why we’d want to make some more antimatter
Maybe the investors behind Planetary Resources should consider creating antimatter instead of building fuel depots on asteroids they want to mine since all they’d need to do to guarantee unimaginable profits is just a single gram of the stuff. Granted, the collider they’d have to build to smash ions until they decay into positrons and anti-hydrogen would cost tens of billions to build and hundreds of millions per year to maintain, but with a current retail price of roughly $62 trillion per gram, they’ll make they money back handsomely, even if their economies of scale drive the price down to just a hundredth of what it is today.
Weapons designers and space agencies would form a line around whatever mountain complex would house their giant ion smasher, since adding an infinitesimal quantity of this bizarre stuff adds a very powerful punch to any explosive reaction. And what about the energy industry using matter-antimatter reactions to catalyze fusion? After all, antimatter is the only fuel we know to offer perfect 100% efficiency. If we ever learn how to produce even a few kilograms of it per year, we’d be well on our way to cheap, plentiful energy and exploring the cosmos with relativistic rockets. And believe it or not, but that last part may actually be a lot easier then it sounds and we may be closer to it than we think.
When talking about rockets, it’s very important to keep in mind that there are different kinds or thrust we could produce and what would be extremely efficient in space would flop on Earth. To leave the planet, we need big, controlled explosions and while an antimatter additive would make for a much bigger boom and generate an incredible amount of thrust, a pure antimatter engine wouldn’t do much but irradiate everyone and everything around it. Instead, it would work more like an ion thruster, releasing tiny particles that slowly but surely push a spacecraft to incredible velocities rather than provide a quick, swift kick up to speed like liquid hydrogen does in conventional rocketry.
So the basic idea is that antimatter in a Penning trap, would be fired at any matter we aren’t very fond of anymore, annihilate it producing the amount of energy predicted by Einstein’s mass-energy equivalence equation, and as that energy starts leaving the nozzle, it decays into tiny short lived particles that physicists call pi mesons, or pions for short. Blasting out a stream of pions at very high speed would be what gives antimatter powered spacecraft their relativistic velocities. The only problem is that while the annihilation in their engines’ cores is perfectly efficient, the nozzles are not, and previous studies came up with somewhat disappointing numbers, giving the engine a 36% efficiency rating at the very most. Not good news at all.
However, according to a new paper by a duo of physicists using the same software that CERN uses to figure out how particles are colliding in the LHC, these past models are outdated and with just a little tweaking here and there, antimatter engines could actually be 85% efficient, allowing a spacecraft to reach 0.7c which works out to a blistering 756,000,000 km/h. For comparison, the ISS orbits at 28,000 km/h and the fastest spaceship currently traveling through our solar system, New Horizons, tops out at 58,536 km/h. They also found that the magnetic fields needed to govern the matter-antimatter reactions would have a strength of 12 Tesla. Today, a magnet operating at 25 Tesla can be found at a university research lab, so the technology need to operate an extremely potent antimatter powered engine actually exists right now.
The only problem is that we just lack the adequate amount of fuel to make it work. We’ve made millions of antimatter particles but the production is an extremely inefficient process and less than 1% of all the antimatter created is effectively trapped. There are natural processes that make antimatter and magnetic fields around planets do trap it, however this antimatter is very short lived and very rare. You’d need to get to the center of the galaxy to find enough of it to even think of powering a spaceship with it. But the paper’s authors are more optimistic, pointing out that no one has really tried to tackle the issue of antimatter production for industrial use, and that most fuel sources see their supply increased exponentially as we learn more about them and their uses, which drives the demand for them.
Maybe they’re right. Maybe we could explore trapping naturally occurring antimatter or exploiting a new means of creating billions of antiparticles at a time with lasers and millimeter thick gold leaf as part of an engine or a reactor, immediately channeling them into a reaction chamber rather than trying to trap them. Certainly all the energy required to make the antimatter would mean that it’s a highly inefficient fuel source on its own, but that hardly matters for rockets because we’re far more concerned with the reaction being efficient rather than trying to balance the energy equation, and when using tiny amounts of it as a powerful additive to more conventional fuels, its contribution could offset the costs of producing it.
For example, if we could use antimatter to create a powerful pulsed nuclear laser capable of creating a tiny artificial black hole we would use as an engine for a spacecraft or a power source, we could get more antimatter as that tiny little black hole feeds and belches an occasional stream of antiparticles under the right conditions. Of course a scenario like that is not exactly a weekend project on the horizon, but it’s amazing what sorts of things you find out when you actually try to figure out how to accomplish something ambitious and complicated. In theory, we have some very interesting uses for antimatter as a fuel. Maybe we should try to make more of it to find out how it works in the real world…
See: Keane, Ronan and Zhang, Wei-Ming. (2012). Beamed Core Antimatter Propulsion: Engine Design and Optimization arXiv: 1205.2281v1