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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Statistical prediction with Kanerva's sparse distributed memory

A new viewpoint of the processing performed by Kanerva's sparse distributed memory (SDM) is presented. In conditions of near- or over-capacity, where the associative-memory behavior of the model breaks down, the processing performed by the model can be interpreted as that of a statistical predictor. Mathematical results are presented which serve as the framework for a new statistical viewpoint of sparse distributed memory and for which the standard formulation of SDM is a special case. This viewpoint suggests possible enhancements to the SDM model, including a procedure for improving the predictiveness of the system based on Holland's work with genetic algorithms, and a method for improving the capacity of SDM even when used as an associative memory.

Rogers, David↗
NASA NTRS1991

Kaolinite-catalyzed air oxidation of hydrazine: Consideration of several compositional, structural and energetic factors in surface activation

Clay minerals have been shown to have numerous, curious, energetic properties by virtue of ultra-violet light release which can be triggered by gentle environmental changes such as wetting and dewetting by a variety of liquids, unique among them water and hydrazine. Since both water and hydrazine play multiple key roles in the air-oxidation of hydrazine on kaolinite surfaces, this reaction would seem to have prime potential for studying interrelationships of energy storage, release and chemical reactivity of clay surfaces, capacities basic to either the Bernal or Cairns-Smith roles of minerals in the origin of life. Establishment of the capacity for stored electronic energy to significantly alter surface chemistry is important, regardless of the reaction chosen to demonstrate it. Hydrazine air oxidation is overawingly complex, given the possibilities for step-wise control and monitoring of parameters. In the light of recently extended characterization of the kaolinite and model sheet catalysts we used to study hydrazine oxidation and gamma-irradiated silica, previous studies of hydrazine air-oxidation on aluminosilicate surfaces have been reevaluated. Our former conclusion remains intact that, whereas trace structural and surface contaminants do play some role in the catalysis of oxidation, they are not the only, nor even the dominant, catalytic centers. Initial intermediates in the oxidation can now be proposed which are consistent with production via O(-)-centers as well as ferric iron centers. The greater than square dependence of the initial reaction rate on the weight of the clay is discussed in the light of these various mechanistic possibilities.

Coyne, L. M.↗
NASA NTRS1991

Mobile telephony through LEO satellites: To OBP or not

GLOBALSTAR is a satellite-based mobile communications system that is interoperable with the current and future Public Land Mobile Network (PLMN) and Public Switched Telephone Network (PSTN). The selection of the transponder type, bent-pipe, or onboard processing (OBP), for GLOBALSTAR is based on many criteria, each of which is essential to the commercial and technological feasibility of GLOBALSTAR. The trade study that was done to determine the pros and cons of a bent-pipe transponder or an onboard processing transponder is described. The design of GLOBALSTAR's telecommunications system is a multi-variable cost optimization between the cost and complexity of individual satellites, the number of satellites required to provide coverage to the service areas, the cost of launching the satellites into their selected orbits, the ground segment cost, user equipment cost, satellite voice channel capacity, and other issues. Emphasis is on the cost and complexity of the individual satellites, specifically the transponder type and the impact of the transponder type on satellite and ground segment cost, satellite power and weight, and satellite voice channel capacity.

Monte, Paul A.↗
NASA NTRS1992

Summary of LDEF battery analyses

Tests and analyses of NiCd, LiSO2, and LiCf batteries flown on the Long Duration Exposure Facility (LDEF) includes results from NASA, Aerospace, and commercial labs. The LiSO2 cells illustrate six-year degradation of internal components acceptable for space applications, with up to 85 percent battery capacity remaining on discharge of some returned cells. LiCf batteries completed their mission, but lost any remaining capacity due to internal degradation. Returned NiCd batteries tested an GSFC showed slight case distortion due to pressure build up, but were functioning as designed.

Johnson, Chris↗
NASA NTRS1990

Position reporting system using small satellites

A system able to provide position reporting and monitoring services for mobile applications represents a natural complement to the Global Positioning System (GPS) navigation system. The system architecture is defined on the basis of the communications requirements derived by user needs, allowing maximum flexibility in the use of channel capacity, and a very simple and low cost terminal. The payload is sketched, outlining the block modularity and the use of qualified hardware. The global system capacity is also derived. The spacecraft characteristics are defined on the basis of the payload requirements. A small bus optimized for Ariane IV, Delta II vehicles and based on the modularity concept is presented. The design takes full advantage of each launcher with a common basic bus or bus elements for a mass production.

Pavesi, B.↗
NASA NTRS1990

Advanced communications payload for mobile applications

An advanced satellite payload is proposed for single hop linking of mobile terminals of all classes as well as Very Small Aperture Terminal's (VSAT's). It relies on an intensive use of communications on-board processing and beam hopping for efficient link design to maximize capacity and a large satellite antenna aperture and high satellite transmitter power to minimize the cost of the ground terminals. Intersatellite links are used to improve the link quality and for high capacity relay. Power budgets are presented for links between the satellite and mobile, VSAT, and hub terminals. Defeating the effects of shadowing and fading requires the use of differentially coherent demodulation, concatenated forward error correction coding, and interleaving, all on a single link basis.

