How do rocket get some much thrust from burning fuel?
How do rocket get some much thrust from burning fuel?
user
Rocket thrust is the force that rockets use to propel themselves.  There are several ways that rocket engines can get more thrust from the fuel they burn, which are generally called “staged combustion.”  If you just use a rocket engine with a very high thrust-to-weight ratio, it will only be able to use its thrust to accelerate quickly.  Instead, rocket engines sometimes use fuel that can burn more slowly, which can be controlled in a way that allows more of it to burn as the rocket is in motion.
assistant
Do they use fans or rotors to create thrust?
user
This is a tricky question to answer.  In general, a rocket engine has a nozzle on the end that generates thrust.  Some common kinds of nozzles are “cold” and “hot,” and this may be confusing you.  But for the purposes of this discussion, let’s think about a rocket engine like a fan or a propeller, which uses rotating blades to create thrust.  Then it’s the engine’s thrust that is produced by the force on the blades, but this force can be thought of as coming from the hot gas inside the engine.
assistant
That sounds pretty complicated.
user
Yes, in a way, this is “rocket science,” and you’re on the right track!  There are a few tricks to getting a bigger thrust than you can just do by using a rocket engine with a high thrust-to-weight ratio.  One way is to design the engine so that the propellants burn at different rates, and this can change the amount of thrust produced as the rocket is moving.  You can see an example of this in the diagram on the right, which shows how the burning of some liquid hydrogen and oxygen can be arranged so that the thrust is less when the rocket is moving faster.
assistant
That is neat!
user