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At least 811 records · Page 45

Magnetosphere, ionosphere and atmosphere interactions

In the present review, the general nature of the earth's space environment is discussed with particular reference to the physical processes which link the magnetosphere, the ionosphere, and the upper atmosphere. Recent theoretical and experimental research has revealed the existence of subtle couplings which closely link the electrical and mass properties of these regions. Some of these couplings have been known for many years. Recent discoveries include such couplings as the formation of the plasmasphere through the mutual action of convective electric fields and ionospheric plasma flows. However, there is still insufficient information to define accurately the basic processes associated with space plasma dynamics when cool thermal plasma of ionospheric origin interacts with the neutral atmosphere, the energetic plasma of the ionosphere, and the solar wind. The primary objective of the discussion is to provide a general introduction to the more challenging processes as they are presently known.

Banks, P. M.↗

Advanced ceramic material for high temperature turbine tip seals

Forty-one material systems were evaluated for potential use in turbine blade tip seal applications at 1370 C. Both ceramic blade tip inserts and abradable ceramic tip shoes were tested. Hot gas erosion, impact resistance, thermal stability, and dynamic rub performance were the criteria used in rating the various materials. Silicon carbide and silicon nitride were used, both as blade tips and abradables. The blade tip inserts were fabricated by hot pressing while low density and honeycomb abradables were sintered or reaction bonded.

Vogan, J. W.↗

The acoustical structure of highly porous open-cell foams

This work concerns both the theoretical prediction and measurement of structural parameters in open-cell highly porous polyurethane foams. Of particular interest are the dynamic flow resistance, thermal time constant, and mass structure factor and their dependence on frequency and geometry of the cellular structure. The predictions of cell size parameters, static flow resistance, and heat transfer as accounted for by a Nusselt number are compared with measurement. Since the static flow resistance and inverse thermal time constant are interrelated via the 'mean' pore size parameter of Biot, only two independent measurements such as volume porosity and mean filament diameter are required to make the predictions for a given fluid condition. The agreements between this theory and nonacoustical experiments are excellent.

Lambert, R. F.↗

Flare loop radiative hydrodynamics. I - Basic methods

The study presented here has two goals. The first is to examine the role of energy transport mechanisms in flare dynamics, for instance, thermal cone conduction in the corona and radiative transfer in the chromosphere. The second is to provide diagnostics of flare energization processes by predicting the evolutionary behavior of concurrent emissions from all regions of the flaring atmosphere. To attain these ends, a numerical method is developed for the simultaneous solution of thy continuity, momentum, and energy equations; the time-dependent atomic rate equations describing ionization and excitation; and the radiative transfer equations. With the physical model and computational methods used here, all components of the plasma move as a single fluid and in the initial studies are assumed to have a common kinetic temperature. The plasma is constrained to move in one dimension along the axis of a loop of nonuniform cross section, the geometry of which is defined by a sufficiently strong magnetic field.

Mcclymont, A. N.↗

Mature thunderstorm cloud top structure - Three-dimensional numerical simulation versus satellite observations

Preliminary results of four runs with a three-dimensional model of the effects of vertical wind shear on cloud top height/temperature structure and the internal properties of isolate midlatitude thunderstorms are reported. The model is being developed as an aid to analyses of GEO remote sensing satellite data. The grid is a 27 x 27 x 20 mesh with 2 km horizontal resolution and 0.9 vertical resolution. The total grid is 54 km on a side and 18 km deep. A second-order Crowley scheme for advecting momentum is extended with a third-order correction for spatial truncation error, and the earth-relative horizontal surface wind components are decreased to 50 percent of their values at 0.45 km. A temperature increase with height is included, together with an initial impulse consisting of a nonrotating cylindrical weak buoyant updraft 10 km in radius. The results of the runs are discussed in terms of the time variation of the vertical velocity extrema, the effects of strong and weak shear on a storm, the cloud top height, the Lagrangian dynamics of a thermal couplet, and data from a real storm.