Ames, S. A.↗
NASA NTRS1992

Kanerva's sparse distributed memory with multiple hamming thresholds

If the stored input patterns of Kanerva's Sparse Distributed Memory (SDM) are highly correlated, utilization of the storage capacity is very low compared to the case of uniformly distributed random input patterns. We consider a variation of SDM that has a better storage capacity utilization for correlated input patterns. This approach uses a separate selection threshold for each physical storage address or hard location. The selection of the hard locations for reading or writing can be done in parallel of which SDM implementations can benefit.

Pohja, Seppo↗
NASA NTRS1992

Tailored metal matrix composites for high-temperature performance

A multi-objective tailoring methodology is presented to maximize stiffness and load carrying capacity of a metal matrix cross-ply laminated at elevated temperatures. The fabrication process and fiber volume ratio are used as the design variables. A unique feature is the concurrent effects from fabrication, residual stresses, material nonlinearity, and thermo-mechanical loading on the laminate properties at the post-fabrication phase. For a (0/90)(sub s) graphite/copper laminate, strong coupling was observed between the fabrication process, laminate characteristics, and thermo-mechanical loading. The multi-objective tailoring was found to be more effective than single objective tailoring. Results indicate the potential to increase laminate stiffness and load carrying capacity by controlling the critical parameters of the fabrication process and the laminate.

Morel, M. R.↗
NASA NTRS1992

Progress update of NASA's free-piston Stirling space power converter technology project

A progress update is presented of the NASA LeRC Free-Piston Stirling Space Power Converter Technology Project. This work is being conducted under NASA's Civil Space Technology Initiative (CSTI). The goal of the CSTI High Capacity Power Element is to develop the technology base needed to meet the long duration, high capacity power requirements for future NASA space initiatives. Efforts are focused upon increasing system power output and system thermal and electric energy conversion efficiency at least five fold over current SP-100 technology, and on achieving systems that are compatible with space nuclear reactors. This paper will discuss progress toward 1050 K Stirling Space Power Converters. Fabrication is nearly completed for the 1050 K Component Test Power Converter (CTPC); results of motoring tests of the cold end (525 K), are presented. The success of these and future designs is dependent upon supporting research and technology efforts including heat pipes, bearings, superalloy joining technologies, high efficiency alternators, life and reliability testing, and predictive methodologies. This paper will compare progress in significant areas of component development from the start of the program with the Space Power Development Engine (SPDE) to the present work on CTPC.

Dudenhoefer, James E.↗
NASA NTRS1991

A space transfer vehicle for lunar missions

Two 'low profile' strategies for supporting the lunar outpost concept developed by NASA-JSC Planetary Surface Systems are examined. The first strategy involves the design of missions that require only a single launch of a derivative 'National Launch System' (NLS) vehicle. The launch capacity of the derivatives range from 80 to 140 percent of the Apollo/Saturn capacity and use only conventional cryogenic or stable chemical propulsion. The second strategy involves the design of missions that only require the currently planned NASA NLS vehicle to be built. This strategy uses either one or two launches with an earth and/or lunar orbit rendezvous for stage assembly. Advance propulsion concepts, in addition to cryogenics, for the translunar injection stage are addressed.

Andrews, Dana↗
NASA NTRS1991

A comparison of cooling methods for the airframe nozzle of a single-stage-to-orbit aircraft

A comparison is made between two different cooling schemes, including a complete system thermal analysis and weight accounting for each. A hydrogen-direct system operates at a higher pressure (34.5 Mpa) and greater temperature rise in the coolant. There is no temperature limit on the coolant itself and high injector temperatures may be achieved, but the pressure lines must be routed over great distances (10 m). The system is simple, and the coolant is almost weightless. In contrast, an indirect system operates at a lower pressure (3.8n MPa) and the liquid coolant has a much greater thermal capacity. The greater thermal capacity causes much less of a temperature rise in the coolant. The chosen coolant is Syltherm 800. This nontoxic fluid is compatible with any metal, including titanium. The loop requires a separate fuel/coolant heat exchanger and coolant pump. The indirect system offers some distinct safety advantages but is heavier than the direct hydrogen coolant system.

Jones, Stuart C.↗
NASA NTRS1992

Vegetation canopy PAR absorptance and the normalized difference vegetation index - An assessment using the SAIL model

Relationships are studied between the normalized-difference vegetation index (NDVI) and absorbed photosynthetically active radiation (APAR) in a vegetation canopy. The SAIL model of bidirectional canopy radiative transfer is employed to compare NDVI measurements that are instantaneous with diurnally integrated canopy APAR capacity. The NDVI measurements - taken at solar-zenith angles of more than 60 deg and sensor views of less than 40 deg from nadir - give stable near-linear estimates of diurnal APAR capacity. Discrepancies in the relations between APAR and NDVI are associated with variations in the optical properties of the canopy and with background spectral reflectance. The results are significant for the practical use of these remote sensing techniques but suggest that instantaneous observations can be used to characterize the diurnally integrated APAR in vegetation canopies.

