DEEP-IN, also known as Directed Energy Propulsion for Interstellar Exploration, is a spaceflight propulsion concept that uses photonic laser propulsion with beamed power to propel a spacecraft in deep space. The concept, in development by NASA Innovative Advanced Concepts, is notable as the first concept for photonic laser propulsion backed by NASA. The concept is heavily derived from DE-STAR, a planetary defense satellite concept that also uses directed energy. The system is scalable and modular.