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  • 1
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    TOPEX orbit determination and gravity recovery using global positioning system data from repeat orbits (1992)
    American Geophysical Union
    Details
    Publication Date: 1992-02-10
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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    PAPER CURRENT
  • 2
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    Incorporation of a priori gravity field information in satellite orbit determination using bin parameters (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A method to determine satellite orbits using tracking data and a priori gravitational field is described. The a priori constraint on the orbit dynamics is determined by the covariance matrix of the spherical harmonic coefficients for the gravity model, so that the optimal combination of the measurements and gravitational field is achieved. A set of bin parameters is introduced to represent the perturbation of the gravitational field on the position of the satellite orbit. The covariance matrix of a conventional gravity model is transformed into that for the bin parameters by the variational partial derivatives. The covariance matrices of the bin parameters and the epoch state are combined to form the covariance matrix of the satellite positions at the measurement times. The combined matrix is used as the a priori information to estimate the satellite positions with measurements.
    Keywords: ASTRODYNAMICS
    Type: Journal of the Astronautical Sciences (ISSN 0021-9142); 40; 4; p. 547-555.
    Format: text
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  • 3
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    Orbit determination by solving for gravity parameters with multiple arc data (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The orbit of a satellite that repeats in the earth fixed coordinates is determined by combining GPS tracking data from multiple arcs. The satellite dynamics are modeled with the epoch state and a set of parameters, called the bin parameters, that account for the effect of the local gravitational field on the satellite current state. The epoch state is specific to each arc, and the bin parameters are common to all repeat arcs. The estimation algorithm is based on the Square Root Information Filter. It involves partitioning of the measurement matrix and use of the Householder transformation to combine multiple arc data and solve for the epoch states and the bin parameters. The bin parameters can then be converted into the earth's gravitational field with a modest amount of computation.
    Keywords: ASTRODYNAMICS
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 15; 304-313
    Format: text
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  • 4
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    Strategies for sub-decimeter satellite tracking with GPS (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Decimeter tracking of low earth orbiters can be achieved with a variety of differential GPS techniques. A precisely known global network of GPS ground receivers and a receiver aboard the user satellite are needed, and all techniques must simultaneously estimate the user and GPS satellite orbits. Three basic strategies include a purely geometric, a fully dynamic, and a hybrid strategy, the last of which combines dynamic GPS solutions with a geometric user solution. Two powerful extensions of the hybrid strategy show the most promise. The first uses a quasi-optimal synthesis of dynamics and geometry in the user solution, while the second uses a novel gravity adjustment method to exploit data from repeat ground tracks in a computationally efficient way. The best of these techniques promise to deliver sub-decimeter accuracy down to the lowest possible orbits.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Format: text
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  • 5
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    Precise tracking of remote sensing satellites with the Global Positioning System (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The Global Positioning System (GPS) can be applied in a number of ways to track remote sensing satellites at altitudes below 3000 km with accuracies of better than 10 cm. All techniques use a precise global network of GPS ground receivers operating in concert with a receiver aboard the user satellite, and all estimate the user orbit, GPS orbits, and selected ground locations simultaneously. The GPS orbit solutions are always dynamic, relying on the laws of motion, while the user orbit solution can range from purely dynamic to purely kinematic (geometric). Two variations show considerable promise. The first one features an optimal synthesis of dynamics and kinematics in the user solution, while the second introduces a novel gravity model adjustment technique to exploit data from repeat ground tracks. These techniques, to be demonstrated on the Topex/Poseidon mission in 1992, will offer subdecimeter tracking accuracy for dynamically unpredictable satellites down to the lowest orbital altitudes.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 28; 108-116
    Format: text
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  • 6
