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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Design and initial application of the extended aircraft interrogation and display system: Multiprocessing ground support equipment for digital flight systems

A pipelined, multiprocessor, general-purpose ground support equipment for digital flight systems has been developed and placed in service at the NASA Ames Research Center's Dryden Flight Research Facility. The design is an outgrowth of the earlier aircraft interrogation and display system (AIDS) used in support of several research projects to provide engineering-units display of internal control system parameters during development and qualification testing activities. The new system, incorporating multiple 16-bit processors, is called extended AIDS (XAIDS) and is now supporting the X-29A forward-swept-wing aircraft project. This report describes the design and mechanization of XAIDS and shows the steps whereby a typical user may take advantage of its high throughput and flexible features.

Glover, Richard D.↗
NASA NTRS1987

Error control techniques for satellite and space communications

During the period June 1, 1986 through November 30, 1986, progress was made in the following areas: undetected error probability and throughput analysis of a concatenated coding scheme; capacity and cutoff rate analysis of concatenated codes; concatenated codes using bandwidth efficient trellis inner codes; bounds on the minimum free Euclidean distance of bandwidth efficient trellis codes; and construction of multidimensional bandwidth efficient trellis codes for use as inner codes in a concatenated coding system.

Costello, Daniel J., Jr.↗
NASA NTRS1986

Advanced dendritic web growth development and development of single-crystal silicon dendritic ribbon and high-efficiency solar cell program

Efforts to demonstrate that the dendritic web technology is ready for commercial use by the end of 1986 continues. A commercial readiness goal involves improvements to crystal growth furnace throughput to demonstrate an area growth rate of greater than 15 sq cm/min while simultaneously growing 10 meters or more of ribbon under conditions of continuous melt replenishment. Continuous means that the silicon melt is being replenished at the same rate that it is being consumed by ribbon growth so that the melt level remains constant. Efforts continue on computer thermal modeling required to define high speed, low stress, continuous growth configurations; the study of convective effects in the molten silicon and growth furnace cover gas; on furnace component modifications; on web quality assessments; and on experimental growth activities.

Duncan, C. S.↗
NASA NTRS1987

Channel access schemes and fiber optic configurations for integrated-services local area networks

Local Area Networks are in common use for data communications and have enjoyed great success. Recently, there is a growing interest in using a single network to support many applications in addition to traditional data traffic. These additional applications introduce new requirements in terms of volume of traffic and real-time delivery of data which are not met by existing networks. To satisfy these requirements, a high-bandwidth tranmission medium, such as fiber optics, and a distributed channel access scheme for the efficient sharing of the bandwidth among the various applications are needed. As far as the throughput-delay requirements of the various application are concerned, a network structure along with a distributed channel access are proposed which incorporate appropriate scheduling policies for the transmission of outstanding messages on the network. A dynamic scheduling policy was devised which outperforms all existing policies in terms of minimizing the expected cost per message. A broadcast mechanism was devised for the efficient dissemination of all relevant information. Fiber optic technology is considered for the high-bandwidth transmisison medium.

Nassehi, M. Mehdi↗
NASA NTRS1987

Error control coding for satellite and space communications

The optical direct detection channel is discussed. It is shown how simple trellis coded modulation can be used to improve performance or increase throughput (in bits per second) without a bandwidth expansion and no performance loss. In fact, a modest performance gain can be achieved. The concentration is on signals derived from the pulse-position modulation format by allowing overlap.

Georghiades, Costas N.↗
NASA NTRS1984

Uprated fine guidance sensor study

Future orbital observatories will require star trackers of extremely high precision. These sensors must maintain high pointing accuracy and pointing stability simultaneously with a low light level signal from a guide star. To establish the fine guidance sensing requirements and to evaluate candidate fine guidance sensing concepts, the Space Telescope Optical Telescope Assembly was used as the reference optical system. The requirements review was separated into three areas: Optical Telescope Assembly (OTA), Fine Guidance Sensing and astrometry. The results show that the detectors should be installed directly onto the focal surface presented by the optics. This would maximize throughput and minimize point stability error by not incoporating any additional optical elements.

Source record↗
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 MMICs 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 MMICs 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 NTRS1985

MAX: A space station computer option

Information on Max, a space station computer option, is given in viewgraph form. The computer option is characterized by embedded, real-time applications; synchronous, cyclic operation and asynchronous, event driven operation; computationally intensive and data intensive processing; a wide range of throughput and memory requirements; a range of fault tolerant requirements from none to full; and maintainability, including capability for on-line substitution in critical systems.

Smith, D. B.↗
NASA NTRS1985

Advanced Digital SAR Processor (ADSP)

The objectives are to develop the technology required to meet the synthetic aperture radar (SAR) processing needs for missions in the late 1980's, and to build and demonstrate a high performance engineering model flexible enough to be easily adapted to a wide variety of SAR processing tasks and capable of real-time or near real-time throughput rates. Information on the Advanced Digital SAR Processor is given in the form of outlines, carts and diagrams.

