Say at some point the human race gets its act together and actually decides to send a spaceship to another star. We’ll say it’s unmanned because that makes everything so much easier; it’s just a robot probe that’s intended to sate our curiosity about what Alpha Centauri actually bloody looks like, and so we don’t need any life support systems or generation ship malarkey going on. We’ll also say that getting the probe out of the Earth’s gravity well – aka the trickiest part of spaceflight – is similarly not an issue because we’re building it in orbit or something. This leaves us just one, fairly major problem: how do we make it go?
