Because they are inexpensive platforms for satellites, CubeSats have become a low-cost way for universities and even developing countries to have access to space technology. This paper presents the ITASAT design, particularly the Attitude Determination and Control Subsystem, the Onboard Software, and the Assembly, Integration and Testing program. The ITASAT is a 6U CubeSat nano-satellite in development at the Instituto Tecnologico de Aeronautica, in Sao Jose dos Campos, Brazil. The platform and its subsystems will be provided by industry while the payloads are being designed and developed by the principal investigators. The ITASAT Attitude Determination and Control Subsystem will rely on a 3-axis magnetometer, 6 analog cosine sun sensors, 3-axis MEMS gyroscopes, 3 magnetic torque coils, and 3 reaction wheels. The Attitude Determination and Control Subsystem operating modes, control laws, and embedded software are under the responsibility of the Instituto Tecnologico de Aeronautica. A Kalman filter shall be employed to estimate the quaternion attitude and gyroscope biases from sensor measurements. The Attitude Determination and Control Subsystem operating modes are the nominal mode, with geocentric pointing attitude control and the stabilization mode, in which only the satellite angular velocity is controlled. The nominal mode will be split into 2 sub-modes: reaction wheel control plus magnetic wheel desaturation and 3-axis magnetic attitude control. Simulation results have shown that the attitude can be controlled with 1-degree accuracy in nominal mode with the reaction wheels, but these errors grow as much as 20 degrees or higher with the 3-axis magnetic control. ; Inst Nacl Pesquisas Espaciais Engn, Sao Jose Dos Campos, SP, Brazil ; Tecnol Espaciais Div Mecan Espacial Control, Sao Jose Dos Campos, SP, Brazil ; Inst Tecnol Aeronaut, Dept Ciencia & Tecnol Aeroespacial, Div Engn Aeronaut, Praca Marechal Eduardo Gomes 50 Vila Acacias, BR-12230901 Sao Jose Dos Campos, SP, Brazil ; Univ Fed Sao Paulo, Inst Ciencia & Tecnol, Dept Ciencia Computacao, Sao Jose Dos Campos, SP, Brazil ; Univ Fed Sao Paulo, Inst Ciencia & Tecnol, Dept Engn Computacao, Sao Jose Dos Campos, SP, Brazil ; Inst Tecnol Aeronaut, Dept Ciencia & Tecnol Aeroespacial, Div Engn Eletr & Computacao, Sao Jose Dos Campos, SP, Brazil ; Univ Fed Sao Paulo, Inst Ciencia & Tecnol, Dept Engn Computacao, Sao Jose Dos Campos, SP, Brazil ; Web of Science