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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Space facilities: Meeting future needs for research, development, and operations

The National Facilities Study (NFS) represents an interagency effort to develop a comprehensive and integrated long-term plan for world-class aeronautical and space facilities that meet current and projected needs for commercial and government aerospace research and development and space operations. At the request of NASA and the DOD, the National Research Council's Committee on Space Facilities has reviewed the space related findings of the NFS. The inventory of more than 2800 facilities will be an important resource, especially if it continues to be updated and maintained as the NFS report recommends. The data in the inventory provide the basis for a much better understanding of the resources available in the national facilities infrastructure, as well as extensive information on which to base rational decisions about current and future facilities needs. The working groups have used the inventory data and other information to make a set of recommendations that include estimates of cast savings and steps for implementation. While it is natural that the NFS focused on cost reduction and consolidations, such a study is most useful to future planning if it gives equal weight to guiding the direction of future facilities needed to satisfy legitimate national aspirations. Even in the context of cost reduction through facilities closures and consolidations, the study is timid about recognizing and proposing program changes and realignments of roles and missions to capture what could be significant savings and increased effectiveness. The recommendations of the Committee on Space Facilities are driven by the clear need to be more realistic and precise both in recognizing current incentives and disincentives in the aerospace industry and in forecasting future conditions for U.S. space activities.

Source record↗
NASA NTRS1990

Directional solidification of superalloys

This invention relates to the directional solidification of superalloys, in particular nickel-based superalloys, by imposition of a predetermined temperature profile in the solidification front and, depending on the desired results, a predetermined rate of advance of said solidification front, whereas castings of markedly superior fatigue resistance are produced.

Schmidt, Deborah Diane↗
NASA NTRS2000

Characterizing the Use of Ultrasonic Energy in Promoting Uniform Composite Growth in Immiscible Alloys

The results of experimental investigation and mathematical modeling for immiscible alloys subjected to ultrasonic influence are presented. It is known that in inoculated light alloy melts, ultrasonic treatment creates a new type of cast structure with extremely fine grains of uniform composition. This effect is produced across a wide range of freezing rates and technologies. However, it has not been demonstrated that the process can be successfully applied during controlled directional solidification processing. In this work we present the results from a set of directional solidification experiments and suggest describing the droplet size versus ultrasonic frequency and amplitude using an energy approach, followed with a more detailed analysis through numerical modeling of the ultrasonic field.

Grugel, Richard N.↗
NASA NTRS1971

Apollo 14 composite casting demonstration

This program assisted in the design and implementation of the composite casting demonstration for the Apollo 14 mission. Both flight and control samples were evaluated. Some conclusions resulting from a comparison of the flight and control samples were: (1) Solidification in neither the flight nor control samples was truly directional. (2) Apparent intermittent contact of the melt with the container in the flight samples led to unusual nucleation and growth structures. (3) There was greater uniformity, on a macro scale, of both pores and structural features in the flight sample; presumably the result of the reduced gravity conditions. (4) It seems quite feasible to produce enhanced dispersions of gases and dense phases in a melt which is solidified in reduced gravity. (5) A two-stage heating/cooling cycle may help directional solidification. (6) Sample materials should be selected from materials in which the dispersant fully wets the matrix material. (7) Experiments should be conducted in two modes: (1) where the melt is in good thermal contact with the container, and (2) where the melt is in a free-float condition.

