Antimatter would seem to be an ideal propulsion candidate for starships. After all, the annihilation of matter and antimatter is mind-bogglingly efficient, releasing energies that fission or fusion engines could not hope to achieve. A single gram of antimatter meeting a gram of ordinary matter would release the energy of a 20-kiloton bomb. And talk about mass ratios — Robert Forward calculated that a one-ton Centauri probe moving at a tenth of lightspeed would require no more than four tons of liquid hydrogen and forty pounds of antimatter.
In fact, antimatter sounds great until you realize that current production runs in the range of nanograms per year. And even if we could magically boost antimatter production, containment remains a problem. A Penning trap, which uses electrical and magnetic fields to hold the charged particles in suspension from normal matter, is heavy, hard to manage and houses only a small amount of antimatter, although Penn State’s Mark I offered a significant improvement. NASA’s work on HiPAT (High Performance Antiproton Trap) aims at improving the situation still more through the use of strong magnetic fields and extreme cooling.
HiPAT is part of the incremental work that needs doing as we build the capacity to create more antimatter and store it efficiently. But there are other storage approaches, as exemplified by the work of Japanese researcher Masaki Hori. Currently working at the Max-Planck-Institute of Quantum Optics, Hori wants to change the paradigm by using radio frequency waves rather than magnetic fields to store anti-protons. He calls his device a ‘superconducting radiofrequency quadrupole trap.’ and thinks it can offer antimatter storage in a device the size of an office wastebasket. His next move is to go to work on what’s in it.
For part of improving our understanding of antimatter is figuring out whether it truly is the exact opposite of normal matter. Hori puts it this way:
“Scientists believe that nature, at a very fundamental level, possesses a symmetry called ‘CPT’ (Charge, Parity, and Time-reversal): this means, if we were to imagine an ‘antiworld’, where all the matter in the universe were replaced with antimatter, the left and right directions inverted as if in a mirror, and the flow of time reversed, it would be completely indistinguishable from our real matter world. Since this symmetry is of such crucial importance in our understanding of the world, it is of the first importance to test it at the highest possible precision.”
Hori’s earlier work on the anti-proton involved measuring its mass and charge to a precision of several parts per billion. The result: The anti-proton does indeed show identical mass compared to the proton, and an exactly equal but opposite charge. He now intends to use his experimental storage techniques to create complete atoms made up of antimatter, working with them to pursue and extend his studies of symmetry. That work has been given a powerful boost by the European Science Foundation and the European Heads of Research Councils, which have bestowed a EURYI Award on the researcher.
The idea behind the award is to boost Europe’s younger scientists, but Hori, 34, will take from it something more than a lift in morale. The EURYI offers awards in Nobel Prize range, between €1,000,000 and €1,250,000. That financial infusion should help the researcher pursue antimatter manipulation techniques that may help us find new ways to store the stuff. Even so, the researcher downplays antimatter’s uses in space.
But I’m not so sure. We build our skills in increments, and it is already emerging that interesting propulsion concepts using antimatter don’t have to wait for Forward’s forty pound antimatter packages. Steve Howe (Hbar Technologies) has worked out the basics of a so-called ‘antimatter sail’ with help from Phase I and II awards from NASA’s Institute for Advanced Concepts. Anti-hydrogen in milligram quantities released from the spacecraft itself would power up nuclear fission on a sail coated with a layer of uranium-235. Howe talks about velocities of well over 100 kilometers per second (see An Antimatter-Driven Sail to the Kuiper Belt for more on this concept, and here’s a link to the NIAC Phase I study).
We’re a long, long way from even milligram levels of antimatter production at this point, but learning what might be done with smaller amounts while extending propulsion technology is a valuable theoretical step. Get something moving at 100 kilometers a second and the outer planets are opened up to a wide variety of missions; Howe believes the method could deliver a 10-kilogram payload well into the Kuiper Belt at 250 AU with a flight time of ten years. Such exotic syntheses of different propulsion concepts stimulate our thinking. We build technologies one step at a time, and although still beyond our practical reach, antimatter propulsion may not always be in the realm of science fiction.