Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “INCLINATION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The rings of Uranus

Stellar occultation data on the Uranian rings are summarized. Spatial resolution is 0.1 km, for positions of ring segments, 4 km for structural details. The system consists of 9 narrow rings with average geometric albedo of 0.02. The data are well fitted by a kinematic model that describes the rings as ellipses, inclined to the equatorial plane of Uranus and precess due to harmonic terms in the Uranian potential fields. The main characteristics of the Uranian ring system that need a confirmed theoretical explanation are: narrow rings; sharp edges; uniform orbital precession; origin of the eccentricities and inclinations; the structure of the epsilon ring; the structure of the eta ring; and the origin of the ring system.

Elliot, J. L.↗
NASA NTRS1985

Simultaneous Earth observations from 2 satellites

Simultaneous co-located observations from two different orbits lead to several advantages (i.e., cross calibration of sensors and a wider range of solar-zenith and sensor look angles). The question was asked how many times per year (on the average) do the sub-satellite points of two satellites simultaneously come within D kilometers of each other?. For the Space Station (altitude: 500 km, inclination: 28 deg) and a Sun synchronous satellite (altitude 705 km, inclination 98.21 deg) the answers are 16, 41 and 82 times per year for encounter distances D of 20, 50, and 100 km espectively. The relationship between encounters per year and distance D is linear. The answers were obtained in two ways: (1) a closed form statistical approach which led to a simple algebraic expression, and (2) a Monte Carlo type computer solution. The largest difference between the two solutions was less than 12%.

Montgomery, H. E.↗
NASA NTRS1984

Predicted changes in advanced turboprop noise with shaft angle of attack

Advanced turboprop blade designs and new propeller installation schemes motivated an effort to include unsteady loading effects in existing propeller noise prediction computer programs. The present work validates the prediction capability while studing the effects of shaft inclination on the radiated sound field. Classical methods of propeller performance analysis supply the time-dependent blade loading needed to calculate noise. Polar plots of the sound pressure level (SPL) of the first four harmonics and overall SPL are indicative of the change in directivity pattern as a function of propeller angle of attack. Noise predictions are compared with newly available wind tunnel data and the accuracy and applicability of the prediction method are discussed. It is concluded that unsteady blade loading caused by inclining the propeller with respect to the flow changes the directionality and the intensity of the radiated noise. These changes are well modeled by the present quasi-steady prediction method.

Padula, S. L.↗
NASA NTRS1983

Into mesh lubrication of spur gears with arbitrary offset oil jet. I - For jet velocity less than or equal to gear velocity

An analysis was conducted for into mesh oil jet lubrication with an arbitrary offset and inclination angle from the pitch point for the case where the oil jet velocity is equal to or less than pitch line velocity. The analysis includes the case for the oil jet offset from the pitch point in the direction of the pinion and where the oil jet is inclined to intersect the common pitch point. Equations were developed for the minimum oil jet velocity required to impinge on the pinion or gear and the optimum oil jet velocity to obtain the maximum impingement depth.

Akin, L. S.↗
NASA NTRS1984

Multiple spacecraft Michelson stellar interferometer

Results of an orbital analysis and performance assessment of SAMSI (Spacecraft Array for Michelson Spatial Interferometry) are presented. The device considered includes two one-meter telescopes in orbits which are identical except for slightly different inclinations; the telescopes achieve separations as large as 10 km and relay starlight to a central station which has a one-meter optical delay line in one interferometer arm. It is shown that a 1000-km altitude, zero mean inclination orbit affords natural scanning of the 10-km baseline with departures from optical pathlength equality which are well within the corrective capacity of the optical delay line. Electric propulsion is completely adequate to provide the required spacecraft motions, principally those needed for repointing. Resolution of 0.00001 arcsec and magnitude limits of 15 to 20 are achievable.

Stachnik, R. V.↗
NASA NTRS1984

Dynamics of narrow rings

The ring models described here were developed to account for the dynamical problems posed by the narrow rings of Uranus. Some of these rings are now known to be eccentric, inclined, nonuniform in width, optically thick, and narrow, with very sharp edges. The eccentric rings have common pericenters and large, positive eccentricity gradients. The theory of shepherding satellites successfully accounts for most of these features and can also account for some features of the narrow Saturnian rings, in particular, waves, kinks, and periodic variations in brightness. Outstanding problems include the putative relation between eccentricity and inclination displayed by eight of the nine Uranian rings, and the magnitudes of the tidal torques acting on the shepherding satellites. The horseshoe-orbit model, although viable, probably has more application to the narrow rings from which the Saturnian coorbital satellites formed. The angular momentum flow rate due to particle collisions is a minimum at the Lagrangian equilibrium points L(4) and L(5), and one can expect accretion to be rapid at these points.

