Andrew Skolnick drew my attention to this great article by John Eades, a CERN senior scientist, about antimatter engines and weapons.
Antimatter Pseudoscience by John Eades in the Skeptical Inquirer http://www.csicop.org/si/show/antimatter_pseudoscience/
We, Andrew Skolnick and I, did the calculations and showed that it would cost 42,876x our 2011 World GDP to use antimatter as a propulsion fuel to get to Alpha Centauri!!
John Eades goes one better and shows that it is not technologically feasible, ever. His article is facinating reading, and shows that we cannot base our hopes to leave Earth on antimatter drives.
Benjamin T Solomon is the author & principal investigator of the 12-year study into the theoretical & technological feasibility of gravitation modification, titled An Introduction to Gravity Modification, to achieve interstellar travel in our lifetimes. For more information visit iSETI LLC, Interstellar Space Exploration Technology Initiative