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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Application of global positioning system to determination of tectonic plate movements and crustal deformations

It is shown that pseudo-range measurements to four GPS satellites based on correlation of the pseudo random code transmissions from the satellites can be used to determine the relative position of ground stations which are separated by several hundred kilometers to a precision at the centimeter level. Carrier signal measurements during the course of passage of satellites over a pair of stations also yield centimeter precision in the relative position, but oscillator instabilities limit the accuracy. The accuracy of solutions based on either type of data is limited by unmodeled tropospheric refraction effects which would reach 5 centimeters at low elevation angles for widely separated stations.

Anderle, R. J.↗
NASA NTRS1979

Effect of outboard vertical-fin position and orientation on the low-speed aerodynamic performance of highly swept wings

A theoretical study was conducted to determine the potential low-speed performance improvements which can be achieved by altering the position and orientation of the outboard vertical fins of low-aspect-ratio highly swept wings. Results show that the magnitude of the performance improvements is solely a function of the span-load distribution. Both the vertical-fin-chordwise position and toe angle provided effective means for adjusting the overall span-load distribution.

Johnson, V. S.↗
NASA NTRS1977

Time determination for spacecraft users of the Navstar Global Positioning System /GPS/

Global Positioning System (GPS) navigation is performed by time measurements. A description is presented of a two body model of spacecraft motion. Orbit determination is the process of inferring the position, velocity, and clock offset of the user from measurements made of the user motion in the Newtonian coordinate system. To illustrate the effect of clock errors and the accuracy with which the user spacecraft time and orbit may be determined, a low-earth-orbit spacecraft (Seasat) as tracked by six Phase I GPS space vehicles is considered. The obtained results indicate that in the absence of unmodeled dynamic parameter errors clock biases may be determined to the nanosecond level. There is, however, a high correlation between the clock bias and the uncertainty in the gravitational parameter GM, i.e., the product of the universal gravitational constant and the total mass of the earth. It is, therefore, not possible to determine clock bias to better than 25 nanosecond accuracy in the presence of a gravitational error of one part per million.

Grenchik, T. J.↗
NASA NTRS1977

Positions of three X-ray burst sources

Precise (20-30 arcsec) positions are reported for three steady X-ray sources that have been identified recently as X-ray burst sources: 4U (MXB) 1636-53, 4U 1728-33 (MXB 1728-34), and 4U (MXB) 1735-44. The positions were derived from data obtained with the SAS 3 rotating modulation collimators during a survey of the galactic plane. Possible optical counterparts are noted.

Jernigan, J. G.↗
NASA NTRS1978

Negative and positive cesium ion studies

Mass spectrometric analyses have been performed on the positive and negative species from discharges in Cs, He-Cs, and He-H2-Cs mixtures. Sampling was conducted through the electrodes of normal glow discharges and from close-spaced heated-cathode conditions, which approximate a cesium thermionic converter. No negative Cs ions were observed for Cs pressures less than .01 torr. Identified species included Cs(+), Cs2(+), Cs(-), and what appeared to be multiply charged ions. Low-mass negative and positive ions attributed to H2 were observed when an He-H2 mixture was also present in the discharge region.

Kuehn, D. G.↗
NASA NTRS1979

Rotation at 30 RPM about the Z axis after 6 hours in the 10-deg head-down position - Effect on susceptibility to motion sickness

Intraindividual differences in susceptibility to motion sickness were measured in 14 subjects for two conditions of rotation at 30 rpm in the 10-deg head-down position. In one condition, subjects were in the 10-deg head-down position for 6 h prior to the onset of rotation; in the other condition, the delay was only 15 min. In both conditions, there were changes in vital capacity, indicating a redistribution of movable body fluids. Subjects tended to be less susceptible to motion sickness when they were recumbent for 6 h prior to rotation. These results are counterevidence for the hypothesis that shifts of body fluid are responsible in large part for the motion sickness elicited in orbital space flight.

