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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Advanced ion thruster research

A series of experiments conducted on a ring cusp magnetic field ion thruster; in which the anode, cathode and discharge chamber backplate were moved relative to the magnetic cusp; are described. Optimum locations for the anode, cathode and backplate which yield the lowest energy cost per plasma ion and highest extracted ion fraction are identified. The results are discussed in terms of simple physical models. The results of preliminary experiments into the operation of hollow cathodes on nitrogen and xenon over a large pressure range (0.1 to 100 Torr) are presented. They show that the cathode discharge transfers from the cathode insert to the exterior edge of the orifice plate as the interelectrode pressure is increased. Experimental evidence showing that a new ion extractor grid concept can be used to stabilize the plasma sheath at the screen grid is presented. This concept, identified by the term constrained sheath optics, is shown to hold ion beamlet divergence and impingement characteristics to stable values as the beamlet current and the net and total accelerating voltages are changed. The current status of a study of beamlet vectoring induced by displacing the accelerator and/or decelerator grids of a three grid ion extraction system relative to the screen grid is discussed.

Wilbur, P. J.↗
NASA NTRS1984

A high performance magnetoplasmadynamic thruster

A flared-anode MPD thruster has been modified to permit injection of propellant through the backplate near the anode wall. At 6 g/sec argon, this thruster displays an onset current of 41.4 kA, almost double the value observed for propellant injection at the cathode and intermediate radial positions. A magnetic field survey of the interelectrode region shows current density is highest at the upstream and downstream ends of the chamber. The operating efficiency at onset current inferred from magnetic field data exceeds 50 percent, but swinging-gate thrust stand measurements reveal a progressive divergence between inferred and actual thrust with increasing power. Near onset, the measured thrust is approximately 20 percent lower than that inferred from magnetic probing. Explanations for this behavior have been explored with viscous drag emerging as the most probable cause of performance degradation.

Wolff, M.↗
NASA NTRS1985

Electronic readout systems for microchannel plates

The modes of operation of position-sensitive electronic readout systems which use high-gain microchannel plate (MCP) electron multipliers are described, and their performance characteristics, along with those of the MCP, are compared. Among the structures presented are the wedge-and-strip, Codacon, and multilayer coincidence-anode MAMA (Multimode Microchannel Array) arrays. Spatial resolution of 25 x 25 sq microns (coincidence anode arrays) is achieved with an array format of 256 x 1024 pixels. On the basis of the performance data it is concluded that the readout systems using only conducting electrodes offer the best performance characteristics.

Timothy, J. G.↗
NASA NTRS1984

Corrosion behavior of magnetron sputter-deposited (Mo/0.6/Ru/0.4/)82B18 and Mo82B18 amorphous metal films

Amorphous metallic films of Mo49Ru33B18 and Mo82B18 have been prepared by magnetron sputtering, and their corrosion behavior was investigated and compared with amorphous liquid-quenched Mo49Ru33B18 and crystalline Mo i acidic and basic solutions. Sputtered Mo49Ru33B18 showed lower corrosion rates compared with liquid-quenched Mo49Ru33B18, owing to the superior surface smoothness and uniformity of the former. Amorphous Mo82B18 showed low corrosion rates in both acidic and basic aqueous solutions. Comparison of the corrosion properties of Mo49Ru33B18 with Mo82B18 and Mo demonstrates the roles of the alloys' constituents. Ru significantly extends the passive region to high-anodic potentials, but, at less-anodic potentials, Mo82B18 has the lowest corrosion rate.

Williams, R. M.↗
NASA NTRS1985

Magnetoplasmadynamic thruster erosion research

Magnetoplasmadynamic thruster (MPdT) lifetime at sustained multimagawatt power levels is unknown but will be governed by plasma erosion of thruster surfaces. Before the thruster can be developed for an orbital propulsion application the physics of the erosion mechanisms must be studied. The following key questions that must be resolved to understand erosion are addressed: (1) what are the erosion mechanisms on the anode, cathode, and insulator and what are the quantitative rates for each; (2) what governs the cathode heat balance at high current density and magawatt power levels; (3) what governs the anode heat balance; and (4) how does the cathode work function change with time, and what effect does this have on erosion. The approach aims at developing an understanding of the erosion of the electrode and insulator surfaces by conducting experiments on a steady-state, scaled-down MPD device, and by analysis of key processes.

