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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

A Flexible Alignment Fixture for the Fabrication of Replication Mandrels

NASA uses precision diamond turning technology to fabricate replication mandrels for its X-ray Calibration Facility (XRCF) optics. The XRCF optics are tubular, and the internal surface contains a parabolic profile over the first section and a hyperbolic profile over the last. The optic is fabricated by depositing layers of gold and nickel on to the replication mandrel and then separating it from the mandrel. Since the mandrel serves as a replication form, it must contain the inverse image of the surface. The difficulty in aligning the mandrel comes from the fabrication steps which it undergoes. The mandrel is rough machined and heat treated prior to diamond turning. After diamond turning, silicon rubber separators which are undercut in radius by 3 mm (0.12 in.) are inserted between the two end caps of the mandrel to allow the plating to wrap around the ends (to prevent flaking). The mandrel is then plated with a nickel-phosphor alloy using an electroless nickel process. At this point, the separators are removed and the mandrel is reassembled for the final cut on the DTM. The mandrel is measured for profile and finish, and polished to achieve an acceptable surface finish. Wrapping the plating around the edges helps to prevent flaking, but it also destroys the alignment surfaces between the parts of the mandrel that insure that the axes of the parts are coincident. Several mandrels have been realigned by trial-and-error methods, consuming significant amounts of setup time. When the mandrel studied in this paper was reassembled, multiple efforts resulted in a minimum radial error motion of 100 microns. Since 50 microns of nickel plating was to be removed, and a minimum plating thickness of 25 microns was to remain on the part, the radial error motion had to be reduced to less than 25 microns. The mandrel was therefore not usable in its current state.

Cuttino, James F.↗
NASA NTRS1996

Computational Modeling of Multi-Phase/Multi-Species Flows with Applications to Liquid Rocket Engines

Accurate prediction of all physical phenomena in a combustion chamber is essential for better understanding of the system performance. Atomization, evaporation, combustion, chemical kinetics, and turbulence are those processes of great importance that need to be well understood. Processes involving the liquid phase in a combustion chamber will be further complicated under supercritical conditions. More advanced and accurate numerical techniques are required to extend our understanding of the above phenomena. A computer program for multi-species/multi-phase flow was developed for NASA/MSFC in 1992. This code, called Liquid Thrust Chamber Performance (LTCP) program takes an Eulerian- Eulerian approach and is based on the Total Variation Diminishing (TVD) technique with Lax-Friedrichs upwind method. Under the NASA/ASEE SFFP the LTCP code was used to predict the performance characteristics of several engines that were of particular interest to NASA. This code was also successful in a combustion detonation study. Converting the program to the PC platform was accomplished which extends usability and makes it available to a wider range of users. The Eulerian formulation of the liquid phase provides a suitable model that can be extended to include combustion modeling under supercritical conditions. The results have been compared against the ones of other codes and available measured data. The algorithm proved to be robust and efficient for problems with stiff source terms.

Navaz, Homayun K.↗
NASA NTRS1997

The Development of a User Inclusion Strategy for CLCS Display Design

This report summarizes a ten week effort to evaluate the software development process in the Checkout and Launch Control System (CLCS) for the presence of user inclusion in the design operation. A background is presented that highlights the value of achieving usability through user inclusion, progress-to-date is described, and future work is suggested so that a user inclusive design environment can be accomplished.

Jacko, Julie A.↗
NASA NTRS1959

An Investigation of the Performance of Various Reaction Control Devices

An investigation of a small-scale reaction control devices in still air with both subsonic and supersonic internal flows has shown that lateral forces approaching 70 percent of the resultant force of the undeflected jet can be obtained. These results were obtained with a tilted extension at a deflection of 40 deg. The tests of tilted extensions indicated an optimum length-to-diameter ratio of approximately 0.75 to 1.00, dependent upon the deflection angle. For the two geometric types of spoiler tabs tested, blockage-area ratio appears to be the only variable affecting the lateral force developed. Usable values of lateral force were developed by the full-eyelid type of device with reasonably small losses in the thrust and weight flow. Somewhat larger values of lateral force were developed by injecting a secondary flow normal to the primary jet, but for conditions of these tests the losses in thrust and weight flow were large. Relatively good agreement with other investigations was obtained for several of the devices. The agreement of the present results with those of an investigation made with larger-scale equipment indicates that Reynolds number may not be critical for these tests. In as much as the effects of external flow could influence the performance and other factors affecting the choice of a reaction control for a specific use, it would appear desirable to make further tests of the devices described in this report in the presence of external flow.

