A theoretical space craft is under development that would be able to achieve speeds up to around 10% of the speed of light.
Powered by plasma directed through a magnetic nozzle, the Mini-Mag Orion is proposed as a method of exploring the solar system in relatively short time frames. The system could be used to reach Jupiter with a 100 tonne payload in a around a year.
The Advanced Nanotechnology blog has examined the numbers required to achieve this and has concluded that some areas are open to refinement. This includes the use of carbon nanotubes in some components to reduce their weight to only 10% of the original part.