Source record↗
NASA NTRS2004

Improved Estimate of Phobos Secular Acceleration from MOLA Observations

We report on new observations of the orbital position of Phobos, and use them to obtain a new and improved estimate of the rate of secular acceleration in longitude due to tidal dissipation within Mars. Phobos is the inner-most natural satellite of Mars, and one of the few natural satellites in the solar system with orbital period shorter than the rotation period of its primary. As a result, any departure from a perfect elastic response by Mars in the tides raised on it by Phobos will cause a transfer of angular momentum from the orbit of Phobos to the spin of Mars. Since its discovery in 1877, Phobos has completed over 145,500 orbits, and has one of the best studied orbits in the solar system, with over 6000 earth-based astrometric observations, and over 300 spacecraft observations. As early as 1945, Sharpless noted that there is a secular acceleration in mean longitude, with rate (1.88 + 0.25) 10(exp -3) degrees per square year. In preparation for the 1989 Russian spacecraft mission to Phobos, considerable work was done compiling past observations, and refining the orbital model. All of the published estimates from that era are in good agreement. A typical solution (Jacobson et al., 1989) yields (1.249 + 0.018) 10(exp -3) degrees per square year. The MOLA instrument on MGS is a laser altimeter, and was designed to measure the topography of Mars. However, it has also been used to make observations of the position of Phobos. In 1998, a direct range measurement was made, which indicated that Phobos was slightly ahead of the predicted position. The MOLA detector views the surface of Mars in a narrow field of view, at 1064 nanometer wavelength, and can detect shadows cast by Phobos on the surface of Mars. We have found 15 such serendipitous shadow transit events over the interval from xx to xx, and all of them show Phobos to be ahead of schedule, and getting progressively farther ahead of the predicted position. In contrast, the cross-track positions are quite close to the predicted values. Assuming that the along-track discrepancy is small enough that we can linearize the corrections, we model the mean orbital longitude as a quadratic function of time, and solve for corrections to the constant, linear, and quadratic terms. The time span of the recent observations is insufficient to properly resolve this issue alone, but when the 127 years of prior observations are added, we find a solution which reduces misfit to the new observations considerably, and makes no significant change to the fit to earlier observations. Our estimate for the secular acceleration term is (1.367 + 0.006) degrees per square year. The corresponding rate of energy dissipation is 3.34 MW. From a geophysical perspective, a more interesting parameter than the secular acceleration itself is the tidal lag angle, or tidal quality factor Q, for Mars. Unfortunately, the limiting error source in that determination is remaining uncertainty in the tidal Love numbers at harmonic degrees 2,3, and even 4. Until those parameters are better constrained, improvement in the orbital model of Phobos will not provide corresponding benefits for understanding the interior of Mars.

Bills, Bruce↗
NASA NTRSDate not supplied

Bridging Current Indirect and Future Direct Estimates of Convective Mass Flux Toward Quantifying the Role of Convective Cores on Anvil Area Time Tendencies

Anvil cloud spatial extent is strongly driven by convective mass flux. However, the lack of convective mass flux observations precludes global analyses of the functional relationship between anvil cloud area growth tendencies and convective areal coverage and vertical mass flux. Partly informed by analyses of a hierarchy of WRF mesoscale convective system (MCS) simulations, in this presentation, we discuss new work on estimating convective mass flux by way of an approach that casts the problem of quantifying convective mass flux into terms related to diabatic heating vertical structure, convective area and tropospheric stability. We demonstrate the usefulness of this approach at the MCS spatial scale via development of a simple, robust model that analytically connects system-scale convective mass flux and anvil cloud area growth rates. We show that the model predicts anvil area size changes in agreement with those observed in a global convective system tracking database (TOOCAN). An additional advantage of this approach for estimating convective mass flux is that it bridges future satellite mission plans for directly observing convective mass flux (e.g., AOS) with longer-record observations made by TRMM, GPM and satellite sounder mission data (the latter used for estimating stability) that, when combined, can be used for inferring convective mass fluxes at the MCS spatial scale spanning slowly changing, diverse environments. An evaluation and bridging of both direct and indirect approaches supports convective process analyses varying over longer time periods in this “era of convection.”

convective mass flux↗
NASA NTRSDate not supplied

Bridging current indirect and future direct estimates of convective mass flux toward quantifying the role of convective cores on anvil area time tendencies

Anvil cloud spatial extent is strongly driven by convective mass flux. However, the lack of convective mass flux observations precludes global analyses of the functional relationship between anvil cloud area growth tendencies and convective areal coverage and vertical mass flux. Partly informed by analyses of a hierarchy of WRF mesoscale convective system (MCS) simulations, in this presentation, we discuss new work on estimating convective mass flux by way of an approach that casts the problem of quantifying convective mass flux into terms related to diabatic heating vertical structure, convective area and tropospheric stability. We demonstrate the usefulness of this approach at the MCS spatial scale via development of a simple, robust model that analytically connects system-scale convective mass flux and anvil cloud area growth rates. We show that the model predicts anvil area size changes in agreement with those observed in a global convective system tracking database (TOOCAN). An additional advantage of this approach for estimating convective mass flux is that it bridges future satellite mission plans for directly observing convective mass flux (e.g., AOS) with longer-record observations made by TRMM, GPM and satellite sounder mission data (the latter used for estimating stability) that, when combined, can be used for inferring convective mass fluxes at the MCS spatial scale spanning slowly changing, diverse environments. An evaluation and bridging of both direct and indirect approaches supports convective process analyses varying over longer time periods in this “era of convection.”

