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At least 289 records · Page 16

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NASA NTRS1992

Developments of new force reflecting control schemes and an application to a teleoperation training simulator

Two schemes of force reflecting control, position-error based force reflection and low-pass-filtered force reflection, both combined with shared compliance control, were developed for dissimilar master-slave arms. These schemes enabled high force reflection gains, which were not possible with a conventional scheme when the slave arm was much stiffer than the master arm. The experimental results with a peg-in-hole task indicated that the newly force reflecting control schemes combined with compliance control resulted in best task performances. As a related application, a simulated force reflection/shared compliance control teleoperation trainer was developed that provided the operator with the feel of kinesthetic force virtual reality.

Kim, Won S.↗

NASA NTRS1955

Tensile Properties of 7075-T6 and 2024-T3 Aluminum-alloy Sheet Heated at Uniform Temperature Rates Under Constant Load

Results are presented of tests to determine the effect of heating at uniform temperature rates from 0.2 degrees to 100 degrees F. per second on the tensile properties of 7075-T6 d(75s-T6) and 2024-T3 (24s-T3) aluminum-alloy sheet under constant-load conditions. Yield and rupture stresses, obtained under rapid-heating conditions, are compared with results of elevated-temperature stress-strain tests for 1/2-hour exposure. Master yield-and-rupture-stress curves based on linear temperature-rate parameter are presented. Yield and rupture stresses and temperatures may be predicted by means of master curves and the parameter.

Heimerl, George J↗

NASA NTRS1990

Electrodynamics of the Middle Atmosphere: Superpressure Balloon Program

This project called Electrodynamics of the Middle Atmosphere (EMA): Superpressure Balloon Program was begun by the PI at the Aerospace Corporation in Los Angeles under joint NSF and NASA funding originally combined in one grant ATM80-17071 and has continued at the University of Washington under grants ATM8212283, ATM84-11326 and ATM86-15628 and NASA grants NAGW-724 and NAGS-635. In the EMA experiment a comprehensive set of electrical parameters was measured during eight long-duration balloon flights in the Southern Hemisphere stratosphere. These flights resulted in the largest vector electric field data set ever collected from the stratosphere which has been a treasure-trove of new phenomena. Since the stratosphere has never been electrodynamically sampled in this systematic manner before, it is perhaps not surprising that several new discoveries have been made and reported. Another way to measure the success of this first EMA project is to note that all together the total data rate was about 1 bit/sec/payload amounting to 12 MBytes (1/3 of 1 standard 1600 BPI magnetic tape) which nevertheless has resulted in 14 papers and 2 masters theses (so far! . Ten of these papers and one masters thesis specifically acknowledge the support by NASA grant NAGS-635 are discussed herein.

Holzworth, Robert H.↗

NASA NTRS1993

Publication of science data on CD-ROM: A guide and example

CD-ROM (Compact Disk-Read Only Memory) is becoming the standard media not only in audio recording, but also in the publication of data and information accessible on many computer platforms. Little has been written about the complicated process involved in creating easy-to-use, high quality, and useful CD-ROM's containing scientific data. This document is a manual designed to aid those who are responsible for the publication of scientific data on CD-ROM. All aspects and steps of the procedure are covered, from feasibility assessment through disk design, data preparation, disc mastering, and CD-ROM distribution. General advice and actual examples are based on lessons learned from the publication of scientific data for an interdisciplinary field experiment. Appendices include actual files from a CD-ROM, a purchase request for CD-ROM mastering services, and the disk art for the first disk published for the project.

Angelici, Gary↗

NASA NTRS1994

Separation tool for multipin electrical connectors

A hydraulic tool for safely separating one multipin electrical connector from another is presented. The separation tool consists of a master cylinder which operates a pair of slave cylinders. Each slave cylinder has a corresponding operative shaft and an extraction tab. The slave cylinders are spaced apart from one another so that they may be positioned on either side of mated connector pairs of different sizes and so that their extraction tabs may be slid between the connectors. When the master cylinder's plunger is operated, its operation is hydraulically transmitted to the operative shafts of the slave cylinders which extend outward and, once pressed against a substrate, causes the slave cylinders and corresponding extractor tabs to move away and separate one connector from the other. A second preferred separation tool includes an additional pair of extractor tabs, one at the end of each operative shaft, so that the tool can be used to separate a mated connector pair hanging in free space.

