Photonic solution to phase sensing and control for light-based interstellar propulsion

Reaching another star system within a human timescale requires traveling at a sizeable fraction of the speed of light. To achieve this, the Breakthrough Starshot program proposes a ground-based laser array to accelerate a gram-scale spacecraft through photon radiation pressure, requiring of order 100 GW of continuous wave optical power. The coherent combination of many lasers is one avenue to achieve a high optical power output.Here we present a photonic solution for optical phase sensing and control to enable the coherent combination of order 108 individual lasers, including the ability to sense and compensate for atmospheric distortions, assuming the laser system is ground based.