Bicknell, Tom↗
NASA NTRS1986

Sensitivity studies of 4D descent strategies in an advanced metering environment

An investigation of utilizing various 4D airplane descent strategies in an advanced time-based metering environment was conducted. The three strategies considered were clean-idle Mach/CAS, constant flight path angle (CFPA) Mach/CAS, and fuel-optimal. Traffic inputs consisted of all combinatory pairs of three types of commercial turbojets (B737-300, B747-200, and B767-200) and two weight classes for each airplane type. Sensitivities of traffic throughput and fleet fuel to descent strategies, both among themselves and in combination, for different assigned meter fix times and traffic pairings were studied under controlled initial conditions.

Izumi, K. H.↗
NASA NTRS1986

406-MHz geostationary SAR experiment

The ability of a 406-MHz satellite to detect and locate aeronautical, maritime, and terrestrial distress incidents is investigated. The geostationary satellite, uplink and downlink budgets, and processors utilized in the experiment are described. The experiment involves: (1) benchmark testing, (2) verification of spacecraft repeater performance, (3) system evaluation, and (4) environmental testing. The Canadian processor data reveal that the processor threshold is 28 dB Hz, the degradation at 27 dB Hz is significant, the median distress message throughput time is 6 minutes, and the microcomputer can handle 10 distress incidents per hour.

Dumont, P.↗
NASA NTRS1986

Advances in gallium arsenide monolithic microwave integrated-circuit technology for space communications systems

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. In this paper, current developments in GaAs MMIC technology are described, and the status and prospects of the technology are assessed.

Bhasin, K. B.↗
NASA NTRS1986

A reflection grating spectrometer for the X-ray Multi-Mirror (XMM) space observatory - Design and calculated performance

Attention is given to a spectrometer design candidate for the X-ray Multi-Mirror observatory, being planned by the European Space Agency as a long-lived large-area array of telescopes. The science requirement of moderate resolution spectroscopy in a two octave region with extremely high throughput leads to the use of grazing incidence reflection gratings. It is noted that the sensitivity of the instrument is sufficient to permit the first spectral detection of soft X-ray features in external galaxies.

Hettrick, Michael C.↗
NASA NTRS1986

Optical efficiency of far-infrared photoconductors

The present optimization of the geometry of far-IR photoconductive detectors with diffraction-limited throughput, on the basis of experimental and theoretical results, gives attention to the internal optical path relative to measured absorption length, photoconductive gain, uniformity of illumination, cosmic ray cross section, and design compatibility with the requirements of one- and two-dimensional arrays. It is demonstrated that a rod-shaped, square cross section detector geometry, having lateral face electrodes and a beveled backface with which to trap the radiation by total internal reflection, exhibits responsivity commensurate with that of the best available detectors in integrating cavities.

Wang, J.-Q.↗
NASA NTRS1986

Laser diode combining for free space optical communication

The maximization of photon delivery to a distant collector in free space optical communications systems calls for a laser diode-combining technique employing wavelength and/or polarization as the bases of its operation. Design considerations for such a combiner encompass high throughput efficiency, diffraction-limited angular divergence, and reasonable volume constraints. Combiners are presently found to require a generalized Strehl ratio concept which includes relative source misalignment; diffraction grating combiners may have a limited number of laser sources which can meet spectral requirements. Methods for the incorporation of a combiner into a communication system are compared. Power combining is concluded to be the best tradeoff of performance and complexity for all systems, except those that are severely limited by either background radiation or component bandwidth.

Mecherle, G. Stephen↗
NASA NTRS1986

A reliable pipelining protocol for the message service of the Mobile Satellite Experiment

This paper describes and analyzes a pipelining protocol for the data message communications of MSAT-X, a proposed experimental satellite-based mobile communications network. A demand assigned multiple access protocol using pure ALOHA for making reservation requests has been developed for MSAT-X under error-free assumptions. Preliminary propagation studies indicate that the short term bit error rate of satellite channels in a mobile environment can be as high as 0.001. Therefore, error-control schemes must be developed to ensure reliable transmissions. A retransmission scheme using selective repeat to minimize the end-to-end delay is proposed. Slotted ALOHA for making reservation requests is used to increase the overall system throughput. Since the number of channels available for reservation and data channels is essentially fixed for a given voice call blocking probability and a fixed call arrival rate, the analysis presented in this paper is also applicable to the integrated voice and data services of MSAT-X. Various operational scenarios have been investigated.

Li, V. O. K.↗
NASA NTRS1986

The Extreme Ultraviolet Explorer - Optics fabrication and performance

The fabrication methods, testing and evaluation techniques, and performance results are presented for the mirrors for the Extreme Ultraviolet Explorer (EUVE). The finest mirror produced to date has a measured half energy width of 8 arcsec at optical wavelengths. With a polished nickel surface, the telescope throughput was 35 percent at 44 A and 60 percent at 256 A. The surface roughness is 20 A rms.

Green, J.↗