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NASA NTRS1979

The role of thermophysics in the design, optimization and understanding of semiconductor crystal growth in space

The compound semiconductor material PbSnTe has been investigated by NASA Langley Research Center as part of the Material Processing in Space (MPS) experiment in the framework of the Space Shuttle program. The long-range goal of the research is the improving of the performance of infrared detectors for use in remote sensing experiments. Three distinct techniques will be used in the low-g environment of space: two techniques involving bulk growth from melt and a vapor growth technique. In order to establish realistic estimates of the required time for experiments and to determine the thermal gradients that will be required to avoid constitutional supercooling, the diffusion coefficients must be accurately measured, however more data especially in the vapor-solid phase relations are needed.

Crouch, R. K.↗

NASA NTRS1982

Magnetohydrodynamic equilibrium. III - Helically symmetric fields. IV - Nonequilibrium of nonsymmetric hydrodynamic topologies

It is pointed out that plasma confinement in stable equilibrium states constitutes a fundamental and still unresolved question in plasma astrophysics and thermonuclear fusion research. The problem has two parts related to the equilibrium states themselves and their mechanical stability. The question of the existence of general solutions of the field and fluid equations for the steady dynamical interaction of inviscid compressible fluids of high electrical conductivity with magnetic and gravity fields is considered. In the absence of fluid motions, the presented equations become the familiar equations of magnetostatics supplemented by an equation of state. Starting from this simplest case of magnetostatic equilibrium, the investigation proceeds to the more complex case of magnetohydrodynamic equilibrium. Examples of helically symmetric fields are presented to illustrate the use of the formulation for treating the dynamics of helically symmetric hydromagnetic flows.

Tsinganos, K. C.↗

NASA NTRS1991

Examination of the effect of propulsion system performance variables on the life prediction for the SSME Lox Post

The main objective is to calculate damage evolution at the critical location of selected components of reusable space propulsion systems as the function of their operating environments and to relate the evolution of damage at the critical locations to the performance variables of the propulsion system using advanced constitutive and damage models. The models so developed will be oriented toward use in an advanced diagnostic/prognostic health monitoring system for reusable propulsion systems. The components to be modelled include a Lox Post (injector element), a thrust chamber, and a turbine blade. The study conducted on the Lox Post is reported.

Russell, D. A.↗

NASA NTRS1999

Planar Strain-Rate-Free Diffusion Flames: Initiation, Properties, and Extinction

An effectively strain-rate-free diffusion flame constitutes the most vigorous laminar combustion of initially unmixed reactive gases. Such a diffusion flame is characterized by a relatively long residence time and by a relatively large characteristic length scale. If such a flame were also planar, providing high symmetry, it would be particularly suitable for experimental and theoretical investigations of key combustion phenomena, such as multicomponent diffusion, chemical kinetics, and soot inception, growth, and oxidation. Unfortunately, a planar strain-rate-free diffusion flame is highly disrupted in earth-gravity (e.g., in a counterflow-diffusion-flame apparatus) because of the very rapid onset (approx. 100 ms) of gravity-induced instability. Accordingly, a specially dedicated apparatus was designed, fabricated, and initially checked out for the examination of a planar strain-rate-free diffusion flame in microgravity. Such a diffusion flame may be formed within a hollowed-out squat container (initially configured as 25 cm x 25 cm x 9 cm), with isothermal, noncatalytic, impervious walls. At test initiation, a thin metallic sheet (approx. 1 mm in thickness) that separates the internal volume into two equal portions, each of dimensions 25 cm x 25 cm x 4.5 cm, is withdrawn, by uniform translation (approx. 50 cm/s) in its own plane, through a tightly fitting slit in one side wall. Thereupon, diluted fuel vapor (initially confined to one half-volume of the container) gains access to diluted oxygen (initially with the same pressure, density, and temperature as the fuel, but initially confined to the other half-volume). After a brief delay (approx. 10 ms), to permit limited but sufficient-for-flammability diffusional interpenetration of fuel vapor and oxidizer, burning is initiated by discharge of a line igniter, located along that side wall from which the trailing edge of the separator withdraws. The ignition spawns a triple-flame propagation across the 25 cm x 25 cm centerplane. When a diffusion flame is emplaced in the centerplane, any subsequent travel, and change in temperature, of that planar diffusion flame may be tracked, along with the effectively spatially uniform but temporally evolving pressure within the container. Eventually, nearly complete depletion of the stoichiometrically deficient reactant, along with heat loss to the container surfaces, effects extinction. These data afford an opportunity to check theoretical models of diffusion and chemical kinetics under conditions ranging from intense burning to flame out, or, alternatively, to evolve simple empirical representations of these phenomena. Thus, the project sought to utilize microgravity testing to elucidate commonly encountered phenomenology, arising in the commonly-encountered mode of combustion (whether related to heating, manufacturing, boiling, and propulsion, or to uncontrolled, free-burning fire in structures and wildland vegetation), of those commonly utilized fuels usually categorized as gaseous fuels (such as hydrogen, natural gas, and propane, which are gaseous under atmospheric conditions).

