re: Photon Drive...
"Any suggestions?"
Don't know much about anti-matter drives, but it seems to me that the
big advantage of anti-matter is that it's a very concentrated form of energy. So rather than how big or even how efficent in terms of ISP, I would ask how small can you make one of these things? What is the absolutely smallest engine which could be made using anti-matter as a fuel source? I mean, small like say insect size.