The ultra-long duration balloon (ULDB) Pathfinder Project is developing a small pumpkin balloon system and a new communication package based on the iridium satellites technology to demonstrate a global, 100-day duration capability that is scalable to the full-scale ULDB. A set of trade studies has been conducted to determine the volume, mass and cost of the balloon system to support up to 90 kg payload mass to an altitude of 35 km. The Pathfinder test balloons will provide valuable data in the development of performance models for future ULDB flights. The iridium based communication package will include a power subsystem, a command and data-handling unit, a GPS receiver, and an iridium L-Band Transceiver (LBT) for global communications. The flight data will include, at a minimum: latitude, longitude, altitude, horizontal and vertical speeds, heading, time, and other balloon performance parameters (i.e., system voltages, temperatures, etc.). Although the system will be designed for global launch capability, initial flights will be launched from the proposed full-scale ULDB mission launch locations. This paper will present and discuss the initial series of trade studies conducted for the development of the pathfinder balloon and the design concept of the iridium based communication package.