Rockets are able to fly in a vacuum, such as outer space, because they do not rely on the presence of air for propulsion. The key principle behind how rockets work in a vacuum is Newton's third law of motion, which states that for every action, there is an equal and opposite reaction.

When a rocket operates, it expels a high-speed stream of exhaust gases out of its engines in one direction. As the exhaust gases are pushed backward, the rocket experiences an equal and opposite reaction, pushing it forward. This reaction force is what propels the rocket forward, regardless of whether there is air or any other medium to push against.