How Rocket Engines Work in A Vacuum

If we walk by pushing our feet against the ground, birds fly by flapping their wings against the air, and fish swim by pushing their fins against water; then how can possibly a rocket move in a vacuum?

Rockets are able to move in space by making use of the law of nature described in the Newton’s laws of motion, and the law of conservation of momentum.

A rocket engine works by releasing mass at a very high velocity. This mass is called ‘propellant’. The spacecraft will move to the opposite direction from which the propellant is released.

In addition to the propellant, rockets also need to carry fuel. Here lies another problem frequently brought out by flat-Earthers. In a vacuum, there’s no air, and no oxygen, so it must be impossible to burn things. To solve this problem, in addition to the fuel, rockets also need to carry the fuel oxidizer with them.

The propellant can also have stored energy, in which case it also serve as the fuel.

Rockets can also be electrically powered by ion thrusters. In ion engines, rockets can harness energy from the Sun through solar panels. They still have to carry the propellant, though. A popular propellant is xenon gas. The power generated by ion engines is relatively small, so launches from the surface of the Earth cannot utilize ion engines. It can be used after the spacecraft is in orbit, where only relatively small amount of power is required to propel the spacecraft into desired orbit or position.



  • Illustration is from the movie WALL-E, © Disney & Pixar.