The Puppet Master (PM) claims through the Smug package drop and the WORMS book, that ZEUS is a low earth orbit satellite, capable of both imaging and delivery of FM or AM audio messages to a ground target on the earth's surface equal to or greater than 6 metres (600 cm) in diameter; for reception by commodity receiver (meaning any commercially available radio); for the purpose of delivering messages and encoding key-space.
It is believed that an orbiting platform, whether equipped with advanced (phased array) antennas, or not, would be incapable of delivering a transmission beam to the earth surface of only 600 cm, so it is assumed that ZEUS messages will be delivered by hidden FM transmitters (much like MP3 player transmitters used in cars), placed as though they were dead-drops and precisely timed to transmit a given message, during the allocated time-slot.
It has be eluded to by a former GCHQ Cryptanalyst that 'ZEUS' may refer to the code-name of an an 'old-hat' satellite system. This would presumably include all pre-early-1990s systems. However, while the name may be similar, it can't be assumed that they are one and the same.