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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 235 records · Page 13

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NASA NTRS1991

Computer aided reliability, availability, and safety modeling for fault-tolerant computer systems with commentary on the HARP program

Many of the most challenging reliability problems of our present decade involve complex distributed systems such as interconnected telephone switching computers, air traffic control centers, aircraft and space vehicles, and local area and wide area computer networks. In addition to the challenge of complexity, modern fault-tolerant computer systems require very high levels of reliability, e.g., avionic computers with MTTF goals of one billion hours. Most analysts find that it is too difficult to model such complex systems without computer aided design programs. In response to this need, NASA has developed a suite of computer aided reliability modeling programs beginning with CARE 3 and including a group of new programs such as: HARP, HARP-PC, Reliability Analysts Workbench (Combination of model solvers SURE, STEM, PAWS, and common front-end model ASSIST), and the Fault Tree Compiler. The HARP program is studied and how well the user can model systems using this program is investigated. One of the important objectives will be to study how user friendly this program is, e.g., how easy it is to model the system, provide the input information, and interpret the results. The experiences of the author and his graduate students who used HARP in two graduate courses are described. Some brief comparisons were made with the ARIES program which the students also used. Theoretical studies of the modeling techniques used in HARP are also included. Of course no answer can be any more accurate than the fidelity of the model, thus an Appendix is included which discusses modeling accuracy. A broad viewpoint is taken and all problems which occurred in the use of HARP are discussed. Such problems include: computer system problems, installation manual problems, user manual problems, program inconsistencies, program limitations, confusing notation, long run times, accuracy problems, etc.

Shooman, Martin L.↗

NASA NTRS1993

Flexible high speed CODEC

HARRIS, under contract with NASA Lewis, has developed a hard decision BCH (Bose-Chaudhuri-Hocquenghem) triple error correcting block CODEC ASIC, that can be used in either a bursted or continuous mode. the ASIC contains both encoder and decoder functions, programmable lock thresholds, and PSK related functions. The CODEC provides up to 4 dB of coding gain for data rates up to 300 Mbps. The overhead is selectable from 7/8 to 15/16 resulting in minimal band spreading, for a given BER. Many of the internal calculations are brought out enabling the CODEC to be incorporated in more complex designs. The ASIC has been tested in BPSK, QPSK and 16-ary PSK link simulators and found to perform to within 0.1 dB of theory for BER's of 10(exp -2) to 10(exp -9). The ASIC itself, being a hard decision CODEC, is not limited to PSK modulation formats. Unlike most hard decision CODEC's, the HARRIS CODEC doesn't upgrade BER performance significantly at high BER's but rather becomes transparent.

Wernlund, James V.↗

NASA NTRS1993

IUE observations of cataclysmic variable

Twenty two approved International Ultraviolet Explorer (IUE) programs were studied over a 14 year period. These programs are listed. The observations and subsequent analysis centered on cataclysmic variables (close binaries with a late main sequence star transferring material to a primary white dwarf via an accretion disk). The early studies highlighted the flux distribution of the accretion disk at outburst and quiescence, while later studies accomplished time-resolved observations throughout the orbital cycles, the study of the outflowing winds present at outburst, the study of the white dwarf in those systems with low accretion rate. There are 39 publications resulting from this work which are listed. These results include those for individual systems (Stepanian's star, Lanning 10, AM Her, MV Lyr, TV Col, VW Hyi, T Leo, IR Gem, TT Ari, Z Cam, BV Pup, IP Peg, PG1030+590, V1315 Aql, SW UMa, V426 Oph, WZ Sge, BY Cam, and U Gem) as well as review articles in journals and publications from reviews at meetings that summarize the impact of IUE on the study of accretion disks, white dwarfs, and hot spots resulting from stream impact as well as magnetic accretion columns.

Szkody, Paula↗

NASA NTRS1992

Ginga observations of X-ray flares on Algol

The Ginga X-ray satellite observed Algol (Beta Per) for 2 days in 1989 January, including both the primary optical eclipse and most of the secondary eclipse. We derive upper limits of about 20 and 10 percent, respectively, for the eclipsed flux fraction during the two eclipses. A large flare lasting over 12 hr was seen prior to and during secondary eclipse. High-temperature Fe line emission is clearly detected in the proportional counter data. The Fe line equivalent width is variable during the flare, ranging from 0.4-1.0 keV. Except for two intervals during the flare rise, the observed equivalent width is lower than predicted using solar abundances and an optically thin plasma model. Similar behavior has also been observed by Ginga in a large flare on UX Ari: in both events, opacity effects at line center may be playing a significant role. Loop model analysis of the large flare suggests that it involves a substantially longer loop or loops than a shorter duration Algol flare seen with Exosat.

