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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Upset susceptibility study employing circuit analysis and digital simulation

This paper describes an approach to predicting the susceptibility of digital systems to signal disturbances. Electrical disturbances on a digital system's input and output lines can be induced by activities and conditions including static electricity, lightning discharge, Electromagnetic Interference (EMI) and Electromagnetic Pulsation (EMP). The electrical signal disturbances employed for the susceptibility study were limited to nondestructive levels, i.e., the system does not sustain partial or total physical damage and reset and/or reload will bring the system to an operational status. The front-end transition from the electrical disturbances to the equivalent digital signals was accomplished by computer-aided circuit analysis. The Super-Sceptre (system for circuit evaluation of transient radiation effects) Program was used. Gate models were developed according to manufacturers' performance specifications and parameters resulting from construction processes characteristic of the technology. Digital simulation at the gate and functional level was employed to determine the impact of the abnormal signals on system performance and to study the propagation characteristics of these signals through the system architecture. Example results are included for an Intel 8080 processor configuration.

Carreno, V. A.↗
NASA NTRS1984

Crystal gazing. Part 2: Implications of advanced in digital data storage technology

During the next 5-10 years it is likely that the bit density available in digital mass storage systems (magnetic tapes, optical and magnetic disks) will be increased to such an extent that it will greatly exceed that of the conventional photographic emulsions like IIIaJ which are used in astronomy. These developments imply that it will soon be advantageous for astronomers to use microdensitometers to completely digitize all photographic plates soon after they are developed. Distribution of digital copies of sky surveys and the contents of plate vaults will probably become feasible within ten years. Copies of other astronomical archieves (e.g., Space Telescope) could also be distributed with the same techniques. The implications for designers of future microdensitometers are: (1) there will be a continuing need for precision digitization of large-format photographic imagery, and (2) that the need for real-time analysis of the output of microdensitometers will decrease.

Wells, D. C.↗
NASA NTRS1984

Propulsion control experience used in the Highly Integrated Digital Electronic Control (HIDEC) program

The highly integrated digital electronic control (HIDEC) program will integrate the propulsion and flight control systems on an F-15 airplane at NASA Ames Research Center's Dryden Flight Research Facility. Ames-Dryden has conducted several propulsion control programs that have contributed to the HIDEC program. The digital electronic engine control (DEEC) flight evaluation investigated the performance and operability of the F100 engine equipped with a full-authority digital electronic control system. Investigations of nozzle instability, fault detection and accommodation, and augmentor transient capability provided important information for the HIDEC program. The F100 engine model derivative (EMD) was also flown in the F-15 airplane, and airplane performance was significantly improved. A throttle response problem was found and solved with a software fix to the control logic. For the HIDEC program, the F100 EMD engines equipped with DEEC controls will be integrated with the digital flight control system. The control modes to be implemented are an integrated flightpath management mode and an integrated adaptive engine control system mode. The engine control experience that will be used in the HIDEC program is discussed.

Myers, L. P.↗
NASA NTRS1984

Digital avionics - The best is yet to come

The history and background of digital avionics and the possibilities for the future are reviewed. There are payoffs in many areas from digital avionics; however, the ultimate benefits are increased mission effectiveness and lower costs. Two major U.S. Air Force avionics programs designed to increase mission effectiveness are reviewed. Major barriers to the expanded use of digital avionics in civil transports as a means to lower operating costs are examined. The paper also examines lightning effects, architectures, optical components, displays, and voice-interactive control, which are current research areas that promise to yield significant advances for digital avionics systems.

Spitzer, C. R.↗
NASA NTRS1984

Upset susceptibility study employing circuit analysis and digital simulation

An approach to predict the susceptibility of digital systems to signal disturbances is described. Electrical disturbances on a digital system's input and output lines can be induced by activities and conditions including static electricity, lightning discharge, electromagnetic interference (EMI), and electromagnetic pulsation (EMP). The electrical signal disturbances employed for the susceptibility study were limited to nondestructive levels, i.e., the system does not sustain partial or total physical damage and reset and/or reload brings the system to an operational status. The front-end transition from the electrical disturbances to the equivalent digital signals was accomplished by computer-aided circuit analysis. The super-sceptre (system for circuit evaluation of transient radiation effects) programs was used. Gate models were developed according to manufacturers' performance specifications and parameters resulting from construction processes characteristic of the technology. Digital simulation at the gate and functional level was employed to determine the impact of the abnormal signals on system performance and to study the propagation characteristics of these signals through the system architecture. Example results are included for an Intel 8080 processor configuration.

Carreno, V. A.↗
NASA NTRS1985

Digital control of diode laser for atmospheric spectroscopy

A system is described for remote absorption spectroscopy of trace species using a diode laser tunable over a useful spectral region of 50 to 200 cm(-1) by control of diode laser temperature over range from 15 K to 100 K, and tunable over a smaller region of typically 0.1 to 10 cm(-1) by control of the diode laser current over a range from 0 to 2 amps. Diode laser temperature and current set points are transmitted to the instrument in digital form and stored in memory for retrieval under control of a microprocessor during measurements. The laser diode current is determined by a digital to analog converter through a field effect transistor for a high degree of ambient temperature stability, while the laser diode temperature is determined by set points entered into a digital to analog converter under control of the microprocessor. Temperature of the laser diode is sensed by a sensor diode to provide negative feedback to the temperature control circuit that responds to the temperature control digital to analog converter.

