I think it is good that people are thinking very far out of the box for this. Reason? What we think we can do now isn’t enough, so if we want to go to Mars, <i>some</i> ridiculous idea must eventually turn out to be practical.<p>For that reason, I would not worry too much about that 11%. _If_ we go into space, we will have to build enormous solar arrays in space, and they could provide order of magnitude more power than we produce now.<p>I would not aim for Mars, though. Instead, send it out to overtake Voyager. To do that, you do not need to decelerate, and you do not need to goto 0.3c, either.<p>(Actually, some billionaire should put a huge price on the first one to overtake Voyager and send a video of it back to earth. That could become a fun race, with later, faster, spaceships overtaking early entries.)