Larry D Smith↗

NASA NTRS1993

A critical evaluation of theories for predicting microcracking in composite laminates

We present experimental results on 21 different layups of Hercules AS4 carbon fiber/3501-6 epoxy laminates. All laminates had 90 deg plies; some had them in the middle, while some had them on a free surface. During tensile loading, the first form of damage in all laminates was microcracking of the 90 deg plies. For each laminate, we recorded both the crack density and the complete distribution of crack spacings as a function of the applied load. By rearranging various microcracking theories, we developed a master-curve approach that permitted plotting the results from all laminates on a single plot. By comparing master-curve plots for different theories, it was possible to critically evaluate the quality of those theories. We found that a critical-energy-release-rate criterion calculated using a 2D variational stress analysis gave the best results. All microcracking theories based on a strength-failure criteria gave poor results. All microcracking theories using 1D stress analyses, regardless of the failure criterion, also gave poor results.

Nairn, John A.↗

NASA NTRS1994

Decoherence and dissipation for a quantum system coupled to a local environment

Decoherence and dissipation in quantum systems has been studied extensively in the context of Quantum Brownian Motion. Effective decoherence in coarse grained quantum systems has been a central issue in recent efforts by Zurek and by Hartle and Gell-Mann to address the Quantum Measurement Problem. Although these models can yield very general classical phenomenology, they are incapable of reproducing relevant characteristics expected of a local environment on a quantum system, such as the characteristic dependence of decoherence on environment spatial correlations. I discuss the characteristics of Quantum Brownian Motion in a local environment by examining aspects of first principle calculations and by the construction of phenomenological models. Effective quantum Langevin equations and master equations are presented in a variety of representations. Comparisons are made with standard results such as the Caldeira-Leggett master equation.

Gallis, Michael R.↗

NASA NTRS1995

Composite-Material Propfan Blades For A Wind-Tunnel Model

Report discusses design and sequence of operations performed in fabricating set of graphite-fiber/epoxy-matrix composite propfan blades. Describes major phases of fabrication of blades, including machining of metal master blades, fabrication of molds from master blades, cutting of graphite-fiber/epoxy prepreg sheets to form plies, stacking of plies to obtain preforms, assembly of pressure-and suction-side preforms into unitary blade preforms, curing preforms in molds, final light finishing, and inspection.

Fite, E. Brian↗

NASA NTRS1996

Transient Sub-Poissonian Distribution for Single-Mode Lasers

In this paper, the transient photon statistics for single-mode lasers is investigated by making use of the theory of quantum electrodynamics. By taking into account of the transitive time l,we obtain the master equation for Jaynes-Cummings model. The relation between the Mandel factor and the time is obtained by directly solving the master equation. The result shows that a transient phenomenon from the transient super-Poissonian distribution to the transient sub-Poissonian distribution occurs for single-mode lasers. In addition, the influences of the thermal light field and the cavity loss on the transient sub-Poissonian distribution are also studied.

