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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 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Launch window analysis in a new perspective with examples of departures from Earth to Mars

Earth-departure windows are investigated for two round trip stopover missions to Mars. These are the 1981 inbound Venus swingby mission and the 1986 direct minimum-energy mission. The secular effects of planetary oblateness are used to predict the motion of the parking orbit. A procedure is developed for matching the motion of the parking orbit and the escape asymptote. Earth-departure velocity penalties, caused by orbital plane misalinement, are reduced by synchronizing the motion of the parking orbit and the escape trajectory.

Thibodeau, J. R., III↗
NASA NTRS1973

Experimental study of flow about a stalled two-dimensional airfoil

Wind tunnel tests to determine the flow characteristics of a stalled wing are described. The advantages of the plane wing over the ring wing for wind tunnel investigations are presented. The general flow pattern for stalled ring airfoils is developed. Photographs of the test equipment and installation are provided.

Coles, D. E.↗
NASA NTRS1972

Profiling microcraters using stereomicrographs.

The determination of the population, shape, and size of microcraters on lunar rocks enables space scientists to study cosmic erosion, survival times of rocks on the lunar surface, and the flux of primary cosmic particles. A graphical method of profiling and contouring microcraters on lunar rocks from a pair of stereomicrographs obtained by a scanning electron microscope was developed. The graphical method utilizes the simple geometry of photography generated by a parallel bundle of rays, orthogonal to the image plane.

Malhotra, R. C.↗
NASA NTRS1975

The motion of a proton in the equatorial magnetosphere

In a time-independent model of the magnetosphere including a dipole magnetic field, a convection electric field (deduced from polar orbit observations), and an electric field due to the earth's rotation, the motion of a proton in the equatorial plane is analyzed. By means of the Hamiltonian of the motion, three regimes of motion are identified. A method is then developed for determining for any given observation point which arrival energies correspond to trapped particles and which represent 'open' trajectories.

Stern, D. P.↗
NASA NTRS1975

Preservation of wing leading edge suction at the plane of symmetry as a factor in wing-fuselage design

Most fuselage geometries cover a portion of the wing leading edge near the plane of symmetry, and it seems reasonable to expect that a large fraction of the leading edge suction which would be developed by the covered wing at high angles of attack is not developed on the fuselage. This is one of the reasons that the Oswald span efficiency factor for the wing body combination fails to approach the value predicted by lifting line theory for the isolated wing. Some traditional and recent literature on wing-body interference is discussed and high Reynolds number data on wing-body-nacelle drag are reviewed. An exposed central leading edge geometry has been developed for a sailplane configuration. Low Reynolds number tests have not validated the design concept.

Larrabee, E. E.↗
NASA NTRS1977

Theory of the rotation of the rigid earth

Equations of motion for a triaxial rigid earth are derived in Andoyer variables. The reference plane is the ecliptic of date which is moving as a result of planetary perturbations. By using this noninertial system, the development of the disturbing function for the sun and moon is simplified, with an additional term appearing in the Hamiltonian which, however, contributes only to precessional motion. The nutation terms derived are compared with those of Woolard.

Kinoshita, H.↗
NASA NTRS1978

Backscattering from a Gaussian-distributed perfectly conducting rough surface

The original intent of the reported investigation was to find a solution to the composite surface scattering problem which provided for a continuous transition between the near-specular physical optics and wide-angle tilted plane Bragg solutions. The employed approach is based on analytical techniques rather than physical considerations. The analysis employs a perturbation technique developed by Burrows (1967, 1968, 1973), which because of its simplicity, is the key to the entire solution. The analysis is restricted to the case of backscattering from a perfectly conducting surface. General expressions are presented for the scattering from a Gaussian perfectly conducting surface characterized by an anisotropic spectrum and possessing many scales of roughness. The accuracy of the result is dependent upon the large-scale structure having large height excursions and small curvature.

