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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Evaluation of the application of some gas chromatographic methods for the determination of properties of synthetic fuels

The purpose of the investigation was to evaluate the applicability, to some synthetic fuels, of some gas chromatographic methods now under development for use with petroleum based fuels. Thirty-two jet and diesel fuel samples which were prepared from oil shale and coal syncrudes were examined. The boiling range distribution of each was determined by gas chromatography, and from that data distillation properties were calculated. The calculated results gave sufficient agreement with the measured values that the equations could be useable in their present form. Bulk fuel properties were calculated for the 16 JP-5 and Diesel No. 2 type fuels. The results show that the equations would not give useable results. Capillary column gas chromatography was used to determine the n-alkane content of the eight JP-5 type samples and the results related to the observed freezing points. The results show that the concentrations of the long straight chain molecules in the fuels exert influence on the freezing point but are not the complete controlling factor.

Antoine, A. C.↗
NASA NTRS1979

Simplified and refined finite element approaches for determining stresses and internal forces in geometrically nonlinear structural analysis

Two methods for determining stresses and internal forces in geometrically nonlinear structural analysis are presented. The simplified approach uses the mid-deformed structural position to evaluate strains when rigid body rotation is present. The important feature of this approach is that it can easily be used with a general-purpose finite-element computer program. The refined approach uses element intrinsic or corotational coordinates and a geometric transformation to determine element strains from joint displacements. Results are presented which demonstrate the capabilities of these potentially useful approaches for geometrically nonlinear structural analysis.

Robinson, J. C.↗
NASA NTRS1978

On-board orbit determination for applications satellites

An algorithm for satellite orbit determination is described which would be suitable for use with an on-board computer with limited core storage. The proposed filter is recursive on a pass-by-pass basis and features a fading memory to account for the effect of gravity field error. Only a single pass of Doppler data needs to be stored at any time and the data may be acquired from two reference beacons located within the Continental United States. The results of both simulated data and real data reductions demonstrate that the satellite's position can be determined to within one kilometer when a 4 x 4 recovery field is used.

Morduch, G. E.↗
NASA NTRS1978

Orbit determination accuracies using satellite-to-satellite tracking

Results of the ATS-6/GEOS-3 and the ATS-6/NIMBUS-6 satellite-to-satellite tracking orbit determination experiments to be applied to the NASA geostationary Tracking and Data Relay Satellite System (TDRSS) starting in 1980, are presented. A satellite radio or laser tracking system performed measurements of such parameters as range, range ratio, angles and direction cosines to a spacecraft relative to a given tracking station. Resolutions of 1 meter in range and .03 cm/sec in range rate for a 1 second averaging were achieved showing that with proper data reduction procedures the tracking data relay satellite system should provide orbit determination capability comparable to what is normally obtainable from ground based systems.

Vonbun, F. O.↗
NASA NTRS1979

The JPL orbit determination software system

The Jet Propulsion Laboratory (JPL) orbit determination software system is described. Consisting of a set of computer programs, this system has been developed at JPL for the primary purpose of determining the flight path of deep-space mission spacecraft in NASA's planetary program. Secondary uses include science studies in celestial mechanics and extraterrestrial atmospherics. Attention is given to such features as the capability for processing 30 data types from up to 15 tracking stations, and for precise navigation to natural satellites of outer planets. In addition, the system contains models for such conditions as mascons, atmospheric drag, attitude control, and finite motor burns, to provide for extensive solve-on capabilities.

Ekelund, J. E.↗
NASA NTRS1979

Orbit determination strategy and results for the Pioneer Venus Orbiter mission

This paper examines the orbit of the Pioneer Venus Orbiter as determined from earth based radio data. The basic orbit determination strategy together with its associated accuracy is presented, and the effect of the changing earth-Venus geometry on that accuracy is discussed. Orbital evolution from insertion to the present time is described and related to the primary forces acting on the spacecraft as well as to the weekly periapsis altitude trim maneuvers. Lastly, the technique used for orbit prediction in the presence of the uncertain Venus atmosphere and gravity environment is discussed.

