NASA under the George W Bush Administration is going to put major work into a nuclear propulsion engine for future space flights. NASA wants to launch a mission to Pluto, but that planet will be out of position for a chemical rocket probe in a few years. Building a nuclear engine will give an extra decade or two. Such an engine would make unmanned orbital probes of the outer planets possible; chemical rockets can push only a small fly-by probe without the fuel mass to enter orbit. A manned nuclear spacecraft could reach Mars in only four months, compared to nearly a year for a chemically-powered craft. Such a powerful spacecraft could in theory make it possible for a manned spacecraft to reach (and redirect) a small asteroid into a continent-smashing weapon.--Stephen V Cole