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At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Modal identification experiment

The Modal Identification Experiment (MIE) is a proposed on-orbit experiment being developed by NASA's Office of Aeronautics and Space Technology wherein a series of vibration measurements would be made on various configurations of Space Station Freedom (SSF) during its on-orbit assembly phase. The experiment is to be conducted in conjunction with station reboost operations and consists of measuring the dynamic responses of the spacecraft produced by station-based attitude control system and reboost thrusters, recording and transmitting the data, and processing the data on the ground to identify the natural frequencies, damping factors, and shapes of significant vibratory modes. The experiment would likely be a part of the Space Station on-orbit verification. Basic research objectives of MIE are to evaluate and improve methods for analytically modeling large space structures, to develop techniques for performing in-space modal testing, and to validate candidate techniques for in-space modal identification. From an engineering point of view, MIE will provide the first opportunity to obtain vibration data for the fully-assembled structure because SSF is too large and too flexible to be tested as a single unit on the ground. Such full-system data is essential for validating the analytical model of SSF which would be used in any engineering efforts associated with structural or control system changes that might be made to the station as missions evolve over time. Extensive analytical simulations of on-orbit tests, as well exploratory laboratory simulations using small-scale models, have been conducted in-house and under contract to develop a measurement plan and evaluate its potential performance. In particular, performance trade and parametric studies conducted as part of these simulations were used to resolve issues related to the number and location of the measurements, the type of excitation, data acquisition and data processing, effects of noise and nonlinearities, selection of target vibration modes, and the appropriate type of data analysis scheme. The purpose of this talk is to provide an executive-summary-type overview of the modal identification experiment which has emerged from the conceptual design studies conducted to-date. Emphasis throughout is on those aspects of the experiment which should be of interest to those attending the subject utilization conference. The presentation begins with some preparatory remarks to provide background and motivation for the experiment, describe the experiment in general terms, and cite the specific technical objectives. This is followed by a summary of the major results of the conceptual design studies conducted to define the baseline experiment. The baseline experiment which has resulted from the studies is then described.

Kvaternik, Raymond G.↗
NASA NTRS1994

Composite Load Spectra for Select Space Propulsion Structural Components

Generic load models are described with multiple levels of progressive sophistication to simulate the composite (combined) load spectra (CLS) that are induced in space propulsion system components, representative of Space Shuttle Main Engines (SSME), such as transfer ducts, turbine blades and liquid oxygen (LOX) posts. These generic (coupled) models combine the deterministic models for composite load dynamic, acoustic, high-pressure and high rotational speed, etc., load simulation using statistically varying coefficients. These coefficients are then determined using advanced probabilistic simulation methods with and without strategically selected experimental data. The entire simulation process is included in a CLS computer code. Applications of the computer code to various components in conjunction with the PSAM (Probabilistic Structural Analysis Method) to perform probabilistic load evaluation and life prediction evaluations are also described to illustrate the effectiveness of the coupled model approach.

Ho, Hing W.↗
NASA NTRS1983

Shock Tube Studies of Soot Formation

The objective of this research is to record the time histories of the major and minor species which appear in the pyrolysis of toluene, benzene, butadiene, allene, and acetylene; to develop a set of reactions that will model the observed profiles over a wide temperature and concentration range; to identify the critical reactions that influence the pre-particle soot formation process. Toluene and benzene were chosen as two key aromatic compounds which are representative of the pyrolytic process. Butadiene, allene, and acetylene were selected to investigate the formation of aromatic compounds from non-cyclic species. The experimental apparatus used for the study consists of a shock tube coupled to a time-of-flight mass spectrometer Spectra are recorded at 30 microsecond intervals for a total observation time of 0.50 - 1.20 milliseconds. Peak heights of the species of interest in the m/e range 12-300 are measured as a function of reaction time. Calibration curves are constructed which aid the conversion of peak heights to concentrations. The mixtures range from 1 percent-6 percent fuel; the balance is neon diluent.

R D Kern↗
NASA NTRS1995

Design tool for multiprocessor scheduling and evaluation of iterative dataflow algorithms

A graph-theoretic design process and software tool is defined for selecting a multiprocessing scheduling solution for a class of computational problems. The problems of interest are those that can be described with a dataflow graph and are intended to be executed repetitively on a set of identical processors. Typical applications include signal processing and control law problems. Graph-search algorithms and analysis techniques are introduced and shown to effectively determine performance bounds, scheduling constraints, and resource requirements. The software tool applies the design process to a given problem and includes performance optimization through the inclusion of additional precedence constraints among the schedulable tasks.

