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At least 397 records · Page 22

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NASA NTRS1979

An efficient approach for computing the geometrical optics field reflected from a numerically specified surface

An approach for computing the geometrical optic fields reflected from a numerically specified surface is presented. The approach includes the step of deriving a specular point and begins with computing the reflected rays off the surface at the points where their coordinates, as well as the partial derivatives (or equivalently, the direction of the normal), are numerically specified. Then, a cluster of three adjacent rays are chosen to define a 'mean ray' and the divergence factor associated with this mean ray. Finally, the ampilitude, phase, and vector direction of the reflected field at a given observation point are derived by associating this point with the nearest mean ray and determining its position relative to such a ray.

Mittra, R.↗

NASA NTRS1979

The magnetic field of Mercury

The paper examines the magnetic field observations and their analyses relating to the determination of the Mercury magnetic field. Methods of analyzing data included: (1) comparison of bow shock and magnetopause relative positions at Mercury to the earth, (2) direct spherical harmonic analysis, (3) magnetosphere modeling by an image dipole, and (4) scaling of a mathematical model for the terrestrial magnetosphere. Dipole moments were determined using partial quadrupole and octupole terms to improve the least-square fit of models to observations; analyses by method (2) yield a convergent series of dipole moments values considered to best represent the intrinsic planetary field. Finally, it is suggested that the origin of the magnetic field of Mercury cannot be uniquely determined, but the sources of convective energy may be radiogenic decay and heat release, gravitational settling, and differentiation of processional torques.

Ness, N. F.↗

NASA NTRS1980

Structural features of the nonionic surfactants stabilizing long-lived bubble nuclei

A study of the effects of various electrolytes and one organic compound on bubble production in agarose gels is presented. Several preparations of ultrapure agarose were compared for 42 electrolytes and phenol to identify trends in bubble formation. The anion and cation sequences of bubble suppression are similar to processes for salting out of nonionic surfactants. The reduction of bubble number by polyvalent ions and 1% phenol suggests that the polar portions of these nonionic surfactants represent amide groups. The evidence for amide groups is consistent with the relative positions of Mg(2+) in all cation sequences; this result makes it unlikely that either linkages contribute to the hydrophilicity of the nonionic surfactants stabilizing bubble nuclei in the different aqueous gels tested.

Darrigo, J. S.↗

NASA NTRS1980

An airborne system for detection of volcanic surface deformations

A technique is proposed for measuring volcanic deformation on the order of centimeters per day to centimeters per year. An airborne multifrequency pulsed radar, tracking passive ground reflectors spaced at 1 kilometer intervals over a 50 square kilometer area is employed. Identification of targets is accomplished by Doppler and range resolution techniques, with final relative position measurements accomplished by phase comparison of multifrequency signals. Atmospheric path length errors are corrected by an airborne refractometer, meteorological instruments, or other refractive index measuring devices. Anticipated system accuracy is 1-2 cm, with measuring times on the order of minutes. Potential problems exist in the high intrinsic data assimilation rate required of the system to overcome ground backscatter noise.

Lunine, J.↗

NASA NTRS1981

Introduction to ball bearings

The purpose of a ball bearing is to provide a relative positioning and rotational freedom while transmitting a load between two structures, usually a shaft and a housing. For high rotational speeds (e.g., in gyroscope ball bearings) the purpose can be expanded to include rotational freedom with practically no wear in the bearing. This condition can be achieved by separating the bearing parts with a coherent film of fluid known as an elastohydrodynamic film. This film can be maintained not only when the bearing carries the load on a shaft, but also when the bearing is preloaded to position the shaft to within micro- or nano-inch accuracy and stability. Background information on ball bearings is provided, different types of ball bearings and their geometry and kinematics are defined, bearing materials, manufacturing processes, and separators are discussed. It is assumed, for the purposes of analysis, that the bearing carries no load.

Hamrock, B. J.↗

NASA NTRS1981

Orbit improvement of the satellites of the outer planets

Data reduced from 127 plates showing Jupiter's and Saturn's satellites in the interval 1972 to 1974 are available on computer cards in the form of (O-C) residuals. Initial orbit calculations and several later orbit improvements for Jupiter XIII (Leda) culminated in an extended ephemeris for Leda to the year 2000. The possible existence of several small satellites just outside Saturns rings was predicted. De Sitter's incomplete theory for the motion of the Galilean satellites was reviewed and an outline for a revised, complete theory was developed. Observations of nearly 100 relative positions of the Galilean satellite with a mean accuracy of about 100 km (0.03 arc sec) were used to improve Sampson's theory for these satellites. Results were published on (1) a long term upper limit to Jupiter's orbital eccentricity; (2) deviation of an accurate modern value of the ellipticity of Uranus from balloon-borne images and consequent evaluation of the planet's rotation rate; and (3) identification of features in Saturn's rings as produced by heretofore undetected tesseral harmonics of Saturn's gravitational field.