Zang, J. Y.↗

NASA NTRS1996

GPS Monitor Station Upgrade Program at the Naval Research Laboratory

One of the measurements made by the Global Positioning System (GPS) monitor stations is to measure the continuous pseudo-range of all the passing GPS satellites. The pseudo-range contains GPS and monitor station clock errors as well as GPS satellite navigation errors. Currently the time at the GPS monitor station is obtained from the GPS constellation and has an inherent inaccuracy as a result. Improved timing accuracy at the GPS monitoring stations will improve GPS performance. The US Naval Research Laboratory (NRL) is developing hardware and software for the GPS monitor station upgrade program to improve the monitor station clock accuracy. This upgrade will allow a method independent of the GPS satellite constellation of measuring and correcting monitor station time to US Naval Observatory (USNO) time. THe hardware consists of a high performance atomic cesium frequency standard (CFS) and a computer which is used to ensemble the CFS with the two CFS's currently located at the monitor station by use of a dual-mixer system. The dual-mixer system achieves phase measurements between the high-performance CFS and the existing monitor station CFS's to within 400 femtoseconds. Time transfer between USNO and a given monitor station is achieved via a two way satellite time transfer modem. The computer at the monitor station disciplines the CFS based on a comparison of one pulse per second sent from the master site at USNO. The monitor station computer is also used to perform housekeeping functions, as well as recording the health status of all three CFS's. This information is sent to the USNO through the time transfer modem. Laboratory time synchronization results in the sub nanosecond range have been observed and the ability to maintain the monitor station CFS frequency to within 3.0 x 10 (sup minus 14) of the master site at USNO.

Galysh, Ivan J.↗

NASA NTRS1996

NASDA's earth observation satellite data archive policy for the earth observation data and information system (EOIS)

NASDA's new Advanced Earth Observing Satellite (ADEOS) is scheduled for launch in August, 1996. ADEOS carries 8 sensors to observe earth environmental phenomena and sends their data to NASDA, NASA, and other foreign ground stations around the world. The downlink data bit rate for ADEOS is 126 MB/s and the total volume of data is about 100 GB per day. To archive and manage such a large quantity of data with high reliability and easy accessibility it was necessary to develop a new mass storage system with a catalogue information database using advanced database management technology. The data will be archived and maintained in the Master Data Storage Subsystem (MDSS) which is one subsystem in NASDA's new Earth Observation data and Information System (EOIS). The MDSS is based on a SONY ID1 digital tape robotics system. This paper provides an overview of the EOIS system, with a focus on the Master Data Storage Subsystem and the NASDA Earth Observation Center (EOC) archive policy for earth observation satellite data.

Sobue, Shin-ichi↗

NASA NTRS1996

The Aggregate Representation of Terrestrial Land Covers Within Global Climate Models (GCM)

This project had four initial objectives: (1) to create a realistic coupled surface-atmosphere model to investigate the aggregate description of heterogeneous surfaces; (2) to develop a simple heuristic model of surface-atmosphere interactions; (3) using the above models, to test aggregation rules for a variety of realistic cover and meteorological conditions; and (4) to reconcile biosphere-atmosphere transfer scheme (BATS) land covers with those that can be recognized from space; Our progress in meeting these objectives can be summarized as follows. Objective 1: The first objective was achieved in the first year of the project by coupling the Biosphere-Atmosphere Transfer Scheme (BATS) with a proven two-dimensional model of the atmospheric boundary layer. The resulting model, BATS-ABL, is described in detail in a Masters thesis and reported in a paper in the Journal of Hydrology Objective 2: The potential value of the heuristic model was re-evaluated early in the project and a decision was made to focus subsequent research around modeling studies with the BATS-ABL model. The value of using such coupled surface-atmosphere models in this research area was further confirmed by the success of the Tucson Aggregation Workshop. Objective 3: There was excellent progress in using the BATS-ABL model to test aggregation rules for a variety of realistic covers. The foci of attention have been the site of the First International Satellite Land Surface Climatology Project Field Experiment (FIFE) in Kansas and one of the study sites of the Anglo-Brazilian Amazonian Climate Observational Study (ABRACOS) near the city of Manaus, Amazonas, Brazil. These two sites were selected because of the ready availability of relevant field data to validate and initiate the BATS-ABL model. The results of these tests are given in a Masters thesis, and reported in two papers. Objective 4: Progress far exceeded original expectations not only in reconciling BATS land covers with those that can be recognized from space, but also in then applying remotely-sensed land cover data to map aggregate values of BATS parameters for heterogeneous covers and interpreting these parameters in terms of surface-atmosphere exchanges.

