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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The advanced thermionic converter with microwave power as an auxiliary ionization source

In the search for auxiliary sources of ionization for the advanced thermionic converter plasma, as required for terrestial applications, the use of externally applied microwave power is considered. The present work is part of the advanced model thermionic converter development research currently performed at the laboratory for Power and Environmental Studies at SUNY Buffalo. Microwave power in the frequency range 1-3 GHz is used to externally pump a thermionic converter and the results are compared to the theoretical model proposed by Lam (1976) in describing the thermionic converter plasma. The electron temperature of the plasma is found to be raised considerably by effective microwave heating which results in the disappearance of the double sheath ordinarily erected in front of the emitter. The experimental data agree satisfactorily with theory in the low current region.

Manikopoulos, C. N.↗
NASA NTRS1979

Current leakage for low altitude satellites

Ionospheric plasma densities exceeding 1,000,000 per cu cm exist around satellites in low earth orbit. Operation of large solar arrays at high voltage may drive substantial leakage currents through this surrounding plasma. Power losses exceeding solar cell output have been observed for small arrays biased above +2,000 V. Estimates of these effects for very large power systems are developed. Recent large scale (10 meter) lab tests are reported. Estimates based on calculations of space charge limited sheath dimensions are identified as a good working model, leading to projected power losses for large arrays increasing much more slowly than for small arrays.

Mccoy, J. E.↗
NASA NTRS1978

Increasing the FOD tolerance of composites

An experimental program was conducted for the purpose of increasing the foreign object damage tolerance of resin matrix composites in gas turbine engine fan blade applications. The superhybrid concept consisting of a resin matrix composite core surrounded by a sheath of boron/aluminum and titanium was found to be the most promising approach.

Novak, R. C.↗
NASA NTRS1979

Mechanisms of boron fiber strengthening by thermal treatment

The fracture strain for boron on tungsten fibers can be improved by heat treatment under vacuum or argon environments. The mechanical basis for this improvement is thermally-induced axial contraction of the entire fiber, whereby strength-controlling core flaws are compressed and fiber fracture strain increased by the value of the contraction strain. By highly sensitive measurements of fiber density and volume, the physical mechanisms responsible for contraction under both environments was identified as boron atom diffusion out of the fiber sheath. The fiber contracts because the average volume of the resulting microvoid was determined to be only 0.26 + or - 0.09 the average atomic volume of the removed atom. The basic and practical implications of these results are discussed with particular emphasis on the theory, use, and limitations of heat-induced contraction as a simple cost-effective secondary processing method.

Dicarlo, J. A.↗
NASA NTRS1979

NASCAP modelling of high-voltage power system interactions with space charged-particle environments

The NASA Charging Analyzer Program (NASCAP), an engineering tool capable of analyzing the impact of the charged particle environment on spacecraft surfaces and systems, is described. NASCAP is a quasi-static computational program which analyzes the charging of a 3-dimensional complex body as a function of time and system-generated voltages for given space environmental conditions. The material properties of the surfaces are taken into account; the surface potentials, low energy sheath, potential distribution in space and particle trajectories are calculated. An application of NASCAP to a simple space solar power station consisting of two 6 m by 18 m solar array wings surrounding a central body is presented. Each solar array wing is considered to be divided into three regions operating at 2000 volts. Results of NASCAP analysis of the system for a normal environment and a moderate geomagnetic substorm environment are discussed.

Stevens, N. J.↗
NASA NTRS1981

Gentle arrester for moving bodies

Wire cable absorbs energy at constant rate with reduced shock and rebounding. Cable typically elongates to 90 percent of its potential, but is surrounded by braided sheath to absorb remaining energy should it break prematurely. Applications of arrester include passenger restraint in air and land vehicles, parachute risers, and ground snatch by aircraft. Possible cable material is type 302 stainless steel.

Hull, R. A.↗
NASA NTRS1979

Prediction of spacecraft potentials at geosynchronous orbit

Two relatively straightforward techniques are outlined for determining spacecraft potentials in the limit of a 'thick sheath' surrounding the spacecraft. A statistical model of the various features of the geosynchronous environment based on ATS-5 and ATS-6 data and an analytic model capable of detailed simulation of the low energy geosynchronous environment are also discussed. The results from these two environmental models are then combined with the charging models in order to provide estimates of the relationships between the geomagnetic index and spacecraft potential. The results are compared with actual potential measurements from ATS-5 and ATS-6.