Brown, G. S.↗
NASA NTRS1980

Solid state systems concepts

Two prototype solid state phased array systems concepts for potential use in the Solar Power Satellite are described; the end-mounted and the sandwich systems. In both concepts, the beam is centered on the rectenna by means of phase conjugation of a pilot signal emanating from the ground. In the end-mounted system 36-watt amplifiers are mounted on the ground-plane, whereas in the sandwich the amplifiers are elevated to the dipoles, and their waste heat is dissipated by beryllium oxide discs. The feed lines are underneath the ground-plane, and a coaxial transmission line is carried all the way to the amplifier input. Also discussed is solid state amplifier development.

Schroeder, I. K.↗
NASA NTRS1980

A consistent set of trial functions for conical shells

A consistent approach is developed for the determination of trial functions for a class of shells of revolution. The trial functions satisfy the in-plane and out-of-plane boundary conditions at the shell ends and include the effects of tangential inertia. The resulting expressions converge rapidly for the problem of linear free vibration

El-Raheb, M.↗
NASA NTRS1980

A high-altitude barium radial injection experiment

A rocket launched from Poker Flat, Alaska, carried a new type of high-explosive barium shaped charge to 571 km, where detonation injected a thin disk of barium vapor with high velocity nearly perpendicular to the magnetic field. The TV images of the injection are spectacular, revealing three major regimes of expanding plasma which showed early instabilities in the neutral gas. The most unusual effect of the injection is a peculiar rayed barium-ion structure lying in the injection plane and centered on a 5 km 'black hole' surrounding the injection point. Preliminary electrostatic computer simulations show a similar rayed development.

Wescott, E. M.↗
NASA NTRS1980

Recent developments in the design, testing and impact-damage tolerance of stiffened composite panels

The structural technology of laminated filamentary-composite stiffened-panel structures under combined in-plane and lateral loadings is discussed. Emphasis is on analyzing the behavior of the structures under load, determining appropriate structural proportions for weight efficient configurations, and effects of impact damage and geometric imperfections on structural performance. Experimental data on buckling of panels under in-plane compression validate the analysis and sizing methods, and illustrate structural performance and efficiency obtained from representative structures. It is shown that the strength of panels under in-plane compression can be degraded by low-velocity impact damage, and data are presented which indicate that the matrix is a significant factor influencing tolerance to impact damage.

Williams, J. G.↗
NASA NTRS1982

Response of a Doppler canceling system to plane gravitational waves

This paper discusses the interaction of long periodic gravitational waves with a three-link microwave system known as the Doppler canceling system. This system, which was developed for a gravitational red-shift experiment, uses one-way and two-way Doppler information to construct the beat signal of two reference oscillators moving with respect to each other. The geometric-optics approximation is used to derive the frequency shift produced on a light signal propagating in a gravitational-wave space-time. The signature left on the Doppler-cancelled beat by bursts and continuous gravitational waves is analyzed. A comparison is made between the response to gravitational waves of the Doppler canceling system and that of a (NASA) Doppler tracking system which employs two-way, round-trip radio waves. A threefold repetition of the gravitational wave form is found to be a common feature of the response functions of both systems. These two functions otherwise exhibit interesting differences.

Caporali, A.↗
NASA NTRS1984

Algorithm for astronomical, point source, signal to noise ratio calculations

An algorithm was developed to simulate the expected signal to noise ratios as a function of observation time in the charge coupled device detector plane of an optical telescope located outside the Earth's atmosphere for a signal star, and an optional secondary star, embedded in a uniform cosmic background. By choosing the appropriate input values, the expected point source signal to noise ratio can be computed for the Hubble Space Telescope using the Wide Field/Planetary Camera science instrument.

Jayroe, R. R.↗
NASA NTRS1985

Stress analysis of the space telescope focal plane structure joint

Two major efforts were begun concerning the Space Telescope focal plane structure joint. The 3-D solid finite element modeling of the bipod flexure plate was carried out. Conceptual models were developed for the load transfer through the three major bolts to the flexure plate. The flexure plate drawings were reconstructed using DADAM for the purpose of developing a file from which the coordinates of any point on the flexure plate could be determined and also to locate the attachment points of the various components which connect with the flexure plate. For modeling convenience the CADAM drawing of the flexure plate has been divided into several regions which will be subdivided into finite elements using MSGMESH, which is a finite element mesh generator available with MSC/NASTRAN. In addition to the CADAM work on the flexure plate, an effort was also begun to develop computer aided drawings of the peripheral beam which will be used to assist in modeling the connection between it and the flexure plate.

