The Emthruster: Thrust without reaction?

[stevebowers]

A recent study building on Forward's ideas is here
http://arxiv.org/ftp/arxiv/papers/1205/1205.2281.pdf
Ronan Keane and Wei-Ming Zhang have refined the beamed-core concept, so that it can achieve an effective exhaust speed of 0.69c, more than twice earlier estimates.
I think there would still be a significant problem with radiation (and waste heat) from such a system, but this is significantly better than previously thought.