An inter-planetary propulsion system comprises magnetic wheels located either inside or outside of a spacecraft. Rotation of the magnets is intended to provide linear motion or thrust to the spacecraft. The magnetic wheels may be driven by electric motors. The magnetic wheels may be provided on either side of a rocket fuselage 5 or may be provided as rings within a flying saucer shaped craft. The rocket may have a ring of magnets around its perimeter which interact with the magnetic wheels. The flying saucer may have an engine at its centre or one engine per wheel, each located near to the wheel it powers.