Hunter, Paul A.↗
NASA NTRS1998

Development of a Probabilistic Dynamic Synthesis Method for the Analysis of Nondeterministic Structures

Accounting for the statistical geometric and material variability of structures in analysis has been a topic of considerable research for the last 30 years. The determination of quantifiable measures of statistical probability of a desired response variable, such as natural frequency, maximum displacement, or stress, to replace experience-based "safety factors" has been a primary goal of these studies. There are, however, several problems associated with their satisfactory application to realistic structures, such as bladed disks in turbomachinery. These include the accurate definition of the input random variables (rv's), the large size of the finite element models frequently used to simulate these structures, which makes even a single deterministic analysis expensive, and accurate generation of the cumulative distribution function (CDF) necessary to obtain the probability of the desired response variables. The research presented here applies a methodology called probabilistic dynamic synthesis (PDS) to solve these problems. The PDS method uses dynamic characteristics of substructures measured from modal test as the input rv's, rather than "primitive" rv's such as material or geometric uncertainties. These dynamic characteristics, which are the free-free eigenvalues, eigenvectors, and residual flexibility (RF), are readily measured and for many substructures, a reasonable sample set of these measurements can be obtained. The statistics for these rv's accurately account for the entire random character of the substructure. Using the RF method of component mode synthesis, these dynamic characteristics are used to generate reduced-size sample models of the substructures, which are then coupled to form system models. These sample models are used to obtain the CDF of the response variable by either applying Monte Carlo simulation or by generating data points for use in the response surface reliability method, which can perform the probabilistic analysis with an order of magnitude less computational effort. Both free- and forced-response analyses have been performed, and the results indicate that, while there is considerable room for improvement, the method produces usable and more representative solutions for the design of realistic structures with a substantial savings in computer time.

Brown, A. M.↗
NASA NTRS1998

Flow/Damage Surfaces for Fiber-Reinforced Metals Having Different Periodic Microstructures

Flow/damage surfaces can be defined in terms of stress, inelastic strain rate, and internal variables using a thermodynamics framework. A macroscale definition relevant to thermodynamics and usable in an experimental program is employed to map out surfaces of constant inelastic power in various stress planes. The inelastic flow of a model silicon carbide/ titanium composite system having rectangular, hexagonal, and square diagonal fiber packing arrays subjected to biaxial stresses is quantified by flow/damage surfaces that are determined numerically from micromechanics, using both finite element analysis and the generalized method of cells. Residual stresses from processing are explicitly included and damage in the form of fiber-matrix debonding under transverse tensile and/or shear loading is represented by a simple interface model. The influence of microstructural architecture is largest whenever fiber-matrix debonding is not an issue; for example in the presence of transverse compressive stresses. Additionally, as the fiber volume fraction increases, so does the effect of microstructural architecture. With regard to the micromechanics analysis, the overall inelastic flow predicted by the generalized method of cells is in excellent agreement with that predicted using a large number of displacement-based finite elements.

Lissenden, Cliff J.↗
NASA NTRS1998

Flow/Damage Surfaces for Fiber-Reinforced Metals having Different Periodic Microstructures

Flow/damage surfaces can be defined in terms of stress, inelastic strain rate, and internal variables using a thermodynamics framework. A macroscale definition relevant to thermodynamics and usable in an experimental program is employed to map out surfaces of constant inelastic power in various stress planes. The inelastic flow of a model silicon carbide/ titanium composite system having rectangular, hexagonal, and square diagonal fiber packing, arrays subjected to biaxial stresses is quantified by flow/damage surfaces that are determined numerically from micromechanics. using both finite element analysis and the generalized method of cells. Residual stresses from processing are explicitly included and damage in the form of fiber-matrix debonding under transverse tensile and/or shear loading is represented by a simple interface model. The influence of microstructural architecture is largest whenever fiber-matrix debonding is not an issue, for example in the presence of transverse compressive stresses. Additionally, as the fiber volume fraction increases, so does the effect of microstructural architecture. With regard to the micromechanics analysis, the overall inelastic flow predicted by the generalized method of cells is in excellent agreement with that predicted using a large number of displacement-based finite elements.

