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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

The noncavitating performance and life of a small vane-type positive displacement pump in liquid hydrogen

The low flow rate and high head rise requirements of hydrogen/oxygen auxiliary propulsion systems make the application of centrifugal pumps difficult. Positive displacement pumps are well-suited for these flow conditions, but little is known about their performance and life characteristics in liquid hydrogen. An experimental and analytical investigation was conducted to determine the performance and life characteristics of a vane-type, positive displacement pump. In the experimental part of this effort, mass flow rate and shaft torque were determined as functions of shaft speed and pump pressure rise. Since liquid hydrogen offers little lubrication in a rubbing situation, pump life is an issue. During the life test, the pump was operated intermittently for 10 hr at the steady-state point of 0.074 lbm/sec (0.03 kg/sec) flow rate, 3000 psid (2.07 MPa) pressure rise, and 8000 rpm (838 rad/sec) shaft speed. Pump performance was monitored during the life test series and the results indicated no loss in performance. Material loss from the vanes was recorded and wear of the other components was documented. In the analytical part of this effort, a comprehensive pump performance analysis computer code, developed in-house, was used to predict pump performance. The results of the experimental investigation are presented and compared with the results of the analysis. Results of the life test are also presented.

Ulbricht, T. E.↗
NASA NTRS1986

Wavelength-division multiplexed digital optical position transducer

A novel concept for a digital optical position tranducer is presented. This compact and rugged device is electrically passive and requires only a dual-fiber optical link. Wavelength division of a broad-spectrum semiconductor light source is employed to multiplex the channels of a 10-bit digital position encoder. A preliminary design was evaluated and found to have a 10-dB on-off contrast ratio and a 12-dB insertion loss.

Fritsch, K.↗
NASA NTRS1985

Improving the absolute positioning accuracy of robot manipulators

The absolute positioning accuracy of robot manipulator can be increased substantially by updating the nominal link parameters in the control software. This paper presents a general method to estimate the link parameter errors for any serial link manipulator (i.e., n links, and any combination of revolute and prismatic joints). The parameters are estimated through a linear kinematic model which relates the link bias errors to the end-effector positioning error. Only end-effector measurements are required instead of individual link measurements to implement this method.

Hayati, S.↗
NASA NTRS1986

Optical identifications of radio sources with accurate positions using the United Kingdom Schmidt Telescope (UKST) IIIa-J plates

Several programs are making use of UKST Sky Survey plates to identify southern radio sources. The fine-grain modern plates and accurate radio positions give a much improved identification rate. It seems that it will very soon be possible to determine whether or not there is a quasar redshift cut-off at z of about 4. There is an urgent need for more accurate fundamental reference star positions in the South.

Savage, A.↗
NASA NTRS1986

Probing the magnetic field of radio pulsars - A reexamination of polarization position angle swings

A vacuum magnetic field is assumed in the present calculation of the polarization position angle as a function of pulse longitude and polarization-limiting radius in radio pulsars. The polarization-limiting radius is estimated on the basis of results of Cheng and Ruderman (1980) and Stinebring (1982). The average change in position angle is also calculated, and this is found to be consistent with observations studied by Narayan and Vivekanand (1983); an alternative interpretation of the data is given, however, which is further supported by the frequency dependence of polarization angle swing in the Crab pulsar.

Barnard, J. J.↗
NASA NTRS1986

Qualification Testing of General Electric 50 Ah Nickel-Cadmium Cells with New Separator and New Positive Plate Processing

Forty-two 50 Ah aerospace nickel-cadmium cells were delivered to Goddard Space Flight Center (GSFC) by General Electric (GE) in February, 1985, for the purpose of evaluating and qualifying a new nylon separator material Pellon 2536, and the new GE Positive Plate Nickel Attack Control Passivation process. Testing began in May, 1985, at the Naval Weapons Support Center (NWSC) in Crane, Indiana with standard initial evaluation tests. Life cycling in both Low Earth Orbit (LEO) and Geosynchronous Orbit (GEO) began in July, 1985, with approximately 1200 LEO cycles complete at this writting. Early test results show that cells with positive plate passivation exhibit higher than normal charge voltage characteristics. Other aspects of performance were nominal.