King, D. Q.↗
NASA NTRS1986

Development of composite tube protective coatings

Protective coatings for graphite/epoxy (Gr/Ep) tubular structures proposed for the Space Station are evaluated. The program was divided into four parts; System Definition, Coating Concept Selection and Evaluation, Scale-up and Assembly, and Reporting. System Definition involved defining the structural and environmental properties required of the Gr/Ep tubes. The prepreg and ply sequence selected was a P75S/934 (O2, + or - 20, O2)sub s layup which meets the various structural requirements of the Space Station. Coating Concept and Selection comprised the main emphasis of the effort. Concepts for protectively coating the Gr/Ep tubes included the use of metal foil and electroplating. The program results demonstrated that both phosphoric and chromic acid anodized Al foil provided adequate adhesion to the Gr/Ep tubes and stability of optical properties when subjected to atomic oxygen and thermal cycling representative of the LEO environment. SiO2/Al coatings sputtered onto Al foils also resulted in an excellent protective coating. The electroplated Ni possessed unacceptable adhesion loss to the Gr/Ep tubes during atomic oxygen testing. Scale-Up and Assembly involved fabricating and wrapping 8-ft-long by 2-in-diameter Gr/EP tubes with chromic acid anodized foil and delivering these tubes, along with representative Space Station erectable end fittings, to NASA LaRC.

Dursch, H.↗
NASA NTRS1986

Observation of radiative surface plasmons in metal-oxide-metal tunnel junctions

A peak in the UV region of the spectrum of light emitted from metal-oxide-metal (MOM) tunnel junctions has been observed at room temperature. Both the amplitude and wavelength of the peak are sensitive to applied junction bias. The UV peak corresponds to the normal or radiative surface plasmon mode while a visible peak, also present in the present spectra and reported in past MOM literature, is due to the tangential or nonradiative mode. The radiative mode requires no surface roughness or gratings for photon coupling. The results show that it is possible to obtain radiative surface plasmon production followed by a direct decay into photons with MOM tunnel diodes. A MOM diode with a double anode structure is found to emit light associated only with the nonradiative mode. The thickness dependence of the UV peak, along with the experimental results of the double anode MOM diode and the ratio of the UV peak to visible peak, support the contention that the UV light emission is indeed due to the radiative surface plasmon.

Donohue, J. F.↗
NASA NTRS1986

The NASA Aerospace Battery Safety Handbook

This handbook has been written for the purpose of acquainting those involved with batteries with the information necessary for the safe handling, storage, and disposal of these energy storage devices. Included in the document is a discussion of the cell and battery design considerations and the role of the components within a cell. The cell and battery hazards are related to user- and/or manufacturer-induced causes. The Johnson Space Center (JSC) Payload Safety Guidelines for battery use in Shuttle applications are also provided. The electrochemical systems are divided into zinc anode and lithium anode primaries, secondary cells, and fuel cells. Each system is briefly described, typical applications are given, advantages and disadvantages are tabulated, and most importantly, safety hazards associated with its use are given.

Halpert, Gerald↗
NASA NTRS1986

A study of pulse surface flashover in a vacuum

The prebreakdown phenomenon of pulsed surface flashover across solid insulators has been observed in a vacuum using image converter photography. A very good time and space resolution has been obtained. In summary, it was found that visible light (low luminosity) is initially emitted from the cathode and the light front propagates at a constant speed of approximately 1 X 10 to the 7th power ms. This low luminous light has a banded structure corresponding to the electron hopping distance as proposed in theoretical flashover models, and the light intensity gradually increases as it travels towards the anode. The bright light starts from the anode and expands towards the cathode, bridging the gap within 0.5 ns.