Jones, Robert L., III↗
NASA NTRS1995

Structure/Permeability Relationships Of Polyimide Membranes

Report describes experimental study of permeabilities, by each of five gases, of membranes made of four different polyimides. Conducted to gain understanding of effects of molecular structures of membranes on permeabilities and to assess potential for exploitation of selective permeability in gas-separation processes. Gases used: H2, O2, N2, CO2, and CH4.

St. Clair, A. K.↗
NASA NTRS1995

The CCD/Transit Instrument (CTI) data-analysis system

The automated software system for archiving, analyzing, and interrogating data from the CCD/Transit Instrument (CTI) is described. The CTI collects up to 450 Mbytes of image-data each clear night in the form of a narrow strip of sky observed in two colors. The large data-volumes and the scientific aims of the project make it imperative that the data are analyzed within the 24-hour period following the observations. To this end a fully automatic and self evaluating software system has been developed. The data are collected from the telescope in real-time and then transported to Tucson for analysis. Verification is performed by visual inspection of random subsets of the data and obvious cosmic rays are detected and removed before permanent archival is made to the optical disc. The analysis phase is performed by a pair of linked algorithms, one operating on the absolute pixel-values and the other on the spatial derivative of the data. In this way both isolated and merged images are reliably detected in a single pass. In order to isolate the latter algorithm from the effects of noise spikes a 3x3 Hanning filter is applied to the raw data before the analysis is run. The algorithms reduce the input pixel-data to a database of measured parameters for each image which has been found. A contrast filter is applied in order to assign a detection-probability to each image and then x-y calibration and intensity calibration are performed using known reference stars in the strip. These are added to as necessary by secondary standards boot-strapped from the CTI data itself. The final stages involve merging the new data into the CTI Master-list and History-list and the automatic comparison of each new detection with a set of pre-defined templates in parameter-space to find interesting objects such as supernovae, quasars and variable stars. Each stage of the processing from verification to interesting image selection is performed under a data-logging system which both controls the pipe-lining of data through the system and records key performance monitor parameters which are built into the software. Furthermore, the data from each stage are stored in databases to facilitate evaluation, and all stages offer the facility to enter keyword-indexed free-format text into the data-logging system. In this way a large measure of certification is built into the system to provide the necessary confidence in the end results.

Cawson, M. G. M.↗
NASA NTRS1997

Enantiomeric Cross-Inhibition in the Synthesis of Oligonucleotides on a Nonchiral Template

Prebiotic syntheses of chiral monomers always yield racemic mixtures. Living systems, however, utilize L-amino acids and D-nucleotides in their biopolymers. The generation of optical asymmetry by selection and amplification in an autocatalytic process is, therefore, an important element in many theories of the origin of life. Replication of polynucleotides in template-directed syntheses is an obvious candidate for such an amplification step in a pre-'RNA world'. A serious objection to this suggestion is the observation that the efficiency of template-directed syntheses of RNA is limited by enantiomeric cross-inhibition. Peptide Nucleic Acids (PNAs), amide-linked, nonchiral analogues of RNA, have been 'copied' into RNA and constitute an alternative to chiral polynucleotides as an informational replicating system. Here, we use PNA as model for a hypothetical, nonchiral precursor of RNA in experiments re-examining enantiomeric cross-inhibition. We find that enantiomeric cross-inhibition is as serious in the polymerization of nucleotides on a PNA template as it is on a conventional RNA or DNA template.