convective mass flux↗
NASA NTRS1982

Analysis, design, and test of a graphite/polyimide Shuttle orbiter body flap segment

For future missions, increases in Space Shuttle orbiter deliverable and recoverable payload weight capability may be needed. Such increases could be obtained by reducing the inert weight of the Shuttle. The application of advanced composites in orbiter structural components would make it possible to achieve such reductions. In 1975, NASA selected the orbiter body flap as a demonstration component for the Composite for Advanced Space Transportation Systems (CASTS) program. The progress made in 1977 through 1980 was integrated into a design of a graphite/polyimide (Gr/Pi) body flap technology demonstration segment (TDS). Aspects of composite body flap design and analysis are discussed, taking into account the direct-bond fibrous refractory composite insulation (FRCI) tile on Gr/Pi structure, Gr/Pi body flap weight savings, the body flap design concept, and composite body flap analysis. Details regarding the Gr/Pi technology demonstration segment are also examined.

Graves, S. R.↗
NASA NTRS1996

Methodology for Sensitivity Analysis, Approximate Analysis, and Design Optimization in CFD for Multidisciplinary Applications

An incremental iterative formulation together with the well-known spatially split approximate-factorization algorithm, is presented for solving the large, sparse systems of linear equations that are associated with aerodynamic sensitivity analysis. This formulation is also known as the 'delta' or 'correction' form. For the smaller two dimensional problems, a direct method can be applied to solve these linear equations in either the standard or the incremental form, in which case the two are equivalent. However, iterative methods are needed for larger two-dimensional and three dimensional applications because direct methods require more computer memory than is currently available. Iterative methods for solving these equations in the standard form are generally unsatisfactory due to an ill-conditioned coefficient matrix; this problem is overcome when these equations are cast in the incremental form. The methodology is successfully implemented and tested using an upwind cell-centered finite-volume formulation applied in two dimensions to the thin-layer Navier-Stokes equations for external flow over an airfoil. In three dimensions this methodology is demonstrated with a marching-solution algorithm for the Euler equations to calculate supersonic flow over the High-Speed Civil Transport configuration (HSCT 24E). The sensitivity derivatives obtained with the incremental iterative method from a marching Euler code are used in a design-improvement study of the HSCT configuration that involves thickness. camber, and planform design variables.

Taylor, Arthur C., III↗
NASA NTRS1972

A finite element procedure for nonlinear prebuckling and initial postbuckling analysis

A procedure cast in a form appropriate to the finite element method is presented for geometrically nonlinear prebuckling and postbuckling structural analysis, including the identification of snap-through type of buckling. The principal features of this procedure are the use of direct iteration for solution of the nonlinear algebraic equations in the prebuckling range, an interpolation scheme for determination of the initial bifurcation point, a perturbation method in definition of the load-displacement behavior through the postbuckling regime, and extrapolation in determination of the limit point for snap-through buckling. Three numerical examples are presented in illustration of the procedure and in comparison with alternative approaches.