Fendell, Francis↗

NASA NTRS2006

Ubiquitous Low-FeO Relict Grains in Type II Chondrules and Limited Overgrowths on Phenocrysts Following the Final Melting Event

Type II porphyritic chondrules commonly contain several large (>40 microns) olivine phenocrysts; furnace-based cooling rates based on the assumption that these phenocrysts grew in a single-stage melting-cooling event yield chondrule cooling-rate estimates of 0.01-1 K/s. Because other evidence indicates much higher cooling rates, we examined type 11 chondrules in the CO3.0 chondrites that have experienced only minimal parent-body alteration. We discovered three kinds of evidence indicating that only minor (4-10 microns) olivine growth occurred after the final melting event: (1) Nearly all (>90%) type II chondrules in CO3.0 chondrites contain low-FeO relict grains; overgrowths on these relicts are narrow, in the range of 2-12 microns. (2) Most type II chondrules contain some FeO-rich olivine grains with decurved surfaces and acute angles between faces indicating that the grains are fragments from an earlier generation of chondrules; the limited overgrowth thicknesses following the last melting event are too thin to disguise the shard-like nature of these grains. (3) Most type II chondrules contain many small (<20 microns) euhedral or subhedral phenocrysts with central compositions that are much more ferroan than the centers of the large phenocrysts; their small sizes document the small amount of growth that occurred after the final melting event. If overgrowth thicknesses were small (4-10 microns) after the final melting event, it follows that large fractions of coarse (>40 microns) high-FeO phenocrysts are relicts from earlier generations of chondrules, and that cooling rates after the last melting event were much more rapid than indicated by models based on a single melting event. These observations are thus inconsistent with the "classic" igneous model of formation of type II porphyritic chondrules by near-total melting of a precursor mix followed by olivine nucleation on a very limited number of nuclei (say, <10) and by growth to produce the large phenocrysts during a period of monotonic (and roughly linear) cooling. Our observations that recycled chondrule materials constitute a large component of the phenocrysts of type II chondrules also imply that this kind of chondrule formed relatively late during the chondrule-forming period.

Wasson, John T.↗

NASA NTRS2004

Nanofluidic Size-Exclusion Chromatograph

Efforts are under way to develop a nanofluidic size-exclusion chromatograph (SEC), which would be a compact, robust, lightweight instrument for separating molecules of interest according to their sizes and measuring their relative abundances in small samples. About as large as a deck of playing cards, the nanofluidic SEC would serve, in effect, as a laboratory on a chip that would perform the functions of a much larger, conventional, bench-top SEC and ancillary equipment, while consuming much less power and much smaller quantities of reagent and sample materials. Its compactness and low power demand would render it attractive for field applications in which, typically, it would be used to identify and quantitate a broad range of polar and nonpolar organic compounds in soil, ice, and water samples. Size-exclusion chromatography is a special case of high-performance liquid chromatography. In a conventional SEC, a sample plug is driven by pressure along a column packed with silica or polymer beads that contain uniform nanopores. The interstices between, and the pores in, the beads collectively constitute a size-exclusion network. Molecules follow different paths through the size-exclusion network, such that characteristic elution times can be related to sizes of molecules: basically, smaller molecules reach the downstream end of the column after the larger ones do because the smaller ones enter minor pores and stay there for a while, whereas the larger ones do not enter the pores. The volume accessible to molecules gradually diminishes as their size increases. All molecules bigger than a pore size elute together. For most substances, the elution times and sizes of molecules can be correlated directly with molecular weights. Hence, by measuring the flux of molecules arriving at the downstream end as a function of time, one can obtain a liquid mass spectrum for the molecules present in a sample over a broad range of molecular weights.

