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NASA NTRS1986

High-purity silicon crystal growth investigations

Information is given on evaporation and segregation contributions to impurity profiles of floating zone crystals (FZ); high-purity silicon float zoning (FZ); minority-carrier lifetime measurement of heavily doped silicon crystals; the effect of some crystal growth parameters on minority-carrier lifetime; and defect investigations by X-ray topography in graphical and tabular form. It was concluded that evaporation contributes substantially to impurity reduction when FZ or cold-crucible growth is conducted in a vacuum; boron and gallium may be more favorable dopants than indium or aluminum for obtaining high minority-carrier lifetimes; minority-carrier lifetimes greater than 100 microseconds are feasible at a 2 times 10 to the 17th power cm-3 doping level; minority-carrier lifetime decreases with increasing crystal cooling rate and also with the presence of dislocations; the method used to clean silicon feed rods affects lifetime; and microdefect densities in dislocation-free FZ crystals appear to be lower with Ga doping than with B doping.

Ciszek, T. F.↗

NASA NTRS1985

Constitutive modeling for isotropic materials

The first year of progress on a NASA-Lewis contract with the General Electric Co is documented. The purpose of this contract (NAS3-23927) is to develop and evaluate unified constitutive equations for applications to hot-path components of aircraft gas turbine engines such as high pressure turbine blades and vanes. To accomplish this goal, uniaxial, notched, and multiaxial specimens made of conventionally cast Rene 80 are being tested under conditions that simulate engine operating conditions. To reduce the raw data, automated data reduction techniques are being developed that produce computer files containing the information needed to analyze proposed constitutive theories. Described are the analytical methods being developed to determine the parameters for these nonlinear unified theories by using the reduced data files. In another activity, a dedicated finite-element computer code is being developed to use unified theories in the structural analysis of hot-section components. This code was extensively verified for one such theory by successfully predicting the strain histories measured experimentally at the notch root of complex specimens taken from complex laboratory specimens.

Ramaswamy, V. G.↗

NASA NTRS1990

Modeling and analysis of the space shuttle nose-gear tire with semianalytic finite elements

A computational procedure is presented for the geometrically nonlinear analysis of aircraft tires. The Space Shuttle Orbiter nose gear tire was modeled by using a two-dimensional laminated anisotropic shell theory with the effects of variation in material and geometric parameters included. The four key elements of the procedure are: (1) semianalytic finite elements in which the shell variables are represented by Fourier series in the circumferential direction and piecewise polynominals in the meridional direction; (2) a mixed formulation with the fundamental unknowns consisting of strain parameters, stress-resultant parameters, and generalized displacements; (3) multilevel operator splitting to effect successive simplifications, and to uncouple the equations associated with different Fourier harmonics; and (4) multilevel iterative procedures and reduction techniques to generate the response of the shell. Numerical results of the Space Shuttle Orbiter nose gear tire model are compared with experimental measurements of the tire subjected to inflation loading.

Kim, Kyun O.↗

NASA NTRS1990

Analysis of aircraft tires via semianalytic finite elements

A computational procedure is presented for the geometrically nonlinear analysis of aircraft tires. The tire was modeled by using a two-dimensional laminated anisotropic shell theory with the effects of variation in material and geometric parameters included. The four key elements of the procedure are: (1) semianalytic finite elements in which the shell variables are represented by Fourier series in the circumferential direction and piecewise polynomials in the meridional direction; (2) a mixed formulation with the fundamental unknowns consisting of strain parameters, stress-resultant parameters, and generalized displacements; (3) multilevel operator splitting to effect successive simplifications, and to uncouple the equations associated with different Fourier harmonics; and (4) multilevel iterative procedures and reduction techniques to generate the response of the shell.

Noor, Ahmed K.↗

NASA NTRS1991

PDEMOD: Software for control/structures optimization

Because of the possibility of adverse interaction between the control system and the structural dynamics of large, flexible spacecraft, great care must be taken to ensure stability and system performance. Because of the high cost of insertion of mass into low earth orbit, it is prudent to optimize the roles of structure and control systems simultaneously. Because of the difficulty and the computational burden in modeling and analyzing the control structure system dynamics, the total problem is often split and treated iteratively. It would aid design if the control structure system dynamics could be represented in a single system of equations. With the use of the software PDEMOD (Partial Differential Equation Model), it is now possible to optimize structure and control systems simultaneously. The distributed parameter modeling approach enables embedding the control system dynamics into the same equations for the structural dynamics model. By doing this, the current difficulties involved in model order reduction are avoided. The NASA Mini-MAST truss is used an an example for studying integrated control structure design.

