To explore the depths of the hydrocarbon rich seas on the Saturn moon Titan, a conceptual design of an unmanned submarine concept was recently developed for a Phase I NASA Innovative Advanced Concept (NIAC) study. Data from Cassini Huygens indicates that the Titan polar environment sustains stable seas of variable concentrations of ethane, methane, and nitrogen, with a surface temperature around 93 K. To meet science exploration objectives, the submarine must operate autonomously, study atmosphere/sea exchange, interact with the seabed at pressures up to 10 atm, traverse large distances with limited energy, hover at the surface and at any depth within the sea, and be capable of tolerating multiple different concentration levels of hydrocarbons. Therefore Titan presents many cryogenic design challenges. This paper presents the trade studies with emphasis on the preliminary design of the power, thermal, and ballast control subsystems for the Saturn Titan submarine.