I have seen a lot of bits about why interstellar travel may never be practical. All of them seem to assume not only travel in the flesh, but round-trip travel. Realistically, by the time we can build something that can travel to the stars, it seems quite likely that we also can download conciousness into a robot. Send a robotic (one-way) mission to build bodies and transmission equipment, then have the real travellers download themselves, or copies of themselves, via radio. No need for life support or suffer through the boredom of even relativistic travel.