Ah ok, Now I check again the Keane and Zhang analysis and it seems that I missunderstood some numbers. 0.6c sounds super good, even 0.25c is a lot higher than fussion, the only problem with low ISP in antimater propulsion that the ships requires more radiators to release the excess of heat. Yeah, does calculation was already done it by many researchers, like mattoff, zubrin, adam crowl, etc. Each one with different parameters on sail density and sun periapsys. http://crowlspace.com/?p=1882 http