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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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NASA NTRS1979

Future exploration of the asteroids

Future possibilities for the further study of the asteroids are reviewed, with particular attention paid to space missions for their direct exploration. The role of traditional ground-based and earth orbiting techniques is examined briefly, and it is concluded that although astronomical techniques are presently at their peak, and despite the opportunities provided by the Infrared Astronomical satellite, the Space Telescope and Spacelab Infrared Telescope Facility, the next major step will require direct exploration by space probes to obtain information on asteroid surface chemistry, geology and bulk properties. Various mission modes and propulsion systems for a first multi-target asteroid mission are discussed, including flyby, rendezvous, landing and sample return, and ion-drive propulsion systems. Science payloads for a basic rendezvous mission are considered, and target selection for multi-asteroid flyby tours and rendezvous tours is discussed. Consideration is also given to sample return missions for the evaluation of the asteroid as potential resources.

Morrison, D.↗

NASA NTRS1982

Shock-fitted Euler solutions to shock vortex interactions

The interaction of a planar shock wave with one or more vortexes is computed using a pseudospectral method and a finite difference method. The development of the spectral method is emphasized. In both methods the shock wave is fitted as a boundary of the computational domain. The results show good agreement between both computational methods. The spectral method is, however, restricted to smaller time steps and requires use of filtering techniques.

Salas, M. D.↗

NASA NTRS1984

Plasma-Sprayed Copper Tie-In for Nickel Plating

Foam insulation nickel-plated with one less step. Changing tie-in layer from plasma-sprayed nickel to plasma-sprayed copper eliminates intermediate copper electroplating step previously required.

Lombard, J. W.↗

NASA NTRS1982

An implicit formulation for the one-dimensional two-phase multi-interface Stefan Problem

In recent years there has been an intensified effort in the analysis of the Stefan Problem. Particular interest is directed towards determining the location of the interface between the solid and liquid phases of the substance being analyzed. A method has been developed using an implicit finite difference scheme which provides an accurate calculation of the phase change interface locations for a problem with simultaneous multiple phases. This is achieved through an iterative technique which requires the phase change energy to be correctly distributed within the nodes which are undergoing a phase transition. The new method predicts the interface locations without requiring time step size control or node size modification at the interfaces.

Williams, S. D.↗

NASA NTRS1982

Computer modeling of thermoelectric generator performance

Features of the DEGRA 2 computer code for simulating the operations of a spacecraft thermoelectric generator are described. The code models the physical processes occurring during operation. Input variables include the thermoelectric couple geometry and composition, the thermoelectric materials' properties, interfaces and insulation in the thermopile, the heat source characteristics, mission trajectory, and generator electrical requirements. Time steps can be specified and sublimation of the leg and hot shoe is accounted for, as are shorts between legs. Calculations are performed for conduction, Peltier, Thomson, and Joule heating, the cold junction can be adjusted for solar radition, and the legs of the thermoelectric couple are segmented to enhance the approximation accuracy. A trial run covering 18 couple modules yielded data with 0.3% accuracy with regard to test data. The model has been successful with selenide materials, SiGe, and SiN4, with output of all critical operational variables.

Chmielewski, A. B.↗

NASA NTRS1985

Fabricating Thin-Shell Heat-Transfer Models

Freestanding shells produced for experimental aerodynamic-heating tests. Heat transfer shells require several steps and several precise molds. First, interlocking aluminum male and female molds fabricated. Holes for thermocouples drilled through male mold at desired locations. Wires having same diameter as thermocouple wire placed through holes in male mold flush to female mold. Epoxy exposed to vacuum to remove air bubbles poured between male and female molds to form thin female mold. Once mold cured, wires removed and aluminum molds separated.

Avery, D. E.↗

NASA NTRS1982

Shock-fitted Euler solutions to shock-vortex interactions

Salas, M. D.↗

NASA NTRS1986

Evolution of the luminosity function of extragalactic objects

A nonparametric procedure for determining the evolution of the luminosity function (LF) of extragalactic objects is described. The following steps are required: (1) selection of complete samples with known observational selection effects, (2) choice of a cosmological model, (3) statistical analysis of the sample and determination of the evolution of the luminosity function, and (4) the use of the luminosity function for the determination of the formation rate and the physical evolution of the objects. When the present technique is applied to a sample of optically selected quasars with redshifts less than two, it is shown that the LF evolves more strongly for higher luminosities, indicating a larger quasar activity at earlier epochs and a more rapid evolution of the objects during their higher luminosity phases.

