Tethers Unlimited, Inc. proposes to develop the PowerCube, an integrated power, propulsion, and pointing solution for CubeSats. The PowerCube combines three innovative components: a high-power deployable solar array able to provide up to 100W peak power to the CubeSat, a regenerative fuel cell energy storage system that doubles as a gH2/gO2 thruster, and a 'carpal joint' gimbal that enables sun pointing of the solar panel as well as precise pointing of payloads. This highly integrated system will provide power generation, power storage, propulsion, attitude control, and payload pointing capabilities that will enable the CubeSat platform to be used to perform missions previously possible only on much larger platforms. Our Phase I effort will focus on design and implementation of the regenerative fuel cell/thruster component, with the objective of maximizing orbit average power capabilities, and in the Phase II effort we will combine this power storage/propulsion technology with deployable panel and gimbal technologies we are currently developing under a separate program to create the PowerCube system. This highly-integrated, compact subsystem will provide order-of-magnitude performance improvements in several metrics for CubeSats, enabling this low-cost platform to perform challenging science and exploration missions that previously could only be accomplished by much larger spacecraft.