Schlesinger, R. E.↗

Development of baseline random vibration environment criteria for Shuttle pallet payload subsystems

This paper presents a statistical evaluation of measured random vibration response data obtained from the Office of Space Science-1 (OSS-1) pallet payload. The data were measured during the acoustic test simulation (September 1980) and the ascent phase of the flight of STS-3, Orbiter 102 (launched from the Kennedy Space Center on March 22, 1982). Acoustic test efficiency factors are evaluated based on the Dynamic, Acoustic and Thermal Environments (DATE) instrumentation as the source of the measured vibration data. Test efficiency correction to test data is applied in the extrapolation of non-DATE acoustic test data to increase sample population size for improved statistical evaluation. For baseline criteria evaluation and development, data are grouped in accordance with the payload zone in which the component is mounted.

On, F. J.↗

Development of baseline random vibration criteria for STS pallet payloads

This paper presents a statistical evaluation of measured random vibration response data obtained from the Office of Space Science-1 (OSS-1) pallet payload. The data were measured during the acoustic test simulation (September 1980) and the ascent phase of the flight of STS-3, Orbiter 102 (launched from the Kennedy Space Center on March 22, 1982). Acoustic test efficiency factors are evaluated based on the Dynamic, Acoustic and Thermal Environments (DATE) instrumentation as the source of the measured vibration data. Test efficiency correction to test data is applied in the extrapolation of non-DATE acoustic test data to increase sample population size for improved statistical evaluation. For baseline criteria evaluation and development, data are grouped in accordance with the payload 'zone' in which the component is mounted.

On, F. J.↗

Dynamics of interfacial pattern formation

A phenomenological model of dendritic solidification incorporating interfacial kinetics, crystalline anisotropy, and a local approximation for the dynamics of the thermal diffusion field is proposed. The preliminary results are in qualitative agreement with natural dendrite-like pattern formation.

Ben-Jacob, E.↗

Solar Array Experiment (SAE) Flight Experience

The space flight testing of a large, flat, flexible panel solar array is examined. The experiment objectives are: to demonstrate the functional operational of the wind deployment and packaging system; Electrical performance; Thermal performance; and dynamic performance. A complete description of the experiment and the flight results are given.

Hill, H. C.↗

Technology for large space systems: A bibliography with indexes (supplement 11)

This bibliography contains 539 abstracts of reports, articles and other documents introduced into the NASA scientific and technical information system between January 1, 1984 and December 31, 1984. Abstracts are arranged in the following categories: systems; analysis and design techniques; structural concepts; structural and thermal analysis; structural dynamics and control; electronics; advanced materials; assembly concepts; propulsion; and miscellaneous. Subject, personal author, corporate source, contract number, report number, and accession number indexes are listed.

Source record↗

Space Shuttle Main Engine nozzle thermal protection system

Two of the three Space Shuttle Main Engine (SSME) nozzles are exposed to significant reentry aeroheating loads. To ensure reusability of the Nozzle Assembly, the nozzle primary structure must not exceed specific temperature limits. Due to the thermal, pressure, and dynamic flexing of the nozzle during a mission cycle, an appropriate insulating system must have significant flexibility. Recent missions have demonstrated nozzle reentry aeroheating rates and heat loads much higher than predictions, higher than the capability of the original insulating system. A new insulating system has been developed using similar materials in an aerodynamically 'smooth' shape to both reduce the incoming heating and increase radiation cooling.

Nordlund, R. M.↗

Evolution of primoridal gas clouds

The dynamical, chemical, and thermal evolution of zero-metal gas clouds was modeled to study conditions of star formation in the early universe. Numerical results are given for the collapse of spherical clouds of mass 1000 and 50000 solar mass. Cooling by H2 lines and by photons emitted in H + e(-) yields H(-) = h (sup nu) maintains collapse until formation of an equilibrium protostellar core of mass 0.02 solar mass. The cooling by photons produced with H is essential for low mass star formation. If the cloud is fragmented, the evolution of the pieces is similar to that of the parent cloud, but the equilibrium core has larger density and mass.

