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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Generalizing the compressible pairwise interaction extended point-particle model

Ejecta physics plays an important role in material interfaces that are impacted by a strong shock wave. When a shock impacts a rough surface of solid material and melts it, the Richtmyer–Meshkov instability grows perturbations on the surface, which can eject particles. After release, the ejecta travel through the post-shock compressible flow. To accurately simulate a large number of ejecta particles, an Euler–Lagrange approach is preferred, which requires modeling the subgrid-scale physics involved with fluid–particle interactions. We generalize the previous work from Hsiao et al. (2023) to consider systems of moving particles subject to any loading shock. The following improvements were made: (1) Particles are allowed to move relative to each other (2) Non-planar shocks are accounted for along with allowing for variable shock speeds. As a result, the generalized algorithm was tested with particle-resolved simulations for canonical test cases. The results of these tests are discussed and analyzed.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1991

Creep and fracture of dispersion-strengthened materials

The creep and fracture of dispersion strengthened materials is reviewed. A compilation of creep data on several alloys showed that the reported values of the stress exponent for creep varied between 3.5 and 100. The activation energy for creep exceeded that for lattice self diffusion in the matrix in the case of some materials and a threshold stress behavior was generally reported in these instances. The threshold stress is shown to be dependent on the interparticle spacing and it is significantly affected by the initial microstructure. The effect of particle size and the nature of the dispersoid on the threshold stress is not well understood at the present time. In general, most studies indicate that the microstructure after creep is similar to that before testing and very few dislocations are usually observed. It is shown that the stress acting on a dispersoid due to a rapidly moving dislocation can exceed the particle yield strength of the G sub p/1000, where G sub p is the shear modulus of the dispersoid. The case when the particle deforms is examined and it is suggested that the dislocation creep threshold stress of the alloy is equal to the yield strength of the dispersoid under these conditions. These results indicate that the possibility that the dispersoid creep threshold stress is determined by either the particle yield strength or the stress required to detach a dislocation from the dispersoid matrix interface. The conditions under which the threshold stress is influenced by one or the other mechanism are discussed and it is shown that the particle yield strength is important until the extent of dislocation core relaxation at the dispersoid matrix interface exceeds about 25 pct. depending on the nature of the particle matrix combination. Finally, the effect of grain boundaries and grain morphology on the creep and fracture behavior of dispersoid strengthened alloys is examined.

Raj, Sai V.↗
NASA NTRS1994

Surgery applications of virtual reality

Virtual reality is a computer-generated technology which allows information to be displayed in a simulated, bus lifelike, environment. In this simulated 'world', users can move and interact as if they were actually a part of that world. This new technology will be useful in many different fields, including the field of surgery. Virtual reality systems can be used to teach surgical anatomy, diagnose surgical problems, plan operations, simulate and perform surgical procedures (telesurgery), and predict the outcomes of surgery. The authors of this paper describe the basic components of a virtual reality surgical system. These components include: the virtual world, the virtual tools, the anatomical model, the software platform, the host computer, the interface, and the head-coupled display. In the chapter they also review the progress towards using virtual reality for surgical training, planning, telesurgery, and predicting outcomes. Finally, the authors present a training system being developed for the practice of new procedures in abdominal surgery.

Rosen, Joseph↗
NASA NTRS1992

A distributed clients/distributed servers model for STARCAT

STARCAT, the Space Telescope ARchive and CATalogue user interface has been along for a number of years already. During this time it has been enhanced and augmented in a number of different fields. This time, we would like to dwell on a new capability allowing geographically distributed user interfaces to connect to geographically distributed data servers. This new concept permits users anywhere on the internet running STARCAT on their local hardware to access e.g., whichever of the 3 existing HST archive sites is available, or get information on the CFHT archive through a transparent connection to the CADC in BC or to get the La Silla weather by connecting to the ESO database in Munich during the same session. Similarly PreView (or quick look) images and spectra will also flow directly to the user from wherever it is available. Moving towards an 'X'-based STARCAT is another goal being pursued: a graphic/image server and a help/doc server are currently being added to it. They should further enhance the user independence and access transparency.

