In a time division multiple access spacecraft communication system, each ground station determines when to send its information packets to arrive at the spacecraft at the beginning of a time slot. The calculation is based upon knowledge of the locations of the spacecraft and the transmitting ground station....http://www.google.de/patents/US5878034?utm_source=gb-gplus-sharePatent US5878034 - Spacecraft TDMA communications system with synchronization by spread spectrum overlay channel
