You are not logged in.
if you were really smart, you would make the landers powered by NERVA's, and use them to push the return propellant supply to Mars. All 3 vehicle configurations get smaller when you do that. You get to pay less and make more landings while there.
I'm in full agreement with you on the landers. A Mars lander powered by a NTR could obtain its own propellant for hops over the planet, or a boost back into Mars orbit via subsurface water depots. You could lower the overall cost for a return trip by refueling at mars. (Ofc this only works with NERVA designed engines - as mentioned above -, which would be orders of magnitude easier to refuel; trying to refuel chemical engines at mars without the infrastructure would be much harder)
No rover will ever drive supersonic, so ram jet is not a solution.
He was thinking in terms of aircraft - not a rover.
As GW mentioned, a ramjet engine is an attractive option for Mars - in terms of air breathing propulsion; they have been known to operate efficient sustained flight on earth at heights up to 80k - 85k feet (I imagine one could be designed to operate even higher) - NASA has a concept for an ionospheric ramjet - able to operate above 100km - point being, a ramjet can be designed to work perfectly fine in the thin martian atmosphere. The issue is getting the ramjet up to mach .5 - 1 just so it can start, and mach 3 to achieve the best efficiency (as you know simple ramjets can't take off, land, or work at slow speeds).