Pirenne, B.↗
NASA NTRS2001

Design and Verification of Space Station EVA-Operated Truss Attachment System

This paper describes the design and verification of a system used to attach two segments of the International Space Station (ISS). This system was first used in space to mate the P6 and Z1 trusses together in December 2000, through a combination of robotic and extravehicular tasks. Features that provided capture, coarse alignment, and fine alignment during the berthing process are described. Attachment of this high value hardware was critical to the ISS's sequential assembly, necessitating the inclusion of backup design and operational features. Astronauts checked for the proper performance of the alignment and bolting features during on-orbit operations. During berthing, the system accommodates truss-to-truss relative displacements that are caused by manufacturing tolerances and on-orbit thermal gradients. After bolt installation, the truss interface becomes statically determinate with respect to in-plane shear loads and isolates attach bolts from bending moments. The approach used to estimate relative displacements and the means of accommodating them is explained. Confidence in system performance was achieved through a cost-effective collection of tests and analyses, including thermal, structural, vibration, misalignment, contact dynamics, underwater simulation, and full-scale functional testing. Design considerations that have potential application to other mechanisms include accommodating variations of friction coefficients in the on-orbit joints, wrench torque tolerances, joint preload, moving element clearances at temperature extremes, and bolt-nut torque reaction.

Katell, Gabriel↗
NASA NTRS2015

SPHERES: From Ground Development to Operations on ISS

SPHERES (Synchronized Position Hold Engage and Reorient Experimental Satellites) is an internal International Space Station (ISS) Facility that supports multiple investigations for the development of multi-spacecraft and robotic control algorithms. The SPHERES Facility on ISS is managed and operated by the SPHERES National Lab Facility at NASA Ames Research Center (ARC) at Moffett Field California. The SPHERES Facility on ISS consists of three self-contained eight-inch diameter free-floating satellites which perform the various flight algorithms and serve as a platform to support the integration of experimental hardware. To help make science a reality on the ISS, the SPHERES ARC team supports a Guest Scientist Program (GSP). This program allows anyone with new science the possibility to interface with the SPHERES team and hardware. In addition to highlighting the available SPHERES hardware on ISS and on the ground, this presentation will also highlight ground support, facilities, and resources available to guest researchers. Investigations on the ISS evolve through four main phases: Strategic, Tactical, Operations, and Post Operations. The Strategic Phase encompasses early planning beginning with initial contact by the Principle Investigator (PI) and the SPHERES program who may work with the PI to assess what assistance the PI may need. Once the basic parameters are understood, the investigation moves to the Tactical Phase which involves more detailed planning, development, and testing. Depending on the nature of the investigation, the tactical phase may be split into the Lab Tactical Phase or the ISS Tactical Phase due to the difference in requirements for the two destinations. The Operations Phase is when the actual science is performed; this can be either in the lab, or on the ISS. The Post Operations Phase encompasses data analysis and distribution, and generation of summary status and reports. The SPHERES Operations and Engineering teams at ARC is composed of experts who can guide the Payload Developer (PD) and Principle Investigator (PI) in reaching critical milestones to make their science a reality using the SPHERES platform. From performing integrated safety and verification assessments, to assisting in developing crew procedures and operations products, to organizing, planning, and executing all test sessions, to helping manage data products, the SPHERES team at ARC is available to support microgravity research with the SPEHRES Guest Scientist Program.

ISS Research↗
NASA NTRS2011

CropEx Web-Based Agricultural Monitoring and Decision Support

CropEx is a Web-based agricultural Decision Support System (DSS) that monitors changes in crop health over time. It is designed to be used by a wide range of both public and private organizations, including individual producers and regional government offices with a vested interest in tracking vegetation health. The database and data management system automatically retrieve and ingest data for the area of interest. Another stores results of the processing and supports the DSS. The processing engine will allow server-side analysis of imagery with support for image sub-setting and a set of core raster operations for image classification, creation of vegetation indices, and change detection. The system includes the Web-based (CropEx) interface, data ingestion system, server-side processing engine, and a database processing engine. It contains a Web-based interface that has multi-tiered security profiles for multiple users. The interface provides the ability to identify areas of interest to specific users, user profiles, and methods of processing and data types for selected or created areas of interest. A compilation of programs is used to ingest available data into the system, classify that data, profile that data for quality, and make data available for the processing engine immediately upon the data s availability to the system (near real time). The processing engine consists of methods and algorithms used to process the data in a real-time fashion without copying, storing, or moving the raw data. The engine makes results available to the database processing engine for storage and further manipulation. The database processing engine ingests data from the image processing engine, distills those results into numerical indices, and stores each index for an area of interest. This process happens each time new data is ingested and processed for the area of interest, and upon subsequent database entries, the database processing engine qualifies each value for each area of interest and conducts a logical processing of results indicating when and where thresholds are exceeded. Reports are provided at regular, operator-determined intervals that include variances from thresholds and links to view raw data for verification, if necessary. The technology and method of development allow the code base to easily be modified for varied use in the real-time and near-real-time processing environments. In addition, the final product will be demonstrated as a means for rapid draft assessment of imagery.