Lissenden, Cliff J.↗
NASA NTRS1998

Destructive Evaluation of a Xenon Hollow Cathode after a 28,000 Hour Life Test

International Space Station (ISS) plasma contactor system requires a hollow cathode assembly (HCA) with a lifetime of at least 18,000 hours. In order to demonstrate the lifetime capability of the HCA, a series of hollow cathode wear tests was performed which included a life test operated at the maximum current of the HCA. This test sought to verify hollow cathode lifetime capability and contamination control protocols. This hollow cathode accumulated 27,800 hours of operation before it failed during a restart attempt. The cathode was subsequently destructively analyzed in order to determine the failure mechanism. Microscopic examination of the cathode interior determined that relatively small changes in the cathode physical geometry had occurred and barium tungstates, which are known to limit the emission process, had formed over a majority of the electron emitter surface. Because the final state of the insert was consistent with expected impregnate chemistry, the hollow cathode was believed to have reached the end of its usable life under the test conditions.

Sarver-Verhey, Timothy R.↗
NASA NTRS1996

Evolving the Reuse Process at the Flight Dynamics Division (FDD) Goddard Space Flight Center

This paper presents the interim results from the Software Engineering Laboratory's (SEL) Reuse Study. The team conducting this study has, over the past few months, been studying the Generalized Support Software (GSS) domain asset library and architecture, and the various processes associated with it. In particular, we have characterized the process used to configure GSS-based attitude ground support systems (AGSS) to support satellite missions at NASA's Goddard Space Flight Center. To do this, we built detailed models of the tasks involved, the people who perform these tasks, and the interdependencies and information flows among these people. These models were based on information gleaned from numerous interviews with people involved in this process at various levels. We also analyzed effort data in order to determine the cost savings in moving from actual development of AGSSs to support each mission (which was necessary before GSS was available) to configuring AGSS software from the domain asset library. While characterizing the GSS process, we became aware of several interesting factors which affect the successful continued use of GSS. Many of these issues fall under the subject of evolving technologies, which were not available at the inception of GSS, but are now. Some of these technologies could be incorporated into the GSS process, thus making the whole asset library more usable. Other technologies are being considered as an alternative to the GSS process altogether. In this paper, we outline some of issues we will be considering in our continued study of GSS and the impact of evolving technologies.

Condon, S.↗
NASA NTRS1999

Automated Development of Accurate Algorithms and Efficient Codes for Computational Aeroacoustics

The simulation of sound generation and propagation in three space dimensions with realistic aircraft components is a very large time dependent computation with fine details. Simulations in open domains with embedded objects require accurate and robust algorithms for propagation, for artificial inflow and outflow boundaries, and for the definition of geometrically complex objects. The development, implementation, and validation of methods for solving these demanding problems is being done to support the NASA pillar goals for reducing aircraft noise levels. Our goal is to provide algorithms which are sufficiently accurate and efficient to produce usable results rapidly enough to allow design engineers to study the effects on sound levels of design changes in propulsion systems, and in the integration of propulsion systems with airframes. There is a lack of design tools for these purposes at this time. Our technical approach to this problem combines the development of new, algorithms with the use of Mathematica and Unix utilities to automate the algorithm development, code implementation, and validation. We use explicit methods to ensure effective implementation by domain decomposition for SPMD parallel computing. There are several orders of magnitude difference in the computational efficiencies of the algorithms which we have considered. We currently have new artificial inflow and outflow boundary conditions that are stable, accurate, and unobtrusive, with implementations that match the accuracy and efficiency of the propagation methods. The artificial numerical boundary treatments have been proven to have solutions which converge to the full open domain problems, so that the error from the boundary treatments can be driven as low as is required. The purpose of this paper is to briefly present a method for developing highly accurate algorithms for computational aeroacoustics, the use of computer automation in this process, and a brief survey of the algorithms that have resulted from this work. A review of computational aeroacoustics has recently been given by Lele.

Goodrich, John W.↗
NASA NTRS1998

The Importance of Semi-Major Axis Knowledge in the Determination of Near-Circular Orbits