Graybiel, A.↗
NASA NTRS1979

Ambiguity resolution for satellite Doppler positioning systems

The implementation of satellite-based Doppler positioning systems frequently requires the recovery of transmitter position from a single pass of Doppler data. The least-squares approach to the problem yields conjugate solutions on either side of the satellite subtrack. It is important to develop a procedure for choosing the proper solution which is correct in a high percentage of cases. A test for ambiguity resolution which is the most powerful in the sense that it maximizes the probability of a correct decision is derived. When systematic error sources are properly included in the least-squares reduction process to yield an optimal solution the test reduces to choosing the solution which provides the smaller valuation of the least-squares loss function. When systematic error sources are ignored in the least-squares reduction, the most powerful test is a quadratic form comparison with the weighting matrix of the quadratic form obtained by computing the pseudoinverse of a reduced-rank square matrix. A formula for computing the power of the most powerful test is provided. Numerical examples are included in which the power of the test is computed for situations that are relevant to the design of a satellite-aided search and rescue system.

Argentiero, P.↗
NASA NTRS1979

Low-distortion resistive anodes for two-dimensional position-sensitive MCP systems

Microchannel plates (MCPs) are frequently used with resistive anodes to detect charged particles or photons and yield analog signals from which event positions can be decoded. The paper discusses a four-corner concave circular arc terminated resistive anode that permits theoretically distortionless encoding of Cartesian event positions into pulse charge ratios. The theory of the circular arc terminated anode is discussed along with anode design and performance. Electron beam images obtained by using such an anode are presented to confirm the usefulness of the approach.

Lampton, M.↗
NASA NTRS1979

Differential capacitance sensor as position detector for a magnetic suspension densimeter

In the present work, which consists of adapting a magnetic suspension densimeter for use at pressures up to 350 bars, a differential capacitance sensor is developed for use in the servosystem of a magnetic suspension densimeter for detecting the position of a magnetic buoy. This type of sensor has not been used previously in magnetic suspension densimeters. Its design, performance, and advantages are outlined. A cutaway drawing and a schematic diagram of the capacitance sensor and magnetic buoy are presented and described. The concentric-disk design of the sensor capacitor plates and the high degree of symmetry which results from the printed circuit fabrication approach minimize the sensor sensitivity to lateral displacement of the buoy and to the dielectric constant of the surrounding medium. A high-power microscope is necessary to monitor the position of the buoy relative to the support coil.

Frederick, N. V.↗
NASA NTRS1980

Solar cell angular position transducer

An angular position transducer utilizing photocells and a light source is disclosed. The device uses a fully rotatable baffle which is connected via an actuator shaft to the body whose rotational displacement is to be measured. The baffle blocks the light path between the light source and the photocells so that a constant semicircular beam of light reaches the photocells. The current produced by the photocells is fed through a resistor, a differential amplifier measures the voltage drop across the resistor which indicates the angular position of the actuator shaft and hence of the object.

Sandford, M. C.↗
NASA NTRS1980

VLBI measurements of radio source positions at the Jet Propulsion Laboratory

The results of approximately 1300 observations of 67 radio sources are presented. Most of the measurements were made at the stations of the Deep Space Network in California, Spain, and Australia at wavelengths of 13.1 and 3.6 cm, between 1971 and 1978. The formal errors in the derived source positions are generally in the neighborhood of 0.01 seconds of arc and the positions agree fairly well with those previously published.

Purcell, G. H., Jr.↗
NASA NTRS1979

Submilliarcsecond astrometry via VLBI. I - Relative position of the radio sources 3C 345 and NRAO 512

The relative position and relative proper motion of the radio sources 3C 345 and NRAO 512 are estimated from four sets of VLBI observations spread out over the period from October 1971 to May 1974. The use of phase-connection techniques yields the separation, in 1950.0 coordinates, of the centers of brightness of the compact components of the two sources. An upper bound of 0.0005 arcsec/yr is placed on the relative proper motion (70% estimated confidence limits). Bounds that can be placed on the distances to the two sources are considered, prospects for improvement in the determination of relative position and proper motion of these sources are discussed, and other possible applications of the basic technique are described.

Shapiro, I. I.↗
NASA NTRS1979

Positions and identifications of galactic X-ray sources

A catalog of compact Galactic X-ray sources with precise positions is presented together with a large bibliography. The catalog provides available X-ray, optical, and radio data for the 96 compact Galactic sources that have been identified and contains the most precise of the available optical, X-ray, or radio positions, the maximum and minimum published intensities, references to finding charts, and a comprehensive referenced list of X-ray, optical, and radio characteristics. The catalog also includes X-ray sources in the Magellanic clouds as well as all unidentified hard (greater than 2 keV) compact sources with an error radius of less than 60 arcsec and a Galactic latitude of less than 10 deg (absolute value). The sources list includes 14 X-ray Doppler or eclipsing binaries, seven or eight other X-ray pulsators, 23 transients or X-ray novae, 15 persistent bright bulge sources, seven X-ray sources associated with globular clusters, nine bursters, seven Galactic Center sources, and 18 other identified sources.

