How do multistage rockets work?

Answer 1

In stages.

Answer 2

Very well, thank you. :-)

With any rocket there is a relationship between the size of the payload and the amount of fuel needed to get it into orbit. Of course, the more fuel you add the bigger the fuel tanks need to be, so the more weight you add, so the more fuel you need to add, and so on.

For heavier payloads, this relationship between weight and fuel requirements means that a single rocket would need to be unfeasibly large to actually get to orbit. In fact, depending on the fuel used and the materials for the fuel tanks, it may be impossible for a single rocket to get it up there. Furhter, as the rocket runs it depletes its fuel. Close to the end of the flight the fuel is being used to accelerate largely empty and useless fuel tanks. If those could be ditched the fuel could be used much more effectively. That is where the concept of a multi-stage rocket comes in.

Let's take a three-stage rocket like a Saturn V as an example. The first stage burns and accelerates the rocket from a standing start on the pad. Once its fuel is exhausted the stage is useless, nothing but dead weight, and is discarded. The second stage now fires. The second stage engines now have the job of accelerating a smaller, lighter rocket from a high speed to an even higher speed. On the ground, the second stage rocket engines would not even have been able to lift the fully fuelled second and third stages, but at altitude, and already going at a couple of thousand miles per hour, they can easily provide the extra acceleration required to speed the rocket up still further.

Once the second stage is exhausted it too is thrown away. now the third stage ignites, and that has to accelerate a much smaller rocket already travelling at several thousand miles per hour up to orbital speed (17,500mph).

So, each stage has to accelerate a progressively smaller and lighter rocket which is travelling much faster than when the previous stage started its work. It allows for an overall much smaller rocket to lift a large payload by dividing the work needed to get the payload into orbit between stages, and discarding weight along the journey.

Answer 3

The first stage is the biggest and carries the second stage which is smaller and the third stage is still smaller etc. Each stage fires when the earlier stages are finished and separate by means of small explosive bolts. See NASA and similar sites for details.

Answer 4

Two or three and sometimes couple boosters on the side. A booster fires together with main engine so it does not count as a separate stage even though it is rejected afterwards.