Ever since we imagined the technological sophistication to send ourselves hurtling at escape velocity away from the Earth and toward some unknown pinprick of light in the unending vacuum of open space, obsessive individuals and paranoid governments have spent billions of dollars trying to figure out how to get as far away from our home planet as possible. So far, we haven’t accomplished much, cosmically speaking.
The history of rockets, up until recently, has always been chemical: a reaction takes place at explosive speed, and there, you have your propulsion and propellant. Ion engines, which accelerate electron-stripped atoms through an electric field, have been in use since the 70s, but they only work in the vacuum of space and have very low thrust that can’t be adapted to quick human space travel. As for the next big thing, the general idea that the American government has run with for the past 70 years—from Project Orion to Project Longshot to Project Prometheus—has involved strapping small nuclear bombs to the backs of rockets and hoping for the best. Needless to say, none of these have ever been built or are likely ever to be built; they were dreamed up with a future civilization in mind, one that had conquered the problems of nuclear fusion and international cooperation but still had no control over the Earth’s inevitable solar doom — let alone the effects of climate change that even the ultra-rich can’t escape, at least until they find a way to peace out and leave us to foot the bill.
If you’re wondering why taking a trip to another star is incredibly difficult, blame physics. Conservation of momentum (or Newton’s third law, depending on how you want to look at it) requires a rocket to poop out some amount of mass at some speed (AKA explosive fuel) for the rocket to move. The sticking point is that the fuel still has to push the remaining fuel still unpooped and connected to the payload. This predicament can be turned into a formula that relates the change in speed to the amount of mass pooped out. It’s called the Tsiolkovsky rocket equation, named after the father of modern rocket science. It can tell you that if you have a chemical propellant and you’re going to eject your fuel at, say, the maximum velocity of a nuclear fireball — around 100 km/s — and you want to travel 4.25 light-years over to Proxima Centauri, you’re going to need to have ten thousand trillion trillion trillion trillion times more fuel than payload if you want to get there in around one hundred years. Not to mention that we’d need double the fuel and time to slow down enough to take data from or drop passengers near the star. For a 1 kg payload, the fuel would roughly account for the entire mass of the universe.
Very good article. But he neglects a couple of important things. Physics is still evolving. We don't know everything. And others are coming here, so they've obviously figured out how to do it. To read more, click here.