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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 577 records · Page 32

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NASA NTRS1988

Modeling and optimum time performance for concurrent processing

The development of a new graph theoretic model for describing the relation between a decomposed algorithm and its execution in a data flow environment is presented. Called ATAMM, the model consists of a set of Petri net marked graphs useful for representing decision-free algorithms having large-grained, computationally complex primitive operations. Performance time measures which determine computing speed and throughput capacity are defined, and the ATAMM model is used to develop lower bounds for these times. A concurrent processing operating strategy for achieving optimum time performance is presented and illustrated by example.

Mielke, Roland R.↗

NASA NTRS1987

Monolithic Microwave Integrated Circuit (MMIC) technology for space communications applications

Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. For the more distant future pseudomorphic indium gallium arsenide (InGaAs) and other advanced III-V materials offer the possibility of MMIC subsystems well up into the millimeter wavelength region. All of these technology elements are in NASA's MMIC program. Their status is reviewed.

Connolly, Denis J.↗

NASA NTRS1987

Performance test of a laboratory pump liquid transfer based on the fountain effect

A laboratory scale pump has been tested in detail in order to determine the flow characteristics of a heater-activated all-metal thermomechanical pump (fountain effect pump, FEP). The emphasis is on the functional dependence of the fountain pressure difference versus mass throughput. A modified Vote et al. (1971) power law approximation is employed for a simplified description of the flow rate as a function of the driving force. Flow rates of up to 10 liters/(hr/sq cm) have been obtained despite a large nominal pore size of the porous plug of 2 microns (filtration rating) used for the FEP.

Chen, W. E. W.↗

NASA NTRS1987

Spread-spectrum multiple access using wideband noncoherent MFSK

Two spread-spectrum multiple access systems which use wideband M-ary frequency shift keying (FSK) (MFSK) as the primary modulation are presented. A bit error rate performance analysis is presented and system throughput is calculated for sample C band and Ku band satellite systems. Sample link analyses are included to illustrate power and adjacent satellite interference considerations in practical multiple access systems.

Ha, Tri T.↗

NASA NTRS1987

Telemetry handling on the Space Station data management system

This paper examines the impact of telemetry handling on the design of the onboard networks that are part of the Space Station Data Management System (DMS). An architectural approach to satisfying the DMS requirement for support of the high throughput needed for telemetry transport and for servicing distributed computer systems is discussed. Several of the functionality vs. performance tradeoffs that must be made in developing an optimized mechanism for handling telemetry data in the DMS are considered.

Whitelaw, Virginia A.↗

NASA NTRS1987

Data relay system for Space Shuttle and payload pre-launch checkout

Engineering requirements and design characteristics of the coherent throughput relay system which supports the East Coast prelaunch checkout of NASA's Space Shuttle and its payloads are presented. Link requirements and design constraints are reviewed, and gain/loss analysis is given. Group delay distortion is considered and isolation and antenna siting are discussed. The systems controlling various aspects of the relays are examined.

O'Donnell, Hugh B.↗

NASA NTRS1988

Figured grazing incidence mirrors from reheated float glass

High throughput grazing incidence mirrors have been fabricated from float glass using a new inexpensive technique. An array of twelve such mirrors including grazing angles from 3 to 15 deg has been fabricated and tested. Optical measurement of this array shows a line spread function of 6.3-min of arc FWHM with 90 percent of the energy enclosed within 13 min of arc. Three-mirror arrays are used to provide one-dimensional focusing for a diffuse extreme ultraviolet spectrometer. This paper presents the fabrication techniques and testing procedures used, as well as the mirror performance results.

Labov, Simon E.↗

NASA NTRS1987

Model of hot-film sensor with substrate

A detailed model is constructed to investigate parameters influencing a hot-film anemometer system used to study cross-flow phenomena on swept wings. This anemometer is designed to detect vortices set up by cross-flow. The nature of the vortices is not well known, and a well-verified instrumentation model is considered essential to allow accurate interpretation of experimental results. Previous investigators have indicated that heat conduction to the film's substrate is significant. Two variations on the inclusion of substrate effects in the model are discussed. In the first, the substrate is assumed to have a constant temperature throughput: in the second more elaborate model, the temperature of the substrate is allowed to vary. This variation is related to the convective heat removal at the substrate/gas interface.

Mcree, Griffith J.↗

NASA NTRS1987

Contamination control approach for the Extreme Ultraviolet Explorer satellite instrumentation

The Extreme Ultraviolet Explorer will perform an all-sky survey and spectroscopic observations over the wavelength range 80-900A. Hydrocarbon and particulate contamination will potentially affect the throughput and signal to noise ratio of the signal detected by the instruments. A witness sample program is here used to investigate and monitor the effects of specific contaminants on EUV reflectivity. Witness samples were intentionally contaminated with thin layers of pump oil. An oil layer 150 A thick was applied and found to evaporate over 8 hours. The EUV reflectivity and imaging properties were then measured and found to be acceptable for grazing angles between 5 and 30 deg. In a second test, layers 500 A thick were deposited and then allowed to evaporate in vacuum; once the oil had evaporated to at least 350 A, the final sample reflectivity was degraded less than 10 percent, but the image was degraded severely by scattering. An outline of the contamination control program is also presented.

