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

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At least 577 records · Page 32
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NASA NTRS1987

Numerical simulation of three dimensional transonic flows

The three-dimensional flow over a projectile has been computed using an implicit, approximately factored, partially flux-split algorithm. A simple composite grid scheme has been developed in which a single grid is partitioned into a series of smaller grids for applications which require an external large memory device such as the SSD of the CRAY X-MP/48, or multitasking. The accuracy and stability of the composite grid scheme has been tested by numerically simulating the flow over an ellipsoid at angle of attack and comparing the solution with a single grid solution. The flowfield over a projectile at M = 0.96 and 4 deg angle-of-attack has been computed using a fine grid, and compared with experiment.

Sahu, Jubaraj↗
NASA NTRS1987

The control networks of the satellites of Uranus

The present photogrammetric derivation of control networks for the five Uranus satellites Miranda, Ariel, Umbriel, Titania, and Oberon, on the basis of Voyager 2 images, covers the illuminated southern hemisphere of each satellite and respectively yields 103, 52, 43, 46, and 34 coordinate points. It is found that Titania is ellipsoidal, with 241-, 235-, and 232-km radii.In addition, mean radii are determined to be 579 km for Ariel, 586 km for Umbriel, 790 km for Titania, and 762 km for Oberon. Some of the control points used have been identified on the U.S. Geological Survey maps of these satellites.

Davies, Merton E.↗
NASA NTRS1988

Piezoviscosity In Lubrication Of Nonconformal Contacts

Developments in theory of lubrication. Analysis of piezoviscous-rigid regime of lubrication of two ellipsoidal contacts. Begins with Reynolds equation for point contact. Equation nondimensionalized using Roelands empirical formula and Dowson and Higginson formula. Equation solved numerically. Solutions obtained for full spectrum of conditions to find effects of dimensionless load, speed, parameters of lubricated and lubricating materials, and angle between direction of rolling and direction of entrainment of lubricant.

Jeng, Yeau-Ren↗
NASA NTRS1987

Aeroassisted manned transfer vehicle (TAXI) for advanced Mars Transportation: NASA/USRA 1987 Senior Design Project

A conceptual design study of an aeroassisted orbital transfer vehicle is discussed. Nicknamed TAXI, it will ferry personnel and cargo: (1) between low Earth orbit and a spacecraft circling around the Sun in permanent orbit intersecting gravitational fields of Earth and Mars, and (2) between the cycling spacecraft and a Mars orbiting station, co-orbiting with Phobos. Crew safety and mission flexibility (in terms of ability to provide a wide range of delta-V) were given high priority. Three versions were considered, using the same overall configuration based on a low L/D aerobrake with the geometry of a raked off elliptical cone with ellipsoidal nose and a toroidal skirt. The propulsion system consists of three gimballed LOX/LH2 engines firing away from the aerobrake. The versions differ mainly in the size of the aeroshields and propellant tanks. TAXI A version resulted from an initial effort to design a single transfer vehicle able to meet all delta-V requirements during the 15-year period (2025 to 2040) of Mars mission operations. TAXI B is designed to function with the cycling spacecraft moving in a simplified, nominal trajectory. On Mars missions, TAXI B would be able to meet the requirements of all the missions with a relative approach velocity near Mars of less than 9.3 km/sec. Finally, TAXI C is a revision of TAXI A, a transfer vehicle designed for missions with a relative velocity near Mars larger than 9.3 km/sec. All versions carry a crew of 9 (11 with modifications) and a cargo of 10000 lbm. Trip duration varies from 1 day for transfer from LEO to the cycling ship to nearly 5 days for transfer from the ship to the Phobos orbit.

Source record↗
NASA NTRS1988

Speckle interferometry of asteroids

This final report for NASA Contract NAGw-867 consists of abstracts of the first three papers in a series of four appearing in Icarus that were funded by the preceding contract NAGw-224: (1) Speckle Interferometry of Asteroids I. 433 Eros; (2) Speckle Interferometry of Asteroids II. 532 Herculina; (3) Speckle Interferometry of Asteroids III. 511 Davida and its Photometry; and the fourth abstract attributed to NAGw-867, (4) Speckle Interferometry of Asteroids IV. Reconstructed images of 4 Vesta; and a review of the results from the asteroid interferometry program at Steward Observatory prepared for the Asteroids II book, (5) Speckle Interferometry of Asteroids. Two papers on asteroids, indirectly related to speckle interferometry, were written in part under NAGw-867. One is in press and its abstract is included here: Photometric Geodesy of Main-Belt Asteroids. II. Analysis of Lightcurves for Poles, Periods and Shapes; and the other paper, Triaxial Ellipsoid Dimensions and Rotational Pole of 2 Pallas from Two Stellar Occultations, is included in full.