Feldman, Sabrina↗

NASA NTRS1981

Studies conducted as a search for physical mechanisms relating solar variability and the troposphere

Chains of causative mechanisms that are hypothesized to relate solar variability to the behavior of the Earth's lower atmosphere were assessed. Solar variations believed most likely to constitute the forcing functions in hypothesized solar terrestrial atmosphere chain, changes in the Earth's atmospheric electrical characteristics due to solar variability, and the observed variations in atmospheric behavior that are influenced by solar variability were also examined.

Wu, S. T.↗

NASA NTRS1993

The Hyades cluster-supercluster connection - Evidence for a local concentration of dark matter

Stars that evaporate from the Hyades cluster will remain within a few hundred parsecs of the cluster only if they are dynamically bound to a much more massive entity containing the cluster. A local mass enhancement of at least (5-10) x 10 exp 5 solar masses, with a radius of about 100 pc, can trap stars with an origin related to that of the Hyades cluster and explains the excess of stars with velocities near the Hyades velocity that constitutes the Hyades supercluster. Part of this mass enhancement can be in visible stars, but a substantial fraction is likely to be in the form of dark matter.

Casertano, Stefano↗

NASA NTRS2004

Predicting the Influence of Nano-Scale Material Structure on the In-Plane Buckling of Orthotropic Plates

A multi-scale analysis of the structural stability of a carbon nanotube-polymer composite material is developed. The influence of intrinsic molecular structure, such as nanotube length, volume fraction, orientation and chemical functionalization, is investigated by assessing the relative change in critical, in-plane buckling loads. The analysis method relies on elastic properties predicted using the hierarchical, constitutive equations developed from the equivalent-continuum modeling technique applied to the buckling analysis of an orthotropic plate. The results indicate that for the specific composite materials considered in this study, a composite with randomly orientated carbon nanotubes consistently provides the highest values of critical buckling load and that for low volume fraction composites, the non-functionalized nanotube material provides an increase in critical buckling stability with respect to the functionalized system.

Gates, Thomas S.↗

NASA NTRS2022

Chapter 7: Sun Photometers

Sun photometry is an extended technique for monitoring the atmospheric composition and support satellite product validation. By measuring the direct solar irradiance, the amount and characteristics of the atmospheric aerosol particles, precipitable water vapor column, and ozone columns can be derived. Global operational networks such as the Aerosol Robotic Network (AERONET), Global Atmosphere Watch-Precision Filter Radiometer Network (GAW-PFR), Maritime Aerosol Network (MAN), or the Brewer spectrophotometer networks constitute sustained efforts for long-term monitoring of the atmosphere, with invaluable data production using cost-effective and relatively simple instrumentation. The data quality relies on the standardization of these networks, with special emphasis on the calibration as the key element in Sun photometry.

Sun photometry↗

NASA NTRS1951

NACA Investigations of Icing-Protection Systems for Turbojet-Engine Installations

Investigations have been made in flight and in wind tunnels to determine which components of turbojet installations are most critical in icing conditions, and to evaluate several methods of icing protection. From these studies, the requirements necessary for adequate icing protection and the consequent penalties on engine performance can be estimated. Because investigations have indicated that the compressor-inlet screen constitutes the greatest icing hazard and is difficult to protect, complete removal or retraction of the screen upon encountering an icing condition is recommended. In the absence of the screen, the inlet guide vanes of an axial-flow-type turbojet engine constitute the greatest danger to engine operation in an icing condition; a centrifugal-type engine, on the other hand, is relatively unsusceptible to icing once the screen has been removed. Of the three icing-protection systems investigated, surface heating, hot-gas bleedback, and inertia-separation inlets, only the first two offer an acceptable solution to the problem of engine icing protection. Surface heating, either by gas heating or electrical means, appears to be the most acceptable icing-protection method with regard to performance losses. Hot-gas bleedback, although causing undesirable thrust losses, offers an easy means of obtaining icing protection for some installations. The final choice of an icing-protection system depends, however, on the supply of heated gas and electrical power available and on the allowable performance and. weight penalties associated with each system.

VonGlahn, Uwe↗

NASA NTRS1990

Nonlinear analysis of AS4/PEEK thermoplastic composite laminate using a one parameter plasticity model

A one-parameter plasticity model was shown to adequately describe the orthotropic plastic deformation of AS4/PEEK (APC-2) unidirectional thermoplastic composite. This model was verified further for unidirectional and laminated composite panels with and without a hole. The nonlinear stress-strain relations were measured and compared with those predicted by the finite element analysis using the one-parameter elastic-plastic constitutive model. The results show that the one-parameter orthotropic plasticity model is suitable for the analysis of elastic-plastic deformation of AS4/PEEK composite laminates.

