Recession of Martian north polar cap - 1979-1980 Viking observations

The polar regression curve for the Martian northern polar cap, derived from Viking observations for the 1979-1980 regression, is discussed, and comparisons with previous regression curves are made. Differences in the curves may be due to dust storms affecting the deposition of the cap. It is not possible to unambiguously ascribe differences between the curves to dynamical effects, since detailed information on the longitudinal dependence, which was an uncontrolled variable, is not available.

James, P. B.↗

NASA NTRS1983

Characterization of geometric isomers of Norbornene end-capped imides

Three geometric isomers from the thermal isomerization of methylene-4,4' bis(endo-N-phenylbicyclo/2.2.1/hept-2-ene-5,6-di carboximide) (I) were chromatographically separated and isolated in order to investigate the thermal cure of norbornene end-capped imide oligomers, which display considerable promise for use in various aerospace adhesive and composite applications. Endo-endo (I), endo-exo (II), and exo-exo (III) configurations were assigned to each compound based on the results of NMR spectroscopy. Several chromatographic, spectroscopic, and thermal techniques were then used to characterize these three isomers which serve as model compounds for norbornene end-capped polyimides. It was found that each compound thermally isomerized to an equilibrium mixture of all three compounds prior to cure. It is proposed that these compounds react by different mechanisms in air and nitrogen.

Young, P. R.↗

NASA NTRS1985

Beam-Cap-Forming Machine

Graphite reinforced plastic strip transformed into continuous beam cap. Report describes machine that fabricates beam caps from graphite reinforced thermoplastic materials supplied as strip stock.

Marx, W.↗

NASA NTRS1984

Protein and carotenoid synthesis and turnover in gravistimulated root caps

In certain cultivars of corn gravitropic bending occurs only after the root cap, the site of gravity perception, is exposed to light. Light appears to trigger or to remove some block in the gravity translation process. Using light sensitive cultivars of corn, it was shown that light affects various processes in the cap. The roles of these light-induced processes in gravitropic bending in roots were studied.

Feldman, L. J.↗

NASA NTRS1983

The Thematic Mapper Tasseled Cap - A preliminary formulation

A transformation is described which rotates Thematic Mapper data (excluding the thermal band) in a manner analogous to that used in the MSS Tasseled Cap Transformation, thus providing a direct view of the planes of data dispersion and a direct association of spectral features with physical scene characteristics. This TM Tasseled Cap Transformation includes MSS-equivalent Grenness and Brightness features, as well as at least one additional important feature. The new feature, tentatively termed 'Wetness', offers promise of enhanced ability to assess soil conditions, monitor vegetative development, and delineate cover classes. Relationships between scene characteristics and spectral variation in the transformed data space are discussed based on both simulated and actual TM data.

Crist, E. P.↗

NASA NTRS1983

Polar cap electron densities from DE 1 plasma wave observations

Electric-field-spectum measurements from the plasma-wave instrument on the Dynamics Explorer 1 spacecraft are used to study the local electron density at high altitudes in the northern polar-cap region. The electron density is determined from the upper cutoff of whistler-mode radiation at the electron plasma frequency. Median density values over the polar cap at L greater than 10 are found to vary from 35.2 + or - 8.5 cu cm at 2.1 earth radii to 0.99 + or - 0.51 cu cm at 4.66 earth radii. The steady-state radial-outflow model is examined for consistency with the observed density profile. A power-law fit to the radial variation of the electron density yields an exponent of - 3.85 + or - 0.32, which for the radial-outflow model implies a flow velocity increasing nearly linearly with incresing radial distance. Comparison of the observed electron densities with theoretical polar-wind densities yields consistent results up to 2.8 earth radii. A comparison of the observed electron densities with low-altitude density profiles from the Alouette II and ISIS 1 spacecraft illustrates transitions in the slope of the profile at 1.16 earth radii and between 1.55 and 2.0 earth radii. The changes in the density profile suggest that changes occur in the basic radial-transport processes at these altitudes.

