A research group at the University of Washington, funded by NASA, is about to build a fusion-powered rocket. This rocket, if it can be successfully built, could propel a manned spacecraft to Mars in just 30 days — compared to NASA’s estimate of four years for a Martian round trip using current technology.
The UW team, led by John Slough, have spent the last few years developing and testing each of the various stages of a fusion rocket. Now it is time to bring these isolated tests together to produce an actual fusion rocket. To succeed, Slough and co will need to create a fusion process that generates more power than it requires to get the fusion reaction started — a caveat that, despite billions of dollars of research, has eluded some of the world’s finest scientists for more than 60 years. Fusion is an ideal method of rocket propulsion, as fusion fuel has immense energy density — something on the scale of 7 million times more dense than conventional rocket fuel. The weight (and expense) of fuel is one of the biggest barriers to space travel.
The UW fusion rocket design is mechanically simple and also ingenious. In essence, there’s a pellet of deuterium-tritium (hydrogen isotopes; the usual fuel used with fusion), and some large metal rings made of lithium. When the pellet is in the right place, flowing through the combustion chamber towards the exhaust, a huge magnetic field is triggered, causing the metal rings to slam closed around the pellet of fuel. These rings then implode with such pressure that the fuel compresses into fusion — much in the same way that a car compresses diesel into combustion. The fusion causes a massive explosion, ejecting the metal rings out of the rocket at 67,000 mph (108,000 kmh), generating thrust. This reaction would be repeated every 10 seconds, eventually accelerating the rocket to somewhere around 200,000 miles per hour — about 10 times the speed of Curiosity as it hurtled through space from Earth to Mars.
That’s the theory, anyway. So far, as far as we can tell, the scientists haven’t actually created fusion yet; they’ve tested the imploding metal rings, but they haven’t inserted the deuterium-tritium fuel and propelled a super-heated ionized lump of metal at 67,000 mph out the back of a rocket. That’s the next and very large step.
To be considered a success, the UW fusion rocket must fulfill two criteria: It must work reliably, and it must be capable of generating more thermal energy than the electrical energy required to start the fusion reaction. It is this second factor that has so far proved impossible to fulfill, despite dozens of attempts and billions of research and development dollars. Basically, it’s easy enough to start a fusion reaction — you just need a very strong magnetic field, lasers, or a nuclear bomb — but it’s very hard to continue the reaction after that. Fusion releases a vast amount of thermal energy — but you need to be able to convert enough of that thermal energy into electrical energy, to continue the reaction.