Attitude stability of a symmetric satellite at the equilibrium points in the restricted three-body problem.
abstract missing
Kane, T. R.↗
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Tests and comparisons of gravity models.
Optical observations of the GEOS satellites were used to obtain orbital solutions with different sets of geopotential coefficients. The solutions were compared before and after modification to high order terms (necessary because of resonance) and were then analyzed by comparing subsequent observations with predicted trajectories. The most important source of error in orbit determination and prediction for the GEOS satellites is the effect of resonance found in most published sets of geopotential coefficients. Modifications to the sets yield greatly improved orbits in most cases. The results of these comparisons suggest that with the best optical tracking systems and gravity models, satellite position error due to gravity model uncertainty can reach 50-100 m during a heavily observed 5-6 day orbital arc. If resonant coefficients are estimated, the uncertainty is reduced considerably.
Marsh, J. G.↗
Measurement of lattice damage caused by ion-implantation doping of semiconductors.
Discussion of two new techniques used to measure the lattice damage produced in GaAs by the implantation of 60 keV cadmium ions. In the first method, optical reflection spectra of the ion-implanted samples were measured in the wavelength range from 2000 to 4600 A. The decrease in reflectivity resulting from ion-implantation was used to determine the relative amount of lattice damage as a function of ion dose. The second technique employed the scanning electron microscope. Patterns very similar in appearance to Kikuchi electron diffraction patterns are obtained when the secondary and/or backscattered electron intensity is displayed as a function of the angle of incidence of the electron beam on a single crystal surface. The results of measurements made by both methods are compared with each other and with data obtained by the method of measuring lattice damage by Rutherford scattering of 1 MeV helium ions.
Hunsperger, R. G.↗
GaAs transistors formed by Be or Mg ion implantation
N-p-n transistor structures have been formed in GaAs by implanting n-type substrates with Be ions to form base regions and then implanting them with 20-keV Si ions to form emitters. P-type layers have been produced in GaAs by implantation of either Mg or Be ions, with substrate at room temperature, followed by annealing at higher temperatures.
Hunsperger, R. G.↗
Tidal perturbations on the orbits of GEOS-1 and GEOS-2
Analysis of the luni-solar tidal perturbations of the inclination of GEOS-1 (1965-89A) and GEOS-2 (1968-002A) yielded the values k2 = 0.22 (sigma = 0.02) and 0.31 (sigma = 0.01) respectively for the second degree Love number. For GEOS-1 a new, purely numerical method involving osculating elements was employed. For GEOS-2 it was necessary to analyze the variations of the mean elements because of the very long period (450d) of the dominant solar tidal perturbation. An additional analysis of the variation of the mean elements of GEOS-1 confirmed the value of k2 obtained from the osculating elements.
Douglas, B. C.↗
Lipid-absorbing Polymers
The removal of bile acids and cholesterol by polymeric absorption is discussed in terms of micelle-polymer interaction. The results obtained with a polymer composed of 75 parts PEO and 25 parts PB plus curing ingredients show an absorption of 305 to 309%, based on original polymer weight. Particle size effects on absorption rate are analyzed. It is concluded that crosslinked polyethylene oxide polymers will absorb water, crosslinked polybutadiene polymers will absorb lipids; neither polymer will absorb appreciable amounts of lipids from micellar solutions of lipids in water.
Marsh, H. E., Jr.↗
Simultaneous observation solutions for NASA-MOTS and SPEOPT station positions on the North American datum
Simultaneous observations of the GEOS-I and II flashing lamps by the NASA MOTS and SPEOPT cameras on the North American Datum (NAD) were analyzed using geometrical techniques to provide an adjustment of the station coordinates. Two separate adjustments were obtained. An optical data only solution was computed in which the solution scale was provided by the Rosman-Mojave distance obtained from a dynamic station solution. In a second adjustment, scaling was provided by processing simultaneous laser ranging data from Greenbelt and Wallops Island in a combined optical-laser solution. Comparisons of these results with previous GSFC dynamical solutions indicate an rms agreement on the order of 4 meters or better in each coordinate. Comparison with a detailed gravimetric geoid of North America yields agreement of 3 meters or better for mainland U.S. stations and 7 and 3 meters, respectively, for Bermuda and Puerto Rico.
Reece, J. S.↗
A global station coordinate solution based upon camera and laser data - GSFC 1973
Results for the geocentric coordinates of 72 globally distributed satellite tracking stations consisting of 58 cameras and 14 lasers are presented. The observational data for this solution consists of over 65,000 optical observations and more than 350 laser passes recorded during the National Geodetic Satellite Program, the 1968 Centre National d'Etudes Spatiales/Smithsonian Astrophysical Observatory (SAO) Program, and International Satellite Geodesy Experiment Program. Dynamic methods were used. The data were analyzed with the GSFC GEM and SAO 1969 Standard Earth Gravity Models. The recent value of GM = 398600.8 cu km/sec square derived at the Jet Propulsion Laboratory (JPL) gave the best results for this combination laser/optical solution. Solutions are made with the deep space solution of JPL (LS-25 solution) including results obtained at GSFC from Mariner-9 Unified B-Band tracking. Datum transformation parameters relating North America, Europe, South America, and Australia are given, enabling the positions of some 200 other tracking stations to be placed in the geocentric system.
Marsh, J. G.↗
A detailed gravimetric geoid of North America, the North Atlantic, Eurasia, and Australia
A computer program was developed for the calculation of a goid based upon a combination of satellite and surface gravity data. A detailed gravimetric geoid of North America, the North Atlantic, Eurasia, and Australia was derived by using this program.