Morrow, G. W.↗
NASA NTRS1987

Stability characteristics of a supersonic boundary layer and their relation to the position of the laminar-turbulent transition point

By comparing the calculated results with experimental data, it is demonstrated that the position of the laminar-boundary transition point of a boundary layer can be estimated by using the e-exp-n method. The effect of the Mach number, pressure gradient, and heat transfer on the laminar-turbulent transition is discussed. It is found that under conditions of strong cooling, the effect of the pressure gradient on the position of the transition point is less pronounced than in the absence of heat transfer.

Lysenko, V. I.↗
NASA NTRS1987

A new linear quadratic optimal controller for the 34-meter high efficiency antenna position loop

The design of a new position loop controller for the 34-meter High Efficiency Deep Space antennas using linear quadratic (LQ) optimal control techniques is discussed. The LQ optimal control theory is reviewed, and model development and verification are discussed. Families of optimal gain vectors are generated by varying weight parameters. Performance specifications were used to select a final gain vector. Estimator dynamics were selected and the corresponding gain vectors were computed. Final estimator selection was based on position, commanded rate, and estimator error responses.

Nickerson, J. A.↗
NASA NTRS1986

Wavelength dependence of position angle in polarization standards

Eleven of the 15 stars on Serkowski's (1974) list of 'Standard Stars with Large Interstellar Polarization' were investigated to determine whether the orientation of the plane of their linear polarization showed any dependence on wavelength. Nine of the eleven stars exhibited a statistically significant wavelength dependence of position angle when measured with an accuracy of about 0.1 deg standard deviation. For the majority of these stars, the effect is caused primarily by intrinsic polarization. The calibration of polarimeter position angles in a celestial coordinate frame must evidently be done at the 0.1 deg level of accuracy by using only carefully selected standard stars or by using other astronomical or laboratory methods.

Dolan, J. F.↗
NASA NTRS1986

The noncavitating performance and life of a small vane-type positive displacement pump in liquid hydrogen

The low flow rate and high head rise requirements of hydrogen/oxygen auxiliary propulsion systems make the application of centrifugal pumps difficult. Positive displacement pumps are well-suited for these flow conditions, but little is known about their performance and life characteristics in liquid hydrogen. An experimental and analytical investigation was conducted to determine the performance and life characteristics of a vane-type, positive displacement pump. In the experimental part of this effort, mass flow rate and shaft torque were determined as functions of shaft speed and pump pressure rise. Since liquid hydrogen offers little lubrication in a rubbing situation, pump life is an issue. During the life test, the pump was operated intermittently for 10 hr at the steady-state point of 0.074 lbm/sec (0.03 kg/sec) flow rate, 3000 psid (2.07 MPa) pressure rise, and 9000 rpm (938 rad/sec) shaft speed. Pump performance was monitored during the life test series and the results indicated no loss in performance. Material loss from the vanes was recorded and wear of the other components was documented. In the analytical part of this effort, a comprehensive pump performance analysis computer code, developed in-house, was used to predict pump performance. The results of the experimental investigation are presented and compared with the results of the analysis. Results of the life test are also presented.

Ulbricht, T. E.↗
NASA NTRS1986

Radio-source positions from VLBI

Positions of 85 compact extragalactic radio sources and the Galactic object Beta Persei (Algol) have been determined in the J2000.0 coordinate system for analysis of VLBI observations made with the bandwidth-synthesis technique. Twenty-four of these sources were observed with the Mark I VLBI system in 37 sessions distributed between April 1972 and May 1978, and 82 of the sources were observed with the Mark III system in 85 sessions distributed between August 1979 and December 1982. Each session spanned at least 24 hr. Standard errors for the estimated positions on the sky of the about 10 sources frequently observed with the Mark I system are about 1 mas, except for the declinations of nearly equatorial sources, where these errors approach 5 mas. Corresponding uncertainties for the about 20 sources frequently observed with the Mark III system are 0.3 and 2 mas, respectively.

Ma, C.↗
NASA NTRS1986

Precision of vertical position estimates from very long baseline interferometry

It is found that the precision of VLBI measurements of vertical crustal motions is limited by errors in the modeling of the propagation delay through the earth's neutral atmosphere, and by errors in finding the orientation of a fixed crust coordinate system in the VLBI reference frame. The repeatability of baseline length measurements study indicates a vertical position precision of about 8 cm, averaged over 13 sites and 4.5 years of data, while the repeatability of vertical position estimates for a Richmond, FL site is found to yield a precision of about 7 cm for 42 observations made over an 11-month period. An overall precision of 8 cm for a 24-hour VLBI observing session is obtained, and the effects of earth orientation parameter errors is contingent on the distances between the VLBI sites.