Lakdawala, Vishnukumar K.↗
NASA NTRS1987

Development of ambient temperature secondary lithium cells

JPL is developing ambient temperature secondary lithium cells for future spacecraft applications. Prior studies on experimental laboratory type Li-TiS2 cells yielded promising results in terms of cycle life and rate capability. To further assess the performance of this cell, 5 Ah engineering model cells were developed. Initially baseline cells were designed and fabricated. Each cell had 15 cathodes and 16 anodes and the ratio of anode to cathode capacity is 6:1. A solution of 1.5 molar LiAsF6 in 2Me-THF was used as the electrolyte. Cells were evaluated for their cycle life at C/1 and C/5 discharge rates and 100 percent depth of discharge. The cells were cycled between voltage limits 1.7 and 2.8 volts. The rate of charge in all cases is C/10. The results obtained indicate that cells can operate at C/10 to C/2 discharge rates and have an initial energy density of 70 Wh/kg. Cells delivered more than 100 cycles at C/2 discharge rate. The details of cell design, the test program, and the results obtained are described.

Subbarao, S.↗
NASA NTRS1985

Concentration of carbon dioxide by a high-temperature electrochemical membrane cell

The performance of a molten carbonate carbon dioxide concentrator (MCCDC) cell, as a device for removal of CO2 from manned spacecraft cabins without fuel expenditure, is investigated. The test system consists of an electrochemical cell (with an Li2CO3-38 mol pct K2CO3 membrane contained in a LiAlO2 matrix), a furnace, and a flow IR analyzer for monitoring CO2. Operation of the MCCDC-driven cell was found to be suitable for the task of CO2 removal: the cell performed at extremely low CO2 partial pressures (at or above 0.1 mm Hg); cathode CO2 efficiencies of 97 percent were achieved with 0.25 CO2 inlet concentration at 19 mA sq cm, at temperatures near 873 K. Anode concentrations of up to 5.8 percent were obtained. Simple cathode and anode performance equations applied to correlate cell performance agreed well with those measured experimentally. A flow diagram for the process is included.

Kang, M. P.↗
NASA NTRS1986

A position sensitive microchannel photomultiplier for ultraviolet space astronomy

The 25-mm microchannel-plate, position-sensitive UV astronomy photomultiplier tube presented is intended for the EOM-1 Spacelab Mission's FAUST payload and conducts wide-field imaging surveys in the VUV over the 1400-1800-A range. The sealed detector encompasses a CsI photocathode deposited on the inner surface of a MgF2 window, a stack of microchannel plates, and a wedge-and-strip two-dimensional position-sensing anode. Since the wedge-and-strip principle requires only three anode signals, flight electronics can be reduced to three charge amplifiers and three analog-to-digital converters.

Lampton, M.↗
NASA NTRS1986

Hybrid analog/digital, large format, photon counting detectors for astronomy

The development of a new microchannel plate photon-counting detector with an analog readout method based on a resistive anode is reported. This detector exhibits extremely high, stable electron gains of 10 to the 8th. At this gain, the spatial resolution is no longer primarily limited by the noise of the resistive anode, so that digital methods of readout, such as discrete conductors, lose their advantage. These detectors can be readily scaled to 40 mm and 70 mm formats to match plate scales of 2-m (and larger) telescopes. New, high speed digital electronics fully exploit the high spatial and time resolution made possible by gains of this level. Analysis of the theoretical performance of this detector shows that the major limitation to the spatial resolution is the proximity focus of the photocathode and the first microchannel plate. The detector has been mated to an echelle spectrograph developed.

Crocker, J.↗
NASA NTRS1986

Application of wedge and strip image readout systems to detectors for astronomy

Microchannel plate (MCP) detector systems that use wedge and strip anodes for imaging radiation in the range 50 A to 8000 A are described. Test data, obtained from the calibration of the Extreme Ultraviolet Explorer Satellite detectors and the ARIA EUV aeronomy sensor is presented. The long-term performance characteristics of Z-stack microchannel plates are investigated and it is shown that stable operation is achieved after an initial settling period. Conventional and new anode designs and their potential for increasing the position resolution are discussed. Position resolution of better than 80 microns FWHM has been attained for 50 mm devices, and this is shown to be essentially independent of event location. Image nonlinearity of less than 0.3 percent has been achieved with stability to better than 0.1 percent. Differential nonlinearity of less than 1 percent and stability to better than 1 percent have been obtained. Measurements of the quantum efficiency of a CsI photocathode on an MCP are presented, demonstrating efficiencies as high as 47 percent.