Petrosian, V.↗

NASA NTRS1989

Patterning of dispenser cathode surfaces to a controlled porosity

A process to pattern slots approximately 1.25 microns in width into 25-micron-thick W films that have been deposited onto flat or concave surfaces is discussed. A 25-micron-thick W film with a high degree of (100) orientation is chemically vapor deposited (CVD) onto a flat or concave Mo mandrel. A 5-micron-thick Al film is deposited onto the CVD W, followed by 2 microns of photoresist. On concave cathodes, XeCl2 laser ablation or X-ray lithography is used to pattern the photoresist, whereas on flat cathodes deep UV lithography can be used. The patterned photoresist serves as the mask in a Cl ion-beam-assisted etching (IBAE) process to pattern the Al. An alternative process is to deposit Al2O3 films onto the W and pattern the Al2O3 using laser ablation. The W film is then patterned to 3-6-micron slot widths using IBAE + ClF3 with the patterned Al or Al2O3 as the mask. Finally, a sputter deposition step is required to close up the slots to approximately 1 micron. The process described is capable of patterning concave dispenser cathodes to a controlled and precise porosity.

Garner, Charles E.↗

NASA NTRS1989

Numerical solutions of forward-flight rotor flow using an upwind method

A finite-volume upwind algorithm for solving the 3-D Euler equations with a moving grid has been developed for computing helicopter forward-flight rotor flows. The computed pressure distributions and shock positions of high-speed rotor flow are compared with various experimental data as well as with other numerical results, and the agreement is encouraging. A comparison of quasi-steady solutions with unsteady solutions reveals that when a shock occurs in the flowfield, the assumption of quasi-steady flow may fail due to the time-lag of the shock motion. Similarly, three-dimensional effects cannot be neglected. Sufficient subiterations for each time step are required to avoid numerical lag effects in using the present method. The redistribution of the residual due to the coordinate transformation is discussed. For high-order MUSCL-type schemes, a coordinate-independent solution can be obtained by interpolating primitive variables.

Chen, C. L.↗

NASA NTRS1990

Apparatus for mixing solutions in low gravity environments

An apparatus is disclosed for allowing mixing of solutions in low gravity environments so as to carry out crystallization of proteins and other small molecules or other chemical syntheses, under conditions that maximize crystal growth and minimize disruptive turbulent effects. The apparatus is comprised of a housing, a plurality of chambers, and a cylindrical rotatable valve disposed between at least two of the chambers, said valve having an internal passageway so as to allow fluid movement between the chambers by rotation of the valve. In an alternate embodiment of the invention, a valve is provided having an additional internal passage way so that fluid from a third chamber can be mixed with the fluids of the first two chambers. This alternate embodiment of the invention is particularly desirable when it is necessary to provide a termination step to the crystal growth, or if a second synthetic step is required.

Carter, Daniel C.↗

NASA NTRS1990

A comparison of ISCCP and FIRE satellite cloud parameters

One of the goals of the First ISCCP Regional Experiment (FIRE) is the quantification of the uncertainties in the cloud parameter products derived by the International Satellite Cloud Climatology Project (ISCCP). This validation effort has many facets including sensitivity analyses and comparisons to similar data or theoretical results with known accuracies. The FIRE provides cloud-truth data at particular points or along particular lines from surface and aircraft measurement systems. Relating these data to the larger, area-averaged ISCCP results requires intermediate steps using higher resolution satellite data analyses. Errors in the cloud products derived with a particular method can be determined by performing analyses of high resolution satellite data over the area surrounding the point or line measurement. This same analysis technique may then be used to derive cloud parameters over a larger area containing similar cloud fields. It is assumed that the uncertainties found for the small scale analyses are the same for the large scale so that the method has been calibrated for the particular cloud type; i.e., its accuracy is known. Differences between the large scale results using the ISCCP technique and the calibrated method can be computed and used to determine if any significant biases or rms errors occur in the ISCCP results. Selected ISCCP results are compared to cloud parameters derived using the hybrid bispectral threshold method over the FIRE IFO and extended observation areas.

Gibson, Gary G.↗

NASA NTRS1990

Combustion instability analysis

A theory and computer program for combustion instability analysis are presented. The basic theoretical foundation resides in the concept of entropy-controlled energy growth or decay. Third order perturbation expansion is performed on the entropy-controlled acoustic energy equation to obtain the first order integrodifferential equation for the energy growth factor in terms of the linear, second, and third order energy growth parameters. These parameters are calculated from Navier-Stokes solutions with time averages performed on as many Navier-Stokes time steps as required to cover at least one peak wave period. Applications are made for a 1-D Navier-Stokes solution for the Space Shuttle Main Engine (SSME) thrust chamber with cross section area variations taken into account. It is shown that instability occurs when the mean pressure is set at 2000 psi with 30 percent disturbances. Instability also arises when the mean pressure is set at 2935 psi with 20 percent disturbances. The system with mean pressures and disturbances more adverse that these cases were shown to be unstable.

