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  • 1
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    Venus: Global gravity and topography (1993)
    American Geophysical Union
    Details
    Publication Date: 1993-05-25
    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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    A high resolution gravity model for Venus: GVM-1 (1993)
    American Geophysical Union
    Details
    Publication Date: 1993-04-09
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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    PAPER CURRENT
  • 3
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    Venus - Global gravity and topography (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A new gravity field determination that has been produced combines both the Pioneer Venus Orbiter (PVO) and the Magellan Doppler radio data. Comparisonsbetween this estimate, a spherical harmonic model of degree and order 21, and previous models show that significant improvements have been made. Results are displayed as gravity contours overlaying a topographic map. We also calculate a new spherical harmonic model of topography based on Magellan altimetry, with PVO altimetry included where gaps exist in the Magellan data. This model is also of degree and order 21, so in conjunction with the gravity model, Bouguer and isostatic anomaly maps can be produced. These results are very consistent with previous results, but reveal more spatial resolution in the higher latitudes.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; E5; p. 9113-9128.
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  • 4
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    A high resolution gravity model for Venus - GVM-1 (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A spherical harmonic model of the gravitational field of Venus complete to degree and order 50 has been developed using the S-band Doppler tracking data of the Pioneer Venus Orbiter (PVO) collected between 1979 and 1982. The short wavelengths of this model could only be resolved near the PVO periapse location (about 14 deg N latitude), therefore a priori constraints were applied to the model to bias poorly observed coefficients towards zero. The resulting model has a half-wavelength resolution of 400 km near the PVO periapse location, but the resolution degrades to greater than 1000 km near the poles. This gravity model correlates well with a degree 50 spherical harmonic expansion of the Venus topography derived from a combination of Magellan and PVO data. New tracking data from Magellan's gravity mission should provide some improvement to this model, although a complete model of the Venusian gravity field will depend on tracking of Magellan after the circularization of its orbit using aerobraking.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 20; 7; p. 599-602.
    Format: text
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  • 5
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    A gravity field to support Magellan navigation and science at Venus (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The development and validation of the revised JPL Venus Gravity Model are described with attention given to the incorporation of data regarding the longitudinal coverage. The motivation for the JPL Venus Gravity Model 1B (VGM1B) is related to the determination of orbit-support requirements for the Magellan mission. Existing gravity models for Venus are reviewed, and the present model is based on orbit-prediction data taken from Doppler tracking data from the Pioneer Venus Orbiter (PVO). Revised information arrays are developed incorporating more complete data describing the longitudinal conditions of the gravity field. Improvements are noted in the Doppler residual statistics taken from field-validation fits to the PVO and Magellan tracking data by using the VGM1B harmonic field. The VGM1B gravity field is also shown to reduce the trajectory errors from PVO and Magellan navigation.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: Journal of the Astronautical Sciences (ISSN 0021-9142); 40; 107-134
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  • 6
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    Determination and prediction of Magellan's orbit (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The Magellan spacecraft has been systematically mapping the surface of Venus since September 15, 1990, using a synthetic aperture radar. The spacecraft orbit about Venus is nearly polar, with an orbital period of 3.26 hours and periapsis altitude of 295 km. The radiometric measurements and the data reduction method used to determine and predict the spacecraft state are described. Orbit determination and prediction results are given for the first 146 days of mapping (through February 8, 1991, 60 percent of the first rotation of Venus). Orbit accuracy requirements of 150 meters in the radial position, and 1 km in the along-track and cross-track positions are shown to be met, but with exceptions. All error requirements were exceeded during a combined period of limited in-plane orbit observability due to earth-orbit relative geometry, and increased measurement noise due to superior conjunction.
    Keywords: ASTRODYNAMICS
    Type: AAS PAPER 91-180 , In: Spaceflight mechanics 1991; Proceedings of the 1st AAS(AIAA Annual Spaceflight Mechanics Meeting, Houston, TX, Feb. 11-13, 1991. Pt. 2 (A93-17901 05-13); p. 1143-1160.
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  • 7
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    A gravity field comparison and analysis to support Magellan navigation (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The orbit characteristics of Magellan are such that the spacecraft is extremely sensitive to gravity perturbations; therefore, the precision orbit determination required to construct the radar images is very dependent on accurate gravitational field modeling. As such, a comparison and analysis is presented of four global harmonic Venusian gravity fields generated by two-way S-band Doppler tracking data from the Pioneer Venus Orbiter in order to support the precise navigational requirements of the Magellan spacecraft. The four fields are: (1) one of degree and order 10 (a 10 x 10) from Mottinger et al. (1985), (2) an 18 x 18 from Bills et al. (1987), (3) a 21 x 21 from McNamee et al. (1990), and (4) a 36 x 36 from Smith et al. (1991). Least-square fits are done with each gravity field on 36 8-rev Magellan X-band data arcs, spaced at 10-deg longitude intervals, completely encircling Venus. Trajectory differences are also performed for two distinct cases, one where the gravity field modeling coincides, and the other where the gravity fields are very different. Although all of the above fields are found to model Venus gravity fairly well, the results show that there is still much room for improvement in Venus gravity modeling.
    Keywords: ASTRODYNAMICS
    Type: AAS PAPER 91-392 , AAS/AIAA Astrodynamics Conference; Aug 19, 1991 - Aug 22, 1991; Durango, CO; United States
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  • 8
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    An improved Venus gravity field from Doppler tracking of the Pioneer Venus Orbiter and Magellan spacecraft (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A total of 365,000 Pioneer Venus Orbiter (PVO) S-band Doppler data points were fit in arcs ranging from one to four revolutions in length by estimating the spacecraft position and velocity, atmospheric density, and a solar pressure parameter at each arc epoch. The resultant converged PVO orbits were used to produce 194 information arrays for the Venus spherical harmonic coefficients complete to degree and order 21. A similar procedure was used to produce a second set of 72 information arrays for a 21 x 21 gravitational field from a limited, but global, sampling of Magellan S- and X-band data from cycles 1 and 2. The PVO and Magellan information arrays were combined and solved to obtain the 21 x 21 spherical harmonic expansion designated JPL-Venus Gravity Model 6A (VGM6A). The VGM6A harmonic field field produced significant improvements in the Doppler residual statistics obtained from field validation fits to both PVO and Magellan tracking data in comparison with alternative representations of Venus gravity.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 92-4666 , 1992 AIAA/AAS Astrodynamics Conference; Aug 10, 1992 - Aug 12, 1992; Hilton Head Island, SC; United States
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