Directed energy photon propulsion via free-space coherent beam combination Author: Jonathan Suen, Ph.D. Researcher, University of California Santa Barbara Abstract: Directed energy photon propulsion via free-space coherent beam combination avoids the inherent scaling limits of ultra-high-power lasers and telescopes. By using thousands, millions, or even billions of apertures, flux at each aperture is reduced to reasonable levels, while an incredibly directive CW beam of up to 100 gigawatts can be formed. For such a beam to be synthesized efficiently, a feedback system must actively compensate for atmospheric turbulence, mechanical disturbances, as well as phase noise in interconnecting fibers and amplifiers. We will discuss techniques, models, and results covering the scalable coherent phasing of large arrays. Due to the sheer number of elements, it is necessary that modules be able to compensate for phase noise in parallel, autonomous, and inexpensive manner. We find that with the use of a beacon-feedback architecture, this technology is largely available today.