Chung, T. J.↗

NASA NTRS1992

Lunar and Martian environmental interactions with nuclear power system radiators

Future NASA space missions include a permanent manned presence on the moon and an expedition to the planet Mars. Such steps will require careful consideration of environmental interactions in the selection and design of required power systems. Several environmental constituents may be hazardous to performance integrity. Potential threats common to both the moon and Mars are low ambient temperatures, wide daily temperature swings, solar flux, and large quantities of dust. The surface of Mars provides the additional challenges of dust storms, winds, and a carbon dioxide atmosphere. In this review, the anticipated environmental interactions with surface power system radiators are described, as well as the impacts of these interactions on radiator durability, which were identified at NASA Lewis Research Center.

Perez-Davis, Marla E.↗

NASA NTRS1993

Formal methods for life-critical software

The use of computer software in life-critical applications, such as for civil air transports, demands the use of rigorous formal mathematical verification procedures. This paper demonstrates how to apply formal methods to the development and verification of software by leading the reader step-by-step through requirements analysis, design, implementation, and verification of an electronic phone book application. The current maturity and limitations of formal methods tools and techniques are then discussed, and a number of examples of the successful use of formal methods by industry are cited.

Butler, Ricky W.↗

NASA NTRS1994

Automated synthesis of image processing procedures using AI planning techniques

This paper describes the Multimission VICAR (Video Image Communication and Retrieval) Planner (MVP) (Chien 1994) system, which uses artificial intelligence planning techniques (Iwasaki & Friedland, 1985, Pemberthy & Weld, 1992, Stefik, 1981) to automatically construct executable complex image processing procedures (using models of the smaller constituent image processing subprograms) in response to image processing requests made to the JPL Multimission Image Processing Laboratory (MIPL). The MVP system allows the user to specify the image processing requirements in terms of the various types of correction required. Given this information, MVP derives unspecified required processing steps and determines appropriate image processing programs and parameters to achieve the specified image processing goals. This information is output as an executable image processing program which can then be executed to fill the processing request.

Chien, Steve↗

NASA NTRS1997

High redshift quasars and high metallicities

A large-scale code called Cloudy was designed to simulate non-equilibrium plasmas and predict their spectra. The goal was to apply it to studies of galactic and extragalactic emission line objects in order to reliably deduce abundances and luminosities. Quasars are of particular interest because they are the most luminous objects in the universe and the highest redshift objects that can be observed spectroscopically, and their emission lines can reveal the composition of the interstellar medium (ISM) of the universe when it was well under a billion years old. The lines are produced by warm (approximately 10(sup 4)K) gas with moderate to low density (n less than or equal to 10(sup 12) cm(sup -3)). Cloudy has been extended to include approximately 10(sup 4) resonance lines from the 495 possible stages of ionization of the lightest 30 elements, an extension that required several steps. The charge transfer database was expanded to complete the needed reactions between hydrogen and the first four ions and fit all reactions with a common approximation. Radiative recombination rate coefficients were derived for recombination from all closed shells, where this process should dominate. Analytical fits to Opacity Project (OP) and other recent photoionization cross sections were produced. Finally, rescaled OP oscillator strengths were used to compile a complete set of data for 5971 resonance lines. The major discovery has been that high redshift quasars have very high metallicities and there is strong evidence that the quasar phenomenon is associated with the birth of massive elliptical galaxies.

Ferland, Gary J.↗

NASA NTRS1997

High Accuracy Evaluation of the Finite Fourier Transform Using Sampled Data

Many system identification and signal processing procedures can be done advantageously in the frequency domain. A required preliminary step for this approach is the transformation of sampled time domain data into the frequency domain. The analytical tool used for this transformation is the finite Fourier transform. Inaccuracy in the transformation can degrade system identification and signal processing results. This work presents a method for evaluating the finite Fourier transform using cubic interpolation of sampled time domain data for high accuracy, and the chirp Zeta-transform for arbitrary frequency resolution. The accuracy of the technique is demonstrated in example cases where the transformation can be evaluated analytically. Arbitrary frequency resolution is shown to be important for capturing details of the data in the frequency domain. The technique is demonstrated using flight test data from a longitudinal maneuver of the F-18 High Alpha Research Vehicle.

Morelli, Eugene A.↗