Siegmund, O. H. W.↗
NASA NTRS1986

Hollow cathode plasma coupling study, 1986

The electron collection and emission characteristics of a simple hollow cathode contactor, an extended anode hollow cathode contactor supplied by JSC, and a ring cusp magnetic field contactor are presented and the effects of discharge power and argon or xenon expellant flowrate on these characteristics are examined. All of the contactors are shown to exhibit good electron emission performance over a wide range of discharge power and expellant type and flowrate. Good electron performance is shown to be more difficult to achieve. Results suggest that the extended anode and ring cusp contactors should perform satisfactorily to electron emission currents beyond 1000 mA and electron collection currents beyond 500 mA. All contactors performed better on xenon than argon. A general theory of plasma contactor operation in both the electron collection and electron emission modes, which describes the current-limiting effects of space-charge phenomena is given. This current-limiting and collecting phenomenon is shown to be a function of driving potential differences and emitting and collecting surface radius ratio for the case of a spherical geometry. Discharge power did not appear to influence the electron collection current substantially in the experiments so it is suggested in light of the model that the contactors are generally not limited by their ion production capabilities under conditions at which they were tested.

Wilbur, Paul J.↗
NASA NTRS1988

Space plasma contactor research, 1987

A simple model describing the process of electron collection from a low pressure ambient plasma in the absence of magnetic field and contactor velocity effects is presented. Experimental measurments of the plasma surrounding the contactor are used to demonstrate that a double-sheath generally develops and separates the ambient plasma from a higher density, anode plasma located adjacent to the contactor. Agreement between the predictions of the model and experimental measurements obtained at the electron collection current levels ranging to 1 A suggests the surface area at the ambient plasma boundary of the double-sheath is equal to the electron current being collected divided by the ambient plasma random electron current density; the surface area of the higher density anode plasma boundary of the double-sheath is equal to the ion current being emitted across this boundary divided by the ion current density required to sustain a stable sheath; and the voltage drop across the sheath is determined by the requirement that the ion and electron currents counterflowing across the boundaries be at space-charge limited levels. The efficiency of contactor operation is shown to improve when significant ionization and excitation is induced by electrons that stream from the ambient plasma through the double-sheath and collide with neutral atoms being supplied through the hollow cathode.

Wilbur, Paul J.↗
NASA NTRS1988

Construction and evaluation of an imaging focussed-mesh electron multiplier for space instrumentation

A focused-mesh electron multiplier (FMEM) has been combined with a wedge and strip position-sensitive anode to create a novel detector that is considered likely to have a number of applications in space astronomy and laboratory image sensing. Results from the first application of a wedge and strip anode to an FMEM are presented including spatial resolution, spatial linearity, background rate, and pulse risetime. The converted multiplier retains the attributes of an FMEM that made it attractive in the first place, such as low background, high speed, and high dynamic range.

Vallerga, J.↗
NASA NTRS1988

Analysis of a used pair of arcjet electrodes

The anode and cathode of a 30-kW class arcjet engine have been sectioned and analyzed. This arcjet was operated for a total time of 573 hours at power levels between 25 and 30 kW with ammonia at flow rates of 0.25 and 0.27 gm/s. The accumulated run time was sufficient to clearly establish erosion patterns and their causes. The type of electron emission from various parts of the cathode surface was made clear by Scanning Electron Microscope analysis. A Scanning Electron Microscope was used to study recrystallization on the hot anode surface. These electrodes were made of 2 percent thoriated tungsten and the surface thorium content and gradient perpendicular to the surfaces was determined by quantitative microprobe analysis. The results of this material analysis on the electrodes and recommendations for improving electrode operational life time are presented.

Pivirotto, Thomas J.↗