To quote:

One of the beauties of antimatter is its efficiency. A fission reaction uses up about 1 percent of the available energy inside matter, whereas the annihilation of antimatter and matter converts 100 percent of the mass into energy. No wonder tiny amounts of antimatter can have such powerful effects. Put a gram of matter together with a gram of antimatter and you release the equivalent of a 20 kiloton bomb, about the size of the one that destroyed Hiroshima.

And if you really want to see antimatter’s potential, consider what it does to mass ratios, which compare the weight of a fully fueled spacecraft with that of an empty one. In his book Mirror Matter: Pioneering Antimatter Physics (New York: John Wiley & Sons, 1988), Robert Forward spoke of antimatter-driven spacecraft with mass ratios of 5 to 1 (by contrast, the Apollo missions operated with a ratio of 600 to 1). Indeed, Forward believed that a 1-ton probe to Alpha Centauri would require roughly four tons of liquid hydrogen and forty pounds of antimatter.

All of which takes us back to Gerald Smith’s intriguing work with positrons. I first ran into Smith’s ideas when he collaborated with Steven Howe, Raymond Lewis, and Kirby Meyer on a project called AIMStar (Antimatter Initiated Microfusion Starship). Here’s a link, but beware: it’s a PDF file. With a mission goal of reaching 10,000 AU — the domain of the Oort Cloud’s comets — in fifty years, AIMStar would use antimatter to ignite a fusion reaction. Building on an earlier design that used antiprotons to trigger fission, AIMStar would tap tens of micrograms of antimatter to create the reaction, injecting deuterium and helium-3 into a cloud of antiprotons.

Full article here:

http://www.centauri-dreams.org/?p=629