122 - "On this I disagree. Chemical, ion, VASMIR, nuclear, etc. are just fine for planetary exploration and exploitation. "
Sorry, I can't agree. What can we 'exploit' when fuel costs $10,000 per pound of payload.
To 'expolit' anything in space we need something equivalent to the economics of the giant container ships. You can't haul or exploit very much in a rowboat.
You have to build the infrastructure first. Spending money on "anti gravity" and the like is not the path to take IMHO. If we used lunar mass drivers as an example, getting material into orbit becomes far easier than from the gravity well we inhabit.