This paper presents an attitude control method using quaternions as feedback attitude errors. The Euler's eigenaxis rotation provides the shortest angular path between two attitudes. This eigenaxis rotation can be achieved by using quaternions since quaternions are related with the eigenaxis. The suggested controller uses error quaternions and their integrations, body angular rates to generate a decoupling control torque that counteracts the natural gyroscopic coupling torque. A 4-reaction wheel cluster is considered as a control torque actuator and the momentum dumping strategy using the earth magnetic field is also applied to unload the angular momentum of the reaction wheels.
