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At least 865 records · Page 48

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NASA NTRS1988

Laser Diagnostics for combustion temperature and species measurements

Laser optical diagnostic techniques for the measurement of combustion gaseous-phase temperatures and, or species concentrations are discussed. The techniques fall into two classes: incoherent (Rayleigh scattering, spontaneous Raman scattering, laser induced fluorescence spectroscopy) and coherent (coherent anti-Stokes Raman spectroscopy). The advantages, disadvantages and applicability of each method are outlined.

Eckbreth, Alan C.↗

NASA NTRS1988

Diagnostic studies of the HxOy-NzOy-O3 photochemical system using data from NASA GTE field expeditions

Spring 1084 GTE CITE-1 flight data from the field exercise was obtained from a GTE Data Archive Tape. Chemical and supporting meteorological data taken over the Pacific Ocean was statistically and diagnostically analyzed to identify the key processes affecting the concentrations of ozone and its chemical precursors in the region. The analysis was completed. The analysis of the GTE CITE-2 data is being performed in collaboration with Dr. D.D. Davis and other GTE scientists. Initial results of the analysis were presented and work begun on the paper describing the results.

Chameides, William L.↗

NASA NTRS1987

The infrared diagnostic of a dusty plasma with applications to supernova remnants

IRAS observations of infrared emission from supernova remnants constitute the first observational evidence of shock-heated dust in the interstellar medium. These observations can provide valuable information on the morphology of supernova remnants, and on their interaction with the ambient interstellar medium. In particular, they can be used to study the physical condition and the cooling rate of dusty astrophysical plasmas. In this paper, consideration is given to the possibilities and limitations of using the infrared observations as a diagnostic for the shocked gas, and as a means of determining remnant parameters. The paper presents improved calculations for the cooling rate of a dusty plasma by means of gas-grain collisions, and the equilibrium temperature of the dust for a variety of plasma conditions. These results are then used to define the density-temperature parameter space of the plasma, which, given its infrared spectrum, should be occupied by the observed remnant. This constraint can be used to estimate distances to supernova remnants and to set limits on various parameters that determine their evolution. The analysis is applied to the remnants Cas A and the Cygnus Loop.

Dwek, Eli↗

NASA NTRS1987

In situ process diagnostics of silane plasma for device-quality a-Si:H deposition

Coherent anti-Stokes Raman spectroscopy (CARS) and mass spectrometry (MS) have been applied to in situ process diagnostics of a silane plasma for device-quality a-Si:H film deposition. Silane depletion was directly measured by CARS and is linearly dependent on RF power in the region of 4-12 W with a slope of 0.5 percent/mW-sq cm. The depletion is also dependent on SiH4 flow rate starting with a 50 percent depletion at a low flow rate of 5.6 sccm and asymptotically approaching an 8 percent depletion at a flow rate of 80 sccm. The mass spectral line signal intensity of disilane increases with RF power and shows an apparent transition at 6 W. Disilane formation in silane plasma, film deposition rate, and silane depletion ratio as a function of the RF power indicate that the film growth mechanism in the low-power region of 3.5-6.5 W is substantially different from that in the high-power region of 6.5-12 W.

Shing, Y. H.↗

NASA NTRS1987

Infrared surface imaging as a flowfield diagnostic tool

An infrared imaging system supported by a dedicated image processing system was evaluated as a diagnostic tool for aerodynamic research. Results are reported characterizing the system's capability for performing a variety of experimental investigations, such as temperature transients, air velocity distributions, capture of vortices, boundary layer flows, and separated flows over a flat plate with a two-dimensional rearward-facing step.

Gartenberg, Ehud↗

NASA NTRS1988

Non-intrusive Space Shuttle Main Engine nozzle exit diagnostics

The results of a conceptual design study on the feasibility of nonintrusive optical diagnostics have shown that UV laser-excited Raman scattering can furnish reliable and accurate temperature and multiple-species data for the Space Shuttle Main Engine's exhaust flow. Enhanced OH flow tagging by UV photodissociation of H2O was used in velocity measurements; a time-delayed pulsed dye laser beam at 308 nm excites fluorescence from OH, and the location of the convected enhanced OH zone is measured with an optical multichannel detector.

Shirley, John A.↗

NASA NTRS1988

Tunable diode laser spectral diagnostic studies of a pressure modulator radiometer

The successful application of high-resolution tunable diode laser spectroscopy to the diagnostic measurement of a pressure modulator radiometer (PMR) is reported, and recorded line transmission profiles for a single N2O line at 1272/cm are presented. PMR measurements obtained for mean cell pressures of about 10, 20, and 30 Torr were found to be consistent with theoretical predictions. The validity of single-pressure and two-pressure approximation representations of the mean and modulated PMR transmission spectra has been verified.

