Humanity has been in space for a while, but we really haven’t managed to go very far. Carl Sagan once said that "the surface of the Earth is the shore of the cosmic ocean, and recently we’ve waded a little way out, maybe ankle deep"—that was in 1980, and we haven’t risked testing the water any deeper since then.

read the complete article: Engine in development could cut Mars travel time to three months | Ars Technica.