eli5: If space is a vacuum, how can rockets work? What are the thrusters pushing *against* if there is nothing out there?

Question

I’ve never really understood the physics of this. Obviously it works somehow — I’m not a moonlanding denier or anything — but my (admittedly primitive) brain continues to insist that a rocket thruster needs something to push *against* in order to work.

So what is it pushing against if space is essentially a void?

In: 7157

Answer 1

Rockets don’t work by pushing against the world around them, they work by pushing against their own exhaust. The gasses expanding inside the combustion chamber and nozzle are pushing outward in all directions, and since nozzle is open on one end, they can only push against the engine in one direction, pushing it forward.