Iridium TTC Ground Station Number and Location Optimization

The commercialization of space missions has led to the need for cost minimization in order to make these ventures commercially viable. In the past, commercial space systems have generally consisted of a single satellite in a geo-stationary orbit. Command and control of these systems required only a single ground station and cost was not an issue. However, with the crowding of the geo-stationary belt and the desire for truly global wireless communication, companies have now begun developing mission concepts using proliferated low Earth orbit (LEO) satellite systems. These systems cannot be commanded by a single ground station. Therefore, in order to minimize cost for the system, the minimum number of ground stations required for command and control operations must be determined. This paper develops a method for determining the minimal number of ground stations required to command and control Motorola's iridium satellite constellation during the mission phase. The method relies on the use of the iridium satellites' ability to communicate with other satellites in the system, that is the satellites' cross-link abilities. Using a computer model, the method will determine which satellite is currently in view of a given "candidate" ground station position. Then, based on delay time for ground station processing and satellite processing, the method will determine how many satellites the current ground station could command using satellite cross-links. It does this for every latitude and longitude position until it finds the position that can command the most satellites in the system. From there, the method determines the next ground station position in the same manner, until all the satellites have been commanded. Limitations of the given method as well as generalizations that can be made to the method in order to determine the minimal number of ground stations required for normal operations of any proliferated LEO satellite system are discussed.