Menzies, R. T.↗
NASA NTRS1986

Pseudolog Digital-to-Analog Converter

Sensitivity decreases by 10 at beginning of each input decade. Method conceived to convert binary-coded data to suitable linear form for stripchart recording. Strip-chart recordings obtained from typical pressure readings in a vacuum system during pumpdown. In reading curve, BCD digital vacuum-gage output processed by analog-to-digital converter in such way that only reading digits (but not range) appear in output. In range and reading, range also converted to analog and placed as most significant digit.

Gooder, S. T.↗
NASA NTRS1986

Digital filtering and acceleration pulse interpretation

It was concluded that the post processing digital filter is quite effective for removing unwanted high frequency and noise without distorting the signal. In addition, digital filtering is effective for smoothing low-level low resolution digital data where the digital stairstep phenomena are pronounced. Integrating the acceleration data to obtain velocity traces is quite useful. The velocity change provides a check on the validity of the acceleration trace. (Zero offsets in acceleration must be removed before integrating.) Average accelerations can be obtained from the velocity trace by dividing the change in velocity for an acceleration pulse by the pulse duration. One can obtain the peak of an equivalent triangular pulse by doubling the average acceleration.

Pasanella, E. L.↗
NASA NTRS1985

Microcomputer-based digital image processing - A tutorial package for exploration geologists

An Apple II microcomputer-based software package for analysis of digital data developed at the University of Oklahoma, the Digital Image Analysis System (DIAS), provides a relatively low-cost, portable alternative to large, dedicated minicomputers for digital image processing education. Digital processing techniques for analysis of Landsat MSS data and a series of tutorial exercises for exploration geologists are described and evaluated. DIAS allows in-house training that does not interfere with computer-based prospect analysis objectives.

Harrington, J. A., Jr.↗
NASA NTRS1987

Satellite analog FDMA/FM to digital TDMA conversion

The results of a study which investigated design issues regarding the use of analog to digital (A/D) conversion on board a satellite are presented. The need for A/D, and of course D/A as well, conversion arose from a satellite design which required analog FDMA/FM up and down links to/from a digitally modulated intersatellite link. There are also some advantages when one must interconnect a large number of various spot beams which are using analog, and therefore cannot take advantage of SS/TDMA switching among the beams, thus resulting in low fill factors. Various tradeoffs were performed regarding the implementation of on-board A/D processing, including mass, power, and costs. The various technologies which were considered included flash ADCs, surface acoustic wave (SAW) devices, and digital signal processing (DSP) chips. Impact analyses were also performed to determine the effect on ground stations to convert to digital if the A/D approach were not implemented.

Driggers, T.↗
NASA NTRS1987

Digital control of highly augmented combat rotorcraft

Proposed concepts for the next generation of combat helicopters are to be embodied in a complex, highly maneuverable, multiroled vehicle with avionics systems. Single pilot and nap-of-the-Earth operations require handling qualities which minimize the involvement of the pilot in basic stabilization tasks. To meet these requirements will demand a full authority, high-gain, multimode, multiply-redundant, digital flight-control system. The gap between these requirements and current low-authority, low-bandwidth operational rotorcraft flight-control technology is considerable. This research aims at smoothing the transition between current technology and advanced concept requirements. The state of the art of high-bandwidth digital flight-control systems are reviewed; areas of specific concern for flight-control systems of modern combat are exposed; and the important concepts are illustrated in design and analysis of high-gain, digital systems with a detailed case study involving a current rotorcraft system. Approximate and exact methods are explained and illustrated for treating the important concerns which are unique to digital systems.

Tischler, Mark B.↗
NASA NTRS1986

All-digital jets are taking off

The functions and advantages of second-generation digital avionics systems are described. These digital systems have increased integration, increased reliability and flexibility, and improved man-machine interface, and they provide increases in the mean time between removal of line-replacable units and fuel savings. Different redundant processors and software are utilized to achieve fault-tolerance performance of flight control systems. The improved landing capabilities, front-panel instruments, sidestick controllers, back-lighted liquid-crystal displays, and fly-by-wire system possible with digital avionics are examined. The applications of digital avionics to military and commercial aircraft are discussed and examples are provided.