Foster, W. A., Jr.↗
NASA NTRS1985

A cracked orthotropic sheet stiffened by a semi-infinite orthotropic sheet

The stress intensity factor is determined for a cracked orthotropic sheet adhesively bonded to an orthotropic stringer. Since the stringer is modeled as a semiinfinite sheet, the solution is most appropriate for a crack tip located near a stringer edge. Both adherends are treated as homogeneous, orthotropic media. It is assumed they are in plane stress and the adhesive is in pure shear. From Green's functions and the complex variable theory of orthotropic elasticity developed by Lekhnitskiy, a set of integral equations is obtained. The integral equations are replaced by an equivalent set of algebraic equations which is solved to obtain the shear stress distribution in the adhesive layer. With these stresses, equations for the stress intensity factors at both crack tips are found. A parametric study is conducted to determine the sensitivity of the system to material properties and specimen configuration. Unless the crack tip is very close to or under the stringer the stress intensity factor is approximately that of an unstiffened sheet. However, as the crack propagates beneath the stringer, the stress intensity factor decreases significantly. Increasing the stiffness of the stringer or the adhesive also results in a decrease in the stress intensity factor.

Bigelow, C. A.↗
NASA NTRS1984

The influence of ocean surface temperature gradient and continentality on the Walker circulation. I - Prescribed tropical changes

A coarse mesh global climate model has been developed to assess ocean surface temperature (OST) gradient and continentality influences on the Walker circulation, which is characterized in the zonal plane by three pairs of clockwise and counterclockwise cells in the troposphere. The model response exhibits statistically significant changes in the intensity of the various cells and branches with small shifts in the east-west extent. The overall structure in the zonal plane for experiments with the coldest and with mean temperatures, however, remained unchanged. In an experiment involving the replacement of the South American continent by an ocean with OSTs linearly interpolated from the eastern Pacific to the western Atlantic, a dramatic change took place in the structure of the Walker circulation. It is concluded that both continentality and OST gradient are important Walker circulation forcing mechanisms.

Chervin, R. M.↗
NASA NTRS1986

Measurements of a turbulent horseshoe vortex formed around a cylinder

An experimental investigation was conducted to characterize a symmetrical horseshoe vortex system in front of and around a single large-diameter right cylinder centered between the sidewalls of a wind tunnel. Surface flow visualization and surface static pressure measurements as well as extensive mean velocity and pressure measurements in and around the vortex system were acquired. The results lend new insight into the formation and development of the vortex system. Contrary to what has been assumed previously, a strong vortex was not identified in the streamwise plane of symmetry, but started a significant angular distance away from it. Rather than the multiple vortex systems reported by others, only a single primary vortex and saddle point were found. The scale of the separation process at the saddle point was much smaller than the scale of the approaching boundary layer thickness. Results of the present study not only shed light on such phenomena as the nonsymmetrical endwall flow in axial turbomachinery but can also be used as a test case for three-dimensional computational fluid mechanics computer codes.

Eckerle, W. A.↗
NASA NTRS1986

Horseshoe vortex formation around a cylinder

An experimental investigation was conducted to characterize a symmetrical horseshoe vortex system in front of and a around a single large-diameter right cylinder centered between the sidewalls of a wind tunnel. Surface flow visualization anad surface static pressure measurements as well as extensive mean velocity and pressure measurements in and around the vortex system were acquired. The results lend new insight into the formation and development of the vortex system. Contrary to what has been assumed previously, a strong vortex was not identified in the streamwise plane of symmetry, but started a significant angular distance away from it. Rather than the multiple vortex systems reported by others, only a single primary vortex and saddle point were found. The scale of the separation process at the saddle point was much smaller than the scale of the approaching bundary layer thickness. Results of the present study not only shed light on such phenomena as the nonsymmetrical endwall flow in axial turbomachinery but can also be used as a test case for three-dimensional computational fluid mechanics computer codes.

Eckerle, W. A.↗