Marsh, J. G.↗
The geoid and free air gravity anomalies corresponding to the GEM-4 earth gravitational model
Contour maps are presented of the global geoid. Free air gravity anomalies of the GEM-4 earth gravitational model are also included.
Marsh, J. G.↗
Tracking-station coordinates from Geos 1 and Geos 2 optical flash data.
Center-of-mass coordinates for 28 NASA MOTS and SAO Baker-Nunn camera sites have been obtained from optical flash data from Geos 1 (1965 89A) and Geos 2 (1968 002A). More than 25,000 observations in about 100 two-day arcs were used in dynamical solutions (SAO 1969 AGU gravity model). Comparison of results with local survey solutions and with solutions from deep-space vehicle tracking suggests accuracy of about 2 meters in longitude and height and 5 meters in latitude. The relatively larger error in latitude arose from propagation of gravity-model error largely along the track of these high-inclination satellites. The results have also been compared with the solutions of the SAO 1969 standard earth for station coordinates on the North American datum. The solution obtained in the present work is much closer to the survey results in chord length between stations.
Marsh, J. G.↗
Detailed gravimetric geoid for the United States.
A detailed gravimetric geoid was computed for the United States using a combination of satellite-derived spherical harmonic coefficients and 1 by 1 deg mean gravity values from surface gravimetry. Comparisons of this geoid with astrogeodetic geoid data indicate that a precision of plus or minus 2 meters has been obtained. Translations only were used to convert the NAD astrogeodetic geoid heights to geocentric astrogeodetic heights. On the basis of the agreement between the geocentric astrogeodetic geoid heights and the gravimetric geoid heights, no evidence is found for rotation in the North American datum. The value of the zero-order undulation can vary by 10 to 20 meters, depending on which investigator's station positions are used to establish it.
Strange, W. E.↗
Mean elements of GEOS 1 and GEOS 2.
A combined analytical-numerical procedure for determining mean orbital elements is presented and applied to the orbits of GEOS 1 and GEOS 2. The precision of the mean semi-major axes of these orbits is a few tens of centimeters when optical flash data are used to determine 2 day orbital arcs. Four day Minitrack orbits give mean semi-major axes of a few meters precision. The mean orientation parameters determined from the optical data are obtained to a precision of about 0.1 sec.
Douglas, B. C.↗
Solid propellants.
The basic principles underlying propulsion by rocket motor are examined together with the configuration of a solid propellant motor. Solid propellants and their preparation are discussed, giving attention to homogeneous propellants, composite propellants, energetic considerations in choosing a solid propellant, the processing of composite propellants, and some examples of new developments. The performance of solid propellants is investigated, taking into account characteristics velocity, the specific impulse, and performance calculations. Aspects of propellant development considered include nonperformance requirements for solid propellants, the approach to development, propellant mechanical properties, and future trends.
Marsh, H. E., Jr.↗
Attitude control of a large flexible spacecraft using three-axis mass expulsion control.
A study of the elastic effects of large area solar arrays on attitude control of a spacecraft was conducted. It is demonstrated for sufficiently low structural frequencies that excitation of certain modes can induce instability in the pitch axis. Stiffening the arrays can eliminate the instability. However, a severe weight penalty is associated with such modification. A more efficient means of minimizing the structural interaction effects is to change the shape of the array. For stable configurations, another problem may be encountered. This is the imposition of high rates on the spacecraft bus by oscillation of the solar arrays. Since low rates are required to obtain accurate science experiment results, it is imperative that the high rate problem be resolved. This also is possible by changing the solar array configuration.
Marsh, E. L.↗
Polymers used to absorb fats and oils: A concept
One approach to problem of excessive oils and fats is to develop method by which oil is absorbed into solid mixture for elimination as solid waste. Materials proposed for these purposes are cross-linked (network) polymers that have high affinity for aliphatic substances, i. e., petroleum, animal, and vegetable oils.
Marsh, H. E., Jr.↗
Detailed geoid computations for GEOS-C altimeter experiment areas
The GEOS-C spacecraft is scheduled to carry onboard a radar altimeter for the purpose of measuring the geoid undulations in oceanic areas. An independently derived geoid map will provide a valuable complement to these experiments. A detailed gravimetric geoid is presented for the Atlantic and northeast Pacific Ocean areas based upon a combination of the Goddard Space Flight Center GEM-6 earth model and surface 1 deg x 1 deg gravity data. As part of this work a number of satellite derived gravity models were evaluated to establish the model which best represented the long wave length features of the geoid in the above mentioned area. Comparisons of the detailed geoid with the astrogeodetic data provided by the National Ocean Survey and dynamically derived tracking station heights indicate that the accuracy of this combined geoid is on the order of 2 meters or better where data was dense and 5 to 7 meters where data was less dense.
Marsh, J. G.↗
Global detailed gravimetric geoid
A global detailed gravimetric geoid has been computed by combining the Goddard Space Flight Center GEM-4 gravity model derived from satellite and surface gravity data and surface 1 deg-by-1 deg mean free air gravity anomaly data. The accuracy of the geoid is + or - 2 meters on continents, 5 to 7 meters in areas where surface gravity data are sparse, and 10 to 15 meters in areas where no surface gravity data are available. Comparisons have been made with the astrogeodetic data provided by Rice (United States), Bomford (Europe), and Mather (Australia). Comparisons have also been carried out with geoid heights derived from satellite solutions for geocentric station coordinates in North America, the Caribbean, Europe, and Australia.
Vincent, S.↗