[redthrowaway]

Why send humans at all? By that time I'd assume we'd have reasonable AI; just send it along with a bunch of frozen embryos anywhere you please. The AI can incubate and raise the children. It could even terraform the planet until it was habitable. You wouldn't even need to explore; just send out probes willy-nilly. If they never reach a suitable location, then it's no big loss.

A fire-and-forget method of human space colonization is not only far more feasible, but also far more economical.