> But rather than explaining all this stuff, I think there's a 
  > better way: build, land and operate a rover here on Earth.

Is this implying that building a rover here would provide an explanation for their technical choices? With a 2kg payload limit for a balloon-launched rover, you might be better off with the latest technology. GPS on a chip rather than separate components making up GPS circuitry. Or a tiny, power-efficient mobile chip rather than some power-hungry chip from a decade ago.