Persoon, A. M.↗

NASA NTRS1984

Dependence of the polar cap geometry on the IMF

The geometry of the open field line region in the polar region is computed for a variety of the interplanetary magnetic field (IMF) orientation. The open field line region can be identified as the area bounded by the auroral oval, namely the polar cap. The polar cap geometry varies considerably with the orientation of the IMF and magnitude, particularly when the IMF Bz component is positive and large. The corresponding exit points of the open field lines on the magnetopause are also examined. The results are useful in interpreting various upper atmospheric phenomena in the highest latitude region of the earth and also in observing chemical releases outside the magnetopause.

Akasofu, S.-I.↗

NASA NTRS1984

Polar cap formation on Ganymede

It is argued that Ganymede's polar caps are the remnants of a more extensive covering of water ice that formed during a period in which the satellite was geologically active. It is inferred that the initial thickness of this covering was a significant fraction of the gardening depth since the covering formed. This suggests an initial thickness of at least a few meters over heavily cratered regions such as the south polar grooved terrain. The absence of similar polar caps on Callisto apparently reflects the absence of comparable geologic activity in the history of this satellite.

Shaya, E. J.↗

NASA NTRS1984

Some photometric properties of the Martian south polar cap region during the 1971 apparition

High-quality earth-based photographs from the Lowell Observatory Planetary Research Center collection have been analyzed to derive some photometric parameters for the Martian south polar cap region during the 1971 apparition. The optical thickness of the atmosphere above the cap varied with wavelength from 0.35 + or - 0.05 in red light to 0.58 + or 0.06 in UV light. The effective geometric albedo is calculated from the 30 deg phase data assuming isotropic scattering: it varies from 0.85 + or - 0.04 (in red light) to 0.63 + or 0.05 (in UV light).

Lumme, K.↗

NASA NTRS1985

Auroral-polar cap environment and its impact on spacecraft plasma interactions

The high density of the plasma at shuttle altitude is likely to increase greatly the possibility of arcing and shorting of exposed high voltage surfaces. For military missions over the polar caps and through the auoroal zones, the added hazards of high energy auroral particle fluxes or solar flares will further increase the hazard to shuttle, its crew, and its mission. A review of the role that the auroral and polar cap environment play in causing these interactions was conducted. A simple, though comprehensive attempt at modelling the shuttle environment at 400 km will be described that can be used to evaluate the importance of the interactions. The results of this evaluation are then used to define areas where adequate environmental measurements will be necessary if a true spacecraft interactions technology is to be developed for the shuttle.

Garrett, H. B.↗

NASA NTRS1984

Thermospheric circulation, temperature, and compositional structure of the southern hemisphere polar cap during October-November 1981

Results of NCAR thermospheric general circulation model (TGCM) simulations were compared with Dynamics Explorer (DE2) data on the neutral wind, temperature and O and N2 number variations over the south polar cap in the F region in October-November 1981. Attention was focused on variations in the thermospheric characteristics. All variations reached a maximum over the magnetic polar cap, with the largest O and N2 changes being present in the dawn sector of the auroral oval, where Joule heating was maximized. The TGCM simulations for conditions similar to the DE2 passes agreed well with the satellite data, indicating that the variations in the wind, temperature and compositional characteristics are dependent on the magnitude of magnetospheric convection and influenced by the separation between the geomagnetic and geographic poles.

Roble, R. G.↗

NASA NTRS1984

Cross-polar cap potential drop and the energy coupling function

A numerical model is formulated for correlations between the cross polar cap potential, the solar wind, and the AI index and compared with satellite data. The conductivity model was devised from empirically defined relationships between the Hall and Pedersen conductivities and the measured magnitude of the horizontal magnetic disturbance near College, AK. An instantaneous conductivity distribution was generated from data gathered at, e.g., six IMS meridian chain stations. A strong correlation appeared between an energy coupling function (ECF) and the polar cap potential drop. The ECF was derived from the chain station data, implying that potential drop estimates can be made from ground-based magnetometer data.

Ahn, B.-H.↗