If you want to go anywhere in space quickly, the smartest way to go about it is to leave the propulsion energy source on Earth (or in orbit around the Sun)—that’s the only way to escape the tyranny of the rocket equation, regardless of whether your rocket is propelled by black powder or a matter-antimatter drive. Directed energy technology (beamed power) uses lasers or microwave beams to transmit power to a spacecraft where it is reflected by a lightweight sail and converted directly into propulsion. Since such beams are also useful for applications such as destroying incoming missiles or killer drone swarms, research and development of them has been heavily funded by the military, and space systems can piggyback on this work. In this talk, Prof. Philip Lubin of the University of California, Santa Barbara, describes the rationale for directed energy propulsion, compares it to alternatives, and shows work underway to demonstrate the phased array and beam shaping technologies a practical system will require. Here are Solar System missions a mature system would enable.
Dr Lubin’s books are “The Path to Transformational Space Exploration” (two volumes).