Schmidt, Jurgen G.↗
NASA NTRS1999

Stirling Space Engine Program: Final Report - Volume 1

The objective of this program was to develop the technology necessary for operating Stirling power converters in a space environment and to demonstrate this technology in full-scale engine tests. Hardware development focused on the Component Test Power Converter (CTPC), a single cylinder, 12.5-kWe engine. Design parameters for the CTPC were 150 bar operating pressure, 70 Hz frequency, and hot-and cold-end temperatures of 1050 K and 525 K, respectively. The CTPC was also designed for integration with an annular sodium heat pipe at the hot end, which incorporated a unique "Starfish" heater head that eliminated highly stressed brazed or weld joints exposed to liquid metal and used a shaped-tubed electrochemical milling process to achieve precise positional tolerances. Selection of materials that could withstand high operating temperatures with long life were another focus. Significant progress was made in the heater head (Udimet 700 and Inconel 718 and a sodium-filled heat pipe); the alternator (polyimide-coated wire with polyimide adhesive between turns and a polyimide-impregnated fiberglass overwrap and samarium cobalt magnets); and the hydrostatic gas bearings (carbon graphite and aluminum oxide for wear couple surfaces). Tests on the CTPC were performed in three phases: cold end testing (525 K), engine testing with slot radiant heaters, and integrated heat pipe engine system testing. Each test phase was successful, with the integrated engine system demonstrating a power level of 12.5 kWe and an overall efficiency of 22 percent in its maiden test. A 1500-hour endurance test was then successfully completed. These results indicate the significant achievements made by this program that demonstrate the viability of Stirling engine technology for space applications.

Dhar, Manmohan↗
NASA NTRS1998

NASA's Microgravity Materials Science Program

Materials Science research programs are funded by NASA through the Microgravity Research Division. Such programs are normally designated as flight definition or ground based and can be awarded initially for up to four years. Selection is through a peer review process in response to a biennial NASA Research Announcement (NRA). The next announcement is due in November 1998 with proposals due in March 1999. Topics of special interest to NASA are described in the guidelines for proposal writing within the NRA. NASA's interest in materials is wide and covers a range which includes metals and alloys, ceramics, glasses, polymers, non-linear optics, aerogels and nanostructures. With increasing interest in the Human Exploration and Development of Space (HEDS) program, the materials research funded will not be exclusively devoted to processes dependent on microgravity, but will also support materials of strategic interest in meeting NASA's long range plans of interplanetary travel.

Gillies, Donald C.↗
NASA NTRS2000

Research Opportunities on the Low Temperature Microgravity Physics Facility (LTMPF) on the International Space Station

The Low Temperature Microgravity Physics Facility (LTMPF) is a state-of-the-art facility for long duration science Investigations whose objectives can only be achieved in microgravity and at low temperature. LTMPF consists of two reusable, cryogenic facilities with self-contained electronics, software and communication capabilities. The Facility will be first launched by Japanese HIIA Rocket in 2003 and retrieved by the Space Shuttle, and will have at least five months cryogen lifetime on the Japanese Experiment Module Exposed Facility (JEM EF) of the International Space Station. A number of high precision sensors of temperature, pressure and capacitance will be available, which can be further tailored to accommodate a wide variety of low temperature experiments. This paper will describe the LTMPF and its goals and design requirements. Currently there are six candidate experiments in the flight definition phase to fly on LTMPF. Future candidate experiments will be selected through the NASA Research Announcement process. Opportunities for utilization and collaboration with international partners will also be discussed. This work is being carried out by the Jet Propulsion Laboratory, California Institute of Technology under contract to the National Aeronautics and Space Administration. The work was funded by NASA Microgravity Research Division.

Liu, Feng-Chuan↗
NASA NTRS2001

A High-Speed, Event-Driven, Active Pixel Sensor Readout for Photon-Counting Microchannel Plate Detectors

Silicon array readouts for microchannel plate intensifiers offer several attractive features. In this class of detector, the electron cloud output of the MCP intensifier is converted to visible light by a phosphor; that light is then fiber-optically coupled to the silicon array. In photon-counting mode, the resulting light splashes on the silicon array are recognized and centroided to fractional pixel accuracy by off-chip electronics. This process can result in very high (MCP-limited) spatial resolution for the readout while operating at a modest MCP gain (desirable for dynamic range and long term stability). The principal limitation of intensified CCD systems of this type is their severely limited local dynamic range, as accurate photon counting is achieved only if there are not overlapping event splashes within the frame time of the device. This problem can be ameliorated somewhat by processing events only in pre-selected windows of interest or by using an addressable charge injection device (CID) for the readout array. We are currently pursuing the development of an intriguing alternative readout concept based on using an event-driven CMOS Active Pixel Sensor. APS technology permits the incorporation of discriminator circuitry within each pixel. When coupled with suitable CMOS logic outside the array area, the discriminator circuitry can be used to trigger the readout of small sub-array windows only when and where an event splash has been detected, completely eliminating the local dynamic range problem, while achieving a high global count rate capability and maintaining high spatial resolution. We elaborate on this concept and present our progress toward implementing an event-driven APS readout.