Aksnes, K.↗

NASA NTRS1981

Cold plasma boundaries and auroral arcs

Auroral arcs often extend for more than a thousand kilometers with little deviation of their relative position within the auroral oval. At high altitudes, the outer limits of the plasmasphere are usually marked by sharp decreases in the cold plasma densities. It is suggested that some auroral arcs follow the ionospheric trace of these boundary shells.

Mcilwain, C. E.↗

NASA NTRS1981

Development of a radio-astrometric catalog by means of very long baseline interferometry observations

The Jet Propulsion Laboratory has been developing a radio-astrometric catalogue for use in the application of radio interferometry to interplanetary navigation and geodesy. The catalogue consists of approximately 100 compact extragalactic radio sources whose relative positions have formal uncertainties of the order of 0.01 arcsec. The sources cover nearly all of the celestial sphere above -40 deg declination. By using the optical counterparts of many of these radio sources, this radio reference frame has been tied to the FK4 optical system with a global accuracy of approximately 0.1 arcsec. This paper describes the status of this work.

Fanselow, J. L.↗

NASA NTRS1983

Mutagenic screening of diamine monomers

The effects of phenyl ring coupling moieties, of isomeric amine positions relative to the coupling groups, and of insertion of other coupling groups on the mutagenic response of a series of dianilines were investigated using the Ames Salmonella assay. Generally, S-9 metabolic activation from Aroclor-induced rat liver was required for mutagenic expression. The range of mutagenicity of steric isomers of several dianiline series was also investigated. No mutagenicity was found for purified samples of o,o' and m,p' isomers of methylene dianiline (MDA) and diaminobenzophenone, while varying degrees of mutagenicity were found for other isomers. The mutagenicity of "benzylogs" of MDA decreased as the degree of linear separation of the m,m' anilino groups by aromatic rings increased. Methylation and two-year storage increased mutagenic response in certain isomers of MDA. However, high performance liquid chromatography indicated there was no discernible change in m,p'-MDA samples aged under varied conditions over four months. Likewise, no change in mutagenicity was found.

Ross, W. D.↗

NASA NTRS1983

Development of an autonomous video rendezvous and docking system, phase 2

The critical elements of an autonomous video rendezvous and docking system were built and used successfully in a physical laboratory simulation. The laboratory system demonstrated that a small, inexpensive electronic package and a flight computer of modest size can analyze television images to derive guidance information for spacecraft. In the ultimate application, the system would use a docking aid consisting of three flashing lights mounted on a passive target spacecraft. Television imagery of the docking aid would be processed aboard an active chase vehicle to derive relative positions and attitudes of the two spacecraft. The demonstration system used scale models of the target spacecraft with working docking aids. A television camera mounted on a 6 degree of freedom (DOF) simulator provided imagery of the target to simulate observations from the chase vehicle. A hardware video processor extracted statistics from the imagery, from which a computer quickly computed position and attitude. Computer software known as a Kalman filter derived velocity information from position measurements.

Tietz, J. C.↗

NASA NTRS1983

Influence of airplane components on rotational aerodynamic data for a typical single-engine airplane

The influence of airplane components, as well as wing location and tail length, on the rotational flow aerodynamics is discussed for a 1/6-scale general aviation airplane model. Examination of the individual component effects provides insight as to the source of the moment and forces that determine spin characteristics. For the subject airplane, it is seen that the presence of the horizontal tail adversely effects the yaw damping of the vertical tail such that at certain angles of attack the vertical actually becomes a propelling component in spinning motion. It is shown that the level of this adverse interaction is a function of the relative positions of the wing and the tail surfaces, e.g., relocating the wing to the high wing position or shortening the tail moment arm from the basic configuration both reduced or eliminated the adverse tail interference for certain angles of attack. The influence of wing location on the damping characteristics of the horizontal-vertical tail combination would not be addressed in any existing tail design criterion for spinning and could only be discerned through rotary balance testing.

Ralson, J.↗

NASA NTRS1983

The structure of Neptune's upper atmosphere - The stellar occultation of 24 May 1981

Observations of the 24 May 1981 occulation of an uncatalogued star by Neptune made at the Cerro Tololo Inter-American Observatory have been analyzed to yield temperature profiles of Neptune's upper atmosphere for number densities near 5 x 10 to the 13th per cu cm. The mean temperatures at immersion (latitude - 56 deg) and emersion (latitude - 16 deg) obtained by numerical inversion were 140 + or - 10 K and 154 + or - 10 K, respectively. The immersion and emersion profiles are remarkably similar in overall shape, suggestive of global atmospheric layering. From the astrometry of the event, precise relative positions of Neptune and the occulted star were obtained.