Harvey. Craig↗
NASA NTRS2013

Mobile Thread Task Manager

The Mobile Thread Task Manager (MTTM) is being applied to parallelizing existing flight software to understand the benefits and to develop new techniques and architectural concepts for adapting software to multicore architectures. It allocates and load-balances tasks for a group of threads that migrate across processors to improve cache performance. In order to balance-load across threads, the MTTM augments a basic map-reduce strategy to draw jobs from a global queue. In a multicore processor, memory may be "homed" to the cache of a specific processor and must be accessed from that processor. The MTTB architecture wraps access to data with thread management to move threads to the home processor for that data so that the computation follows the data in an attempt to avoid L2 cache misses. Cache homing is also handled by a memory manager that translates identifiers to processor IDs where the data will be homed (according to rules defined by the user). The user can also specify the number of threads and processors separately, which is important for tuning performance for different patterns of computation and memory access. MTTM efficiently processes tasks in parallel on a multiprocessor computer. It also provides an interface to make it easier to adapt existing software to a multiprocessor environment.

Clement, Bradley J.↗
NASA NTRS1979

Influence of convection on free growth of dendrite crystals from solution

The free growth of dendrites in a uniformly supercooled solution was examined using cine photography with a Schlieren optical system. Crystals were grown in the bulk of the solution from a centrally located capillary tube, nucleated at the interface with a liquid nitrogen cooled wire. Crystals propagated along the tube, the slower growing orientations eliminated, and emerged at the tip, usually growing parallel to the tube direction. For both sodium sulfate decahydrate from its solution and ice from sodium chloride solution, growth rate and fineness of dendrites increased with supercooling. In sodium sulfate, upward convection of the less dense depleted solution occurs; downward convection was observed for the rejected, more concentrated sodium chloride solution. In both cases, there was a spatial and temporal delay in the release of the convective plume from the moving dendrite tip. The role of this convection on the growth characteristics and the production of secondary crystals is examined. A proposed low-g experiment to examine differences in growth rate, crystal texture, and secondary nucleation in a reduced convective regime where molecular diffusion is the dominant transfer process is discussed.

Hallett, J.↗
NASA NTRS2006

Multistage Electrophoretic Separators

A multistage electrophoresis apparatus has been invented for use in the separation of cells, protein molecules, and other particles and solutes in concentrated aqueous solutions and suspensions. The design exploits free electrophoresis but overcomes the deficiencies of prior free-electrophoretic separators by incorporating a combination of published advances in mathematical modeling of convection, sedimentation, electro-osmotic flow, and the sedimentation and aggregation of droplets. In comparison with other electrophoretic separators, these apparatuses are easier to use and are better suited to separation in relatively large quantities characterized in the art as preparative (in contradistinction to smaller quantities characterized in the art as analytical). In a multistage electrophoretic separator according to the invention, an applied vertical steady electric field draws the electrically charged particles of interest from within a cuvette to within a collection cavity that has been moved into position of the cuvette. There are multiple collection cavities arranged in a circle; each is aligned with the cuvette for a prescribed short time. The multistage, short-migration-path character of the invention solves, possibly for the first time, the fluid-instability problems associated with free electrophoresis. The figure shows a prototype multistage electrophoretic separator that includes four sample stations and five collection stages per sample. At each sample station, an aqueous solution or suspension containing charged species to be separated is loaded into a cuvette, which is machined into a top plate. The apparatus includes a lower plate, into which 20 collection cavities have been milled. Each cavity is filled with an electrophoresis buffer solution. For the collection of an electrophoretic fraction, the lower plate is rotated to move a designated collection cavity into alignment with the opening of the cuvette. An electric field is then applied between a non-gassing electrode in the collection cavity and an electrolyte compartment, which is separated from the cuvette by a semipermeable membrane. The electrolyte is refreshed by circulation by use of a peristaltic pump. In subsequent steps, the lower plate is rotated to collect other electrophoretic fractions. Later, the collected fractions are removed from the collection cavities through ports that have threaded plugs. The base of the apparatus contains power supplies and a computer interface. The design includes provisions for monitoring and feedback control of cavity position, electric field, and temperature. The operation of the apparatus can easily be automated, as demonstrated by use of software that has already been written for this purpose.