Mau, S. T.↗
NASA NTRS1999

Flight Validation of Atomic Oxygen Resistant Resistant Polymers

Because of its high reactivity, atomic oxygen causes surface erosion on polymeric materials. although the reaction efficiency depends on the chemical structure of the polymer. We have found an organotin compound, bis(triphenyltin) oxide (BTO), which has an unusually high solubility in solutions of a number of commercial high performance polymers. Films of these polymers containing BTO showed a substantial reduction in erosion by atomic oxygen when compared with films of the pure material. Analysis has shown that in the presence of atomic oxygen, erosion of the exposed surfaces of the BTO-containing films leaves a residual protective tin oxide coating . Since the additive is uniformly distributed throughout the polymeric material, any break or puncture in the protective coating is "healed" by the material below. Samples were exposed to the environment of the low earth orbit (LEO) on two Space Shuttle flights, STS-46, in June of 1992, and STS-51 in September of 1993. The analysis of these samples has been reported previously. For both flights, the samples were small (1.3 cm and 1.9 cm respectively) thus limiting the scope of analysis. In the research under this cooperative agreement, films of a polyetherimide, were exposed to the LEO environment on Space Shuttle flight STS-85 in August of 1997 as part of the Evaluation of Space Environment and Effects on Materials (ESEM) experiment. The polyetherimide chosen is available commercially as Ultem, registered to the General Electric Company. Films of pure Ultem, Ultem with 10% BTO by mass, and Ultem with 20% BTO by mass were exposed in the ram direction for 40 hours during STS-85. Ultem has a Tg of 215 deg C and is soluble in common chlorinated solvents. Granules of the polymer were dried at 120 deg C, but otherwise were used as received. Films were cast on a glass plate from a solution of the polymer in a 60/40 (w/w) mixture of chloroform and 1,1,2,2-tetrachloroethane. The plate was placed in a dust-free box for at least 24 hours to allow much of the solvent to evaporate, and then was moved to a vacuum oven and slowly heated from 20 to 220 deg C over a period of two weeks to completely remove all solvent. Each exposed sample was 7.6 cm long and 2.2 cm wide and about 0.025 mm thick. The structures of Ultem and bis(triphenyltin) oxide are shown.

Kiefer, Richard L.↗
NASA NTRS1980

Analysis and calculation of macrosegregation in a casting ingot. MPS solidification model. Volume 3: Operating manual

The operation of solidification model 1 is described. Model 1 calculates the macrosegregation in a rectangular ingot of a binary alloy as a result of horizontal axisymmetric bidirectional solidification. The calculation is restricted to steady-state solidification; there is no variation in final local average composition in the direction of isotherm movement. The physics of the model are given.

Maples, A. L.↗
NASA NTRS1986

Chromospheric explosions

Three issues relative to chromospheric explosions were debated. (1) Resolved: The blue-shifted components of x-ray spectral lines are signatures of chromospheric evaporation. It was concluded that the plasma rising with the corona is indeed the primary source of thermal plasma observed in the corona during flares. (2) Resolved: The excess line broading of UV and X-ray lines is accounted for by a convective velocity distribution in evaporation. It is concluded that the hypothesis that convective evaporation produces the observed X-ray line widths in flares is no more than a hypothesis. It is not supported by any self-consistent physical theory. (3) Resolved: Most chromospheric heating is driven by electron beams. Although it is possible to cast doubt on many lines of evidence for electron beams in the chromosphere, a balanced view that debaters on both sides of the question might agree to is that electron beams probably heat the low corona and upper chromosphere, but their direct impact on evaporating the chromosphere is energetically unimportant when compared to conduction. This represents a major departure from the thick-target flare models that were popular before the Workshop.

Doschek, G. A.↗
NASA NTRS1996

Spectral Analysis and Experimental Modeling of Ice Accretion Roughness

A self-consistent scheme for relating wind tunnel ice accretion roughness to the resulting enhancement of heat transfer is described. First, a spectral technique of quantitative analysis of early ice roughness images is reviewed. The image processing scheme uses a spectral estimation technique (SET) which extracts physically descriptive parameters by comparing scan lines from the experimentally-obtained accretion images to a prescribed test function. Analysis using this technique for both streamwise and spanwise directions of data from the NASA Lewis Icing Research Tunnel (IRT) are presented. An experimental technique is then presented for constructing physical roughness models suitable for wind tunnel testing that match the SET parameters extracted from the IRT images. The icing castings and modeled roughness are tested for enhancement of boundary layer heat transfer using infrared techniques in a "dry" wind tunnel.

