Which is not a current satellite system?

The correct answer identifies L6A as not being a current satellite system. The designations used for satellite systems often reflect specific signal types or groups within established navigation satellite systems.

L6A is not recognized under current active satellite systems, which typically include common systems like GPS, GLONASS, Galileo, and BeiDou. These systems have known signals such as L1 C/A, which is a civilian GPS signal widely utilized and classified within the operational frequency bands of established navigation satellite systems.

L5C refers to a more advanced civilian signal also used in modern satellite systems, such as the modernized GPS, which aims to provide better performance for safety-critical applications. LC2 is another designation that relates to GPS signals under certain specifications.

The existence of these active signals indicates their implementation or planned operation within one of the global navigation satellite systems. Therefore, L6A does not align with the active systems currently functioning or planned for deployment, making it the correct choice for identifying a non-current satellite system.