Bodenheimer, P. H.↗

Calculating Effects of Reflector-Antenna Distortions

Mathematical numerical model accurately predicts effects of systematic distortions on radiation pattern of reflector antenna. Techniques for predicting radiation patterns developed previously for reflectors with perfect surfaces and surfaces with random deviations from perfection. New model treats reflectors distorted by thermal, gravitational, and dynamic effects. Diffraction analysis of reflector antenna depends on interpolation of surface description for farfield radiation integral. Local interpolation scheme uses bicubic or higher order polynomial approximation of surface to express desired surface point in terms of nearby known surface points.

Rahmat-Samii, Y.↗

Voyager 2 at Uranus - A synopsis of atmospheric science results

Knowledge of the Uranian atmosphere took a quantum leap when the Voyager 2 spacecraft made a close approach in January 1986. Among the highlights of the early results are measurements of the atmospheric composition (He mole fraction = 0.15; Ch4 mole fraction = 0.02), rotation period of the deep interior (17.24 h), thermal structure and dynamics (the planet is coldest at midlatitudes; retrograde equatorial winds are inferred), and upper-atmosphere processes (a phenomenon called electroglow is only partly understood and is recognized as an important process n all the major-planet atmospheres examined by Voyager).

West, Robert A.↗

Structure property behavior of polyimide siloxane segmented copolymers

Procedures were developed for preparing soluble fully imidized polyimide-polydimethyl siloxane segmented copolymers of wide ranging compositions. At low siloxane levels, the materails behave as modified polyimides. At higher concentrations, the materials are analogous to thermoplastic elastomers. Characterization by dynamic mechanical and thermal analysis methods will be reported along with an assesment of the bulk mechanical properties and the surface behavior. The surface behavior is particularly interesting since the materials can be tailored to have siloxane surfaces even at rather low siloxane contents. This influences a number of properties such as the coefficient of friction and, importanly, the degradation of these materials under aggressive oxygen environments (e.g., atomic oxygen, oxygen plasma).

Arnold, C. A.↗

Near-infrared observations of Venus

Ground-based near-infrared observations of the Venus night side reveal anomalous bright features at wavelengths near 1.7 and 2.3 micrometer (Allen and Crawford, 1984; Allen, 1987). These features are thought to be formed as thermal radiation from the hot lower atmosphere leaks through holes in the middle and/or lower sulfuric acid cloud decks. Because these holes allow radiation to escape from deep in the troposphere, they provide an opportunity to significantly improve our understanding of the composition, thermal structure, and dynamics of this region of the Venus atmosphere. New near-infrared observations of the Venus night side are needed to address these questions. During the first year of this program, researchers requested and received observing time at six sites and organized a highly-skilled team. The wide array of sites should allow researchers to collect the data needed to meet all of the proposed objectives. High resolution spectra of the Venus night side was obtained. Researchers are currently collecting the first images of Venus from Kitt Peak and Table Mountain. The state-of-the-art infrared array detectors that are being used at these sites are allowing researchers to collect hundreds of high-quality images during each observing day. These images show the expected bright features, but they have not yet begun to track these features.

Crisp, D.↗

Technology for large space systems: A bibliography with indexes (supplement 20)

This bibliography lists 694 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System between July, 1988 and December, 1988. Its purpose is to provide helpful information to the researcher or manager engaged in the development of technologies related to large space systems. Subject areas include mission and program definition, design techniques, structural and thermal analysis, structural dynamics and control systems, electronics, advanced materials, assembly concepts, and propulsion.

Source record↗

Nondestructive Technique To Assess Embrittlement In Steels

Recent research at NASA Langley Research Center led to identification of nondestructive technique for detection of temper embrittlement in HY80 steel. Measures magnetoacoustic emission associated with reversible motion of domain walls at low magnetic fields. Of interest to engineers responsible for reliability and safety of various dynamically loaded and/or thermally cycled steel parts. Applications include testing of landing gears, naval vessels, and parts subjected to heat, such as those found in steam-pipe fittings, boilers, turbine rotors, and nuclear pressure vessels.

Allison, Sidney G.↗