Orr, D. J.↗
NASA NTRS2008

Thermal Stir Welding Development at Marshall Space Flight Center

Solid state welding processes have become the focus of welding process development at NASA's Marshall Space Flight Center. Unlike fusion weld processes such as tungsten inert gas (TIG), variable polarity plasma arc (VPPA), electron beam (EB), etc., solid state welding processes do not melt the material during welding. The resultant microstructure can be characterized as a dynamically recrystallized morphology much different than the casted, dentritic structure typical of fusion weld processes. The primary benefits of solid state processes over fusion weld processes include superior mechanic properties and the elimination of thermal distortion and residual stresses. These solid state processes attributes have profoundly influenced the direction of advanced welding research and development within the NASA agency. Thermal Stir Welding (TSW) is a new solid state welding process being developed at the Marshall Space Flight Center. Unlike friction stir welding, the heating, stirring and forging elements of the weld process can be decoupled for independent control. An induction coil induces energy into a workpiece to attain a desired plastic temperature. An independently controlled stir rod, captured within non-rotating containment plates, then stirs the plasticized material followed by forging plates/rollers that work the stirred weld joint. The independent control (decoupling) of heating, stirring and forging allows, theoretically, for the precision control of microstructure morphology. The TSW process is being used to evaluate the solid state joining of Haynes 230 for ARES J-2X applications. It is also being developed for 500-in (12.5 mm) thick commercially pure grade 2 titanium for navy applications. Other interests include Inconel 718 and stainless steel. This presentation will provide metallurgical and mechanical property data for these high melting temperature alloys.

Ding, Robert J.↗
NASA NTRS1987

Optimal cure cycle design of a resin-fiber composite laminate

A unified computed aided design method was studied for the cure cycle design that incorporates an optimal design technique with the analytical model of a composite cure process. The preliminary results of using this proposed method for optimal cure cycle design are reported and discussed. The cure process of interest is the compression molding of a polyester which is described by a diffusion reaction system. The finite element method is employed to convert the initial boundary value problem into a set of first order differential equations which are solved simultaneously by the DE program. The equations for thermal design sensitivities are derived by using the direct differentiation method and are solved by the DE program. A recursive quadratic programming algorithm with an active set strategy called a linearization method is used to optimally design the cure cycle, subjected to the given design performance requirements. The difficulty of casting the cure cycle design process into a proper mathematical form is recognized. Various optimal design problems are formulated to address theses aspects. The optimal solutions of these formulations are compared and discussed.

Hou, Jean W.↗
NASA NTRS1992

An incremental strategy for calculating consistent discrete CFD sensitivity derivatives

In this preliminary study involving advanced computational fluid dynamic (CFD) codes, an incremental formulation, also known as the 'delta' or 'correction' form, is presented for solving the very large sparse systems of linear equations which are associated with aerodynamic sensitivity analysis. For typical problems in 2D, a direct solution method can be applied to these linear equations which are associated with aerodynamic sensitivity analysis. For typical problems in 2D, a direct solution method can be applied to these linear equations in either the standard or the incremental form, in which case the two are equivalent. Iterative methods appear to be needed for future 3D applications; however, because direct solver methods require much more computer memory than is currently available. Iterative methods for solving these equations in the standard form result in certain difficulties, such as ill-conditioning of the coefficient matrix, which can be overcome when these equations are cast in the incremental form; these and other benefits are discussed. The methodology is successfully implemented and tested in 2D using an upwind, cell-centered, finite volume formulation applied to the thin-layer Navier-Stokes equations. Results are presented for two laminar sample problems: (1) transonic flow through a double-throat nozzle; and (2) flow over an isolated airfoil.

Korivi, Vamshi Mohan↗
NASA NTRS1993

Methodology for sensitivity analysis, approximate analysis, and design optimization in CFD for multidisciplinary applications

In this study involving advanced fluid flow codes, an incremental iterative formulation (also known as the delta or correction form) together with the well-known spatially-split approximate factorization algorithm, is presented for solving the very large sparse systems of linear equations which are associated with aerodynamic sensitivity analysis. For smaller 2D problems, a direct method can be applied to solve these linear equations in either the standard or the incremental form, in which case the two are equivalent. Iterative methods are needed for larger 2D and future 3D applications, however, because direct methods require much more computer memory than is currently available. Iterative methods for solving these equations in the standard form are generally unsatisfactory due to an ill-conditioning of the coefficient matrix; this problem can be overcome when these equations are cast in the incremental form. These and other benefits are discussed. The methodology is successfully implemented and tested in 2D using an upwind, cell-centered, finite volume formulation applied to the thin-layer Navier-Stokes equations. Results are presented for two sample airfoil problems: (1) subsonic low Reynolds number laminar flow; and (2) transonic high Reynolds number turbulent flow.

Taylor, Arthur C., III↗