French, R. G.↗

NASA NTRS1982

Space Shuttle Orbiter onboard rendezvous navigation

Much of the work that the Space Shuttle will perform requires a capability to rendezvous with other orbiting objects. The formulation and design philosophy behind the Space Shuttle Orbiter rendezvous navigation system are the subjects of this paper. The current rendezvous navigation design incorporates a Kalman filter to estimate the relative position and velocity. The filter is augmented with state elements for the estimation of colored measurement noise and acceleration modeling errors. Several measurement types are available to the filter: a manual optical sighting device, an automatic optical tracking instrument, and a rendezvous radar which provides range and range rate measurements as well as the line of sight direction. The filter also includes a technique for detecting highly improbable measurements and excluding them from Kalman processing.

Little, M. J.↗

NASA NTRS1982

Corn and soybean Landsat MSS classification performance as a function of scene characteristics

In order to fully utilize remote sensing to inventory crop production, it is important to identify the factors that affect the accuracy of Landsat classifications. The objective of this study was to investigate the effect of scene characteristics involving crop, soil, and weather variables on the accuracy of Landsat classifications of corn and soybeans. Segments sampling the U.S. Corn Belt were classified using a Gaussian maximum likelihood classifier on multitemporally registered data from two key acquisition periods. Field size had a strong effect on classification accuracy with small fields tending to have low accuracies even when the effect of mixed pixels was eliminated. Other scene characteristics accounting for variability in classification accuracy included proportions of corn and soybeans, crop diversity index, proportion of all field crops, soil drainage, slope, soil order, long-term average soybean yield, maximum yield, relative position of the segment in the Corn Belt, weather, and crop development stage.

Batista, G. T.↗

NASA NTRS1983

An improved celestial radio reference frame: JPL 1982-4

In the development of a celestial radio reference frame, there are now over 100 sources whose relative positions are known with an average uncertainty less than 5 milliarcseconds. These sources are fairly uniformly distributed over the celestial sphere north of -40 deg declination. Their positions are expressed in the new IAU system. This presentation describes the analysis involved in obtaining these results, as well as future plans for linking this system to the JPL planetary ephemerides.

Fanselow, J. L.↗

NASA NTRS1984

Physiological responses to prolonged bed rest and fluid immersion in humans

For many centuries, physicians have used prolonged rest in bed and immersion in water in the treatment of ailments and disease. Both treatments have positive remedial effects. However, adverse physiological responses become evident when patients return to their normal daily activities. The present investigation is concerned with an analysis of the physiological changes during bed rest and the effects produced by water immersion. It is found that abrupt changes in body position related to bed rest cause acute changes in fluid compartment volumes. Attention is given to fluid shifts and body composition, renal function and diuresis, calcium and phosphorus metabolism, and orthostatic tolerance. In a discussion of water immersion, fluid shifts are considered along with cardiovascular-respiratory responses, renal function, and natriuretic and diuretic factors.

Greenleaf, J. E.↗

NASA NTRS1984

Constraints on lunar origin: Evidence preserved in Precambrian stromatolites

The existence of subaqueous unicellular algae and bacteria from the Precambrian period is evidenced by strongly abundant fossilized structures consisting of many layers of usually darker algae-bacterial growth alternating with layers of usually lighter sediment-precipitate. The earliest of these are dated to 3.5 billion years ago. A form of these stromatolites, Anabaria juvensis was analyzed and a sinusoidal columnar growth pattern was interpreted to be a response of stromatolite forming microbes to the changing inclination of the Sun over the seasons, with microbe growth rate positively related to solar intensity. Additional specimens are being used to develop a systematic methodology for extracting data evidencing Earth-Moon-Sun dynamics at the time of stromatolite formation. In particular, stromatolites span the time from 1 to 2 billion years ago, critical for several theories of lunar formation and/or Earth/Moon near encounter. Such cataclysmic events would influence stromatolite formation.

Vanyo, J. P.↗

NASA NTRS1985

Noise constraints effecting optimal propeller designs

A preliminary design tool for advanced propellers was developed combining a fast vortex lattice aerodynamic analysis, a fast subsonic point source noise analysis, and an optimization scheme using a conjugate directions method. Twist, chord and sweep distributions are optimized to simultaneously improve both the aerodynamic performance and the noise observed at a fixed relative position. The optimal noise/performance tradeoffs for straight and advanced concept blades are presented. The techniques used include increasing the blade number, blade sweep, reducing the rotational speed, shifting the spanwise loading and diameter changes.

Miller, C. J.↗