Sun, C. T.↗

NASA NTRS1998

LDAR, A Three-Dimensional Lightning Warning System: Its Development and Use by the Government, and Transition to Public Availability

NASA, at the John F. Kennedy Space Center (KSC), developed and operates a unique high precision lightning location system to provide lightning related weather warnings. These warnings are used to stop lightning-sensitive operations such as space vehicle launches and ground operations where equipment and personnel are at risk. The data is provided to the Range Weather Operations [45th Weather Squadron, U. S. Air Force (USAF)] where it is used with other meteorological data to issue weather advisories and warnings for Cape Canaveral Air Station (CCAS) and KSC operations. This system, called Lightning Detection and Ranging (LDAR), provides users with a graphical display in three dimensions of 66 MHz radio frequency events generated by lightning processes. The locations of these events provide a sound basis for the prediction of lightning hazards. NASA and Global Atmospherics, Inc. are developing a new system that will replace the unique LDAR components with commercially available and maintainable components having improved capabilities. These components will be phased in to ensure full continuity and access to this important warning technology. These LDAR systems are expected to eventually be available for installation and use by the public at specialized facilities, such as airports, and for general weather warnings via the National Weather Service (NWS) or television broadcast. The NWS in Melbourne has had access to real-time LDAR data since 1993 on an experimental basis. This use of LDAR has shown promise for the improvement of aviation forecasts and severe weather warnings. More so, it has opened the door to investigate the feasibility of issuing lightning-related public advisories. The success of its early use suggests that this technology may improve safety and potentially save lives, therefore constituting a significant benefit to the public. This paper describes the LDR system, the plans and progress of these upgrades, and the potential benefits of its use.

Starr, Stan↗

NASA NTRS1999

A Methodology for Investigating Adaptive Postural Control

Our research on postural control and human-environment interactions provides an appropriate scientific foundation for understanding the skill of mass handling by astronauts in weightless conditions (e.g., extravehicular activity or EVA). We conducted an investigation of such skills in NASA's principal mass-handling simulator, the Precision Air-Bearing Floor, at the Johnson Space Center. We have studied skilled movement-body within a multidisciplinary context that draws on concepts and methods from biological and behavioral sciences (e.g., psychology, kinesiology and neurophysiology) as well as bioengineering. Our multidisciplinary research has led to the development of measures, for manual interactions between individuals and the substantial environment, that plausibly are observable by human sensory systems. We consider these methods to be the most important general contribution of our EVA investigation. We describe our perspective as control theoretic because it draws more on fundamental concepts about control systems in engineering than it does on working constructs from the subdisciplines of biomechanics and motor control in the bio-behavioral sciences. At the same time, we have attempted to identify the theoretical underpinnings of control-systems engineering that are most relevant to control by human beings. We believe that these underpinnings are implicit in the assumptions that cut across diverse methods in control-systems engineering, especially the various methods associated with "nonlinear control", "fuzzy control," and "adaptive control" in engineering. Our methods are based on these theoretical foundations rather than on the mathematical formalisms that are associated with particular methods in control-systems engineering. The most important aspects of the human-environment interaction in our investigation of mass handling are the functional consequences that body configuration and stability have for the pick up of information or the achievement of overt goals. It follows that an essential characteristic of postural behavior is the effective maintenance of the orientation and stability of the sensory and motor "platforms" (e.g., head or shoulders) over variations in the human, the environment and the task. This general skill suggests that individuals should be sensitive to the functional consequences of body configuration and stability. In other words, individuals should perceive the relation between configuration, stability, and performance so that they can adaptively control their interaction with the surroundings. Human-environment interactions constitute robust systems in that individuals can maintain the stability of such interactions over uncertainty about and variations in the dynamics of the interaction. Robust interactions allow individuals to adopt orientations and configurations that are not optimal with respect to purely energetic criteria. Individuals can tolerate variation in postural states, and such variation can serve an important function in adaptive systems. Postural variability generates stimulation which is "textured" by the dynamics of the human-environment system. The texture or structure in stimulation provides information about variation in dynamics, and such information can be sufficient to guide adaption in control strategies. Our method were designed to measure informative patterns of movement variability.