Stern, R. A.↗

NASA NTRS1992

Representation and presentation of requirements knowledge

An approach to representation and presentation of knowledge used in the ARIES, an experimental requirements/specification environment, is described. The approach applies the notion of a representation architecture to the domain of software engineering and incorporates a strong coupling to a transformation system. It is characterized by a single highly expressive underlying representation, interfaced simultaneously to multiple presentations, each with notations of differing degrees of expressivity. This enables analysts to use multiple languages for describing systems and have these descriptions yield a single consistent model of the system.

Johnson, W. L.↗

NASA NTRS1992

SiC lightweight telescopes for advanced space applications. II - Structures technology

A critical technology area for lightweight SiC-based telescope systems is the structural integrity and thermal stability over spaceborne environmental launch and thermal operating conditions. Note, it is highly desirable to have an inherently athermal design of both SiC mirrors and structure. SSG has developed an 8 inch diameter SiC telescope system for brassboard level optical and thermal testing. The brassboard telescope has demonstrated less than 0.2 waves P-V in the visible wavefront change over +50 C to -200 C temperature range. SSG has also fabricated a SiC truss structural assembly and successfully qualified this hardware at environmental levels greater than 3 times higher than normal Delta, Titan, and ARIES launch loads. SSG is currently developing two SiC telescopes; an 20 cm diameter off-axis 3 mirror re-imaging and a 60 cm aperture on-axis 3 mirror re-imager. Both hardware developments will be tested to flight level environmental, optical, and thermal specifications.

Anapol, Michael I.↗

NASA NTRS1993

Digital data over video channels - Techniques for Spacelab

A study was made of various techniques for transmitting digital data over a composite video channel. Transmitting data from experiments on the Space Shuttle Orbiter over a video channel is attractive since extra channel capacity is needed. Broadcast television telecommunications schemes and other techniques described in the literature were reviewed and compared. PSK (Phase Shift Keying), MPSK (m-ary PSK), or PAM (Pulse Amplitude Modulation) can be transmitted on visible lines of a frame, unassigned lines of the VBI (Vertical Blanking Interval), or during the HBI (Horizontal Blanking Interval). All three modulation techniques can be attractive under the proper conditions. However, PAM on visible lines or during the VBI should be relatively easy to implement, provide adequate average data rates, and give acceptable BERs (Bit Error Rates).

Smith, Dean L.↗

NASA NTRS1992

Time-series photometric spot modeling. I - Parameter study and application to HD 17433 = VY Arietis

New UBVRI photometry of the active chromosphere binary HD 17433 (VY) Ari from 1987 through 1991 is presented, and the long-term and short-term spot behavior is studied. A 0.2 mag variation of the mean brightness and a maximum wave amplitude of up to 0.4 mag in 1988 are found. The newly measured photometric period of 16.42 d suggests asynchronous rotation of the primary component by about 30 percent.

Strassmeier, K. G.↗

NASA NTRS1993

Techniques for transmitting digital data on the Spacelab's analog video channel

Smith, Dean L.↗

NASA NTRS1994

Optimum Detection Of Slow-Frequency-Hopping Signals

Two papers present theoretical analyses of various schemes for coherent and noncoherent detection of M-ary-frequency-shift-keyed (MFSK) signals with slow frequency hopping. Special attention focused on continuous-phase-modulation (CPM) subset of SFH/MFSK signals, for which frequency modulation such carrier phase remains continuous (albeit unknown) during each hop.

Levitt, Barry K.↗

NASA NTRS1993

Telemetering and telecommunications research

The New Mexico State University (NMSU) Center for Space Telemetering and Telecommunications systems is engaged in advanced communications systems research. Four areas of study that are being sponsored concern investigations into the use of trellis-coded modulation (TCM). In particular, two areas concentrate on carrier synchronization research in TCM M-ary phase shift key (MPSK) systems. A third research topic is the study of interference effects on TCM, while the fourth research area is in the field of concatenated TCM systems.

