Actually, assemble multiple water-filled cylinders in earth orbit and then put those in staggered cycle orbits. Power requirements are low so all you’d need is

Actually, assemble multiple water-filled cylinders in earth orbit and then put those in staggered cycle orbits. Power requirements are low so all you’d need is a regular engine with a large fuel tank. Once those are in cycle orbit you now have giant water cylinders that you can catch every once in a while to ride to earth/Mars. Forever. With a tiny energy budget for corrections. Just wait till one passes by and slip your vessel inside it. Man I am good.