2012 IR&D Annual Report

TiME Discovery Phase A Science Support: Producing an Atmospheric
Engineering Model for Titan, 15-R8251

Principal Investigators
Hunter Waite
Jared Bell

Inclusive Dates:  08/19/11 – 12/31/11

Background — The Titan Mare Explorer (TiME) was the first mission proposed to land on an extraterrestrial sea. It represents a unique opportunity to explore Titan's methane cycle, a multi-phase planetary surface, and the limits of life. In situ exploration of a major sea is the essential next step for advancing our understanding of Titan and provides an unprecedented opportunity to engage the public in the excitement inherent in visiting a fascinating new environment on this alien world. TiME makes that possible — within the Discovery program and within the coming decade. The objective of this project was to generate a Titan atmospheric engineering model in support of the TiME. The model was used by NASA Langley engineers to design the descent and landing phases of the TiME mission and by NASA AMES engineers to simulate the aerodynamics of the spacecraft and heat shield. Previous Titan atmospheric engineering models were constructed to design the entry and landing of the ESA-Huygen's Titan lander (Yelle et al., 1997). However, the Cassini-Huygens mission has supplied a wealth of new data that must be incorporated into a new engineering model to support the TiME mission design. The model can serve as an engineering and science tool for the design of any future orbiter aerocapture or lander missions to Titan.

Approach — Titan's atmosphere has been extensively studied during the Cassini-Huygens Mission. The polar environment undergoes considerable seasonal variation and is distinct from the more quiescent equatorial environment experienced by the Huygens probe in 2005. The thermal structure of the upper atmosphere is affected by interaction of Titan's atmosphere with the plasma and energetic particles in Saturn's magnetosphere or in the solar wind. Titan's polar regions, and its hydrocarbon lakes in particular, are of interest for future exploration. Thus specific environmental models are required for polar exploration. Furthermore, the models developed to support the design of Huygens had to accommodate wide uncertainties, requiring large design margins. The extensive observations by the Cassini spacecraft (and indeed Huygens itself) provide a basis for narrowing these uncertainties, notably in composition.

Accomplishments — The empirically constrained neutral temperatures and densities presented here also have important implications for fundamental chemical modeling. Detailed chemical models, such as Krasnopolsky [2009, 2010], Wilson and Atreya [2004] among others, typically rely upon specified major neutral densities and temperatures. The empirical modeling presented here would provide much-needed constraints on these models, and thus lead to improved estimations of chemical products. This would, in turn, provide improved estimates for important science questions at Titan, such as (1) global production of aerosol haze particles, (2) estimates of the deposition of heavy hydrocarbons on the surface of Titan, and (3) better constraints for photoionization of the upper atmosphere. This paper describes a new model of Titan's atmospheric structure to guide both scientific studies and studies of entry and descent. Of particular interest is the proposed Titan Mare Explorer (TiME) mission in the period 2023–2025.

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