This is a master’s project report submitted to the mechanical engineering department of the University of Hawaiʻi at Mānoa. It discusses the design and simulated performance of the Attitude Determination and Control Subsystem of a 3U cube satellite named Hoʻoponopono (H2). H2 was developed at the UH Mānoa College of Engineering’s Small-Satellite Laboratory. Its mission was to aid in the radar calibration process of U.S. Air Force radar stations by providing a calibration source in orbit. Its gravity-gradient ADCS was designed to point H2 in the nadir direction for the entirety of its mission lifetime. The unique issues associated with achieving gravity-gradient stabilization is discussed. To ensure that the functionality and performance requirements were satisfied, the Nanosatellite Attitude Dynamics & Determination Simulator (NADDS) was developed and used to determine the energies and times required for H2 to achieve nadir pointing.