Project Orion was a proposal to propel spaceships by means of pulsed nuclear explosions. It had the support of Freeman Dyson, Werner von Braun, Stanislaw Ulam and other physicists and rocket scientists, but was abandoned by the Air Force in 1959 and rendered illegal by the Test Ban Treaty of 1963.
Click on Project Orion: Its Birth, Death and Possible Rebirth for details.
Asteroid mining would be a means of making space exploration economically self-sustaining. Click on Space Future: The Technical and Economic Feasibility of Mining the Near-Earth Asteroids for the argument that this is practical.
Click on PlanetQuest: The Search for Another Earth for NASA’s report on the discovery of planets in other solar systems.
Click on Nomad planets: stepping stones to interstellar space? for one possible way interstellar travel could be feasible.
When I was a teenager in the late 1940s and early 1950s, I took it for granted that by 2012, there would be human colonies on the Moon and Mars. I thought Robert A. Heinlein’s Future History was a plausible scenario for what would happen. I’m no longer sure colonization of the Solar System is feasible, let alone sending starships to other solar systems. All I can say is that I would like to think it is possible for humankind can venture out into the rest of the universe, and I think the possibility is worth exploring.
Newt Gingrich is regarded as a crackpot for advocating a mission to Mars, but not for advocating an attack on Iran. The latter would be at best a monstrous crime, the former at worst a glorious folly.
Click on xkcd for more cartoons.