Kimble, Randy A.↗
NASA NTRS2002

Materials Properties Research at MSFC

MSFC is currently planning, organizing and directing test coupon fabrication and subsequent CTE testing for two mirror materials of specific interest to the AMSD and NGST programs, Beryllium 0-30H (Be 0-30H) and Ultra Low Expansion glass (ULE). The ULE test coupons are being fabricated at MSFC from AMSD core residuals provided by Kodak, The Be 0-30H test coupons are being fabricated at Brush Wellman using residuals from the SBMD. Both sets of test coupons will be sent to a test vendor selected through the NASA competitive proposal process with the test results being provided by written report to MSFC by the end of the fiscal year. The test results will become model input data for the AMSD analysts, both MSFC and contractor, providing an enhancement to the historical CTE data currently available.

Presson, Joan B.↗
NASA NTRS2002

A High-Speed, Event-Driven, Active Pixel Sensor Readout for Photon-Counting Microchannel Plate Detectors

Silicon array readouts for microchannel plate intensifiers offer several attractive features. In this class of detector, the electron cloud output of the MCP intensifier is converted to visible light by a phosphor; that light is then fiber-optically coupled to the silicon array. In photon-counting mode, the resulting light splashes on the silicon array are recognized and centroided to fractional pixel accuracy by off-chip electronics. This process can result in very high (MCP-limited) spatial resolution while operating at a modest MCP gain (desirable for dynamic range and long term stability). The principal limitation of intensified CCD systems of this type is their severely limited local dynamic range, as accurate photon counting is achieved only if there are not overlapping event splashes within the frame time of the device. This problem can be ameliorated somewhat by processing events only in pre-selected windows of interest of by using an addressable charge injection device (CID) for the readout array. We are currently pursuing the development of an intriguing alternative readout concept based on using an event-driven CMOS Active Pixel Sensor. APS technology permits the incorporation of discriminator circuitry within each pixel. When coupled with suitable CMOS logic outside the array area, the discriminator circuitry can be used to trigger the readout of small sub-array windows only when and where an event splash has been detected, completely eliminating the local dynamic range problem, while achieving a high global count rate capability and maintaining high spatial resolution. We elaborate on this concept and present our progress toward implementing an event-driven APS readout.

Kimble, Randy A.↗
NASA NTRS2002

Development and Design of a Zero-G Liquid Quantity Gauge for a Solar Thermal Vehicle

The development and design of a cryogenic liquid quantity gauge for zero-g applications is described. The gauge, named the Compression Mass Gauge (CMG), operates on the principle of slightly changing the volume of the tank by an oscillating bellows. The resulting pressure change is measured and used to predict the volume of vapor in the tank, from which the volume of liquid is computed. For each gauging instance, pressures are measured for several different bellows frequencies to enable minor real-gas effects to be quantified and thereby to obtain a gauging accuracy of +/- 1% of tank volume. Southwest Research Institute (Tm) and NASA-GRC (Glenn Research Center) have developed several previous breadboard and engineering development gauges and tested them in cryogenic hydrogen and nitrogen to establish the gauge capabilities, to resolve several design issues, and to formulate data processing algorithms. The CMG has been selected by NASA's Future X program for a flight demonstration on the USAF (United States Air Force) / Boeing Solar Thermal Vehicle Space Experiment (SOTVSE). This paper reviews the design trade studies needed to satisfy the SOTVSE limitations on CMG power, volume, and mass, and describes the mechanical design of the CMG.

Dodge, Franklin T.↗
NASA NTRS2002

Method and Apparatus for Obtaining a Precision Thickness in Semiconductor and Other Wafers

A method and apparatus for processing a wafer comprising a material selected from an electrical semiconducting material and an electrical insulating material is presented. The wafer has opposed generally planar front and rear sides and a peripheral edge, wherein said wafer is pressed against a pad in the presence of a slurry to reduce its thickness. The thickness of the wafer is controlled by first forming a recess such as a dimple on the rear side of the wafer. A first electrical conducting strip extends from a first electrical connection means to the base surface of the recess to the second electrical connector. The first electrical conducting strip overlies the base surface of the recess. There is also a second electrical conductor with an electrical potential source between the first electrical connector and the second electrical connector to form. In combination with the first electrical conducting strip, the second electrical conductor forms a closed electrical circuit, and an electrical current flows through the closed electrical circuit. From the front side of the wafer the initial thickness of the wafer is reduced by lapping until the base surface of the recess is reached. The conductive strip is at least partially removed from the base surface to automatically stop the lapping procedure and thereby achieve the desired thickness.

