Large scale directed energy offers the possibility of radical transformation in a variety of areas, including the ability to achieve relativistic flight that will enable the first interstellar missions as well as rapid interplanetary transit. In addition, the same technology opens a wide mission space that allows a diverse range of options from long range beamed power to remote spacecraft and outposts to planetary defense to remote composition analysis and manipulation of asteroids, among others. Directed energy relies on photonics, which like electronics is an exponentially expanding growth area driven by diverse economic interests that allows transformational advances in space exploration and capability. In order to begin to fully exploit this capability it is important to understand not only the possibilities enabled by it, but also the technological challenges involved and to have a logical roadmap to exploit this option. This capability is both synergistic with conventional propulsion and offers a road to a future currently not possible with conventional capabilities.