Herring, T. A.↗
NASA NTRS1986

Precise VLA positions and flux-density measurements of the Jupiter system

VLA C array configuration observations at 2 and 6 cm are presented for Europa, Ganymede, and Callisto at eastern and western elongations with respect to Jupiter, which allowed measurements in right ascension and declination of the satellites with an rms precision of about + or - 0.03 arcsec. The transfer of the mean offsets of Ganymede to Jupiter yields offsets of -0.185 + or - 0.03 arcsec and -0.06 + or - 0.03 arcsec, with respect to JPL-DE-200, at the mean epoch of April 28, 1983; the large offset in right ascension is a combination of the Jupiter ephemeris error and the error in the frame tie of the Jovian planets with the VLBI system of precise positions which was used as the absolute reference frame for the observations. A significant error is noted in the orbital position of Callisto with respect to Ganymede.

Muhleman, Duane O.↗
NASA NTRS1986

Nightside plasmapause positions observed by DE-1 as a function of geomagnetic indices - Comparison with whistler observations and model calculations

The paper analyzes 28 plasmapause crossings made by the DE1 satellite in the night local time sector (from January to March 1982). Different signatures obtained by the Retarding Ion Mass Spectrometer instrument have been used for this analysis. The observed plasmapause positions (Lpp) have been organized as a function of geomagnetic indices. They are compared with the empirical relationship deduced by Carpenter and Parks (1973) from whistler observations. Moreover, the dependence of Lpp versus Kp has been inferred from model calculations using Kp dependent electric and magnetic fields derived from McIlwain's (1974) E3H electric field model and M2 magnetic field model respectively. Stationary models as well as time dependent ones, have been used to determine the positions of the plasmapause. The results of the model calculations are compared to the observations.

Decreau, P. M. E.↗
NASA NTRS1986

A position sensitive microchannel photomultiplier for ultraviolet space astronomy

The 25-mm microchannel-plate, position-sensitive UV astronomy photomultiplier tube presented is intended for the EOM-1 Spacelab Mission's FAUST payload and conducts wide-field imaging surveys in the VUV over the 1400-1800-A range. The sealed detector encompasses a CsI photocathode deposited on the inner surface of a MgF2 window, a stack of microchannel plates, and a wedge-and-strip two-dimensional position-sensing anode. Since the wedge-and-strip principle requires only three anode signals, flight electronics can be reduced to three charge amplifiers and three analog-to-digital converters.

Lampton, M.↗
NASA NTRS1987

Positive ions of the first- and second-row transition metal hydrides

Theoretical dissociation energies for the first- and second-row transition metal hydride positive ions are critically compared against recent experimental values obtained from ion beam reactive scattering methods. Theoretical spectroscopic parameters and dipole moments are presented for the ground and several low-lying excited states. The calculations employ large Gaussian basis sets and account for electron correlation using the single-reference single- and double-excitation configuration interaction and coupled-pair-functional methods. The Darwin and mass-velocity contributions to the relativistic energy are included in the all-electron calculations on the first-row systems using first-order perturbation theory, and in the second-row systems using the Hay and Wadt relativistic effective core potentials. The theoretical D(0) values for the second-row transition metal hydride positive ions should provide a critical measure of the experimental values, which are not as refined as many of those in the first transition row.

Pettersson, Lars G. M.↗
NASA NTRS1988

Nondynamic Tracking Using The Global Positioning System

Report describes technique for using Global Positioning System (GPS) to determine position of low Earth orbiter without need for dynamic models. Differential observing strategy requires GPS receiver on user vehicle and network of six ground receivers. Computationally efficient technique delivers decimeter accuracy on orbits down to lowest altitudes. New technique nondynamic long-arc strategy having potential for accuracy of best dynamic techniques while retaining much of computational simplicity of geometric techniques.

Yunck, T. P.↗
NASA NTRS1988

Method for Determining Artillery Position

A method is described for determining the position of artillery in which a circle of four closely spaced microphones is located at two measurement sites for acoustic radio direction finding of muzzle blasts. A method for determining the position of artillery using this procedure is discussed.

Meuser, Wilfried↗