Taylor, Lawrence W., Jr.↗

NASA NTRS1991

Estimation of geopotential differences over intercontinental locations using satellite and terrestrial measurements

An error analysis study was conducted in order to assess the current accuracies and the future anticipated improvements in the estimation of geopotential differences over intercontinental locations. An observation/estimation scheme was proposed and studied, whereby gravity disturbance measurements on the Earth's surface, in caps surrounding the estimation points, are combined with corresponding data in caps directly over these points at the altitude of a low orbiting satellite, for the estimation of the geopotential difference between the terrestrial stations. The mathematical modeling required to relate the primary observables to the parameters to be estimated, was studied for the terrestrial data and the data at altitude. Emphasis was placed on the examination of systematic effects and on the corresponding reductions that need to be applied to the measurements to avoid systematic errors. The error estimation for the geopotential differences was performed using both truncation theory and least squares collocation with ring averages, in case observations on the Earth's surface only are used. The error analysis indicated that with the currently available global geopotential model OSU89B and with gravity disturbance data in 2 deg caps surrounding the estimation points, the error of the geopotential difference arising from errors in the reference model and the cap data is about 23 kgal cm, for 30 deg station separation.

Pavlis, Nikolaos K.↗

NASA NTRS1992

Data reduction formulas for the 16-foot transonic tunnel: NASA Langley Research Center, revision 2

The equations used by the 16-Foot Transonic Wind Tunnel in the data reduction programs are presented in nine modules. Each module consists of equations necessary to achieve a specific purpose. These modules are categorized in the following groups: (1) tunnel parameters; (2) jet exhaust measurements; (3) skin friction drag; (4) balance loads and model attitudes calculations; (5) internal drag (or exit-flow distribution); (6) pressure coefficients and integrated forces; (7) thrust removal options; (8) turboprop options; and (9) inlet distortion.

Mercer, Charles E.↗

NASA NTRS2011

Optimal Asteroid Mass Determination from Planetary Range Observations: A Study of a Simplified Test Model

Mars ranging observations are available over the past 10 years with an accuracy of a few meters. Such precise measurements of the Earth-Mars distance provide valuable constraints on the masses of the asteroids perturbing both planets. Today more than 30 asteroid masses have thus been estimated from planetary ranging data (see [1] and [2]). Obtaining unbiased mass estimations is nevertheless difficult. Various systematic errors can be introduced by imperfect reduction of spacecraft tracking observations to planetary ranging data. The large number of asteroids and the limited a priori knowledge of their masses is also an obstacle for parameter selection. Fitting in a model a mass of a negligible perturber, or on the contrary omitting a significant perturber, will induce important bias in determined asteroid masses. In this communication, we investigate a simplified version of the mass determination problem. Instead of planetary ranging observations from spacecraft or radar data, we consider synthetic ranging observations generated with the INPOP [2] ephemeris for a test model containing ~25000 asteroids. We then suggest a method for optimal parameter selection and estimation in this simplified framework.

asteroids↗

NASA NTRSDate not supplied

Improvements in VLBI Data Analysis for Advanced in Geodesy

I will provide an overview of advances in VLBI data analysis implemented at NASA GSFC. That include the use of B-splines for modeling non-linear station position evolution, the use of all non-tidal mass loadings in data reduction, the use of slant a priori path delays from the output of numerical weather models, the use of B-splines for evaluation of the Earth orientation parameters as a continuous function, the use of elevation-dependent weighting, processing both 24 hr and 1 hr experiments in a single least square solutions and other innovations. I will show how this changes in data analysis affect space geodesy results, such as estimation of station positions, Earth orientation parameters, and source coordinates.

Leonid Petrov↗

NASA NTRS1985

Dynamic modeling and adaptive control for space stations

Of all large space structural systems, space stations present a unique challenge and requirement to advanced control technology. Their operations require control system stability over an extremely broad range of parameter changes and high level of disturbances. During shuttle docking the system mass may suddenly increase by more than 100% and during station assembly the mass may vary even more drastically. These coupled with the inherent dynamic model uncertainties associated with large space structural systems require highly sophisticated control systems that can grow as the stations evolve and cope with the uncertainties and time-varying elements to maintain the stability and pointing of the space stations. The aspects of space station operational properties are first examined, including configurations, dynamic models, shuttle docking contact dynamics, solar panel interaction, and load reduction to yield a set of system models and conditions. A model reference adaptive control algorithm along with the inner-loop plant augmentation design for controlling the space stations under severe operational conditions of shuttle docking, excessive model parameter errors, and model truncation are then investigated. The instability problem caused by the zero-frequency rigid body modes and a proposed solution using plant augmentation are addressed. Two sets of sufficient conditions which guarantee the globablly asymptotic stability for the space station systems are obtained.