Drummond, Jack↗
NASA NTRS1988

Modeling and estimation of a low degree geopotential model from terrestrial gravity data

The development of appropriate modeling and adjustment procedures for the estimation of harmonic coefficients of the geopotential, from surface gravity data was studied, in order to provide an optimum way of utilizing the terrestrial gravity information in combination solutions currently developed at NASA/Goddard Space Flight Center, for use in the TOPEX/POSEIDON mission. The mathematical modeling was based on the fundamental boundary condition of the linearized Molodensky boundary value problem. Atmospheric and ellipsoidal corrections were applied to the surface anomalies. Terrestrial gravity solutions were found to be in good agreement with the satellite ones over areas which are well surveyed (gravimetrically), such as North America or Australia. However, systematic differences between the terrestrial only models and GEMT1, over extended regions in Africa, the Soviet Union, and China were found. In Africa, gravity anomaly differences on the order of 20 mgals and undulation differences on the order of 15 meters, over regions extending 2000 km in diameter, occur. Comparisons of the GEMT1 implied undulations with 32 well distributed Doppler derived undulations gave an RMS difference of 2.6 m, while corresponding comparison with undulations implied by the terrestrial solution gave RMS difference on the order of 15 m, which implies that the terrestrial data in that region are substantially in error.

Pavlis, Nikolaos K.↗
NASA NTRS1988

Inevitable inflation in Einstein-Cartan theory with improved energy-momentum tensor with spin

Generalized, or power-law, inflation is shown to necessarily exist for a simple, anisotropic, (Bianchi Type-1) cosmology in the Einstein-Cartan gravitational theory with the Ray-Smalley improved energy momentum tensor with spin. Formal solution of the EC field equations with the fluid equations of motion explicitly shows inflation caused by the RS spin angular kinetic energy density. Shear is not effective in preventing inflation in the ECRS model. The relation between fluid vorticity, torsion, reference axis rotation, and shear ellipsoid precession shows through clearly.

Fennelly, A. J.↗
NASA NTRS1987

Solar active region physical parameters inferred from a thermal cyclotron line and soft X-ray spectral lines

Simultaneous high-resolution observations of coronal loops were made at the 20-cm wavelength with the VLA and at soft X-ray wavelengths with the SMM FCS. The images obtained at both wavelengths have nearly identical sizes and ellipsoidal shapes, with the emission stretching between and across regions of opposite magnetic polarity in the underlying photosphere. The results indicate that the radiation at 20 cm and soft X-ray wavelengths originates from the same region, and that 20 cm maps can image X-ray coronal loops. The X-ray spectral lines were used to obtain values of electron temperature, T(e), of about 2.6 x 10 to the 6th K and electron density, N(e), of about 3.1 x 10 to the 9th/cu cm. These parameters were used to show that the layers emitting 20-cm radiation can be optically thick to either thermal bremsstrahlung or thermal gyroresonance radiation, depending upon unknown but plausible values of loop thickness, magnetic scale height, and magnetic field strength.

Lang, Kenneth R.↗
NASA NTRS1988

Infrared supernova light curves and asymmetric stellar mass loss

Infrared dust emission echos from Type II supernovae are a natural consequence of the heating of circumstellar dust by the supernova light. Red supergiants, the likely progenitors of most Type II supernovae, are known in some cases to have asymmetric circumstellar envelopes. It is noted that an asymmetric dust distribution can have a substantial effect on the evolution of an infrared echo and results are presented for an ellipsoidal dust distribution. The angle between the symmetry axis and the line of sight is unknown in any particular case so that detailed observations of a number of supernovae will be necessary to test for asymmetries. Asymmetries may also be observable in the radio structure of supernovae and in a possible scattered-light echo.

Emmering, Robert T.↗
NASA NTRS1988

Speckle interferometry of asteroids. IV - Reconstructed images of 4 Vesta

The images of 4 Vesta obtained by means of speckle interferometric observations on November 16 and 17, 1983, support a 5-hr 20.5-min rotational period. The 4 Vesta visible light curve was approximately matched by the placing of circular 'spots' with 135-km diameter over the three dark and three bright features, followed by the assigning of albedos of 0 to the dark spots and 2 to the bright. The light curve is found to be primarily defined by albedo structure, rather than shape; this results in one maximum and one minimum/rotation, rather than the two of each that would be associated with 4 Vesta's triaxial ellipsoid morphology.

Drummond, J.↗
NASA NTRS1988

Aberrations for grazing incidence telescopes

The wavefront aberration polynomial and transverse ray aberration expansions will be derived for grazing incidence two-mirror Wolter telescopes including all paraboloid-hyperboloid and paraboloid-ellipsoid combinations. The reference sphere is determined with the help of the principal surface of the telescope, and the aberration polynomials will be given as functions of the coordinates of the ray intersection with the reference sphere. Third -and some of the fifth-order and seventh-order aberration terms will be analyzed. Also, the well-known relationship between wavefront aberration polynomials and transverse ray aberration polynomials will be verified.

