I understand that rockets create a lot of gas which is pushed out of the back and because of equal and opposite reactions the rocket is propelled forwards.
What I don’t quite understand is this:
The interstellar space is a vacuum so the gas that the rocket creates is going to naturally want to try to fill this empty space. If this is the case then how is it creating a force that pushes the rocket?
So in the classic gun example where a bullet is shot which in turn pushes back on the gun, there is a gas pressure pushing them both. In space, there is nothing for the gas to push on. It seems that it is simply moving to fill an empty space so I don’t understand where the force is coming from.
Would it be that the rockets just create so much gas that pressure is able to build up in the back of the rocket even though the gas is trying to leave naturally?