Whether you're a marathon runner, a dayvan cowboy or an interstellar spaceship, you're going to need to refuel along the way. Marathoners can just reach out and accept a cup of water from volunteers, and countless gas stations await pit stops from road-tripping van enthusiasts. But just where's a star ship supposed to tank up on fuel? The fusion runway concept offers one possible answer.
I chatted with Tau Zero Foundation writer Paul Gilster on just this topic the other day and yes, scientists have given some serious thought to the fuel woes of interstellar travel. Space is vast and life is short, so we have to figure out how to traverse extraordinary distances in a limited period of relativistic time. For many theoretical propulsion methods, this means jacking up the speed and jacking up fuel consumption.
So let's say you want to get from Earth to Alpha Centuari, the closest star system to us. That's a distance of roughly 4.3 light-years. Essentially, the fusion runway premise means stashing fuel along your projected flight path. Each fuel stash would consist of a locator beacon, some minor navigational thrusters, a guidance system to keep everything lined up and a pellet of fuel to power a nuclear fusion propulsion engine.
As laid out by physicist Geoffrey Landis, we'd send these fuel pellets out ahead of time -- and we wouldn't actually have to line the entire highway to Alpha Centuari with them. Remember, an actual airplane runway is just there so the plane can build up enough speed to generate lift. Likewise, the fusion runway would allow a spaceship to build up enough speed to carry it through the rest of its voyage.
As Gilster points out in this fascinating Centauri Dreams blog entry, a manned spacecraft could make it to Alpha Centuari off a fusion runway just one-tenth of a light-year long.
The resulting journey would take roughly 40 years. So, needless to say, you're going to want to pack that star trekking dayvan with plenty of snacks.