McDonald, P. V.↗

NASA NTRS1996

Mechanics of Granular Materials (MGM)

The constitutive behavior of uncemented granular materials such as strength, stiffness, and localization of deformations are to a large extend derived from interparticle friction transmitted between solid particles and particle groups. Interparticle forces are highly dependent on gravitational body forces. At very low effective confining pressures, the true nature of the Mohr envelope, which defines the Mohr-Coulomb failure criterion for soils, as well as the relative contribution of each of non-frictional components to soil's shear strength cannot be evaluated in terrestrial laboratories. Because of the impossibility of eliminating gravitational body forces on earth, the weight of soil grains develops interparticle compressive stresses which mask true soil constitutive behavior even in the smallest samples of models. Therefore the microgravity environment induced by near-earth orbits of spacecraft provides unique experimental opportunities for testing theories related to the mechanical behavior of terrestrial granular materials. Such materials may include cohesionless soils, industrial powders, crushed coal, etc. This paper will describe the microgravity experiment, 'Mechanics of Granular Materials (MGM)', scheduled to be flown on Space Shuttle-MIR missions. The paper will describe the experiment's hardware, instrumentation, specimen preparation procedures, testing procedures in flight, as well as a brief summary of the post-mission analysis. It is expected that the experimental results will significantly improve the understanding of the behavior of granular materials under very low effective stress levels.

Alshibli, Khalid A.↗

NASA NTRS1986

Performance measurements of a data link protocol

The end-to-end performance of a program implementing IEEE Std 802.2 logical link control protocol, which provides virtual circuit and datagram service and which constitutes the top sublayer of the data link layer of the reference model for Local Area Networks is studied. The measurements of relative execution times of various functions required in transferring data, over virtual circuits or as datagrams, showed that most of the program execution time is spent in a few relatively low-level functions. One of these functions performs block movement of data in memory, and two other functions provide access to various queues. Based on this result, two alternative versions of the program which move data efficiently were written and measured. In this paper the results of the study are reported and their impact on designing hardware and software systems for a network interface are discussed.

Kanakia, Hemant↗

NASA NTRS1995

Blending Velocities In Task Space In Computing Robot Motions

Blending of linear and angular velocities between sequential specified points in task space constitutes theoretical basis of improved method of computing trajectories followed by robotic manipulators. In method, generalized velocity-vector-blending technique provides relatively simple, common conceptual framework for blending linear, angular, and other parametric velocities. Velocity vectors originate from straight-line segments connecting specified task-space points, called "via frames" and represent specified robot poses. Linear-velocity-blending functions chosen from among first-order, third-order-polynomial, and cycloidal options. Angular velocities blended by use of first-order approximation of previous orientation-matrix-blending formulation. Angular-velocity approximation yields small residual error, quantified and corrected. Method offers both relative simplicity and speed needed for generation of robot-manipulator trajectories in real time.

Volpe, Richard A.↗

NASA NTRS1996

A viscoelastic higher-order beam finite element

A viscoelastic internal variable constitutive theory is applied to a higher-order elastic beam theory and finite element formulation. The behavior of the viscous material in the beam is approximately modeled as a Maxwell solid. The finite element formulation requires additional sets of nodal variables for each relaxation time constant needed by the Maxwell solid. Recent developments in modeling viscoelastic material behavior with strain variables that are conjugate to the elastic strain measures are combined with advances in modeling through-the-thickness stresses and strains in thick beams. The result is a viscous thick-beam finite element that possesses superior characteristics for transient analysis since its nodal viscous forces are not linearly dependent an the nodal velocities, which is the case when damping matrices are used. Instead, the nodal viscous forces are directly dependent on the material's relaxation spectrum and the history of the nodal variables through a differential form of the constitutive law for a Maxwell solid. The thick beam quasistatic analysis is explored herein as a first step towards developing more complex viscoelastic models for thick plates and shells, and for dynamic analyses. The internal variable constitutive theory is derived directly from the Boltzmann superposition theorem. The mechanical strains and the conjugate internal strains are shown to be related through a system of first-order, ordinary differential equations. The total time-dependent stress is the superposition of its elastic and viscous components. Equations of motion for the solid are derived from the virtual work principle using the total time-dependent stress. Numerical examples for the problems of relaxation, creep, and cyclic creep are carried out for a beam made from an orthotropic Maxwell solid.

Johnson, Arthur R.↗