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The Determination of Titan Gravity Field from Doppler Tracking of the Cassini SpacecraftIn its tour of the Saturnian system, the spacecraft Cassini is carrying out measurements of the gravity field of Titan, whose knowledge is crucial for constraining the internal structure of the satellite. In the five flybys devoted to gravity science, the spacecraft is tracked in X (8.4 GHz) and Ka band (32.5 GHz) from the antennas of NASA's Deep Space Network. The use of a dual frequency downlink is used to mitigate the effects of interplanetary plasma, the largest noise source affecting Doppler measurements. Variations in the wet path delay are effectively compensated by means of advanced water vapor radiometers placed close to the ground antennas. The first three flybys occurred on February 27, 2006, December 28, 2006, and June 29, 2007. Two additional flybys are planned in July 2008 and May 2010. This paper presents the estimation of the mass and quadrupole field of Titan from the first two flybys, carried out by the Cassini Radio Science Team using a short arc orbit determination. The data from the two flybys are first independently fit using a dynamical model of the spacecraft and the bodies of the Saturnian system, and then combined in a multi-arc solution. Under the assumption that the higher degree harmonics are negligible, the estimated values of the gravity parameters from the combined, multi-arc solution are GM = 8978.1337 +/- 0.0025 km(exp 3) / s(exp 2), J (sub 2) = (2.7221 +/- 0.0185) 10 (exp -5) and C (sub 22) = (1.1159 +/- 0.0040) 10 (exp -5) The excellent agreement (within 1.7 sigma) of the results from the two flybys further increases the confidence in the solution and provides an a posteriori validation of the dynamical model.
Document ID
20080012651
Document Type
Conference Paper
Authors
Iess, L. (Rome Univ. Rome, Italy)
Armstrong, J. W. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Aamar, S. W. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
DiBenedetto, M. (Rome Univ. Rome, Italy)
Graziani, A. (Bologna Univ. Italy)
Mackenzie, R. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Racioppa, P. (Rome Univ. Rome, Italy)
Rappaport, N. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Tortora, P. (Bologna Univ. Italy)
Date Acquired
August 24, 2013
Publication Date
September 24, 2007
Publication Information
Publication: Proceedings of the 20th International Symposium on Space Flight Dynamics
Subject Category
Spacecraft Design, Testing and Performance
Distribution Limits
Public
Copyright
Public Use Permitted.

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IDRelationTitle20080012629Analytic PrimaryProceedings of the 20th International Symposium on Space Flight Dynamics