Depending on its orbit, the satellite may be in contact with the ground almost all of the time, sending data via its antennas so that the control centre can keep track of operations. In turn, ground controllers regularly uplink commands to reconfigure the onboard computer or equipment.
To accomplish their mission, get enough power and communicate with Earth, the satellite’s instruments and antennas must maintain a precise orientation in space, which is obtained by rotating the bus. Satellite positioning and stationkeeping operations also involve performing orbital manoeuvres.
|Le saviez-vous ?|
Turn left at the star|
Seen from the ground, a satellite is just a dot in the sky. It is impossible to determine its attitude, or orientation, directly. For this reason, it is equipped with star sensors or star trackers able to measure their position with respect to the Sun, certain stars or a point on Earth. On the basis of this positional information, we can calculate the satellite’s orientation.