# How NASA Rockets Lift Off

By Tony Cleary

Topic: Space

[Open the interactive Jig](https://ask.jig.com/j/5KRTQly0aanz)

## Guide

### 1. Meet the rocket

This is NASA's Space Launch System, or SLS, standing on its launch pad in Florida at dawn\. It is 98 metres tall, taller than the Statue of Liberty\. How does something this big and heavy leave the ground?

Fully fuelled, it weighs about 2\.6 million kilograms: as much as 400 elephants\.

### 2. Super\-cold fuel

The tall orange core stage fills with liquid hydrogen, the fuel, and liquid oxygen, which lets the fuel burn\. Both are so cold they only stay liquid deep below freezing\. The orange skin is foam insulation that keeps them cold\.

The core holds about 2\.8 million litres\. The white wisps are cold vapour drifting away\.

### 3. A flood of water

Just before the engines start, giant sprayers flood the launcher deck and the trench beneath it\. The water is not for putting out fires\. It soaks up the rocket's thunderous sound so the noise cannot shake the rocket and pad\.

About 1\.7 million litres of water pour out in under 30 seconds\.

### 4. The main engines light

About six seconds before liftoff, four RS\-25 engines under the core stage roar to life\. Clamps still hold the rocket down while computers check every engine\. Burning hydrogen makes a pale, almost see\-through flame\.

The flame trench under the pad steers the blast sideways, away from the rocket\.

### 5. Liftoff\!

At zero, the two white solid rocket boosters ignite\. Once lit, they cannot be switched off\. The clamps let go and the rocket begins to climb on a pillar of fire and a rolling cloud of steam\.

The boosters give more than three quarters of the push at liftoff\.

### 6. Push gas down, go up

Inside every engine, burning fuel makes hot gas\. The nozzles blast that gas downward very fast \(orange arrow\)\. Pushing the gas down pushes the rocket up \(white arrow\): every push comes with an equal push back\.

A rocket does not push against the ground or the air\. It works even better in space\.

### 7. Slow at first, then faster

The upward push \(white\) is only about one and a half times the rocket's weight \(blue\), so it climbs slowly at first\. The boosters burn about six tonnes of propellant every second, so the rocket keeps getting lighter and faster\.

Liftoff push: about 39 million newtons, more than the famous Saturn V moon rocket\.

### 8. Off over the ocean

Soon the rocket leans east and arcs out over the Atlantic Ocean\. After about two minutes the boosters fall away, and the core stage keeps firing for about eight minutes on the way to space\.

The cloud left on the pad is mostly steam from all that water\.