Attitude Control System (ACS)

• There are two ways to make a satellite stable in orbit: 1) Spin stabilization, 2) Three axes body stabilization.

• Spin stabilization is most commonly used method, the body of the satellite is rotated at a rate between 30 to 100 rpm. This creates a gyroscopic effect, which makes the spin axes point in the same direction. Satellite using spin stabilizations for attitude control are called spinners. Hughes 376, which is called Boing 376 now, is an example of a spinner satellite. Cylindrical shaped satellites uses spin stabilization.

• A misbalanced satellite may display its motion on any of the three axes called Yaw, Roll and Pitch axes. If the satellite is stabilized about these three axes, then the stabilization is called three axes body stabilization. Satellite using three axes body stabilization for control is termed as three axes body stabilized satellite. Hughes (Boing) 701 is an example of three axes body stabilized satellite.

• The position of a GEO satellite and its stabilization with respect to the three axes are shown in fig4. Yaw axis is towards the earth’s centre and the Pitch axis is normal to the orbital plane.