Journey to Deepest Space

Interstellar space travel is manned or unmanned travel between stars. Interstellar travel is much more difficult than interplanetary travel: the distances between the planets in the Solar System are typically measured in standard astronomical units while the distances between stars are typically hundreds of thousands of AU, and usually expressed in light years. Because of this some combination of great speed (some percentage of the speed of light) and huge travel time (lasting from years to millennia) would be required.