Saha, Timo T.↗
NASA NTRS1988

Physical properties of the planet Mercury

The global physical properties of Mercury are summarized with attention given to its figure and orbital parameters. The combination of properties suggests that Mercury has an extensive iron-rich core, possibly with a still-functioning dynamo, which is 42 percent of the interior by volume. Mercury's three major axes are comparable in size, indicating that the planet is a triaxial ellipsoid rather than an oblate spheroid. In terms of the domination of its surface by an intermediate plains terrane, it is more Venus- or Mars-like; however, due to the presence of a large metallic magnetic core, its interior may be more earth-like.

Clark, Pamela E.↗
NASA NTRS1988

Internal structure and shape of Mimas

The observed triaxial ellipsoid shape of Mimas, in conjunction with a mean density of 1137 kg/cu cm, is presently used as the basis of hydrostatic equilibrium and nonhydrostatic models of internal structure whose outer layers are sufficiently strong to support part of the tidal load. Such plausible internal structures are consistent with the shape and density constraints as (1) a two-layer model in hydrostatic equilibrium, (2) a hydrostatic model with four layers of equal depth, and (3) a nonhydrostatic constant-density model with an elastic lithosphere; these models admit either homogeneous or heterogeneous accretion, as well as either a cold thermal history or melting and differentiation.

Ross, M. N.↗
NASA NTRS1989

Thermal Analysis Of Reluctant Glass Formers

Thermocouple holds sample and monitors temperature during cooling. Ellipsoidal furnace provides controlled cooling rates for studies of thermal properties of reluctant glass formers. Glass tube inserted into furnace and used to blow helium on specimen to cool rapidly. Cooling curve analyzed to determine rate of cooling and such properties of sample as nucleation and recalescence temperatures at cooling rate. Continuous-cooling-crystallization boundaries determined empirically from plots of nucleation time vs. nucleation temperature from runs at large number of different rates of cooling. Apparatus used to examine glass-formation ability of material and critical cooling rate to form glass.

Ethridge, Edwin C.↗
NASA NTRS1988

A model for radiative transfer in heterogeneous three-dimensional canopies

A model, dubbed TRIM, for the interaction of electromagnetic radiation with inhomogeneous vegetation canopies is presented. It is based on the four flux theory for homogeneous canopies. The canopy is assumed to consist of ellipsoidal subcanopies located on the ground at periodic intervals. The model is inverted with field measured data for reflectance from corn canopies in the near infrared region. It is shown that TRIM correctly identifies the architecture of the canopy (homogeneous or row canopy, percentage of ground cover) and gives a good estimate of leaf area index.

Goel, N. S.↗
NASA NTRS1987

Curved channel MCP improvement program

Blowholes and blemishes were determined to start at two stages of manufacturing. Sperical blowholes resulted from trapped gas between the high melting temperature bond glass and the MCP wafer. During thermal processing, the trapped gas expanded and displaced the softened channel glass to form a spherical inclusion. This defect was eliminated by grinding the prefritted bond wafer and channel plate wafer to a flatness which ensured intimate contact prior to fusion. Elliptical blowholes or blemishes were introduced during the fiber draw stage. Contaminants trapped between the core bar and clad tubing volatized providing large quantities of expanding gas. These pockets of gas became elongated to an ellipsoidal shape during fiber draw. Special cleanliness procedures were developed for the grinding, polishing, and acid etching of core bars. Improvements in channel curvature fabrication were implemented. The design of the shearing fixture was evaluated. A new design was developed which eliminated an off-axis moment. The shearing furnace design was evaluated. Steady state thermal conditions instead of thermal transient conditions were determined to reduce curvature nonuniformity.

Laprade, Bruce N.↗
NASA NTRS1987

Proposed earth-based cratering experiments at low g in hard vacuum

In order to address the question of whether the cratering scale which was developed can be extrapolated to low velocity (of planetesimals appropriate for conditions during accretions of planets and the impact mechanics of encounters for both asteroids and the solid objects which comprise the rings of the outer major planets), a series of experiments at low gravity and at high vacuum are proposed. Specific issues which could be addressed include: the effect of very low gravity on cratering efficiency and final crater shape; and the dynamics of impact into a strengthless spherical and ellipsoidal liquid target.

Ahrens, Thomas J.↗
NASA NTRS1988

Observations of the 8 December 1987 occultation of AG+40 deg 0783 by 324 Bamberga

The occultation of AG+40 deg 0783 by 324 Bamberga on 8 December 1987 was observed at 13 sites in the United States, Japan, and China. At four sites the event was observed photoelectrically; the other observations were visual. A least-squares fit of a circular limb profile to the data gives a diameter of 227.6 + or - 1.9 km. However, this solution is inconsistent with a negative visual observation near the northern edge of the ground track. The inconsistency cannot be removed by assuming an elliptical profile. The data suggest that Bamberga, despite its low-amplitude lightcurve, may depart significantly from a spherical or ellipsoidal shape. The asteroid also appears to be at least 10 percent smaller than indicated by infrared radiometry.

Millis, R. L.↗