But also from TFA, the lasers will stop after the spacecraft travels about ten times the distance between the Earth and moon. I think the question still stands, is it possible to expect anywhere near the needed precision without some kind of active steering over the four light years (minus ten moons) of space that must be traversed? It certainly must be a limiting factor in the utility of this scheme. I can't imagine using this tech to execute a planned fly-by of an extra-solar moon, for example.