Bradt, H. V.↗
NASA NTRS1979

Position and shape of the Venus bow shock - Pioneer Venus Orbiter observations

Magnetometer data from the Pioneer Venus Orbiter is used to examine the position and shape of this planet's bow shock. Utilizing crossings identified on 86 occasions during the first 65 orbits a mean shock surface is defined for sun-Venus-satellite angles of 60-110 deg. Both the shock shape and variance in location are found to be very similar to the terrestrial case for the range in SVS angle considered. However, while the spread in shock positions at the earth is due predominantly to the magnetopause location varying in response to solar wind dynamic pressure, ionopause altitude variations can have little effect on total obstacle radius. Thus, the Cytherean shock is sometimes observed much closer to or farther from the planet than previously predicted by gasdynamic theory applied to the deflection of flow about a blunt body which acts neither as source nor sink for any portion of the flow.

Slavin, J. A.↗
NASA NTRS1980

The position and polarization of Type III solar bursts

The position and polarization of Type III solar bursts in the range of 24-220 MHz are studied, with emphasis on the bursts continuing to frequencies lower than 24 MHz. Consideration is given to the statistics of burst polarization, the relation between polarization and source position, and brightness temperature, flux densities, and source sizes.

Dulk, G. A.↗
NASA NTRS1980

The position and polarization of Type V solar bursts

Observations of the position and polarization of Type V solar radio bursts and their preceding Type III bursts are presented. The polarization, frequency range, source position, source movement, source size and brightness temperature of the bursts were measured using a 24-220 MHz spectropolarimeter, an 8-8000 MHz spectrograph and a three-frequency radioheliograph. Type V radiation is frequently found to have the opposite sense of circular polarization from that of the preceding Type III burst, with a degree of polarization similar to that of harmonic Type III radiation. A reversal of polarization is not observed when the accompanying Type III burst has no fundamental-harmonic structure, or when the Type V radiation is poorly developed. Possible mechanisms for the reversal are examined, including opposite magnetic field directions in Type III and V bursts, changes in mode coupling and a change in the mode of emission from o-mode for Type III to x-mode for Type V, and conditions needed for the mode change which is considered the most likely mechanism, are determined.

Dulk, G. A.↗
NASA NTRS1980

Experimental analysis of the boundary layer transition with zero and positive pressure gradient

The influence of a positive pressure gradient on the boundary layer transition is studied. The mean velocity and turbulence profiles of four cases are examined. As the intensity of the pressure gradient is increased, the Reynolds number of the transition onset and the length of the transition region are reduced. The Tollmein-Schlichting waves disturb the laminar regime; the amplification of these waves is in good agreement with the stability theory. The three dimensional deformation of the waves leads finally to the appearance of turbulence. In the case of zero pressure gradient, the properties of the turbulent spots are studied by conditional sampling of the hot-wire signal; in the case of positive pressure gradient, the turbulence appears in a progressive manner and the turbulent spots are much more difficult to characterize.

Arnal, D.↗
NASA NTRS1980

State of gas exchange in recumbent and orthostatic positions and under physical load in healthy persons of varying age, sex and body build

Age effect on gas exchange was studied in the recumbent and orthostatic positions and under physical load. In the case of the older age group and for normal as compared with hypersthenic persons, oxygen consumption during rest and during moderate physical overload diminishes. When the vertical position is assumed oxygen consumption in persons of various age groups is distinctly increased, particularly in the elderly group. There is a reduction in the amount of oxygen consumption, oxygen pulse, recovery coefficient, and work efficiency under moderate overload. In persons over 50, physical labor induces a large oxygen requirement and a sharp rise in the level of lactic acid and the blood's lactate/pyruvate ratio. No distinct difference was noted in the amount of oxygen consumed during rest and during physical overload in men and women of the same physical development and age.

Glezer, G. A.↗