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  • 1
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    Gravity field of Venus - A preliminary analysis (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The gravitational field of Venus obtained by tracking the Pioneer Venus Orbiter is examined. For each spacecraft orbit, two hours of Doppler data centered around periapsis were used to estimate spacecraft position and velocity and the velocity residuals obtained were spline fit and differentiated to produce line of sight gravitational accelerations. Consistent variations in line of sight accelerations from orbit to orbit reveal the presence of gravitational anomalies. A simulation of isostatic compensation for an elevated region on the surface of Venus indicates that the mean depth of compensation is no greater than about 100 km. Gravitational spectra obtained from a Fourier analysis of line of sight accelerations from selected Venus orbits are compared to the earth's gravitational spectrum and spherical harmonic gravitational potential power spectra of the earth, the moon and Mars. The Venus power spectrum is found to be remarkably similar to that of the earth, however systematic variations in the harmonics suggest differences in dynamic processes or lithospheric behavior.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 205; July 6
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Secular acceleration of Phobos and Q of Mars (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Reductions of Mariner 9 TV data of Phobos and Deimos tend to corroborate the existence of a secular acceleration of Phobos commensurate with two recently reported values based on a reprocessing of earth-based data. These values of secular acceleration have been used together with Mariner 9 data on the physical size of Phobos and earth-based photoelectric observations which infer a carbonaceous composition for Phobos to place upper and lower bounds of 50 and 150, respectively, on the tidal dissipation function of Mars. The corresponding upper and lower bounds on the tidal lag angle are 0.19 and 0.57 deg.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 27; Jan. 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Quantitative mass distribution models for Mare Orientale (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Six theoretical models for the mass distribution of Mare Orientale were tested using five gravity profiles extracted from radio-tracking data of orbiting spacecraft. The models with surface mass and moho relief produced the best results. Although there is a mascon-type anomaly in the central maria region, Mare Orientale is a large negative gravity anomaly. This is produced primarily by the empty ring basin. Had the basin filled with maria material it seems likely that it would have produced a mascon such as those presently existing in flooded frontside circular basins.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Science Conference; Mar 15, 1976 - Mar 19, 1976; Houston, TX
    Format: text
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    NASA TECHNICAL REPORTS
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