Rockets are the sticks that go boom on one end and fly real fast the other. They range from the little bottle rocket on the 4th of July to the football-field-tall Saturn V which took astronauts to the Moon.

Saturn V rocket stages shown separated.

You’ll notice that the Saturn V rocket has a few segments. We call these segments stages. Why do rockets have stages? Why are there rocket engines inside the rocket?

The short answer is: to save mass to go faster. Why do we have to save mass? Think of it this way, you can roll a bowling ball much faster than a boulder.

Rockets need to go very fast in order to reach orbit. They need to go even faster if they are to escape orbit and go to other places. The notion of orbiting itself can be a bit tricky: It’s moving so fast that you are falling down at the same rate as the surface of the earth is curving away from you, so you end up falling around the Earth.

Have you ever dropped a coin in one of those big funnels and watched it spiral down into the hole? Orbiting is essentially the same thing: the coin falls around the hole and gently slows down and spirals into the hole. In space there is no friction to slow the spacecraft down, so it would be like the coin just rolling around in a circle forever.

So the difference between going to space and going into orbit is speed. Space is just up- orbit is going and staying up. Going back to staging- a rocket is basically made of three things: the tanks, the engines, and the fuel. The fuel is by far the heaviest thing on board, but requires tanks to hold it. When a tank empties, you continue to carry the empty tank.

Staging allows you to shed the mass of emptying tanks, so you can push the remaining pieces of the rocket even faster. Second to that (and the focus of a future article), the rocket engines for different stages are designed to best work either at the ground, going really fast, or going really fast in space. By dropping early engines you can start up new engines that are best suited for that phase of the mission.


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