Jacobson, R. A.↗
NASA NTRS1980

Proposed method for determining the thickness of glass in solar collector panels

An analytical method was developed for determining the minimum thickness for simply supported, rectangular glass plates subjected to uniform normal pressure environmental loads such as wind, earthquake, snow, and deadweight. The method consists of comparing an analytical prediction of the stress in the glass panel to a glass breakage stress determined from fracture mechanics considerations. Based on extensive analysis using the nonlinear finite element structural analysis program ARGUS, design curves for the structural analysis of simply supported rectangular plates were developed. These curves yield the center deflection, center stress and corner stress as a function of a dimensionless parameter describing the load intensity. A method of estimating the glass breakage stress as a function of a specified failure rate, degree of glass temper, design life, load duration time, and panel size is also presented.

Moore, D. M.↗
NASA NTRS1980

Autonomous satellite orbit determination during the development phases of the global positioning system

An onboard navigation system was developed to aid the design and evaluation of algorithms used in autonomous satellite navigation with Global Positioning System (GPS) data. The performance of the algorithms designed for a GPS Receiver/Processor Assembly (R/PA) intended for LANDSAT-D was investigated during the development phases of the GPS (four to six satellites in the constellation). This evaluation emphasized the effects on the orbit determination accuracy of the expected user clock errors, GPS satellite visibility, force model approximations, and state and covariance propagation approximations. Results are presented giving the sensitivity of orbit determination accuracy to these constraints.

Dunham, J. B.↗
NASA NTRS1980

Determination of the time of occurrence of gamma flares at different points in space

The problem of determining the time of occurrence of gamma flares at different points in space is considered. This problem arises in the localization of sources of gamma flares by the triangulation method using several spacecraft. A study is made of different methods for determining the time at which the flare reaches the spacecraft and algorithms are given for estimating their accuracy. Results of processing the model information are also given.

Novak, B. L.↗
NASA NTRS1980

A computer program for determining truncation error coefficients for Runge-Kutta methods

The basic structure of a program to generate the truncation error coefficients for Runge-Kutta (RK) methods is reformulated to reduce storage requirements significantly and to accommodate variable dimensioning. This FORTRAN program, SUBROUTINE RKEQ, determines truncation error coefficients for RK algorithms for orders 1 through 10 and extends the order of coefficients through 12 with the 11th- and 12th-order terms determined following the patterns used to establish the lower order coefficients. Both subroutines (the original and RKEQ) are also written to treat RK m-fold methods which utilize m known derivatives of f to increase the order of the algorithm. Setting m = 0 gives the classical RK algorithm.

Horn, M. K.↗
NASA NTRS1980

Fracture toughness of brittle materials determined with chevron notch specimens

The use of chevron-notch specimens for determining the plane strain fracture toughness (K sub Ic) of brittle materials is discussed. Three chevron-notch specimens were investigated: short bar, short rod, and four-point-bend. The dimensionless stress intensity coefficient used in computing K sub Ic is derived for the short bar specimen from the superposition of ligament-dependent and ligament-independent solutions for the straight through crack, and also from experimental compliance calibrations. Coefficients for the four-point-bend specimen were developed by the same superposition procedure, and with additional refinement using the slice model of Bluhm. Short rod specimen stress intensity coefficients were determined only by experimental compliance calibration. Performance of the three chevron-notch specimens and their stress intensity factor relations were evaluated by tests on hot-pressed silicon nitride and sintered aluminum oxide. Results obtained with the short bar and the four-point-bend specimens on silicon nitride are in good agreement and relatively free of specimen geometry and size effects within the range investigated. Results on aluminum oxide were affected by specimen size and chevron-notch geometry, believed due to a rising crack growth resistance curve for the material. Only the results for the short bar specimen are presented in detail.

Shannon, J. L., Jr.↗
NASA NTRS1979

A form-factor method for determining the structure of distorted stars

The equilibrium equations of a uniformly rotating and tidally distorted star are reduced to the same form as for a spherical star except for the inclusion of two form factors. One factor, expressing the buoyancy effects of centrifugal force, is determined directly from the integrated structure variables. The other factor, expressing the deviation from spherical shape, is shown to be relatively insensitive to errors in the assumed shape, so that accurate solutions are obtained in spite of the use of an a priori shape. The method is employed by adding computations for the factors to an existing spherical model program. Upper Main Sequence models determined by this method compare closely with results from the double approximation method even for critical rotation and tidal distortion.