Osborne, William↗

NASA NTRS1993

Exploiting the cannibalistic traits of Reed-Solomon codes

In Reed-Solomon codes and all other maximum distance separable codes, there is an intrinsic relationship between the size of the symbols in a codeword and the length of the codeword. Increasing the number of symbols in a codeword to improve the efficiency of the coding system thus requires using a larger set of symbols. However, long Reed-Solomon codes are difficult to implement and many communications or storage systems cannot easily accommodate an increased symbol size, e.g., M-ary frequency shift keying (FSK) and photon-counting pulse-position modulation demand a fixed symbol size. A technique for sharing redundancy among many different Reed-Solomon codewords to achieve the efficiency attainable in long Reed-Solomon codes without increasing the symbol size is described. Techniques both for calculating the performance of these new codes and for determining their encoder and decoder complexities is presented. These complexities are usually found to be substantially lower than conventional Reed-Solomon codes of similar performance.

Collins, O.↗

NASA NTRS1993

Automated rendezvous and capture demonstration study

This study was instituted to assist NASA and MSFC in the development of ground and flight options to demonstrate the capability of Automated Rendezvous and Capture (AR&C). Study goals placed emphasis on low cost approaches and the need to be responsive to newly developing programs and studies such as Space Station Freedom and the Cargo Transfer Vehicle. This study provides an assessment of vehicle options and AR&C requirements to assist in the meaningful development of an AR&C capability. This report documents study activities performed at Applied Research, Inc. (ARI) between 1 Apr. 1992 and May 1993.

Source record↗

NASA NTRS1994

A study of low mass x-ray binaries

The entire effort under this contract during the period through January 1992 was devoted to a study of the cost and schedule required to put an upgraded Aries payload on the ASTRO-SPAS carrier provided by the German space agency, DARA. The ASTRO-SPAS is flown on the Space Shuttle, deployed by the crew for 5 to 7 days of free-flying observations and then recovered and returned to Earth. The spectrograph was to be provided by a collaboration involving the Lockheed Palo Alto Research Laboratory (LPARL), the Center for Astrophysics and Space Astronomy (CASA) at the U. of Colorado and the Mullard Space Science Laboratory (MSSL) in England. The payload for the ASTRO-SPAS mission included our own spectrograph and an instrument provided by Dr. Joachim Trumper of the Max Planck Institute (MPI) in Garching, Germany. A meeting was held in late July, 1991 with German scientists, DARA representatives and MBB, the ASTRO-SPAS spacecraft contractor. Sufficient information was exchanged to allow us to complete the study and the name LEXSA (Low Energy X-ray Spectrograph on ASTRO-SPAS) was given to our instrument and HERTA (High Energy x-Ray Telescope on ASTR0-SPAS) to the German instrument. The combination was called SPECTRO-SPAS. On October 1, 1991 CASA and LPARL submitted a cost and brief technical proposal to NASA on results of the study. The total cost over 4 fiscal years was 6.16 M dollars including CASA costs. NASA Headquarters was briefed on 3 October on details of the proposal. They found our costs reasonable, but indicated that the NASA FY '92 budget is extremely tight, they could not readily identify where the -S2.3M for LEXSA could be found and it was not clear that FY '93 would improve.

Catura, Richard C.↗

NASA NTRS1995

Technical report series on global modeling and data assimilation. Volume 5: Documentation of the AIRES/GEOS dynamical core, version 2

A detailed description of the numerical formulation of Version 2 of the ARIES/GEOS 'dynamical core' is presented. This code is a nearly 'plug-compatible' dynamics for use in atmospheric general circulation models (GCMs). It is a finite difference model on a staggered latitude-longitude C-grid. It uses second-order differences for all terms except the advection of vorticity by the rotation part of the flow, which is done at fourth-order accuracy. This dynamical core is currently being used in the climate (ARIES) and data assimilation (GEOS) GCMs at Goddard.