Dermott, S. F.↗
NASA NTRS1985

The large-scale structure of the asteroid belt

The distributions of 2888 numbered minor planets over orbital inclination, eccentricity, and semimajor axis are examined, and 19 zones believed to adequately isolate the selection biases in survey programs of the physical properties of minor planets are defined. Six numbered asteroids have exceptional orbits and fall into no zone. Attention is called to rather sharp upper limits, which become increasingly stringent at larger heliocentric distances, on orbital inclinations and eccentricity.

Zellner, B.↗
NASA NTRS1985

Procedure for utilizing the lift and thrust forces of ornithopters

This procedure is distinguished by two beating wings which together describe, in space, a succession of interlaced triangles. On these wings, whose incidence varies automatically, identical forces are exerted: simultaneous lift and thrust when they make their descent, which is inclined toward the front of the craft, and lift alone when they make their ascent, which is inclined toward the rear of the craft and follows a slide horizontal movement. A mechanical device makes these movements possible. It includes: two wings with hollow profiles, connected by a framework located above a rigid frame and attached to it by bars with joints. These bars are moved with control rods which gear down the drive force. A mechanism with elastic bands or springs automatically varies the incidence of the wings.

Bezard, C.↗
NASA NTRS1985

Cosmic ray simulation and testing program

Single event upset (SEU) and latchup vulnerabilities were determined for a number of parts of interest to NASA space programs. In cases where a threshold linear energy transfer (LET) for SEU could be measured, an upset rate in a low inclination Space Shuttle orbit was computed. The predicted upset rates are extremely low, except for the devices with LET thresholds below the geomagnetic cutoff for altitude and inclination of the Space Shuttle orbit. While some of the devices do exhibit latchup, the cross sections and threshold LETs are such that the risk associated with flying these devices in low, near equatorial orbits is small if not negligible.

Kolasinski, W. A.↗
NASA NTRS1985

Observations of complex oscillations in a closed thermosyphon

Observations have been made of thermal oscillations in a slightly inclined closed thermosyphon. The thermosyphon is made up of two isothermal tubes, capped at the outer ends, and joined along their axes by an insulating section. The tube assembly is filled with liquid and inclined slightly with respect to the vertical. The lower isothermal section is hotter than the upper one and convection is driven across the insulating region. Between the applied temperature difference at which simple steady convection occurs, and that required for persistent turbulent motions, there is a wide range over which thermal oscillations are observed. These oscillations reflect quasi-periodic flows as well as a type of periodic chaos.

Hart, J. E.↗
NASA NTRS1986

Upwind Navier-Stokes solutions for separated periodic flows

The application of an upwind implicit approximate factorization Navier-Stokes algorithm to highly separated flow is described. Using both the thin-layer and complete forms of the Navier-Stokes equations, the low Reynolds number laminar flow around a circular cylinder with periodic shedding is solved. The effect of grid density, grid extent, and time step on the Strouhal number is shown. Results from both sets of equations agree within the experimental data band. Unsteady, laminar flow computations around inclined plates and separated airfoils are also described. Strouhal numbers agree to within 5 percent of experiments for inclined plates. Differences between the complete equations and the thin-layer approximation for separated periodic flows are discussed. Computations of an impulsively started circular cylinder and airfoil yield time-accurate flowfield shapes in good agreement with experimental flow visualizations. The turbulent computation of an airfoil at a high angle-of-attack is massively separated, but shows no evidence of periodicity.

Rumsey, C. L.↗
NASA NTRS1985

Structure of turbulence in the presence of uniform shear

The structure of the vorticity field in homogeneous turbulent shear flow is analyzed using a database generated by direct numerical solution of the unsteady Navier-Stokes equations with up to 128x128x128 grid points. For two Reynolds numbers, the probability distribution of the inclination angle of the vorticity vectors, two-point correlations of the velocity and vorticity fields, and the instantaneous vorticity vectors and vortex lines in three-dimensional space were examined. It is shown that homogeneous turbulent shear flow contains a large number of horseshoe vortices. These vortices are most often found in planes inclined at 45 deg to the flow direction and are formed from the roll-up of sheets of transverse vorticity. These findings and similar results obtained in turbulent channel flow, lead to the conclusion that hairpin vortices are the characteristic vortical structures in all turbulent shear flows.