May, Randy D.↗

NASA NTRS1988

On the diagnostic emulation technique and its use in the AIRLAB

An aid is presented for understanding and judging the relevance of the diagnostic emulation technique to studies of highly reliable, digital computing systems for aircraft. A short review is presented of the need for and the use of the technique as well as an explanation of its principles of operation and implementation. Details that would be needed for operational control or modification of existing versions of the technique are not described.

Migneault, Gerard E.↗

NASA NTRS1987

Vertical O(sub 3) distribution as a diagnostic for eddy diffusion profile

A model study of the distribution of ozone on Mars is presented. It is showed that knowledge of the vertical ozone distribution, such as could be obtained from ultraviolet measurements from an orbiter, could be used to infer vertical transport rates at various levels in the atmosphere. The dependence of the vertical distribution of O(sub 3) on the height variation of eddy diffusion coefficient is illustrated. Ozone abundance is a valuable diagnostic for other climatological parameters. In addition, the sensitivity of O(sub 3) distribution to eddy diffusion may aid in determining the role of surface oxidation and recombination processes and lead to a better understanding of the volatiles released or adsorbed cyclically in the Martian regolith.

Tyler, A. L.↗

NASA NTRS1988

Diagnostic studies of the 1987 Antarctic spring vortex

Dynamical fields form the UK Meteorological office global forecast model were used throughout the 1987 Airborne Antarctic Ozone Experiment (AAOE) for flight planning and diagnostic studies. Here, several studies based on the Meteorological Office global analysis (resolution 1.5 degrees lattitude x 1.875 degrees longitude, Lyne et al.) are described. The wind and temperature data derived from the model analysis are compared with observations made from both the DCB and ER-2, and an assessment of the model performance given. Derived quantities such as potential vorticity and model data and discrepancies due to the model data are discussed.

Austin, J.↗

NASA NTRS1988

Graph-based real-time fault diagnostics

A real-time fault detection and diagnosis capability is absolutely crucial in the design of large-scale space systems. Some of the existing AI-based fault diagnostic techniques like expert systems and qualitative modelling are frequently ill-suited for this purpose. Expert systems are often inadequately structured, difficult to validate and suffer from knowledge acquisition bottlenecks. Qualitative modelling techniques sometimes generate a large number of failure source alternatives, thus hampering speedy diagnosis. In this paper we present a graph-based technique which is well suited for real-time fault diagnosis, structured knowledge representation and acquisition and testing and validation. A Hierarchical Fault Model of the system to be diagnosed is developed. At each level of hierarchy, there exist fault propagation digraphs denoting causal relations between failure modes of subsystems. The edges of such a digraph are weighted with fault propagation time intervals. Efficient and restartable graph algorithms are used for on-line speedy identification of failure source components.

Padalkar, S.↗

NASA NTRS1986

Paranoia.Ada: A diagnostic program to evaluate Ada floating-point arithmetic

Many essential software functions in the mission critical computer resource application domain depend on floating point arithmetic. Numerically intensive functions associated with the Space Station project, such as emphemeris generation or the implementation of Kalman filters, are likely to employ the floating point facilities of Ada. Paranoia.Ada appears to be a valuabe program to insure that Ada environments and their underlying hardware exhibit the precision and correctness required to satisfy mission computational requirements. As a diagnostic tool, Paranoia.Ada reveals many essential characteristics of an Ada floating point implementation. Equipped with such knowledge, programmers need not tremble before the complex task of floating point computation.

Hjermstad, Chris↗

NASA NTRS1989

Spacelab Life Sciences-1 electrical diagnostic expert system

The Spacelab Life Sciences-1 (SLS-1) Electrical Diagnostic (SLED) expert system is a continuous, real time knowledge-based system to monitor and diagnose electrical system problems in the Spacelab. After fault isolation, the SLED system provides corrective procedures and advice to the ground-based console operator. The SLED system updates its knowledge about the status of Spacelab every 3 seconds. The system supports multiprocessing of malfunctions and allows multiple failures to be handled simultaneously. Information which is readily available via a mouse click includes: general information about the system and each component, the electrical schematics, the recovery procedures of each malfunction, and an explanation of the diagnosis.

