For over a century, rocket propulsion has followed a simple principle; burn fuel, expel it backward, and Newton’s third law pushes you forward. Since Konstantin Tsiolkovsky first formulated the rocket equation in 1903, spacecraft have carried their propellant with them, limiting mission capabilities by the mass ratios. The more fuel you carry, the heavier your rocket becomes, requiring even more fuel to lift that fuel, in a vicious cycle that makes interstellar travel seem impossibly distant. But what if spacecraft didn’t need to carry propellant at all?