The control of the orientation of a spacecraft. The position of stars is used to calculate this, and attitude is maintained by the attitude and orbit control subsystem (AOCS). This employs control moment gyroscopes or other stabilizers to measure a spacecraft's attitude, and uses a computer program to correct problems via the thrusters, turning the spacecraft through a roll, pitch, or yaw angle. The AOCS also controls and maintains the spacecraft's orbit by the use of thrusters.