Ih, C. H. C.↗

NASA NTRS2006

Observations of the Hot Horizontal Branch Stars in the Metal-Rich Bulge Globular Cluster NGC 6388

The metal-rich bulge globular cluster NGC 6388 shows a distinct blue horizontal-branch tail in its colour-magnitude diagram (Rich et al. 1997) and is thus a strong case of the well-known 2nd Parameter Problem. In addition, its horizontal branch (HB) shows an upward tilt toward bluer colours, which cannot be explained by canonical evolutionary models. Several non-canonical scenarios have been proposed to explain these puzzling observations. In order to test the predictions of these scenarios, we have obtained medium resolution spectra to determine the atmospheric parameters of a sample of the blue HB stars in NGC 6388.Using the medium resolution spectra, we determine effective temperatures, surface gravities and helium abundances by fitting the observed Balmer and helium lines with appropriate theoretical stellar spectra. As we know the distance to the cluster, we can verify our results by determining masses for the stars. During the data reduction we took special care to correctly subtract the background, which is dominated by the overlapping spectra of cool stars. The cool blue tail stars in our sample with T(sub eff) approximately 10000 K have lower than canonical surface gravities, suggesting that these stars are, on average, approximately equal to 0.4 mag brighter than canonical HB stars in agreement with the observed upward slope of the HB in NGC 6388. Moreover, the mean mass of these stars agrees well with theoretical predictions. In contrast, the hot blue tail stars in our sample with T(sub eff) greater than or equal to 12000 K show significantly lower surface gravities than predicted by any scenario, which can reproduce the photometric observations. Their masses are also too low by about a factor of 2 compared to theoretical predictions. The physical parameters of the blue HB stars at about 10,000 K support the helium pollution scenario. The low gravities and masses of the hot blue tail stars, however, are probably caused by problems with the data reduction, most likely due to remaining background light in the spectra, which would affect the fainter hot blue tail stars much more strongly than the brighter cool blue tail stars. Our study of the hot blue tail stars in NGC 6388 illustrates the obstacles which are encountered when attempting to determine the atmospheric parameters of hot HB stars in very crowded fields using ground-based observations. We discuss these obstacles and offer possible solutions for future projects.

Moehler, S.↗

NASA NTRS2010

Validation of On-Orbit Methodology for the Assessment of Cardiac Function and Changes in the Circulating Volume Using Ultrasound and Braslet-M Occlusion Cuffs

The objective of this joint U.S. - Russian project was the development and validation of an in-flight methodology to assess a number of cardiac and vascular parameters associated with circulating volume and its manipulation in long-duration space flight. Responses to modified Valsalva and Mueller maneuvers were measured by cardiac and vascular ultrasound (US) before, during, and after temporary volume reduction by means of Braslet-M thigh occlusion cuffs (Russia). Materials and Methods: The study protocol was conducted in 14 sessions on 9 ISS crewmembers, with an average exposure to microgravity of 122 days. Baseline cardiovascular measurements were taken by echocardiography in multiple modes (including tissue Doppler of both ventricles) and femoral and jugular vein imaging on the International Space Station (ISS). The Braslet devices were then applied and measurements were repeated after >10 minutes. The cuffs were then released and the hemodynamic recovery process was monitored. Modified Valsalva and Mueller maneuvers were used throughout the protocol. All US data were acquired by the HDI-5000 ultrasound system aboard the ISS (ATL/Philips, USA) during remotely guided sessions. The study protocol, including the use of Braslet-M for this purpose, was approved by the ISS Human Research Multilateral Review Board (HRMRB). Results: The effects of fluid sequestration on a number of echocardiographic and vascular parameters were readily detectable by in-flight US, as were responses to respiratory maneuvers. The overall volume status assessment methodology appears to be valid and practical, with a decrease in left heart lateral E (tissue Doppler) as one of the most reliable measures. Increase in the femoral vein cross-sectional areas was consistently observed with Braslet application. Other significant differences and trends within the extensive cardiovascular data were also observed. (Decreased - RV and LV preload indices, Cardiac Output, LV E all maneuvers, LV Stroke Volume). Conclusions: This Study: 1) Addressed specific aspects of operational space medicine and space physiology, including assessment of circulating volume disturbances 2) Expanded the applications of diagnostic ultrasound imaging and Doppler techniques in microgravity. 3) Used respiratory maneuvers against the background of acute circulating volume manipulations which appear to enhance our ability to noninvasively detect volume-dependency in a number of cardiac and vascular parameters. 4) Determined that Tei index is not clinically changed therefore contractility not altered in the face of reduced preload. 5) Determined that increased Femoral Vein Area indicating blood being sequestered in lower extremities correlates with reduced preload and cardiac output. 6) That Braslet may be the only feasible means of acutely treating high pressure pulmonary edema in reduced gravity environments.