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    Near-optimal strategies for sub-decimeter satellite tracking with GPS (1986)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: Decimeter tracking of low Earth orbiters using differential Global Positioning System (GPS) techniques is discussed. A precisely known global network of GPS ground receivers and a receiver aboard the user satellite are needed, and all techniques simultaneously estimate the user and GPS satellite orbits. Strategies include a purely geometric, a fully dynamic, and a hybrid strategy. The last combines dynamic GPS solutions with a geometric user solution. Two powerful extensions of the hybrid strategy show the most promise. The first uses an optimized synthesis of dynamics and geometry in the user solution, while the second uses a gravity adjustment method to exploit data from repeat ground tracks. These techniques promise to deliver subdecimeter accuracy down to the lowest satellite altitudes.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: ESA Proceedings of the Second International Symposium on Spacecraft Flight Dynamics; p 233-238
    Format: text
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  • 7
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    Refinement of Earth's gravity field with Topex GPS measurements (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The NASA Ocean Topography Experiment satellite TOPEX will carry a microwave altimeter accurate to a few centimeters for the measurement of ocean height. The capability can be fully exploited only if TOPEX altitude can be independently determined to 15 cm or better. This in turn requires an accurate gravity model. The gravity will be tuned with selected nine 10-day arcs of laser ranging, which will be the baseline tracking data type, collected in the first six months of TOPEX flight. TOPEX will also carry onboard an experimental Global Positioning System (GPS) flight receiver capable of simultaneously observing six GPS satellites above its horizon to demonstrate the capability of GPS carrier phase and P-code pseudorange for precise determination of the TOPEX orbit. It was found that subdecimeter orbit accuracy can be achieved with a mere two-hour arc of GPS tracking data, provided that simultaneous measurements are also made at six of more ground tracking sites. The precision GPS data from TOPEX are also valuable for refining the gravity model. An efficient technique is presented for gravity tuning using GPS measurements. Unlike conventional global gravity tuning, this technique solves for far fewer gravity parameters in each filter run. These gravity parameters yield local gravity anomalies which can later be combined with the solutions over other parts of the earth to generate a global gravity map. No supercomputing power will be needed for such combining. The approaches used in this study are described and preliminary results of a covariance analysis presented.
    Keywords: GEOPHYSICS
    Type: Ohio State Univ., Progress in the Determination of the Earth's Gravity Field; p 155-158
    Format: application/pdf
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  • 8
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    Topex orbit determination and gravity recovery using GPS data from repeat orbits (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A covariance analysis is presented for a differential GPS-based technique for satellite tracking and gravity recovery to be demonstrated on Topex in the early 1990's. The technique employs data from an ensemble of repeat ground tracks to recover a unique satellite epoch state for each track and a set of invariant local gravity parameters common to all tracks. For satellites above about 800 km altitude, where gravity modeling is the dominant systematic error, averaging of random error over many arcs and adjustment of the gravity model reduces the final satellite position error. The local gravity parameters can then be used to produce a refined global gravity model. The analysis indicates that errors ranging from 5 to 8 cm in Topex altitude and 0.05 to 0.2 mgal for the gravity field can be achieved, depending on the number of repeat arcs used.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 88-0575
    Format: text
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  • 9
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    Reducing S/A Errors In TOPEX GPS Measurements (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Proposed scheme for postprocessing of data acquired by receivers monitoring broadcasts from Global Positioning System (GPS) satellites reduces those errors in computed positions of receivers caused by pseudorandom offsets introduced into transmitted signals. Offsets canceled exactly with help of codes available to privileged users and intended to degrade accuracies available to nonpriviledged users, pursuant to policy called "selective availability" (S/A). Proposed scheme devised primarily for GPS receivers aboard TOPEX satellite and at associated ground stations.
    Keywords: ELECTRONIC SYSTEMS
    Type: NPO-18326 , NASA Tech Briefs (ISSN 0145-319X); 16; 12; P. 38
    Format: text
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  • 10
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    Compensating For GPS Ephemeris Error (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Method of computing position of user station receiving signals from Global Positioning System (GPS) of navigational satellites compensates for most of GPS ephemeris error. Present method enables user station to reduce error in its computed position substantially. User station must have access to two or more reference stations at precisely known positions several hundred kilometers apart and must be in neighborhood of reference stations. Based on fact that when GPS data used to compute baseline between reference station and user station, vector error in computed baseline is proportional ephemeris error and length of baseline.
    Keywords: ELECTRONIC SYSTEMS
    Type: NPO-18416 , NASA Tech Briefs (ISSN 0145-319X); 16; 11; P. 56
    Format: text
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