Kao, C. Y.↗

NASA NTRS1989

REDEX: The ranging equipment diagnostic expert system

REDEX, an advanced prototype expert system that diagnoses hardware failures in the Ranging Equipment (RE) at NASA's Ground Network tracking stations is described. REDEX will help the RE technician identify faulty circuit cards or modules that must be replaced, and thereby reduce troubleshooting time. It features a highly graphical user interface that uses color block diagrams and layout diagrams to illustrate the location of a fault. A semantic network knowledge representation technique was used to model the design structure of the RE. A catalog of generic troubleshooting rules was compiled to represent heuristics that are applied in diagnosing electronic equipment. Specific troubleshooting rules were identified to represent additional diagnostic knowledge that is unique to the RE. Over 50 generic and 250 specific troubleshooting rules have been derived. REDEX is implemented in Prolog on an IBM PC AT-compatible workstation. Block diagram graphics displays are color-coded to identify signals that have been monitored or inferred to have nominal values, signals that are out of tolerance, and circuit cards and functions that are diagnosed as faulty. A hypertext-like scheme is used to allow the user to easily navigate through the space of diagrams and tables. Over 50 graphic and tabular displays have been implemented. REDEX is currently being evaluated in a stand-alone mode using simulated RE fault scenarios. It will soon be interfaced to the RE and tested in an online environment. When completed and fielded, REDEX will be a concrete example of the application of expert systems technology to the problem of improving performance and reducing the lifecycle costs of operating NASA's communications networks in the 1990's.

Luczak, Edward C.↗

NASA NTRS1988

Plasma diagnostics package. Volume 2: Spacelab 2 section. Part B: Thesis projects

Pickett, Jolene S.↗

NASA NTRS1988

Plasma diagnostics package. Volume 1: OSS-1 section

This volume (1) of the Plasma Diagnostics Package (PDP) final science report contains a summary of all of the data reduction and scientific analyses which were performed using PDP data obtained on STS-3 as a part of the Office of Space Science first payload (OSS-1). This work was performed during the period of launch, March 22, l982, through June 30, l983. During this period the primary data reduction effort consisted of processing summary plots of the data received by the 14 instruments located on the PDP and submitting these data to the National Space Science Data Center (NSSDC). The scientific analyses during the performance period consisted of general studies which incorporated the results of several of the PDP's instruments, detailed studies which concentrated on data from only one or two of the instruments, and joint studies of beam-plasma interactions with the OSS-1 Fast Pulse Electron Generator (FPEG) of the Vehicle Charging and Potential Investigation (VCAP). Internal reports, published papers and oral presentations which involve PDP/OSS-1 data are listed in Sections 3 and 4. A PDP/OSS-1 scientific results meeting was held at the University of Iowa on April 19-20, 1983. This meeting was attended by most of the PDP and VCAP investigators and provided a forum for discussing and comparing the various results, particularly with regard to the shuttle orbiter environment. One of the most important functional objectives of the PDP on OSS-1 was to characterize the orbiter environment.

Pickett, Jolene S.↗

NASA NTRS1988

Plasma diagnostics package. Volume 2: Spacelab 2 section, part A

This volume (2), which consists of two parts (A and B), of the Plasma Diagnostics Package (PDP) Final Science Report contains a summary of all of the data reduction and scientific analyses which were performed using PDP data obtained on STS-51F as a part of the Spacelab 2 (SL-2) payload. This work was performed during the period of launch, July 29, l985, through June 30, l988. During this period the primary data reduction effort consisted of processing summary plots of the data received by 12 of the 14 instruments located on the PDP and submitting these data to the National Space Science Data Center (NSSDC). The scientific analyses during the performance period consisted of follow-up studies of shuttle orbiter environment and orbiter/ionosphere interactions and various plasma particle and wave studies which dealt with data taken when the PDP was on the Remote Manipulator System (RMS) arm and when the PDP was in free flight. Of particular interest during the RMS operations and free flight were the orbiter wake studies and joint studies of beam/plasma interactions with the SL-2 Fast Pulse Electron Generator (FPEG) of the Vehicle Charging and Potential Investigation (VCAP). Internal reports, published papers and presentations which involve PDP/SL-2 data are listed in Sections 3 and 4. A PDP/SL-2 scientific results meeting was held at the University of Iowa on June 10, l986. This meeting was attended by most of the PDP and VCAP investigators and provided a forum for discussing and comparing the various results, particularly with regard to the PDP free flight.

Pickett, Jolene S.↗

NASA NTRS1989

H-alpha redshifts as a diagnostic of solar flare heating

The dynamics of chomospheric condensations formed during chromospheric evaporation are studied using coordinated X-ray and H-alpha observations of five solar flares. It is shown that the peak downflow velocity of condensations predicted by simple hydrodynamic compression of the chromosphere is in good agreement with empirical downflow velocities implied by impulsive phase H-alpha red wing Doppler shifts. It is found that the H-alpha wing redshift provides a diagnostic of the pressure excess in the evaporating region and the coronal energy flux driving chromospheric evaporation. Because preflare coronal pressures derived for each of the flares are high, it is suggested that the chromosphere succeeds in radiating excess flare heat energy without undergoing explosive chromospheric evaporation.

Zarro, Dominic M.↗