Comms to rovers etc use store-and-forward protocols with pre-planning of when which node will be able to see which other node. (E.g. it's calculated when which dish on earth can send a signal that will be seen by a probe around e.g. Mars, and then when the probe can downlink to a rover on the surface, and when the replies can be transmitted)

Look into "Delay-tolerant networking" for more details.