“Unless you can get the Amish to be space family Robinsons, i think the second might have more chance of success!”
Back in 1966 I was invited to attend a professor’s evening conference at his university in which the topic of discussion was interstellar space travel. It took some time, effort, and expense to travel to that university; so, I was more than a little annoyed by what happened. The professor started the event by asking the question and then ran a ten minute diatribe and litany of ridicule against the very idea such a possibility could even be suggested. He then proceeded to change the discussion to the completely unrelated discussion of Carbon tetrachloride and related chemistries for the remainder of the conference.
To maintain decorum I had to remain silent, but it later proved to be an experience which ably demonstrated the poor caliber of this large public university and its academics.
Suffice it to note the professor demonstrated his utter want of knowledge and commonsense. Interstellar space travel by humans is very possible with technologies little better than what was available in 1966 or now in 2015. The only catch is that doing so will require multiple human lifetimes aboard an asteroid that has been converted into a permanent human habitat for a large human population. Furthermore, once humans have learned to survive and prosper indefinitely in asteroidal habitats, it is unlikely that humans will see much need to colonize planets except to maintain outposts to extract useful resources.
The asteroids in the Solar System are sufficient in number, size, and resources to support a total human population numbering in the trillions of people. Long after the Sun has expanded in size to become a red giant star and destroyed Mercury, Venus, and perhaps the Earth as well, the human colonies among the asteroids can remain safe and prosper farther out in the Solar System. Any human communities who choose to accept the risks and the separation from the rest of the human societies due to conflicts or simply for a desire for discovery can slowly accelerate their asteroid or asteroids to the escape velocity necessary to begin an interstellar journey. Along the journey to another star, the voyagers may discover a number of starless rogue planets and asteroids along the way.
Upon arrival at another star system the travelers may choose not to decelerate their asteroidal ship to orbit the star or a planet in that star system. Instead, they would likely send out spacecraft to explore anything of interest as the asteroid passes through the star system on its perpetual journey through interstellar space. The exploerers would have little reason to stay in the other star system unless it was to colonize its asteroids as had been done before in the Solar System.
The principal risks to the human populations living among the asteroids would be disease and pandemics resulting from the development of diseases without the development of corresponding immunities.
The risk is also "tribal" warfare, as unless committed to and unified under a purpose, and proven moral code and government, including a judiciary, they will realize the same conflicts they may have wanted to escape, and worse, and with more destructive consequences.