Mrowka, Stan↗

NASA NTRS1988

The ATAMM procedure model for concurrent processing of large grained control and signal processing algorithms

An overview is presented of a model for describing data and control flow associated with the execution of large-grained, decision-free algorithms in a special distributed computer environment. The ATAMM (Algorithm-To-Architecture Mapping Model) model provides a basis for relating an algorithm to its execution in a dataflow multicomputer environment. The ATAMM model features a marked graph Petri net description of the algorithm behavior with regard to both data and control flow. The model provides an analytical basis for calculating performance bounds on throughput characteristics which are demonstrated here.

Stoughton, John W.↗

NASA NTRS1988

Commercial aspects of epitaxial thin film growth in outer space

A new concept for materials processing in space exploits the ultra vacuum component of space for thin film epitaxial growth. The unique low earth orbit space environment is expected to yield 10 to the -14th torr or better pressures, semiinfinite pumping speeds and large ultra vacuum volume (about 100 cu m) without walls. These space ultra vacuum properties promise major improvement in the quality, unique nature, and the throughput of epitaxially grown materials especially in the area of semiconductors for microelectronics use. For such thin film materials there is expected a very large value added from space ultra vacuum processing, and as a result the application of the epitaxial thin film growth technology to space could lead to major commercial efforts in space.

Ignatiev, Alex↗

NASA NTRS1988

Performance test of a laboratory pump for liquid transfer based on the fountain effect

A laboratory scale pump which determines the flow characteristics of a heater-activated all-metal thermomechanical fountain-effect pump (FEP) is evaluated. Results are presented on the functional dependence of the fountain pressure difference versus mass throughput. A modified Vote et al. (1971) power law approximation is used to obtain the flow rate as a function of the driving force. Despite a large nominal pore size of the porous plug used for the FEP, flow rates of up to 10 liter/hr sq cm have been obtained.

Chen, W. E. W.↗

NASA NTRS1989

Strain-Layer-Superlattice Light Modulator

Conceptual device combines resonant reflection and photovoltaic action to enable one light beam to impose spatial and temporal modulation on another light beam. Such spatial light modulator, with high speed and multiplicity of parallel signal channels, used in image processing or similar computation requiring high data-throughput rates. Microstructures of GaAs and InAs with multiple quantum wells and compositional superlattices grown by molecular-beam epitaxy. Enhanced electro-optical properties of arrangement of alternating layers enables writing light beam to modulate reading light beam.

Maserjian, Joseph↗

NASA NTRS1989

Balanced-Load Real-Time Multiprocessor System

Modularity and parallelism provide tolerance to faults and high throughput capacity. System, called MAX, is network of interconnected computers. MAX cluster consists of group of modules - each semiautonomous computer. Modules connected to each other and to other clusters by global bus and circuit-switched communication mesh.

Rasmussen, Robert D.↗

NASA NTRS1989

Dynamic Transfers Of Tasks Among Computers

Allocation scheme gives jobs to idle computers. Ideal resource-sharing algorithm should have following characteristics: Dynamics, decentralized, and heterogeneous. Proposed enhanced receiver-initiated dynamic algorithm (ERIDA) for resource sharing fulfills all above criteria. Provides method balancing workload among hosts, resulting in improvement in response time and throughput performance of total system. Adjusts dynamically to traffic load of each station.

Liu, Howard T.↗

NASA NTRS1987

Teleoperated position control of a PUMA robot

A laboratory distributed computer control teleoperator system is developed to support NASA's future space telerobotic operation. This teleoperator system uses a universal force-reflecting hand controller in the local iste as the operator's input device. In the remote site, a PUMA controller recieves the Cartesian position commands and implements PID control laws to position the PUMA robot. The local site uses two microprocessors while the remote site uses three. The processors communicate with each other through shared memory. The PUMA robot controller was interfaced through custom made electronics to bypass VAL. The development status of this teleoperator system is reported. The execution time of each processor is analyzed, and the overall system throughput rate is reported. Methods to improve the efficiency and performance are discussed.

Austin, Edmund↗

NASA NTRS1988

WF/PC internal molecular contamination during system thermal-vacuum test

During the recent system thermal vacuum test of the Wide-Field/Planetary Camera (WF/PC), instrumentation was added to the WF/PC to characterize the internal molecular contamination and verify the instrument throughput down to 1470 angstroms. Analysis of data elements revealed two contaminants affecting the far-ultraviolet (FUV) performance of the WF/PC. The one contaminant (heavy volatile) is correlated with the electronic and housing temperature, and the contamination is significantly reduced when the electronics are operated below plus 8 degrees to plus 10 degrees C. The other contaminant (light volatile) is controlled by the heat pipe temperature, and the contamination is significantly reduced when the Thermal Electric Cooler (TEC) hot-junction temperature is below minus 40 degrees to minus 50 degrees C. The utility of contamination sensors located behind instruments during system tests was demonstrated.

Taylor, Daniel M.↗

NASA NTRS1988

A consideration of the use of optical fibers to remotely couple photometers to telescopes

The possible use of optical fibers to remotely couple photometers to telescopes is considered. Such an application offers the apparent prospect of enhancing photometric stability as a consequence of the benefits of remote operation and decreased sensitivity to image details. A properly designed fiber optic coupler will probably show no significant changes in optical transmisssion due to normal variations in the fiber configuration. It may be more difficult to eliminate configuration-dependent effects on the pupil of the transmitted beam, and thus achieve photometric stability to guiding and seeing errors. In addition, there is some evidence for significant changes in the optical throughputs of fibers over the temperature range normally encountered in astronomical observatories.

Heacox, William D.↗