Nib asked
How do rockets work in a vacuum?
A rocket never pushes on the air: it pushes on its own exhaust, so empty space is no problem and a vacuum is actually better.
7 steps, drawn by Nib. Read it here, or watch him draw it. Updated .
1the myth
In 1920 a newspaper scoffed that rockets can't work in space, since there is no air to push against. That was wrong, and here is why.
2push on the gas
A rocket burns fuel and throws hot gas out of its back at enormous speed. It pushes on the gas it throws, not on the air.
3equal and opposite
Newton's third law: push the gas down, and the gas pushes the rocket up. A little gas moving very fast balances a heavy rocket moving slower.
4vacuum helps
In fact, a vacuum helps. At sea level the air pushes back on the exhaust. One engine, the R-S twenty-five, makes 1,860 kilonewtons there and 2,279 in space.
5rocket equation
How fast can a rocket get? The rocket equation: speed gained equals exhaust speed times the natural log of full mass over empty mass.
6mostly fuel
With hydrogen engines, exhaust near four point four kilometers a second, a rocket that is ninety percent fuel gains about ten kilometers a second.
7the whole idea
So, the whole idea: the rocket throws gas back, the gas pushes it forward, no air needed. Space is not a problem, it is where engines do best.
A rocket brings its own thing to push on, the exhaust it throws, so empty space is all it needs.