Shuttleworth, W. James↗

NASA NTRS1996

Effect of Dust Coagulation Dynamics on the Geometry of Aggregates

Master equation gives a more fundamental description of stochastic coagulation processes rather than popular Smoluchowski's equation. In order to examine the effect of the dynamics on the geometry of resulting aggregates, we study Master equation with a rigorous Monte Carlo algorithm. It is found that Cluster-Cluster aggregation model is a good approximation of orderly growth and the aggregates have fluffy structures with a fractal dimension approx. 2. A scaling analysis of Smoluchowski's equation also supports this conclusion.

Nakamura, R.↗

NASA NTRS1994

Satellite Communications Applications Research

This report describes work performed by SDL in the development of monolithically-integrated master oscillator power amplifiers under the NASA-SCAR research contract. The goals of the program were to demonstrate high power diffraction-limited operation from a semiconductor laser with the following characteristics: (1) Output power of 0.5 to 1.0 W continuous-wave (cw); (2) Single spectral mode with greater than 20 dB of side mode suppression; (3) Single spatial mode operation; (4) Modulation capability of 0.5 GHz; and (5) Operating wavelength between 830-860 nm. Cw diffraction-limited output powers as high as 2.2 W were achieved while maintaining a single longitudinal mode. Side mode suppression ratios greater than 20 dB are typically obtained. The single spatial mode output has a Strehl ratio estimated at 0.85, and a high-speed modulation capability was demonstrated with a small-signal 3-dB roll-off at 1.0 GHz. Finally, all of this performance was obtained in the 860 nm wavelength band, which corresponds to the peak sensitivity of Si detectors. During the first option period, three deliverables were fabricated and delivered that included 1 distributed Bragg reflector (DBR) laser operating at 970 nm, 1 DBR laser operating at 860 nm, and one monolithic flared amplifier master oscillator power amplifier (MFA-MOPA) providing 0.5 W cw diffraction-limited output. During the second option period, a total of 5 MFA-MOPA devices were delivered, each operating to better than 1 W cw diffraction-limited at 860 nm.

Lang, Robert J.↗

NASA NTRS1997

Colloids and Nucleation

The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range (0.505 to 0.575) and compared to classical nucleation rate calculations. The experimental nucleation rate density varies with volume fraction more slowly than expected theoretically. Gravity may influence nucleation because crystal nuclei are more dense than the surrounding fluid and may be gravitationally convected. The largest observed crystal size was near volume fraction 0.52. Near the freezing point, crystals should grow to large size because nuclei are sparse and there is plenty of room to grow without contacting other crystals. Near melting the opposite is true, with crystals growing into one another shortly after nucleation. The maximum crystal size seen near 0.52 volume fraction suggests that gravitational stresses are limiting crystal growth near freezing.

Ackerson, Bruce↗

NASA NTRS1999

Establishing a Distance Learning Plan for International Space Station (ISS) Interactive Video Education Events (IVEE)

Educational outreach is an integral part of the International Space Station (ISS) mandate. In a few scant years, the International Space Station has already established a tradition of successful, general outreach activities. However, as the number of outreach events increased and began to reach school classrooms, those events came under greater scrutiny by the education community. Some of the ISS electronic field trips, while informative and helpful, did not meet the generally accepted criteria for education events, especially within the context of the classroom. To make classroom outreach events more acceptable to educators, the ISS outreach program must differentiate between communication events (meant to disseminate information to the general public) and education events (designed to facilitate student learning). In contrast to communication events, education events: are directed toward a relatively homogeneous audience who are gathered together for the purpose of learning, have specific performance objectives which the students are expected to master, include a method of assessing student performance, and include a series of structured activities that will help the students to master the desired skill(s). The core of the ISS education events is an interactive videoconference between students and ISS representatives. This interactive videoconference is to be preceded by and followed by classroom activities which help the students aftain the specified learning objectives. Using the interactive videoconference as the centerpiece of the education event lends a special excitement and allows students to ask questions about what they are learning and about the International Space Station and NASA. Whenever possible, the ISS outreach education events should be congruent with national guidelines for student achievement. ISS outreach staff should recognize that there are a number of different groups that will review the events, and that each group has different criteria for acceptance. For example, school administrators are more likely to be concerned about an event meeting national standards and the cost of the event. In contrast, a teacher's acceptance of an education event may be directly related to the amount of extra work the event imposes upon that teacher. ISS education events must be marketed differently to the different groups of educators, and must never increase the workload of the average teacher.

