Getting into space isn’t easy, and it takes a few steps. First, let’s think about where “space” itself begins.
Some time ago, some experts decided that one point above us is where “space” begins. They marked it with an invisible line, the Kármán line.
This line goes around the earth and is about 100 km above us. To help you understand how high that is, a normal airplane flies only about 10 km above the ground.
Can we take a plane to space?
We can’t just use an airplane to go into space for many reasons. An important one is that the higher we go, the less air there is — or specifically, the less “oxygen” there is in the air.
The engine is what helps the plane fly. And just like car engines, airplane engines need oxygen to run. Fortunately, the air we breathe is made up of 21% oxygen (although you can’t see it)!
Aircraft suck in air from the front, with large fans on either side. They then mix this air with jet fuel, creating a mixture of fuel and oxygen that is then burned, making the air hotter. The hot air is then shot backward at a very high speed, pushing the aircraft forward.
But a plane trying to fly too close to space, where there isn’t enough oxygen, would be like a person trying to breathe in a room without air.
The major difference between rocket and jet engines used in aircraft is that rocket engines do not need to extract oxygen from the air. Instead, they carry their oxygen with them. That’s why we need rockets to get into space.
In some ways, this is bad because rocket engines have to carry something that an airplane can easily get around. This means there is less space on a rocket for other cargo, such as passengers and luggage.
But on the plus side, being able to carry oxygen for the journey means rockets can operate in space, much higher than where most planes fly.
How does a rocket engine work?
Like an airplane’s jet engine, rocket engines shoot very hot gas from the back of the rocket. As the throttle is pushed back, the rocket is pushed forward.
This is an example of a rule in science called the third law of motion, first discovered by a famous scientist named Isaac Newton. This law says that every action has an equal and opposite reaction.
You can even make a very simple “rocket” at home with some help from an adult! When you get a balloon, blow it up and let it go without tying the end; the air inside will shoot out and send it flying around the room – just like a badly controlled rocket!
Chris James, ARC DECRA Fellow, Center for Hypersonics, School of Mechanical and Mining Engineering, University of Queensland
This article is republished from The Conversation under a Creative Commons license. Read the original article.