The atmosphere has mass, absence of an atmosphere is prohibiting, that's your problem in understanding.  Whether liquid, gas, or solid, your theory still hasn't overcome the sheer weight needed to obtain interstellar flight, and an effect a guidance system Dylan why do you think it's prohibitive? if I recall my physics courses correctly, flying a rocket on a vacuum would be actually  easier  than doing it in the presence of gas like the atmosphere, with an atmosphere you have to overcome yet another force: air resistance, in a vacuum you have no resistance.    As I understand this discussion, so far, has come to prove that a relatively small amount of propelled fuel or any other mass for that matter, if  accelerated  enough can create the force necessary to move a much heavier object than it would  without acceleration , am I right?    About steering, if we can agree that an object in or out of a vacuum can be moved in the opposite direction of a projectile (be it a solid, a fluid or a gas) steering simply comes down to doing the same from strategical points in the object: in the front for braking, on the sides for steering, of course in the appropriate amounts to create the desired effect, a little on the right side would cause a slight change of trajectory to the left, a bigger one would cause a sharper change, an effect on the top would make the rocket into a standstill, even more it would go backwards, and so on.