Wallington, Clint↗

NASA NTRS1998

Multidisciplinary Design Technology Development: A Comparative Investigation of Integrated Aerospace Vehicle Design Tools

This research effort is a joint program between the Departments of Aerospace and Mechanical Engineering and the Computer Science and Engineering Department at the University of Notre Dame. Three Principal Investigators; Drs. Renaud, Brockman and Batill directed this effort. During the four and a half year grant period, six Aerospace and Mechanical Engineering Ph.D. students and one Masters student received full or partial support, while four Computer Science and Engineering Ph.D. students and one Masters student were supported. During each of the summers up to four undergraduate students were involved in related research activities. The purpose of the project was to develop a framework and systematic methodology to facilitate the application of Multidisciplinary Design Optimization (N4DO) to a diverse class of system design problems. For all practical aerospace systems, the design of a systems is a complex sequence of events which integrates the activities of a variety of discipline "experts" and their associated "tools". The development, archiving and exchange of information between these individual experts is central to the design task and it is this information which provides the basis for these experts to make coordinated design decisions (i.e., compromises and trade-offs) - resulting in the final product design. Grant efforts focused on developing and evaluating frameworks for effective design coordination within a MDO environment. Central to these research efforts was the concept that the individual discipline "expert", using the most appropriate "tools" available and the most complete description of the system should be empowered to have the greatest impact on the design decisions and final design. This means that the overall process must be highly interactive and efficiently conducted if the resulting design is to be developed in a manner consistent with cost and time requirements. The methods developed as part of this research effort include; extensions to a sensitivity based Concurrent Subspace Optimization (CSSO) MDO algorithm; the development of a neural network response surface based CSSO-MDO algorithm; and the integration of distributed computing and process scheduling into the MDO environment. This report overviews research efforts in each of these focus. A complete bibliography of research produced with support of this grant is attached.

Renaud, John E.↗

NASA NTRS1999

EOS Terra Validation Program

The EOS Terra mission will be launched in July 1999. This mission has great relevance to the atmospheric radiation community and global change issues. Terra instruments include ASTER, CERES, MISR, MODIS and MOPITT. In addition to the fundamental radiance data sets, numerous global science data products will be generated, including various Earth radiation budget, cloud and aerosol parameters, as well as land surface, terrestrial ecology, ocean color, and atmospheric chemistry parameters. Significant investments have been made in on-board calibration to ensure the quality of the radiance observations. A key component of the Terra mission is the validation of the science data products. This is essential for a mission focused on global change issues and the underlying processes. The Terra algorithms have been subject to extensive pre-launch testing with field data whenever possible. Intensive efforts will be made to validate the Terra data products after launch. These include validation of instrument calibration (vicarious calibration) experiments, instrument and cross-platform comparisons, routine collection of high quality correlative data from ground-based networks, such as AERONET, and intensive sites, such as the SGP ARM site, as well as a variety field experiments, cruises, etc. Airborne simulator instruments have been developed for the field experiment and underflight activities including the MODIS Airborne Simulator (MAS), AirMISR, MASTER (MODIS-ASTER), and MOPITT-A. All are integrated on the NASA ER-2, though low altitude platforms are more typically used for MASTER. MATR is an additional sensor used for MOPITT algorithm development and validation. The intensive validation activities planned for the first year of the Terra mission will be described with emphasis on derived geophysical parameters of most relevance to the atmospheric radiation community. Detailed information about the EOS Terra validation Program can be found on the EOS Validation program homepage i/e.: http://ospso.gsfc.nasa.gov/validation/valpage.html).

Starr, David↗