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  • 1
    Publication Date: 2011-08-24
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 15; 5, Se; 1306-130
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  • 2
    Publication Date: 2019-06-28
    Description: Multiple arc data from repeated ground track are combined to reduce the error due to gravity field uncertainty in the determination of TOPEX orbit. The TOPEX dynamics is modeled with relatively few gravity parameters to account for the effect of the local gravity field. The gravity parameters are common to all arcs. The estimation algorithm uses the Householder transformation to combine multiple arc data and solve for the gravity parameters. The earth gravity field can be recovered with very modest amount of calculation.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 85-411
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  • 3
    Publication Date: 2019-06-28
    Description: NASA's Ocean Topographic Experiment (TOPEX), to be launched in 1991, is the first mission designed to reach the decimeter accuracy needed for the solution of the general mean circulation problem. An experimental tracking capability for TOPEX is studied using differential measurements with satellites of the U.S. DOD's Global Positioning System (GPS). Two data types are studied: (1) integrated Doppler from GPS carrier phase, and (2) GPS P-code pseudo-range. Results of covariance analysis predict that with differential GPS techniques, 5-10 cm average TOPEX altitude accuracies can be achieved over data arcs of two hours.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 85-401
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  • 4
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: This paper discusses the estimation problem for a GPS based tracking system which is used for low earth satellite orbit determination and for geodynamic research. The clock errors involved in the measurements are eliminated in order to obtain a solution. Two methods used to eliminate the clock errors, the double differencing method and the linear combination method are discussed and compared. The accuracy of the solution, the redundancy and the correlation of the differenced or the combined data are investigated. Numerical results of the two methods are presented.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 84-2052
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  • 5
    Publication Date: 2019-07-13
    Description: Dual-frequency pseudorange and carrier phase data streams can be analytically combined into a single equivalent data stream, reducing the data volume and computing time in the filtering process for parameter estimation by a factor of 2 to 4. The resulting single data stream is that of carrier phase measurements with both data noise and bias uncertainty strictly defined. Based on these analytical formulas the equivalent GPS measurements can be formed by simple and efficient numerical calculations without any degradation in data strength. Formulation for the equivalent GPS measurements and their covariances are given in closed form; and a numerical simulation is performed to demonstrate the validity and effectiveness of the equivalent measurements.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 91-538 , AAS/AIAA Astrodynamics Conference; Aug 19, 1991 - Aug 22, 1991; Durango, CO; United States
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  • 6
    Publication Date: 2019-07-13
    Description: The observed carrier phase in the Global Positioning System depends on the orientation of the antennas of the transmitter and the receiver as well as the direction of the line of sight. Two equivalent analytic formulas are derived for the correction based on the property of circularly polarized wave. The magnitude of the correction is evaluated with a simulation. Result from a GPS experiment is shown for the effect of the phase correction. A general formula useful for qualitative evaluation of the differenced measurements is given in terms of the solid angles subtended at the center of the earth by the receivers and transmitters involved.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 91-537 , AAS/AIAA Astrodynamics Conference; Aug 19, 1991 - Aug 22, 1991; Durango, CO; United States
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  • 7
    Publication Date: 2019-07-13
    Description: A covariance analysis is performed using a realistic scenario for processing 10 days of GPS data, to obtain the expected improvement to the GEM-T2 gravity field. The gravity bin technique has been refined to compute the covariance matrix associated with the spherical harmonic gravity field. It is shown that the GPS data from one ten-day arc of Topex/Poseidon with no a priori can improve medium degree and order (3-26) sigmas for the parameters in the GEM-T2 gravity field by more than an order of magnitude.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 90-2944 , AIAA/AAS Astrodynamics Conference; Aug 20, 1990 - Aug 22, 1990; Portland, OR; United States
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  • 8
    Publication Date: 2019-07-13
    Description: GPS measurements made at Topex/Poseidon and the accompanying ground tracking sites will be affected by the selective availability. Although in principle the effects may be removed by differencing between receivers observing the same GPS satellites, this requires accurate synchronization of all receiver clocks. In the case of Topex/Poseidon application, there are two sources of imperfect clock synchronization. The first and larger is due to the constantly drifting clock onboard Topex, which may cause a residual effect as large as 10 cm on Topex carrier phase and 1 m on Topex pseudorange. The second is due to light-time differences between receivers observing the same GPS satellites, which may amount to a few mm error. In this paper a data reduction scheme which incorporates a low-order polynomial interpolation and carrier phase smoothing on pseudorange acquired at Topex and ground receivers is described; a simulation analysis is given demonstrating the effectiveness of the scheme for reducing the GPS S/A effects; and comparison with other schemes is discussed.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 90-2942 , AIAA/AAS Astrodynamics Conference; Aug 20, 1990 - Aug 22, 1990; Portland, OR; United States
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  • 9
    Publication Date: 2019-07-13
    Description: When Topex is launched in mid-1992 it will carry a high quality GPS receiver which will operate in concert with a worldwide network of precision GPS ground receivers. The data from these receivers can be used to recover new information about the earth's gravity field at longer wavelengths. Software and algorithms have been developed which will allow this gravity field information to be recovered with much greater efficiency than with traditional techniques. The basis for these algorithms is the gravity bin formulation and related filtering techniques that exploit the repeat orbit of Topex and the sparse matrix structure of the problem. This new software has been used to evaluate the expected improvement in the gravity field using multiple ten-day arcs of GPS data from Topex.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 89-360 , AAS/AIAA Astrodynamics Conference 1989; Aug 07, 1989 - Aug 10, 1989; Stowe, VT; United States
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