Solar Sail, Laser Sail, Electric Sail, Magnetic Sail, Mini-magnetospheric plasma sail, MagBeam, Plasma Magnet Sail, Photon Drive, Bussard Ramjet, Ram-Augmented Interstellar Rocket.
Basically any spacecraft that does not carry its own propellant. Most of these have either pathetic thrust or are way beyond our current state-of-the-art.
Basically any spacecraft that does not carry its own propellant. Most of these have either pathetic thrust or are way beyond our current state-of-the-art.