 The idea that for every action there's an equal and opposite reaction works in space. So if you're firing your thrusters, you're expending that fuel and other things in that direction, and you're lightening the part of the rocket where the fuel was, you're actually creating propulsion that way. So, you know, rockets do work in space. It's just that the physics of how they work in space is very different to how things had been understood to fly in the atmosphere.