Okojie, Robert S.↗
NASA NTRS2002

The Overgrid Interface for Computational Simulations on Overset Grids

Computational simulations using overset grids typically involve multiple steps and a variety of software modules. A graphical interface called OVERGRID has been specially designed for such purposes. Data required and created by the different steps include geometry, grids, domain connectivity information and flow solver input parameters. The interface provides a unified environment for the visualization, processing, generation and diagnosis of such data. General modules are available for the manipulation of structured grids and unstructured surface triangulations. Modules more specific for the overset approach include surface curve generators, hyperbolic and algebraic surface grid generators, a hyperbolic volume grid generator, Cartesian box grid generators, and domain connectivity: pre-processing tools. An interface provides automatic selection and viewing of flow solver boundary conditions, and various other flow solver inputs. For problems involving multiple components in relative motion, a module is available to build the component/grid relationships and to prescribe and animate the dynamics of the different components.

Chan, William M.↗
NASA NTRS2003

Fiber Reinforcement Architectures of PMCs on the Hygrothermal-Mechanical Performance for Aeropropulsion Applications

A rigid lightweight sandwich support structure, for the combustor chamber of a new generation liquid propellant rocket engine, was designed and fabricated using Polymer Matric Composite (PMC) facesheet on a Ti honeycomb or Carbon foam core. The facesheet consisted of high stiffness carbon fiber, M40JB, and high temperature Polyimides, such as PMR-11-50 and HFPE-II. Six different fiber architectures; 4HS woven fabric, uni-fabric, woven-uni hybrid, stitched woven fabric, stitched uni-fabric and tri-axial braided structures have been investigated for optimum stiffness-thickness-weight-performance design criteria for the hygrothermal-mechanical propulsion service exposure conditions including rapid heating up to 200 F/sec, maximum operating temperature of 600 F, internal pressure up to 100 psi. An extensive property and performance database including dry-wet mechanical properties at both 25 F and 600 F in various loading modes, thermal and physical properties including blistering onset condition was developed for fiber architecture down-selection and design guidelines. Various optimized process methods including vacuum bag compression molding, solvent assistant RTM (SaRTM), resin film infusion (RFI) were utilized for PMC panel fabrication depending on the architecture type. In the case of stitched woven fabric architecture, the optimal stitch pattern was chosen in terms of stitch density and yarn size, based on both in-plane mechanical properties and blistering performance. Potential reduction of the in-plane properties transverse to the line of stitching was also evaluated. Attempt to correlate the experimental results with theoretical micro-mechanics predictions will be presented.

Shin, Eugene↗
NASA NTRS2003

Effects of Fiber Reinforcement Architecture on the Hygrothermal-Mechanical Performance of Polyimide Matrix Composites for Aeropropulsion Applications

A lightweight sandwich support structure, for the combustor chamber of a new generation liquid propellant rocket engine, was designed and fabricated using a polymer matrix composite (PMC) facesheet on a Ti honeycomb core. The PMC facesheet consisted of high stiffness carbon fiber, M40JB, and high temperature Polyimides, such as PMR-II-50 and HFPE-II-52. Six different fiber architectures; four harness satin (4HS) woven fabric, uni-tape, woven-uni hybrid, stitched woven fabric, stitched uni-tape and triaxial braided structures have been investigated for optimum stiffness-thickness-weight-hygrothermal performance design criteria for the hygrothermal-mechanical propulsion service exposure conditions including rapid heating up to 200 F/sec, maximum operating temperature of 600 F, internal pressure up to 100 psi. One of the specific objectives in this study is to improve composite blistering resistance in z-direction at minimum expense of in-plane mechanical properties. An extensive property-performance database including dry-wet mechanical properties at various temperatures, thermal-physical properties, such as blistering onset condition was generated for fiber architecture down-selection and design guidelines. Various optimized process methods such as vacuum bag compression molding, solvent assistant resin transfer molding (SaRTM), resin film infusion (RFI) and autoclaving were utilized for PMC panel fabrication depending on the architecture type. In the case of stitched woven fabric architecture, the stitch pattern in terms of stitch density and yarn size was optimized based on both in-plane mechanical properties and blistering performance. Potential reduction of the in-plane properties transverse to the line of stitching was also evaluated. Efforts have been made to correlate the experimental results with theoretical micro-mechanics predictions. Changes in deformation mechanism and failure sequences in terms of fiber architecture will be discussed.

Shin, E. Eugene↗