Why do space rockets burn oxygen?
You need to go REALLY fast
On page 14, you learned that planes push up against gravity with their engines to fly and then surf over air like a bird. Well, rockets don’t surf. They shoot off into space like a firework. They don’t glide over air like a plane, so their wings are much smaller. The problem is, gravity is incredibly strong. You need to push the rocket into space faster than gravity can pull you down, which means you have to use a LOT of energy to escape gravity. You need to travel at 11.2 kilometres per second! That’s 25,000 mp/h or 40,315 km/h. (you could fly from Seoul to New York in about 15 minutes. You might think that sounds reasonably fast, but consider this - a normal plane travels at about 576 mp/h or 926 km/h.
Weight Gravity is incredibly strong - that’s clear - but why can’t we just use oil in spaceships? Oil is a great fuel for long journeys for planes and cars and most other things, yet for a rocket, oil doesn’t give enough energy quickly enough and it’s far too heavy. Imagine carrying a bucket of water everywhere you go. It’s going to slow you down significantly. A rocket needs to be efficient and carry less weight, so oil can’t be used. The answer to this problem, strangely, is to burn the thing that we breathe - oxygen! You can turn oxygen into a liquid and use it to help other things to burn faster and more powerfully.
So, rockets take another element - hydrogen - as fuel and mix it with oxygen. These can burn extremely powerfully and release enough energy to help the rocket reach 11.2 kilometres per second and escape gravity! Hurray! Brilliant! The strange thing is, oxygen and hydrogen mixed together in another way make.......drum roll.....water! What!???? It’s all about weight. Hydrogen is the lightest element, but is full of energy. Oxygen is also very light and helps hydrogen to burn more effectively. You just need to be careful not to turn them into a giant bucket....I mean....space rocket full of water!