Thomas, Nathan↗
NASA NTRS1993

Magneto-optic superlattice thin films: Fabrication, structural and magnetic characterization

During this quarter studies were extended to determine the electronic contribution to the perpendicular interface anisotropy in Co-based multilayers. Using in situ Kerr effect measurements, the influences of different transition metals (TM = Ag, Au, Cu, and Pd) on the magnetic properties of single-crystal Co films grown on Pd (111) and Au (111) surfaces are investigated. Last quarter the discovery of a large peak in the perpendicular anisotropy when approximately one monolayer of Cu or Ag is deposited on the Co surface was reported. We now have added a computer-controlled stepper-motor drive to our MBE sample transfer mechanism. The motor allows us to move the sample at a constant velocity from behind a shutter during deposition. The film, therefore, is deposited as a wedge with a linear variation of thickness across the substrate. In this way, a continuous range of coverage on a single sample is studied. The stepper motor also provides the necessary control for precisely positioning the sample in the laser beam for Kerr effect measurements at the different coverages.

Falco, C. M.↗
NASA NTRS2000

Mechanisms of Protonic Nonvolatile Memory Device

A nonvolatile memory device based on protonic transport in oxides has been proposed. The mobile H+ ions are introduced into the SiO2 layer by annealing Si/SiO2/Si structures in H2 at temperatures greater than 500 deg C. This effect has only been observed for confined oxides that have been annealed at greater than or equal to 1100 C prior to the hydrogenation anneal. This includes buried oxides such as Unibond and SIMOX as well as thermal oxides annealed with a polysilicon cap. An applied field moves the charge within the oxide and the charge stops moving when the field is removed. In a memory device, the hydrogen-annealed oxide is the gate oxide and the position of the mobile charge is sensed by the shift of the I-V curve. Much is still not understood about the motion of the charge across the buried oxide. Previous work has assumed that H+ transport and the time it takes to traverse the oxide is governed by interactions within the bulk of the oxide. Based on parameters that affect the transport time, we conclude that H+ trapping and detrapping at the Si/SiO2 interface are more important than H+ interactions within the oxide bulk. These parameters include the applied field, the H+ concentration and the oxide thickness. One consequence is that projections of device write-time based on the previous assumptions of H+ transport mechanisms may be overly optimistic.

P J Macfarlane↗
NASA NTRS1988

LDR structural experiment definition

A study was performed to develop the definition of a structural flight experiment for a large precision segmented reflector that would utilize the Space Station. The objective of the study was to use the Large Deployable Reflector (LDR) baseline configuration for focusing on experiment definition activity which would identify the Space Station accommodation requirements and interface constraints. Results of the study defined three Space Station based experiments to demonstrate the technologies needed for an LDR type structure. The basic experiment configurations are the same as the JPL baseline except that the primary mirror truss is 10 meters in diameter instead of 20. The primary objectives of the first experiment are to construct the primary mirror support truss and to determine its structural and thermal characteristics. Addition of the optical bench, thermal shield and primary mirror segments and alignment of the optical components occur on the second experiment. The structure will then be moved to the payload pointing system for pointing, optical control and scientific optical measurement for the third experiment.

Russell, Richard A.↗
NASA NTRS2004

A Low-Cost Clustered Archive Approach for Storing Remote Sensing Data

As part of NASA's Earth Observing System (EOS) Data and Information System (EOSDIS), the Moderate Resolution Imaging Spectrometer (MODIS) Data Processing System (MODAPS) is now processing data from two instruments on the EOS flag ship spacecraft Terra and Aqua. Between the two, MODAPS is generating over 1 Terrabyte of data per day and has surpassed 3 Petabytes of total data. The bulk of the data is stored near-line in StorageTek Powerhorn tape jukeboxes. Accessing data that has been moved to tape involves submitting an order, scheduling the tape, and waiting for the data to become available. I am developing a low cost clustered archive that could enable storing a very large amount of data such as the MODIS data described above in an organized fashion on a cluster of commodity hardware using low cost SATA hard drives such that the files are directly available online. The system takes full advantage of Open Source software, using the GNULinux operating system, PostgreSQL relational database and the Apache HTTP Server. This poster session will depict my approach, the interface to the archive, a brief discussion of the internals of the system and some performance numbers from my prototyping. I will also describe various costs and benefits of this approach versus the traditional large tape jukebox approach currently in use in the EOSDIS.

Tilmes, Curt↗
NASA NTRS1983

Shuttle/Centaur - More capability for the 1980's

Design features of the Centaur upper stage for the Shuttle are described, noting interfaces with the Orbiter and intended missions. The Shuttle will carry the Centaur stage into a 241 km eastward orbit, open the payload doors, and by the fourth orbit rotate the Centaur 45 deg so it points out of the bay. An integrated support system will limit the actual equipment added to the Orbiter to 122 kg. Separation from the Orbiter will be effected by a spring-loaded mechanism that will impart a 1/3 m/sec velocity to the Centaur, which carries its own LOX/LH2 fuel supply for two RL 10A-3-3A engines. The fuel is moved to the bottom of the tanks by auxiliary thrusters which propel the Centaur forward. Planned missions for the Shuttle-Centaur are boosting the ESA Solar Polar Mission and launching the Galileo probe in 1986, possibly followed by a Venus radar mapper mission in 1988.

