Paragon Space Development Corporation proposes an Ellipsoidal Propellant Tank (EPT) innovative pressure vessel designed to provide the lowest cost and mass solution to the long-term containment of cryogenic fluids. The design is based on Thin Red Line Aerospace’s (TRLA) Ultra-High Pressure Vessel (UHPV) technology which has the highest specific strength of any competing design. In EPT, a cryogenic propellant tank design was matured to demonstrate a 500+ psig system with a factory of safety of 2.5. Fluid barrier materials exhibit low helium leak rates and can be used in a launch configuration or launched in a stowed configuration for on-orbit or planetary deployment for use in propellant depot, propellant storage for long-duration exploration missions, and for such innovative uses as surface cryogen storage on the Moon. Results from this effort indicate a more mass efficiency and volume efficient design that utilizes 73% of required volume envelope as compared to 66% for traditional spherical tanks. Additionally, EPT exhibits masses at 70% of the current NASA counterpart with a baselined polar bulkhead design. System integration of EPT based on current SOA tanks was evaluated for integration, as well as bulkhead analysis and pressure restraint analysis. These efforts informed a barrier layer demonstrator design for the EPT which we then evaluate through helium coupon leak testing to validate the barrier materials selection and manufacturing process. The results of Phase I provide feasibility demonstration of the materials and processes to provide a helium leak tight barrier and an overall pressure vessel design for Phase II prototyping and test. Future efforts will mature bulkhead design for greater reductions in mass, system integration, and the barrier laminate. Additionally, thermal management will be evaluated with integration of traditional MLI and our CELSIUS, expandable, deployable, high mass efficiency MMOD/MLI system previously funded by NASA.