Modem orbit determination has mostly been accomplished using Cartesian coordinates. This usage has carried over in recent years to the use of GPS for satellite orbit determination. The unprecedented positioning accuracy of GPS has tended to focus attention more on the system's capability to locate the spacecraft's location at a particular epoch than on its accuracy in determination of the orbit, per se. As is well-known, the latter depends on a coordinated knowledge of position, velocity, and the correlation between their errors. Failure to determine a properly coordinated position/velocity state vector at a given epoch can lead to an epoch state that does not propagate well, and/or may not be usable for the execution of orbit adjustment maneuvers. For the quite common case of near-circular orbits, the degree to which position and velocity estimates are properly coordinated is largely captured by the error in semi-major axis (SMA) they jointly produce. Figure 1 depicts the relationships among radius error, speed error, and their correlation which exist for a typical low altitude Earth orbit. Two familiar consequences are the relationship Figure 1 shows are the following: (1) downrange position error grows at the per orbit rate of 3(pi) times the SMA error; (2) a velocity change imparted to the orbit will have an error of (pi) divided by the orbit period times the SMA error. A less familiar consequence occurs in the problem of initializing the covariance matrix for a sequential orbit determination filter. An initial covariance consistent with orbital dynamics should be used if the covariance is to propagate well. Properly accounting for the SMA error of the initial state in the construction of the initial covariance accomplishes half of this objective, by specifying the partition of the covariance corresponding to down-track position and radial velocity errors. The remainder of the in-plane covariance partition may be specified in terms of the flight path angle error of the initial state. Figure 2 illustrates the effect of properly and not properly initializing a covariance. This figure was produced by propagating the covariance shown on the plot, without process noise, in a circular low Earth orbit whose period is 5828.5 seconds. The upper subplot, in which the proper relationships among position, velocity, and their correlation has been used, shows overall error growth, in terms of the standard deviations of the inertial position coordinates, of about half of the lower subplot, whose initial covariance was based on other considerations.

Carpenter, J. Russell↗
NASA NTRS1999

Design of a Channel Error Simulator using Virtual Instrument Techniques for the Initial Testing of TCP/IP and SCPS Protocols

There exists a need for designers and developers to have a method to conveniently test a variety of communications parameters for an overall system design. This is no different when testing network protocols as when testing modulation formats. In this report, we discuss a means of providing a networking test device specifically designed to be used for space communications. This test device is a PC-based Virtual Instrument (VI) programmed using the LabVIEW(TM) version 5 software suite developed by National Instruments(TM)TM. This instrument was designed to be portable and usable by others without special, additional equipment. The programming was designed to replicate a VME-based hardware module developed earlier at New Mexico State University (NMSU) and to provide expanded capabilities exceeding the baseline configuration existing in that module. This report describes the design goals for the VI module in the next section and follows that with a description of the design of the VI instrument. This is followed with a description of the validation tests run on the VI. An application of the error-generating VI to networking protocols is then given.

Horan, Stephen↗
NASA NTRS1999

Study the Effects of Charged Particle Radiation on Gravitational Sensors in Space

Space-flight charging of free floating masses poses an unusual problem-- how can one control charge on the object without exerting a significant force on it? One approach is to make contact to the object with a fine wire. However, for many precision applications no physical contact is permissible, so charge must be conveyed in, a more sophisticated manner. One method has already been developed: Gravitational Probe B (GP-B) uses an ultraviolet photo-emission system described in ref 1. This system meets the experiment requirements, yet poses a number of constraints, including high power dissipation (approximately 10 W peak, approximately 1 W average), low current output (approximately 10(exp -13) A), and potential reliability problems associated with fiber optics system and the UV source. The aim of the current research is to improve this situation and, if possible, develop a more rugged and lower power alternative, usable in a wide range of situations. An potential alternative to the UV electron source is a Spindt-type field emission cathode. These consist of an array of extremely sharp silicon tips mounted in a standard IC package with provision for biasing them relative to the case potential. They are attractive as electron sources for space applications due to their low power consumption (10(exp -5) W), high current levels (10(exp -9) to 10(exp -5) A), and the absence of mechanical switching. Unfortunately, existing cathodes require special handling to avoid contamination and gas absorption. These contaminants can cause severe current fluctuations and eventual destruction of the cathode tips. Another potential drawback is the absence of any data indicating the possibility of bipolar current flow. This capability is needed because of the large uncertainties in the net charge transfer from cosmic rays to a free floating mass in space. More recent devices reduce the current fluctuations and destructive arcing by mounting the tips on a resistive substrate rather than a good conductor. This effectively wires a resistor to each individual tip, providing a current limit and thus greatly reducing the possibility of destructive arcing through an individual tip. An issue with this resistive layer is its range of operating temperatures. From the experience with the GP-B system, we hypothesized about using secondary electron emission for control of net charge transfer to an object. An important goal of the testing described below was to demonstrate the ability to apply both positive and negative charges to the test object from a single emitter.

Lipa, John A.↗
NASA NTRS1999

Software Development Processes Applied to Computational Icing Simulation

The development of computational icing simulation methods is making the transition form the research to common place use in design and certification efforts. As such, standards of code management, design validation, and documentation must be adjusted to accommodate the increased expectations of the user community with respect to accuracy, reliability, capability, and usability. This paper discusses these concepts with regard to current and future icing simulation code development efforts as implemented by the Icing Branch of the NASA Lewis Research Center in collaboration with the NASA Lewis Engineering Design and Analysis Division. With the application of the techniques outlined in this paper, the LEWICE ice accretion code has become a more stable and reliable software product.

