The aviation industry has been challenged to increase the sustainability of its technologies, which is the main driving force in research and exploration of fully electrified propulsion. This paper presents the initial steps in the design and modeling of the Cryogenic High-Efficiency Electrical Technologies for Aircraft (CHEETA) that would form the basis for hybrid-electric aircraft power systems. To this end, different power system configurations for fully electrified propulsion are proposed and analyzed. Novel, multi-domain components used in both the power system model and the cryogenic thermal system model are introduced and explained in detail. This paper also presents initial results for the different power system configurations under steady-state conditions.