It sounds like science fiction, but it's eminently possible, researchers say: Robotic spacecraft could get to Mars after a journey of just three days. The key to making this happen is photon propulsion, which would use a powerful laser to accelerate spacecraft to relativistic speeds, said Philip Lubin, a physics professor at the University of California, Santa Barbara. "There are recent advances which take this from science fiction to science reality," Lubin said at the 2015 NASA Innovative Advanced Concepts (NIAC) fall symposium last October. "There's no known reason why we cannot do this." Lubin and his team were awarded...