ADCS

During the early phase of the launch, the satellite carries some rotation about its center of gravity relative to earth. An Attitude Determination and Control System (ADCS) orients the satellite in a manner such that maximum solar energy is incident on solar panels. Also during imaging satellite has to point at a fixed point on earth in order to capture better images. From communication point of view, control of the attitude is necessary so that the antennas, which have narrow beams, are pointed correctly towards the earth.

A number of factors tend to cause the spacecraft to rotate. Gravitational forces from the sun, moon, and planets set up rotational moments if the satellite is not properly balanced. Solar pressure acting on the antennas, satellite body may also create rotational forces. Also, magnetic fields create disturbances. Since the satellite moves around the earth's center in its orbit, the forces described above vary cyclically. This tends to set up nutation (wobble) of the satellite, which must be damped.