[mrsmith]

An adjunct to the "propulsion is the only thing" argument:
I wonder how much the "risk" of advances in propulsion deters investors?

Present schemes for space profit envision 20 to 30 year payoff periods.
Any project built at 10k per KG wouldn't be able to compete against one built at say, 1k per kg.

An intra-solar nuclear rocket is an all-around good idea.

[RightWhale]

Present schemes for space profit envision 20 to 30 year payoff periods.

I would call them business plans rather than schemes, but your estimate of time to payoff is reasonable. First delivery of material mined from asteroids would be 20 years from project start if all goes well. Would your credit union would be interested?

[Project Orion]

http://www.projectorion.com

http://www.angelfire.com/stars2/projectorion/orionpage.html

http://www.projectorion.org/