What is the best radio protocol for long range serial communication?
What is the best radio protocol for ... distance of upwards to 80M km? 


For that distance, people use ISDCS protocols.


  The long-haul standards are the internationally-agreed CCSDS “Packet Telemetry” and “Packet Telecommand”, which respectively permit the fully-standardized communication of spacecraft measurement and control information. These protocols have been specifically tailored to provide very high performance over weak, long-delay radio channels.


Ref

Obviously, to get "near-time (&lt;= 3 mins)" comms - you have to wait for Mars to get a bit closer.