Hamilton, Douglas↗

NASA NTRS2004

Parametric Testing of Chevrons on Single Flow Hot Jets

A parametric family of chevron nozzles have been studied, looking for relationships between chevron geometric parameters, flow characteristics, and far-field noise. Both cold and hot conditions have been run at acoustic Mach number 0.9. Ten models have been tested, varying chevron count, penetration, length, and chevron symmetry. Four comparative studies were defined from these datasets which show: that chevron length is not a major impact on either flow or sound; that chevron penetration increases noise at high frequency and lowers it at low frequency, especially for low chevron counts; that chevron count is a strong player with good low frequency reductions being achieved with high chevron count without strong high frequency penalty; and that chevron asymmetry slightly reduces the impact of the chevron. Finally, it is shown that although the hot jets differ systematically from the cold one, the overall trends with chevron parameters is the same.

Bridges, James↗

NASA NTRS1978

Experimental clean combustor program: Phase 3: Turbulence measurement addendum

Airflow turbulence parameters were measured in the high pressure, high temperature flow stream leaving the compressor of an operating gas turbine engine. A water cooled hot film turbulence probe was used to determine the turbulence intensity and length scale in the compressor exit flow stream of the CF6-50 engine. Data were obtained only at idle operating conditions. At engine power levels above idle conditions, durability problems and erratic data readings were encountered with the turbulence measurement probes. Turbulence measurements were made at three radial immersions at a point 15.5 cm downstream of the compressor outlet guide vanes in the compressor exit diffuser. The passage height at this point is 5.54 cm. Data reduction was accomplished with a time-data fast Fourier transform (FFT) system. This system finds the power spectral density distribution (PSD) of a large number of data samples using a direct Fourier transform algorithm and finds the autocorrelation parameter for these data by doing an FFT analysis of the PSD curves for a series of time delay intervals.

Taylor, J. R.↗

NASA NTRS1977

The application of remote sensing to the development and formulation of hydrologic planning models: Executive summary

Methods for the reduction of remotely sensed data and its application in hydrologic land use assessment, surface water inventory, and soil property studies are presented. LANDSAT data is used to provide quantitative parameters and coefficients to construct watershed transfer functions for a hydrologic planning model aimed at estimating peak outflow from rainfall inputs.

Castruccio, P. A.↗

NASA NTRS1977

Remote estimation of surface temperature in pollution measurement experiments

The procedure described was developed for inferring the effective brightness temperature (EBT) of the underlying surface (at a given altitude) from the computed value of the radiance corresponding to a known surface temperature. A standard temperature correction to EBT (termed 'base correction') is first determined by using a 'base model atmosphere' for computing the upwelling radiance. Additional temperature corrections are then determined by considering several variations of the different surface and atmospheric parameters from their 'base model' values. Empirical relations are derived between the deviations of various surface and atmospheric parameters (from their base model values) and the additional corrections required for the EBT as a result of these variations. Use of such relations for large-scale data reduction, instead of radiative transfer calculations, is expected to result in drastic cost decrease.

Gupta, S. K.↗

NASA NTRS1988

Viscous shock-layer solutions with nonequilibrium chemistry for hypersonic flows past slender bodies

Laminar nonequilibrium heat transfer to slender vehicles is discussed, with heating-rate results presented as a ratio of the noncatalytic to the corresponding fully catalytic value to illustrate the maximum potential for a heating reduction in dissociated nonequilibrium flow at a given flight condition. Larger blunted cone half-angles are shown to produce the most significant nonequilibrium effects at distances beyond 100 nose radii, except in the fore-cone region. Increasing nose bluntness is found to produce large reductions in the ratio for the smaller cone angles at relatively large downstream surface lengths. It is noted that the nose radius and freestream density are not independent scaling parameters in nonequilibrium flow.

Zoby, E. V.↗

NASA NTRS1990

Grounding, bonding and shielding for safety and signal interference control

Aircraft models and other aerodynamic tests are conducted at the NASA Ames Research Center National Full Scale Aerodynamics Complex (NFAC). The models, tested in NFAC's wind tunnels, are sometimes heavily instrumented and are connected to a data acquisition system. Besides recording data for evaluation, certain critical information must be monitored to be sure the model is within operational limits. The signals for these parameters are for the most part low-level signals that require good instrumentation amplification. These amplifiers need to be grounded and shielded for common mode rejection and noise reduction. The instrumentation also needs to be grounded to prevent electrical shock hazards. The purpose of this paper is to present an understanding of the principles and purpose of grounding, bonding, and shielding.

Forsyth, T. J.↗