One of the most feasible, yet controversial, methods of powering spacecraft on long journeys is by using nuclear energy. Our current chemical engines produce relatively little power. They have to make use of planetary alignments, or 'launch windows', to provide an extra gravitational slingshot effect, helping to catapult them further out into space. Nuclear rockets would be more powerful and wouldn't need to take advantage of these chance planetary patterns.

            There are two types of possible nuclear rockets, utilizing the different types of nuclear reactions: fission, when atoms split apart; and fusion, when they join together. Nuclear plants on Earth produce energy from nuclear fission and the technology needed to build a rocket powered by fission is not far beyond our current means. In fact, they could fly within the next ten years.

            Rockets run by nuclear fission are more fuel efficient, and so much lighter than chemical rockets. This means that nuclear spaceships could travel twice as fast as our current chemical spacecraft. A nuclear powered craft could reach Saturn in as little as three years, rather than the current journey time of seven years. What's more, because the fuel lasts longer, the spacecraft would still have enough energy left to tour the Solar System for up to 15 years.