Suarez, Max J.↗

NASA NTRS1995

The composite classification problem in optical information processing

Optical pattern recognition allows objects to be recognized from their images and permits their positional parameters to be estimated accurately in real time. The guiding principle behind optical pattern recognition is that a lens focusing a beam of coherent light modulated with an image produces the two-dimensinal Fourier transform of that image. When the resulting output is further transformed by the matched filter corresponding to the original image, one obtains the autocorrelation function of the original image, which has a peak at the origin. Such a device is called an optical correlator and may be used to recognize the locate the image for which it is designed. (From a practical perspective, an approximation to the matched filter must be used since the spatial light modulator (SLM) on which the filter is implemented usually does not allow one to independently control both the magnitude and phase of the filter.) Generally, one is not just concerned with recognizing a single image but is interested in recognizing a variety of rotated and scaled views of a particular image. In order to recognize these different views using an optical correlator, one may select a subset of these views (whose elements are called training images) and then use a composite filter that is designed to produce a correlation peak for each training image. Presumably, these peaks should be sharp and easily distinguishable from the surrounding correlation plane values. In this report we consider two areas of research regarding composite optical correlators. First, we consider the question of how best to choose the training images that are used to design the composite filter. With regard to quantity, the number of training images should be large enough to adequately represent all possible views of the targeted object yet small enough to ensure that the resolution of the filter is not exhausted. As for the images themselves, they should be distinct enough to avoid numerical difficulties yet similar enough to avoid gaps in which certain views of the target will be unrecognized. One method that we introduce to study this problem is called probing and involves the creation of the artificial imagery. The second problem we consider involves the clasification of the composite filter's correlation plane data. In particular, we would like to determine not only whether or not we are viewing a training image, but, in the former case, we would like to determine which training image is being viewed. This second problem is investigated using traditional M-ary hypothesis testing techniques.

Hall, Eric B.↗

NASA NTRS1996

Decision-Aiding and Optimization for Vertical Navigation of Long-Haul Aircraft

Most decisions made in the cockpit are related to safety, and have therefore been proceduralized in order to reduce risk. There are very few which are made on the basis of a value metric such as economic cost. One which can be shown to be value based, however, is the selection of a flight profile. Fuel consumption and flight time both have a substantial effect on aircraft operating cost, but they cannot be minimized simultaneously. In addition, winds, turbulence, and performance x,ary widely with altitude and time. These factors make it important and difficult for pilots to (a) evaluate the outcomes associated with a particular trajectory before it is flown and (b) decide among possible trajectories. The two elements of this problem considered here are (1) determining, what constitutes optimality, and (2) finding optimal trajectories. Pilots and dispatchers from major U.S. airlines were surveyed to determine which attributes of the outcome of a flight they considered the most important. Avoiding turbulence-for passenger comfort topped the list of items which were not safety related. Pilots' decision making about the selection of flight profile on the basis of flight time, fuel burn, and exposure to turbulence was then observed. Of the several behavioral and prescriptive decision models invoked to explain the pilots' choices, utility maximization is shown to best reproduce the pilots' decisions. After considering more traditional methods for optimizing trajectories, a novel method is developed using a genetic algorithm (GA) operating on a discrete representation of the trajectory search space. The representation is a sequence of command altitudes, and was chosen to be compatible with the constraints imposed by Air Traffic Control, and with the training given to pilots. Since trajectory evaluation for the GA is performed holistically, a wide class of objective functions can be optimized easily. Also, using the GA it is possible to compare the costs associated with different airspace design and air traffic management policies. A decision aid is proposed which would combine the pilot's notion of optimility with the GA-based optimization, provide the pilot with a number of alternative pareto-optimal trajectories, and allow him to consider un-modelled attributes and constraints in choosing among them. A solution to the problem of displaying alternatives in a multi-attribute decision space is also presented.

Patrick, Nicholas J. M.↗

NASA NTRS1992

Specification Reformulation During Specification Validation

The goal of the ARIES Simulation Component (ASC) is to uncover behavioral errors by 'running' a specification at the earliest possible points during the specification development process. The problems to be overcome are the obvious ones the specification may be large, incomplete, underconstrained, and/or uncompilable. This paper describes how specification reformulation is used to mitigate these problems. ASC begins by decomposing validation into specific validation questions. Next, the specification is reformulated to abstract out all those features unrelated to the identified validation question thus creating a new specialized specification. ASC relies on a precise statement of the validation question and a careful application of transformations so as to preserve the essential specification semantics in the resulting specialized specification. This technique is a win if the resulting specialized specification is small enough so the user my easily handle any remaining obstacles to execution. This paper will: (1) describe what a validation question is; (2) outline analysis techniques for identifying what concepts are and are not relevant to a validation question; and (3) identify and apply transformations which remove these less relevant concepts while preserving those which are relevant.

Benner, Kevin M.↗