Efficient Spacing of Synchronous Communication Satellites

When a satellite is in an orbit whose period is equal to that of the earth's rotation, it is said to be synchronous. A satellite in a synchronous, circular, equatorial (in the plane of the equator) orbit will appear stationary when viewed from the earth. The number of such satellites that can be used in a communication system in the same frequency band is limited by the directivity of the ground-based antennas. 1 The maximum number would be obtained by spacing them equally, at an angular separation just sufficient to keep crosstalk clown to a tolerable level. If the synchronous orbit is inclined to the equator, a satellite will no longer appear stationary when viewed from the earth, but will appear to move in a figure 8. By placing several satellites in a single 8, and spacing different 8's regularly along the equator, a greater number of synchronous communication satellites can be used than with an equatorial orbit alone. 2379 2418 T H E BELL SYSTEM T E C H N I C A L J O U R N A L , DECEMBER I!)