When the aircraft's SDU responds to messages sent from the ground station, it uses the aircraft's navigation system to determine the aircraft's position, track, and ground speed and adjusts the transmit frequency to compensate for the Doppler shift on the uplink signal, based on the satellite being located in its nominal position in geostationary orbit (35786 km above the equator) at 64.5°E. 24 11 The initial analysis was calculated with the satellite at its nominal location in geostationary orbit, 35786 kilometers above the equator at 64.5°E longitude.