Spurlock, O. F.↗
NASA NTRS1999

Ion Thruster and Power Processor Developed for the Deep Space 1 Mission

The NASA Solar Electric Propulsion Technology Applications Readiness (NSTAR) Program has provided a single-string primary propulsion system to NASA's Deep Space 1 spacecraft. This spacecraft will carry about 81 kg of xenon propellant for the ion thruster, which can be throttled down from 2.3 to 0.5 kW as the spacecraft moves away from the Sun. The propellant load will provide about 20 months of propulsion at the one-half power throttle setpoint of 1.2 kW. This mission will validate the 2.5-kW ion propulsion system and will fly by the asteroid 1992 KD in 1999. If funding permits, Deep Space 1 also will encounter comets Wilson-Harrington and Borrelly in 2001. NASA Lewis Research Center's On-Board Propulsion Branch was responsible for the development of the 30-cm-diameter ion thruster, the 2.5-kW power processor unit (PPU), and the Digital Control and Interface Unit (DCIU) that controls the PPU/thruster/feed system and provides data and recovery from fault conditions. Lewis transferred the thruster and PPU technologies to the Hughes Electron Dynamics Division, which was selected to build two sets of flight thrusters, as well as the PPU's and DCIU's. Hughes subcontracted the DCIU development to Spectrum Astro Incorporated. The Jet Propulsion Laboratory (JPL) was primarily responsible for the NSTAR project management, thruster lifetests, the feed system, diagnostics, and the propulsion subsystem integration. A total of four engineering model thrusters and three breadboard PPU's were built, integrated, and tested. More than 50 development tests were conducted along with thruster design verification tests of 2000 and 1000 hours. In addition, an 8000-hr life demonstration test was successfully completed and demonstrated wear-rates consistent with full-power lifetimes in excess of 12,000 hours.

Sovey, James S.↗
NASA NTRS1984

Orbital transfer vehicle propulsion issues

The development of a reusable and space-based orbital transfer vehicle (OTV) necessitates an integral approach toward structural and propulsion subsystems design. A single engine installation necessitates moving the engine further aft and/or relocation of the engine gimbal point to accommodate vehicle control requirements. Penalties associated with gimbal point relocation without increasing stage length or modifying typical advanced engine concepts, as well as a method for minimizing such penalties, are presented for a single engine toroidal tank OTV configuration. Alternative integrated vehicle structure/engine concepts are also presented for multi-engine configurations. Features of these potential concepts are given which indicate the need for substantial additional study of feedline gimbal alternatives before firmly establishing advanced engine design. The issue of vehicle/engine integration is addressed in three areas: interfaces (physical and functional), installation requirements, and reliability apportionment (i.e., number of engines required to assure mission completion).

Bergeron, R. P.↗
NASA NTRS1994

Equilibrium fluid interface behavior under low- and zero-gravity conditions

We describe here some of our recent mathematical work, which forms a basis for the Interface Configuration Experiment scheduled for USML-2. The work relates to the design of apparatus that exploits microgravity conditions for accurate determination of contact angle. The underlying motivation for the procedures rests on a discontinuous dependence of the capillary free surface interface S on the contact angle gamma, in a cylindrical capillary tube whose section (base) omega contains a protruding corner with opening angle 2 alpha. Specifically, in a gravity-free environment, omega can be chosen so that, for all sufficiently large fluid volume, the height of S is uniquely determined as a (single-valued) function mu(x,y) entirely covering the base; the height mu is bounded over omega uniformly in gamma throughout the range absolute value of (gamma -(pion/2)) less than or equal to alpha, while for absolute value of (gamma - (pion/2)) greater than alpha fluid will necessarily move to the corner and uncover the base, rising to infinity (or falling to negative infinity) at the vertex, regardless of volume. We mention here only that procedures based on the phenomenon promise excellent accuracy when gamma is close pion/2 but may be subject to experimental error when gamma is close to zero (orpion), as the 'singular' part of the domain over which the fluid accumulates (or disappears) when a critical angle gamma theta is crossed then becomes very small and may be difficult to observe. We ignore the trivial case gamma is equal to pion/2 (planar free surface), to simplify the discussion.

Concus, Paul↗