Wolfe, R. H., Jr.↗
NASA NTRS1980

The determination of transport parameters of minority carriers in n-p junctions by means of an electron microscope - Critique of recent developments

It has recently been shown that amplitude modulated electron beams provide a novel means for the determination of minority carrier lifetimes, diffusion lengths, etc., in n-p junctions. In this paper it is shown that: (1) a recently published analysis based on a cylindrically symmetric configuration is incorrect, (2) the correct approach leads to a system of dual integral equations for which the formal solution is given, (3) in general, the short circuit current can only be determined by means of extensive computer calculations except in the case of large front surface recombination velocities, and (4) the difficulties encountered with cylindrically symmetric configurations (circular ohmic contacts and the like) are completely avoided with a choice of a planar geometry since simple closed form expressions for the short circuit current are readily available in this case.

Von Roos, O.↗
NASA NTRS1980

An overview of earth satellite orbit determination

This paper considers orbit determination for artificial satellites within the geosynchronous distance of the earth. A brief description of the systems used to gather data (past, present and future) will be presented as well as the accuracies of the data and the accuracies of the resultant orbits. The methods of analyzing the data and the applications and future trends of earth satellite orbit determination will be discussed.

Kolenkiewicz, R.↗
NASA NTRS1980

Crop emergence date determination from spectral data

Estimating the emergence of a given crop, such as wheat or barley, is proposed using an analytic method which relies on the hypothesis that in the region (lambda = 0.70-1.35 microns) a given crop, after emergence, has a unique spectral profile in time. If the crop emerges early or late, relative to a reference standard determined for a given segment, the profile is displaced but has the same shape. Therefore, given the crop specific constants of the reference profile and a sufficient number of Landsat observations of reflectivity at specific times, the emergence date of a field can be determined.

Badhwar, G. D.↗
NASA NTRS1980

A determination of the orbit of GX 301-2

The pulse phase of GX 301-2(4U 1223-62) was tracked for 30 days with the SAS 3 satellite during 1979 January and February. It is suggested that most of the observed changes in pulse period are the result of Doppler shifts in a binary orbit, as opposed to changes in the intrinsic pulse period alone. The SAS 3 data allow orbital periods P(orb) equal to or greater than 23 days when a constant rate of change in the intrinsic pulse period is allowed as a free parameter in the orbital fits. For each trial orbital period the other orbital elements of the binary system are well determined. The SAS 3 data is combined with the Ariel 5 pulse arrival-time data to further restrict the allowed orbits. In both data sets a sharp minimum is observed in the Doppler delays of the pulse arrival times. Evidence is presented that the correct orbit is most likely the one with P(orb) = 35.0d, a projected semimajor axis for the neutron star of 304 light-seconds, and an eccentricity of 0.44. The relation of this system to the six X-ray binaries whose orbits have been determined previously is also discussed.

Kelley, R.↗
NASA NTRS1980

Attitude determination of Galileo spacecraft from star data

An entirely autonomous attitude determination algorithm has been developed for the dual spin Galileo spacecraft in its mission to Jupiter. A batch mode process is established which identifies three stars within the scanner's field-of-view based on the criteria of intensity and geometry. This is followed by a continuous star acquisition procedure which provides star transit times and a spacecraft spin rate estimate. A least-squares estimator then sequentially determines the spacecraft's attitude from successive star crossings by minimizing an error derived using the necessary condition of star and scanner slit normal orthogonality. Simulation results are presented, showing successful star identification and attitude convergence in the presence of nutation and star transit time uncertainty.

Wong, E. C.↗
NASA NTRS1980

Determination of optimum voltages of ion focusing devices using computer techniques

Electric potentials for two dimensional cross sections of ion focusing devices used in a mass spectrometer are calculated via a series of computer programs designed to compute potentials between areas of fixed voltages. Ion trajectories within these devices may be determined by computer and a histogram obtained which plots ion density against ion position along a plate of the focusing device. For each lens system, a plate voltage may be changed, the electric potentials recalculated, and a new histogram calculated in order to determine if the new voltage configuration has increased the device's efficiency. This process may be repeated until the optimum voltage values have been found for maximum particle transmission in each focusing device.

Eckstein, B. A.↗