Spitzer, C. R.↗
NASA NTRS1987

Detection of signals by the digital integrate-and-dump filter with offset sampling

The Integrate and Dump Filter (IDF) is used as a matched filter for the detection of signals in additive white Gaussian noise. The performance of the digital integrate and dump filter is evaluated. The case considered is when symbol times are known and the sampling clock is free running at a constant rate, i.e., the sampling clock is not phase locked to the symbol clock. Degradations in the output signal to noise ratio of the digital implementation due to sampling rate, sampling offset, and finite bandwidth, resulting from the anti-aliasing low pass prefilter, are computed and compared with those of the analog counterpart. It is shown that the digital IDF performs within 0.6 dB of the ideal analog IDF whenever the prefilter bandwidth exceeds four times the symbol rate and when sampling is performed at the Nyquist rate. The loss can be reduced to 0.3 dB by doubling the sampling rate, where 0.2 dB loss results from finite bandwidth and 0.1 dB results from the digital IDF.

Sadr, R.↗
NASA NTRS1987

Diagnostic reasoning in digital systems

Described is an efficient method for fault diagnosis in digital systems based on the technique of reasoning. The methodology operates on the observed erroneous behavior and the structure of the system. The behavior consists of the error(s) observed on the circuit's output lines and specific values on the circuit's input lines. The techniques described improve on previously published research on diagnostic reasoning in two ways. Previous work has stressed system independent techniques which could be used to diagnose any faulty system whose structure can be represented. By concentrating on the specific case of diagnosing faulty digital circuits, it is possible to simplify the representation of the structure of the system. This representation, in the form of an AND/OR fault tree, efficiently abstracts the structure of a faulty digital system. More importantly, a method for partitioning the digital system is introduced which can considerably reduce the runtime complexity of a diagnosis.

Thearling, Kurt Henry↗
NASA NTRS1987

Digital signal processing algorithms for automatic voice recognition

The current digital signal analysis algorithms are investigated that are implemented in automatic voice recognition algorithms. Automatic voice recognition means, the capability of a computer to recognize and interact with verbal commands. The digital signal is focused on, rather than the linguistic, analysis of speech signal. Several digital signal processing algorithms are available for voice recognition. Some of these algorithms are: Linear Predictive Coding (LPC), Short-time Fourier Analysis, and Cepstrum Analysis. Among these algorithms, the LPC is the most widely used. This algorithm has short execution time and do not require large memory storage. However, it has several limitations due to the assumptions used to develop it. The other 2 algorithms are frequency domain algorithms with not many assumptions, but they are not widely implemented or investigated. However, with the recent advances in the digital technology, namely signal processors, these 2 frequency domain algorithms may be investigated in order to implement them in voice recognition. This research is concerned with real time, microprocessor based recognition algorithms.

Botros, Nazeih M.↗
NASA NTRS1987

Digital cartography of the planets - New methods, its status, and its future

A system has been developed that establishes a standardized cartographic database for each of the 19 planets and major satellites that have been explored to date. Compilation of the databases involves both traditional and newly developed digital image processing and mosaicking techniques, including radiometric and geometric corrections of the images. Each database, or digital image model (DIM), is a digital mosaic of spacecraft images that have been radiometrically and geometrically corrected and photometrically modeled. During compilation, ancillary data files such as radiometric calibrations and refined photometric values for all camera lens and filter combinations and refined camera-orientation matrices for all images used in the mapping are produced. The system is designed to aid in the following: access to and utilization of spatial data returned by planetary spacecraft; coregistration of cartographic image and topographic elevation models with geological, geophysical, and geochemical databases; and the design and preparation of both standard and custom map products. A major goal of the project is to publish the DIMs on compact computer-compatible media such as digital-optical (CD-ROM) disks.

Batson, R. M.↗
NASA NTRS1987

Geometric processing of digital images of the planets

New procedures and software have been developed for geometric transformation of images to support digital cartography of the planets. The procedures involve the correction of spacecraft camera orientation of each image with the use of ground control and the transformation of each image to a Sinusoidal Equal-Area map projection with an algorithm which allows the number of transformation calculations to vary as the distortion varies within the image. When the distortion is low in an area of an image, few transformation computations are required, and most pixels can be interpolated. When distortion is extreme, the location of each pixel is computed. Mosaics are made of these images and stored as digital databases. Completed Sinusoidal databases may be used for digital analysis and registration with other spatial data. They may also be reproduced as published image maps by digitally transforming them to appropriate map projections.

Edwards, Kathleen↗
NASA NTRS1988

Monolithic GaAs digitizer for space-based laser pulse spreading effect

A 6-bit 1-GHz digitizer was designed to analyze the 1-ns pulse spreading effects in a space based altimeter. The digitizer consisted of four 4-bit flash A/D converters and a 6-bit encoder. Also, the converter utilized four 4-bit converters and a 4-to-6 bit encoder to achieve 6 bit resolution at the 1 GHz sample rate. The design was unique because it utilized only the inverters and NOR gates for the converters and encoder, hence it could be fabricated using the existing state-of-the-art GaAs processing techniques. This GHz digitizer has many commercial applications. It could be applicable to: (1) digital microwave transmission system for the telecommunication industries, (2) pulse monitoring in high kinetic chemical reactions, (3) transient signals in the medical field, and (4) microwave signals in astronomy.

Lao, Bennig↗