Coming from a military background, I used the acronym C2 for "command and control." It has nothing to do with boosters except perhaps in the cruise phase to Mars, should they change the design to send multiple MERs on a single bus.

The C2 I have in mind deals with command and control of the rovers on Mars. Without a good communications relay system like the proposed Mars Network, each rover requires a fair amount of support by the Deep Space Network at a time when there are several other deep space missions (e.g. Cassini) that also need DSN antenna time. A properly implemented Mars Network system could accept uplinks from several rovers and relay all of the data to a single DSN antenna.

If you have 4 MER-type rovers on Mars, you're going to need a more personnel to operate them than is currently available. JPL may be able to streamline the crew size somewhat but it has to be more than they have today. You'll also probably need to upgrade the ground computer systems to handle the increased workload.

Related Military Acronyms:
C2 - command and control
C3 - command, control, and communications
C4 - command, control, communications, and computers
C3I - command, control, communications and intelligence
C4I - command, control, communications, computers and intelligence
C4ISR - adds surveillance and reconnaissance to C4I