Levinson, Laurie H.↗
NASA NTRS1999

Numerical Investigation of the ARMSEF Arc-Jet

The NASA/JSC 10 MW Atmospheric Reentry Materials and Structures Evaluation Facility (ARMSEF) is used for the development and evaluation of thermal protection systems for manned reentry vehicles. In an effort at better understanding the flow characteristics of an arc-jet wind tunnel and hence the correlation between simulation and actual flight conditions, preliminary numerical analyses have been made. Difficulties in defining inlet boundary conditions to the plenum chamber, where there is very little usable experimental data, are discussed. Two different boundary conditions for the plenum, a straight profile and parabolic profile, are employed to describe the conditions in this very important flow defining region. Comparisons are made to experimental data with the results showing that some type of parabolic or step profile is needed to adequately resolve the strong core flow that is present in the nozzle and plume region. Recommendations are made regarding future efforts in analyzing this challenging flow field.

Cox, Carey F.↗
NASA NTRS1999

A Cutoff in the X-Ray Fluctuation Power Density Spectrum of the Seyfert 1 Galaxy NGC 3516

During 1997 March-July, RXTE observed the bright, strongly variable Seyfert 1 galaxy NGC 3516 once every approx. 12.8 hr for 4.5 months and nearly continuously (with interruptions due to SAA passage but not Earth occultation) for a 4.2 day period in the middle. These were followed by ongoing monitoring once every approx. 4.3 days. These data are used to construct the first well-determined X-ray fluctuation power density spectrum (PDS) of an active galaxy to span more than 4 decades of usable temporal frequency. The PDS shows no signs of any strict or quasi-periodicity, but does show a progressive flattening of the power-low slope from -1.74 at short time scales to -0.73 at longer time scales. This is the clearest observation to date of the long-predicted cutoff in the PDS. The characteristic variability time scale corresponding to this cutoff temporal frequency is approx. 1 month. Although it is unclear how this time scale may be interpreted in terms of a physical size or process, there are several promising candidate models. The PDS appears similar to those seen for Galactic black hole candidates such as Cyg X-1, suggesting that these two classes of objects with very different luminosities and putative black hole masses (differing by more than a factor of 10(exp 5)) may have similar X-ray generation processes and structures.

Edelson, Rick↗
NASA NTRS1999

Integrated Chemical and Microorganism Monitoring of Air Using Gas Chromatography/Ion Mobility Spectometry: Toward an Expanded-Use Volatile Organic Analyzer (VOA)

The work described in this research program originated with the choice by NASA of an ion mobility spectrometer for air quality monitoring on-board the international spacestation. Though the gas chromatograph-ion mobility spectrometer analyzer known as VOA met or exceeded expectations, limitations in the basic understanding of response and the utilization of foundational principles into usable technology was considered unacceptable. In this research program, a comprehensive model for the origins of mobility spectra was proposed, tested and verified. The principles considered responsible for the appearance of mobility spectra have now been elucidated through this project. This understanding has been applied in automated identification of mobility spectra using neural networks and routine procedures for this now exist. Finally, the limitation on linear range has been shown to be a technical limitation and not a fundamental limitation so that a hardware component was crafted to extend the linear range of a mobility spectrometer by 10X. This project has led to one Ph.D. dissertation and one MS thesis. In addition, over ten public presentations at professional meetings and six journal publications have resulted from this program of research. The findings are so plentiful that total analysis of the findings may require four to six years or more. The findings confirm that the decision to use VOA was sound and that the chemical and physical principles of mobility spectrometry are both understandable and predictable.

Eiceman, G. A.↗
NASA NTRS1999

Preliminary Results from Analysis of NOAA 15 HIRS/AMSU Data

We have begun analyzing NOAA 15 MRS3/AMSU A/AMSU B data in a manner basically analogous to that used to produce the TOVS Pathfinder Data Set, with some minor improvements to the processing system. Temperature retrievals using NOAA 15 HIRS3/AMSU A are found to be similar, but superior to, those using nearly colocated NOAA 11 HMS2/MSU/SSU data. AMSU B has some calibration problems related to RFI from the transmitters on the satellite. We have developed methodology to account for this interference and have shown that the data is usable for improved moisture profiling capability over previous satellites.

Susskind, Joel↗