Garrett, H. B.↗
NASA NTRS1980

Design, fabrication, test, and qualification and price analysis of third generation design solar cell modules

The Block 4 shingle type module makes it possible to apply a photovoltaic array to the sloping roof of a residential building by simply nailing the overlapping hexagon shaped shingles to the plywood roof sheathing. This third-generation shingle module design consists of nineteen series connected 100 mm diameter solar cells which are arranged in a closely packed hexagon configuration to provide in excess of 75 watts/sq m of exposed module area under standard operating conditions. The solar cells are individually bonded to the embossed underside of a 4.4 mm thick thermally tempered piece of glass. An experimental silicone pottant was used as the transparent bonding adhesive between the cells and glass. The semi-flexible portion of each shingle module is a composite laminate construction consisting of an outer layer of FLEXSEAL bonded to an inner core of closed cell polyethylene foam. Silaprene is used as the substrate laminating adhesive. The module design has satisfactorily survived qualification testing program which includes 50 thermal cycles between -40 and +90 C, a seven day temperature-humidity exposure test, and a wind resistance test.

Shepard, N. F.↗
NASA NTRS1980

A computer model of solar panel-plasma interactions

High power solar arrays for satellite power systems are presently being planned with dimensions of kilometers, and with tens of kilovolts distributed over their surface. Such systems face many plasma interaction problems, such as power leakage to the plasma, particle focusing, and anomalous arcing. These effects cannot be adequately modeled without detailed knowledge of the plasma sheath structure and space charge effects. Laboratory studies of 1 by 10 meter solar array in a simulated low Earth orbit plasma are discussed. The plasma screening process is discussed, program theory is outlined, and a series of calibration models is presented. These models are designed to demonstrate that PANEL is capable of accurate self consistant space charge calculations. Such models include PANEL predictions for the Child-Langmuir diode problem.

Cooke, D. L.↗
NASA NTRS1979

Soil stabilization by a prokaryotic desert crust - Implications for Precambrian land biota

The ecology of the cyanophyte-dominated stromatolitic mat forming the ground cover over desert areas of Utah and Colorado is investigated and implications for the formation of mature Precambrian soils are discussed. The activation of the growth of the two species of filamentous cyanophyte identified and the mobility of their multiple trichromes upon wetting are observed, accompanied by the production and deposition of a sheath capable of accreting and stabilizing sand and clay particles. The formation of calcium carbonate precipitates upon the repeated wetting and drying of desert crust is noted, and it is suggested that the desert crust community may appear in fossil calcrete deposits as lithified microscopic tubes and cellular remains of algal trichromes. The invasion of dry land by both marine and freshwater algae on the model of the desert crust is proposed to be responsible for the accumulation, stabilization and biogenic modification of mature Precambrian soils.

Campbell, S. E.↗
NASA NTRS1980

Plasma collection by high voltage spacecraft at low earth orbit

A computer model of the three-dimensional sheath formation and plasma current collection by high voltage spacecraft has been developed. By using new space charge density and plasma collection algorithms, it is practical to perform calculations for large, complex spacecraft. The model uses NASCAP compatible objects and geometries. Results indicate that ion focusing observed in the laboratory during high voltage collection experiments is probably due to voltage gradients on the collecting surfaces.

