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Evidence of Temporal Variation of Titan Atmospheric Density in 2005-2013One major science objective of the Cassini mission is an investigation of Titan's atmosphere constituent abundances. Titan's atmospheric density is of interest not only to planetary scientists but also to mission design and mission control engineers. Knowledge of the dependency of Titan's atmospheric density with altitude is important because any unexpectedly high atmospheric density has the potential to tumble the spacecraft during a flyby. During low-altitude Titan flyby, thrusters are fired to counter the torque imparted on the spacecraft due to the Titan atmosphere. The denser the Titan's atmosphere is, the higher are the duty cycles of the thruster firings. Therefore thruster firing telemetry data could be used to estimate the atmospheric torque imparted on the spacecraft. Since the atmospheric torque imparted on the spacecraft is related to the Titan's atmospheric density, atmospheric densities are estimated accordingly. In 2005-2013, forty-three low-altitude Titan flybys were executed. The closest approach altitudes of these Titan flybys ranged from 878 to 1,074.8 km. Our density results are also compared with those reported by other investigation teams: Voyager-1 (in November 1980) and the Huygens Atmospheric Structure Instrument, HASI (in January 2005). From our results, we observe a temporal variation of the Titan atmospheric density in 2005-2013. The observed temporal variation is significant and it isn't due to the estimation uncertainty (5.8%, 1 sigma) of the density estimation methodology. Factors that contributed to this temporal variation have been conjectured but are largely unknown. The observed temporal variation will require synergetic analysis with measurements made by other Cassini science instruments and future years of laboratory and modeling efforts to solve. The estimated atmospheric density results are given in this paper help scientists to better understand and model the density structure of the Titan atmosphere.
Document ID
20150008682
Acquisition Source
Jet Propulsion Laboratory
Document Type
Conference Paper
External Source(s)
Authors
Lee, Allan Y.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Lim, Ryan S.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
May 21, 2015
Publication Date
August 19, 2013
Subject Category
Astrodynamics
Lunar And Planetary Science And Exploration
Meeting Information
Meeting: AIAA Guidance, Navigation, and Control Conference
Location: Boston, MA
Country: United States
Start Date: August 19, 2013
End Date: August 22, 2013
Sponsors: American Inst. of Aeronautics and Astronautics
Distribution Limits
Public
Copyright
Other
Keywords
Atmosphere
Huygens Atmospheric Structure Instrument (HASI)
Cassini/Huygens
Density Structure

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