Zubrin is an aeronautical engineer at Martin Marietta, Wagner the former editor of the National Space Society's magazine, Ad Astra, and together they make a forceful argument for the exploration and settlement of Mars. Zubrin has long advocated the ""Mars Direct"" plan, which could get off the ground for $30 billion, in contrast to the $450-billion Space Exploration Initiative (SEI) timidly proposed by President Bush and quickly torpedoed in Congress. SEI was to take 30 years and make use of a space station (where components of the mission would be assembled), and it featured elaborate safety plans. But this is the frontier, Zubrin says, and risk is inherent when we venture forth. The most radical feature of the Mars Direct plan is the manufacture of propellants (for getting around while there and for getting back) on the surface of Mars by an unmanned module before the arrival of astronauts. But Zubrin and Wagner's discussion makes this idea, and the plan in general, seem reasonable rather than radical, and their plan would clearly save money. A mission that doesn't have to carry return fuel could use rockets that already exist, such as the Russian Energia. Mars Direct would also utilize conjunction trajectories (that is, launches when Mars is in line with Earth outward from the sun), avoiding the opposition trajectories the SEI plan advocated, and it allows for much more time to be spent exploring the surface of Mars. The authors are propagandists, so dismissive of NASA's plans that they call them ""silly,"" but they are persuasive and even demonstrate a shrewd grasp of political realities, going so far as to incorporate Newt Gingrich's thinking with regard to privatizing the Mars Direct mission. With exposure on CNN, a vigorous presence on the Internet, and a new groundswell of support at NASA, this plan may well prove to be the one, at long last, to fly.