"The Prescient answered, Fusion Engines."
The biggest of all fusion reactors? The Sun.
Public DomainThe biggest of all fusion reactors? The Sun. - Credit: NASA Goddard Laboratory for Atmospheres

Fusion power is created when two atomic nuclei fuse together, causing the release of huge amounts of energy. This kind of power has yet to be harnessed, largely due to a lack of scientific understanding and an inability to contain the reaction within safe parameters. No commercially available nuclear engine is expected before 2050, however, its potential as a source of renewable energy is regarded to be enormous. Cars would be able to travel at twice their current maximum speeds and some experts believe that fusion power could provide the earth's energy needs for millions of years. Deuterium, the main fuel in the reaction, is abundant within the ocean and unlike some renewable resources (e.g. solar power and wind power) would provide an uninterrupted source of energy.