A three-axis magnetometer, redundant solar aspect sensors and an IR earth sensor are used for attitude determination. Attitude determination is done on the ground from sensor collected at the optimum location along the orbit and stored in an onboard memory. An attitude vector is determined at least once a day. However, because of the long wire booms the satellite is subject to strong gravity-gradient torques, so the spin vector drifts a few degrees per day. Therefore, interpolation between consecutive attitude vectors is required.
Redundancy is used whenever possible.