Hello, I'm a second year physics student and I'm interested in new approaches to spacecraft propulsion. I apologize if this has been asked many times - while this interest may be partially inspired by science fiction, I am well aware that the real-life situation is not at all as glamorous. But, I would still like to make a contribution of some sort. I would be very grateful if someone who is in the know could give me some guidance. What are some of the potentially superior alternatives to chemical propellant? I'm vaguely aware of ion thrusters as well as nuclear and electric propulsion, but that's about it. Are there any other proposed methods? Do any of them seem particularly promising? Thank you very much for your help.