Katz, I.↗
NASA NTRS1980

Energetic ion beam magnetosphere injection and solar power satellite transport

The effects of ion beam injection in the magnetosphere are considered. The beam's parameters are those characteristic of the ion propulsion engines envisioned for use in solar power satellite placement (Hanley and Guttman, 1978). Specifically, from a detailed analysis of the beam's propagation through the magnetosphere it is shown that the bulk of the ion beam is not stopped in the magnetosphere. However, the relatively small fraction of the beam which is deposited via the beam's sheath loss may give rise to a large distortion in the magnetospheric plasma population. Possible loss mechanisms from the magnetosphere for this artificial energetic ion component are evaluated. Electron Coulomb scattering yields the shortest lifetime throughout most of the plasmasphere provided that plasmasphere heating by beam ions is not too intense. Charge exchange dominates beyond the plasmasphere. The effects of pitch angle scattering due to beam ion turbulence may appreciably shorten beam ion lifetimes throughout the magnetosphere

Curtis, S. A.↗
NASA NTRS1982

Temperature-Controlled Support for a Seed Crystal

A rodlike structure called a sting has been proposed for supporting a seed crystal at center of a body of saturated fluid and for controlling temperature/time profile of seed for experiments on crystal growth. Seed crystal is cooled or heated by thermoelectric modules while surrounding sheath remains at solution temperature. Heat is withdrawn to cooling fins by heat pipe, which replaces solid copper rod in a previous design.

Reeve, J. L.↗
NASA NTRS1982

Weatherproof Crimp Connector

Concept for electrical connector combines environmental durability of a sealed connection with simplicity and economy of a crimped connection. Device should provide convenient and reliable outdoor electrical connections. Environmental durability and crimpability are ensured by elastomer tube and metal barrel. An external metal sheath protects elastomer from damage during crimping.

Mosna, F. J.↗
NASA NTRS1981

Theoretical investigation of the generation and injection of electromagnetic waves in space plasma by means of a long-orbiting tether

Analysis of the various mechanisms of electromagnetic wave generation by the shuttle-borne orbiting tether of the T.S.S. Facility shows that significant electrodynamic power levels are available even when overestimating the loss mechanisms expected to intervene. This electrodynamic power is in part dissipated by Joule losses in the tether, in part goes to accelerate electrons through the sheath surrounding the balloon (when in a downward deployment), and in part goes into e.m. wave generation. A preliminary estimate shows that a 100 km tether in orbit would produce ULF/ELF signals that are detectable on the ground with state-of-the-art magnetometric instrumentation.

Dobrowolny, M.↗
NASA NTRS1981

Magnetic loop behind an interplanetary shock: Voyager, Helios and IMP-8 observations

The shock was followed by a turbulent sheath in which there were large fluctuations in both the strength and direction of the magnetic field. This in turn was followed by a region (magnetic cloud) in which the magnetic field vectors were observed to change by rotating nearly parallel to a plane, consistent with the passage of a magnetic loop. This loop extended at least 30 deg in longitude between 1-2 AU, and its radial dimension was approximately 0.5 AU. In the cloud the field strength was high and the density and temperature were relatively low. Thus, the dominant pressure in the cloud was that of the magnetic field.

Burlaga, L.↗
NASA NTRS1980

Inert gas thrusters

Some advances in component technology for inert gas thrusters are described. The maximum electron emission of a hollow cathode with Ar was increased 60-70% by the use of an enclosed keeper configuration. Operation with Ar, but without emissive oxide, was also obtained. A 30 cm thruster operated with Ar at moderate discharge voltages give double-ion measurements consistent with a double ion correlation developed previously using 15 cm thruster data. An attempt was made to reduce discharge losses by biasing anodes positive of the discharge plasma. The reason this attempt was unsuccessful is not yet clear. The performance of a single-grid ion-optics configuration was evaluated. The ion impingement on the single grid accelerator was found to approach the value expected from the projected blockage when the sheath thickness next to the accelerator was 2-3 times the aperture diameter.

Kaufman, H. R.↗
NASA NTRS1980

The effect of solar array voltage patterns on plasma power losses

The use of high-voltage solar arrays in space is discussed in connection with the draining of array power by currents flowing between exposed surfaces through the surrounding plasma. The possibility of reducing the power loss by arranging solar cell strings in repeated small-area modules to eliminate any large areas at high potentials is investigated. It is found that the difference in power loss between modular and linear patterned high-voltage arrays is fairly small. Although the use of modular patterns can reduce the effective mean potential by about 10%, for the type of configuration being considered there is also a 10% increase in sheath area, leading to only a few percent change in total power loss. It is concluded that plasma power loss should not be a primary consideration in designing the physical arrangement of high-voltage arrays.

Mandell, M. J.↗