Robert Zubrin has been argueing for a Mars mission based on living off the land and other design principles. He's shown that we can get to mars for comparative inexpensive price(500 Billion dollars) without nuclear; now, imagine what one can do with nuclear propulsion? This is how I've felt about the Zubrin Mars Direct plan. We have the means to do nuclear propulsion; this isn't 'unobtaineum.' Nuclear energy for space energy is what can open up the solar system frontier anyways(it can open up the path to the stars; but, even then, maybe anti-matter or even a laser solar sail would be better!).