Moin, P.↗
NASA NTRS1986

Analysis and application of frozen orbits for the TOPEX mission

This paper identifies and analyzes frozen orbits for use by the Topography Experiment (TOPEX) mission. Frozen orbits are characterized by almost no long-term change in eccentricity or argument of periapsis. The standard method of frozen orbit prediction is shown to be inadequate for TOPEX inclinations due to the effect of higher degree zonal harmonic gravity terms. A method is described from which long-term motion in mean eccentricity, argument of periapsis, and inclination can be predicted without numerical integration and is used to locate frozen orbits. A zonal gravity field of degree 13 is shown to be necessary and sufficient for TOPEX frozen orbit prediction. Results are verified by numerical integration methods. Frozen orbits are available for most TOPEX orbits under consideration and short-term altitude variations and maximum altitude rates are specified. Alternatives to the frozen orbit which may result in lower altitude variations and rates are briefly examined.

Smith, J. C., Jr.↗
NASA NTRS1986

Preliminary analysis of the IRAS solar system dust data

The structure of the solar system dust cloud as revealed by IRAS all-sky survey data is discussed. Fourier analysis was used to separate the smooth, large-scale zodiacal background from the narrower dust lanes. The geometry of the background zodiacal cloud appears to show features associated with both the forced inclinations and the forced eccentricities of the dust particle orbits. The ecliptic latitude of the peak of the background zodiacal emission varies nearly sinusoidally with ecliptic longitude with an amplitude of 2.1 + or -0.2 degrees. However, there are marked displacements, both in latitude and longitude, between the leading or ascending curve and the trailing or descending curve, implying that the curves exhibit significant deviations from a simple sinusoidal variation. It is suggested that the plane of symmetry of the background cloud is inclined to the ecliptic by 1.47 + or -0.10 degrees with a descending node of 230 + or -4 degrees, and that the sun is not at the center of symmetry of the cloud.

Dermott, S. F.↗
NASA NTRS1986

The heliospheric current sheet - 3-dimensional structure and solar cycle changes

The reversal in polarity of the interplanetary current sheet/sector structure is investigated during the recent solar maximum. Multipoint observations by ISEE-3 and Pioneer 11 show that a simple two sector or occasional four sector structure persisted throughout the maximum and out to distances of 10 AU. The polarity reversal occurred between March 1979 and October 1980, without any indication of an abrupt transition that might permit a more precise timing. The reversal coincided approximately with the reversal in the sun's polar cap fields. The current sheet appeared to be highly inclined during the ascending and descending phases of the solar cycle but was apparently too complex to describe as a simple inclined current sheet during solar maximum.

Smith, E. J.↗
NASA NTRS1986

Simultaneous earth observations from two satellites

Simultaneous co-located observations from two different orbits lead to several advantages (i.e., cross calibration of sensors and a wider range of solar-zenith and sensor look angles). The question was asked how many times per year (on the average) do the sub-satellite points of two satellites simultaneously come within D kilometers of each other? For the Space Station (altitude: 500 km, inclination: 28 deg) and a Sun synchronous satellite (altitude 705 km, inclination 98.21 deg) the answers are 16, 41 and 82 times per year for encounter distances D of 20, 50, and 100 km respectively. The relationship between encounters per year and distance D is linear. The answers were obtained in two ways: (1) a closed form statistical approach which led to a simple algebraic expression, and (2) a Monte Carlo type computer solution. The largest difference between the two solutions was less than 12 percent.

Montgomery, H. E.↗
NASA NTRS1987

Quasi-steady flight to quasi-steady flight transition in a windshear - Trajectory guidance

The control (via the angle of attack) of the vertical flight of an aircraft taking off at maximum power in a horizontal wind shear with downdraft is investigated analytically. Optimal trajectories to recover the initial path inclination or to recover quasi-steady flight (the relative values of the velocity, path inclination, and angle of attack) are derived using a Chebyshev approach and shown to be nearly identical in the shear but divergent after the shear. These results are then applied to construct a trajectory-guidance control comprising a variable-gamma guidance scheme for the shear trajectory, a constant-gamma guidance scheme for the immediate postshear trajectory, and a constant-rate-of-climb guidance scheme for the aftershear trajectory. Numerical results demonstrating the near-optimal performance of the control are presented in tables and graphs.

Miele, A.↗
NASA NTRS1986

Space Infrared Telescope Facility (SIRTF) observatory design

The NASA Space IR Telescope Facility (SIRTF) is a 1-m aperture, cryogenically cooled IR observatory scheduled for launch into orbit in the mid-1990s. SIRTF will operate in the 2-700 micron range and yield a 1000-fold increase in sensitivity over NASA's IRAS observatory. A low inclination orbit compatible with Space Shuttle operations will be used. Results from comparisons of a system error budget allocation for the f/24 optical configuration with recent test data indicate that a figured fused silica mirror and a blade flexure mounting system can be cooled to cryogenic temperature while meeting required wavefront tolerances for substrate deformation. An all-He cooling system will be used in the low inclination orbit.

Brooks, W. F.↗