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  • SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING  (8)
  • 1
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    Precise GPS orbit determination results from 1985 field tests (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Data from three different receiver types have been used to obtain precise orbits for the satellites of the Global Positioning System (GPS). The data were collected during the 1985 March-April GPS experiment to test and validate GPS techniques for precision orbit determination and geodesy. A new software package developed at the Jet Propulsion Laboratory (JPL), GIPSY (GPS Inferred Positioning SYstem), was used to process the data. To assess orbit accuracy, solutions are compared using integrated doppler data from various different receiver types, different fiducial sites, and independent data arcs, including one spanning six days. From these intercomparisons, orbit accuracy for a well-tracked GPS satellite of three meters in altitude and about five meters in each of down and cross-track components are inferred.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 86-2170
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    NASA TECHNICAL REPORTS
  • 2
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    Differential Very Long Baseline Interferometry for 50 nanoradian deep space navigation - Results from quasar pair experiments (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Deep space tracking experiments completed at JPL have demonstrated a 50-nanoradian angular positioning accuracy with wideband differential Very Long Baseline Interferometry (delta VLBI). This meets the stringent navigation requirements of NASA's Galileo mission, scheduled for launch in May 1986 and for encounter with Jupiter in December 1988. Pairs of extragalactic radio sources (quasars) with well-known coordinates were used to simulate deep space navigation passes in which quasar-spacecraft pairs are observed. This paper discusses the accuracy of the delta VLBI technique and how it is affected by source separations, source elevations, source strengths, solar plasma and ionosphere. Several observation strategies are discussed and one is shown to be especially effective in minimizing these major error sources.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 85-311
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    NASA TECHNICAL REPORTS
  • 3
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    Precise positioning capabilities for TOPEX using differential GPS (1986)
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    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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    NASA TECHNICAL REPORTS
  • 4
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    Tracking Landsat-5 by a differential GPS technique (1986)
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    Publication Date: 2019-06-28
    Description: As part of an international campaign to develop precise geodetic applications of the Global Positioning System (GPS), the Jet Propulsion Laboratory is conducting a demonstration of differential GPS tracking using Landsat-5. Two strategies have been investigated: one in which only the Landsat-5 orbit is estimated, and one in which both the Landsat-5 and GPS orbits are estimated together. Error studies show that under the limited conditions of the experiment, three-dimensional Landsat-5 position accuracies of about 5 m with the first strategy and 2 m with the second strategy can be achieved over a 20-min period of good observing geometry. Orbit determination results using a version of the first strategy appear to achieve the 5 m goal. This is supported by various formal error measures and independent comparisons. The more powerful strategy has yet to be carried out.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 86-2215
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  • 5
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    Gravity mismodelling on TOPEX orbit determination (1986)
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    Publication Date: 2019-06-28
    Description: Gravity mismodeling limits the dynamic orbit determination accuracy of TOPEX which requires an altitude accuracy of about 15 cm or better. This paper provides an assessment of this effect for a dynamic GPS tracking scheme, and investigates a nondynamic GPS tracking technique that eliminates the problem. Analysis indicates that TOPEX altitude error could be affected by as much as 30-40 cm when dynamic differential GPS tracking is used, although efforts now underway to improve the gravity model could reduce this. With the nondynamic technique, the positional change of TOPEX is inferred from the accurate, continuous GPS carrier phase measurements rather than from a dynamic model which is prone to gravity error. TOPEX altitude accuracy better than 15 cm is attainable with nondynamic tracking over a few hours.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 86-2056
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  • 6
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    Monitoring global geodynamical parameter variations with GPS and low earth satellites (1992)
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    Publication Date: 2019-07-13
    Description: A low earth satellite enhances global geodynamical parameters determination with GPS in two ways. First, it improves the GPS orbits, which in turn improve the estimates of other parameters. Secondly, a low earth satellite completes an orbit cycle in far shorter time (90 to 120 minutes) than do GPS satellites (12 hours); it observes more GPS satellites than a ground receiver does in shorter time and increases the correlation between GPS orbit errors. This reduces the error in the determination of nonrotational coordinate parameters, i.e., geocentric offset of ground tracking sites. Covariance results with the global geodynamical parameters modeled as constants, and as random-walk parameters to closer reflect the actual variations, are compared. The effects of using different GPS data quality and different ground tracking network are studied. The case of using two earth satellites in orthogonal orbital planes is also investigated.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 91-540 , AAS/AIAA Astrodynamics Conference; Aug 19, 1991 - Aug 22, 1991; Durango, CO; United States
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  • 7
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    Effects of antenna orientation on GPS carrier phase (1992)
    In:  Other Sources
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    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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  • 8
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    High-precision orbit determination for high-earth elliptical orbiters using the Global Positioning System (1990)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Orbit covariance analyses pertaining to the Japanese VLBI Space Observatory Program (VSOP) MUSES-B satellite and to the International VLBI Satellite are presented. It is determined that a combination of Doppler and GPS measurements can provide the orbit accuracy required to support advanced radio interferometric experiments. For the VSOP, the required orbit accuracy of 130 m is easily met with two-way Doppler as the primary type of data; the 0.4 cm/s VSOP velocity requirement is also feasible provided that precise ground calibrations of tropospheric delays and station coordinates are available. It is concluded that combining the data from a VSOP GPS flight instrument with the ground GPS and two-way Doppler data will significantly enhance orbit determination accuracy in position and velocity.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 90-2954 , AIAA/AAS Astrodynamics Conference; Aug 20, 1990 - Aug 22, 1990; Portland, OR; United States
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