Goward, Samuel N.↗
NASA NTRS1990

Calorimetric determination of thermal parameters for the Li/BrCl in SOCl2 (BCX) chemistry

The heat capacity of a Li-BCX DD-cell was found to be dependent on its state of charge by drop calorimetry measurements. The method of drop calorimetry involves measuring the energy (joules) gained or lost from a sample that is transferred from a bath at temperature A to one at temperature B. The thermoneutral potential is defined as the cell potential where the cell electrochemical reactions are neither exothermic nor endothermic. A Hart scientific calorimeter system, Model No. S77XX, designed for heat conduction calorimetry and drop calorimetry was used. Calorimetric analysis yielded a thermoneutral potential of 4.14 volts and a cell heat capacity dependent on the state of charge.

Darcy, Eric C.↗
NASA NTRS1990

Low temperature performance of lithium/silver vanadium oxide cells

Lithium/silver vanadium oxide cells for low temperature applications have been developed. Prismatic and spirally wound AA cells were tested under constant load discharge of 0.3 to 1.8 amps or pulse discharge of 0.225 or 1.0 amps at temperatures from -40 to 25 C. At -40 C with current densities of 2.5 mA/cm2, 23 percent of theoretical capacity was achieved under constant load discharge and 40 percent of theoretical capacity was achieved under pulse test. Self-discharge estimates of 0.7 percent per year at 25 C were obtained from microcalorimetry. Preliminary safety testing of the cells revealed no violent performance under short circuit or crush tests.

Takeuchi, E. S.↗
NASA NTRS1992

Experimental investigation of freezing blowby in a copper/water heat pipe

An experimental investigation designed to evaluate and better define the overall characteristics of freezing blowby in a copper/water heat pipe was conducted. The results from various rates of restart heat addition and channel blockage, indicate that upon breakthrough the depressurization of the evaporator may result in an effective heat transport capacity far in excess of the steady-state transport limit. The resulting transient conditions imposed on the heat pipe by the effective increased heat transport capacity can cause a loss of liquid in the evaporator and potential dryout. Evidence is presented which indicates that in order to prevent either temporary or permanent dryout, sufficient liquid inventory must be present in the evaporator wicking structure to accommodate the increased transient thermal load and allow sufficient time for the capillary wicking structure to reprime.

Ochterbeck, J. M.↗
NASA NTRS1992

Cardiovascular orthostatic function of Space Shuttle astronauts during and after return from orbit

Routine entry, landing, and seat egress after Space Shuttle flights is observed to be associated with drops in blood pressure and increases in heart rate that indicate that the cardiovascular system is performing at its maximum capacity in a large fraction (30 percent) of the study population. It is not apparent that adequate cardiovascular reserve capacity remains to accommodate unaided emergency egress after either current or extended space flights.

Charles, John B.↗
NASA NTRS1992

The effects of in-flight treadmill exercise on postflight orthostatic tolerance

In-flight aerobic exercise is thought to decrease the deconditioning effects of microgravity. Two deconditioning characteristics are the decreases in aerobic capacity (maximum O2 uptake) and an increased cardiovascular response to orthostatic stress (supine to standing). Changes in both parameters were examined after Shuttle flights of 8 to 11 days in astronauts who performed no in-flight exercise, a lower than normal volume of exercise, and a near-normal volume of exercise. The exercise regimen was a traditional continuous protocol. Maximum O2 uptake was maintained in astronauts who completed a near-normal exercise volume of in-flight exercise. Cardiovascular responses to stand test were equivocal among the groups. The use of the traditional exercise regimen as a means to maintain adequate orthostatic responses produced equivocal responses. A different exercise prescription may be more effective in maintaining both exercise capacity and orthostatic tolerance.

Siconolfi, Steven F.↗
NASA NTRS1992

ICAN/DAMP-integrated composite analyzer with damping analysis capabilities: User's manual

This manual describes the use of the computer code ICAN/DAMP (Integrated Composite Analyzer with Damping Analysis Capabilities) for the prediction of damping in polymer-matrix composites. The code is written in FORTRAN 77 and is a version of the ICAN (Integrated Composite ANalyzer) computer program. The code incorporates a new module for synthesizing the material damping from micromechanics to laminate level. Explicit micromechanics equations based on hysteretic damping are programmed relating the on-axis damping capacities to the fiber and matrix properties and fiber volume ratio. The damping capacities of unidirectional composites subjected to off-axis loading are synthesized from on-axis damping values. The hygrothermal effect on the damping performance of unidirectional composites caused by temperature and moisture variation is modeled along with the damping contributions from interfacial friction between broken fibers and matrix. The temperature rise is continuously vibrating composite plies and composite laminates is also estimated. The ICAN/DAMP user's manual provides descriptions of the damping analysis module's functions, structure, input requirements, output interpretation, and execution requirements. It only addresses the changes required to conduct the damping analysis and is used in conjunction with the 'Second Generation Integrated Composite Analyzer (ICAN) Computer Code' user's manual (NASA TP-3290).

Saravanos, Dimitrious A.↗